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Meta TitleSignificant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea
Meta DescriptionThe marine environment has long been affected by chronic operational oil pollution, leading to the deaths of hundreds of thousands of seabirds. In many countries Beached Bird Survey programmes have been established, in which dead birds with oil-contaminated plumage are counted along shorelines. This study analyses data from Beached Bird Surveys conducted in the western Gulf of GdaƄsk (southern Baltic Sea) between 1965/66 and 2024/25 to assess long-term trends in oil pollution. Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded, of which 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95%. During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals. A significant decline in the number of oiled birds occurred in the early 1980s, and, apart from two anomalous seasons in the mid-1990s, numbers have remained low since then. This sharp drop coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect oil spills and identify violators. The resulting reduction in ship-based pollution has supported more sustainable use of this ecologically important marine region. The findings highlight the effectiveness of international regulations and monitoring efforts in reducing chronic oil pollution and improving the health of the Baltic Sea ecosystem.
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Logical Operator Operator Search Text Search Type add_circle_outline remove_circle_outline Article Menu Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open Access Editor’s Choice Article by WƂodzimierz Meissner Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of GdaƄsk, Wita Stwosza 59, 80-308 GdaƄsk, Poland Submission received: 8 August 2025 / Revised: 29 August 2025 / Accepted: 30 August 2025 / Published: 6 September 2025 Abstract The marine environment has long been affected by chronic operational oil pollution, leading to the deaths of hundreds of thousands of seabirds. In many countries Beached Bird Survey programmes have been established, in which dead birds with oil-contaminated plumage are counted along shorelines. This study analyses data from Beached Bird Surveys conducted in the western Gulf of GdaƄsk (southern Baltic Sea) between 1965/66 and 2024/25 to assess long-term trends in oil pollution. Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded, of which 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95%. During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals. A significant decline in the number of oiled birds occurred in the early 1980s, and, apart from two anomalous seasons in the mid-1990s, numbers have remained low since then. This sharp drop coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect oil spills and identify violators. The resulting reduction in ship-based pollution has supported more sustainable use of this ecologically important marine region. The findings highlight the effectiveness of international regulations and monitoring efforts in reducing chronic oil pollution and improving the health of the Baltic Sea ecosystem. 1. Introduction The largest spills from damaged tankers into the marine environment have caused the deaths of tens of thousands, or even hundreds of thousands, of birds [ 1 , 2 , 3 , 4 , 5 ]. These highly publicized oil tanker disasters have drawn significant public attention to the effects of oil pollution on coastal and oceanic ecosystems. The impacts of these disasters on birds remained evident many years later in the form of reduced population numbers and altered habitat use [ 6 , 7 ]. However, there are no significant correlations between the volume of oil spilled and the number of seabirds affected during such events [ 8 ], suggesting that other factors, such as spill location, timing, and bird density, play a critical role. While catastrophic spills receive the most public attention, routine and often unreported discharges, such as those from normal shipping operations, tank washing, and bilge water disposal, introduce even larger cumulative volumes of oil into marine ecosystems over time. Moreover, sources of oil pollution include land-based runoff, originating from cities, highways, and vehicles, as well as natural oil seeps [ 9 , 10 , 11 ]. These small but frequent releases, known as chronic oil pollution, pose significant risks to seabirds and other marine wildlife worldwide [ 12 ]. Across large ocean regions and extended time frames, chronic oil pollution has been shown to cause sustained mortality with greater long-term impacts on seabird populations than occasional large-scale spills [ 12 , 13 , 14 ]. Reports of dead, oiled seabirds stranded on beaches first appeared in the late 19th and early 20th centuries [ 15 ]. Since then, oil spills and operational discharges resulting in bird mortality have been widely documented, e.g., [ 15 , 16 , 17 ], and the number of oiled birds found along coastlines has begun to be reported worldwide, e.g., [ 18 , 19 , 20 , 21 , 22 ]. Oil pollution has also affected the Baltic Sea, one of the world’s largest brackish seas [ 23 ]. Despite covering only 0.1% of the global ocean surface, it is one of the most intensively used seas in the world, handling 15% of global maritime trade [ 24 ]. Both oil spills following shipwrecks, resulting in the death of thousands of birds, and chronic pollution of marine waters with petroleum products have been recorded here, with the first published reports dating back to 1910 [ 15 , 25 ]. Currently, along with oil spills from Crude Oil Tanker-, Chemical Oil Tanker-, and Bunkering Oil Tanker-class vessels, oils used in the food and chemical industries, such as vegetable oils (palm, coconut, rapeseed), also pose a threat when they enter the sea [ 26 ]. Oil and its derivatives floating on the water’s surface can easily adhere to a bird’s feathers, damaging the feather structure and causing a rapid drop in body temperature. However, the effects of oil on birds are not limited to thermoregulatory disorders due to the loss of this protective layer; they also include systemic poisoning caused by toxic hydrocarbons. Contaminated birds instinctively attempt to clean their plumage and reapply secretions from the uropygial gland. During this process, the oil is transferred to the bill and ingested. The swallowed oil can cause inflammation throughout the digestive tract. The intestinal villi clump together, impairing nutrient absorption. Hypothermia increases the bird’s energy demands, which it cannot meet due to its compromised digestive function [ 27 ]. In addition, vapours from spilled oil are toxic. Benzene, toluene, and other light hydrocarbons are rapidly absorbed into the bloodstream through the lungs [ 28 ]. This can lead to the destruction of red and white blood cells, as well as disruptions to the reproductive system, immune system, liver, spleen, and kidneys [ 29 , 30 , 31 ]. Although oil can be washed off feathers using appropriate detergents [ 32 , 33 ], systemic poisoning and inflammation of the gastrointestinal tract result in a very low survival rate for birds, even with intensive treatment in wildlife rescue centres, [ 34 ] but see [ 35 ]. Most often, the first sign of an oil spill at sea is the presence of oil-covered birds on beaches. Therefore, in many countries, regular counts of bird carcasses along the coast were implemented as a simple tool for monitoring seabird mortality caused by oil pollution, known as the Beached Bird Survey (BBS) [ 15 , 36 ]. The results of the counts are expressed as densities, that is, the number of birds found per kilometre surveyed, and as the oil rate, defined as the proportion of oiled birds among all birds collected [ 36 ]. Species-specific oiling rates reflect the risk of birds becoming oil-fouled at sea and can be analysed separately for species that occur primarily offshore and those that remain in the coastal zone [ 37 ]. Additionally, the species composition of oiled birds indicates differences in exposure risk, as oiling rates are usually much higher in pelagic seabirds, which spend much of their time on the water and often dive and swim rather than fly. In contrast, species that remain predominantly near the coast and move mainly by flying are oiled less frequently [ 37 , 38 , 39 ]. The proportion of birds from these two groups can indicate the area of the sea where the birds encountered the oil slick drifting on the surface [ 25 ]. Although only a small proportion of birds that die at sea wash up on shore, as many sink, are scavenged, or drift away from land [ 40 , 41 , 42 , 43 ], this cost-effective method still allows for the detection of long-term trends in oil pollution, e.g., [ 42 , 44 , 45 , 46 , 47 ]. Beached Bird Surveys were also implemented along the Polish Baltic coast, with regular surveys covering a significant part of the coastline beginning in the 1970s [ 25 ]. However, these counts have continued to the present day only along the western coast of the Gulf of GdaƄsk. The aim of this study is to analyse BBS results from this part of the Polish coast, focusing on long-term changes in the density and proportion of oiled birds, as well as the proportion of typical marine species and those associated with coastal waters. 2. Materials and Methods 2.1. Study Area The Gulf of GdaƄsk is a part of the southern Baltic Sea, with its western part hosting industrial centres, shipyards, sea and fishing ports, and a naval base. As a result, this area is particularly vulnerable to adverse impacts on various elements that contribute to its high natural value, including the large numbers of waterbirds that winter here, and there is significant conflict between marine space use and nature conservation [ 48 , 49 ]. There are two large seaports on the western coast of the Gulf of GdaƄsk: GdaƄsk and Gdynia ( Figure 1 ). Together, they account for over 60% of the total cargo handled in Polish seaports, more than 66 million tons, and serve over 8000 vessels annually [ 50 ]. More than 34% of this traffic comprises chemical tankers, gas tankers, and oil tankers [ 50 , 51 ]. The intensity of ship traffic in the Baltic Sea region is expected to increase in the coming years [ 52 ]. This growth of shipping traffic increases the risk of accidents, especially the risk of oil pollution. A noticeable increase in the transport of hazardous and environmentally harmful goods to ports in the Gulf of GdaƄsk occurred after the opening of the Northern Port in GdaƄsk in 1975, which included a petroleum product transhipment terminal accessible to ships with a draft of up to 15 m [ 50 ]. Therefore, the Gulf of GdaƄsk is one of two areas within the Polish Baltic zone with the highest number of oil spills detected [ 14 , 53 ]. Figure 1. Study area with surveyed section of coastline in the western part of the Gulf of GdaƄsk, between the mouth of the Vistula River and Cape Rozewie. Large seaports are marked with a blue square, large fishing ports with a blue circle. 2.2. Field Study Surveys were conducted in the western part of the Gulf of GdaƄsk between the mouth of the Vistula River to the east and Cape Rozewie to the west ( Figure 1 ). The coastline in this area is mainly characterized by sandy beaches, with only small patches of reedbeds, which makes it easier to spot dead birds. Dead birds were collected along the coast during seasonal surveys conducted once per month between September and April, covering the period between the 1987/88 and 2024/25 seasons. In the previous three seasons, counting was carried out between November and April at three-week intervals ( Table 1 ). Data from other seasons come from counts organised by students of the University of GdaƄsk (unpublished data from seasons 1979/80, 1980/81, and 1982/83) and from the literature sources ( Table 1 ). Therefore, this study includes a total of 60 seasons, spanning from 1965/66 to 2024/25, excluding five seasons for which no data were available ( Table 1 ). In this study, a season is defined as the period from autumn to the following summer, reflecting the phenology of most waterbirds in the southern Baltic, which arrive in large numbers in autumn, remain through the winter, and depart for their breeding grounds in spring [ 49 , 54 ]. Table 1. Length of coastline surveyed and number of surveys across subsequent seasons. Dead birds were counted according to standard procedures used in Beached Bird Surveys [ 36 ]. During each survey, the coastline was patrolled in search of dead and dying birds. Species were identified, and the birds were examined for traces of oil pollution on their feathers. Birds with plumage contaminated with petroleum substances were classified as oiled birds, while the rest were classified as non-oiled birds. The carcasses were then removed from the shore to prevent repeated counts during subsequent inspections. Birds found in fishing harbours that had drowned in fishing nets were excluded from analyses. In total 12,264 birds found in the western part of the Gulf of GdaƄsk were included in the analysis ( Table A1 ). 2.3. Data Analysis The length of the patrolled coastline varied significantly from season to season, especially before 1984 ( Table 1 ). Therefore, the number of birds found was expressed per kilometre surveyed. In addition, as in other analyses of BBS results, the oil rate, i.e., the proportion of oiled birds among all birds collected, was also reported. There is species-specific variation in oiling rates observed in Beached Bird Surveys. Therefore, the 49 identified species and 10 birds identified only to the genus level in this study were grouped into three categories: (1) ichthyophagous and benthophagous species that forage mainly by diving (e.g., divers, auks, and sea ducks), which winter predominantly in the open sea, far from the coast; (2) waterbirds that primarily remain near the coastline (e.g., dabbling ducks, swans, coots, and diving ducks not classified as sea ducks); and (3) gulls, which may forage and reside in both offshore waters and coastal areas, including ports and urbanised zones. In the latter group, unidentified grebes were included, as different grebe species may inhabit either offshore or coastal zones during the non-breeding season ( Table A1 ). In the analysis of species-specific variability in oiling rates over time, gulls and unidentified grebes were excluded, allowing the focus to remain on two groups of species that differ markedly in their primary areas of concentration. 3. Results Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded along the western coast of the Gulf of GdaƄsk ( Table A1 ). Among them, 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95% ( Figure 2 ). During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals and a maximum of 31 individuals per 10 km, observed before the 1970/71 season. As late as the 1982/83 season, high densities of dead birds were recorded, amounting to 19 individuals per 10 km, 57% of which had oiled plumage ( Figure 2 ). From the 1984/85 season onward, both the density of oiled birds and the oil rate declined substantially. Notably, the density did not exceed four individuals per 10 km. An exception occurred during the 1994/95 and 1995/96 seasons, when 78% and 88% of birds were oiled and densities reached 8 and 12 individuals per 10 km, respectively. During these two seasons, an exceptionally high number of oiled coastal birds was documented, primarily due to one species, the Mute Swan, which alone accounted for 35% of all oiled individuals. The next most affected species was the Long-tailed Duck, a species typical of the open sea zone, with a 26% share. Since the 2007/08 season, the density of oiled birds has been very low, with no oiled individuals found in 10 of the seasons ( Figure 2 ). Figure 2. Percentage (bars) of birds with oiled plumage (based on total number of birds found) and number of oiled birds per 10 km of coastline per survey (line) across seasons. Asterisks denote seasons with missing data. Only in three seasons did the density of non-oiled birds exceed 5 individuals per 10 km, with the highest values of 18 and 14 recorded in 1969/70 and 1982/83, respectively ( Figure 3 ). In the remaining seasons, values ranged from 0.2 to 4.6, with no clear decreasing trend in later seasons, unlike the pattern observed in the density of oiled birds. Figure 3. Number of birds with non-oiled plumage per 10 km of coastline per survey across seasons. Asterisks denote seasons with missing data. Among the oiled birds found in the Gulf of GdaƄsk in most seasons, species associated with the open sea predominate ( Figure 4 ). The proportion of birds associated with the coastal zone has increased clearly since the 1984/85 season, reaching as much as 95% in the 1995/96 season, when oiled Mute Swans accounted for as much as 87% of all birds with oiled plumage. During the last 29 seasons (1996/97–2024/25), when the number of oiled birds was very low, the proportion of birds associated with the open sea was once again high, reaching 82% ( Figure 4 ). Figure 4. Proportion of birds with oiled plumage among coastal zone species (green) and offshore zone species (blue) across seasons. Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. 4. Discussion For centuries, economic concerns were the primary focus of the maritime economy, with little attention paid to sustainable development. It was only after several widely publicized tanker disasters, which were extensively reported in the media, that the public began to realize the impact of oil pollution on the maritime environment. In general, there has been a decline in the proportion of oiled birds found on the beaches of the North Sea [ 37 , 61 ] and the southern Baltic (this study). However, local oil rates remained high in both areas [ 47 , 62 ]. The conspicuous decrease in oiling rates and the density of oiled birds found on the coast of the Gulf of GdaƄsk began in the mid-1980s, whereas on the southern coasts of the North Sea, the number of birds washing ashore with very high oil rates increased dramatically during this period [ 46 , 61 ]. Significant decreases in the number of oil slicks detected in the North Sea were observed much later, at the beginning of the 21st century [ 61 , 63 ]. Outside Europe, the situation varies considerably. A decline in the number of oiled birds has been reported along the central California coast [ 64 ]. In some parts of British Columbia, a similar decline has been observed, though not in others [ 65 ]. Beached Bird Surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland was among the highest in the world during a comparable time period [ 20 ]. It is estimated that between 1998 and 2000, approximately 300,000 seabirds were killed annually in this region due to illegal oil discharges from ships [ 66 ]. The decline in oil pollution in the western part of the Gulf of GdaƄsk occurred despite a strong increase in ship traffic [ 67 ], amount of oil transported [ 68 ], and increase in the number of shipping accidents in the Baltic Sea [ 69 ]. However, only 7% of these accidents resulted in some kind of pollution, usually containing not more than 0.1–1 tons of oil [ 69 ]. The number of detected illegal oil spills in the Baltic also decreased [ 68 ]. This drop coincides with the implementation of the MARPOL Convention in 1983, which designated the Baltic Sea as a Special Area under Annex I (the oil pollution annex), establishing it as a zero-discharge zone. In contrast, the same regulation entered into force in the North Sea much later, in 1999 [ 61 ], resulting in a correspondingly later decline in the number of oiled birds compared to the Baltic. Additionally, in 2000, the European Community adopted the EU Directive on Port Reception Facilities for ship-generated waste and cargo residues (2000/59/EC), obliging ships to deliver their oily waste to adequate reception facilities before leaving a port within the European Community [ 70 ]. Moreover, in 1992, MARPOL was amended to make it mandatory for tankers of 5000 dwt to be fitted with double hulls (regulation 19 in Annex I of MARPOL), which also contributes to reducing marine pollution. An important factor contributing to the sharp reduction in illegal oil discharges from ships was the introduction of regular aerial patrols to detect oil spills and identify violators. Cooperation on aerial surveillance in the Baltic Sea region began in the 1980s under the framework of HELCOM. The parties to this agreement have since developed and implemented surveillance measures covering the entire Baltic Sea to detect and monitor oil and other substances entering the marine environment. This primarily involves aircraft patrolling their respective economic zones, with extensive cooperation starting in 1988 [ 53 ]. The Polish sector of the Baltic Sea has been regularly patrolled for oil spills since 1985 [ 71 ]. In 2004, daily satellite-based remote sensing for pollution detection was introduced [ 72 ], significantly enhancing the system for identifying oil spills and their sources. This should be followed by effective enforcement of penalties for oil pollution, which are considered insignificant compared to the profits of most firms involved [ 73 , 74 ]. In the southern North Sea, regular aerial surveys were introduced in the early 1990s, later than in the Baltic Sea [ 75 , 76 ], which likely contributed to the later recorded decrease in oil pollution in that region. A BBS based on standardized protocols is a cheap and easy method for monitoring the degree of marine oil pollution, but it raises some doubts, as changes in the rate at which seabirds are beached are a complex function of bio-physical coupling in the coastal marine environment [ 43 , 77 ]. The number of birds at sea at a given location depends on the quality of the food base, which may change seasonally [ 78 , 79 , 80 ]. Moreover, surface currents and local winds affect the likelihood of bird carcasses drifting ashore [ 43 , 77 ]. Therefore, the number of bird corpses on the coast, to some extent, reflects the interannual variability of prevailing weather conditions [ 77 ]. Furthermore, birds that die at sea may sink, drift away from shore, be scavenged, decompose at sea, or be washed back out to sea, which means that the number of bird carcasses found on beaches will always be lower than the actual number of birds that died at sea. Without detailed analyses based on data on sea currents and wind strength and direction, it is not possible to determine how many birds are affected by this problem [ 43 , 77 ]. Despite these limitations, the BBS is a widely used method that is considered to accurately reflect the state of marine oil pollution and allows for tracking changes over long periods of time [ 15 , 19 , 21 , 47 ]. In the western part of the Gulf of GdaƄsk, a sharp decline in the number of oiled birds occurred in the early 1980s. After the 1984/85 season, the proportion of oiled birds sometimes reached higher values, reaching up to 20–30%. However, during this period, with the exception of the seasons 1994/95 and 1995/96, the number of dead birds found on beaches was very low. After this sharp decline in the number of oiled birds, a short increase was recorded only during the 1994/95 and 1995/96 seasons. In the first season, the main victim of oil pollution was the Mute Swan, a species that stays exclusively close to the coast. In the following season, both Mute Swans and typical offshore species, such as Long-tailed Ducks, were most frequently oiled. This reflects the various locations where oil pollution enters the sea. In recent seasons, however, very few oiled birds have been recorded, and when they are, they are predominantly species from the open sea. This suggests that oil spills are not as frequent as they were fifty years ago, and when they do occur, they tend to happen farther from the shore. The density of dead, oil uncontaminated birds during this period varied only slightly, which probably corresponded to natural mortality. The high number of dead, uncontaminated birds in the 1969/70 and 1983/83 seasons is probably due to the inclusion of birds drowned in fishing nets, which were omitted from the data from the 1984/85 season onwards. The lack of established rules for data collection in earlier years of this research has already been pointed out [ 58 ]. The Baltic Sea is one of the world’s busiest seas, with around 15% of the world’s cargo traffic passing through the region [ 24 ]. Approximately 20% of the ships in the Baltic Sea are tankers carrying a combined total of over 200 million tonnes of oil [ 81 ]. This indicates that the Baltic Sea is particularly vulnerable to oil pollution, which in the past has led to mass mortality events among seabirds in the area [ 25 , 82 , 83 ]. Results from the BBS conducted in the western part of the Gulf of GdaƄsk clearly indicate a sharp decline in bird mortality due to oil pollution, attributable to a reduction in chronic water pollution levels in this region. This decline coincides with Poland’s introduction of aerial patrols to detect oil slicks at sea and to hold responsible parties accountable. Over recent decades, HELCOM’s efforts have produced several concrete and successful regulatory proposals that reduce pollution from ships in the Baltic Sea, promoting a more sustainable use of this critically important marine area, which holds great significance for both the natural environment and human well-being. Therefore, the Beached Bird Surveys programme should be continued in this area of the Polish Baltic coast, as it will enable ongoing monitoring of bird mortality and of the currently low levels of marine pollution by petroleum products. It will also facilitate a rapid response to any deterioration in seawater quality following oil spills. 5. Conclusions Chronic pollution of marine waters with petroleum products and oil spills following shipwrecks has historically resulted in the death of thousands of birds. To monitor seabird mortality caused by oil pollution, regular counts of bird carcasses along the coast were implemented as a simple tool, known as the Beached Bird Survey. This method has certain limitations, as surface currents and local winds influence the likelihood of bird carcasses being washed ashore. Birds that die at sea may sink, drift offshore, be consumed by scavengers, decompose in the water, or be washed back out to sea. Consequently, the number of carcasses found on beaches will always underestimate the actual number of birds that have died at sea. Furthermore, the number of birds present in a given area depends on food availability, which can vary seasonally. Nevertheless, this method is widely used in many countries because it provides comparable results within a given area. Based on 55 years of data from dead birds found along the coastline of the western Gulf of GdaƄsk, this study shows that both the density of oiled birds and the oiling rate declined substantially despite marked increases in ship traffic, the volume of oil transported, and the number of shipping accidents in the Baltic Sea. Most oiled birds recorded were species associated with the open sea, although a short-term rise in mortality during the 1994/95 and 1995/96 seasons affected both coastal and offshore species. Since 2007/08, the density of oiled birds has remained very low, with no oiled individuals recorded during 10 seasons. This sharp decline coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect spills and prosecute offenders. Overall, the results demonstrate that regulatory measures coordinated by HELCOM have been effective in reducing oil pollution in the Baltic Sea. This publication presents the results of one of the longest series of long-term studies on birds washed ashore. The findings indicate the need for continued research to confirm that oil pollution levels in the western part of the Gulf of GdaƄsk are not increasing. Funding This research received no external funding. Institutional Review Board Statement Not applicable. Informed Consent Statement Not applicable. Data Availability Statement The data are available upon request to the author. Acknowledgments I would like to thank everyone who participated in counting dead birds along the beaches of the Gulf of GdaƄsk, especially former biology students from the University of GdaƄsk. Conflicts of Interest The author declares no conflicts of interest. Appendix A Table A1. List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. Table A1. List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. Offshore Species Coastal Species Coastal–Offshore Species Species Name N Species Name N Species Name N Alca or Uria 1 Anas acuta 4 Chroicocephalus ridibundus 953 Alca torda 42 Anas crecca 3 Hydrocoloeus minutus 2 Alle alle 1 Anas platyrhynchos 147 Larus argentatus 2169 Cepphus grylle 49 Anas sp. 1 Larus canus 334 Clangula hyemalis 2336 Anser albifrons 2 Larus hyperboreus 2 Gavia adamsii 1 Anser anser 3 Larus fuscus 28 Gavia arctica 93 Anser fabalis 5 Larus marinus 239 Gavia sp. 7 Anser sp. 1 Larus sp. 40 Gavia stellata 28 Aytha ferina 6 Podiceps sp. 9 Melanitta fusca 793 Aythya fuligula 122 Rissa tridactyla 4 Melanitta nigra 145 Aythya marila 29 Podiceps auritus 16 Aythya sp. 8 Podiceps grisegena 11 Branta bernicla 2 Puffinus sp. 1 Branta leucopis 1 Somateria mollissima 107 Bucephala clangula 75 Stercorarius pomarinus 1 Cygnus columbianus 1 Stercorarius sp. 1 Cygnus cygnus 11 Uria aalge 74 Cygnus olor 2734 Cygnus sp. 3 Fulica atra 740 Mareca penelope 9 Mareca strepera 2 Mergellus albellus 3 Mergus merganser 17 Mergus serrator 124 Mergus sp. 1 Phalacorocorax carbo 272 Podiceps cristatus 443 Spatula querquedula 1 Tachybaptus ruficollis 3 Tadorna tadorna 4 Total 3707 4777 3780 References Bourne, W.; Parrack, J.; Potts, G. 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Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. Table 1. Length of coastline surveyed and number of surveys across subsequent seasons. Season Length of Coastline Surveyed (km) Number of Surveys Data Source 1965/66 6 1 [ 55 ] 1966/67 12 1 [ 55 ] 1969/70 16 1 [ 56 ] 1970/71 18 12 [ 57 ] 1971/72 18 5 [ 57 ] 1972/73 18 3 [ 57 ] 1973/74 31 8 [ 57 ] 1974/75 91 12 [ 58 ] 1975/76 75 12 [ 59 ] 1976/77 91 12 [ 60 ] 1977/78 81 12 [ 60 ] 1979/80 41 5 This study 1980/81 74 8 This study 1982/83 53 4 This study 1984/85–1985/86 121 9 This study 1987/88–2024/25 127 8 This study Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. © 2025 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/ ). Share and Cite MDPI and ACS Style Meissner, W. Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. Sustainability 2025 , 17 , 8037. https://doi.org/10.3390/su17178037 AMA Style Meissner W. Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. Sustainability . 2025; 17(17):8037. https://doi.org/10.3390/su17178037 Chicago/Turabian Style Meissner, WƂodzimierz. 2025. "Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea" Sustainability 17, no. 17: 8037. https://doi.org/10.3390/su17178037 APA Style Meissner, W. (2025). Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. Sustainability , 17 (17), 8037. https://doi.org/10.3390/su17178037 Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here . Article Metrics Article Access Statistics Created with Highcharts 4.0.4 Chart context menu Article access statistics Article Views 12. Jan 13. Jan 14. Jan 15. Jan 16. Jan 17. Jan 18. Jan 19. Jan 20. Jan 21. Jan 22. Jan 23. Jan 24. Jan 25. Jan 26. Jan 27. Jan 28. Jan 29. Jan 30. Jan 31. Jan 1. Feb 2. Feb 3. Feb 4. Feb 5. Feb 6. Feb 7. Feb 8. Feb 9. Feb 10. Feb 11. Feb 12. Feb 13. Feb 14. 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[Academic Editor](https://www.mdpi.com/2071-1050/17/17/8037#academic_editors) [![](https://www.mdpi.com/profiles/1365731/thumb/Tim_Gray.png)Tim Gray](https://sciprofiles.com/profile/1365731?utm_source=mdpi.com&utm_medium=website&utm_campaign=avatar_name) - [Recommended Articles](https://www.mdpi.com/2071-1050/17/17/8037) - [Related Info Link](https://www.mdpi.com/2071-1050/17/17/8037#related) - [Google Scholar](http://scholar.google.com/scholar?q=Significant%20Reduction%20in%20the%20Impact%20of%20Oil%20Spills%20and%20Chronic%20Oil%20Pollution%20on%20Seabirds%3A%20A%20Long-Term%20Case%20Study%20from%20the%20Gulf%20of%20Gda%C5%84sk%2C%20Southern%20Baltic%20Sea) - [More by Author Links](https://www.mdpi.com/2071-1050/17/17/8037#authors) - [on DOAJ]() - [Meissner, W.](http://doaj.org/search/articles?source=%7B%22query%22%3A%7B%22query_string%22%3A%7B%22query%22%3A%22%5C%22W%C5%82odzimierz%20Meissner%5C%22%22%2C%22default_operator%22%3A%22AND%22%2C%22default_field%22%3A%22bibjson.author.name%22%7D%7D%7D) - 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[Get Information](https://www.mdpi.com/authors) [*clear*]() ## JSmol Viewer [*clear*]() *first\_page* [Download PDF](https://www.mdpi.com/2071-1050/17/17/8037/pdf?version=1757139533) *settings* [Order Article Reprints](https://www.mdpi.com/2071-1050/17/17/8037/reprints) Font Type: *Arial* *Georgia* *Verdana* Font Size: Aa Aa Aa Line Spacing: ** ** ** Column Width: ** ** ** Background: Open AccessEditor’s ChoiceArticle # Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea by WƂodzimierz Meissner ![](https://www.mdpi.com/bundles/mdpisciprofileslink/img/unknown-user.png)WƂodzimierz Meissner [SciProfiles](https://sciprofiles.com/profile/1906918?utm_source=mdpi.com&utm_medium=website&utm_campaign=avatar_name) [Scilit](https://scilit.com/scholars?q=W%C5%82odzimierz%20Meissner) [Preprints.org](https://www.preprints.org/search?condition_blocks=[{%22value%22:%22W%C5%82odzimierz+Meissner%22,%22type%22:%22author%22,%22operator%22:null}]&sort_field=relevance&sort_dir=desc&page=1&exact_match=true) [Google Scholar](https://scholar.google.com/scholar?q=W%C5%82odzimierz+Meissner) [![](https://pub.mdpi-res.com/img/design/orcid.png?0465bc3812adeb52?1775737989)](https://orcid.org/0000-0001-5995-9185) Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of GdaƄsk, Wita Stwosza 59, 80-308 GdaƄsk, Poland *Sustainability* **2025**, *17*(17), 8037; <https://doi.org/10.3390/su17178037> Submission received: 8 August 2025 / Revised: 29 August 2025 / Accepted: 30 August 2025 / Published: 6 September 2025 (This article belongs to the Section [Pollution Prevention, Mitigation and Sustainability](https://www.mdpi.com/journal/sustainability/sections/Pollution_Prevention_Mitigation)) [Download *keyboard\_arrow\_down*]() [Download PDF](https://www.mdpi.com/2071-1050/17/17/8037/pdf?version=1757139533) [Download PDF with Cover](https://www.mdpi.com/2071-1050/17/17/8037) [Download XML](https://www.mdpi.com/2071-1050/17/17/8037) [Download Epub](https://www.mdpi.com/2071-1050/17/17/8037/epub) [Browse Figures](https://www.mdpi.com/2071-1050/17/17/8037) [Versions Notes](https://www.mdpi.com/2071-1050/17/17/8037/notes) ## Abstract The marine environment has long been affected by chronic operational oil pollution, leading to the deaths of hundreds of thousands of seabirds. In many countries Beached Bird Survey programmes have been established, in which dead birds with oil-contaminated plumage are counted along shorelines. This study analyses data from Beached Bird Surveys conducted in the western Gulf of GdaƄsk (southern Baltic Sea) between 1965/66 and 2024/25 to assess long-term trends in oil pollution. Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded, of which 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95%. During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals. A significant decline in the number of oiled birds occurred in the early 1980s, and, apart from two anomalous seasons in the mid-1990s, numbers have remained low since then. This sharp drop coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect oil spills and identify violators. The resulting reduction in ship-based pollution has supported more sustainable use of this ecologically important marine region. The findings highlight the effectiveness of international regulations and monitoring efforts in reducing chronic oil pollution and improving the health of the Baltic Sea ecosystem. Keywords: [oil pollution](https://www.mdpi.com/search?q=oil+pollution); [oiled wildlife](https://www.mdpi.com/search?q=oiled+wildlife); [avian mortality](https://www.mdpi.com/search?q=avian+mortality); [marine birds](https://www.mdpi.com/search?q=marine+birds); [southern Baltic](https://www.mdpi.com/search?q=southern+Baltic); [HELCOM](https://www.mdpi.com/search?q=HELCOM); [MARPOL](https://www.mdpi.com/search?q=MARPOL) ## 1\. Introduction The largest spills from damaged tankers into the marine environment have caused the deaths of tens of thousands, or even hundreds of thousands, of birds \[[1](https://www.mdpi.com/2071-1050/17/17/8037#B1-sustainability-17-08037),[2](https://www.mdpi.com/2071-1050/17/17/8037#B2-sustainability-17-08037),[3](https://www.mdpi.com/2071-1050/17/17/8037#B3-sustainability-17-08037),[4](https://www.mdpi.com/2071-1050/17/17/8037#B4-sustainability-17-08037),[5](https://www.mdpi.com/2071-1050/17/17/8037#B5-sustainability-17-08037)\]. These highly publicized oil tanker disasters have drawn significant public attention to the effects of oil pollution on coastal and oceanic ecosystems. The impacts of these disasters on birds remained evident many years later in the form of reduced population numbers and altered habitat use \[[6](https://www.mdpi.com/2071-1050/17/17/8037#B6-sustainability-17-08037),[7](https://www.mdpi.com/2071-1050/17/17/8037#B7-sustainability-17-08037)\]. However, there are no significant correlations between the volume of oil spilled and the number of seabirds affected during such events \[[8](https://www.mdpi.com/2071-1050/17/17/8037#B8-sustainability-17-08037)\], suggesting that other factors, such as spill location, timing, and bird density, play a critical role. While catastrophic spills receive the most public attention, routine and often unreported discharges, such as those from normal shipping operations, tank washing, and bilge water disposal, introduce even larger cumulative volumes of oil into marine ecosystems over time. Moreover, sources of oil pollution include land-based runoff, originating from cities, highways, and vehicles, as well as natural oil seeps \[[9](https://www.mdpi.com/2071-1050/17/17/8037#B9-sustainability-17-08037),[10](https://www.mdpi.com/2071-1050/17/17/8037#B10-sustainability-17-08037),[11](https://www.mdpi.com/2071-1050/17/17/8037#B11-sustainability-17-08037)\]. These small but frequent releases, known as chronic oil pollution, pose significant risks to seabirds and other marine wildlife worldwide \[[12](https://www.mdpi.com/2071-1050/17/17/8037#B12-sustainability-17-08037)\]. Across large ocean regions and extended time frames, chronic oil pollution has been shown to cause sustained mortality with greater long-term impacts on seabird populations than occasional large-scale spills \[[12](https://www.mdpi.com/2071-1050/17/17/8037#B12-sustainability-17-08037),[13](https://www.mdpi.com/2071-1050/17/17/8037#B13-sustainability-17-08037),[14](https://www.mdpi.com/2071-1050/17/17/8037#B14-sustainability-17-08037)\]. Reports of dead, oiled seabirds stranded on beaches first appeared in the late 19th and early 20th centuries \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037)\]. Since then, oil spills and operational discharges resulting in bird mortality have been widely documented, e.g., \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[16](https://www.mdpi.com/2071-1050/17/17/8037#B16-sustainability-17-08037),[17](https://www.mdpi.com/2071-1050/17/17/8037#B17-sustainability-17-08037)\], and the number of oiled birds found along coastlines has begun to be reported worldwide, e.g., \[[18](https://www.mdpi.com/2071-1050/17/17/8037#B18-sustainability-17-08037),[19](https://www.mdpi.com/2071-1050/17/17/8037#B19-sustainability-17-08037),[20](https://www.mdpi.com/2071-1050/17/17/8037#B20-sustainability-17-08037),[21](https://www.mdpi.com/2071-1050/17/17/8037#B21-sustainability-17-08037),[22](https://www.mdpi.com/2071-1050/17/17/8037#B22-sustainability-17-08037)\]. Oil pollution has also affected the Baltic Sea, one of the world’s largest brackish seas \[[23](https://www.mdpi.com/2071-1050/17/17/8037#B23-sustainability-17-08037)\]. Despite covering only 0.1% of the global ocean surface, it is one of the most intensively used seas in the world, handling 15% of global maritime trade \[[24](https://www.mdpi.com/2071-1050/17/17/8037#B24-sustainability-17-08037)\]. Both oil spills following shipwrecks, resulting in the death of thousands of birds, and chronic pollution of marine waters with petroleum products have been recorded here, with the first published reports dating back to 1910 \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. Currently, along with oil spills from Crude Oil Tanker-, Chemical Oil Tanker-, and Bunkering Oil Tanker-class vessels, oils used in the food and chemical industries, such as vegetable oils (palm, coconut, rapeseed), also pose a threat when they enter the sea \[[26](https://www.mdpi.com/2071-1050/17/17/8037#B26-sustainability-17-08037)\]. Oil and its derivatives floating on the water’s surface can easily adhere to a bird’s feathers, damaging the feather structure and causing a rapid drop in body temperature. However, the effects of oil on birds are not limited to thermoregulatory disorders due to the loss of this protective layer; they also include systemic poisoning caused by toxic hydrocarbons. Contaminated birds instinctively attempt to clean their plumage and reapply secretions from the uropygial gland. During this process, the oil is transferred to the bill and ingested. The swallowed oil can cause inflammation throughout the digestive tract. The intestinal villi clump together, impairing nutrient absorption. Hypothermia increases the bird’s energy demands, which it cannot meet due to its compromised digestive function \[[27](https://www.mdpi.com/2071-1050/17/17/8037#B27-sustainability-17-08037)\]. In addition, vapours from spilled oil are toxic. Benzene, toluene, and other light hydrocarbons are rapidly absorbed into the bloodstream through the lungs \[[28](https://www.mdpi.com/2071-1050/17/17/8037#B28-sustainability-17-08037)\]. This can lead to the destruction of red and white blood cells, as well as disruptions to the reproductive system, immune system, liver, spleen, and kidneys \[[29](https://www.mdpi.com/2071-1050/17/17/8037#B29-sustainability-17-08037),[30](https://www.mdpi.com/2071-1050/17/17/8037#B30-sustainability-17-08037),[31](https://www.mdpi.com/2071-1050/17/17/8037#B31-sustainability-17-08037)\]. Although oil can be washed off feathers using appropriate detergents \[[32](https://www.mdpi.com/2071-1050/17/17/8037#B32-sustainability-17-08037),[33](https://www.mdpi.com/2071-1050/17/17/8037#B33-sustainability-17-08037)\], systemic poisoning and inflammation of the gastrointestinal tract result in a very low survival rate for birds, even with intensive treatment in wildlife rescue centres, \[[34](https://www.mdpi.com/2071-1050/17/17/8037#B34-sustainability-17-08037)\] but see \[[35](https://www.mdpi.com/2071-1050/17/17/8037#B35-sustainability-17-08037)\]. Most often, the first sign of an oil spill at sea is the presence of oil-covered birds on beaches. Therefore, in many countries, regular counts of bird carcasses along the coast were implemented as a simple tool for monitoring seabird mortality caused by oil pollution, known as the Beached Bird Survey (BBS) \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. The results of the counts are expressed as densities, that is, the number of birds found per kilometre surveyed, and as the oil rate, defined as the proportion of oiled birds among all birds collected \[[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. Species-specific oiling rates reflect the risk of birds becoming oil-fouled at sea and can be analysed separately for species that occur primarily offshore and those that remain in the coastal zone \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037)\]. Additionally, the species composition of oiled birds indicates differences in exposure risk, as oiling rates are usually much higher in pelagic seabirds, which spend much of their time on the water and often dive and swim rather than fly. In contrast, species that remain predominantly near the coast and move mainly by flying are oiled less frequently \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037),[38](https://www.mdpi.com/2071-1050/17/17/8037#B38-sustainability-17-08037),[39](https://www.mdpi.com/2071-1050/17/17/8037#B39-sustainability-17-08037)\]. The proportion of birds from these two groups can indicate the area of the sea where the birds encountered the oil slick drifting on the surface \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. Although only a small proportion of birds that die at sea wash up on shore, as many sink, are scavenged, or drift away from land \[[40](https://www.mdpi.com/2071-1050/17/17/8037#B40-sustainability-17-08037),[41](https://www.mdpi.com/2071-1050/17/17/8037#B41-sustainability-17-08037),[42](https://www.mdpi.com/2071-1050/17/17/8037#B42-sustainability-17-08037),[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037)\], this cost-effective method still allows for the detection of long-term trends in oil pollution, e.g., \[[42](https://www.mdpi.com/2071-1050/17/17/8037#B42-sustainability-17-08037),[44](https://www.mdpi.com/2071-1050/17/17/8037#B44-sustainability-17-08037),[45](https://www.mdpi.com/2071-1050/17/17/8037#B45-sustainability-17-08037),[46](https://www.mdpi.com/2071-1050/17/17/8037#B46-sustainability-17-08037),[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037)\]. Beached Bird Surveys were also implemented along the Polish Baltic coast, with regular surveys covering a significant part of the coastline beginning in the 1970s \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. However, these counts have continued to the present day only along the western coast of the Gulf of GdaƄsk. The aim of this study is to analyse BBS results from this part of the Polish coast, focusing on long-term changes in the density and proportion of oiled birds, as well as the proportion of typical marine species and those associated with coastal waters. ## 2\. Materials and Methods ### 2\.1. Study Area The Gulf of GdaƄsk is a part of the southern Baltic Sea, with its western part hosting industrial centres, shipyards, sea and fishing ports, and a naval base. As a result, this area is particularly vulnerable to adverse impacts on various elements that contribute to its high natural value, including the large numbers of waterbirds that winter here, and there is significant conflict between marine space use and nature conservation \[[48](https://www.mdpi.com/2071-1050/17/17/8037#B48-sustainability-17-08037),[49](https://www.mdpi.com/2071-1050/17/17/8037#B49-sustainability-17-08037)\]. There are two large seaports on the western coast of the Gulf of GdaƄsk: GdaƄsk and Gdynia ([Figure 1](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f001)). Together, they account for over 60% of the total cargo handled in Polish seaports, more than 66 million tons, and serve over 8000 vessels annually \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037)\]. More than 34% of this traffic comprises chemical tankers, gas tankers, and oil tankers \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037),[51](https://www.mdpi.com/2071-1050/17/17/8037#B51-sustainability-17-08037)\]. The intensity of ship traffic in the Baltic Sea region is expected to increase in the coming years \[[52](https://www.mdpi.com/2071-1050/17/17/8037#B52-sustainability-17-08037)\]. This growth of shipping traffic increases the risk of accidents, especially the risk of oil pollution. A noticeable increase in the transport of hazardous and environmentally harmful goods to ports in the Gulf of GdaƄsk occurred after the opening of the Northern Port in GdaƄsk in 1975, which included a petroleum product transhipment terminal accessible to ships with a draft of up to 15 m \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037)\]. Therefore, the Gulf of GdaƄsk is one of two areas within the Polish Baltic zone with the highest number of oil spills detected \[[14](https://www.mdpi.com/2071-1050/17/17/8037#B14-sustainability-17-08037),[53](https://www.mdpi.com/2071-1050/17/17/8037#B53-sustainability-17-08037)\]. ![Sustainability 17 08037 g001](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g001-550.jpg) **Figure 1.** Study area with surveyed section of coastline in the western part of the Gulf of GdaƄsk, between the mouth of the Vistula River and Cape Rozewie. Large seaports are marked with a blue square, large fishing ports with a blue circle. ### 2\.2. Field Study Surveys were conducted in the western part of the Gulf of GdaƄsk between the mouth of the Vistula River to the east and Cape Rozewie to the west ([Figure 1](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f001)). The coastline in this area is mainly characterized by sandy beaches, with only small patches of reedbeds, which makes it easier to spot dead birds. Dead birds were collected along the coast during seasonal surveys conducted once per month between September and April, covering the period between the 1987/88 and 2024/25 seasons. In the previous three seasons, counting was carried out between November and April at three-week intervals ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Data from other seasons come from counts organised by students of the University of GdaƄsk (unpublished data from seasons 1979/80, 1980/81, and 1982/83) and from the literature sources ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Therefore, this study includes a total of 60 seasons, spanning from 1965/66 to 2024/25, excluding five seasons for which no data were available ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). In this study, a season is defined as the period from autumn to the following summer, reflecting the phenology of most waterbirds in the southern Baltic, which arrive in large numbers in autumn, remain through the winter, and depart for their breeding grounds in spring \[[49](https://www.mdpi.com/2071-1050/17/17/8037#B49-sustainability-17-08037),[54](https://www.mdpi.com/2071-1050/17/17/8037#B54-sustainability-17-08037)\]. **Table 1.** Length of coastline surveyed and number of surveys across subsequent seasons. ![](https://pub.mdpi-res.com/img/table.png) Dead birds were counted according to standard procedures used in Beached Bird Surveys \[[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. During each survey, the coastline was patrolled in search of dead and dying birds. Species were identified, and the birds were examined for traces of oil pollution on their feathers. Birds with plumage contaminated with petroleum substances were classified as oiled birds, while the rest were classified as non-oiled birds. The carcasses were then removed from the shore to prevent repeated counts during subsequent inspections. Birds found in fishing harbours that had drowned in fishing nets were excluded from analyses. In total 12,264 birds found in the western part of the Gulf of GdaƄsk were included in the analysis ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). ### 2\.3. Data Analysis The length of the patrolled coastline varied significantly from season to season, especially before 1984 ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Therefore, the number of birds found was expressed per kilometre surveyed. In addition, as in other analyses of BBS results, the oil rate, i.e., the proportion of oiled birds among all birds collected, was also reported. There is species-specific variation in oiling rates observed in Beached Bird Surveys. Therefore, the 49 identified species and 10 birds identified only to the genus level in this study were grouped into three categories: (1) ichthyophagous and benthophagous species that forage mainly by diving (e.g., divers, auks, and sea ducks), which winter predominantly in the open sea, far from the coast; (2) waterbirds that primarily remain near the coastline (e.g., dabbling ducks, swans, coots, and diving ducks not classified as sea ducks); and (3) gulls, which may forage and reside in both offshore waters and coastal areas, including ports and urbanised zones. In the latter group, unidentified grebes were included, as different grebe species may inhabit either offshore or coastal zones during the non-breeding season ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). In the analysis of species-specific variability in oiling rates over time, gulls and unidentified grebes were excluded, allowing the focus to remain on two groups of species that differ markedly in their primary areas of concentration. ## 3\. Results Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded along the western coast of the Gulf of GdaƄsk ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). Among them, 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95% ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals and a maximum of 31 individuals per 10 km, observed before the 1970/71 season. As late as the 1982/83 season, high densities of dead birds were recorded, amounting to 19 individuals per 10 km, 57% of which had oiled plumage ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). From the 1984/85 season onward, both the density of oiled birds and the oil rate declined substantially. Notably, the density did not exceed four individuals per 10 km. An exception occurred during the 1994/95 and 1995/96 seasons, when 78% and 88% of birds were oiled and densities reached 8 and 12 individuals per 10 km, respectively. During these two seasons, an exceptionally high number of oiled coastal birds was documented, primarily due to one species, the Mute Swan, which alone accounted for 35% of all oiled individuals. The next most affected species was the Long-tailed Duck, a species typical of the open sea zone, with a 26% share. Since the 2007/08 season, the density of oiled birds has been very low, with no oiled individuals found in 10 of the seasons ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). ![Sustainability 17 08037 g002](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g002-550.jpg) **Figure 2.** Percentage (bars) of birds with oiled plumage (based on total number of birds found) and number of oiled birds per 10 km of coastline per survey (line) across seasons. Asterisks denote seasons with missing data. Only in three seasons did the density of non-oiled birds exceed 5 individuals per 10 km, with the highest values of 18 and 14 recorded in 1969/70 and 1982/83, respectively ([Figure 3](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f003)). In the remaining seasons, values ranged from 0.2 to 4.6, with no clear decreasing trend in later seasons, unlike the pattern observed in the density of oiled birds. ![Sustainability 17 08037 g003](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g003-550.jpg) **Figure 3.** Number of birds with non-oiled plumage per 10 km of coastline per survey across seasons. Asterisks denote seasons with missing data. Among the oiled birds found in the Gulf of GdaƄsk in most seasons, species associated with the open sea predominate ([Figure 4](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f004)). The proportion of birds associated with the coastal zone has increased clearly since the 1984/85 season, reaching as much as 95% in the 1995/96 season, when oiled Mute Swans accounted for as much as 87% of all birds with oiled plumage. During the last 29 seasons (1996/97–2024/25), when the number of oiled birds was very low, the proportion of birds associated with the open sea was once again high, reaching 82% ([Figure 4](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f004)). ![Sustainability 17 08037 g004](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g004-550.jpg) **Figure 4.** Proportion of birds with oiled plumage among coastal zone species (green) and offshore zone species (blue) across seasons. Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. ## 4\. Discussion For centuries, economic concerns were the primary focus of the maritime economy, with little attention paid to sustainable development. It was only after several widely publicized tanker disasters, which were extensively reported in the media, that the public began to realize the impact of oil pollution on the maritime environment. In general, there has been a decline in the proportion of oiled birds found on the beaches of the North Sea \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037),[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\] and the southern Baltic (this study). However, local oil rates remained high in both areas \[[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037),[62](https://www.mdpi.com/2071-1050/17/17/8037#B62-sustainability-17-08037)\]. The conspicuous decrease in oiling rates and the density of oiled birds found on the coast of the Gulf of GdaƄsk began in the mid-1980s, whereas on the southern coasts of the North Sea, the number of birds washing ashore with very high oil rates increased dramatically during this period \[[46](https://www.mdpi.com/2071-1050/17/17/8037#B46-sustainability-17-08037),[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\]. Significant decreases in the number of oil slicks detected in the North Sea were observed much later, at the beginning of the 21st century \[[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037),[63](https://www.mdpi.com/2071-1050/17/17/8037#B63-sustainability-17-08037)\]. Outside Europe, the situation varies considerably. A decline in the number of oiled birds has been reported along the central California coast \[[64](https://www.mdpi.com/2071-1050/17/17/8037#B64-sustainability-17-08037)\]. In some parts of British Columbia, a similar decline has been observed, though not in others \[[65](https://www.mdpi.com/2071-1050/17/17/8037#B65-sustainability-17-08037)\]. Beached Bird Surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland was among the highest in the world during a comparable time period \[[20](https://www.mdpi.com/2071-1050/17/17/8037#B20-sustainability-17-08037)\]. It is estimated that between 1998 and 2000, approximately 300,000 seabirds were killed annually in this region due to illegal oil discharges from ships \[[66](https://www.mdpi.com/2071-1050/17/17/8037#B66-sustainability-17-08037)\]. The decline in oil pollution in the western part of the Gulf of GdaƄsk occurred despite a strong increase in ship traffic \[[67](https://www.mdpi.com/2071-1050/17/17/8037#B67-sustainability-17-08037)\], amount of oil transported \[[68](https://www.mdpi.com/2071-1050/17/17/8037#B68-sustainability-17-08037)\], and increase in the number of shipping accidents in the Baltic Sea \[[69](https://www.mdpi.com/2071-1050/17/17/8037#B69-sustainability-17-08037)\]. However, only 7% of these accidents resulted in some kind of pollution, usually containing not more than 0.1–1 tons of oil \[[69](https://www.mdpi.com/2071-1050/17/17/8037#B69-sustainability-17-08037)\]. The number of detected illegal oil spills in the Baltic also decreased \[[68](https://www.mdpi.com/2071-1050/17/17/8037#B68-sustainability-17-08037)\]. This drop coincides with the implementation of the MARPOL Convention in 1983, which designated the Baltic Sea as a Special Area under Annex I (the oil pollution annex), establishing it as a zero-discharge zone. In contrast, the same regulation entered into force in the North Sea much later, in 1999 \[[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\], resulting in a correspondingly later decline in the number of oiled birds compared to the Baltic. Additionally, in 2000, the European Community adopted the EU Directive on Port Reception Facilities for ship-generated waste and cargo residues (2000/59/EC), obliging ships to deliver their oily waste to adequate reception facilities before leaving a port within the European Community \[[70](https://www.mdpi.com/2071-1050/17/17/8037#B70-sustainability-17-08037)\]. Moreover, in 1992, MARPOL was amended to make it mandatory for tankers of 5000 dwt to be fitted with double hulls (regulation 19 in Annex I of MARPOL), which also contributes to reducing marine pollution. An important factor contributing to the sharp reduction in illegal oil discharges from ships was the introduction of regular aerial patrols to detect oil spills and identify violators. Cooperation on aerial surveillance in the Baltic Sea region began in the 1980s under the framework of HELCOM. The parties to this agreement have since developed and implemented surveillance measures covering the entire Baltic Sea to detect and monitor oil and other substances entering the marine environment. This primarily involves aircraft patrolling their respective economic zones, with extensive cooperation starting in 1988 \[[53](https://www.mdpi.com/2071-1050/17/17/8037#B53-sustainability-17-08037)\]. The Polish sector of the Baltic Sea has been regularly patrolled for oil spills since 1985 \[[71](https://www.mdpi.com/2071-1050/17/17/8037#B71-sustainability-17-08037)\]. In 2004, daily satellite-based remote sensing for pollution detection was introduced \[[72](https://www.mdpi.com/2071-1050/17/17/8037#B72-sustainability-17-08037)\], significantly enhancing the system for identifying oil spills and their sources. This should be followed by effective enforcement of penalties for oil pollution, which are considered insignificant compared to the profits of most firms involved \[[73](https://www.mdpi.com/2071-1050/17/17/8037#B73-sustainability-17-08037),[74](https://www.mdpi.com/2071-1050/17/17/8037#B74-sustainability-17-08037)\]. In the southern North Sea, regular aerial surveys were introduced in the early 1990s, later than in the Baltic Sea \[[75](https://www.mdpi.com/2071-1050/17/17/8037#B75-sustainability-17-08037),[76](https://www.mdpi.com/2071-1050/17/17/8037#B76-sustainability-17-08037)\], which likely contributed to the later recorded decrease in oil pollution in that region. A BBS based on standardized protocols is a cheap and easy method for monitoring the degree of marine oil pollution, but it raises some doubts, as changes in the rate at which seabirds are beached are a complex function of bio-physical coupling in the coastal marine environment \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. The number of birds at sea at a given location depends on the quality of the food base, which may change seasonally \[[78](https://www.mdpi.com/2071-1050/17/17/8037#B78-sustainability-17-08037),[79](https://www.mdpi.com/2071-1050/17/17/8037#B79-sustainability-17-08037),[80](https://www.mdpi.com/2071-1050/17/17/8037#B80-sustainability-17-08037)\]. Moreover, surface currents and local winds affect the likelihood of bird carcasses drifting ashore \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Therefore, the number of bird corpses on the coast, to some extent, reflects the interannual variability of prevailing weather conditions \[[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Furthermore, birds that die at sea may sink, drift away from shore, be scavenged, decompose at sea, or be washed back out to sea, which means that the number of bird carcasses found on beaches will always be lower than the actual number of birds that died at sea. Without detailed analyses based on data on sea currents and wind strength and direction, it is not possible to determine how many birds are affected by this problem \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Despite these limitations, the BBS is a widely used method that is considered to accurately reflect the state of marine oil pollution and allows for tracking changes over long periods of time \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[19](https://www.mdpi.com/2071-1050/17/17/8037#B19-sustainability-17-08037),[21](https://www.mdpi.com/2071-1050/17/17/8037#B21-sustainability-17-08037),[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037)\]. In the western part of the Gulf of GdaƄsk, a sharp decline in the number of oiled birds occurred in the early 1980s. After the 1984/85 season, the proportion of oiled birds sometimes reached higher values, reaching up to 20–30%. However, during this period, with the exception of the seasons 1994/95 and 1995/96, the number of dead birds found on beaches was very low. After this sharp decline in the number of oiled birds, a short increase was recorded only during the 1994/95 and 1995/96 seasons. In the first season, the main victim of oil pollution was the Mute Swan, a species that stays exclusively close to the coast. In the following season, both Mute Swans and typical offshore species, such as Long-tailed Ducks, were most frequently oiled. This reflects the various locations where oil pollution enters the sea. In recent seasons, however, very few oiled birds have been recorded, and when they are, they are predominantly species from the open sea. This suggests that oil spills are not as frequent as they were fifty years ago, and when they do occur, they tend to happen farther from the shore. The density of dead, oil uncontaminated birds during this period varied only slightly, which probably corresponded to natural mortality. The high number of dead, uncontaminated birds in the 1969/70 and 1983/83 seasons is probably due to the inclusion of birds drowned in fishing nets, which were omitted from the data from the 1984/85 season onwards. The lack of established rules for data collection in earlier years of this research has already been pointed out \[[58](https://www.mdpi.com/2071-1050/17/17/8037#B58-sustainability-17-08037)\]. The Baltic Sea is one of the world’s busiest seas, with around 15% of the world’s cargo traffic passing through the region \[[24](https://www.mdpi.com/2071-1050/17/17/8037#B24-sustainability-17-08037)\]. Approximately 20% of the ships in the Baltic Sea are tankers carrying a combined total of over 200 million tonnes of oil \[[81](https://www.mdpi.com/2071-1050/17/17/8037#B81-sustainability-17-08037)\]. This indicates that the Baltic Sea is particularly vulnerable to oil pollution, which in the past has led to mass mortality events among seabirds in the area \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037),[82](https://www.mdpi.com/2071-1050/17/17/8037#B82-sustainability-17-08037),[83](https://www.mdpi.com/2071-1050/17/17/8037#B83-sustainability-17-08037)\]. Results from the BBS conducted in the western part of the Gulf of GdaƄsk clearly indicate a sharp decline in bird mortality due to oil pollution, attributable to a reduction in chronic water pollution levels in this region. This decline coincides with Poland’s introduction of aerial patrols to detect oil slicks at sea and to hold responsible parties accountable. Over recent decades, HELCOM’s efforts have produced several concrete and successful regulatory proposals that reduce pollution from ships in the Baltic Sea, promoting a more sustainable use of this critically important marine area, which holds great significance for both the natural environment and human well-being. Therefore, the Beached Bird Surveys programme should be continued in this area of the Polish Baltic coast, as it will enable ongoing monitoring of bird mortality and of the currently low levels of marine pollution by petroleum products. It will also facilitate a rapid response to any deterioration in seawater quality following oil spills. ## 5\. Conclusions Chronic pollution of marine waters with petroleum products and oil spills following shipwrecks has historically resulted in the death of thousands of birds. To monitor seabird mortality caused by oil pollution, regular counts of bird carcasses along the coast were implemented as a simple tool, known as the Beached Bird Survey. This method has certain limitations, as surface currents and local winds influence the likelihood of bird carcasses being washed ashore. Birds that die at sea may sink, drift offshore, be consumed by scavengers, decompose in the water, or be washed back out to sea. Consequently, the number of carcasses found on beaches will always underestimate the actual number of birds that have died at sea. Furthermore, the number of birds present in a given area depends on food availability, which can vary seasonally. Nevertheless, this method is widely used in many countries because it provides comparable results within a given area. Based on 55 years of data from dead birds found along the coastline of the western Gulf of GdaƄsk, this study shows that both the density of oiled birds and the oiling rate declined substantially despite marked increases in ship traffic, the volume of oil transported, and the number of shipping accidents in the Baltic Sea. Most oiled birds recorded were species associated with the open sea, although a short-term rise in mortality during the 1994/95 and 1995/96 seasons affected both coastal and offshore species. Since 2007/08, the density of oiled birds has remained very low, with no oiled individuals recorded during 10 seasons. This sharp decline coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect spills and prosecute offenders. Overall, the results demonstrate that regulatory measures coordinated by HELCOM have been effective in reducing oil pollution in the Baltic Sea. This publication presents the results of one of the longest series of long-term studies on birds washed ashore. The findings indicate the need for continued research to confirm that oil pollution levels in the western part of the Gulf of GdaƄsk are not increasing. ## Funding This research received no external funding. ## Institutional Review Board Statement Not applicable. ## Informed Consent Statement Not applicable. ## Data Availability Statement The data are available upon request to the author. ## Acknowledgments I would like to thank everyone who participated in counting dead birds along the beaches of the Gulf of GdaƄsk, especially former biology students from the University of GdaƄsk. ## Conflicts of Interest The author declares no conflicts of interest. ## Appendix A **Table A1.** List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. ![](https://pub.mdpi-res.com/img/table.png) **Table A1.** List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. | Offshore Species | Coastal Species | Coastal–Offshore Species | | | | |---|---|---|---|---|---| | Species Name | N | Species Name | N | Species Name | N | | Alca or Uria | 1 | Anas acuta | 4 | Chroicocephalus ridibundus | 953 | | Alca torda | 42 | Anas crecca | 3 | Hydrocoloeus minutus | 2 | | Alle alle | 1 | Anas platyrhynchos | 147 | Larus argentatus | 2169 | | Cepphus grylle | 49 | Anas sp. | 1 | Larus canus | 334 | | Clangula hyemalis | 2336 | Anser albifrons | 2 | Larus hyperboreus | 2 | | Gavia adamsii | 1 | Anser anser | 3 | Larus fuscus | 28 | | Gavia arctica | 93 | Anser fabalis | 5 | Larus marinus | 239 | | Gavia sp. | 7 | Anser sp. | 1 | Larus sp. | 40 | | Gavia stellata | 28 | Aytha ferina | 6 | Podiceps sp. | 9 | | Melanitta fusca | 793 | Aythya fuligula | 122 | Rissa tridactyla | 4 | | Melanitta nigra | 145 | Aythya marila | 29 | | | | Podiceps auritus | 16 | Aythya sp. | 8 | | | | Podiceps grisegena | 11 | Branta bernicla | 2 | | | | Puffinus sp. | 1 | Branta leucopis | 1 | | | | Somateria mollissima | 107 | Bucephala clangula | 75 | | | | Stercorarius pomarinus | 1 | Cygnus columbianus | 1 | | | | Stercorarius sp. | 1 | Cygnus cygnus | 11 | | | | Uria aalge | 74 | Cygnus olor | 2734 | | | | | | Cygnus sp. | 3 | | | | | | Fulica atra | 740 | | | | | | Mareca penelope | 9 | | | | | | Mareca strepera | 2 | | | | | | Mergellus albellus | 3 | | | | | | Mergus merganser | 17 | | | | | | Mergus serrator | 124 | | | | | | Mergus sp. | 1 | | | | | | Phalacorocorax carbo | 272 | | | | | | Podiceps cristatus | 443 | | | | | | Spatula querquedula | 1 | | | | | | Tachybaptus ruficollis | 3 | | | | | | Tadorna tadorna | 4 | | | | Total | 3707 | | 4777 | | 3780 | ## References 1. 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[![Sustainability 17 08037 g001](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g001.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g001.png) **Figure 2.** Percentage (bars) of birds with oiled plumage (based on total number of birds found) and number of oiled birds per 10 km of coastline per survey (line) across seasons. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g002](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g002.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g002.png) **Figure 3.** Number of birds with non-oiled plumage per 10 km of coastline per survey across seasons. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g003](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g003.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g003.png) **Figure 4.** Proportion of birds with oiled plumage among coastal zone species (green) and offshore zone species (blue) across seasons. Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g004](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g004.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g004.png) **Table 1.** Length of coastline surveyed and number of surveys across subsequent seasons. | Season | Length of Coastline Surveyed (km) | Number of Surveys | Data Source | |---|---|---|---| | 1965/66 | 6 | 1 | \[[55](https://www.mdpi.com/2071-1050/17/17/8037#B55-sustainability-17-08037)\] | | 1966/67 | 12 | 1 | \[[55](https://www.mdpi.com/2071-1050/17/17/8037#B55-sustainability-17-08037)\] | | 1969/70 | 16 | 1 | \[[56](https://www.mdpi.com/2071-1050/17/17/8037#B56-sustainability-17-08037)\] | | 1970/71 | 18 | 12 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1971/72 | 18 | 5 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1972/73 | 18 | 3 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1973/74 | 31 | 8 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1974/75 | 91 | 12 | \[[58](https://www.mdpi.com/2071-1050/17/17/8037#B58-sustainability-17-08037)\] | | 1975/76 | 75 | 12 | \[[59](https://www.mdpi.com/2071-1050/17/17/8037#B59-sustainability-17-08037)\] | | 1976/77 | 91 | 12 | \[[60](https://www.mdpi.com/2071-1050/17/17/8037#B60-sustainability-17-08037)\] | | 1977/78 | 81 | 12 | \[[60](https://www.mdpi.com/2071-1050/17/17/8037#B60-sustainability-17-08037)\] | | 1979/80 | 41 | 5 | This study | | 1980/81 | 74 | 8 | This study | | 1982/83 | 53 | 4 | This study | | 1984/85–1985/86 | 121 | 9 | This study | | 1987/88–2024/25 | 127 | 8 | This study | | | | |---|---| | | **Disclaimer/Publisher’s Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. | © 2025 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (<https://creativecommons.org/licenses/by/4.0/>). ## Share and Cite **MDPI and ACS Style** Meissner, W. Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability* **2025**, *17*, 8037. https://doi.org/10.3390/su17178037 **AMA Style** Meissner W. 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Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability*. 2025; 17(17):8037. https://doi.org/10.3390/su17178037 **Chicago/Turabian Style** Meissner, WƂodzimierz. 2025. "Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea" *Sustainability* 17, no. 17: 8037. https://doi.org/10.3390/su17178037 **APA Style** Meissner, W. (2025). Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability*, *17*(17), 8037. https://doi.org/10.3390/su17178037 Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details [here](https://www.mdpi.com/about/announcements/784). 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[![sustainability-logo](https://pub.mdpi-res.com/img/journals/sustainability-logo.png?3798e4e58c765aed)](https://www.mdpi.com/journal/sustainability) Article Menu Font Type: *Arial* *Georgia* *Verdana* Font Size: Aa Aa Aa Line Spacing: ** ** ** Column Width: ** ** ** Background: Open AccessEditor’s ChoiceArticle by WƂodzimierz Meissner [![](https://pub.mdpi-res.com/img/design/orcid.png?0465bc3812adeb52?1775737989)](https://orcid.org/0000-0001-5995-9185) Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of GdaƄsk, Wita Stwosza 59, 80-308 GdaƄsk, Poland Submission received: 8 August 2025 / Revised: 29 August 2025 / Accepted: 30 August 2025 / Published: 6 September 2025 ## Abstract The marine environment has long been affected by chronic operational oil pollution, leading to the deaths of hundreds of thousands of seabirds. In many countries Beached Bird Survey programmes have been established, in which dead birds with oil-contaminated plumage are counted along shorelines. This study analyses data from Beached Bird Surveys conducted in the western Gulf of GdaƄsk (southern Baltic Sea) between 1965/66 and 2024/25 to assess long-term trends in oil pollution. Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded, of which 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95%. During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals. A significant decline in the number of oiled birds occurred in the early 1980s, and, apart from two anomalous seasons in the mid-1990s, numbers have remained low since then. This sharp drop coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect oil spills and identify violators. The resulting reduction in ship-based pollution has supported more sustainable use of this ecologically important marine region. The findings highlight the effectiveness of international regulations and monitoring efforts in reducing chronic oil pollution and improving the health of the Baltic Sea ecosystem. ## 1\. Introduction The largest spills from damaged tankers into the marine environment have caused the deaths of tens of thousands, or even hundreds of thousands, of birds \[[1](https://www.mdpi.com/2071-1050/17/17/8037#B1-sustainability-17-08037),[2](https://www.mdpi.com/2071-1050/17/17/8037#B2-sustainability-17-08037),[3](https://www.mdpi.com/2071-1050/17/17/8037#B3-sustainability-17-08037),[4](https://www.mdpi.com/2071-1050/17/17/8037#B4-sustainability-17-08037),[5](https://www.mdpi.com/2071-1050/17/17/8037#B5-sustainability-17-08037)\]. These highly publicized oil tanker disasters have drawn significant public attention to the effects of oil pollution on coastal and oceanic ecosystems. The impacts of these disasters on birds remained evident many years later in the form of reduced population numbers and altered habitat use \[[6](https://www.mdpi.com/2071-1050/17/17/8037#B6-sustainability-17-08037),[7](https://www.mdpi.com/2071-1050/17/17/8037#B7-sustainability-17-08037)\]. However, there are no significant correlations between the volume of oil spilled and the number of seabirds affected during such events \[[8](https://www.mdpi.com/2071-1050/17/17/8037#B8-sustainability-17-08037)\], suggesting that other factors, such as spill location, timing, and bird density, play a critical role. While catastrophic spills receive the most public attention, routine and often unreported discharges, such as those from normal shipping operations, tank washing, and bilge water disposal, introduce even larger cumulative volumes of oil into marine ecosystems over time. Moreover, sources of oil pollution include land-based runoff, originating from cities, highways, and vehicles, as well as natural oil seeps \[[9](https://www.mdpi.com/2071-1050/17/17/8037#B9-sustainability-17-08037),[10](https://www.mdpi.com/2071-1050/17/17/8037#B10-sustainability-17-08037),[11](https://www.mdpi.com/2071-1050/17/17/8037#B11-sustainability-17-08037)\]. These small but frequent releases, known as chronic oil pollution, pose significant risks to seabirds and other marine wildlife worldwide \[[12](https://www.mdpi.com/2071-1050/17/17/8037#B12-sustainability-17-08037)\]. Across large ocean regions and extended time frames, chronic oil pollution has been shown to cause sustained mortality with greater long-term impacts on seabird populations than occasional large-scale spills \[[12](https://www.mdpi.com/2071-1050/17/17/8037#B12-sustainability-17-08037),[13](https://www.mdpi.com/2071-1050/17/17/8037#B13-sustainability-17-08037),[14](https://www.mdpi.com/2071-1050/17/17/8037#B14-sustainability-17-08037)\]. Reports of dead, oiled seabirds stranded on beaches first appeared in the late 19th and early 20th centuries \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037)\]. Since then, oil spills and operational discharges resulting in bird mortality have been widely documented, e.g., \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[16](https://www.mdpi.com/2071-1050/17/17/8037#B16-sustainability-17-08037),[17](https://www.mdpi.com/2071-1050/17/17/8037#B17-sustainability-17-08037)\], and the number of oiled birds found along coastlines has begun to be reported worldwide, e.g., \[[18](https://www.mdpi.com/2071-1050/17/17/8037#B18-sustainability-17-08037),[19](https://www.mdpi.com/2071-1050/17/17/8037#B19-sustainability-17-08037),[20](https://www.mdpi.com/2071-1050/17/17/8037#B20-sustainability-17-08037),[21](https://www.mdpi.com/2071-1050/17/17/8037#B21-sustainability-17-08037),[22](https://www.mdpi.com/2071-1050/17/17/8037#B22-sustainability-17-08037)\]. Oil pollution has also affected the Baltic Sea, one of the world’s largest brackish seas \[[23](https://www.mdpi.com/2071-1050/17/17/8037#B23-sustainability-17-08037)\]. Despite covering only 0.1% of the global ocean surface, it is one of the most intensively used seas in the world, handling 15% of global maritime trade \[[24](https://www.mdpi.com/2071-1050/17/17/8037#B24-sustainability-17-08037)\]. Both oil spills following shipwrecks, resulting in the death of thousands of birds, and chronic pollution of marine waters with petroleum products have been recorded here, with the first published reports dating back to 1910 \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. Currently, along with oil spills from Crude Oil Tanker-, Chemical Oil Tanker-, and Bunkering Oil Tanker-class vessels, oils used in the food and chemical industries, such as vegetable oils (palm, coconut, rapeseed), also pose a threat when they enter the sea \[[26](https://www.mdpi.com/2071-1050/17/17/8037#B26-sustainability-17-08037)\]. Oil and its derivatives floating on the water’s surface can easily adhere to a bird’s feathers, damaging the feather structure and causing a rapid drop in body temperature. However, the effects of oil on birds are not limited to thermoregulatory disorders due to the loss of this protective layer; they also include systemic poisoning caused by toxic hydrocarbons. Contaminated birds instinctively attempt to clean their plumage and reapply secretions from the uropygial gland. During this process, the oil is transferred to the bill and ingested. The swallowed oil can cause inflammation throughout the digestive tract. The intestinal villi clump together, impairing nutrient absorption. Hypothermia increases the bird’s energy demands, which it cannot meet due to its compromised digestive function \[[27](https://www.mdpi.com/2071-1050/17/17/8037#B27-sustainability-17-08037)\]. In addition, vapours from spilled oil are toxic. Benzene, toluene, and other light hydrocarbons are rapidly absorbed into the bloodstream through the lungs \[[28](https://www.mdpi.com/2071-1050/17/17/8037#B28-sustainability-17-08037)\]. This can lead to the destruction of red and white blood cells, as well as disruptions to the reproductive system, immune system, liver, spleen, and kidneys \[[29](https://www.mdpi.com/2071-1050/17/17/8037#B29-sustainability-17-08037),[30](https://www.mdpi.com/2071-1050/17/17/8037#B30-sustainability-17-08037),[31](https://www.mdpi.com/2071-1050/17/17/8037#B31-sustainability-17-08037)\]. Although oil can be washed off feathers using appropriate detergents \[[32](https://www.mdpi.com/2071-1050/17/17/8037#B32-sustainability-17-08037),[33](https://www.mdpi.com/2071-1050/17/17/8037#B33-sustainability-17-08037)\], systemic poisoning and inflammation of the gastrointestinal tract result in a very low survival rate for birds, even with intensive treatment in wildlife rescue centres, \[[34](https://www.mdpi.com/2071-1050/17/17/8037#B34-sustainability-17-08037)\] but see \[[35](https://www.mdpi.com/2071-1050/17/17/8037#B35-sustainability-17-08037)\]. Most often, the first sign of an oil spill at sea is the presence of oil-covered birds on beaches. Therefore, in many countries, regular counts of bird carcasses along the coast were implemented as a simple tool for monitoring seabird mortality caused by oil pollution, known as the Beached Bird Survey (BBS) \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. The results of the counts are expressed as densities, that is, the number of birds found per kilometre surveyed, and as the oil rate, defined as the proportion of oiled birds among all birds collected \[[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. Species-specific oiling rates reflect the risk of birds becoming oil-fouled at sea and can be analysed separately for species that occur primarily offshore and those that remain in the coastal zone \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037)\]. Additionally, the species composition of oiled birds indicates differences in exposure risk, as oiling rates are usually much higher in pelagic seabirds, which spend much of their time on the water and often dive and swim rather than fly. In contrast, species that remain predominantly near the coast and move mainly by flying are oiled less frequently \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037),[38](https://www.mdpi.com/2071-1050/17/17/8037#B38-sustainability-17-08037),[39](https://www.mdpi.com/2071-1050/17/17/8037#B39-sustainability-17-08037)\]. The proportion of birds from these two groups can indicate the area of the sea where the birds encountered the oil slick drifting on the surface \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. Although only a small proportion of birds that die at sea wash up on shore, as many sink, are scavenged, or drift away from land \[[40](https://www.mdpi.com/2071-1050/17/17/8037#B40-sustainability-17-08037),[41](https://www.mdpi.com/2071-1050/17/17/8037#B41-sustainability-17-08037),[42](https://www.mdpi.com/2071-1050/17/17/8037#B42-sustainability-17-08037),[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037)\], this cost-effective method still allows for the detection of long-term trends in oil pollution, e.g., \[[42](https://www.mdpi.com/2071-1050/17/17/8037#B42-sustainability-17-08037),[44](https://www.mdpi.com/2071-1050/17/17/8037#B44-sustainability-17-08037),[45](https://www.mdpi.com/2071-1050/17/17/8037#B45-sustainability-17-08037),[46](https://www.mdpi.com/2071-1050/17/17/8037#B46-sustainability-17-08037),[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037)\]. Beached Bird Surveys were also implemented along the Polish Baltic coast, with regular surveys covering a significant part of the coastline beginning in the 1970s \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037)\]. However, these counts have continued to the present day only along the western coast of the Gulf of GdaƄsk. The aim of this study is to analyse BBS results from this part of the Polish coast, focusing on long-term changes in the density and proportion of oiled birds, as well as the proportion of typical marine species and those associated with coastal waters. ## 2\. Materials and Methods ### 2\.1. Study Area The Gulf of GdaƄsk is a part of the southern Baltic Sea, with its western part hosting industrial centres, shipyards, sea and fishing ports, and a naval base. As a result, this area is particularly vulnerable to adverse impacts on various elements that contribute to its high natural value, including the large numbers of waterbirds that winter here, and there is significant conflict between marine space use and nature conservation \[[48](https://www.mdpi.com/2071-1050/17/17/8037#B48-sustainability-17-08037),[49](https://www.mdpi.com/2071-1050/17/17/8037#B49-sustainability-17-08037)\]. There are two large seaports on the western coast of the Gulf of GdaƄsk: GdaƄsk and Gdynia ([Figure 1](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f001)). Together, they account for over 60% of the total cargo handled in Polish seaports, more than 66 million tons, and serve over 8000 vessels annually \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037)\]. More than 34% of this traffic comprises chemical tankers, gas tankers, and oil tankers \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037),[51](https://www.mdpi.com/2071-1050/17/17/8037#B51-sustainability-17-08037)\]. The intensity of ship traffic in the Baltic Sea region is expected to increase in the coming years \[[52](https://www.mdpi.com/2071-1050/17/17/8037#B52-sustainability-17-08037)\]. This growth of shipping traffic increases the risk of accidents, especially the risk of oil pollution. A noticeable increase in the transport of hazardous and environmentally harmful goods to ports in the Gulf of GdaƄsk occurred after the opening of the Northern Port in GdaƄsk in 1975, which included a petroleum product transhipment terminal accessible to ships with a draft of up to 15 m \[[50](https://www.mdpi.com/2071-1050/17/17/8037#B50-sustainability-17-08037)\]. Therefore, the Gulf of GdaƄsk is one of two areas within the Polish Baltic zone with the highest number of oil spills detected \[[14](https://www.mdpi.com/2071-1050/17/17/8037#B14-sustainability-17-08037),[53](https://www.mdpi.com/2071-1050/17/17/8037#B53-sustainability-17-08037)\]. **Figure 1.** Study area with surveyed section of coastline in the western part of the Gulf of GdaƄsk, between the mouth of the Vistula River and Cape Rozewie. Large seaports are marked with a blue square, large fishing ports with a blue circle. ### 2\.2. Field Study Surveys were conducted in the western part of the Gulf of GdaƄsk between the mouth of the Vistula River to the east and Cape Rozewie to the west ([Figure 1](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f001)). The coastline in this area is mainly characterized by sandy beaches, with only small patches of reedbeds, which makes it easier to spot dead birds. Dead birds were collected along the coast during seasonal surveys conducted once per month between September and April, covering the period between the 1987/88 and 2024/25 seasons. In the previous three seasons, counting was carried out between November and April at three-week intervals ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Data from other seasons come from counts organised by students of the University of GdaƄsk (unpublished data from seasons 1979/80, 1980/81, and 1982/83) and from the literature sources ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Therefore, this study includes a total of 60 seasons, spanning from 1965/66 to 2024/25, excluding five seasons for which no data were available ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). In this study, a season is defined as the period from autumn to the following summer, reflecting the phenology of most waterbirds in the southern Baltic, which arrive in large numbers in autumn, remain through the winter, and depart for their breeding grounds in spring \[[49](https://www.mdpi.com/2071-1050/17/17/8037#B49-sustainability-17-08037),[54](https://www.mdpi.com/2071-1050/17/17/8037#B54-sustainability-17-08037)\]. **Table 1.** Length of coastline surveyed and number of surveys across subsequent seasons. Dead birds were counted according to standard procedures used in Beached Bird Surveys \[[36](https://www.mdpi.com/2071-1050/17/17/8037#B36-sustainability-17-08037)\]. During each survey, the coastline was patrolled in search of dead and dying birds. Species were identified, and the birds were examined for traces of oil pollution on their feathers. Birds with plumage contaminated with petroleum substances were classified as oiled birds, while the rest were classified as non-oiled birds. The carcasses were then removed from the shore to prevent repeated counts during subsequent inspections. Birds found in fishing harbours that had drowned in fishing nets were excluded from analyses. In total 12,264 birds found in the western part of the Gulf of GdaƄsk were included in the analysis ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). ### 2\.3. Data Analysis The length of the patrolled coastline varied significantly from season to season, especially before 1984 ([Table 1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t001)). Therefore, the number of birds found was expressed per kilometre surveyed. In addition, as in other analyses of BBS results, the oil rate, i.e., the proportion of oiled birds among all birds collected, was also reported. There is species-specific variation in oiling rates observed in Beached Bird Surveys. Therefore, the 49 identified species and 10 birds identified only to the genus level in this study were grouped into three categories: (1) ichthyophagous and benthophagous species that forage mainly by diving (e.g., divers, auks, and sea ducks), which winter predominantly in the open sea, far from the coast; (2) waterbirds that primarily remain near the coastline (e.g., dabbling ducks, swans, coots, and diving ducks not classified as sea ducks); and (3) gulls, which may forage and reside in both offshore waters and coastal areas, including ports and urbanised zones. In the latter group, unidentified grebes were included, as different grebe species may inhabit either offshore or coastal zones during the non-breeding season ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). In the analysis of species-specific variability in oiling rates over time, gulls and unidentified grebes were excluded, allowing the focus to remain on two groups of species that differ markedly in their primary areas of concentration. ## 3\. Results Over a total of 55 seasons, 12,264 dead birds representing 49 different species were recorded along the western coast of the Gulf of GdaƄsk ([Table A1](https://www.mdpi.com/2071-1050/17/17/8037#table_body_display_sustainability-17-08037-t0A1)). Among them, 2748 individuals (22%) had oiled plumage. The oil rate was very high up to the 1977/78 season, ranging from 58% to 95% ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). During that period, the highest densities of oiled birds were also recorded, with values exceeding 20 individuals and a maximum of 31 individuals per 10 km, observed before the 1970/71 season. As late as the 1982/83 season, high densities of dead birds were recorded, amounting to 19 individuals per 10 km, 57% of which had oiled plumage ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). From the 1984/85 season onward, both the density of oiled birds and the oil rate declined substantially. Notably, the density did not exceed four individuals per 10 km. An exception occurred during the 1994/95 and 1995/96 seasons, when 78% and 88% of birds were oiled and densities reached 8 and 12 individuals per 10 km, respectively. During these two seasons, an exceptionally high number of oiled coastal birds was documented, primarily due to one species, the Mute Swan, which alone accounted for 35% of all oiled individuals. The next most affected species was the Long-tailed Duck, a species typical of the open sea zone, with a 26% share. Since the 2007/08 season, the density of oiled birds has been very low, with no oiled individuals found in 10 of the seasons ([Figure 2](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f002)). **Figure 2.** Percentage (bars) of birds with oiled plumage (based on total number of birds found) and number of oiled birds per 10 km of coastline per survey (line) across seasons. Asterisks denote seasons with missing data. Only in three seasons did the density of non-oiled birds exceed 5 individuals per 10 km, with the highest values of 18 and 14 recorded in 1969/70 and 1982/83, respectively ([Figure 3](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f003)). In the remaining seasons, values ranged from 0.2 to 4.6, with no clear decreasing trend in later seasons, unlike the pattern observed in the density of oiled birds. **Figure 3.** Number of birds with non-oiled plumage per 10 km of coastline per survey across seasons. Asterisks denote seasons with missing data. Among the oiled birds found in the Gulf of GdaƄsk in most seasons, species associated with the open sea predominate ([Figure 4](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f004)). The proportion of birds associated with the coastal zone has increased clearly since the 1984/85 season, reaching as much as 95% in the 1995/96 season, when oiled Mute Swans accounted for as much as 87% of all birds with oiled plumage. During the last 29 seasons (1996/97–2024/25), when the number of oiled birds was very low, the proportion of birds associated with the open sea was once again high, reaching 82% ([Figure 4](https://www.mdpi.com/2071-1050/17/17/8037#fig_body_display_sustainability-17-08037-f004)). **Figure 4.** Proportion of birds with oiled plumage among coastal zone species (green) and offshore zone species (blue) across seasons. Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. ## 4\. Discussion For centuries, economic concerns were the primary focus of the maritime economy, with little attention paid to sustainable development. It was only after several widely publicized tanker disasters, which were extensively reported in the media, that the public began to realize the impact of oil pollution on the maritime environment. In general, there has been a decline in the proportion of oiled birds found on the beaches of the North Sea \[[37](https://www.mdpi.com/2071-1050/17/17/8037#B37-sustainability-17-08037),[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\] and the southern Baltic (this study). However, local oil rates remained high in both areas \[[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037),[62](https://www.mdpi.com/2071-1050/17/17/8037#B62-sustainability-17-08037)\]. The conspicuous decrease in oiling rates and the density of oiled birds found on the coast of the Gulf of GdaƄsk began in the mid-1980s, whereas on the southern coasts of the North Sea, the number of birds washing ashore with very high oil rates increased dramatically during this period \[[46](https://www.mdpi.com/2071-1050/17/17/8037#B46-sustainability-17-08037),[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\]. Significant decreases in the number of oil slicks detected in the North Sea were observed much later, at the beginning of the 21st century \[[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037),[63](https://www.mdpi.com/2071-1050/17/17/8037#B63-sustainability-17-08037)\]. Outside Europe, the situation varies considerably. A decline in the number of oiled birds has been reported along the central California coast \[[64](https://www.mdpi.com/2071-1050/17/17/8037#B64-sustainability-17-08037)\]. In some parts of British Columbia, a similar decline has been observed, though not in others \[[65](https://www.mdpi.com/2071-1050/17/17/8037#B65-sustainability-17-08037)\]. Beached Bird Surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland was among the highest in the world during a comparable time period \[[20](https://www.mdpi.com/2071-1050/17/17/8037#B20-sustainability-17-08037)\]. It is estimated that between 1998 and 2000, approximately 300,000 seabirds were killed annually in this region due to illegal oil discharges from ships \[[66](https://www.mdpi.com/2071-1050/17/17/8037#B66-sustainability-17-08037)\]. The decline in oil pollution in the western part of the Gulf of GdaƄsk occurred despite a strong increase in ship traffic \[[67](https://www.mdpi.com/2071-1050/17/17/8037#B67-sustainability-17-08037)\], amount of oil transported \[[68](https://www.mdpi.com/2071-1050/17/17/8037#B68-sustainability-17-08037)\], and increase in the number of shipping accidents in the Baltic Sea \[[69](https://www.mdpi.com/2071-1050/17/17/8037#B69-sustainability-17-08037)\]. However, only 7% of these accidents resulted in some kind of pollution, usually containing not more than 0.1–1 tons of oil \[[69](https://www.mdpi.com/2071-1050/17/17/8037#B69-sustainability-17-08037)\]. The number of detected illegal oil spills in the Baltic also decreased \[[68](https://www.mdpi.com/2071-1050/17/17/8037#B68-sustainability-17-08037)\]. This drop coincides with the implementation of the MARPOL Convention in 1983, which designated the Baltic Sea as a Special Area under Annex I (the oil pollution annex), establishing it as a zero-discharge zone. In contrast, the same regulation entered into force in the North Sea much later, in 1999 \[[61](https://www.mdpi.com/2071-1050/17/17/8037#B61-sustainability-17-08037)\], resulting in a correspondingly later decline in the number of oiled birds compared to the Baltic. Additionally, in 2000, the European Community adopted the EU Directive on Port Reception Facilities for ship-generated waste and cargo residues (2000/59/EC), obliging ships to deliver their oily waste to adequate reception facilities before leaving a port within the European Community \[[70](https://www.mdpi.com/2071-1050/17/17/8037#B70-sustainability-17-08037)\]. Moreover, in 1992, MARPOL was amended to make it mandatory for tankers of 5000 dwt to be fitted with double hulls (regulation 19 in Annex I of MARPOL), which also contributes to reducing marine pollution. An important factor contributing to the sharp reduction in illegal oil discharges from ships was the introduction of regular aerial patrols to detect oil spills and identify violators. Cooperation on aerial surveillance in the Baltic Sea region began in the 1980s under the framework of HELCOM. The parties to this agreement have since developed and implemented surveillance measures covering the entire Baltic Sea to detect and monitor oil and other substances entering the marine environment. This primarily involves aircraft patrolling their respective economic zones, with extensive cooperation starting in 1988 \[[53](https://www.mdpi.com/2071-1050/17/17/8037#B53-sustainability-17-08037)\]. The Polish sector of the Baltic Sea has been regularly patrolled for oil spills since 1985 \[[71](https://www.mdpi.com/2071-1050/17/17/8037#B71-sustainability-17-08037)\]. In 2004, daily satellite-based remote sensing for pollution detection was introduced \[[72](https://www.mdpi.com/2071-1050/17/17/8037#B72-sustainability-17-08037)\], significantly enhancing the system for identifying oil spills and their sources. This should be followed by effective enforcement of penalties for oil pollution, which are considered insignificant compared to the profits of most firms involved \[[73](https://www.mdpi.com/2071-1050/17/17/8037#B73-sustainability-17-08037),[74](https://www.mdpi.com/2071-1050/17/17/8037#B74-sustainability-17-08037)\]. In the southern North Sea, regular aerial surveys were introduced in the early 1990s, later than in the Baltic Sea \[[75](https://www.mdpi.com/2071-1050/17/17/8037#B75-sustainability-17-08037),[76](https://www.mdpi.com/2071-1050/17/17/8037#B76-sustainability-17-08037)\], which likely contributed to the later recorded decrease in oil pollution in that region. A BBS based on standardized protocols is a cheap and easy method for monitoring the degree of marine oil pollution, but it raises some doubts, as changes in the rate at which seabirds are beached are a complex function of bio-physical coupling in the coastal marine environment \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. The number of birds at sea at a given location depends on the quality of the food base, which may change seasonally \[[78](https://www.mdpi.com/2071-1050/17/17/8037#B78-sustainability-17-08037),[79](https://www.mdpi.com/2071-1050/17/17/8037#B79-sustainability-17-08037),[80](https://www.mdpi.com/2071-1050/17/17/8037#B80-sustainability-17-08037)\]. Moreover, surface currents and local winds affect the likelihood of bird carcasses drifting ashore \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Therefore, the number of bird corpses on the coast, to some extent, reflects the interannual variability of prevailing weather conditions \[[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Furthermore, birds that die at sea may sink, drift away from shore, be scavenged, decompose at sea, or be washed back out to sea, which means that the number of bird carcasses found on beaches will always be lower than the actual number of birds that died at sea. Without detailed analyses based on data on sea currents and wind strength and direction, it is not possible to determine how many birds are affected by this problem \[[43](https://www.mdpi.com/2071-1050/17/17/8037#B43-sustainability-17-08037),[77](https://www.mdpi.com/2071-1050/17/17/8037#B77-sustainability-17-08037)\]. Despite these limitations, the BBS is a widely used method that is considered to accurately reflect the state of marine oil pollution and allows for tracking changes over long periods of time \[[15](https://www.mdpi.com/2071-1050/17/17/8037#B15-sustainability-17-08037),[19](https://www.mdpi.com/2071-1050/17/17/8037#B19-sustainability-17-08037),[21](https://www.mdpi.com/2071-1050/17/17/8037#B21-sustainability-17-08037),[47](https://www.mdpi.com/2071-1050/17/17/8037#B47-sustainability-17-08037)\]. In the western part of the Gulf of GdaƄsk, a sharp decline in the number of oiled birds occurred in the early 1980s. After the 1984/85 season, the proportion of oiled birds sometimes reached higher values, reaching up to 20–30%. However, during this period, with the exception of the seasons 1994/95 and 1995/96, the number of dead birds found on beaches was very low. After this sharp decline in the number of oiled birds, a short increase was recorded only during the 1994/95 and 1995/96 seasons. In the first season, the main victim of oil pollution was the Mute Swan, a species that stays exclusively close to the coast. In the following season, both Mute Swans and typical offshore species, such as Long-tailed Ducks, were most frequently oiled. This reflects the various locations where oil pollution enters the sea. In recent seasons, however, very few oiled birds have been recorded, and when they are, they are predominantly species from the open sea. This suggests that oil spills are not as frequent as they were fifty years ago, and when they do occur, they tend to happen farther from the shore. The density of dead, oil uncontaminated birds during this period varied only slightly, which probably corresponded to natural mortality. The high number of dead, uncontaminated birds in the 1969/70 and 1983/83 seasons is probably due to the inclusion of birds drowned in fishing nets, which were omitted from the data from the 1984/85 season onwards. The lack of established rules for data collection in earlier years of this research has already been pointed out \[[58](https://www.mdpi.com/2071-1050/17/17/8037#B58-sustainability-17-08037)\]. The Baltic Sea is one of the world’s busiest seas, with around 15% of the world’s cargo traffic passing through the region \[[24](https://www.mdpi.com/2071-1050/17/17/8037#B24-sustainability-17-08037)\]. Approximately 20% of the ships in the Baltic Sea are tankers carrying a combined total of over 200 million tonnes of oil \[[81](https://www.mdpi.com/2071-1050/17/17/8037#B81-sustainability-17-08037)\]. This indicates that the Baltic Sea is particularly vulnerable to oil pollution, which in the past has led to mass mortality events among seabirds in the area \[[25](https://www.mdpi.com/2071-1050/17/17/8037#B25-sustainability-17-08037),[82](https://www.mdpi.com/2071-1050/17/17/8037#B82-sustainability-17-08037),[83](https://www.mdpi.com/2071-1050/17/17/8037#B83-sustainability-17-08037)\]. Results from the BBS conducted in the western part of the Gulf of GdaƄsk clearly indicate a sharp decline in bird mortality due to oil pollution, attributable to a reduction in chronic water pollution levels in this region. This decline coincides with Poland’s introduction of aerial patrols to detect oil slicks at sea and to hold responsible parties accountable. Over recent decades, HELCOM’s efforts have produced several concrete and successful regulatory proposals that reduce pollution from ships in the Baltic Sea, promoting a more sustainable use of this critically important marine area, which holds great significance for both the natural environment and human well-being. Therefore, the Beached Bird Surveys programme should be continued in this area of the Polish Baltic coast, as it will enable ongoing monitoring of bird mortality and of the currently low levels of marine pollution by petroleum products. It will also facilitate a rapid response to any deterioration in seawater quality following oil spills. ## 5\. Conclusions Chronic pollution of marine waters with petroleum products and oil spills following shipwrecks has historically resulted in the death of thousands of birds. To monitor seabird mortality caused by oil pollution, regular counts of bird carcasses along the coast were implemented as a simple tool, known as the Beached Bird Survey. This method has certain limitations, as surface currents and local winds influence the likelihood of bird carcasses being washed ashore. Birds that die at sea may sink, drift offshore, be consumed by scavengers, decompose in the water, or be washed back out to sea. Consequently, the number of carcasses found on beaches will always underestimate the actual number of birds that have died at sea. Furthermore, the number of birds present in a given area depends on food availability, which can vary seasonally. Nevertheless, this method is widely used in many countries because it provides comparable results within a given area. Based on 55 years of data from dead birds found along the coastline of the western Gulf of GdaƄsk, this study shows that both the density of oiled birds and the oiling rate declined substantially despite marked increases in ship traffic, the volume of oil transported, and the number of shipping accidents in the Baltic Sea. Most oiled birds recorded were species associated with the open sea, although a short-term rise in mortality during the 1994/95 and 1995/96 seasons affected both coastal and offshore species. Since 2007/08, the density of oiled birds has remained very low, with no oiled individuals recorded during 10 seasons. This sharp decline coincides with the enforcement of MARPOL regulations and the introduction of regular aerial surveillance to detect spills and prosecute offenders. Overall, the results demonstrate that regulatory measures coordinated by HELCOM have been effective in reducing oil pollution in the Baltic Sea. This publication presents the results of one of the longest series of long-term studies on birds washed ashore. The findings indicate the need for continued research to confirm that oil pollution levels in the western part of the Gulf of GdaƄsk are not increasing. ## Funding This research received no external funding. ## Institutional Review Board Statement Not applicable. ## Informed Consent Statement Not applicable. ## Data Availability Statement The data are available upon request to the author. ## Acknowledgments I would like to thank everyone who participated in counting dead birds along the beaches of the Gulf of GdaƄsk, especially former biology students from the University of GdaƄsk. ## Conflicts of Interest The author declares no conflicts of interest. ## Appendix A **Table A1.** List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. **Table A1.** List and number of individuals of taxa found during BBS included in this study, belonging to three groups of species associated with different marine zones. Taxa are arranged in alphabetical order. | Offshore Species | Coastal Species | Coastal–Offshore Species | | | | |---|---|---|---|---|---| | Species Name | N | Species Name | N | Species Name | N | | Alca or Uria | 1 | Anas acuta | 4 | Chroicocephalus ridibundus | 953 | | Alca torda | 42 | Anas crecca | 3 | Hydrocoloeus minutus | 2 | | Alle alle | 1 | Anas platyrhynchos | 147 | Larus argentatus | 2169 | | Cepphus grylle | 49 | Anas sp. | 1 | Larus canus | 334 | | Clangula hyemalis | 2336 | Anser albifrons | 2 | Larus hyperboreus | 2 | | Gavia adamsii | 1 | Anser anser | 3 | Larus fuscus | 28 | | Gavia arctica | 93 | Anser fabalis | 5 | Larus marinus | 239 | | Gavia sp. | 7 | Anser sp. | 1 | Larus sp. | 40 | | Gavia stellata | 28 | Aytha ferina | 6 | Podiceps sp. | 9 | | Melanitta fusca | 793 | Aythya fuligula | 122 | Rissa tridactyla | 4 | | Melanitta nigra | 145 | Aythya marila | 29 | | | | Podiceps auritus | 16 | Aythya sp. | 8 | | | | Podiceps grisegena | 11 | Branta bernicla | 2 | | | | Puffinus sp. | 1 | Branta leucopis | 1 | | | | Somateria mollissima | 107 | Bucephala clangula | 75 | | | | Stercorarius pomarinus | 1 | Cygnus columbianus | 1 | | | | Stercorarius sp. | 1 | Cygnus cygnus | 11 | | | | Uria aalge | 74 | Cygnus olor | 2734 | | | | | | Cygnus sp. | 3 | | | | | | Fulica atra | 740 | | | | | | Mareca penelope | 9 | | | | | | Mareca strepera | 2 | | | | | | Mergellus albellus | 3 | | | | | | Mergus merganser | 17 | | | | | | Mergus serrator | 124 | | | | | | Mergus sp. | 1 | | | | | | Phalacorocorax carbo | 272 | | | | | | Podiceps cristatus | 443 | | | | | | Spatula querquedula | 1 | | | | | | Tachybaptus ruficollis | 3 | | | | | | Tadorna tadorna | 4 | | | | Total | 3707 | | 4777 | | 3780 | ## References 1. 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[![Sustainability 17 08037 g001](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g001.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g001.png) **Figure 2.** Percentage (bars) of birds with oiled plumage (based on total number of birds found) and number of oiled birds per 10 km of coastline per survey (line) across seasons. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g002](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g002.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g002.png) **Figure 3.** Number of birds with non-oiled plumage per 10 km of coastline per survey across seasons. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g003](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g003.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g003.png) **Figure 4.** Proportion of birds with oiled plumage among coastal zone species (green) and offshore zone species (blue) across seasons. Consecutive seasons with low numbers of oiled birds were combined. Sample sizes are indicated above. Asterisks denote seasons with missing data. [![Sustainability 17 08037 g004](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g004.png)](https://www.mdpi.com/sustainability/sustainability-17-08037/article_deploy/html/images/sustainability-17-08037-g004.png) **Table 1.** Length of coastline surveyed and number of surveys across subsequent seasons. | Season | Length of Coastline Surveyed (km) | Number of Surveys | Data Source | |---|---|---|---| | 1965/66 | 6 | 1 | \[[55](https://www.mdpi.com/2071-1050/17/17/8037#B55-sustainability-17-08037)\] | | 1966/67 | 12 | 1 | \[[55](https://www.mdpi.com/2071-1050/17/17/8037#B55-sustainability-17-08037)\] | | 1969/70 | 16 | 1 | \[[56](https://www.mdpi.com/2071-1050/17/17/8037#B56-sustainability-17-08037)\] | | 1970/71 | 18 | 12 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1971/72 | 18 | 5 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1972/73 | 18 | 3 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1973/74 | 31 | 8 | \[[57](https://www.mdpi.com/2071-1050/17/17/8037#B57-sustainability-17-08037)\] | | 1974/75 | 91 | 12 | \[[58](https://www.mdpi.com/2071-1050/17/17/8037#B58-sustainability-17-08037)\] | | 1975/76 | 75 | 12 | \[[59](https://www.mdpi.com/2071-1050/17/17/8037#B59-sustainability-17-08037)\] | | 1976/77 | 91 | 12 | \[[60](https://www.mdpi.com/2071-1050/17/17/8037#B60-sustainability-17-08037)\] | | 1977/78 | 81 | 12 | \[[60](https://www.mdpi.com/2071-1050/17/17/8037#B60-sustainability-17-08037)\] | | 1979/80 | 41 | 5 | This study | | 1980/81 | 74 | 8 | This study | | 1982/83 | 53 | 4 | This study | | 1984/85–1985/86 | 121 | 9 | This study | | 1987/88–2024/25 | 127 | 8 | This study | | | | |---|---| | | **Disclaimer/Publisher’s Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. | © 2025 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (<https://creativecommons.org/licenses/by/4.0/>). ## Share and Cite **MDPI and ACS Style** Meissner, W. Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability* **2025**, *17*, 8037. https://doi.org/10.3390/su17178037 **AMA Style** Meissner W. Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability*. 2025; 17(17):8037. https://doi.org/10.3390/su17178037 **Chicago/Turabian Style** Meissner, WƂodzimierz. 2025. "Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea" *Sustainability* 17, no. 17: 8037. https://doi.org/10.3390/su17178037 **APA Style** Meissner, W. (2025). Significant Reduction in the Impact of Oil Spills and Chronic Oil Pollution on Seabirds: A Long-Term Case Study from the Gulf of GdaƄsk, Southern Baltic Sea. *Sustainability*, *17*(17), 8037. https://doi.org/10.3390/su17178037 Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. 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