Seabird Monitoring in the German North Sea and Baltic Sea 2017

Photo: Harro Müller

Kai Borkenhagen, Nils Guse, Hanna Markones, Nele Markones, Henriette Schwemmer, Stefan Garthe

Research and Technology Centre West Coast (FTZ), Kiel University, Hafentörn 1, D-25761 Büsum Seabird Monitoring 2017

Introduction Seabirds, as top predators, are an important component of marine ecosystems. They are under increasing pressure from anthropogenic activities such as fishing, the development of offshore wind energy, shipping traffic, marine pollution, etc. Recording species occurrence and improving knowledge of the distribution patterns, population trends, and habitat requirements is vital to effectively manage protected areas and associated seabirds. The Birds Directive (BD) and the Marine Strategy Framework Directive (MSFD) of the European Union require their member states to regularly submit reports based on data presented in this report. In addition, the data are used to develop indicators to assess the state of the environment within the framework of the regional sea conventions OSPAR and HELCOM, and the data and knowledge gained are incorporated into marine spatial planning and the assessment of anthropogenic activities.

The marine biodiversity monitoring programme for vertebrates is funded by the German Federal Agency for Nature Conservation (Bundesamt für Naturschutz - BfN) and carried out by the FTZ in collaboration with the German Oceanographic Museum Stralsund (Deutsches Meeresmuseum - DMM) and the Institute for Terrestrial and Aquatic Wildlife Research of the Hanover University of Veterinary Medicine Foundation (Institut für Terrestrische und Aquatische Wildtierforschung der Stiftung Tierärztliche Hochschule Hannover - ITAW), using funds of the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU).

The results presented in this report are based on regular large-scale surveys of seabird occurrence in the German North and Baltic Seas. These observations are based on standardised methods and provide data on spatio-temporal patterns and habitat use of seabirds in the ecosystems of the North Sea and Baltic Sea.

Assessments within the framework of Birds Directive and MSFD and the development of indicators for OSPAR and HELCOM are based on these data. The data and findings furthermore contribute to marine spatial planning and the assessment of anthropogenic activities.

Survey overview

North Sea All aerial surveys planned for winter and spring had to be cancelled due to delays in funding approval. The breeding bird population of Helgoland was recorded during an aerial survey in summer. An observer-based aerial survey was implemented simultaneously to one of two digital comparison surveys for the PhoViComp project, but conditions on the second aerial survey day were unsuitable for an observer flight. An aerial survey of the entire North Sea was carried out as scheduled in autumn. A 15-day ship-based survey in the North Sea was implemented aboard ship of opportunity “Heincke“ of the AWI (Table 1).

Seabird Monitoring 2017

Baltic Sea Four of five aerial surveys scheduled for spring and winter had to be cancelled due to problems with funding approval. One aerial survey could be carried out simultaneously to a digital comparison survey of the PhoViComp project in March. Just one of two aerial surveys of the SPA Pomeranian Bay planned for spring was implemented. The second aerial survey day was cancelled because of logistics (weather, aircraft availability). The three-day aerial survey of the entire German Baltic Sea that was planned for autumn had to be cancelled for logistical reasons as well. The seven-day ship-based autumn survey in the Pomeranian Bay was implemented as a nine-day survey on board of vessel “Ludwig Prandl“ of the HZG (Helmholtz-Zentrum Geesthacht, hereafter HZG). An eight-day ship- based survey in the Baltic Sea was implemented aboard ship of opportunity “Haithabu” of the LLUR (State Agency for Agriculture, Environment and Rural Areas of the German Federal State Schleswig- Holstein) (Table 1).

Table 1: Survey Design and Implementation in 2017. p= plane; sh= ship; EGB = Eastern German Bight; PoBay = Pomeranian Bay; w= winter; sp= spring, s= summer; au= autumn.

planned implemented Survey w sp s au w sp s au SPA EGB and adjacent areas (winter) p 4 0

SPA EGB and adjacent areas (spring) p 2 0 EEZ around Helgoland (summer) p 1 1 entire North Sea Aug/Sept p 5 5

North Sea PhoViComp Amrum Bank p 2 2 0 1 ship-based survey North Sea: vessel of sh 15 15 opportunity SPA Pomeranian Bay ship sh 7 7 7 9

partial survey SPA PoBay spring p 2 0 partial survey SPA PoBay summer p 2 1 full survey autumn p 3 0

Baltic Sea PhoViComp-PoBay p 2 1 0 1 ship-based survey Baltic Sea sh 8 8 (ship of opportunity)

Survey Results The course of the transect, the most important findings and special observations of each individual survey are described below. Densities of all species observed within the transect are shown in the tables, disregarding distance correction. Given that the spatial distribution of survey efforts may differ considerably, any numbers and density values are comparable to a limited extent only. All distribution maps are based on distance-corrected numbers of birds.

North Sea

Aerial seabird survey of the inner German Bight in early summer Seabirds of the inner German Bight were recorded during two aerial surveys on 22nd of May and 21st of June (Figure 1). The northern part of the survey area was covered simultaneously with a digital

Seabird Monitoring 2017

comparison survey (project PhoViComp). The set of species was dominated by typical breeding bird species of Helgoland – northern gannet, kittiwake, and common guillemot – although lesser black- backed gulls and sandwich terns were numerous as well (Table 2). Several divers were still observed in the area in May. The main distribution range of guillemots was in the late Pleistocene paleo Elbe River valley to the west of Helgoland (Figure 2). In addition to seabirds, over 200 harbour porpoises, a white-beaked dolphin and, for the first time, an ocean sunfish were observed.

Figure 1: Transect course of the aerial seabird survey in the inner German Bight in early summer 2017. Counting was interrupted north-northwesterly of Helgoland while the aircraft flew over the wind farm.

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Figure 2: Distribution of common guillemots in the inner German Bight in early summer 2017.

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Table 2: Abundance and average density of species recorded in the transect during the aerial surveys of the German Bight in early summer 2017.

species scientific name count density [ind./km²] red-throated diver Gavia stellata 22 0.021 unidentified diver Gavia spec. 10 0.009 northern fulmar Fulmarus glacialis 3 0.003 northern gannet Morus bassanus 132 0.124 common scoter Melanitta nigra 44 0.041 little gull Hydrocoloeus minutus 26 0.024 black-headed gull Chroicocephalus ridibundus 1 0.001 common gull Larus canus 3 0.003 unidentified small gull 8 0.007 lesser black-backed gull Larus fuscus 298 0.279 herring gull Larus argentatus 8 0.007 unidentified large gull 6 0.006 great/lesser black-backed gull Larus marinus / Larus fuscus 1 0.001 black-legged kittiwake Rissa tridactyla 454 0.425 unidentified gull 8 0.007 sandwich tern Sterna sandvicensis 173 0.162 Arctic tern Sterna paradisaea 1 0.001 common / Arctic tern Sterna hirundo / S. paradisaea 18 0.017 unidentified Sterna-tern Sterna spec. 16 0.015 common guillemot Uria aalge 227 0.213 common guillemot / razorbill Uria aalge / Alca torda 3 0.003 unidentified bird 3 0.003 unidentified songbird 2 0.002 white-beaked dolphin Lagenorhynchus albirostris 1 0.001 harbour porpoise Phocoena phocoena 207 0.194 grey seal Halichoerus grypus 2 0.002 harbour seal Phoca vitulina 25 0.023 grey / harbour seal 10 0.009 unidentified marine mammal 7 0.007 ocean sunfish Mola mola 1 0.001

Ship-based seabird surveys in the German Bight in summer Surveys were conducted aboard ship of opportunity “Heincke“ in the northwestern and central German Bight, joining a benthos survey of the AWI (Alfred-Wegener Institute) from 8th to 18th of May, and a survey of the impact of offshore wind farms on fish occurrence of the IMF (Institute of Marine Ecosystem and Fishery Science) at the University of Hamburg from 28th of June to 5th of July (Figure 3). Northern gannets, lesser black-backed gulls, black-legged kittiwakes and common guillemots dominated the scene. Larger numbers of common and Arctic terns were predominantly observed near the coast (Table 3). Northern gannets were observed in the entire survey area except for the Weser delta (Figure 4). Of note are further a red-necked phalarope and a little auk (Table 3).

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Figure 3: Transect course of the ship-based seabird survey in the German Bight in summer 2017. The survey was implemented aboard a ship of opportunity in two sections, alongside the AWI and the IHF.

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Figure 4: Distribution of northern gannets in the German Bight in summer 2017.

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Table 3. Abundance and average density of species recorded in the transect during the ship-based survey in the German Bight in summer 2017.

species scientific name count density [Ind. /km²] northern fulmar Fulmarus glacialis 13 0.025 northern gannet Morus bassanus 160 0.310 great cormorant Phalacrocorax carbo 23 0.045 common shelduck Tadorna tadorna 3 0.006 common eider Somateria mollissima 6 0.012 common scoter Melanitta nigra 219 0.425 peregrine falcon Falco peregrinus 2 0.004 red-necked phalarope Phalaropus lobatus 1 0.002 great skua Stercorarius skua 1 0.002 little gull Hydrocoloeus minutus 1 0.002 black-headed gull Chroicocephalus ridibundus 49 0.095 common gull Larus canus 13 0.025 lesser black-backed gull Larus fuscus 241 0.468 herring gull Larus argentatus 20 0.039 great black-backed gull Larus marinus 3 0.006 black-legged kittiwake Rissa tridactyla 46 0.089 sandwich tern Sterna sandvicensis 42 0.081 common tern Sterna hirundo 47 0.091 Arctic tern Sterna paradisaea 4 0.008 common / Arctic tern Sterna hirundo / S. paradisaea 5 0.010 common guillemot Uria aalge 70 0.136 common guillemot / razorbill Uria aalge / Alca torda 1 0.002 little auk Alle alle 1 0.002 common swift Apus apus 2 0.004 harbour porpoise Phocoena phocoena 14 0.027 harbour seal Phoca vitulina 6 0.012 grey / harbour seal 1 0.002

Aerial seabird survey in the German Bight in late summer The entire German EEZ (Exclusive Economic Zone) was covered by an aerial seabird survey on 11th of August, 22nd of August, 26th of August, 30th of August, and 3rd of September (Figure 5). In terms of numbers, pelagic species like northern fulmars, northern gannets, lesser black-backed gulls, black- legged kittiwakes, and common guillemots dominated the scene. Several common scoters were observed near the coast. Of note were large numbers of skuas and the sighting of two white-beaked dolphins (Table 4). The distribution patterns of northern fulmar, common guillemot, and skua are very similar to one another. All three species are most abundant in deep-water areas in the western part of the German EEZ (Figure 6, Figure 7, Figure 8).

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Figure 5: Transect course of the aerial seabird survey in the German Bight in late summer 2017.

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Figure 6: Distribution of northern fulmars in the German Bight in late summer 2017.

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Figure 7: Distribution of common guillemots in the German Bight in late summer 2017.

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Figure 8: Distribution of great skuas in the German Bight in late summer 2017.

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Table 4: Abundance and average density of species recorded in the transect during the aerial surveys of the German Bight in late summer 2017.

species scientific name count density [Ind. /km²] northern fulmar Fulmarus glacialis 282 0.117 northern gannet Morus bassanus 274 0.114 great cormorant Phalacrocorax carbo 3 0.001 common scoter Melanitta nigra 1,354 0.564 sparrowhawk Accipiter nisus 1 0.000 dunlin Calidris alpina 1 0.000 unidentified wader Limicolae 5 0.002 pomarine skua Stercorarius pomarinus 1 0.000 Arctic skua Stercorarius parasiticus 1 0.000 great skua Stercorarius skua 23 0.010 Arctic/ pomarine / long-tailed Stercorarius parasiticus / skua S. pomarinus / S. longicaudus 1 0.000 unidentified skua Stercorarius spec. 1 0.000 little gull Hydrocoloeus minutus 57 0.024 black-headed gull Chroicocephalus ridibundus 15 0.006 common gull Larus canus 10 0.004 unidentified small gull 1 0.000 lesser black-backed gull Larus fuscus 900 0.375 herring gull Larus argentatus 61 0.025 great black-backed gull Larus marinus 5 0.002 unidentified large gull 10 0.004 black-legged kittiwake Rissa tridactyla 298 0.124 unidentified gull 6 0.002 sandwich tern Sterna sandvicensis 162 0.067 common tern Sterna hirundo 14 0.006 Arctic tern Sterna paradisaea 3 0.001 common / Arctic tern Sterna hirundo / S. paradisaea 259 0.108 unidentified Sterna-tern Sterna spec. 9 0.004 tern / small gull 12 0.005 common guillemot Uria aalge 2,038 0.848 common guillemot / razorbill Uria aalge / Alca torda 40 0.017 unidentified alcid 1 0.000 unidentified songbird 3 0.001 unidentified bird 11 0.005 white-beaked dolphin Lagenorhynchus albirostris 6 0.002 harbour porpoise Phocoena phocoena 160 0.067 grey seal Halichoerus grypus 2 0.001 harbour seal Phoca vitulina 18 0.007 unidentified marine mammal 2 0.001

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Ship-based seabird surveys in the German Bight in autumn Ship-based seabird surveys took place in the western German Bight at offshore wind farms Global Tech I and BARD Offshore 1 between 12th and 21st of September (Figure 9). It was conducted aboard a ship of opportunity, research vessel “Heincke“, alongside the Institute of Marine Ecosystem and Fishery Science at the University of Hamburg. In terms of numbers, lesser black-backed gulls, black- legged kittiwakes, and common guillemots dominated the scene (Table 5). High densities of black- legged kittiwakes were limited to a very small area (Figure 10).

Figure 9: Transect course of the ship-based seabird survey in the German Bight in September 2017.

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Figure 10: Distribution of black-legged kittiwakes in the German Bight in September 2017.

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Table 5: Abundance and average density of species recorded in the transect during the ship-based surveys of the German Bight in September 2017.

species scientific name count density [ind. /km²] northern fulmar Fulmarus glacialis 11 0.058 northern gannet Morus bassanus 12 0.064 common shelduck Tadorna tadorna 1 0.005 European golden plover Pluvialis apricaria 6 0.032 great skua Stercorarius skua 1 0.005 little gull Hydrocoloeus minutus 6 0.032 black-headed gull Chroicocephalus ridibundus 4 0.021 common gull Larus canus 2 0.011 lesser black-backed gull Larus fuscus 60 0.319 herring gull Larus argentatus 1 0.005 great black-backed gull Larus marinus 9 0.048 unidentified large gull 2 0.011 black-legged kittiwake Rissa tridactyla 68 0.361 sandwich tern Sterna sandvicensis 4 0.021 common tern Sterna hirundo 3 0.016 common / Arctic tern Sterna hirundo / S. paradisaea 1 0.005 common guillemot Uria aalge 50 0.266 harbour seal Phoca vitulina 2 0.011

Seabird Monitoring 2017

Baltic Sea

Ship-based seabird survey in the Pomeranian Bay in winter A ship-based seabird survey of the Pomeranian Bay took place aboard charter vessel “Skoven“ between 16th and 22nd of January (Figure 11). The majority of recorded birds were seaducks, diving ducks, and sawbills. In addition, a number of divers, grebes (particularly great crested grebes), and cormorants were recorded. Particularly noteworthy are a great northern diver, 26 Slavonian grebes and 30 black guillemots (Table 6). High densities of long-tailed ducks were found at Odra Bank, at Adler Ground, at the Bay of Greifswald, and off the coast of Usedom and Rügen (Figure 12). Velvet scoters were particularly common at the Odra Bank and to the west of Greifswalder Oie (Figure 13). Great crested grebes mainly utilised shallow water areas along the coasts of Rügen and Usedom, as well as the Bay of Greifswald (Figure 14). Slavonian grebes were concentrated at the northern and eastern side of the Odra Bank (Figure 15).

Figure 11: Transect course of the ship-based seabird survey in the Pomeranian Bay in January 2017.

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Figure 12: Distribution of long-tailed ducks in the Pomeranian Bay in January 2017.

Figure 13: Distribution of velvet scoters in the Pomeranian Bay in January 2017.

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Figure 14: Distribution of great crested grebes in the Pomeranian Bay in January 2017.

Figure 15: Distribution of Slavonian grebes in the Pomeranian Bay in January 2017.

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Table 6: Abundance and average density of species recorded in the transect during the ship-based surveys of the Pomeranian Bay in January 2017.

Species scientific name count density [ind. /km²] red-throated diver Gavia stellata 5 0.018 black-throated diver Gavia arctica 17 0.061 great northern diver Gavia immer 1 0.004 unidentified diver Gavia spec. 22 0.079 great crested grebe Podiceps cristatus 487 1.750 red-necked grebe Podiceps grisegena 17 0.061 Slavonian grebe Podiceps auritus 26 0.093 unidentified grebe Podicipedidae 8 0.029 great cormorant Phalacrocorax carbo 335 1.204 mute swan Cygnus olor 5 0.018 Eurasian wigeon Anas penelope 28 0.101 Eurasian teal Anas crecca 3 0.011 tufted duck Aythya fuligula 6 0.022 tufted duck / greater scaup Aythya fuligula / Aythya marila 2,302 8.273 greater scaup Aythya marila 270 0.970 common eider Somateria mollissima 6 0.022 long-tailed duck Clangula hyemalis 9,109 32.738 common scoter Melanitta nigra 160 0.575 velvet scoter Melanitta fusca 2,694 9.682 common golden-eye Bucephala clangula 168 0.604 smew Mergus albellus 4 0.014 red-breasted merganser Mergus serrator 286 1.028 goosander Mergus merganser 1,498 5.384 unidentified sawbill Mergus spec. 5 0.018 white-tailed eagle Haliaeetus albicilla 1 0.004 Eurasian coot Fulica atra 406 1.459 black-headed gull Chroicocephalus ridibundus 2 0.007 common gull Larus canus 64 0.230 herring gull Larus argentatus 127 0.456 great black-backed gull Larus marinus 26 0.093 common guillemot Uria aalge 15 0.054 razor bill Alca torda 30 0.108 common guillemot / razor bill Uria aalge / Alca torda 22 0.079 black guillemot Cepphus grylle 30 0.108 grey seal Halichoerus grypus 1 0.004

Ship-based seabird surveys in the western German Baltic Sea in late winter Seabird surveys took place in the western German Baltic Sea aboard LLUR multi-purpose vessel “Haithabu“ between 13th and 16th of February, on 20th of February, and between 7th and 9th of March (Figure 16). These surveys were conducted as part of the Federal/State Measurement Programme for the Marine Environment of the North Sea and the Baltic Sea (BLMP - Bund/Länder-Messprogramm für die Meeresumwelt von Nord- und Ostsee). The majority of birds recorded within the transect were seaducks, sawbills, grebes (213 great crested grebes, 25 red-necked grebes and two Slavonian grebes), cormorants, and diving ducks (Table 7). Common eiders, common scoters, and long-tailed ducks show similar distribution patterns, with their main occurrence at shallow water sites near the

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coast. Nonetheless, their distribution in the Bay of Kiel stretches to the border of the Danish EEZ (Figure 17, Figure 18, Figure 19).

Figure 16: Transect course of the ship-based seabird survey in the western Baltic Sea in February and March 2017.

Figure 17: Distribution of common eiders in the western Baltic Sea in February and March 2017.

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Figure 18: Distribution of common scoters in the western Baltic Sea in February and March 2017.

Figure 19: Distribution of long-tailed ducks in the western Baltic Sea in February and March 2017.

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Table 7: Abundance and average density of species recorded in the transect during the ship-based surveys of the western Baltic Sea in February and March 2017.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 4 0.018 black-throated diver Gavia arctica 6 0.027 unidentified diver Gavia spec. 18 0.081 little grebe Tachybaptus ruficollis 44 0.198 great crested grebe Podiceps cristatus 213 0.960 red-necked grebe Podiceps grisegena 25 0.113 Slavonian grebe Podiceps auritus 2 0.009 black-necked grebe Podiceps nigricollis 6 0.027 unidentified grebe Podicipedidae 11 0.050 northern gannet Morus bassanus 1 0.005 great cormorant Phalacrocorax carbo 192 0.866 grey heron Ardea cinerea 1 0.005 mute swan Cygnus olor 3 0.014 whooper swan Cygnus cygnus 18 0.081 greylag goose Anser anser 6 0.027 brent goose Branta bernicla 27 0.122 Eurasian wigeon Anas penelope 342 1.542 Eurasian teal Anas crecca 4 0.018 mallard Anas platyrhynchos 87 0.392 greater scaup Aythya marila 3,619 16.319 common eider Somateria mollissima 14,193 63.999 long-tailed duck Clangula hyemalis 5,009 22.586 common scoter Melanitta nigra 19,198 86.567 velvet scoter Melanitta fusca 339 1.529 common golden-eye Bucephala clangula 254 1.145 red-breasted merganser Mergus serrator 612 2.760 goosander Mergus merganser 77 0.347 Eurasian coot Fulica atra 1,628 7.341 black-headed gull Chroicocephalus ridibundus 18 0.081 common gull Larus canus 13 0.059 herring gull Larus argentatus 394 1.777 great black-backed gull Larus marinus 53 0.239 common guillemot Uria aalge 6 0.027 razorbill Alca torda 96 0.433 common guillemot / razorbill Uria aalge / Alca torda 21 0.095 black guillemot Cepphus grylle 1 0.005 skylark Alauda arvensis 38 0.171 hooded crow Corvus corone corone 3 0.014 starling Sturnus vulgaris 40 0.180 harbour porpoise Phocoena phocoena 6 0.027

Seabird Monitoring 2017

Aerial seabird survey in the Pomeranian Bay in spring An aerial seabird survey was conducted simultaneously with a digital comparison survey (project PhoViComp) in the Pomeranian Bay and the Bay of Greifswald on 13th of March (Figure 20). The majority of birds were seaducks, but large numbers of divers, cormorants, gulls and guillemots were also sighted (Table 8). While common scoters were mainly concentrated around the Odra Bank and the waters around Greifswalder Oie (Figure 21), long-tailed ducks were numerous at the Adler Ground and the Bay of Greifswald (Figure 22). Red-throated divers mainly utilised areas to the south and west of the Odra Bank (Figure 23).

Figure 20: Transect course of the aerial seabird surveys in the Pomeranian Bay in March 2017.

Figure 21: Distribution of common scoters in the Pomeranian Bay in March 2017.

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Figure 22: Distribution of long-tailed ducks in the Pomeranian Bay in March 2017.

Figure 23: Distribution of red-throated divers in the Pomeranian Bay in March 2017.

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Table 8: Abundance and average density of species recorded in the transect during the aerial surveys of the Pomeranian Bay in March 2017.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 138 0.531 unidentified diver Gavia spec. 23 0.088 great crested grebe Podiceps cristatus 1 0.004 unidentified grebe Podicipedidae 5 0.019 great cormorant Phalacrocorax carbo 108 0.415 mute swan Cygnus olor 62 0.238 mallard Anas platyrhynchos 44 0.169 greater scaup Aythya marila 51 0.196 unidentified diving duck Aythya spec. 100 0.385 common eider Somateria mollissima 3 0.012 long-tailed duck Clangula hyemalis 6,093 23.436 common scoter Melanitta nigra 2,022 7.778 velvet scoter Melanitta fusca 124 0.477 common scoter / velvet scoter Melanitta nigra / Melanitta fusca 26 0.100 common golden-eye Bucephala clangula 123 0.473 red-breasted merganser Mergus serrator 12 0.046 goosander Mergus merganser 4 0.015 unidentified sawbill Mergus spec. 8 0.031 unidentified duck 8 0.031 black-headed gull Chroicocephalus ridibundus 13 0.050 common gull Larus canus 10 0.038 herring gull Larus argentatus 67 0.258 great black-backed gull Larus marinus 11 0.042 unidentified large gull 14 0.054 unidentified gull 153 0.589 common guillemot Uria aalge 9 0.035 razorbill Alca torda 3 0.012 common guillemot / razorbill Uria aalge / Alca torda 94 0.362 woodpigeon Columba palumbus 5 0.019 collared dove Streptopelia decaocto 1 0.004 unidentified bird 122 0.469

Aerial seabird surveys at the Odra Bank in August An aerial seabird survey took place in the Odra Bank area on 23rd of August (Figure 24). Common scoters were the most common species with an average density of 1.3 individuals per km² (Table 9) and a near even distribution along the entire central Odra Bank (Figure 25). Numbers of velvet scoters were significantly lower in comparison. Of note are further the sightings of three harbour porpoises, one long-tailed duck, and one black guillemot.

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Figure 24: Transect course of the aerial seabird surveys at the Odra Bank in August 2017.

Figure 25: Distribution of common scoters along the Odra Bank in August 2017.

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Table 9: Abundance and average density of species recorded in the transect during the aerial surveys at the Odra Bank in August 2017.

species scientific name count density [ind. /km²] unidentified diver Gavia spec. 3 0.008 great cormorant Phalacrocorax carbo 14 0.036 long-tailed duck Clangula hyemalis 1 0.003 common scoter Melanitta nigra 517 1.341 velvet scoter Melanitta fusca 16 0.041 rough-legged buzzard Buteo lagopus 1 0.003 unidentified wader Limicolae 6 0.016 lesser black-backed gull Larus fuscus 2 0.005 herring gull Larus argentatus 3 0.008 unidentified large gull 1 0.003 black guillemot Cepphus grylle 1 0.003 unidentified songbird 4 0.010 unidentified bird 2 0.005 harbour porpoise Phocoena phocoena 3 0.008

Ship-based seabird surveys in the Pomeranian Bay and west of Rügen in autumn A ship-based seabird survey of the Pomeranian Bay, the Bay of Greifswald and the area west of Rügen took place aboard HZG vessel “Ludwig Prandtl“ between 21st and 29th of November (Figure 26). Seaducks, diving ducks, and sawbills dominated the scene. Sightings of black-throated divers were notably more frequent than those of red-throated divers. Of note are 58 Slavonian grebes and 29 black guillemots (Table 10). Long-tailed ducks were spotted throughout the area in shallow waters (Figure 27). Scaups were mainly seen at the Bay of Greifswald, the area around the Greifswalder Oie, the Tromper Wiek, and the northwestern mouth of the Strela Sound (Figure 28).

Figure 26: Transect course of the ship-based seabird surveys in the Pomeranian Bay and west of Rügen in November 2017.

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Figure 27: Distribution of long-tailed ducks in the Pomeranian Bay and west of Rügen in November 2017.

Figure 28: Distribution of greater scaups in the Pomeranian Bay and west of Rügen in November 2017.

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Table 10: Abundance and average density of species recorded in the transect during the ship-based surveys of the Pomeranian Bay and west of Rügen in November 2017.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 19 0.075 black-throated diver Gavia arctica 66 0.260 unidentified diver Gavia spec. 42 0.166 great crested grebe Podiceps cristatus 136 0.536 red-necked grebe Podiceps grisegena 15 0.059 Slavonian grebe Podiceps auritus 58 0.229 unidentified grebe Podicipedidae 6 0.024 great cormorant Phalacrocorax carbo 253 0.997 mute swan Cygnus olor 651 2.566 tundra swan Cygnus bewickii 1 0.004 whooper swan Cygnus cygnus 1 0.004 Eurasian wigeon Anas penelope 237 0.934 mallard Anas platyrhynchos 15 0.059 Northern pintail Anas acuta 44 0.173 tufted duck Aythya fuligula 1,001 3.945 greater scaup Aythya marila 13,117 51.697 common eider Somateria mollissima 87 0.343 long-tailed duck Clangula hyemalis 11,166 44.007 common scoter Melanitta nigra 4,037 15.911 velvet scoter Melanitta fusca 1,765 6.956 common golden-eye Bucephala clangula 404 1.592 red-breasted merganser Mergus serrator 1,181 4.655 goosander Mergus merganser 7 0.028 little gull Hydrocoloeus minutus 1 0.004 black-headed gull Chroicocephalus ridibundus 61 0.240 common gull Larus canus 64 0.252 herring gull Larus argentatus 397 1.565 Caspian gull Larus (argentatus) cachinnans 1 0.004 great black-backed gull Larus marinus 65 0.256 common guillemot Uria aalge 73 0.288 razorbill Alca torda 59 0.233 common guillemot / razorbill Uria aalge / Alca torda 78 0.307 black guillemot Cepphus grylle 29 0.114 hooded crow Corvus corone cornix 1 0.004 Eurasian siskin Carduelis spinus 25 0.099 bullfinch Pyrrhula pyrrhula 1 0.004 harbour porpoise Phocoena phocoena 1 0.004 grey seal Halichoerus grypus 4 0.016

Seabird Monitoring 2017

Distribution pattern of common scoters over the course of the year In recent years, common scoters are a lot less common in the Pomeranian Bay than in the western Baltic Sea in winter. Other than in the western Baltic Sea, their density in the Pomeranian Bay is even lower than the density of velvet scoters (Table 6, Table 7). This development confirms the shift of common scoter distribution to the west, as described in recent years, and is in marked contrast to the situation in the 1990s and 2000s. In spring, common scoter numbers increase significantly in the Pomeranian Bay, by far surpassing the density of velvet scoters (Table 8). In summer, common scoters in the German Baltic Sea are almost exclusively restricted to the Odra Bank region (Table 9, Figure 25) and the density of velvet scoters is low (Table 9). In autumn, the density of common scoters in the Pomeranian Bay rises and is significantly higher than in winter (Table 10). However, it is worth noting that the autumn survey also covered the area west of Rügen with particularly high densities of common scoters in some parts.

Further results Current results of the monitoring surveys, including sighting maps and density maps of all common seabird species, are accessible on the website of the German Federal Agency for Nature Conservation (Bundesamt für Naturschutz - BfN), under geo-information services. https://www.bfn.de/themen/meeresnaturschutz/marines-monitoring.html

Acknowledgements Volker Dierschke helped organise aerial surveys. Observers Jonas Buddemeier, Volker Dierschke, Margus Ellermaa, Martin Gottschling, Nicole Jüngling, Kolja Lehmann-Muriithi, Hilger Lemke, Tabea Löblein, Esther Rickert, and Stefan Weiel significantly contributed to the success of the surveys. HZG made research vessel “Ludwig Prandtl” available for the November cruise. AWI, IHF and LLUR allowed us to join expeditions with the “Heincke” and the “Haithabu”. We would like to thank Volker Dzaak, Lars Gutow, Jens Floeter, and Angela Trumpf for planning and conducting these expeditions. We would also like to express our gratitude to captain, crew and fellow passengers for the cooperation and a pleasant time on board. Further many thanks to all pilots for a pleasant work environment and safe transport during aerial surveys. Eugen Faber and Uwe Lange of Brockmann Consult provided valuable assistance with data management. Many thanks to Harro Müller for providing the cover photo. Thanks also to Bettina Mendel for creating the map templates.