Seabird Monitoring in the German North Sea and 2015

photo: Kai Borkenhagen

Kai Borkenhagen1, Nils Guse1, Mirko Hauswirth2, Nele Markones1, Bettina Mendel1, Henriette Schwemmer1, Stefan Garthe1

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

2) Federal Agency for Nature Conservation, , D-18581 Seabird Monitoring 2015

Introduction Seabirds, as top predators, are an important component of marine ecosystems. Anthropogenic activities, such as fisheries, development of offshore wind energy, shipping, marine pollution, etc. exert increasing pressure on them. The monitoring of their occurrence and precise knowledge of their distribution patterns, population numbers, trends and habitat requirements are prerequisites for their effective protection and successful management of protected areas. The Birds Directive (BD) and the Marine Strategy Framework Directive (MSFD) of the European Union require Member States to submit regular reports, based on the data regularly collected. In addition, the data are used to develop indicators for assessing the environmental status within the framework of the regional sea conventions OSPAR and HELCOM, and the data and knowledge gained is incorporated into marine spatial planning and the assessment of anthropogenic activities.

The marine biodiversity monitoring programme for vertebrates is financed 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 (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) with funds from the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und Nukleare Sicherheit - BMU).

The results presented here are based on repeated large-scale surveys of seabirds in the German North and Baltic Seas. These surveys are carried out following internationally standardized methods, and provide data on spatio-temporal patterns and habitat use of seabirds in the ecosystems of the North Sea and Baltic Sea.

Survey overview

North Sea In winter, a three-day aerial survey of the inner German Bight was planned and completed successfully. For logistical reasons (weather, aircraft availability), two days of the three-day aerial survey of the inner German Bight scheduled for spring had to be cancelled. Instead, an additional survey in the north-western part of the German EEZ, and an aerial survey in parallel to a digital comparison survey were conducted. Eight of the planned 15 days of ship-based survey in the North Sea were implemented. The remaining effort was reallocated to a survey in the Baltic Sea (Table 1).

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Baltic Sea A three-day aerial survey of the entire German Baltic Sea had been scheduled for winter. For logistic reasons all flights had to be cancelled and were reallocated to surveys in spring, summer and autumn in the area of the SPA Bay of . The ship-based surveys in the eastern German Baltic Sea over-fulfilled the original plan (Table 1).

Table 1: Survey plan and implementation of the German seabird monitoring programme in 2015. p= plane; sh= ship; EGB= Eastern German Bight; PomBay= ; wi= winter; sp= spring, su= summer; au= autumn.

planned implemented Survey wi sp su au wi sp su au SPA EGB and adjacent areas (winter) p 3 3

SPA EGB and adjacent areas (spring) p 3 1

EEZ around Helgoland (summer) p 1 2 th Sea th North-western part of EEZ p 1

Nor Ship-based survey North Sea: vessel of sh 15 8 opportunity Entire German Baltic Sea (winter) p 3 0

SPA Bay of Pomerania, ship-based (winter) sh 7 7

Entire German Baltic Sea (spring) p 3 4

SPA PomBay (summer) p 2

Baltic Sea Ship-based Survey Baltic Sea: vessel of sh 4 8 opportunity

Survey results In this chapter the study area, the most important results, and special observations are presented for each survey. Since the surveys sometimes differ considerably in the spatial distribution of the survey effort, the numbers and density values given in the tables are comparable only to a limited extent.

North Sea

Aerial survey of the eastern part of the German Bight in winter On 22nd of January and 11th of February the eastern part of the German Bight was covered with two aerial surveys (Figure 1). Small gaps in survey coverage are due to military activities. With about 14 500 individuals and an average density of 11.7 Ind./km² the Common scoter was the most abundant species (Table 2). The occurrence of Common scoters was concentrated near Eiderstedt, west of the North Frisian Islands, on the Amrumbank and north of the East Frisian Islands (Figure 2). In addition to numerous Common eiders, which were mainly observed in coastal areas, many divers and typical pelagic species, such as Northern gannet, Northern fulmar, auks and Black-legged kittiwake, were registered in the survey area (Table 1).

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Figure 1: Survey transects of the aerial seabird survey in the eastern German Bight in winter 2015.

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Table 2: Number and average density of species registered inside transect during the aerial seabird survey in the eastern German Bight in winter 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 57 0,045 Black-throated diver Gavia arctica 2 0,002 unidentified diver Gavia spec. 48 0,038 Northern fulmar Fulmarus glacialis 26 0,021 Northern gannet Sula bassana 6 0,005 Greylag goose Anser anser 2 0,002 Common eider Somateria mollissima 1 180 0,941 Common scoter Melanitta nigra 14 635 11,667 Velvet scoter Melanitta fusca 1 0,001 Oystercatcher Haematopus ostralegus 1 0,001 Little gull Hydrocoloeus minutus 99 0,079 Black-headed gull Chroicocephalus ridibundus 14 0,011 Common gull Larus canus 125 0,100 unidentified small gull 327 0,261

Lesser black-backed gull Larus fuscus 1 0,001 Herring gull Larus argentatus 552 0,440 Great black-backed gull Larus marinus 23 0,018 unidentified large gull 2 0,002

Black-legged kittiwake Rissa tridactyla 140 0,112 unidentified gull 75 0,060

Common guillemot Uria aalge 67 0,053 Razorbill Alca torda 15 0,012 Common guillemot / Uria aalge / Alca torda 114 0,091 Razorbill Harbour porpoise Phocoena phocoena 67 0,053 Grey seal Halichoerus grypus 2 0,002 Harbour seal Phoca vitulina 7 0,006 Grey seal / Harbour seal 3 0,002

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Figure 2: Distribution of Common scoters in the eastern German Bight in winter 2015.

Aerial survey of the eastern German Bight in spring On 18th of April the inner German Bight in the area of the Elbe estuary was surveyed with an aerial survey (Figure 3). Common scoters and Lesser black-backed gulls were the most abundant species with more than 450 individuals each, while almost 200 divers and more than 100 Little gulls were detected (Table 3). Divers concentrated in the North and West of the area covered, whereas only a few divers were found in the Elbe estuary (Figure 4).

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Figure 3: Survey transects of the aerial seabird survey in the eastern German Bight in spring 2015.

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Table 3: Number and average density of species registered inside transect during the aerial seabird survey in the inner German Bight in spring 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 131 0,104 Black-throated diver Gavia arctica 10 0,008 unidentified diver Gavia spec. 54 0,043 Northern gannet Sula bassana 26 0,021 Great cormorant Phalacrocorax carbo 5 0,004 Common eider Somateria mollissima 1 0,001 Common scoter Melanitta nigra 466 0,371 Velvet scoter Melanitta fusca 2 0,002 Red-breasted merganser Mergus serrator 5 0,004 Little gull Hydrocoloeus minutus 106 0,084 Black-headed gull Chroicocephalus ridibundus 17 0,014 Common gull Larus canus 132 0,105 unidentified small gull 16 0,013 Lesser black-backed gull Larus fuscus 465 0,371 Herring gull Larus argentatus 188 0,150 unidentified large gull 4 0,003 Black-legged kittiwake Rissa tridactyla 180 0,143 unidentified gull 19 0,015 Sandwich tern Sterna sandvicensis 39 0,031 Common / Arctic tern Sterna hirundo / Sterna paradisaea 12 0,010 Common guillemot Uria aalge 58 0,046 Razorbill Alca torda 1 0,001 Common guillemot / Razorbill Uria aalge / Alca torda 20 0,016 unidentified songbird 2 0,002 Harbour porpoise Phocoena phocoena 28 0,022 Grey seal Halichoerus grypus 2 0,002 Harbour seal Phoca vitulina 6 0,005 Grey seal / Harbour seal 2 0,002

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Figure 4: Distribution of divers Gavia spec. in the eastern German Bight in spring 2015.

Aerial survey of the area around Helgoland and the north-western German EEZ in summer On 4th of June, 11th of June, and 11th of July the aerial seabird surveys for summer took place in the German North Sea (Figure 5). In addition to about 2 800 Common scoters, a large number of pelagic species, such as Black-legged kittiwakes, Northern gannets, auks and Northern fulmars, were recorded (Table 4). Next to a hotspot on the Dogger Bank, Black-legged kittiwakes were found throughout the entire area and were only absent in the easternmost part (Figure 6). In addition to seabirds, almost 250 harbour porpoises, one Common minke whale, seven unidentified dolphins and several seals were observed (Table 4). The aerial survey on 11th of July was implemented parallel to a digital comparison survey (HELBIRD project) north of Helgoland and achieved a small-scale picture of bird distribution around the offshore wind farms of the Helgoland cluster.

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Figure 5: Survey transects of the aerial seabird survey in the German North Sea in summer 2015.

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Table 4: Number and average density of species registered inside transect during the aerial seabird survey around Helgoland and in the north-western German EEZ in summer 2015.

species scientific name number density [Ind./km²] Northern fulmar Fulmarus glacialis 109 0,097 Northern gannet Sula bassana 166 0,148 Great cormorant Phalacrocorax carbo 1 0,001 Greylag goose Anser anser 4 0,004 Common scoter Melanitta nigra 2 810 2,509 Velvet scoter Melanitta fusca 3 0,003 Sanderling Calidris alba 40 0,036 unidentified wader Limicolae 1 0,001 Little gull Hydrocoloeus minutus 3 0,003 Black-headed gull Chroicocephalus ridibundus 6 0,005 Common gull Larus canus 4 0,004 Lesser black-backed gull Larus fuscus 364 0,325 Herring gull Larus argentatus 14 0,012 Great black-backed gull Larus marinus 3 0,003 unidentified large gull 1 0,001 Black-legged kittiwake Rissa tridactyla 258 0,230 unidentified gull 1 0,001 Sandwich tern Sterna sandvicensis 43 0,038 Arctic tern Sterna paradisaea 3 0,003 Common / Arctic tern Sterna hirundo / Sterna paradisaea 26 0,023 Common guillemot Uria aalge 182 0,162 Common guillemot/ Razorbill Uria aalge / Alca torda 148 0,132 unidentified songbird 2 0,002 Common minke whale Balaenoptera acutorostrata 1 0,001 unidentified dolphin 7 0,006 Harbour porpoise Phocoena phocoena 241 0,215 Grey seal Halichoerus grypus 14 0,012 Harbour seal Phoca vitulina 8 0,007 Grey seal / Harbour seal 11 0,010

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Figure 6: Distribution of Black-legged kittiwakes in the German North Sea in summer 2015.

Ship-based survey in the North Sea in summer From 27th of July to 20th of August a ship-based seabird survey was carried out in the North Sea with the research vessel “Walter Herwig III” as a vessel of opportunity (Figure 7). Eight survey days of this trip covered the area of the German EEZ. In addition to the seabirds at sea counts, systematic surveys of ship followers and discard use by seabirds were made. The species spectrum was dominated by pelagic species (Table 5). Common guillemots were found in high densities especially in the West of the German EEZ and in the central North Sea (Figure 8). Many of the Common guillemots observed were adults with chicks. During the survey several remarkable seabird observations were recorded, as well as White-beaked dolphins, Killer whales and a Common minke whale (Table 5), although most of these observations were outside German waters.

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Figure 7: Survey transects of the ship-based seabird survey the North Sea in summer 2015.

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Table 5: Number and average density of species registered inside transect during the ship-based seabird survey in the North Sea in summer 2015.

species scientific name number density [Ind./km²] Northern fulmar Fulmarus glacialis 111 0,564 European storm petrel Hydrobates pelagicus 2 0,010 Northern gannet Sula bassana 136 0,692 Great cormorant Phalacrocorax carbo 2 0,010 Dunlin Calidris alpina 11 0,056 Pomarine skua Stercorarius pomarinus 1 0,005 Arctic skua Stercorarius parasiticus 1 0,005 Great skua Stercorarius skua 3 0,015 Black-headed gull Chroicocephalus ridibundus 1 0,005 Common gull Larus canus 9 0,046 Lesser black-backed gull Larus fuscus 92 0,468 Great black-backed gull Larus marinus 3 0,015 Black-legged kittiwake Rissa tridactyla 228 1,159 Sandwich tern Sterna sandvicensis 28 0,142 Common tern Sterna hirundo 10 0,051 Arctic tern Sterna paradisaea 57 0,290 Common / Arctic tern Sterna hirundo / Sterna paradisaea 71 0,361 Black tern Chlidonias niger 9 0,046 Common guillemot Uria aalge 1 163 5,914 Razorbill Alca torda 4 0,020 Common guillemot/ Razorbill Uria aalge / Alca torda 15 0,076 Atlantic puffin Fratercula arctica 70 0,356 unidentified auk 3 0,015 Killer whale Orcinus orca 4 0,020 White-beaked dolphin Lagenorhynchus albirostris 10 0,051 Harbour porpoise Phocoena phocoena 5 0,025 Grey seal Halichoerus grypus 1 0,005 Harbour seal Phoca vitulina 7 0,036 Grey seal / Harbour seal 1 0,005

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Figure 8: Distribution of Common guillemots in the North Sea in summer 2015.

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Baltic Sea

Ship-based survey in the Bay of Pomerania in winter From 17th of January to 23rd of January a ship-based seabird survey with the private research vessel "Laura" was carried out in the Bay of Pomerania (Figure 9). Within seven days a transect area of 280.5 km² was surveyed and 23 bird species were recorded in transect (Table 6).

Figure 9: Survey transects in the various sub-areas during the Bay of Pomerania survey in January 2015.

With almost 8 250 individuals inside the transect and an average density of 29.4 Ind./km², theLong- tailed duck was the most abundant species (Table 6). Especially on the Adler Ground, on the Odra Bank, along the coast of and in the Bay of high densities of the Long-tailed ducks were observed (Figure 10). During the cruise Kjell Larsson from the Kalmar Maritime Academy, Linnaeus University in Kalmar, Sweden investigated the population structure of seaducks using digital 15

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photography. The proportion of juvenile birds was very low at 0.6 %. A roosting site of Great cormorants has established on a wind mast west of the Adler Ground. Approximately 100 individuals rested there on 21st of January noon.

Table 6: Number and average density of species registered inside transect during the ship-based seabird survey in the Bay of Pomerania in January 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 8 0,029 Black-throated diver Gavia arctica 14 0,050 undetermined diver Gavia spec. 21 0,075 Great crested grebe Podiceps cristatus 159 0,567 Red-necked grebe Podiceps grisegena 11 0,039 Slavonian grebe Podiceps auritus 21 0,075 unidentified grebe Podicipedidae 6 0,021 Great cormorant Phalacrocorax carbo 53 0,189 Mute swan Cygnus olor 20 0,071 Greylag goose Anser anser 7 0,025 Common eider Somateria mollissima 3 0,011 Long-tailed duck Clangula hyemalis 8 249 29,407 Common scoter Melanitta nigra 340 1,212 Velvet scoter Melanitta fusca 2 007 7,155 Common goldeneye Bucephala clangula 7 0,025 Red-breasted merganser Mergus serrator 148 0,528 Goosander Mergus merganser 54 0,193 Black-headed gull Chroicocephalus ridibundus 6 0,021 Common gull Larus canus 46 0,164 Herring gull Larus argentatus 206 0,734 Great black-backed gull Larus marinus 39 0,139 Common guillemot Uria aalge 138 0,492 Razorbill Alca torda 67 0,239 Common guillemot/ Razorbill Uria aalge / Alca torda 28 0,100 Black guillemot Cepphus grylle 7 0,025 Hooded crow Corvus corone cornix 1 0,004 unidentified songbird 1 0,004

Grey seal / Harbour seal 1 0,004

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Figure 10: Distribution of Long-tailed ducks in the Bay of Pomerania in January 2015.

Ship-based survey in the Bay of Pomerania and west of Rügen in spring From 9th of March to 16th of March a ship-based seabird survey was carried out in the Bay of Pomerania and west of Rügen with the "Ludwig Prandtl" of the Helmholtz Centre for Materials and Coastal Research, Geesthacht. Within eight days a transect area of 145.2 km² was covered and 31 bird species were recorded inside survey transect (Figure 11, Table 7). The focus species groups of this spring survey were seaducks and divers. In addition to the seabirds at sea counts, the aim of this trip was to take benthos samples with a Van Veen grab sampler. For this purpose, grab samples were taken in a rough grid and additionally below larger flocks of seaducks and in areas with high seaduck densities. Digital photos were taken for the determination of sex ratio and proportion of juvenile birds. The proportion of juveniles for Long-tailed duck was 2.0 %. It is higher than during the previous winter survey, but still quite low.

Like in January the Long-tailed duck was the most abundant species. Almost 14 000 ducks with an average density of ~ 96 Ind./km² were recorded in the transect (Table 7). The average density was clearly higher than in January. The distribution was similar to the situation in January, but the gained in importance (Figure 12). This is probably due to the availability of herring spawn at this time of the year, which is used as food by the Long-tailed duck.

On 12th of March and 13th of March more than 1 000 auks were observed in a relatively small area north of Greifwalder Oie (all observations inside and outside the survey transect combined). Most of these were Razorbills. A rough extrapolation suggests an accumulation of 3 000 to 6 000 auks. This represents an occurrence of international importance according to the 1 % criterion (based on 55 000 razorbills and 50 000 Common guillemots in the Baltic Sea). A comparatively high number of auks was also observed during the aerial survey of the Baltic Sea in spring (see below).

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Table 7: Number and average density of species registered inside transect during the ship-based seabird survey in the Bay of Pomerania and west of Rügen in March 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 11 0,076 Black-throated diver Gavia arctica 10 0,069 undetermined diver Gavia spec. 48 0,331 Great crested grebe Podiceps cristatus 18 0,124 Red-necked grebe Podiceps grisegena 2 0,014 Slavonian grebe Podiceps auritus 37 0,255 unidentified grebe Podicipedidae 4 0,028 Great cormorant Phalacrocorax carbo 612 4,216 Grey heron Ardea cinerea 2 0,014 Mute swan Cygnus olor 283 1,950 Eurasian wigeon Anas penelope 714 4,919 Gadwall Anas strepera 3 0,021 Eurasian teal Anas crecca 2 0,014 Common pochard Aythya ferina 5 0,034 Greater scaup Aythya marila 1 121 7,723 Common eider Somateria mollissima 285 1,963 Long-tailed duck Clangula hyemalis 13 920 95,901 Common scoter Melanitta nigra 7 874 54,247 Velvet scoter Melanitta fusca 2 039 14,048 Common goldeneye Bucephala clangula 486 3,348 Red-breasted merganser Mergus serrator 139 0,958 Goosander Mergus merganser 17 0,117 White-tailed eagle Haliaeetus albicilla 2 0,014 Common buzzard Buteo buteo 1 0,007 Eurasian coot Fulica atra 1 0,007 Black-headed gull Chroicocephalus ridibundus 11 0,076 Common gull Larus canus 19 0,131 Herring gull Larus argentatus 542 3,734 Great black-backed gull Larus marinus 64 0,441 Common guillemot Uria aalge 18 0,124 Razorbill Alca torda 200 1,378 Common guillemot/ Razorbill Uria aalge / Alca torda 537 3,700 Black guillemot Cepphus grylle 9 0,062 Hooded crow Corvus corone cornix 1 0,007 Grey seal Halichoerus grypus 7 0,048

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Figure 11: Survey transects and positions of benthos samples during the ship-based seabird survey in the Bay of Pomerania and west of Rügen in March 2015.

Figure 12: Distribution of Long-tailed ducks in the Bay of Pomerania and west of the Island of Rügen in March 2015.

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Aerial survey of the entire German part of the Baltic Sea in spring On 9th of March, 22nd of March, and 27th of March an aerial survey of the entire German Baltic Sea was implemented (Figure 13). Seaducks were the most abundant birds, but large numbers of -gulls, Great cormorants, divers and auks were observed as well (Table 8). Most Long-tailed ducks occurred east of the Island of Darß, but they were found in substantial densities also in Wismar Bay and in the western Baltic Sea (Figure 14). The pattern observed in the Bay of Pomerania and in the Bay of Greifswald is similar to that of the ship-based observations from winter and spring (Figure 10, Figure 12). Off the coast of the Island of Usedom and east of the Island of Rügen a remarkable number of auks were observed (see above).

Figure 13: Survey transects of the aerial seabird survey in the Baltic Sea in spring 2015.

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Table 8: Number and average density of species registered inside transect during the aerial seabird survey of the German Baltic Sea in spring 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 238 0,154 Black-throated diver Gavia arctica 19 0,012 White-billed diver Gavia adamsii 1 0,001 unidentified diver Gavia spec. 147 0,095 Great crested grebe Podiceps cristatus 3 0,002 Red-necked grebe Podiceps grisegena 2 0,001 Horned grebe Podiceps auritus 1 0,001 unidentified grebe Podicipedidae 7 0,005 Great cormorant Phalacrocorax carbo 621 0,402 Mute swan Cygnus olor 21 0,014 Whooper swan Cygnus cygnus 3 0,002 Common shelduck Tadorna tadorna 4 0,003 Eurasian wigeon Anas penelope 6 0,004 Mallard Anas platyrhynchos 3 0,002 Tufted duck Aythya fuligula 2 0,001 Greater scaup Aythya marila 15 0,010 Common eider Somateria mollissima 8 577 5,558 Long-tailed duck Clangula hyemalis 9 489 6,150 Common scoter Melanitta nigra 12 946 8,390 Velvet scoter Melanitta fusca 2 151 1,394 Common goldeneye Bucephala clangula 52 0,034 Red-breasted merganser Mergus serrator 42 0,027 Goosander Mergus merganser 13 0,008 unidentified wader Limicolae 2 0,001 Little gull Hydrocoloeus minutus 6 0,004 Black-headed gull Chroicocephalus ridibundus 82 0,053 Common gull Larus canus 897 0,581 unidentified small gull 4 0,003 Lesser black-backed gull Larus fuscus 3 0,002 Herring gull Larus argentatus 1 367 0,886 Great black-backed gull Larus marinus 373 0,242 unidentified large gull 5 0,003 unidentified gull 24 0,016 Common guillemot Uria aalge 31 0,020 Razorbill Alca torda 107 0,069 Common guillemot/ Razorbill Uria aalge / Alca torda 134 0,087 Black guillemot Cepphus grylle 3 0,002 Hooded crow Corvus corone cornix 1 0,001 unidentified songbird 5 0,003 unidentified marine mammal 1 0,001 Harbour porpoise Phocoena phocoena 4 0,003 Grey seal Halichoerus grypus 7 0,005 Grey seal / Harbour seal 1 0,001

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Figure 14: Distribution of Long-tailed ducks in the German Baltic Sea in spring 2015.

Aerial seabird surveys in the Bay of Pomerania and in Bay of Greifswald in spring The SPA Bay of Pomerania and Bay of Greifswald were again surveyed on 22nd of April by an aerial seabird survey to collect data on phenology in spring (Figure 15). In addition to numerous Long-tailed ducks, Common and Velvet scoters, several Great cormorants, divers and gulls were observed (Table 9). Divers were particularly abundant at the edges of the Odra Bank (Figure 16). The number of Common scoters in the area was significantly lower than during the corresponding survey carried out a month earlier as part of the Baltic Sea survey (see above).

Figure 15: Survey transects of the aerial seabird survey in the Bay of Pomerania and Bay of Greifswald in spring 2015.

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Figure 16: Distribution of divers in Bay of Pomerania and Bay of Greifswald in spring 2015.

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Table 9: Number and average density of species registered inside transect during the aerial seabird survey in the Bay of Pomerania and Bay of Greifswald in spring 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 29 0,064 unidentified diver Gavia spec. 89 0,195 unidentified grebe Podicipedidae 8 0,018 Great cormorant Phalacrocorax carbo 103 0,226 Mute swan Cygnus olor 58 0,127 Greylag goose Anser anser 3 0,007 unidentified dabbling duck Anas spec. 38 0,083 Greater scaup Aythya marila 20 0,044 Long-tailed duck Clangula hyemalis 1 606 3,525 Common scoter Melanitta nigra 1 882 4,130 Velvet scoter Melanitta fusca 333 0,731 Common goldeneye Bucephala clangula 7 0,015 unidentified duck 40 0,088 Little gull Hydrocoloeus minutus 6 0,013 Black-headed gull Chroicocephalus ridibundus 168 0,369 Common gull Larus canus 38 0,083 unidentified small gull 1 0,002 Lesser black-backed gull Larus fuscus 1 0,002 Herring gull Larus argentatus 97 0,213 Great black-backed gull Larus marinus 5 0,011 unidentified gull 6 0,013 Common guillemot Uria aalge 2 0,004 Common guillemot/ Razorbill Uria aalge / Alca torda 31 0,068 Black guillemot Cepphus grylle 2 0,004 Grey seal / Harbour seal 1 0,002 Grey seal Halichoerus grypus 1 0,002

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Aerial survey of the SPA Bay of Pomerania in summer On 1st of August an aerial seabird survey took place in the SPA Bay of Pomerania, to record the moulting occurrence of Common and Velvet scoters (Figure 17). In addition to the moulting seaducks, some over-summering Black-throated divers were observed (Table 10). Velvet scoters were spread over most of the Odra Bank (Figure 18).

Figure 17: Survey transects of the aerial seabird survey in the SPA Bay of Pomerania in summer 2015.

Table 10: Number and average density of species registered inside transect during the aerial seabird survey in the SPA Bay of Pomerania in summer 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia arctica 16 0,042 Great cormorant Phalacrocorax carbo 4 0,011 Common scoter Melanitta nigra 894 2,349 Velvet scoter Melanitta fusca 93 0,244 unidentified duck 5 0,013 unidentified wader Limicolae 3 0,008 unidentified small gull 1 0,003 Lesser black-backed gull Larus fuscus 1 0,003 Herring gull Larus argentatus 6 0,016 unidentified gull 1 0,003 Common / Arctic tern Sterna hirundo / Sterna paradisaea 1 0,003 Common guillemot Uria aalge 8 0,021 Common guillemot/ Razorbill Uria aalge / Alca torda 9 0,024 Feral pigeon Columba livia domestica 3 0,008 Grey seal Halichoerus grypus 1 0,003

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Figure 18: Distribution of Velvet scoters in the SPA Bay of Pomerania in summer 2015.

Aerial survey of the SPA Bay of Pomerania in autumn Another aerial seabird survey took place on 30th of September on the same transect lines in the SPA Bay of Pomerania to study the phenology of the moulting occurrence of scoters (Figure 19). The density of Common and Velvet scoters was more than ten times higher than in summer (see above) and the diversity of recorded seabird species was much higher as well (Table 11). Compared to summer, the number of divers observed was considerably higher and several hundred Long-tailed ducks were detected already. The large number of Common scoters also extended into the Polish area of the Odra Bank (Figure 20).

Figure 19: Survey transects of the aerial seabird survey in the SPA Bay of Pomerania in autumn 2015.

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Figure 20: Distribution of Common scoters in SPA Bay of Pomerania in summer 2015.

Table 11: Number and average density of species registered inside transect during the aerial seabird survey in the SPA Bay of Pomerania in autumn 2015.

species scientific name number density [Ind./km²] Red-throated diver Gavia stellata 52 0,135 Black-throated diver Gavia arctica 2 0,005 unidentified diver Gavia spec. 70 0,182 Great crested grebe Podiceps cristatus 34 0,088 unidentified grebe Podicipedidae 2 0,005 Great cormorant Phalacrocorax carbo 1 0,003 Grey heron Ardea cinerea 1 0,003 Greater white-fronted goose Anser albifrons 7 0,018 Greylag goose Anser anser 65 0,169 unidentified grey goose Anser spec. 5 0,013 Barnacle goose Branta leucopsis 1 0,003 Eurasian teal Anas crecca 21 0,054 Greater scaup Aythya marila 62 0,161 Common Eider Somateria mollissima 21 0,054 Long-tailed duck Clangula hyemalis 577 1,497 Common scoter Melanitta nigra 10 892 28,260 Common / Velvet scoter Melanitta nigra / Melanitta fusca 42 0,109 Velvet scoter Melanitta fusca 1 533 3,978 Red-breasted merganser Mergus serrator 6 0,016 unidentified wader Limicolae 12 0,031 Black-headed gull Chroicocephalus ridibundus 3 0,008 Common gull Larus canus 6 0,016 Herring gull Larus argentatus 10 0,026 Great black-backed gull Larus marinus 3 0,008 unidentified large gull 3 0,008 Common guillemot Uria aalge 3 0,008 Common guillemot/ Razorbill Uria aalge / Alca torda 26 0,067 Feral pigeon Columba livia domestica 30 0,078 unidentified songbird 8 0,021 27

Seabird Monitoring 2015

Further results Current results of the seabird monitoring programme are presented in the geoinformation service on the website of the Federal Agency for Nature conservation. Sighting maps and density maps aggregated over 3 years are available for all common seabird species. https://www.bfn.de/themen/meeresnaturschutz/marines-monitoring.html (in German)

Acknowledgements The monitoring was organised with the support of Volker Dierschke. Malte Bickel, Volker Dierschke, Martin Gottschling, Henning Volmer and Stefan Weiel contributed as observers to the success of the surveys. Kjell Larsson analysed the sex ratio and the proportion of juvenile birds in Long-tailed ducks during the ship-based survey in the Bay of Pomerania in January, Margus Ellermaa analysed the photos of seaducks from the survey in March. For the survey in March the Helmholtz Centre for Materials and Coastal Research provided us with the research vessel "Ludwig Prandtl". The Thünen- Institute for Sea Fisheries made it possible to participate in a research cruise with the "Walther Herwig III". We thank Volker Dzaak and Matthias Kloppmann for the organisation and management of these surveys and the captains, crews and fellow scientists for the good collaboration and the pleasant time on board. Many thanks to all pilots for the pleasant collaboration and the safe transport during the aerial surveys. Eugen Faber and Uwe Lange from Brockmann Consult supported us considerably in data management.

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