Seabird Monitoring in the German North Sea and 2018

Photo: Kai Borkenhagen

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 2018

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 (Research and Technology Centre, Kiel University) 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), 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 Two aerial survey days in the inner German Bight were successfully carried out, as planned, in winter. Only one of three proposed aerial survey days in the German Bight in spring could be implemented due to logistics (weather, aircraft availability). One day was reallocated to the north-western-most part of the German Exclusive Economic Zone (EEZ), one day was cancelled. In addition, observer- based aerial surveys were carried out simultaneously with two digital comparison surveys of the PhoViComp project in spring. The area around Helgoland was covered by a one-day aerial survey in summer, as scheduled. A number of the flight surveys were carried out simultaneously or near- simultaneously with digital surveys along the same transects. However, this report focusses on results of the observer-based surveys only, because the digital survey data were not available at the time of writing this report. Thirteen of fifteen proposed survey days on ships of opportunity were implemented successfully (Table 1). 1

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Baltic Sea Two days of a proposed three-day ship-based survey of the entire Baltic Sea in winter went ahead as scheduled, one day was cancelled for logistical reasons. Only one of two proposed aerial survey days in the Pomeranian Bay in summer could be implemented, the other one was cancelled due to logistics. Two aerial surveys scheduled alongside the digital comparison surveys of the PhoViComp project had to be cancelled, because weather conditions were unsuitable. A dedicated seven-day ship-based survey in the Pomeranian Bay in winter was carried out successfully aboard chartered vessel „Skoven“ in January. A seven-day ship-based survey in the Pomeranian Bay and west of Rügen in spring was successfully implemented aboard the „Ludwig Prandtl“ of the HZG (Helmholtz-Zentrum Geesthacht) in March. In addition, a seven-day ship-based survey in the Pomeranian Bay and west of Rügen aboard the „Ludwig Prandtl“ of the HZG in autumn was successfully carried out in November. Six of eight scheduled survey days on ships of opportunity were carried out aboard the „Haithabu“ in the western Baltic Sea in February (Table 1).

Table 1: Survey design and implementation in 2018. p= plane; sh= ship; EGB = Eastern German Bight; PoBay = Pomeranian Bay; w = winter; sp= spring, s= summer; au= autumn.

2018 2018 survey w Sp s au w sp s au SPA EGB and environs winter p 2 2

SPA EGB and environs spring p 3 1 EEZ off Helgoland: summer p 1 1 North-western EEZ p 1 North Sea PhoViComp-Amrum Bank p 2 2 ship-based survey North Sea sh 15 13 entire German Baltic Sea January p 3 2

SPA Pomeranian Bay ship sh 7 7 7 7 7 partial survey SPA PoBay summer p 2 1 PhoViComp-PoBay 1 1 0 0 Baltic Sea ship-based survey Baltic Sea (ship of opportunity) sh 8 6

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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 in the inner German Bight in February Two aerial seabird surveys were carried out in the inner German Bight on 6th of February and 22nd of February (Figure 1). Data were collected using a newly launched joint transect design of digital and observer-based surveys. The transect design for the monitoring of seabirds and marine mammals was developed in close coordination between ITAW and FTZ. The surveys were carried out simultaneously or near-simultaneously with digital surveys on the same transects. The SPA Eastern German Bight could not be surveyed by observers due to logistics but was covered digitally. The digital survey data were not available at the time of writing this report.

Auks and gulls made up the majority of sightings, in addition to common eiders and common scoters which were predominantly observed near the coast (Table 2). Black-legged kittiwakes were most frequent in the north-western part of the study site and were completely absent in areas near the coast (Figure 2). The greatest density of common guillemots and razorbills was observed north of the East Frisian Islands and along the late-Pleistocene paleo Elbe River valley (Figure 3). 94% of alcids identified to species-level were common guillemots.

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Figure 1: Transect course of the aerial seabird survey in the inner German Bight in February 2018. Data were collected using a newly launched joint transect design of digital and observer-based surveys of seabirds and marine mammals.

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Figure 2: Distribution of black-legged kittiwakes in the inner German Bight in February 2018.

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Figure 3: Distribution of common guillemots and razorbills in the inner German Bight in February 2018. The common guillemot made up 94% of all individuals identified to species level.

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Table 2: Abundance and average density of species recorded in the transect during the aerial surveys of the inner German Bight in February 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 37 0.043 black-throated diver Gavia arctica 3 0.003 unidentified diver Gavia spec. 66 0.077 northern fulmar Fulmarus glacialis 3 0.003 northern gannet Morus bassanus 15 0.017 greylag goose Anser anser 7 0.008 common eider Somateria mollissima 4,758 5.524 common scoter Melanitta nigra 448 0.520 oystercatcher Haematopus ostralegus 20 0.023 dunlin Calidris alpina 40 0.046 little gull Hydrocoloeus minutus 7 0.008 common gull Larus canus 99 0.115 unidentified small gull 2 0.002 lesser black-backed gull Larus fuscus 2 0.002 herring gull Larus argentatus 209 0.243 great black-backed gull Larus marinus 41 0.048 common / herring gull Larus canus / Larus argentatus 1 0.001 unidentified large gull 1 0.001 black-legged kittiwake Rissa tridactyla 197 0.229 unidentified gull 23 0.027 common guillemot Uria aalge 199 0.231 common guillemot / razorbill Uria aalge / Alca torda 184 0.214 razorbill Alca torda 13 0.015 unidentified bird 9 0.010 harbour porpoise Phocoena phocoena 32 0.037 grey seal / harbour seal 4 0.005 grey seal Halichoerus grypus 3 0.003 harbour seal Phoca vitulina 3 0.003

Aerial seabird survey in the German Bight in spring Parts of the German Bight were covered by aerial seabird surveys on 21st of April, 4th of May, 11th of May, and 15th of May (Figure 4). All surveys were conducted simultaneously with digital surveys. The two surveys north of Helgoland were carried out at the same time as digital comparison surveys of the PhoViComp project. This report only presents results of observer-based surveys.

In terms of numbers, divers, northern gannets, seaducks, gulls, terns, and guillemots dominated the scene (Table 3). Red-throated divers were most frequent in the main density area to the northwest of Helgoland, while almost absent in the northwestern part of the EEZ (Exclusive Economic Zone) and at the mouth of the Elbe River (Figure 5). Of all gulls, the little gull was the most abundant species, They were even more common than the lesser black-backed gull, which is the typical „offshore gull“ of the German Bight between spring and autumn. More than 1,000 little gulls were spotted, both as solitary birds and in large flocks. Almost none were sighted in the northwestern part of the EEZ (Figure 6). Higher densities were found, inter alia, at the late-Pleistocene paleo Elbe River valley which was also heavily frequented by various other species. Lesser black-backed gulls were

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particularly common to the west of the North Frisian Islands near Amrum Bank and to the north of the East Frisian Islands, but were almost completely absent from the north-western part of the EEZ (Figure 7). Black-legged kittiwakes were concentrated around Helgoland and in the northwestern part of the EEZ (Figure 8). The survey showed that terns heavily rely on offshore areas in the German Bight during the spring . Sandwich terns were distributed across most of the inner German Bight, concentrating especially around the mouth of the Elbe River and to the north of Helgoland (Figure 9). Alcids were frequently seen, with common guillemot being the most abundant species. They mainly frequented the area around Helgoland and the northern side of the late- Pleistocene paleo Elbe River valley (Figure 10). Furthermore, a pomarine skua, 14 puffins and two white-beaked dolphins were spotted in the north-western part of the EEZ. A basking shark was sighted approximately 30 km north of Langeoog. In addition, 399 harbour porpoises were recorded (Table 3).

Figure 4: Transect course of the aerial seabird surveys in the German Bight in spring 2018. The north-western tip of the EEZ could not be surveyed on account of fog. Monitoring in the central sub area (which contains parts of the SPA „Eastern German Bight“) was conducted along the survey transects of the project „PhoViComp“. The area was covered twice by aerial survey in spring 2018. The following results give mean density for both survey days.

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Figure 5: Distribution of red-throated divers in the German Bight in spring 2018. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Figure 6: Distribution of little gulls in the German Bight in spring 2018. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Figure 7: Distribution of lesser black-backed gulls in the German Bight in spring 2018. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Figure 8: Distribution of black-legged kittiwakes in the German Bight in spring 2018. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Figure 9: Distribution of sandwich terns in the German Bight in spring 2018. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Figure 10: Distribution of common guillemots and razorbills in the German Bight in spring 2018. The common guillemot made up more than 99% of all identified individuals. The central sub area was covered twice by aerial survey in spring 2018. Results presented here give mean density for both survey days.

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Table 3: Abundance and average density of species recorded in the transect during the aerial surveys of the German Bight in spring 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 642 0.344 black-throated diver Gavia arctica 4 0.002 unidentified diver Gavia spec. 314 0.168 northern fulmar Fulmarus glacialis 130 0.070 northern gannet Morus bassanus 427 0.229 great cormorant Phalacrocorax carbo 4 0.002 common eider Somateria mollissima 1,213 0.649 common scoter Melanitta nigra 7,488 4.008 velvet scoter Melanitta fusca 7 0.004 marsh harrier Circus aeruginosus 1 0.001 oystercatcher Haematopus ostralegus 1 0.001 Eurasian curlew Numenius arquata 1 0.001 unidentified wader Limicolae 16 0.009 pomarine skua Stercorarius pomarinus 1 0.001 Arctic / pomarine / long-tailed Stercorarius parasiticus / skua S. pomarinus / S. longicaudus 1 0.001 little gull Hydrocoloeus minutus 1,083 0.580 black-headed gull Chroicocephalus ridibundus 110 0.059 common gull Larus canus 120 0.064 unidentified small gull 9 0.005 lesser black-backed gull Larus fuscus 799 0.428 herring gull Larus argentatus 203 0.109 great black-backed gull Larus marinus 8 0.004 great black-backed gull / lesser black-backed gull Larus marinus / Larus fuscus 1 0.001 unidentified large gull 15 0.008 black-legged kittiwake Rissa tridactyla 557 0.298 northern fulmar / gull 1 0.001 unidentified gull 23 0.012 sandwich tern Sterna sandvicensis 488 0.261 common tern Sterna hirundo 12 0.006 Arctic tern Sterna paradisaea 5 0.003 common / Arctic tern Sterna hirundo / S. paradisaea 275 0.147 unidentified Sterna-tern Sterna spec. 34 0.018 tern / small gull 2 0.001 common guillemot Uria aalge 616 0.330 razorbill Alca torda 2 0.001 common guillemot / razorbill Uria aalge / Alca torda 341 0.183 puffin Fratercula arctica 14 0.007 unidentified auk 22 0.012 unidentified songbird 6 0.003 unidentified bird 21 0.011 white-beaked dolphin Lagenorhynchus albirostris 2 0.001 harbour porpoise Phocoena phocoena 399 0.214 unidentified small whale 1 0.001 grey seal Halichoerus grypus 6 0.003 harbour seal Phoca vitulina 98 0.052 grey seal / harbour seal 27 0.014 unidentified marine mammal 20 0.011 basking shark Cetorhinus maximus 1 0.001

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Ship-based seabird survey in the German Bight in spring A ship-based seabird survey aboard research vessel „Heincke“ of the AWI (Alfred Wegener Institute) joining a research cruise of the HZG was carried out between 17th and 29th of May (Figure 11). The most common breeding birds of Helgoland – northern gannets, black-legged kittiwakes, lesser black- backed gulls, and common guillemots – dominated the offshore avifauna (Table 4). Northern gannets and black-legged kittiwakes were recorded at particularly high densities to the north and northeast of Helgoland (Figure 12, Figure 13), while lesser black-backed gulls additionally frequented the marine area to the west of Helgoland, as well as the estuary of the Weser River (Figure 14). Common guillemots were also frequently spotted around Helgoland, particularly in the north and northwest (Figure 15).

Figure 11: Transect course of the ship-based seabird surveys in the German Bight in spring 2018. The survey was conducted aboard a ship of opportunity during a HZG research campaign.

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Figure 12: Distribution of northern gannets in the German Bight in spring 2018.

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Figure 13: Distribution of black-legged kittiwakes in the German Bight in spring 2018.

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Figure 14: Distribution of lesser black-backed gulls in the German Bight in spring 2018.

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Figure 15: Distribution of common guillemots in the German Bight in spring 2018.

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Table 4: Abundance and average density of species recorded in the transect during the ship-based surveys in the German Bight in spring 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 1 0.003 northern fulmar Fulmarus glacialis 2 0.005 northern gannet Morus bassanus 153 0.398 brent goose Branta bernicla 7 0.018 common scoter Melanitta nigra 2 0.005 purple sandpiper Calidris maritima 2 0.005 redshank Tringa totanus 1 0.003 little gull Hydrocoloeus minutus 1 0.003 Chroicocephalus black-headed gull ridibundus 22 0.057 common gull Larus canus 18 0.047 lesser black-backed gull Larus fuscus 278 0.723 herring gull Larus argentatus 7 0.018 black-legged kittiwake Rissa tridactyla 149 0.388 sandwich tern Sterna sandvicensis 80 0.208 common tern Sterna hirundo 53 0.138 Arctic tern Sterna paradisaea 3 0.008 black tern Chlidonias niger 4 0.010 common guillemot Uria aalge 263 0.684 razorbill Alca torda 1 0.003 common swift Apus apus 5 0.013 barn swallow Hirundo rustica 7 0.018 house martin Delichon urbica 5 0.013 unidentified songbird 2 0.005 harbour porpoise Phocoena phocoena 27 0.070 grey seal Halichoerus grypus 3 0.008 harbour seal Phoca vitulina 4 0.010

Aerial seabird survey around Helgoland in summer An aerial seabird survey around Helgoland was conducted on 27th of June (Figure 16). Lesser black- backed gulls in particular were sighted frequently, but common scoters and guillemots were recorded in great numbers as well (Table 5). The whole study site registered local concentrations of lesser black-backed gulls (Figure 17). Their distribution pattern is strongly influenced by fisheries, because discards are an important food source for them. Common guillemots were concentrated especially around the late-Pleistocene paleo Elbe River valley to the west of Helgoland (Figure 18).

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Figure 16: Transect course of the aerial seabird survey around Helgoland in summer 2018. Counting was interrupted north-northwesterly of Helgoland, while the aircraft flew over the wind farm.

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Figure 17: Distribution of lesser black-backed gulls around Helgoland in summer 2018.

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Figure 18: Distribution of common guillemots around Helgoland in summer 2018.

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Table 5: Abundance and average density of species recorded in the transect during the aerial surveys around Helgoland in summer 2018.

species scientific name count density [ind. /km²] northern gannet Morus bassanus 50 0.092 Eurasian teal Anas crecca 1 0.002 common eider Somateria mollissima 30 0.055 common scoter Melanitta nigra 260 0.480 little gull Hydrocoloeus minutus 33 0.061 black-headed gull Chroicocephalus ridibundus 53 0.098 common gull Larus canus 2 0.004 unidentified small gull 3 0.006 lesser black-backed gull Larus fuscus 870 1.605 herring gull Larus argentatus 52 0.096 black-legged kittiwake Rissa tridactyla 77 0.142 unidentified gull 7 0.013 sandwich tern Sterna sandvicensis 96 0.177 common tern Sterna hirundo 12 0.022 Arctic tern Sterna paradisaea 3 0.006 common / Arctic tern Sterna hirundo / S. paradisaea 20 0.037 common guillemot Uria aalge 271 0.500 common guillemot / razorbill Uria aalge / Alca torda 3 0.006 harbour porpoise Phocoena phocoena 40 0.074 grey seal Halichoerus grypus 1 0.002 grey seal / harbour seal 2 0.004

Baltic Sea

Ship-based seabird survey in the Pomeranian Bay and the Bay of in January A ship-based seabird survey was conducted in the Pomeranian Bay and the as charter survey with the „Skoven“ between 15th and 21st of January (Figure 19). The majority of recorded birds were seaducks, sawbills, and grebes; comparatively fewer numbers of razorbills and common guillemots were recorded (Table 6). Numbers of long-tailed ducks were particularly high during this survey. Their average density was approximately twice that of the three previous years with 62 ind./km² (with a similar survey design in January 2015: 29 ind./km²; January 2016: 31 ind./km²; January 2017: 33 ind./km²). The species was found almost everywhere across the Odra bank, the Adler Ground, the Bay of Greifswald and in shallow waters near the coast (Figure 20). Common scoters were concentrated around and in front of , and occurred at comparatively lower density at the Odra Bank (Figure 21). Velvet scoters utilised the area around Greifwalder Oie, the Odra Bank and the Adler Ground but were almost completely absent in the Bay of Greifswald and along the coastlines of Rügen and Usedom (Figure 22). Red-breasted mergansers and great crested grebes were recorded in the entire area near the coast and in the Bay of Greifswald, sometimes at high densities, with lower densities in offshore areas (Figure 23, Figure 24). Slavonian grebes were concentrated at the Odra Bank and were otherwise spotted only sporadically (Figure 25). Black guillemots were mostly limited to the Adler Ground (Figure 26). Of note are further two great northern divers and several northern gannets, all of which were, however, spotted outside the transect. 25

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Figure 19: Transect course of the ship-based seabird surveys in the Pomeranian Bay and Bay of Greifswald in January 2018.

Figure 20: Distribution of long-tailed ducks in the Pomeranian Bay and the Bay of Greifswald in January 2018.

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Figure 21: Distribution of common scoters in the Pomeranian Bay and the Bay of Greifswald in January 2018.

Figure 22: Distribution of velvet scoters in the Pomeranian Bay and in the Bay of Greifswald in January 2018.

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Figure 23: Distribution of red-breasted mergansers in the Pomeranian Bay and the Bay of Greifswald in January 2018. Owing to their high density, abundance categories of species with high numbers of individuals were used.

Figure 24: Distribution of great crested grebes in the Pomeranian Bay and the Bay of Greifswald in January 2018. Owing to their high density, abundance categories of species with high numbers of individuals were used.

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Figure 25: Distribution of Slavonian grebes in the Pomeranian Bay and the Bay of Greifswald in January 2018.

Figure 26: Distribution of black guillemots in the Pomeranian Bay and the Bay of Greifswald in January 2018.

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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 and the Bay of Greifswald in January 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 10 0.046 black-throated diver Gavia arctica 9 0.041 unidentified diver Gavia spec. 57 0.262 great crested grebe Podiceps cristatus 948 4.360 red-necked grebe Podiceps grisegena 11 0.051 Slavonian grebe Podiceps auritus 36 0.166 black-necked grebe Podiceps nigricollis 1 0.005 unidentified grebe Podicipedidae 9 0.041 great cormorant Phalacrocorax carbo 132 0.607 mute swan Cygnus olor 15 0.069 Eurasian wigeon Anas penelope 21 0.097 mallard Anas platyrhynchos 38 0.175 greater scaup Aythya marila 9 0.041 common eider Somateria mollissima 4 0.018 long-tailed duck Clangula hyemalis 13,470 61.952 common scoter Melanitta nigra 754 3.468 velvet scoter Melanitta fusca 2,126 9.778 common golden-eye Bucephala clangula 109 0.501 red-breasted merganser Mergus serrator 1,056 4.857 goosander Mergus merganser 86 0.396 Chroicocephalus black-headed gull ridibundus 1 0.005 common gull Larus canus 21 0.097 herring gull Larus argentatus 94 0.432 great black-backed gull Larus marinus 36 0.166 common guillemot Uria aalge 10 0.046 razorbill Alca torda 9 0.041 common guillemot / razorbill Uria aalge / Alca torda 21 0.097 black guillemot Cepphus grylle 25 0.115 hooded crow Corvus corone cornix 1 0.005 grey seal Halichoerus grypus 6 0.028 grey seal / harbour seal 1 0.005

Ship-based seabird survey in the western German Baltic Sea in February Ship-based surveys in the western German Baltic Sea were conducted aboard ship of opportunity „Haithabu“ between 13 and 15 February and between 19th and 21st of February (Figure 27). The multi-purpose vessel is regularly used in the Federal/State North Sea and Baltic Sea Monitoring Programme (BLMP - Bund/Länder-Messprogramm für die Meeresumwelt von Nord- und Ostsee) conducted by the State Office for Agriculture, Environment and Rural Areas Schleswig-Holstein (LLUR - Landesamt für Landwirtschaft, Umwelt und ländliche Räume Schleswig-Holstein). In terms of numbers, the scene was dominated by seaducks, great crested grebes, cormorants, and herring gulls (Table 7). Among auks, razorbills were significantly more abundant than common guillemots. The distribution patterns for eiders, long-tailed ducks, velvet scoters, and common scoters were generally very similar. All of those species were concentrated in shallow water areas (Figure 28, Figure 29, Figure 30, Figure 31). However, common eiders, common scoters, and velvet scoters in the Bay of

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Kiel were also recorded far from the coast near the Danish border. Great crested grebes were mostly found near the coast, preferring fjords and bays (Figure 32). Also worth mentioning are several sightings of northern gannets outside of the transect.

Figure 27: Transect course of the ship-based seabird surveys in the western German Baltic Sea in February 2018. The survey was conducted on a ship of opportunity carrying out a BLMP monitoring survey for the LLUR.

Figure 28: Distribution of common eiders in the western German Baltic Sea in February 2018.

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Figure 29: Distribution of long-tailed ducks in the western German Baltic Sea in February 2018.

Figure 30: Distribution of common scoters in the western German Baltic Sea in February 2018.

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Figure 31: Distribution of velvet scoters in the western German Baltic Sea in February 2018.

Figure 32: Distribution of great crested grebes in the western German Baltic Sea in February 2018.

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Table 7: Abundance and average density of species recorded in the transect during the ship-based surveys of the western German Baltic Sea in February 2018.

species scientific name count density [ind. /km²] black-throated diver Gavia arctica 1 0.007 unidentified diver Gavia spec. 3 0.021 little grebe Tachybaptus ruficollis 60 0.416 great crested grebe Podiceps cristatus 768 5.326 red-necked grebe Podiceps grisegena 8 0.055 Slavonian grebe Podiceps auritus 5 0.035 unidentified grebe Podicipedidae 7 0.049 great cormorant Phalacrocorax carbo 278 1.928 mute swan Cygnus olor 32 0.222 whooper swan Cygnus cygnus 39 0.270 tundra / whooper swan Cygnus bewickii / C. cygnus 6 0.042 greylag goose Anser anser 43 0.298 Brent goose Branta bernicla 5 0.035 common shelduck Tadorna tadorna 3 0.021 Eurasian wigeon Anas penelope 109 0.756 mallard Anas platyrhynchos 192 1.332 tufted duck Aythya fuligula 254 1.762 common eider Somateria mollissima 4,080 28.295 long-tailed duck Clangula hyemalis 1,186 8.225 common scoter Melanitta nigra 3,102 21.513 velvet scoter Melanitta fusca 122 0.846 common golden-eye Bucephala clangula 196 1.359 smew Mergus albellus 5 0.035 red-breasted merganser Mergus serrator 156 1.082 goosander Mergus merganser 35 0.243 Eurasian coot Fulica atra 50 0.347 oystercatcher Haematopus ostralegus 1 0.007 black-headed gull Chroicocephalus ridibundus 13 0.090 common gull Larus canus 24 0.166 herring gull Larus argentatus 346 2.400 great black-backed gull Larus marinus 37 0.257 common guillemot Uria aalge 5 0.035 razorbill Alca torda 69 0.479 common guillemot / razorbill Uria aalge / Alca torda 18 0.125 black guillemot Cepphus grylle 1 0.007 skylark Alauda arvensis 1 0.007 jackdaw Coloeus monedula 2 0.014 rook Corvus frugilegus 3 0.021 hooded crow Corvus corone corone 1 0.007 unidentified crow Corvus spec. 2 0.014

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Aerial seabird survey in the German Baltic Sea in February Two aerial seabird surveys were conducted in the Baltic Sea on 7th of February and 23rd of February (Figure 33). Parts of Hohwacht Bay could not be surveyed on account of military activities. A third aerial survey day planned for the area between Warnemünde and had to be cancelled for logistical reasons. In terms of numbers, seaducks as well as divers and herring gulls were abundant (Table 8). Common eiders only occurred in the western part of the area. High densities were recorded particularly around Fehmarn, in the Bay of Kiel and the Bay of Wismar (Figure 34). Lock- tailed ducks were found throughout the entire study area, with high densities in some areas such as the Pomeranian Bay and the Bay of Greifswald (Figure 35). Common scoters were recorded throughout the area, with densities lower in the eastern part of the study site than in the Bay of Wismar and to the northeast of the Danish Wahld (Figure 36). Velvet scoters frequented the Odra Bank and the Adler Ground and reached high local densities at the Bay of Wismar (Figure 37). The sightings of a white-billed diver and three northern gannets are worthy of mention (Table 8).

Figure 33: Transect course of the aerial seabird survey in the German Baltic Sea in February 2018.

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Figure 34: Distribution of common eiders in the German Baltic Sea in February 2018.

Figure 35: Distribution of long-tailed ducks in the German Baltic Sea in February 2018.

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Figure 36: Distribution of common scoters in the German Baltic Sea in February 2018.

Figure 37: Distribution of velvet scoters in the German Baltic Sea in February 2018.

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Table 8: Abundance and average density of species recorded in the transect during the aerial surveys of the German Baltic Sea in February 2018. species scientific name count density [ind. /km²] red-throated diver Gavia stellata 129 0.142 black-throated diver Gavia arctica 12 0.013 white-billed diver Gavia adamsii 1 0.001 unidentified diver Gavia spec. 395 0.434 great crested grebe Podiceps cristatus 102 0.112 red-necked grebe Podiceps grisegena 3 0.003 Slavonian grebe Podiceps auritus 2 0.002 unidentified grebe Podicipedidae 3 0.003 northern gannet Morus bassanus 3 0.003 great cormorant Phalacrocorax carbo 158 0.174 mute swan Cygnus olor 101 0.111 unidentified swan Cygnus spec. 226 0.248 greylag goose Anser anser 22 0.024 Canada goose Branta canadensis 2 0.002 Brent goose Branta bernicla 6 0.007 Eurasian wigeon Anas penelope 6 0.007 mallard Anas platyrhynchos 407 0.447 Northern pintail Anas acuta 3 0.003 unidentified Anatidae Anas spec. 30 0.033 tufted duck Aythya fuligula 15 0.016 greater scaup Aythya marila 3 0.003 tufted duck / greater scaup Aythya fuligula / Aythya marila 332 0.365 common eider Somateria mollissima 10,153 11.156 long-tailed duck Clangula hyemalis 16,500 18.130 common scoter Melanitta nigra 5,436 5.973 velvet scoter Melanitta fusca 1,028 1.130 common scoter / velvet scoter Melanitta nigra / Melanitta fusca 115 0.126 common golden-eye Bucephala clangula 128 0.141 red-breasted merganser Mergus serrator 11 0.012 unidentified duck 19 0.021 white-tailed eagle Haliaeetus albicilla 1 0.001 common crane Grus grus 2 0.002 little gull Hydrocoloeus minutus 22 0.024 common gull Larus canus 149 0.164 unidentified small gull 3 0.003 lesser black-backed gull Larus fuscus 1 0.001 herring gull Larus argentatus 444 0.488 great black-backed gull Larus marinus 59 0.065 great / lesser black-backed gull Larus marinus / Larus fuscus 1 0.001 common / herring gull Larus canus / Larus argentatus 30 0.033 unidentified large gull 5 0.005 unidentified gull 17 0.019 common guillemot Uria aalge 5 0.005 razorbill Alca torda 31 0.034 common guillemot / razorbill Uria aalge / Alca torda 123 0.135 black guillemot Cepphus grylle 3 0.003 unidentified pigeon/dove 1 0.001 unidentified bird 110 0.121 harbour porpoise Phocoena phocoena 2 0.002 grey seal Halichoerus grypus 5 0.005 unidentified marine mammal 1 0.001 38

Seabird Monitoring 2018

Ship-based seabird survey in the Pomeranian Bay and west of Rügen in March A ship-based seabird survey of the Pomeranian Bay and to the west of Rügen up to Travemünde was carried out aboard HZG research vessel „Ludwig Prandtl“ between 10th of March and 16th of March (Figure 38). Seaducks were the most common birds by far, but cormorants and large gulls were recorded in large numbers as well (Table 9). Long-tailed ducks were particularly common in the Pomeranian Bay, the Bay of Greifswald and to the north of Darß/Zings/Fischland with numbers slowly decreasing towards the west (Figure 39). Common scoters in contrast were only recorded at average density in the Pomeranian Bay, with their main distribution to the west of Rügen (Figure 40). Velvet scoters were concentrated in the Pomeranian Bay, particularly the areas around Greifswalder Oie, at the Odra Bank, at the Adler Ground, and at the (Figure 41). The main distribution range of great crested grebes and cormorants was at the Bay of Greifswald, the Strela and in the coastal waters around Rügen (Figure 42, Figure 43). Great crested grebes moved further away from the coast in comparison to cormorants. A roost on top of a lattice tower facilitates the presence of cormorants at the Adler Ground. The sighting of a white-billed diver (Table 9) is worthy of note.

Figure 38: Transect course of the ship-based seabird survey in the Pomeranian Bay and west of Rügen in March 2018.

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Figure 39: Distribution of long-tailed ducks in the Pomeranian Bay and west of Rügen in March 2018.

Figure 40: Distribution of common scoters in the Pomeranian Bay and west of Rügen in March 2018.

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Figure 41: Distribution of velvet scoters in the Pomeranian Bay and west of Rügen in March 2018.

Figure 42: Distribution of great crested grebes in the Pomeranian Bay and west of Rügen in March 2018. Owing to their high density, abundance categories of species with high numbers of individuals were used.

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Figure 43: Distribution of great cormorants in the Pomeranian Bay and west of Rügen in March 2018.

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Table 9: Abundance and average density of species recorded in the transect during the ship-based surveys of the Pomeranian Bay and west of Rügen in March 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 7 0.030 black-throated diver Gavia arctica 13 0.056 white-billed diver Gavia adamsii 1 0.004 unidentified diver Gavia spec. 176 0.762 great crested grebe Podiceps cristatus 712 3.081 red-necked grebe Podiceps grisegena 13 0.056 Slavonian grebe Podiceps auritus 41 0.177 unidentified grebe Podicipedidae 17 0.074 great cormorant Phalacrocorax carbo 2,275 9.844 grey heron Ardea cinerea 2 0.009 mute swan Cygnus olor 315 1.363 whooper swan Cygnus cygnus 20 0.087 greylag goose Anser anser 3 0.013 Canada goose Branta canadensis 21 0.091 common shelduck Tadorna tadorna 5 0.022 Eurasian wigeon Anas penelope 194 0.839 gadwall Anas strepera 7 0.030 mallard Anas platyrhynchos 4 0.017 Northern pintail Anas acuta 20 0.087 greater scaup Aythya marila 490 2.120 common eider Somateria mollissima 676 2.925 long-tailed duck Clangula hyemalis 22,121 95.720 common scoter Melanitta nigra 12,014 51.986 velvet scoter Melanitta fusca 2,342 10.134 common golden-eye Bucephala clangula 243 1.051 red-breasted merganser Mergus serrator 816 3.531 goosander Mergus merganser 95 0.411 unidentified sawbills Mergus spec. 44 0.190 white-tailed eagle Haliaeetus albicilla 1 0.004 Eurasian coot Fulica atra 196 0.848 black-headed gull Chroicocephalus ridibundus 10 0.043 common gull Larus canus 13 0.056 herring gull Larus argentatus 443 1.917 Caspian gull Larus (argentatus) cachinnans 1 0.004 great black-backed gull Larus marinus 191 0.826 common guillemot Uria aalge 11 0.048 razorbill Alca torda 33 0.143 common guillemot / razorbill Uria aalge / Alca torda 10 0.043 black guillemot Cepphus grylle 9 0.039 skylark Alauda arvensis 9 0.039 starling Sturnus vulgaris 3 0.013 reed bunting Emberiza schoeniclus 1 0.004 grey seal Halichoerus grypus 27 0.117

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Aerial seabird survey of the Odra Bank in August An aerial seabird survey was conducted on 29th of August to record the occurrence of seaducks during moulting season at the Odra Bank in the Baltic Sea (Figure 44). With the exception of common scoters and herring gulls, all species were recorded at low numbers only (Table 1). Common scoters were mainly spotted in shallow water areas of the central Odra Bank (Figure 45), while herring gulls assembled at the southwestern edge of the Odra Bank, which slopes steeply towards deeper water (Figure 46). Velvet scoters were represented only by a single individual in the transect.

Figure 44: Transect course of aerial seabird surveys at the Odra Bank in August 2018.

Figure 45: Distribution of common scoters at the Odra Bank in August 2018.

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Figure 46: Distribution of herring gulls at the Odra Bank in August 2018.

Table 10: Abundance and average density of species recorded in the transect during the aerial surveys of the Odra Bank in August 2018.

Species scientific name count density [ind. /km²] red-throated diver Gavia stellata 2 0.005 unidentified diver Gavia spec. 2 0.005 unidentified grebe Podicipedidae 1 0.003 great cormorant Phalacrocorax carbo 16 0.042 common scoter Melanitta nigra 899 2.343 velvet scoter Melanitta fusca 1 0.003 greenshank Tringa nebularia 1 0.003 little gull Hydrocoloeus minutus 4 0.010 black-headed gull Chroicocephalus ridibundus 1 0.003 common gull Larus canus 3 0.008 herring gull Larus argentatus 69 0.180 great black-backed gull Larus marinus 1 0.003 unidentified gull 1 0.003 common / Arctic tern Sterna hirundo / S. paradisaea 1 0.003 common guillemot Uria aalge 3 0.008 common guillemot / razorbill Uria aalge / Alca torda 1 0.003

Ship-based seabird survey in the Pomeranian Bight and west of Rügen in November A ship-based seabird survey aboard HZG research vessel „Ludwig Prandtl“ was conducted between 9th of November and 16th of November. Survey areas were the Pomeranian Bay and the region to the west of Rügen up to Warnemünde (Figure 47). The most abundant species were red-breasted mergansers, cormorants, and seaducks (Table 11). Similarly to previous surveys in autumn, black- throated divers were much more common than red-throated divers. Common eiders were almost exclusively recorded to the west of Rügen (Figure 48). Long-tailed ducks were concentrated at the Odra Bank, at the Adler Ground, the Bay of Greifswald, the coast of Usedom and to the north of Darß 45

Seabird Monitoring 2018

und Zingst (Figure 49). Common scoters were particularly abundant at the Odra Bank, to the north of Darß and Zingst and northeast of Warnemünde (Figure 50). Velvet scoters were essentially confined to the Odra Bank and were spotted only sporadically in the rest of the survey area (Figure 51). Red- breasted mergansers were observed in great numbers at the Bay of Greifswald, at the Strela Sound and off the coast of Usedom (Figure 52). Cormorants were essentially confined to the Bay of Greifswald and to coastal waters (Figure 53). In contrast, common guillemots and razorbills used areas far offshore (Figure 54). Both species of alcids were represented in unusually large numbers during this survey. 60% of individuals identified at species level were razorbills. Sightings of various pelagic species rarely seen in the Baltic Sea are noteworthy. A fulmar, three black-legged kittiwakes and three northern gannets were spotted within the transect and a further northern gannet was sighted outside the transect.

Figure 47: Transect course of the ship-based seabird survey in the Pomeranian Bay and west of Rügen in November 2018.

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Figure 48: Distribution of common eiders in the Pomeranian Bay and west of Rügen in November 2018.

Figure 49: Distribution of long-tailed ducks in the Pomeranian Bay and west of Rügen in November 2018.

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Figure 50: Distribution of common scoters in the Pomeranian Bay and west of Rügen in November 2018.

Figure 51: Distribution of velvet scoters in the Pomeranian Bay and west of Rügen in November 2018.

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Figure 52: Distribution of red-breasted mergansers in the Pomeranian Bay and west of Rügen in November 2018. Owing to their high density, abundance categories of species with high numbers of individuals were used.

Figure 53: Distribution of great cormorants in the Pomeranian Bay and west of Rügen in November 2018.

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Figure 54: Distribution of common guillemots und razorbills in the Pomeranian Bay and west of Rügen in November 2018.

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Seabird Monitoring 2018

Table 11: 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 2018.

species scientific name count density [ind. /km²] red-throated diver Gavia stellata 10 0.035 black-throated diver Gavia arctica 54 0.188 unidentified diver Gavia spec. 6 0.021 great crested grebe Podiceps cristatus 114 0.396 red-necked grebe Podiceps grisegena 8 0.028 Slavonian grebe Podiceps auritus 15 0.052 unidentified grebe Podicipedidae 4 0.014 northern fulmar Fulmarus glacialis 1 0.003 northern gannet Morus bassanus 3 0.010 great cormorant Phalacrocorax carbo 1,327 4.613 mute swan Cygnus olor 74 0.257 tundra swan Cygnus bewickii 2 0.007 whooper swan Cygnus cygnus 11 0.038 barnacle goose Branta leucopsis 5 0.017 Brent goose Branta bernicla 2 0.007 Eurasian wigeon Anas penelope 138 0.480 mallard Anas platyrhynchos 204 0.709 Northern pintail Anas acuta 14 0.049 shoveler Spatula clypeata 16 0.056 tufted duck Aythya fuligula 1 0.003 greater scaup Aythya marila 62 0.216 tufted duck / greater scaup Aythya fuligula / Aythya marila 60 0.209 common eider Somateria mollissima 1,037 3.605 long-tailed duck Clangula hyemalis 8,369 29.090 common scoter Melanitta nigra 4,970 17.275 velvet scoter Melanitta fusca 1,220 4.241 common golden-eye Bucephala clangula 332 1.154 red-breasted merganser Mergus serrator 810 2.816 Eurasian coot Fulica atra 147 0.511 black-headed gull Chroicocephalus ridibundus 30 0.104 common gull Larus canus 52 0.181 herring gull Larus argentatus 174 0.605 Caspian gull Larus (argentatus) cachinnans 2 0.007 great black-backed gull Larus marinus 44 0.153 black-legged kittiwake Rissa tridactyla 3 0.010 common / herring gull Larus canus / Larus argentatus 1 0.003 common guillemot Uria aalge 72 0.250 razorbill Alca torda 124 0.431 common guillemot / razorbill Uria aalge / Alca torda 131 0.455 black guillemot Cepphus grylle 5 0.017 common redpoll Acanthis flammea 6 0.021 harbour porpoise Phocoena phocoena 2 0.007 grey seal Halichoerus grypus 5 0.017

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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 Modestas Bružas, Jonas Buddemeier, Dagmar Cimiotti, Volker Dierschke, Diego Gonzalez, Nicole Jüngling, Kolja Lehmann-Muriithi, Hilger Lemke, and Stefan Weiel significantly contributed to the success of the surveys. HZG made research vessel "Ludwig Prandtl" available for the March cruise. AWI, HZG and LLUR allowed us to join expeditions with the "Heincke" and the "Haithabu". We would like to thank Justus van Beusekom, Volker Dzaak, 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 Bettina Mendel for creating the map templates.

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