Distribution of ship-following seabirds and their utilization of discards in the North Sea in summer

Prey availability is one of the factors determining the distribution of seabirds at sea. Northern fulmars Fulmarus glaclalis and black-legged kittiwakes Rissa tridactyla were the most regular and frequent ship-followers across the central and northern North Sea during 2 surveys with a fishery research vessel in May-June and July-August 1992. Sixteen other species occurred less often and/or in lower numbers. Birds consumed 84 % of experimentally discarded roundfish and 8 % of discarded flatfish. On average, northern gannets Morus bassanus took the largest individuals of most fish specles, black-legged kittywakes the smallest The average size choices of herring gulls Larus argentatus, lesser black-backed gulls Larus fuscus and northern fulmars lay between these 2 extremes. The choice of fish lengths by birds vaned with different fish species. Northern gannet was the most successful species in consuming discards. Northern fulmars success rates decreased with the presence of larger ship-followers but were never high. Black-headed gull Larus ridibundus and common gull Larus canus were less successful than the more frequent typical ship-following species

Trophic signatures of marine organisms in the Mediterranean as compared with other ecosystems

We compared several large marine ecosystems in terms of species numbers of fishes, sea birds, marine mammals, and cephalopods. We examined how these numbers were distributed by trophic level, from herbivores to top predators. We created group-specific trophic signatures as plots of number of species by trophic level, and used these to identify similarities and discrepancies between taxonomic groups and ecosystems. Preliminary results suggested that trophic signatures are similar for ecosystems previously known to share major features, and different for dissimilar ecosystems. In the Mediterranean, as well as in the other large marine ecosystems, fish clearly dominate the predatory trophic levels above 3.0. Preliminary signatures for cephalopods, marine mammals, and sea birds in the Mediterranean and in the North Sea indicate that these groups are restricted to trophic levels above 3.0, and are represented by many fewer species than are predatory fish. Notably, cephalopods are the only invertebrates present at higher trophic levels (>= 4). Invertebrates other than cephalopods are restricted to trophic levels below 3, with very few exceptions. Trophic signatures appear to be useful tools for better understanding of the roles that different groups of organisms play in different ecosystems. We also applied free-scale network theory to analyse the food web created by trophic links of fishes. Our preliminary results indicated that Mediterranean fishes are, on average, only two trophic links away from each other

Distribution of seabirds and waterbirds in the German Baltic Sea throughout the year

Die Verbreitungsmuster ausgewählter See- und Wasservogelarten in den Offshore-Bereichen der deutschen Ostsee werden erstmals für die vier Jahreszeiträume Frühjahr, Sommer, Herbst und Winter dargestellt. Dabei zeigen sich bei den einzelnen Arten sowohl räumliche als auf saisonale Verbreitungsunterschiede. Die deutschen Ostseewässer stellen für See- und Wasservögel ein wichtiges Rast-, Mauser- und Überwinterungsgebiet dar, einige Arten kommen in international bedeutsamen Konzentrationen vor. Für das im Mai 2004 an die EU-Kommission gemeldete Seevogelschutzgebiet „Östliche Pommersche Bucht“ im Ostteil der deutschen Ostsee werden erstmals aktuelle Bestandszahlen der wichtigsten Seevogelarten vorgestellt. Für im Untersuchungsgebiet nur selten auftretende Seevogelarten werden die Gesamtzahlen aller Nachweise aus den Schiffszählungen angegeben. Ziehende oder nur im Küstenbereich vorkommende Wasservogelarten werden lediglich namentlich aufgelistet. In Ergänzung zu früheren Publikationen liefert der vorliegende Artikel umfassende Informationen über das Vorkommen und die jahreszeitlichen Unterschiede der häufigen See- und Wasservogelarten im Offshore-Bereich der deutschen Ostsee.The German Baltic Sea is a very important area for seabirds and waterbirds. 38 species are regularly found in coastal or offshore waters. Many of them occur in international important concentrations and are subject to various conservation-related conventions and directives, especially the EU Birds Directive and the African-Eurasian Waterbird Agreement (AEWA). From 2000 to 2005, several research projects were dedicated to describe and analyse the distribution and abundance of seabirds in the offshore area in the German Baltic Sea at high spatial and temporal resolutions. In this study, we present for the first time the distribution of seabirds and waterbirds in the German Baltic Sea throughout the year, based on transect counts from ships. The main focus is on the offshore areas. For the most numerous species we present the distribution for the four seasons summer, autumn, winter and spring, defined species-specific. The maps clearly show spatial and temporal differences in the distribution of the various species. While Red-breasted Mergansers, Great Crested Grebes or Great Cormorants occur predominantely close to the coast, Red-necked Grebes, Slavonian Grebes and Common Guillemots, among others, prefer offshore-areas. The most numerous and characteristic species are the sea ducks Common Eider, Long-tailed Duck, Common Scoter and Velvet Scoter. They prefer areas with low water depth along the coast or on shallow banks in the offshore area. While Common Eiders occur chiefly in the western parts of the German Baltic Sea, Velvet Scoters are mainly found in the eastern parts. Both species have high densities in the winter half-year but only small numbers during summer. Long-tail Ducks and Common Scoters are distributed over large areas of the German Baltic Sea, but while the former species occurs in the winter half-year only, the latter species is present throughout the whole year. Gulls are widespread throughout the study area and show only local and/or short-term concentrations. Aggregations are often in the vicinity of high fishing activities. The most frequent gull species is the Herring Gull. Terns occur only in very small numbers in the German Baltic Sea, with Black Terns exhibiting small concentrations in the eastern part during late summer. Species that occur predominantly in coastal areas of the German Baltic Sea are not presented in detail. However, for Mute Swan, Greater Scaup, Common Goldeneye and Goosander we present maps for the winter half-year (October-April), as the nearshore distribution of these species sometimes extent into offshore areas. For species occuring only seldom within the study area we present a list with the total number of individuals seen during the surveys. Coastal or migrating waterbird species are only named. Together with previously published information on the distribution of seabirds and waterbirds in the German Baltic Sea, available mainly for the winter and spring periods, this study gives a comprehensive overview about the spatial and temporal distribution of the most numerous and widespread seabirds and waterbirds in the German Baltic Sea. In addition, current population estimates of these species are given for the recently designated Special Protection Area “Pommersche Bucht” in the Exclusive Economic Zone (EEZ) of the eastern part of the German Baltic Sea

The diet of Common Gulls (Larus canus) breeding on the German North Sea coast

The diet of Common Gulls Larus canus was analysed from pellets and faeces during the breeding period in 1995. Three geographically well-separated colonies were selected: one located close to the open North Sea (Amrum Island), one at the inner edge of the Wadden Sea (Nordstrandischmoor Island}, and one in the tidal river Elbe (Liihesand Island). The birds fed upon a large variety of food types. 1n the two colonies adjacent to the sea, prey types from the tidal flats were most numerous (mainly crustaceans, polychaetes, bivalves). Gadids and Smelt Osmerus eperlanus were the fish identified most often, whereas discards from fisheries were relatively important during the early incubation period on Amrum and Nordstrandischmoor. Terrestrial food was also taken (earthworms, insects) but was less important. On Liihesand, in contrast, Common Gulls fed predominantly on terrestrial food (earthworms, insects, mammals and fruits). These birds hardly utilised the river Elbe and associated freshwater tidal flats. The diet changed in all three colonies over the breeding period. The proportion of mammals increased while that of fish and bivalves (only the two colonies close to the coast) decreased. On Liihesand, a considerable proportion of the pellets consisted of cherry stones during the chickrearing period. Common Gulls were relatively widely distributed in the inner German Bight but all major concentrations were located close to land, chiefly in front of the mouths of the rivers Elbe and Weser. Common Gulls (up to 150 individuals) regularly attended the inshore shrimping vessels

Food choice of birds from the German North Sea coast

Informationen über die Nahrungswahl von See- und Küstenvögeln liefern einen essentiellen Beitrag zum Verständnis mariner Nahrungsnetze. In der vorliegenden Studie wurden Mageninhalte von toten Küstenvögeln ausgewertet, die als Spülsaumfunde entlang der deutschen Nordseeküste gesammelt wurden. Das erste Ziel dieser Studie bestand darin, aktuelle Informationen über die Nahrungswahl von Austernfischern (Haematopus ostralegus), Großen Brachvögeln (Numenius arquata), Knutts (Calidris canutus) und Lachmöwen (Chroicocephalus ridibundus) zu erhalten. Das zweite Ziel der Studie war es, zu prüfen, ob Spülsaumfunde brauchbare Informationen zur Nahrungswahl von Küstenvögeln liefern können. Hierzu wurden insgesamt 59 Individuen der vier Arten durch ein ehrenamtliches Netzwerk von Personen entlang der deutschen Nordseeküste gesammelt und anschließend seziert. Alle Mägen enthielten bestimmbare Reste. Austernfischer und Lachmöwen zeigten ein sehr ähnliches und gleichzeitig das breiteste Nahrungsspektrum. Es bestand vor allem aus Mollusken, Polychaeten (Vielborster), Regenwürmern und Insekten. In den Austernfischermägen traten zu allen Jahreszeiten fast stets marine und terrestrische Nahrungsreste gemeinsam auf, während Lachmöwen zur Brutzeit verstärkt marine Nahrung aufnahmen, außerhalb der Brutzeit aber fast ausschließlich eine terrestrische Ernährungsweise aufwiesen. Große Brachvögel ernährten sich überwiegend von Polychaeten und Krebstieren sowie weniger häufig von Muscheln. Die Ernährung der Knutts unterschied sich am deutlichsten von den anderen Arten und wies die höchste Spezialisierung auf. In allen Mägen wurden Wattschnecken (Hydrobia ulvae) und in einem weiteren hohen Anteil von Mägen Strandschnecken (Littorina littorea) und Muscheln gefunden. Außer beim Großen Brachvogel befanden sich bei allen Arten in einzelnen Mägen kleine Müllpartikel aus Plastik, die wahrscheinlich im marinen Bereich aufgenommen wurden. Bei Lachmöwen stimmen die gefundenen Ergebnisse gut mit bereits veröffentlichten Studien aus Speiballenuntersuchungen überein. Auch die Nahrung der übrigen Arten ähnelte den Ergebnissen aus früheren Studien. Es wird gefolgert, dass die Analyse von Mageninhalten von tot am Strand aufgefundenen Vögeln geeignet ist, um aktuelle Informationen über die Nahrungswahl von Küstenvögeln zu erlangen. Um robuste Erkenntnisse über räumliche und zeitliche Unterschiede in der Nahrungswahl zu erhalten, sollte jedoch die Stichprobe erhöht werden. Darüber hinaus kann ein Vergleich zwischen Mageninhalten und stabilen Isotopen aus Muskelgewebe die Ergebnisse absichern helfen.Sound knowledge on the food choice of seabirds and coastal birds essentially contributes to the understanding of marine food webs. In the present study stomach contents of beached coastal birds from the German North Sea coast were analysed. The first aim of the study was to collect up to date data on the food choice of Oystercatchers (Haematopus ostralegus), Curlews (Numenius arquata), Red Knots (Calidris canutus) and Black-headed Gulls (Chroicocephalus ridibundus). The second aim was to proof, if beached birds are valuable to provide information on food choice of coastal birds. For these purposes overall 59 individuals of the four species were collected by a network of volunteers along the German North Sea coast and subsequently dissected. All stomachs contained prey remains that could be determined. Oystercatchers and Black-headed Gulls showed a very similar and at the same time the broadest prey spectrum. It mainly consisted of molluscs, polychaetes, earthworms and insects. Marine and terrestrial prey remains were found in stomachs of Oystercatchers during all periods of the year, whereas Blackheaded Gulls took up more marine prey during the breeding season and switched to an almost exclusively terrestrial nutrition during other seasons. Most Curlews fed on polychaetes and crustaceans and – less frequently – on bivalves. The food choice of Red Knots differed strongest from the other species and showed the highest degree of specialisation. All stomachs of Red Knot contained mud snails (Hydrobia ulvae) and a high proportion of stomachs contained common periwinkles (Littorina littorea) and bivalves. Several stomachs of all bird species (except Curlews) contained small particles of plastic waste that were most likely taken up in the marine foraging habitat. In Black-headed Gulls, the results of the current study fit well to previous studies based on pellet analyses. The food choice of the other bird species was consistent with previous studies as well. It can be concluded that the analyses of stomach contents of beached coastal birds is a valuable method to collect up to date information on their food choice. However, the sample sizes need to be increased to gain robust data on spatial and temporal difference in food choice. Eventually, a comparison between stomach contents and stable isotope signatures from muscle tissue may help to support the results of the current study

Breeding Lesser Black-backed Gulls Larus graellsii and Herring Gulls Larus argentatus: coexistence or competition?

While Lesser Black-backed Gull Larus graellsii numbers increase substantially at the German North Sea coast since the late 1980s, Herring Gull Larus argentatus numbers have been roughly stable since the mid-1980s. In order to investigate whether a different ecology might explain the current trends, we studied diet, colony attendance, reproductive output and aggressive behaviour in a mixed-colony on Amrum, southeastern North Sea, in 1994 and 1995. During incubation Lesser Black-backed Gulls fed mainly upon crustaceans and molluscs which were taken from the intertidal zone. During chick-rearing, they took mainly crustaceans and fish which were gathered mostly as trawler discards. The main food of Herring Gulls throughout the reproductive season were molluscs and crustaceans which were obtained from the intertidal zone. Numbers of Lesser Black-backed Gulls in the colony mainly varied with season and time of day, those of Herring Gulls with tide and season. Numbers of Herring Gulls commuting to the open sea roughly equalled those commuting to the Wadden Sea. Lesser Black-backed Gulls generally flew to the open sea but hardly towards the Wadden Sea. Nest attendance was significantly higher in Lesser Black-backed Gulls than in Herring Gulls during the chick-rearing period. Hatching success and fledging success tended to be higher in Lesser Black-backed Gulls. Lesser Black-backed Gulls won interspecific aggressive interactions significantly more often than Herring Gulls in the chick-rearing period. Our study indicates that Lesser Black-backed Gulls currently enjoy a few ecological advantages compared with Herring Gulls, particularly because they feed on food of apparently higher quality. We conclude that Lesser Black-backed Gulls have filled an empty niche rather than have out-competed Herring Gulls during the past decade

A preliminary comparison of the trophic structure of some large marine ecosystems

Five large marine ecosystems are compared in respect to the signatures created by plots of number and average size of species by trophic level. Preliminary results suggest that these signatures are similar for similar ecosystems (here: Baltic Sea and Black Sea as examples of brackish, temperate ecosystems, and Caribbean and South China Sea as examples of tropical ecosystems), and different for different ecosystems (here: temperate vs tropical systems). Also, the shape and the position of the signatures appear to be predictable, as shown for the North Sea, which has a similar shape but intermediate position between the species-poor Baltic and Black Sea, and the species-rich tropical systems. Individual signatures can be interpreted and reveal special characteristics, as shown by the lower part of the Caribbean signature, which has a different trend then the other signatures, indicating that the Caribbean has relatively more herbivorous fishes. Fish data were extracted from www.fishbase.org. Preliminary signatures for cephalopods, marine mammals, and marine birds indicate the different roles of these groups in ecosystems. In the North Sea, vertebrates (fish, birds, marine mammals) and cephalopods are restricted to trophic levels above 3, with the exception of very few fish and bird species). Invertebrates are restricted to trophic levels below 3, again with very few exceptions

Effects of agricultural practices on foraging habitats of a seabird species in the Baltic Sea

Omnivorous and opportunistic species may be good indicators of food availability. Gulls often use human-impacted landscapes and may respond to changes by altering their feeding ecology. We investigated the foraging behavior of individual common gulls (Larus canus), focusing on their distribution during foraging and their selected habitat types. We tracked adult common gulls using GPS telemetry at their largest breeding colony in the southwestern Baltic Sea, Germany. Foraging habitats were analyzed from tracking data for three breeding seasons 2016, 2017, and 2019 and were compared with potentially available foraging habitats. Most breeding birds flew toward terrestrial areas. Feeding sites were located on average 11.7-14.3 km from the colony (range 0.9-36.5 km). Corn and sugar beet fields were used significantly and extensively compared with their availability in 2016 and 2017, while wheat, rape, and barley fields were used significantly less. Data from 2019 suggested seasonal shifts in habitat use. Birds spent between 30 and 1300 min per week at their preferred feeding sites, with significant differences between the major habitats selected. We found a stable, clear, multiyear pattern in common gull foraging behavior in relation to agricultural practices. Fields with little or no crop cover and thus access to the soil were preferred over fields with high crop cover. These results suggest that local food availability may be limiting further population increases in this species