Increasing plans for economic activities at sea have recently led to intensive studies of seabird distribution and seabird numbers. However, there are still some temporal gaps concerning seabird numbers, and important up-to-date information is still missing. Thus, the aim of this study is to provide most recent seabird numbers for all seasons and all species that are regularly resting and/or foraging in German waters of the North Sea, split into the politically relevant areas EEZ as well as the 12 nautical miles zones of Niedersachsen and Schleswig-Holstein, respectively.
For our analyses at sea, we investigated seabird numbers from the outer Wadden Sea islands to the outer boarders of German waters, using standardised ship-based (years: 1993–2003) and aerial (2002–2006) transect methods. We calculated and applied species-specific correction factors for birds presumably overlooked in the outer transect area. Using grid maps of seabird distribution, geographic units of similar bird densities were designed for each bird species and each season, covering the entire study area. Then, numbers within each unit were calculated by firstly dividing the total number of birds by the total area surveyed and by secondly multiplying this value by the size of the unit. Finally, the total was derived as the sum across all of these units. In addition to the numbers at sea, we included (1) data from regular counts on Helgoland, (2) data from counts along the German Wadden Sea coast and (3) from aerial censuses for sea ducks as well as (4) colony census data.
When only considering numbers at sea, between 183,000 (autumn) and 265,000 (winter) birds occur in the German part of the North Sea. The most numerous species are Common Scoter Melanitta nigra (130,000 ind.; winter), Lesser Black-backed Gull Larus fuscus (45,000 ind.; summer) and Northern Fulmar Fulmarus glacialis (40,000 ind.; summer). Including coastal areas, total numbers range from 463,000 ind. (autumn) to 693,000 ind. (summer). Common Eiders Somateria mollissima are most numerous (180,000 ind.; autumn), followed by Black-headed Gulls Larus ridibundus (170,000 ind.; autumn) and Common Scoters (135,000 ind.; winter). In relation to their biogegographic populations, Common Eiders (23.7%; autumn), Lesser Blackbacked Gulls (19.9%; summer) and Sandwich Terns Sterna sandvicensis (12.5%; summer) are most important. From a conservation point of view, summer is the most important time of the year. Overall, our results show that 13 species occur in internationally important concentrations in the German North Sea area.