Dierschke, Volker , Exo, Klaus-Michael , Mendel, Bettina and Garthe, Stefan (2012) Gefährdung von Sterntaucher Gavia stellata und Prachttaucher G. arctica in Brut-, Zug- und Überwinterungsgebieten – eine Übersicht mit Schwerpunkt auf den deutschen Meeresgebieten. Vogelwelt, 133 . pp. 163-194.

Abstract

During most sections of the annual cycle, Red-throated and Black-throated Divers breeding in
N Eurasia and wintering in European coastal marine areas are influenced by human activities,
which have impact on habitat quality and eventually on reproduction and mortality. Human
actions in breeding, migration and wintering areas are summarized and their effects predicted
quantitatively with respect to the German sections of North and Baltic Seas.
In the breeding areas, the condition of the breeding lakes influences reproduction and
mortality, for instance regarding water chemistry (food supply, concentration of contaminants)
and disturbance (recreational activities, predation). At the moment, it is difficult to predict the
consequences of climate change for the availablility and quality of breeding lakes. During the
non-breeding season, divers are threatened by the increasing industrial use of their marine
habitats and shipping, but are also prone to anthropogenic mortality due to drowning in gill
nets (fishery) and plumage oiling. Hunting does not play a major role nowadays.
For the German marine areas, habitat loss was calculated for already existing and planned
utilization by offshore wind farms, aggregate extraction and shipping. The results were related to
the wintering stocks of Red-throated Diver (90,000 birds in NW Europe, i.e. in the NE Atlantic)
and Black-throated Diver (31,250 birds in Europe) as well as to the spring staging stocks of both
species in Germany (25,500 and 3,900 birds, respectively). According to current knowledge
a complete avoidance of wind farms including a 2 km buffer was adopted for divers, a 50%
reduction of bird densities was assumed for areas with heavy ship traffic and those designated
for aggregate extraction. The number of divers (presumably) concerned was calculated from
the size of those areas and the diver densities derived from long-year aerial transect surveys.
Arising from this, habitat loss is predicted for c. 5,770 Red-throated and c. 830 Black-throated
Divers (22.6% and 21.3% of the German spring staging stocks, 6.4% and 2.7% of the European
wintering populations, respectively), if all utilizations consented will be realized.
The annual number of birds killed accidentally in gill nets (c. 420 Red-throated and c. 265
Black-throated Divers) and by plumage oiling (25-50 Red-throated and 4-7 Black-throated
Divers) refers to about 1.8% and 7.0% of the German stocks during spring migration and 0.5%
and 0.9% of the European wintering populations.
Given the population biology of the species, the predicted and already existing losses of
habitat (with so far not quantifiable impact on mortality and reproduction) and individuals
is alarming. Their extent in Germany alone is threatening, but the same hazardous factors are
acting in neighbouring marine areas additionally. Therefore, measures to save the two diver
species are essential and should comprise the protection of important habitats in North and
Baltic Seas from industrial utilization (including a spatial regulation of shipping lanes), the
closure of areas with high diver densities for fishery at least temporarily, and more effective
conservation in the marine areas already protected under German or European law.

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