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Endangered Species Research

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ESR 14:157-169 (2011)  -  DOI:

Modelling harbour porpoise seasonal density as a function of the German Bight environment: implications for management

Anita Gilles1,*, Sven Adler1,2, Kristin Kaschner1,3, Meike Scheidat1,4, Ursula Siebert

1Research and Technology Centre (FTZ), Christian-Albrechts-University of Kiel, 25761 Büsum, Germany
2University of Rostock, Institute for Biodiversity, 18057 Rostock, Germany
3Evolutionary Biology & Ecology Lab, Institute of Biology I (Zoology), Albert-Ludwigs-University, 79104 Freiburg, Germany
4Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, Postbus 167, 1790 AD Den Burg, The Netherlands

ABSTRACT: A classical user–environment conflict could arise between the recent expansion plans of offshore wind power in European waters and the protection of the harbour porpoise Phocoena phocoena, an important top predator and indicator species in the North Sea. There is a growing demand for predictive models of porpoise distribution to assess the extent of potential conflicts and to support conservation and management plans. Here, we used a range of oceanographic parameters and generalised additive models to predict harbour porpoise density and to investigate seasonal shifts in porpoise distribution in relation to several static and dynamic predictors. Sightings were collected during dedicated line-transect aerial surveys conducted year-round between 2002 and 2005. Over the 4 yr, survey effort amounted to 38720 km, during which 3887 harbour porpoises were sighted. Porpoises aggregated in distinct hot spots within their seasonal range, but the importance of key habitat descriptors varied between seasons. Predictors explaining most of the variance were the hydrographical parameter ‘residual current’ and proxies for primary production and fronts (chlorophyll and nutrients) as well as the interaction ‘distance to coast/water depth’. Porpoises preferred areas with stronger currents and concentrated in areas where fronts are likely. Internal cross-validation indicated that all models were highly robust. In addition, we successfully externally validated our summer model using an independent data set, which allowed us to extrapolate our predictions to a more regional scale. Our models improve the understanding of determinants of harbour porpoise habitat in the North Sea as a whole and inform management frameworks to determine safe limits of anthropogenic impacts.

KEY WORDS: Habitat modelling · Phocoena phocoena · Conservation · Generalised additive model · North Sea

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Cite this article as: Gilles A, Adler S, Kaschner K, Scheidat M, Siebert U (2011) Modelling harbour porpoise seasonal density as a function of the German Bight environment: implications for management. Endang Species Res 14:157-169.

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