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Seals at sea: modelling seal distribution in the German bight based on aerial survey data

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Abstract

The Wadden Sea is an important habitat for harbour seals and grey seals. They regularly haul-out on sandbanks and islands along the coast. Comparably little is known about the time seals spend at sea and how they use the remainder of the North Sea. Yet, human activity in offshore waters is increasing and information on seal distribution in the North Sea is crucial for conservation and management. Aerial line transect surveys were conducted in the German bight from 2002 to 2007 to investigate the distribution and abundance of marine mammals. Distance sampling methodology was combined with density surface modelling for a spatially explicit analysis of seal distribution in the German North Sea. Depth and distance to coast were found to be relevant predictor variables for seal density. Density surface modelling allowed for a depiction of seal distribution in the study area as well as an abundance estimate. This is the first study to use aerial survey data to develop a density surface model (DSM) for a spatially explicit distribution estimate of seals at sea.

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Notes

  1. In this context, group is defined as a number of animals engaged in similar behaviour, not to be confused with a “social group” as found with e.g. cetaceans.

  2. Animal positioned vertically in the water column with its head out of the water.

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Acknowledgments

The data analysed for this work was collected in several projects funded by the German Federal Agency for Nature Conservation (BfN), the German Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) and the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). We would like to thank Anita Gilles for helpful discussion and Geert Aarts for valuable criticism of an earlier draft. We owe thanks to Kristin Kaschner and Hauke Giewat for their assistance with the database. Our thanks also go to the pilots, from Sylt Air, the Danish Air Survey and FLM Kiel as well as to our enthusiastic observer team.

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Authors and Affiliations

  1. Research and Technology Center, University of Kiel, Hafentoern 1, 25761, Buesum, Germany

    Helena Herr, K. Lehnert & U. Siebert

  2. Wageningen IMARES, Institute for Marine Resources and Ecosystem Studies, PO Box 167, Den Burg, The Netherlands

    M. Scheidat

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  1. Helena Herr
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  2. M. Scheidat
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  4. U. Siebert
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Correspondence to Helena Herr.

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Communicated by U. Sommer.

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Herr, H., Scheidat, M., Lehnert, K. et al. Seals at sea: modelling seal distribution in the German bight based on aerial survey data. Mar Biol 156, 811–820 (2009). https://doi.org/10.1007/s00227-008-1105-x

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