Grey seal, Halichoerus grypus, habitat selection around haulout sites in the Baltic Sea: bathymetry or central-place foraging?

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Abstract
We investigated habitat selection by grey seals, Halichoerus grypus, around haulouts in the Baltic Sea. Home ranges (95% fixed kernel) varied in size from 1088 to 6400 km2. Observed habitat use was tested against the circular home range predicted from a simple central-place model. The overlap between the home ranges predicted by this simple model and actually exhibited by the seals was 51 m deep. Ten of the 11 seals used areas within a 50-km radius around the haulout site for more than 75% of the time. Thus, in spite of their mobility and the availability of many islands, seals usually remained in the vicinity of a specific haulout site for extended periods. The seals did not use the habitat around the haulout site as predicted by the simple central-place model, but selected habitat according to bathymetric characteristics (e.g., water depth). Detection of these relatively small but heavily used home ranges around haulout sites may be of assistance in management plans in order to reduce the growing number of seal-fisheries conflicts.