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MEPS 507:297-308 (2014)  -  DOI: https://doi.org/10.3354/meps10846

Using movement data of Baltic grey seals to examine foraging-site fidelity: implications for seal-fishery conflict mitigation

Sari M. Oksanen1,*, Markus P. Ahola2, Esa Lehtonen3, Mervi Kunnasranta1

1Department of Biology, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland
2Finnish Game and Fisheries Research Institute, Itäinen Pitkäkatu 3, 20520 Turku, Finland
3Finnish Game and Fisheries Research Institute, PO Box 2, 00791 Helsinki, Finland
*Corresponding author:

ABSTRACT: Knowledge of the intensity of spatial overlap between aquatic top predators and fisheries is required to efficiently alleviate the negative effects of marine mammal-fishery interactions. We used satellite telemetry to study the movements and habitat use of Baltic grey seals Halichoerus grypus, with special focus on the degree of site fidelity to foraging and haul-out areas and spatio-temporal overlap with coastal fisheries. Most of the tracked seals (14/16 individuals) were ‘residents’, which remained within 120 ± 62 km (mean ± SD) of their capture sites during the open-water season, whereas 2 ‘transient’ seals occupied much larger areas, over 400 km from their capture sites. Residents used on average 4.3 ± 2.5 haul-out sites, indicating high haul-out site fidelity during the open-water season. Residents had active core areas (58 ± 35 km2, 50% local nearest-neighbour convex hull [LoCoH], excluding haul-out locations) near river estuaries or at other shallow water areas, indicating foraging-site fidelity to these foraging grounds. They overlapped both spatially and temporally with trap-net fishing. The high site fidelity of grey seals indicates that foraging and haul-out areas should be taken into account in population management. Selective removal of seals overlapping with fishery could be a locally focused method to mitigate seal-fishery interactions. However, removal of individuals in foraging areas may also compromise the conservation needs of the population by targeting the same animals that are hauling out in seal sanctuaries.


KEY WORDS: Baltic Sea · GPS phone tag · Habitat preference · Halichoerus grypus · Home range · Seal-fishery overlap · Trap-net fishery


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Cite this article as: Oksanen SM, Ahola MP, Lehtonen E, Kunnasranta M (2014) Using movement data of Baltic grey seals to examine foraging-site fidelity: implications for seal-fishery conflict mitigation. Mar Ecol Prog Ser 507:297-308. https://doi.org/10.3354/meps10846

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