Year‐Round Haulout Activity of Harbor and Gray Seals Derived From Satellite Telemetry in Scandinavian Waters

Abstract

Seal haulout behavior is of interest in relation to energetics and abundance estimation. To assess year‐round and diel haulout patterns and estimate correction factors, data were obtained from 100 seals (66 harbor and 34 gray seals) tagged with satellite transmitters in Kattegat and the western Baltic Sea during 2004–2017. Kattegat harbor seals had highest haulout probability during the night throughout the year, except for adults shifting to daytime preference during the mating season. Western Baltic harbor seals had higher haulout probabilities during daytime, peaking in March–May, with lowest probabilities in December–February. We found no clear differences in haulout behavior among age classes in Kattegat, but pups of the year hauled out more than other age classes in autumn in the western Baltic. Harbor seal haulout probabilities were similar to other parts of their range during autumn, winter, and spring, but lower during summer. Our data on harbor seal haulout probabilities in both June and August, months during which abundance counts are made, suggest that previous abundance estimates were too low. Baltic gray seals mostly hauled out at night throughout the year. Juveniles had highest haulout probabilities in March–April, while pups of the year peaked during molt (May–June). Our data highlight that haulout behavior can be highly variable, even between neighboring areas and should not be geographically extrapolated, and that it is essential to include recent and local knowledge of haulout behavior to adjust the estimates of abundance based on aerial counts.

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