Browsing by Author "Dahlquist, Arvid"

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    Estimating poulation trend and breeding site fidelity for the Baltic grey seal (Halichoerus grypus balticus)
    (2025-08-15) Dahlquist, Arvid; University of Gothenburg / Department of Biological and Environmental Sciences; Göteborgs universitet / Instiutionen för biologi och miljövetenskap
    The Baltic gray seal population has for decades undergone significant changes. The extent of sea ice, which formerly was an important part of the breeding habitat, is reducing every year forcing gray seal mothers to rear pups on islands. Lacking knowledge of gray seal mothers’ site fidelity behavior, scientific methods like examine population trends and site fidelity analyses can lead to more understanding of the breeding behavior and make a huge difference in mother and pup protection. This study will therefore look upon the overall trend of the Baltic gray seal population done with the latest data from aerial surveys from 2003-2024 The study will also investigate the site fidelity behavior by monitoring a specific area in the Stockholm archipelago called Skarv, Sweden’s largest pupping site. The research question examines whether mothers return to this location, assessing its importance for pup rearing. The trend analysis was calculated with two models, exponential and logarithmic where the exponential model gave the best fit. The site fidelity assessment was done by using mark-recapture methods after identifying seals through photo-ID analysis of video material from three consecutive years, 2021-2023 that later was processed in the software Wild ID. The trend model indicates a continued exponential growth of 4.84% each year with a standard error of 0.0026. The mark recapture method resulted in a single recapture for all three years suggesting either low site fidelity behavior or limitations in the sampling. The calculations estimated the female population to N=3967 with upper CI95%=18305 and lower CI95%=1791 and by looking at the confidence intervals the conclusion can be made that uncertainty is affected by the low sample size rather than low site fidelity. Although the maximum growth for a pinniped population is at 13% the trend result suggest that the population continues to recover from historic overhunting. A conclusion for the low recapture rate however is hard to make but with a working methodology this can be used as a foundation to, with further research, establish fidelity rates.