Health and age and sex distributions of Baltic grey seals (Halichoerus grypus) collected from bycatch and hunt in the Gulf of Bothnia

Abstract

Abstract Bäcklin, B-M., Moraeus, C., Roos, A., Eklöf, E., and Lind, Y. 2011. Health and age and sex distributions of Baltic grey seals (Halichoerus grypus) collected from bycatch and hunt in the Gulf of Bothnia. – ICES Journal of Marine Science, 68: 183–188. Age distribution, sex ratio, and season of death were investigated in grey seals taken as bycatch and hunted in the Gulf of Bothnia for the period 2002–2007. In seals 1–20 years old, certain health variables, earlier reported as parts of a disease complex related to persistent organic pollutants, were also investigated. Most of the hunted group were female (60%), but there were more males (62%) in the bycatch group. In spring, there were more bycatch than hunted yearlings. Seals taken as bycatch were leaner than hunted animals, and in hunted seals, there was a significant seasonal difference in blubber thickness that was not observed in seals taken in the bycatch. The prevalence of intestinal ulcers was 18–50% in bycatch and 24–74% in hunted animals. Hunted males 4–20 years old had a significantly greater prevalence of intestinal ulcers than bycatch males in the same age group. Adrenocortical thickening and mean weight of the adrenals increased with age. No lesions were observed in female reproductive organs, and in autumn, nearly all mature females were pregnant. The main differences between hunted and bycatch grey seals were in the season when death occurred, the prevalence of yearlings, the sex ratio, the blubber thickness, and the prevalence of intestinal ulcers.