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Browsing by Subject "Ringed seal"

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  • Mehtonen, Monica (2019)
    The Baltic ringed (Pusa hispida botnica) and grey seal (Halichoerus grypus) populations have experienced dramatic changes in their abundances since the early 20th century, when their populations were much larger than today but since then have declined due to over exploitation and reproductive challenges linked to environmental pollutants. Both populations have however, begun to recover, and their numbers have increased since the 1970s. This increase has led to more seal-inflicted damages to coastal fisheries resulting in the demand to control their populations. In Finland, fishermen have reported significant economic losses, and many consider seals as the main threat to their livelihood. However, our knowledge on the diet composition and foraging behaviour of Baltic ringed and grey seals in Finnish sea area is lacking. In order to achieve sustainable seal management, more information on their diet is thus needed. Therefore, to shed light on the diet composition of Baltic seals in Finland, I examined the stomach contents from 156 ringed and 73 grey seals collected in 2017 across the Finnish sea area. Furthermore, I analysed dietary differences between demographic factors (i.e. age and sex), and seals from different geographic regions. A total of 15 prey taxa, of which 13 fish species or groups were identified. Ringed seal diet was dominated by benthic isopod Saduria entomon that was recovered from over half of the stomachs. In addition to Saduria entomon, herring (Clupea harengus) were the most important fish species consumed. Other important prey were gobies (Gobiidae), smelt (Osmerus eperlanus) and common whitefish (Coregonus lavaretus). In terms of biomass, common whitefish became the most important prey whereas in numbers gobies dominated the diet. For grey seals, herring were the most common and numerous prey consumed that made up most of their diet. Other common species were sprat (Sprattus sprattus) and smelt. Other prey did not contribute substantially to grey seal diet. Additionally, the results of this study showed differences in diet composition between seals of different age and sex.