Abstract
Simple SummaryMarine mammals play an important role in marine ecosystems. However, as they are less accessible for research, relatively little is known about their physiology compared to terrestrial mammals. The stranding scheme of the Deutsches Meeresmuseum (Stralsund, Germany) continuously collects strandings and by-catches of marine mammals in the Baltic Sea in Mecklenburg-Western Pomerania. In this project, the fatty acid composition of the liver, skeletal muscles, and blubber of harbour porpoises and grey seals from the southern Baltic Sea was investigated for the first time. In the liver and blubber tissue, the values and concentrations measured for both species are consistent with studies on other marine mammals. In a direct comparison of the focus species, the skeletal muscles of harbour porpoises exhibit higher concentrations of fatty acids than those of grey seals. In the future, these studies will be extended to the entire Baltic Sea, as we suspect that fatty acid composition can be used to determine the nutritional status of the animals and thus will allow for an objective assessment of the body condition.To date, only limited results on the fatty composition in different tissues of the top predators in the Baltic Sea are available. In the current study, tissue samples of blubber, skeletal muscle, and liver from 8 harbour porpoise (Phocoena phocoena) and 17 grey seals (Halichoerus grypus) in the Baltic Sea off Mecklenburg-Western Pomerania were included in the investigation. While the total fatty acid content in liver and blubber tissue revealed no differences between both species, the total fatty acid content of muscle tissue was significantly differentand showed higher concentrations in harbour porpoise muscle compared with grey seals. The most abundant fatty acids in the blubber of grey seals and harbour porpoises (18:1cis-9, 16:1cis-9, 16:0 and 22:6n-3) were present in similar quantities and ratios to each other as known from other marine top predators. If future studies can show that differences in tissue fatty acid content are caused by variation in the nutritional status, and this may lead to the development of a more objective assessment of body condition in seals and porpoises recovered via stranding schemes.
Highlights
The ecosystem and food web of the Baltic Sea is comparatively young
Animals used in this study showed low decomposition and had a good nutritional status following approved methods taking a thin blubber layer or muscle atrophy, a hollow appearance behind the skull or dorsal fin, or clear protrusion of the lateral process of lumbar vertebrae into account [34]
As we present here a preliminary study on the fatty acid composition in different tissues of grey seals and harbour porpoises in the southern
Summary
The ecosystem and food web of the Baltic Sea is comparatively young. From a geological perspective, the Baltic Sea is a marginal sea of the Atlantic Ocean, with present time environmental conditions reaching back to only about ~7000 years ago. Grey seals (Halichoerus grypus) and harbour porpoise (Phocoena phocoena) currently are the two main mammalian predators in the wider Baltic Sea area, including the Kattegat. These two species have surpassed ringed seals (Pusa hispida), which were formerly the most abundant mammalian species in the Baltic Sea [1,2], harbour seals (Phoca vitulina), and the rarely appearing vagrant cetacean species entering from the North Sea. Grey seal and harbour porpoise have been heavily affected by human impacts over the last centuries [3,4]. In the 1980s, about 2500 grey seals remained in the northern
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