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Advisor(s)
Abstract(s)
Evaluating populational trends of health condition has become an important
topic for marine mammal populations under the Marine Strategy Framework
Directive (MSFD). In the Baltic Sea, under the recommendation of Helsinki
Commission (HELCOM), efforts have been undertaken to use blubber thickness
as an indicator of energy reserves in marine mammals. Current values lack
geographical representation from the entire Baltic Sea area and a large dataset is
only available for grey seals (Halichoerus grypus) from Sweden and Finland.
Knowledge on variation of blubber thickness related to geography throughout
the Baltic Sea is important for its usage as an indicator. Such evaluation can
provide important information about the energy reserves, and hence, food
availability. It is expected that methodological standardization under HELCOM
should include relevant datasets with good geographical coverage that can also
account for natural variability in the resident marine mammal populations. In
this study, seasonal and temporal trends of blubber thickness were evaluated for
three marine mammal species—harbor seal (Phoca vitulina), grey seal
(Halichoerus grypus) and harbor porpoise (Phocoena phocoena)—resident in
the southern Baltic Sea collected and investigated under stranding networks.
Additionally, the effects of age, season and sex were analyzed. Seasonal
variation of blubber thickness was evident for all species, with harbor seals
presenting more pronounced effects in adults and grey seals and harbor
porpoises presenting more pronounced effects in juveniles. For harbor seals
and porpoises, fluctuations were present over the years included in the analysis.
In the seal species, blubber thickness values were generally higher in males. In
harbor seals and porpoises, blubber thickness values differed between the age
classes: while adult harbor seals displayed thicker blubber layers than juveniles,
the opposite was observed for harbor porpoises. Furthermore, while an
important initial screening tool, blubber thickness assessment cannot be
considered a valid methodology for overall health assessment in marine
mammals and should be complemented with data on specific health
parameters developed for each species
Description
Keywords
Blubber thickness Harbor seals Grey seals Harbor porpoises Natural variations HELCOM area
Citation
Siebert, U., Kesselring, T., Lehnert, K., Ronnenberg, K., Gilles, A., Grilo, M. L., Pawliczka, I., Galatius, A., Kyhn, L. A., & Dähne, M. (2022). Variation of blubber thickness for three marine mammal species in the southern Baltic Sea. Frontiers in Physiology, 13. https://doi.org/10.3389/fphys.2022.880465
Publisher
Frontiers Media S.A.