Stable isotopes reveal winter feeding in different habitats in blue, fin and sei whales migrating through the Azores

Abstract

Knowing the migratory movements and behaviour of baleen whales is fundamental to understanding their ecology. We compared δ 15 N and δ 13 C values in the skin of blue ( Balaenoptera musculus ), fin ( Balaenoptera physalus ) and sei ( Balaenoptera borealis ) whales sighted in the Azores in spring with the values of potential prey from different regions within the North Atlantic using Bayesian mixing models to investigate their trophic ecology and migration patterns. Fin whale δ 15 N values were higher than those recorded in blue and sei whales, reflecting feeding at higher trophic levels. Whales' skin δ 15 N and δ 13 C values did not reflect prey from high-latitude summer foraging grounds; instead mixing models identified tropical or subtropical regions as the most likely feeding areas for all species during winter and spring. Yet, differences in δ 13 C values among whale species suggest use of different regions within this range. Blue and sei whales primarily used resources from the Northwest African upwelling and pelagic tropical/subtropical regions, while fin whales fed off Iberia. However, determining feeding habitats from stable isotope values remains difficult. In conclusion, winter feeding appears common among North Atlantic blue, fin and sei whales, and may play a crucial role in determining their winter distribution. A better understanding of winter feeding behaviour is therefore fundamental for the effective conservation of these species.

Decadal shift in foraging strategy of a migratory southern ocean predator

“…Similarly, we used a TEF calculated for fin whale skin (Borrell et al, 2012) as to the best of our knowledge, a species‐specific TEF has not been calculated for SRWs. This TEF (1.28 ± 0.38‰ for δ 13 C and 2.82 ± 0.3‰ for δ 15 N) is similar to the average values for whole animals (≈3‰ for nitrogen and 0 to 1‰ for carbon; Peterson & Fry, 1987), and has previously been used in mixing models to reconstruct blue, sei, fin (Silva et al, 2019) and SRW diet (Valenzuela et al, 2018).…”

Autumn movements of fin whales (Balaenoptera physalus) from Svalbard, Norway, revealed by satellite tracking

“…Fin whales have also been found to feed prior to departing wintering grounds (e.g. around the Azores) before they initiate their northward migrations during spring 12,25 , so the general concept that these whales feed only when at their northern summer grounds, is likely incorrect.…”

“…2). Departures from Svalbard occurred between 10 September and 11 October (all whales tagged in 2019 left between [22][23][24][25][26][27][28][29]. During the Svalbard residency phase for all the whales 49 ± 7% of locations per individual were in ARS, 22 ± 6% in transit and behaviour at 29 ± 6% of the locations was classified as being in an uncertain state.…”

Reconstructing the diet, trophic level, and migration pattern of Mysticete whales based on baleen isotopic composition

“…This suggests that the impacts from fasting on glycogenic δ 15 N values for mysticetes may be more limited than during breeding and molting events in other marine mammals. This smaller observed effect may be due to either the considerable body size and lipid stores or through subsistence with opportunistic feeding offsetting more extreme fasting effects (64). Although limited in scale, isotopic enrichment of the δ 15 NGly values onset in the same manner (during minimum periods) across all individuals regardless of species (Fig.…”