Abstract
Carbon (δ13C) and nitrogen (δ15N) stable isotope variations in baleen plates of sei whales (Balaenoptera borealis) stranded after a mass mortality event in Chilean Patagonia were investigated to assess potential dietary and migratory patterns. Carbon and nitrogen isotope ratios of seven baleens from six individuals were analyzed. The δ13C values ranged from − 19.1 to − 15.9‰ and the δ15N values from 8.7 to 15.4‰. Variations of up to 2.9‰ for δ13C and 5.3‰ for δ15N were observed within one baleen. Carbon and nitrogen isotope records of each baleen were significantly correlated and showed recurring oscillations confirmed by wavelet analyses. Oscillations slightly differed in periodicity indicating variable baleen growth rates between 10.0 and 16.5 cm/year. Food sources of the whales are discussed in terms of available isotope data for potential prey taxa and potential migratory behavior on the basis of latitudinal isotope gradients of particulate organic matter. Cyclicity could be explained by regular migrations of the sei whales from subtropical calving areas to high‐latitude foraging grounds. δ15N records of baleens differed between individuals eventually pointing to diverse feeding and migratory preferences among sei whale individuals.
Highlights
The largest historically documented baleen whale mass mortality event (MME) took place in the Patagonian fjord area (Chile) between February and April 2015
As we found no significant difference between ultrasonic treatment and lipid-extracted samples in both δ15N and δ13C, we refrained from a lipid extraction procedure
Seasonal δ13C and δ15N oscillations were recognizable in all investigated sei whale baleens
Summary
The largest historically documented baleen whale mass mortality event (MME) took place in the Patagonian fjord area (Chile) between February and April 2015. The isotopic composition of an animal's diet in turn is determined by biogeochemical processes, which can vary among geographical regions Such differences are reflected throughout the food web in organic tissues (DeNiro & Epstein, 1978; Hobson, 1999; Tomaszewicz, Seminoff, Ramirez, & Kurle, 2015), including baleen plates (Best & Schell, 1996). Considering their food uptake over wide-ranging geographical regions, baleen whales were frequently studied using stable isotope analyses Isotopic oscillations of their diet are especially well reflected in the metabolically inert baleen plates (Best & Schell, 1996; Busquets-Vass et al, 2017; Hobson, 1999).
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