Abstract
Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of δ13C and δ15N values from bulk baleen have been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here, we apply analysis of δ15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.7–3.8 versus 3–3.2, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. Phenylanine δ15N values confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine δ15N values suggested physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.
Highlights
Mysticete whales are a concern for ecosystem-based management after their populations were decimated by whaling [1,2]
We provide evidence of feeding in different regions due to migration between mid-Atlantic breeding and high-latitude feeding areas through application of isotopic niche areas from trophic level-corrected bulk isotope data from baleen
The δ13C values for all individuals fell within the range of −17.5 to −20‰ across all baleens, with oscillations of 0.5–1.5‰ that generally mirrored changes observed in δ15N values, with some deviations. δ13C values for the fin whales were similar among individuals and higher (−18.9 to −19.2‰) than for the humpback whale (−19.6‰), but lower than for the minke whale (−18.1‰; one-way ANOVA: F4,252 = 77, p < 0.001)
Summary
Mysticete whales are a concern for ecosystem-based management after their populations were decimated by whaling [1,2]. Proteinaceous materials that are continually produced across an animal’s lifetime (e.g. baleen, earplugs) provide a continuous record of metabolic processes [14,15] and dietary composition across the time period that they have been produced These materials are useful in identifying prey composition and feeding strategies over a long period prior to death [7,16]. Baleen is composed almost entirely of keratin derived from metabolites from the bloodstream [17] and captures a continuous, long-term record of the animal’s blood protein during keratin synthesis [18] This is in contrast to erythrocytes or skin tissue that provide a single integrated snapshot of isotopic composition Whole lengths of baleen often reflect the dietary conditions from several months to several years depending on their growth rate and sampling distance from the gums
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