Individual and population dietary specialization decline in fin whales during a period of ecosystem shift

Abstract

This study sought to estimate the effect of an anthropogenic and climate-driven change in prey availability on the degree of individual and population specialization of a large marine predator, the fin whale (Balaenoptera physalus). We examined skin biopsies from 99 fin whales sampled in the St. Lawrence Estuary (Canada) over a nine year period (1998–2006) during which environmental change was documented. We analyzed stable isotope ratios in skin and fatty acid signatures in blubber samples of whales, as well as in seven potential prey species, and diet was quantitatively assessed using Bayesian isotopic models. An abrupt change in fin whale dietary niche coincided with a decrease in biomass of their predominant prey, Arctic krill (Thysanoessa spp.). This dietary niche widening toward generalist diets occurred in nearly 60% of sampled individuals. The fin whale population, typically composed of specialists of either krill or lipid-rich pelagic fishes, shifted toward one composed either of krill specialists or true generalists feeding on various zooplankton and fish prey. This change likely reduced intraspecific competition. In the context of the current “Atlantification” of northern water masses, our findings emphasize the importance of considering individual-specific foraging tactics and not only population or group average responses when assessing population resilience or when implementing conservation measures.

Validation of quantitative fatty acid signature analysis for estimating the diet composition of free-ranging killer whales

“…Stable isotopes of carbon and nitrogen in the skin have revealed some inter and intra-population variation in the feeding patterns of cetaceans, providing diet composition estimates mostly at the trophic level, although species-level precision from stable isotopes remains challenging 7 – 9 . And while higher-resolution fatty acid (FA) signature analysis of blubber has also been applied to a couple of cetacean populations to infer dietary patterns, quantitative estimates of prey species in their diet using FA-based approaches from biopsies of free-ranging individuals have yet to be achieved 10 – 13 .…”

Historical baleen plates indicate that once abundant Antarctic blue and fin whales demonstrated distinct migratory and foraging strategies

“…The remaining fin whale samples largely correspond to migration or winter periods (discussed in the next section), but some summer season samples fall outside the values of Antarctic krill and may have been influenced by small contributions of other prey items (Figure 3 ). A recent study showed that an Atlantic population of fin whales switched to a more generalist diet when krill abundances were low, supporting the trophic flexibility of fin whales in other regions (Jory et al., 2021 ). It should also be noted that the potential prey species used in Figure 3 are from modern studies and have not been Suess corrected to the measured historic baleen plates.…”

Long‐term evolution of the structure of the St. Lawrence (Canada) marine ecosystem in the context of climate change and anthropogenic activities: An isotopic perceptive

“…To assess the ecological impacts of climate change and the previously mentioned stressors on vulnerable species, this study examined long-term changes in the trophic structure of an isotopically well-documented ecosystem: the EGSL (Cabrol et al, 2021;Gavrilchuk et al, 2014;Hammill et al, 2005;Lesage et al, 2001).…”