Long-Term Species, Sexual and Individual Variations in Foraging Strategies of Fur Seals Revealed by Stable Isotopes in Whiskers

Abstract

BackgroundIndividual variations in the use of the species niche are an important component of diversity in trophic interactions. A challenge in testing consistency of individual foraging strategy is the repeated collection of information on the same individuals.Methodology/Principal FindingsThe foraging strategies of sympatric fur seals (Arctocephalus gazella and A. tropicalis) were examined using the stable isotope signature of serially sampled whiskers. Most whiskers exhibited synchronous δ13C and δ15N oscillations that correspond to the seal annual movements over the long term (up to 8 years). δ13C and δ15N values were spread over large ranges, with differences between species, sexes and individuals. The main segregating mechanism operates at the spatial scale. Most seals favored foraging in subantarctic waters (where the Crozet Islands are located) where they fed on myctophids. However, A. gazella dispersed in the Antarctic Zone and A. tropicalis more in the subtropics. Gender differences in annual time budget shape the seal movements. Males that do not perform any parental care exhibited large isotopic oscillations reflecting broad annual migrations, while isotopic values of females confined to a limited foraging range during lactation exhibited smaller changes. Limited inter-individual isotopic variations occurred in female seals and in male A. tropicalis. In contrast, male A. gazella showed large inter-individual variations, with some males migrating repeatedly to high-Antarctic waters where they fed on krill, thus meaning that individual specialization occurred over years.Conclusions/SignificanceWhisker isotopic signature yields unique long-term information on individual behaviour that integrates the spatial, trophic and temporal dimensions of the ecological niche. The method allows depicting the entire realized niche of the species, including some of its less well-known components such as age-, sex-, individual- and migration-related changes. It highlights intrapopulation heterogeneity in foraging strategies that could have important implications for likely demographic responses to environmental variability.

Foraging strategies of a generalist marine predator inhabiting a dynamic environment

“…Given that sea lions were only tracked across a 2-month period, we cannot make conclusions about whether these individual behavioral patterns may persist across longer temporal scales. Studies of other otariids have found that fidelity to a single foraging strategy is often retained across multiple years (Chilvers and Wilkinson 2009;Kernaléguen et al 2012;Baylis et al 2015;Kernaléguen et al 2016); however, many of these studies have focused on populations that inhabit less variable environments than the CCS. Villegas-Amtmann et al (2011) found that adult female California sea lions from the Gulf of Mexico exhibited three foraging strategies during the warm, unproductive season, but only one during the cold season, indicating that the degree of intraspecific variability in behavior may be driven by Dive rate (dives h −1 ) 19.6 ± 6.8 24.7 ± 5.6 NA 13.2 ± 2.8…”

“…In the past decade, there has been increasing documentation of different foraging strategies within pinniped populations, with a particular focus on the various strategies used by individuals in the same demographic group (Cherel and Hobson 2007;Villegas-Amtmann et al 2008;Weise et al2010;Kernaléguen et al 2012;Villegas-Amtmann et al 2013). These foraging strategies often reflect the three basic diving patterns exhibited by air-breathing marine predators (epipelagic, mesopelagic, benthic), but also may be related to associations with oceanographic features, habitat use, or foraging site fidelity.…”

Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals

“…Females from Crozet (and their corresponding whisker isotopic results) are the same individuals as those in the study by Kernaléguen et al . (). Seals breeding in Crozet were also weighed using a suspension scale (±0·1 kg).…”

“…; Kernaléguen et al . ), suggesting an adaptation of the foraging behaviour to the co‐occurrence of the competitor species. Secondly, fur seals have been intensively hunted during the 18th and 19th centuries, with commercial sealing resulting in local extinction of the two species.…”

Vibrissal growth parameters of southern elephant seals Mirounga leonina: obtaining fine-scale, time‑based stable isotope data

“…The vibrissae of otariids, such as Antarctic fur seals Arctocephalus gazella (Walters 2014), and Steller sea lions Eumetopias jubatus (Hirons et al 2001), grow linearly and are retained for multiple years (Hirons et al 2001;Cherel et al 2009;Kernaléguen et al 2012). In contrast, the vibrissae of phocids, such as grey seals Halichoerus grypus, and P. vitulina, grow asymptotically and are characterised by an asynchronous growth and replacement pattern (Greaves et al 2004;Hall-Aspland et al 2005;Beltran et al 2015).…”