Whisker isotopic signature depicts migration patterns and multi-year intra- and inter-individual foraging strategies in fur seals

Abstract

The movement and dietary history of individuals can be studied using stable isotope records in archival keratinous tissues. Here, we present a chronology of temporally fine-scale data on the trophic niche of otariid seals by measuring the isotopic signature of serially sampled whiskers. Whiskers of male Antarctic fur seals breeding at the Crozet Islands showed synchronous and regular oscillations in both their δ 13 C and δ 15 N values that are likely to represent their annual migrations over the long term (mean 4.8 years). At the population level, male Antarctic fur seals showed substantial variation in both δ 13 C and δ 15 N values, occupying nearly all the ‘isotopic space’ created by the diversity of potential oceanic habitats (from high Antarctica to the subtropics) and prey (from Antarctic krill to subantarctic and subtropical mesopelagic fishes). At the individual level, whisker isotopic signatures depict a large diversity of foraging strategies. Some seals remained in either subantarctic or Antarctic waters, while the migratory cycle of most animals encompassed a wide latitudinal gradient where they fed on different prey. The isotopic signature of whiskers, therefore, revealed new multi-year foraging strategies of male Antarctic fur seals and is a powerful tool for investigating the ecological niche during cryptic stages of mammals' life.

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).…”

“…The vibrissae (whiskers) of pinnipeds (Ling 1966) are particularly useful for dietary studies when using SI analysis (e.g., Hirons et al 2001;Greaves et al 2004;Zhao & Schell 2004;Hall-Aspland et al 2005; Lewis et al 2006;Cherel et al 2009;Hindell et al 2012;Walters et al 2014;Rea et al 2015). Vibrissae can be sampled relatively non-invasively and archive ecological information over longer temporal scales at a finer resolution than other tissues, such as blood (Tieszen et al 1983).…”

Seabird year-round and historical feeding ecology: blood and feather δ13C and δ15N values document foraging plasticity of small sympatric petrels

“…data). Foraging progressively further south as summer progresses in order to feed on krill has already been depicted in satellite-tracked white-chinned petrels (Catard & Weimerskirch 1999) and has isotopically been recorded in the vibrissae of some male Antarctic fur seals (Cherel et al 2009). …”

Individual specialists in a generalist population: results from a long-term stable isotope series

“…Nitrogen isotopes typically indicate trophic position (Post 2002), while carbon isotopes reflect variation in baseline producers or habitat (DeNiro & Epstein 1978). Tissues that are created over time and remain inert after synthesis, such as hair, otoliths and baleen, reflect resource use at the time of formation (Hobson 1999) and allow longitudinal sampling with stable isotope analysis of successive microlayers (Cerling et al 2009;Cherel et al 2009). Sea turtles have such a tissue-scutewhich is a keratinized epidermis covering the bony shell of most chelonians.…”