Identifying foraging habitats of adult female long-nosed fur seal Arctocephalus forsteri based on vibrissa stable isotopes

摘要

We investigated how foraging ecotypes of female long-nosed fur seals Arctocephalus forsteri could be identified from vibrissa stable isotopes. We collected regrowths of vibrissae from adult females (n = 18) from Cape Gantheaume, Kangaroo Island, South Australia, from 2 breeding seasons (2016, 2017). The period represented by the regrowth was known, and 8 individuals were administered with N-15-enriched glycine as a biomarker to mark the start date of the regrowth. Non-glycine-marked and glycine-marked vibrissae were used to estimate the rate of the individual vibrissa regrowth. Using individual growth rates (0.18 +/- 0.04 mm d(-1)), we reconstructed a stable isotope (delta C-13 and delta N-15) time series for each regrowth and allocated them to corresponding at-sea locations either based on geolocation tracks (n = 14) or foraging habitat type (shelf or oceanic) based on diving data (n = 2) of the sampled seals. Mean (+/- SD) delta N-15 from vibrissa segments was higher when females foraged on the continental shelf region (16.1 +/- 0.7 parts per thousand, n = 29) compared to oceanic waters (15.1 +/- 0.7 parts per thousand, n = 106) in 2017, whereas it was similar in both regions in 2016 (shelf: 15.3 +/- 0.4 parts per thousand, n = 13; oceanic: 15.4 +/- 0.4 parts per thousand, n = 15). Based on the stable isotope signatures of vibrissa segments, model-based clustering analysis correctly classified 79.8% as originating from shelf or oceanic foraging habitats. This demonstrates the potential of using vibrissa stable isotopes for studying the foraging ecology of an important top marine predator.