Shedding dynamics of the Ross seal (Ommatophoca rossii) whiskers investigated through carbon and nitrogen bulk stable isotope composition

Abstract

Understanding the trophic ecology of pinnipeds is essential to define their role in ecosystems and anticipate their responses as top predators to environmental changes. Incremental analyses of carbon ({delta}13C) and nitrogen ({delta}15N) stable isotopes along their whiskers provide valuable records of their foraging habitat and trophic level over time. The effectiveness of this approach relies on knowledge of species-specific whisker shedding dynamics and growth rates. We investigated the shedding dynamics of Ross seal (Ommatophoca rossii) whiskers and attempted to evaluate the time captured in these tissues by combining whiskers bulk{delta} 13C and{delta} 15N incremental measurements with satellite tracking data, collected after whisker growth. Our tracking data are consistent with previous studies, in that Ross seals migrate post-moult between the marginal ice zone and the Antarctic Polar Front. Stable isotope profiles of whiskers did not show the typical decrease in{delta} {superscript 1}3C and increase in{delta} {superscript 1}N values at the whiskers tip that would be expected if shedding coincided with the annual fur moult, when fasting typically occurs. The occurrence of similar isotope variations, which were offset between the left and right whiskers of the same individual in relation to distance from the muzzle, further suggest asynchronous, non-seasonal whisker shedding. Our inability to identify known cyclic phenological events (i.e., fasting periods or seasonal migrations) prevented the determination of the average growth rate of whiskers. The additional data on whisker shedding dynamics of Ross seals is a valuable first step in support of future ecological studies based on the whiskers of this species.