Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands

Abstract

Antarctic (Arctocephalus gazella) and Subantarctic (A. tropicalis) fur seals are important predators in the Southern Ocean. Marion Island (southern Indian Ocean) hosts the largest sympatric breeding populations of these two species. Environmental and population changes here over two decades may have influenced their diet and trophic interactions. To quantify diet, we analysed prey remains in scat samples from Antarctic (661 scats) and Subantarctic (750 scats) fur seals collected at Marion Island (2006-2010). We assessed diet composition over time and calculated dietary overlap. The diet of both species was dominated by fish prey (98.2% and 99.4% of prey items), mainly myctophids. Antarctic fur seals consumed small numbers of penguins, cephalopods and crustaceans. In Subantarctic fur seal scats, crustaceans and cephalopods were rare and penguin remains were absent. The diets of the two species overlapped substantially (Pianka's index = 0.98), however, small but significant differences in the relative proportions of prey were evident. Seasonal and annual diet changes suggest that their diet is similarly influenced by patterns of local prey availability and abundance. Despite substantial changes in the population size and trajectory of Antarctic and Subantarctic fur sealswhich would be expected to influence trophic interactions between themcomparing our data to those from earlier studies (1989-2000) did not reveal significant long-term dietary changes in either species.

Karyotype Evolution in 10 Pinniped Species: Variability of Heterochromatin versus High Conservatism of Euchromatin as Revealed by Comparative Molecular Cytogenetics

“…Heterochromatin regions in pinnipeds may contribute to interspecific differences and may perform a regulatory function. Given that species of fur seals differ in forage and sexual behavior, in characteristics of the fur coat, and in vocalization [ 55 , 56 , 57 ], further research is needed to determine functional properties of the repeated sequences in their genomes.…”

Geographical, temporal, and individual‐based differences in the trophic ecology of female Cape fur seals

“…In addition, life cycles of prey species (recruitment, spawning) further impact on their availability at different spatiotemporal scales (Croxall et al, 1985 ). Marine predators are expected to alter their foraging in response to such heterogeneity and consequently, temporal differences in foraging effort (Angel et al, 2015 ; Harding et al, 2007 ), behavior (Botha & Pistorius, 2018 ; Foo et al, 2019 ) and diet (Chambellant et al, 2013 ; Reisinger et al, 2018 ) have been well documented.…”

Canine morphometrics as a tool for distinguishing species, sex, and age class in Southern Ocean fur seals

“…Current populations are descended from a few survivors and show relatively little genetic diversity (Wynen et al, 2000 ). Antarctic fur seal populations have a varied diet (Hofmeyr, 2016 ; Jones et al, 2020 ; Walters et al, 2020 ), with those from Bouvet Island feeding primarily on krill (Kirkman et al, 2000 ), and those from Marion Island being generalists (including myctophids, cephalopods, and even penguins; Hofmeyr & Bester, 1993 ; Makhado et al, 2008 ; Reisinger et al, 2018 ). While greater tooth wear (and thus shorter crown length) would be expected for species or populations that feed on sharks for example (Allen & Huveneers, 2005 ; Byron & Morgan, 2016 ; Condit & Le Boeuf, 1984 ; Fallows et al, 2015 ) due to the abrasive nature of shark skin, neither of the tested Antarctic fur seal populations have been recorded to consume sharks and it's unlikely that the observed differences in diet between the two islands would result in change in tooth wear.…”