Habitat selection and influence on hunting success in female Australian fur seals

Abstract

Determining the factors influencing habitat selection and hunting success in top predators is crucial for understanding how these species may respond to environmental changes. For marine top predators, such factors have been documented in pelagic foragers, with habitat use and hunting success being linked to chlorophyll-a concentrations, sea surface temperature and light conditions. In contrast, little is known about the determinants of benthic marine predators. The Australian fur seal (Arctocephalus pusillus doriferus) is a benthic-diving forager that has a breeding and foraging distribution largely restricted to Bass Strait, the shallow (max. depth 80 m) continental shelf region between the Australian mainland and Tasmania. The species forages mostly on benthic prey and represents the greatest resident marine predator biomass in south-eastern Australia. The region is also one of the world's fastest-warming marine areas and oceanographic changes are influencing shifts in prey distribution and abundance. In the present study, GPS-derived locations of benthic dives (n = 288,449) and dive behaviour metrics were used to determine seafloor habitat selection and factors influencing hunting success in 113 lactating adult females from Kanowna Island during the winters of 2006-2021. Individuals non-randomly selected foraging habitats comprised of deeper, steeper sloped, muddy-sandy areas with less gravel and highly disturbed regions (P < 0.01). Hunting success was greatest in shallower rocky reefs (< 30 m) and deep areas (> 40 m) characterised by moderate presence of gravel (25-50%) and substantial rock composition (50-75%) on the seabed. These findings suggest that habitat use and hunting success in adult female Australian fur seals could be impacted by predicted oceanographic changes, such as rising temperature, altered currents and waves which may modify seafloor characteristics and benthic communities.

Keywords: Australian fur seals; Habitat selection; Hunting success.

Fig. 1

The foraging areas of adult female Australian fur seals from Kanowna Island (blue location marker) in Bass Strait, southeastern Australia, with the locations of successful (green) and unsuccessful (pink) benthic dives (a) and the most significant environmental variables in their foraging habitat selection (b-f). Australian fur seal colonies are indicated by black location markers: A: West Moncoeur; B: Rag Island; C: Judgments Rocks; D: Wright Rocks; E: Double Island; F: Moriarty Rocks; G: Tenth Rock; H: Bull Rock; I: Seal Rock. The grey line represents the continental shelf, isobath 200 m.

Fig. 2

Habitat selection by 113 adult female Australian fur seals from Kanowna Island. (a) variables loadings on the two first factorial axes (axis 1: x axis; axis 2: y axis) , (b) the marginality vectors of individuals on the first factorial plane, the end of the arrows correspond to the mean characteristics of the habitat on the relocation of individuals, and (c) the marginality vectors of individuals after re-centering each home range composition which is axis 1 and axis 2.

Fig. 3

Relationship between the benthic environmental variables of bathymetry (a), gravel cover (log_10%; b) and rock (c) and hunting success in 113 adult female Australian fur seals.

Fig. 4

Spatial prediction from a general additive mixed effect model of successful foraging areas for adult female Australian fur seals from Kanowna Island. Darker shades of orange indicate areas of predicted greater hunting success based on the important variables derived from the model.