The cost of a meal: factors influencing prey profitability in Australian fur seals

Abstract

Knowledge of the factors shaping the foraging behaviour of species is central to understanding their ecosystem role and predicting their response to environmental variability. To maximise survival and reproduction, foraging strategies must balance the costs and benefits related to energy needed to pursue, manipulate, and consume prey with the nutritional reward obtained. While such information is vital for understanding how changes in prey assemblages may affect predators, determining these components is inherently difficult in cryptic predators. The present study used animal-borne video data loggers to investigate the costs and benefits related to different prey types for female Australian fur seals (Arctocephalus pusillus doriferus), a primarily benthic foraging species in the low productivity Bass Strait, south-eastern Australia. A total of 1,263 prey captures, resulting from 2,027 prey detections, were observed in 84.5 h of video recordings from 23 individuals. Substantial differences in prey pursuit and handling times, gross energy gain and total energy expenditure were observed between prey types. Importantly, the profitability of prey was not significantly different between prey types, with the exception of elasmobranchs. This study highlights the benefit of animal-borne video data loggers for understanding the factors that influence foraging decisions in predators. Further studies incorporating search times for different prey types would further elucidate how profitability differs with prey type.

Fine-scale hunting strategies in Australian fur seals

“…While this could reflect an increase in prey encounters due to changes in search direction (Bell, 2012), the directional changes may reflect intentional movements towards detected prey (Bianco et al, 2011). Indeed, previous studies of AUFS instrumented with animal-borne video cameras have revealed individuals often make sharp turns upon detecting prey with a high degree of capture success (73%) (Meyers et al, 2021). However, without additional video data, it is not possible to disentangle the observed relationship between prey capture rate and directional changes during sea floor searches by AUFS.…”

“…Pelagic foragers use the entirety of the dive in search of prey (Arnould and Costa, 2006), exploiting highdensity patches of small schooling species (fish, crustacea and cephalopods) which can be distributed throughout the water column (Chimienti et al, 2017). In contrast, benthic foragers search for larger, cryptic prey on the seafloor (Meyers et al, 2021). The high energetic costs of diving to the sea floor (Costa, 1991) are balanced by the profitability of spatial and temporal predictability of benthic prey abundance and distribution (Arnould and Costa, 2006).…”