Environmental influences on foraging effort, success and efficiency in female Australian fur seals

Cassie N Speakman,Mark A Hindell,Jason R Hartog,John P Y Arnould,Daniel P Costa,Andrew J Hoskins,Alistair J Hobday

doi:10.1038/s41598-020-73579-y

Abstract

Understanding the factors which influence foraging behaviour and success in marine mammals is crucial to predicting how their populations may respond to environmental change. The Australian fur seal (Arctocephalus pusillus doriferus, AUFS) is a predominantly benthic forager on the shallow continental shelf of Bass Strait, and represents the greatest biomass of marine predators in south-eastern Australia. The south-east Australian region is experiencing rapid oceanic warming, predicted to lead to substantial alterations in prey diversity, distribution and abundance. In the present study, foraging effort and indices of foraging success and efficiency were investigated in 138 adult female AUFS (970 foraging trips) during the winters of 1998–2019. Large scale climate conditions had a strong influence on foraging effort, foraging success and efficiency. Foraging effort and foraging success were also strongly influenced by winter chlorophyll-a concentrations and sea-surface height anomalies in Bass Strait. The results suggest increasing foraging effort and decreasing foraging success and efficiency under anticipated environmental conditions, which may have population-level impacts.

Highlights

Understanding the factors which influence foraging behaviour and success in marine mammals is crucial to predicting how their populations may respond to environmental change
If environmental conditions result in prey patches shifting beyond reasonable energetic limits of the central place, animals need to respond by increasing foraging effort or switching prey type to lower quality prey to account for depleted resources or to abandon offspring in order to access areas of higher p roductivity[5]
The Australian fur seal (Arctocephalus pusillus doriferus; AUFS) population is still recovering from the overexploitation of the commercial sealing era (1798–1825), with an annual pup production currently estimated at ca 28–47% of pre-sealing levels[27,28]

Summary

Introduction

Understanding the factors which influence foraging behaviour and success in marine mammals is crucial to predicting how their populations may respond to environmental change. Anthropogenic activity has caused an accelerated rate of change which is predicted to continue into the future[9], including shifts in the frequency or severity of large-scale climate events[10,11,12] These anticipated climatic changes will alter entire marine ecosystems, with significant compound effect for higher trophic levels including reductions in foraging efficiency and the relocation of foraging z ones[13]. Changes in sea-surface temperature (SST) can greatly influence juvenile red cod (Pseudophycis bachus) survivorship reducing adult recruitment in subsequent y ears[14] This impacts the foraging conditions of the predators that depend on them[14,15], leading to reduced foraging efficiency, poor reproductive outcomes and/or reduced survivorship[14]. Changes in prey diversity, distribution and availability can substantially affect their foraging efficiency, altering offspring provisioning rates and, reproductive s uccess[5]

Methods

Results

Conclusion