Investigating the effects of climatic variability on long term behavioural activity budgets of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia

Abstract

Extreme climatic events (ECEs) can alter key animal behaviours. Understanding how animals are likely to respond behaviourally to ECEs will help inform conservation decisions in the face of climate change. However, upon reviewing the literature on animal behavioural responses to ECEs, it is clear that there remains a large gap in our understanding. This study aims to address this research gap by investigating the effects of climatic variability, including the Southern Oscillation Index and sea surface temperatures, on the behavioural activity budgets of Shark Bay’s Indo-Pacific bottlenose dolphin population. An individual level approach was used for two study sites, including the eastern gulf, with a sample size of 198 males and 164 females from 1991-2020, and the western gulf, with a sample size of 86 males and 51 females from 2009-2019. A population level approach was also taken in the eastern gulf and included 2,055 individuals from 2009-2020. Foraging and socialising activity were significantly affected by extreme Southern Oscillation events, including La Niña and El Niño. Focusing on a 2011 marine heatwave event, individual foraging budgets dropped significantly immediately after this ECE, and then increased to peak levels in 2016. Prey availability likely peaked immediately post-heatwave as seagrass cover declined, then became scarce thereafter, requiring greater foraging effort. In contrast, individual socialising budgets increased immediately after the ECE and then dropped in subsequent years. Between sex differences in behavioural response were also detected, including lower foraging activity budgets and higher socialising activity budgets for male dolphins, likely due to sex-differences in reproductive strategies. Differences in activity budgets of tool-users vs non-tool-users were also investigated, with tool-using dolphins spending more time foraging than non-tool-using dolphins, which confirms previous research. This work indicates that ECEs can have a significant and long-lasting impact on the key behaviours of even behaviourally flexible marine predators.

Date of Award	21 Jun 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Stephanie L King (Supervisor) & Simon Allen (Supervisor)