Understanding and quantifying shark depredation in a recreational fishery in the Ningaloo region of Western Australia

Abstract

Shark depredation, where a shark consumes an animal caught by fishing gear before it can be retrieved to the fishing vessel, occurs in commercial and recreational fisheries worldwide, leading to higher mortality for target species, injury to sharks and costly loss of catch and fishing gear. Despite this, depredation remains relatively understudied compared to other fisheries issues such as bycatch and post-release mortality. This thesis presents a multi-disciplinary investigation of shark depredation, which brings together aspects of biology, behaviour and socio-economics, as well as providing information that addresses key management questions related to depredation. The first goal of this research was to conduct a detailed global review of the shark depredation literature, to collate all existing information on this topic, compare rates of depredation in diverse commercial and recreational fisheries around the world, and identify shark species potentially responsible for depredation. The review was also designed to highlight key research gaps relating to this topic that need to be addressed. Building on this, the research sought to quantify shark depredation rates in a popular recreational fishery in the Ningaloo region of Western Australia, where depredation has been reported to be a management issue. Alongside this, assessing the socio-economic impact of shark depredation was another objective of the research, as well as predicting the potential efficacy of fisheries closures as a management measure to reduce depredation rates. Lastly, this study sought to identify the shark species responsible for depredation in the Ningaloo region, to determine whether protected species or those subject to management measures were involved, and to investigate the dynamics of shark behavioural interactions with fishing gear.