Oral Presentation Australian Society for Fish Biology Conference 2017

Understanding and quantifying shark depredation in a recreational fishery (#97)

Jonathan D. Mitchell 1 , Timothy J. Langlois 1 , Dianne L. McLean 1 , Shaun P. Collin 1
  1. University of Western Australia, Crawley, WA, Australia

Shark depredation, where a live hooked fish is consumed by a shark before it can be retrieved to a fishing vessel, can occur in recreational fisheries around Australia. This results in additional mortality to target species, potential injury to sharks from ingested fishing gear, and can negatively impact the recreational fishing experience. This research sought to quantify the spatial occurrence and frequency of shark depredation in a recreational fishery within Ningaloo Marine Park and Exmouth Gulf, Western Australia. A large-scale survey was conducted at four boat ramps in these areas, from July 2015 - May 2016, to collect quantitative data on shark depredation and the variables influencing it. For the 407 boats interviewed across the study area, 12.15 ± 2.08 % of hooked fish were depredated by sharks, with 39.8 % of fishing trips experiencing depredation. Generalised Additive Mixed Models (GAMMs) quantified the effect of fishing method and environmental factors on depredation rate, with results showing a positive effect of increasing fishing depth on depredation in Ningaloo Marine Park, and peak depredation occurring at 60m. Higher localised fishing effort led to increasing depredation rates, and time of year also positively influenced depredation in Ningaloo Marine Park. In Exmouth Gulf, cumulative spatial fishing pressure and decreasing latitude showed a positive effect on depredation rate, with the latter potentially reflecting a change in benthic habitat throughout the Gulf. This research was the first in-depth quantitative assessment of shark depredation in a recreational fishery in Australia, and determined the extent to which environmental factors and fishing methods influenced its occurrence and spatial variation. This information can be used to develop strategies for reducing shark depredation and mitigating potential negative impacts on target fish, sharks and recreational fishers.