Reconstructing Western Australian white shark (Carcharodon carcharias) catches based on interviews with fishers

Abstract

The assessment of fisheries-related effects on protected species, such as white sharks (Carcharodon carcharias), is often hampered by a lack of historical catch information. In the present study, historical catch estimates derived from interviews with fishers operating in the Western Australian Temperate Demersal Gill-net and Demersal Longline Fisheries were matched with fishing effort data reported in statutory fishing returns. Catch estimates obtained from interviewed fishers were extrapolated to account for total catch in two different ways, resulting in mean (95% confidence intervals) estimates of 1232 (476–2245) and 1039 (505–2096) white sharks caught between 1988 and 2012. These estimates were then used to reconstruct catches over a 59-year period, from the start of commercial gillnetting in the mid-1950s. The reconstructed catch trend reflected the history of gill-net fishing effort, peaking in the late 1980s at a level approximately fourfold greater than the estimated catch of ~30 sharks year–1 in 2014. More than one-third of fishers interviewed expressed doubts about the accuracy of self-reported white shark catch data, a requirement of current legislation. Given the benefits of reporting data from protected species bycatch, efforts to accurately record this information should be continued and improved.