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Marine Ecology Progress Series

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MEPS 676:19-35 (2021)  -  DOI:

Shark depredation in a commercial trolling fishery in sub-tropical Australia

Harrison Carmody1,*, Tim Langlois1,2, Jonathan Mitchell1,2,3, Matthew Navarro1,2, Nestor Bosch1,2, Dianne McLean2,4, Jacquomo Monk5, Paul Lewis6, Gary Jackson6

1School of Biological Sciences, The University of Western Australia, Perth, Western Australia 6009, Australia
2The Oceans Institute, Indian Ocean Marine Research Centre, Perth, Western Australia 6009, Australia
3Queensland Government, Department of Agriculture and Fisheries, Dutton Park, Queensland 4102, Australia
4Australian Institute of Marine Science - Perth, Indian Ocean Marine Research Centre, Perth, Western Australia 6009, Australia
5Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia 2001, Australia
6Western Australia Fisheries and Marine Research Laboratories, Department of Primary Industries and Regional Development, Government of Western Australia, Hillarys, Western Australia 6025, Australia
*Corresponding author:

ABSTRACT: Shark depredation, whereby hooked fish are partially or completely consumed before they can be retrieved, occurs globally in commercial and recreational fisheries. Depredation can damage fishing gear, injure sharks, cause additional mortality to targeted fish species and result in economic losses to fishers. Knowledge of the mechanisms behind depredation is limited. We used a 13 yr dataset of fishery-dependent commercial daily logbook data for the Mackerel Managed Fishery in Western Australia, which covers 15° of latitude and 10000 km of coastline, to quantify how fishing effort and environmental variables influence depredation. We found that shark depredation rates were relatively low in comparison with previous studies and varied across the 3 management zones of the fishery, with 1.7% of hooked fish being depredated in the northern Zone 1, 2.5% in the central Zone 2 and 5.7% in the southern Zone 3. Generalized additive mixed models found that measures of commercial fishing activity and a proxy for recreational fishing effort (distance from town centre) were positively correlated with shark depredation across Zones 1 and 2. Depredation rates increased during the 13 yr period in Zones 2 and 3, and were higher at dawn and dusk, suggesting crepuscular feeding in Zone 1. This study provides one of the first quantitative assessments of shark depredation in a commercial fishery in Western Australia, and for a trolling fishery globally. The results demonstrate a correlation between fishing effort and depredation, suggesting greater fishing effort in a concentrated area may change shark behaviour, leading to high rates of depredation.

KEY WORDS: Depredation · Fishing effort · Shark behaviour · Fisheries management · Generalized additive mixed models · Spanish mackerel · Scomberomorus commerson

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Cite this article as: Carmody H, Langlois T, Mitchell J, Navarro M and others (2021) Shark depredation in a commercial trolling fishery in sub-tropical Australia. Mar Ecol Prog Ser 676:19-35.

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