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Diseases of Aquatic Organisms

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DAO 80:51-61 (2008)  -  DOI:

Mortality of discards from southeastern Australian beach seines and gillnets

Matt K. Broadhurst1,*, Russell B. Millar2, Craig P. Brand1, Sebastian S. Uhlmann3

1New South Wales (NSW) Department of Primary Industries, Fisheries Conservation Technology Unit, PO Box J321, Coffs Harbour, New South Wales 2450, Australia
2Department of Statistics, The University of Auckland, Private Bag 92019, Auckland, New Zealand
3School of Environmental Sciences and Natural Resources Management, University of New England, PO Box J321, Coffs Harbour, New South Wales 2450, Australia

ABSTRACT: Two experiments were done in an Australian estuary to quantify the mortalities and contributing factors for key species discarded during 8 and 9 deployments of commercial beach (or shore) seines and gillnets, respectively. In both experiments, bycatches (2347 individuals comprising 16 species) were handled according to conventional practices and assessed for immediate mortalities before live samples of selected species were discarded into replicate cages along with appropriate controls, and monitored for short-term mortalities (≤10 d). All of the seined or gilled fish were alive prior to discarding. During the beach seine experiment, 20% of caged seined-and-discarded surf bream Acanthopagrus australis (n = 290) were dead after 5 d, with most mortalities occurring between the second and fifth day. In the gillnet experiment, 42 and 11% of gilled-and-discarded A. australis (n = 161) and lesser salmon catfish Neoarius graeffei (n = 67), respectively, died during a 10 d monitoring period, mostly within the first 5 d. There were no deaths in any controls for these fish. Mixed-effects logistic models revealed that the mortality of A. australis discarded from both gears was significantly (p < 0.01) and negatively correlated with their total length, while N. graeffei had a significantly (p < 0.05) greater (5-fold) probability of dying when jellyfish Catostylus sp. were present in the gillnet. Simple modifications to the operations of beach seines and gillnets and/or post-capture handling procedures, such as close regulation of size selectivity for the target species, careful removal of fish from meshes, and abstention from setting during high abundances of jellyfish will maximise the survival of discarded bycatch.

KEY WORDS: Beach seine · Bycatch · Discards · Gillnet · Mortality · Unaccounted fishing mortality

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Cite this article as: Broadhurst MK, Millar RB, Brand CP, Uhlmann SS (2008) Mortality of discards from southeastern Australian beach seines and gillnets. Dis Aquat Org 80:51-61.

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