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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 4, 2009
ICES Journal of Marine Science: Journal du Conseil 2009 66(10):2077-2081; doi:10.1093/icesjms/fsp155
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Using a double codend to reduce discard mortality

Matt K. Broadhurst1, Russell B. Millar2 and Sebastian S. Uhlmann1

1 NSW Department of Primary Industries, Fisheries Conservation Technology Unit, PO Box J321, Coffs Harbour, NSW 2450, Australia
2 Department of Statistics, The University of Auckland, Private Bag, 92019 Auckland, New Zealand

Correspondence to M. K. Broadhurst: tel: +61 2 6648 3905; fax: +61 2 6651 6580; e-mail: mbroadhurst{at}nmsc.edu.au

Broadhurst, M. K., Millar, R. B., and Uhlmann, S. S. 2009. Using a double codend to reduce discard mortality. – ICES Journal of Marine Science, 66: 2077–2081.

Traditional technical strategies for mitigating collateral fishing mortality have involved improving gear selectivity (to reduce bycatch) and, more recently, concomitant changes to onboard handling procedures to reduce some of the negative impacts to the remaining discards. A less common approach is to modify gears physically to minimize deleterious catching mechanisms and subsequent mortalities during fishing. This study aimed to investigate the utility of the latter category of modifications for penaeid trawls by separating a codend into two compartments (termed a double codend) to alleviate interactions between catches. Compared with a conventional design, the double codend significantly reduced the immediate (from 17.1 to 13.8%) and short-term (22.5 to 17.1%) mortalities of discarded juvenile school prawns (Metapenaeus macleayi). The effectiveness of the double codend remained independent of other factors known to affect the fate of discarded juvenile M. macleayi, including cloud cover and, owing to minimal variability, the weight of the total catch. However, irrespective of the codend configuration, overall mortalities were also positively correlated with the quantity of jellyfish. We conclude that when combined with modifications to improve selectivity and appropriate onboard handling strategies, compartmentalizing codend catches could cumulatively reduce unaccounted fishing mortality.

Keywords: bycatch, discard mortality, Metapenaeus macleayi, trawling, unaccounted fishing mortality

Received 18 March 2009; accepted 20 April 2009; advance access publication 4 June 2009.


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