Using a double codend to reduce discard mortality

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. [ABSTRACT FROM PUBLISHER] Copyright of ICES Journal of Marine Science / Journal du Conseil is the property of Oxford University Press / UK and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)