Quantifying catch performance of turtle excluder devices in the Northwest Atlantic bottom trawl fishery
Simons, S.L. (2011). Quantifying catch performance of turtle excluder devices in the Northwest Atlantic bottom trawl fishery. MSc Thesis. Universidade do Algarve: Faro. 41 pp.
The U.S. fishing industry generated more than $189 billion in sales and supported more than two million jobs in 2009. However, the ecological costs of commercial fisheries, such as the incidental catch of non target organisms, plus the fisheries’ impact on marine resources and the environment remain a problem. Discards of endangered species are a concern in commercial bottom trawling, which is listed as the largest anthropogenic source of mortality for threatened and endangered sea turtles. Sorting grids, such as the Turtle Excluder Devices (TEDs), were developed to mitigate sea turtle bycatch and reduce non-target species catch in shrimp trawling, seeking win–win solutions where fishing and conservation may coexist. Nevertheless, TEDs may not be an effective method in many fisheries, because variations among fisheries, regions and seasons result in strikingly different impacts on catch rates for both bycatch and target species. To better understand this variability, the present study (i) quantified the catch performance of three TED designs in reducing target and marketable bycatch species, and (ii) tested the catchability of the three TED designs based on species of similar morphologies. A general linear model revealed a poor catch performance for all three TED designs varying with environmental conditions. The Spearman correlation coefficient confirmed the contribution of clogging and/or increased codend weight of TEDs to target species loss. Although the TED designs showed some effect on species composition, the results obtained from one-tailed, paired t-tests were not consistent enough to draw any conclusion. Finally, the outcomes of this study indicate the need for additional research on improving the catch efficiency of TEDs on target species when considering an implementation in the northwest Atlantic bottom trawl fishery.
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