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Abstract
Discarding practices of bottom trawlers were studied seasonally in the Thracian Sea from autumn 1996 to May 1998. Sampling was conducted following normal, commercial fishing practices. Overall, 114 hauls were performed at depths ranging from 19 to 356 m. In total, 141 fish species, belonging to 53 families, were caught. Of those, 17 were exclusively marketable, 58 discarded, and 66 species had individuals in both the marketable and discarded fractions. The mean trophic level increased with depth, both for the discarded and marketable catches. In addition, the mean weighted trophic level of the discarded fishes was significantly lower (P<0.05) than that of the marketable ones by approximately 0.5–0.6 trophic level units. This might indicate that trawling in the north Aegean removes species of higher trophic level from the ecosystem, thus contributing to fishing down.
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Acknowledgements
This study took place in the context of the EU research project “Analysis of trawls' discard operation in the central and eastern Mediterranean Sea” (Contract No 95/061). The authors wish to express their gratitude to the fishers M. Aganikolas and P. Aganikolas for assisting with the sampling, and to two anonymous reviewers and Dr Enric Sala for their helpful comments and suggestions.
