COMPARISON BETWEEN THE CATCH COMPOSITION OF THE FRENCH AND ORE TYPE BEAM TRAWLS ON DEEP-SEA DECAPOD CRUSTACEANS: IMPLICATIONS FOR QUANTITATIVE SAMPLING OF THE DEEP-SEA DECAPOD BIODIVERSITY

The French beam trawl and the ORE beam trawl are common research sampling gears for deep-sea biodiversity. The French beam trawl is equipped with a tickler chain and a pair of iron sides. The ORE beam trawl has a larger mouth area than the French beam trawl and has no tickler chain. With a tickler chain, the French beam trawl appears to yield more benthic catches, whilst the ORE beam trawl may be able to collect more bathypelagic species, due to its larger mouth area. In the present study, the assemblages of decapod crustaceans in Taiwan deep waters collected with the French type and the ORE type beam trawls were compared at depths of 250, 500, and 1200 meters. With multivariate analysis, the species abundance of the catches collected by both methods appeared similar, but the catches in the French beam trawl had higher taxonomic distinctness and yielded more benthic species (especially Brachyura) at depths of 250 m and 500 m when compared to the ORE beam trawl. There were no differences in abundance of pelagic species between the two trawls, suggesting that the degree of net avoidance by species in both trawls was similar. The sizes of the dominant catches were similar in both trawls, indicating that the mesh escapement was similar in both the French beam trawl and the ORE beam trawl. During operations, the French beam trawl appears to be more robust to work on rougher terrains (e. g., with lots of sunken wood and mud). In the present study, we revealed that both French beam trawl and ORE beam trawl generally show a similar performance in collecting deep-sea decapod crustaceans, except that the French beam trawl may yield a greater diversity of benthic species at the 250 and 500 m levels. Further research is needed to compare the performance of the two trawls for catching other groups of deep-sea benthic animals (e. g., molluscs and fishes), which is essential for gear consideration in quantitative community studies.