Influence of Velocity and Types of Beam Trawl Towing on Deep-Sea Demersal Fish and Decapod Crustacean Samples |
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Authors: | Hsin-Ming Yeh Suguru Ohta |
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Institution: | (1) Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo 164-8639, Japan |
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Abstract: | The sampling efficiency of two types of beam trawl towed at different velocities was compared when sampling deep-sea demersal
fish and decapod crustaceans. The trawls were a Sigsbee-Agassiz type of 2 m span, and an Oregon type of 3 m span. The different
hauls caught by the Oregon type beam trawl of 3 m span towed at 1.5 knot (3m 1.5 kt), the Oregon type towed at 0.8 knot (3m
0.8 kt) and the Sigsbee-Agassiz type towed at 1.5 knot (2m 1.5 kt) were compared by analysis of variance (ANOVA), the Tukey
test, cluster analysis based on Morisita-Horn index, and correspondence analysis. The minimum viable sample size was determined
by a randomization test. For demersal fish, the type of gear used had more influenced on the samples obtained than the towing
velocity. For decapod crustaceans, no significant difference was detected between different trawls towed at different velocities.
The common idea that if these types of trawl are towed at 1 knot or more, they cannot efficiently sample epifauna, but demersal
fish can be well sampled, should be abandoned. The samples of demersal fish caught by 3m 1.5 kt revealed the greatest consistency
and lowest variation than the others. We recommend using an Oregon type beam trawl of 3 m span towed at 1.5 knot as an ordinary
deep-sea sampling device. Only a single successful haul or a sample size of 52 individuals was sufficient for estimating demersal
fish diversity, but at least two successful hauls or a sample size of 54 individuals were needed for decapod crustaceans.
If possible, seven successful hauls or a sample size of 189 individuals of decapod crustaceans are recommended for community
study.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Deep-sea demersal fish decapod crustaceans beam trawl multivariate analysis randomization catchability biomass abundance diversity |
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