1National Fisheries Research and Development Institute, Busan 619-902, Korea, 2Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan
This paper presents size selectivity of dredge bagnet for a clam, equilateral Venus Gomphina melanaegis using cover-net fishing experiments with test bagnets of four mesh sizes; 24, 30, 41, 47 mm and covernet of 13 mm mesh size. In the master curve analysis process, master curve equation of mesh selectivity for the clam was estimated to be r(R)=1/[1+exp (−8.63R+5.13)], where R is the ratio of shell length to mesh size. Also, size selectivity was estimated, of a sieve with grid of 12.5 mm bar spacing currently used on the fishing boat deck by fishermen to sort larger size clams from smaller ones of no commercial value. Shell width of the 50 percent retention was 12.7 mm, close to 12.5 mm bar spacing of the grid. This means that the size selectivity of the on-deck sieve was a kind of contact selection. Bar spacing of the grid should be enlarged to retain the clams of commercial size over 35 mm shell length on the on-deck sieve. Enlargement in mesh size of bagnet and other methods to avoid catching small clams of no commercial value were also discussed.