Nippon Suisan Gakkaishi 78 (6), 1112-1117 (2012)

Catching efficiency of toothed dredges for ark shell Scapharca broughtonii in Sendai Bay, Northeastern Japan

TORU TANABE,* KAZUHITO WATANABE, NORIAKI SUZUKI AND TOSHINORI ONO

Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Miyagi 986-2135, Japan

The catching efficiency of toothed dredges estimated in the 1960-70s is still used for stock assessments of ark shell Scapharca broughtonii, although the fishing power of ark shell dredge fishery has improved during the last four decades with the modification of fishing gear and vessels. This study presents the catching efficiency of the toothed dredges currently used for ark shell fishery in Sendai Bay, based on the results of mark-recapture experiments. An experimental area was located at a depth of 23 m in the central part of the fishing ground. The experimental area where the marked ark shells were released extended 20 m in length from north to south in the area. After marked shells had been released along the area, they were recaptured the next day by towing ark shell dredges across the area from west to east. The catching efficiency was estimated to be 0.54 from the catchability coefficient estimated by the DeLury method and the ratio of the experimental area to the dredge-swept area, and was higher than those obtained in previous studies. This result suggests that it is necessary to reconsider the underestimated efficiency for the stock assessment and fisheries management of ark shell. To investigate ark shell resources, the obtained result should be substituted for the previous catching efficiency of ark shell dredges.


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