The Surf Clam Beam Trawl Fishery and its Biological Management in Sendai Bay

Parameters of the Sakhalin surf clam Spisula sachalinensis stock in Sendai Bay were estimated by analyzing the fishery data to examine the management of fishery. The fishing has been greatly influenced by the fluctuation in recruitment, since the age structure has skewed to younger side. The average fishing mortality coefficient F and natural mortality coefficient M during 1980–84 were 0.6358±0.2735, and 0.5323±0.0915, respectively. The catchability coefficient q was 3.164 x 10^-5. Since the natural mortality coefficient is high, we can expect higher yield per recruit from higher F and lower age of first capture. The most important problem in the management of the stock recruited intermittently by the strong year class, however, is to secure the minimum level of stock which could produce a lot of progeny if the circumstances might become favorable. Since it might be difficult to predict the recruitment from the stock-recruitment relationship, two models were proposed to follow successive stock density. Optimum fishing mortality coefficient is presumed to be between 0.5 and 0.6, which would be able to hold the stock at a level enough to produce recruits under deteriorated conditions.