It is the purpose of this paper to discuss the fishing efficiency of purse seiner of one-boat and two-boat operation types against jack mackerel, Trachurus japonicus (TEMMINCK et SCHLEGEL), based on the daily records of catch during the eight-year period (1956-1963) in the East China Sea, by the purse seiner.
Results obtained are as follows:
1) In Table 2, the power factor of the purse seiner is given, by type of fisheries and class of vessel sizes in ton.
2) The power factor of the larger-sized vessel is higher than that of the smaller-sized one. In the case of the same size, the factor of the two-boat operation type is higher than that of the one-boat operation type.
3) In the jack mackerel fishing in the East China Sea in recent years, the purse seiner of one-boat operation type of 50-100 ton outnumber all other classes. The number of actual fishing units of the purse seiner has been decreasing year by year since 1957 as the peak, and in 1963 the number decreased to about two thirds of that in 1957. On the other hand, the power factor has shown a rising tendency since 1956, and in recent years has reached a level about twice that in 1956. Judging from the above facts, it is clear that the fishing pressure on the jack mackerel resources in the East China Sea has not decreased as generally thought.