Characteristics of yearly fluctuation in the size of tile fish population in Wakasa Bay and its mean generation time.

Abstract

Analyses were made with yearly fluctuation in tile fish population size in the fishing area of the sweeping trammel net fishery in the central region of Wakasa Bay in order to obtain its characteristics, using the data on the fishery over the period of 1961 to 1981. The estimated population size ranged from 45 to 229 tons and showed a remarkably cyclical pattern with the period of less than five years, 1961-1981. The length and market size category compositions indicated that the cyclical pattern resulted mainly from the great year classes of 1959, 1964, 1968, 1971, 1975 and 1977 and negligibly poor year classes of the other years. Consequently, it follows that the six dominant year classes mainly supported the population, and hence the fishery, in that period. The time intervals between two subsequent dominant year classes are nearly within the mean number of breeding seasons of the female fish for a situation in which fishing pressure was hardly exerted on the population.