Relationship between Annual Catch Fluctuations and Reproduction in the Swimming Crab in Hiuchi Nada, the Seto Inland Sea

Abstract

The occurrence of recruitment fluctuations and their relationship to reproduction in the swimming crab Portunus trituberculatus were investigated on the southern coast of Hiuchi Nada. In particular, relationships between adult catch, new recruits, and numbers of megalopa collected from 1980 to 1989 were considered.
A significant positive correlation was found between the abundance of megalopa and subsequent recruitment (r=0.856, p<0.01), although the relationship between the parent and subsequent megalopa was not significant (r=0.454).
It is considered that the survival rate from hatching to megalopa varied considerably year by year, that the survival rate from megalopa to recruitment was relatively certain, and that the recruitment abundance for each year was established by the megalopa stage. It was concluded that the fluctuations in annual catch of swimming crabs in Hiuchi Nada were caused by abrupt increases in megalopa numbers due to high larval survival rates, and that gradual decreases in stock numbers reflect overfishing.