Stock enhancement of the Japanese scallop Patinopecten yessoensis in Hokkaido

Abstract

Prior to the early 1940s, harvests of scallops from Japan fluctuated from ∼10 to 80,000 tonnes per anum. However, the fishery collapsed in 1945 and production remained at chronically low levels (<100 tonnes p.a.) in key areas. A breakthrough in methods for catching juvenile scallops (spat) for grow-out in hanging culture paved the way for the restoration and eventual stock enhancement of the major scallop fisheries in Hokkaido Prefecture. Following this breakthrough, scallop fisheries were managed using a system based mainly on: (1) mass-release of cultured juveniles, (2) removal of predators, and (3) rotational fishing, i.e., partitioning fishing grounds into four areas, releasing 1-year-old juveniles into one area each year, then harvesting them 3 years later. This management system was pioneered largely by the fisheries cooperative at Sarufutsu, Hokkaido, and catches there improved from <100 tonnes to consistent harvests of 40,000 tonnes p.a. Similar management systems have been adopted by neighboring fisheries cooperatives, resulting in current total harvests of scallops from stock enhancement in Hokkaido of ∼300,000 tonnes p.a. The success of scallop stock enhancement in Hokkaido is attributed to: a good supply of larvae, development of simple and effective methods for catching and rearing spat, ideal habitat for growth of scallops, removal of predators, and devolution of management to fisheries cooperatives. The management system developed in Hokkaido should be transferable to other locations where there is a good natural supply of spat, low levels of predation, currents that retain larvae, and incentives for fishermen to invest in the capture, rearing and release of spat and the implementation of rotational fishing.