Effects of extensive seeding on abalone, Haliotis discus discus,abundance on the Pacific Coast of Boso Peninsula, Japan

摘要

Abalone resources in Chiba Prefecture, the Pacific coast of central Japan, have been severely reduced in recent years. Our investigations have revealed that the density of the mature abalone in this area is 0.019 ind./m super(2), which may be insufficient for successful reproduction. In this study, we investigate the effects of extensive seeding on stock enhancement of abalone, Haliotis discus discus. We experimentally released 400,000 juveniles (3.0 cm in shell length, SL) to the research field of 8,000 m super(2) in May 1998 and investigated the growth and stock conditions by SCUBA. The abalone seeds grew up to 10.2 cm SL on average in 3 y and 12.8 cm SL in 4 y, exceeding the legal catch size (12.0 cm) by the Chiba Prefectural Regulation of Fisheries Adjustment, and subsequently commercial catches started in 2002. The catch per unit effort (CUPE) was increased to a great extent from 3 kg/day-boat to 9 kg/day-boat. The inhabited area was considered to be expanded to 100,000 m super(2) based on the catch logs by the local fishermen. As of May, 2002, a production of 57,000 abalones was estimated to be attained by the extensive seeding.