Effectiveness of stock enhancement of hatchery-released black rockfish Sebastes schlegeli in Yamada Bay — Evaluation by a Fish Market survey

Black rockfish Sebastes schlegeli is considered a promising species for stock enhancement because of its high growth rate and limited area of movement. This study evaluated the stocking effectiveness of black rockfish released in Yamada Bay, off the northeastern Pacific coast of Japan, using three indices estimated from survey data collected on all business days at the Yamada Fish Market over a period of 11 years. Eight annual cohorts of hatchery-raised, marked juveniles were released into the bay from 1989–1991 and 1993–1997. During the market census, all landed black rockfish were investigated for TL and presence or absence of marks. The census indicated that 51,512 fish out of 447,400 hatchery-released juveniles were landed commercially and recorded at the market. Of the returned fish, 1-year-old fish accounted for 61.2%, 2-year-old fish for 30.3%, and ≧3 year-old fish for 8.6%. Return rates of each year class ranged from 9.3% to 15.4% showing stable and rather high values. However, the economic return rate (landed sales values / hatchery costs) ranged between 0.68 and 1.25; 5 of the 8 year classes showed rates of less than 1, where hatchery costs exceeded their associated benefit. To make stocking of black rockfish feasible, raising the market price of this species through fishery management, decreasing hatchery production costs, and developing effective release strategies such as optimum release size are needed.