Determining Optimal Release Habitat for Black Rockfish, Sebastes schlegelii: Examining Growth Rate, Feeding Condition, and Return Rate

Abstract

The effects of release habitat on the effectiveness of stocking were evaluated in Miyako Bay, Iwate, Japan. Hatchery-reared black rockfish juveniles were released at four different stations characterized by different habitat conditions from 2002–2007, and a survey was conducted of landed fish at Miyako Fish Market. Growth rate and feeding condition of wild and released juveniles sampled from two known wild nursery areas (Stn. 1 and Stn. 2) were also examined to elucidate the conditions that form optimal habitat. Comparisons of growth and feeding condition of juveniles between Stn. 1 and Stn. 2 indicated that Stn. 1, with its brackish waters, seagrass beds, abundant mysids, and large gammarids, supported better growth and survival of released fish, which in turn led to a higher market return rate. The highest market return rate was estimated as 8.3% (for 45-mm total length juveniles released at Stn. 1 in 2007), corresponding to a maximum economic return rate (value of recaptured fish divided by hatchery and release costs) of 1.32.

Keywords:

• density-dependent growth
• intraspecific competition
• nursery ground
• stock enhancement
• mysids
• gammarids

ACKNOWLEDGMENTS

The authors would like to thank Dr. Masato Aritaki (Research Center for Fisheries and Environment in the Ariake and Yatsushiro Bays, Seikai National Fisheries Research Institute, FRA), Dr. Michelle L. Walsh (NOAA Fisheries Service Fishery Policy Analyst), and the staff at FRA Miyako Station for their valuable advice and support on this study. All experimental work conducted for this study complies with the current laws of Japan.