Assessment of stocking effectiveness of hatchery-reared age-0 and age-1 masu salmon smolts through a fish market survey in Hokkaido

Abstract

SUMMARY: Enhancement strategies for masu salmon Oncorhynchus masou have been developed during the last 20 years in northern Japan. The introduction of age-1 smolts is regarded as the most effective method although age-0 smolts are produced experimentally by accelerated incubation and rearing at the Hokkaido Fish Hatchery. In this study, we estimated recoveries of hatchery-reared age-0 and age-1 masu salmon smolts through a two-stage sampling survey of commercial landings in western Hokkaido, Japan. Recovery rates ranged between 0.1 and 4.5% for age-0 smolts and 0.2 and 3.5% for age-1 smolts. Increased smolt weight at release had positive effects on recovery rates of age-1 smolts, and increases in condition factor had negative effects on the recovery rates of age-0 smolts. KEY WORDS: masu salmon, smolt, hatchery, recovery, fish market, Hokkaido INTRODUCTION MATERIALS AND METHODS Masu salmon Oncorhynchus masou is an important commercial fish species in northern Japan. Recent declines in the commercial landings resulted in increased efforts to enhance this species in Hokkaido. Since the 1980s, stocking technology has been developed.