Larval parameters determining preschooling juvenile production of Pacific saury (Cololabis saira) in the northwestern Pacific

Abstract

Production of larvae in the hatching size-class of Pacific saury (Cololabis saira) was highest in autumn 1990-1994, implying that spawning activity was highest in this season. Growth and mortality rates were stable in the winter-spawned cohorts in Kuroshio waters (south of Honshu); variable rates were found in the autumn- and spring-spawned cohorts in the mixed water region to the northeast. Although no particular period of high mortality was detected through the larval and juvenile stages, overall percent survival through the larval and juvenile stages differed by an order of magnitude among seasons. Production of 40-mm preschooling juveniles was determined by larval production in the smallest size-class in the winter cohort, but by overall percent survival through the larval and juvenile stages in the spring and autumn cohorts. Over the last 44 yr, percentage of winter-spawned cohorts in commercial catches was stable, compared with large interannual variations of autumn- and spring-spawned cohorts. These observations were assumed to stem from stable juvenile production in winter and variable production in autumn and spring, suggesting the possibility of recruitment forecasts of seasonally spawned cohorts of saury based on preschooling juvenile production estimates in the northwestern Pacific.