Young-of-the-year (YOY) Sebastes inermis uses seagrass beds as a temporary nursery ground after completing the planktonic stage in offshore waters. In the present study, the otolith microstructure was used to reveal the early life history of this species in a Zostera marina bed in Matsushima Bay, northern Japan. In 1998 and 1999, the settlement season began in early spring and catch per unit effort (CPUE) of YOY decreased markedly during the summer months. The smallest YOY S. inermis collected were 20 and 21 mm total length (TL) at 70-80 days after extrusion in 1998 and 1999, respectively. In both years, YOY that were extruded earlier (mostly in January) first appeared in the Zostera bed, and they were the first to leave, whereas those YOY extruded later (mainly in February) tended to stay beyond the summer in the Zostera belt. Birth dates of YOY showed two distinct cohorts, January and February, which showed a similar pattern of growth in both years; rapid growth after settlement peaking in May in 1998 (mean = 0.73 mm/day) and in April in 1999 (mean = 0.61 mm/day), decreasing during the summer months, with the lowest mean values in August in both years (mean = 0.40 mm/day for 1998 and 0.30 mm/day for 1999). In both years, the decrease in both CPUE and growth rates in summer months synchronized with a decline in biomass, density, leaf length and shoot weight of Z. marina. Total CPUE was higher in 1999 than in 1998, whereas the recent growth rate (i.e. 1 week before the fish were collected) was significantly higher in 1998 than in 1999, suggesting a density-dependent mechanism.
- Daily growth
- Otolith microstructure