Early life history of the black rockfish, Sebastes inermis as determined by otolith microstructure analysis

In this study otolith microstructure was used to reveal the early life history events of the black rockfish S. inermis immigrating into a temperate seagrass bed northern Japan in 1998 and 1999. Otolith had a prominent check, which was linked to settlement. Extrusion dates were distributed from late December to early March. Planktonic period showed a wide range from 55 to 110 days in 1998, and from 65 to 113 days in 1999, suggesting the delay in metamorphosis. Settlement dates extended from late March to late May and synchronized closely to both the first-third quarter moon cycle (neap tides) and the new-full moon cycle (spring tides) in 1998 and 1999, respectively. Back-calculated size at settlement did not vary significantly among settlement groups, which suggests the existence of a competent size to settle. Recent growth rates were high after settlement and regressed directly with shoot weight and height of Zostera marina, and inversely with water temperature. We discussed the “tidal control” and “settlement linkage” hypotheses concerning temporal settlement patterns as well as growth traits of S. inermis in relation to the utilization of Z. marina beds as a nursery ground.