Life history traits of the bigeye scad, Selar crumenophthalmus, in the coastal waters of Okinawa Island, southwestern Japan

Abstract

The bigeye scad, Selar crumenophthalmus, is an important coastal fishery resource in Okinawa Prefecture. However, much is still unknown about its life history traits. Age, growth, sexual maturation, reproductive cycle, and food habits of the bigeye scad were demonstrated based on 418 specimens collected in coastal waters near Okinawa Island. Annual formation of otolith opaque zones from May to October was validated by monthly changes in otolith edge types. Maximum ages observed in the specimens were 6.7 years and 6.1 years for females and males, respectively. No significant difference was observed in growth between sexes. Younger individuals [8–9 cm fork length (FL)] were recruited in July and grew up in shallow coastal areas, reaching 19–24 cm FL one year after hatching. At this time, piscivory became more evident, and 80% of females reached maturity. The spawning season was estimated to last from April to October, peaking in July through September. Mean fecundity was 1.09 × 10⁵ oocytes. In the coastal waters near Okinawa Island, this species was caught mainly using set nets, and small-sized immature individuals generally accounted for more than 30% of the examined individuals between August and December. For a sustainable fishery of S. crumenophthalmus in coastal waters of Okinawa Island, immature individuals must be protected to avoid growth overfishing.