Age, growth and year-class composition of brown barracuda Sphyraena pinguis in Kagoshima Bay, southern Japan

Abstract

The ages of brown barracuda Sphyraena pinguis sampled from Kagoshima Bay, southern Japan were determined from transverse sections of otoliths. The following two methods were used for age validation: (1) monthly change in marginal growth rate for 1574 sectioned otoliths sampled from the waters, and (2) monitoring of strong or weak year classes during five survey years. The former method revealed that one annulus was formed per year during spring to early summer months. The latter one also validated one annulus per year. Assuming a birth date of June 1 from the monthly change in gonadosomatic indices, ages were assigned to every individual according to the number of opaque zones, and then fitted to the von Bertalanffy growth equations. Equations obtained were Lt=304.6{1-exp [-0.433(t+3.385)]} for males, and Lt=337.5{1-exp [-0.421 (t+ 2.972)]} for females, where L t is fork length (mm) at age t (year). These two equations were significantly different (p<0.01) and the length of females calculated from the equation was larger than that of males at any age. Maximum age observed was 11 years for males and 8 years for females.