Age, growth, reproductive biology and spawning periodicity of the forktail rabbitfish (Siganus argenteus) from the Mariana Islands

Abstract

In the present study, life-history traits of importance to fisheries management were estimated for the forktail rabbitfish (Siganus argenteus) based on fishery-dependent samples collected over a 2-year period in the Commonwealth of the Northern Mariana Islands. Age-based and reproductive information was derived from analysis of sagittal otoliths and gonads. The species is short-lived, with a maximum age of 7+ years, and females reach sexual maturity at ~1.3 years (21.8-cm fork length). Age distributions and total mortality rates were similar between sexes. However, females on average reached larger asymptotic sizes, with estimates of mean asymptotic length exceeding that of males by 2cm. Reproductive cycles, based on temporal variation in gonadosomatic index values and proportional frequency of active ovaries, demonstrated two annual activity peaks, consistent across 2years of sampling. Peak spawning occurred from March to May–June, whereas a second, smaller peak spanned August and September. In the Mariana Islands, S. argenteus represents a short-lived species with potential for rapid population turnover; 85% of the population is under 3years of age, whereas approximately half of all harvested individuals have reached reproductive maturity. Derived estimates of natural and fishing mortality indicate minimal concerns for the long-term fishery sustainability of this species under present levels of exploitation.