Many immature individuals and largest size classes lacked females for three coral reef fishes (Actinopterygii) in Fiji market surveys: Implications for fishery management

Abstract

Data-limited fisheries benefit from using life-history traits as biological indicators of targeted stocks. We used histology-based reproductive analyses to estimate size at maturity, per capita egg production, and the number and biomass of immature individuals in the catch for three common coral reef fishes in Fiji market surveys during 2010–2019. We studied Lutjanus gibbus (Forsskål, 1775), Parupeneus indicus (Shaw, 1803), and Chlorurus microrhinos (Bleeker, 1854), which represent three families: Lutjanidae, Mullidae, and Scaridae, respectively. Fork length comprising 50% mature individuals for females of L. gibbus was 22.7 cm, that of P. indicus was 25.9 cm, attaining 38.0 cm for C. microrhinos. Females were rare or absent in the largest size classes of all three species. Immature fish represented up to 50% by number and 41% by biomass of the catch in market surveys, with P. indicus having the greatest immature number (8%‒50%) and biomass (6%‒41%), followed by C. microrhinos (20%‒30% by count, 11%‒18% by biomass) and L. gibbus (9%‒28% by count, 5%‒14% by biomass). Individuals ≤ 30 cm for L. gibbus and P. indicus and ≤ 45 cm for C. microrhinos were responsible for ≥ 90% of egg production per spawning. Skewed size-specific sex ratios suggested that exploitation of the largest size classes had minimal effect on overall egg production. Decreased catches of immature fishes would increase the reproductive population sizes for these species.