AGE, GROWTH, REPRODUCTION, AND MORTALITY OF THE LINED SURGEONFISH (ACANTHURUS LINEATUS) FROM SAIPAN, NORTHERN MARIANAS

Abstract

Fisheries in the Commonwealth of the Northern Mariana Islands (CNMI) consist of shore‐based and boat‐based catches of coral reef species. Surgeonfish (Family Acanthuridae), especially Lined Surgeonfish Acanthurus lineatus, contribute significantly to total landings in the nearshore coral reef fishery of the CNMI. Despite being an important component of the nearshore fishery, there is very little known about the biology and life history of the Lined Surgeonfish in the CNMI. The objective of this study was to investigate the age-based demography and reproductive biology of Acanthurus lineatus from Saipan, CNMI to enhance our understanding of their life history. To determine age and growth, longevity, mortality rates, age- and length-at-maturity, and spawning seasonality, fishery-dependent specimens collected during May 2017 to October 2019 were examined. There were no significant mean length differences between the distribution of male and female specimens. The combined length-weight relationship for all specimens across all years was ?=0.031×10−5^2.957. Growth model parameters were a mean asymptotic length (? ∞) of 20.5 cm FL, a growth coefficient (K) of 0.24 ?−1 and a ?0 of -3.2 years. The maximum recorded age was 20 years. Otolith weight was a good predictor of age for both males and females. Estimated total mortality was 0.495 ?−1, natural mortality (M) was 0.315 ?−1, and fishing mortality was 0.18 ? −1. The overall sex ratio was male to female = 1:1.81. For females, the length at 50% sexual maturity (? 50) was 18.8 cm fork length and age at 50% maturity (?50) was 6.2 years. Maturity for males was not estimated due to an insufficient number of immature males. Spawning capable and active A. lineatus females and males were observed during all months with sample collection, potentially supporting a year-round spawning cycle. The outcomes of the work could be used to inform length-based fishery regulations and indicator-based single species stock assessment approaches to support the sustainable fishery management of A. lineatus in the CNMI.