Age, growth, maturity, and mortality of an understudied Gray Snapper fishery from the north-central Gulf of Mexico

Abstract

Objective

Gray Snapper Lutjanus griseus constitute a significant recreational fishery and minor commercial fishery throughout the Gulf of Mexico. The overall stock appears healthy based on the results of the most recent assessment; in fact, shifting climate conditions have led to range expansions and subsequent population growth in the north-central Gulf of Mexico, a region for which the full suite of basic biological data is currently lacking for this species. This work presents the results of a comprehensive study on the age, growth, maturity, and mortality of Gray Snapper in Alabama and Mississippi waters.

Methods

From 2011 to 2021, otoliths (n = 886) and gonads (n = 364) were sampled and processed according to standard microscopic techniques. Age data were used to fit three separate growth functions and derive estimates of total, natural, and fishing mortality, while testes and ovaries were categorized by reproductive phase to determine maturity at length and age.

Result

Ages ranged from 0 to 27 years, representing one of the most comprehensive collections across published studies to date. Sex-specific growth curves constructed using the von Bertalanffy growth function were preferred over the Gompertz and logistic models based on Akaike information criterion and suggest that males reach a higher mean asymptotic length $\left(L_t=731.52\left(1-e^{-0.15\left(t+1.34\right)}\right)\right)$ than females $\left(L_t=704.28\left(1-e^{-0.14\left(t+1.62\right)}\right)\right)$. Based on histological analyses, we estimate total length at 50% maturity to be 181 mm for males and 273 mm for females and total length at 90% maturity to be 215 mm for males and 354 mm for females. We estimate the age at 50% maturity to be <1.0 year for males and 2.0 years for females and the age at 90% maturity to be 1.4 years for males and 3.6 years for females. Mortality rates calculated using preferred estimators (Z = 0.30–0.38; M = 0.26; F = 0.04–0.12) indicate relatively low levels of exploitation in the north-central Gulf of Mexico, with full recruitment to the fishery occurring at age 4.

Conclusion

Based on these results, the Gray Snapper population in the north-central Gulf of Mexico is characterized by a relatively unexploited age structure with moderate longevity that has been subject to minimal fishing pressure. The findings from this study introduce new regional data for incorporation into assessments and provide an informed basis for future management decisions in this fishery.