Age, growth and mortality of mutton snapper, Lutjanus analis, from the east coast of Florida, with a brief discussion of management implications

Abstract

Mutton snapper, Lutjanus analis, were sampled from recreational headboat and commercial vessels along the east coast of Florida, 1992–2000. Marginal increment analysis on sectioned otoliths ( n=1391) confirmed annulus formation during March–May. Mutton snapper were aged up to 29 years, and the largest fish measured 880 mm TL (total length). The weight–TL relationship was described by: W=1.01×10 −8× TL 3.05 ( R 2=0.96, n=413 ), where W is the whole weight (kg). The TL–fork length (FL, in mm) relationship ( R 2=0.99, n=249 ) was described by: TL=8.91+1.08×FL. The TL–otolith radius (OR) relationship ( R 2=0.81, n=1400 ) is described by the equation: TL=(177.09×OR)−131.56. Mean lengths at age from back-calculations to the last annulus ranged from 216 mm at the end of age 1 to 810 mm at age 17. Growth was not significantly different between sexes, and the von Bertalanffy growth equation for combined sexes was L t =869(1−e −0.16( t+0.94) ). Estimates of instantaneous natural mortality ( M) ranged from 0.29 to 0.49. Estimates of instantaneous total mortality ( Z) averaged 0.43 for all fisheries combined, 1986–1998, and were similar to single cohort estimates derived for the 1981–1986 year classes (mean Z=0.49). Mutton snapper were fully recruited to the headboat fishery by age 4, the commercial fishery by age 6, and the private recreational fishery by age 3. The problems inherent in managing a species that forms spawning aggregations and the more general problem of using a single statistic, such as spawning stock ratio (SSR), to assess a stock are discussed.