Age determination in the snapper Lutjanus guttatus (Pisces, Lutjanidae) and investigation of fishery management strategies in the Pacific Coast of Guatemala

Abstract

The rose-spotted snapper, Lutjanus guttatus, seems to be sequentially exploited by the shrimp trawler and the artisanal fleet along the Pacific Coast of Guatemala. The growth parameters of the snapper were estimated in the present study with basis on material collected in two fishing harbours. Other biological and fishery information was compiled to simulate stock dynamics with a yield-per-recruit model. This single-species model allowed the evaluation of possible outcomes of fleet interactions, in terms of relative yield, spawning stock development and profit. A large emphasis was put in the evaluation of skeletal structures, otoliths and vertebrae, to determine age. Vertebrae seem to be the best structure for ageing, as they revealed better ring definition, and resulted in more adequate growth patterns and plausible Von Bertalanffy growth parameters. The VBGF (total length-at-age) obtained with vertebrae was Lt = 66.4(1-exp(-0.13(t-0.03))). The age of first-capture (Tc) for the trawl and the artisanal fleets were estimated to be about 1 and 3 years, respectively. The age-dependent mortality was suggested to follow unimodal curves for the two fleets, owing to the patterns of selectivity of the gear and availability of the fish. The yield-per-recruit scenarios showed that for the suggested biological and fishery parameters, the highest yield of snapper is not being attained. Further, the model suggests that with the present fishing pattern high rates of fishing mortality could deplete the spawning stock. Implementation of size-selective practices that minimise the trawlers’ by-catch of L. guttatus, and an increase of the artisanal Tc (to above the maturation age, Tm, about 4.5 years) are likely to result in increased yield, total profit, and prevent recruitment overfishing.