Length-based growth estimates for Pacific sardine (Sardinops sagax) in theGulf of California, Mexico

Monthly length-frequency distributions for Sardinops sagax in the Gulf of C alifornia for fishing seasons 1972-73 to 1989-90 were used to estimate grow th by the Shepherd length-composition analysis (SLCA). Data were organized into annual sets, and the parameters of the von Bertalanffy growth curve we re computed. Estimates for K and L-infinity values were compared to others reported for the Gulf of California and derived from otoliths, scales, and other length-based methods. Otoliths and scales supported growth estimates with SLCA. On the assumption that variability observed in the values of gro wth parameters over 16 years represents individual variation, a maximum lik elihood algorithm was used in the growth performance index, phi', to estima te confidence intervals (CI), for K and L-infinity, as well as an average. Ranges for 90% CI were 0.34 < K year(-1) < 0.39, 27.0 > L-infinity (TL) cm > 25.2; ranges for 75% CI were 0.33 < K year(-1) < 0.33, 26.6 < L-infinity (TL) cm < 23.5. The best estimate was L infinity = 25.7 cm, K = 0.38 year(- 1), and t(0) = -0.3. This variability was interpreted as influences in the annual cohorts. These estimates were also compared with those ti-om the Pac ific coasts of Mexico, the United States, and Canada. Results suggest there are differences. In general terms, both K and L-infinity tend to be lower in the Gulf of California. This was interpreted to be a consequence of diff erences in the ecosystem dynamics.