Length-based growth estimates for pacific sardine (Sardinops sagax) in the Gulf of California, Mexico

Monthly length-frequency distributions for Sardinops sagax in the Gulf of California for fishing seasons 1972-73 to 1989-90 were used to estimate growth by the Shepherd length-composition analysis (SLCA). Data were organized into annual sets, and the parameters of the von Bertalanffy growth curve were computed. Estimates for K and L_∞ 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 growth parameters over 16 years represents individual variation, a maximum likelihood algorithm was used in the growth performance index, φ′, to estimate confidence intervals (CI), for K and L_∞, as well as an average. Ranges for 90% CI were 0.34 < K year^-1 < 0.39, 27.0 > L_∞ (TL) cm > 25.2; ranges for 75% CI were 0.33 < K year^-1 < 0.43, 26.6 < L_∞ (TL) cm < 23.5. The best estimate was L_∞ = 25.7 cm, K = 0.38 year^-1, and t₀ = -0.3. This variability was interpreted as influences in the annual cohorts. These estimates were also compared with those from the Pacific coasts of Mexico, the United States, and Canada. Results suggest there are differences. In general terms, both K and L_∞ tend to be lower in the Gulf of California. This was interpreted to be a consequence of differences in the ecosystem dynamics.