Population parameters of the snail Astraea undosa (Wood, 1828) from the west coast of the Baja California Peninsula

Growth and mortality of the snail Astraea undosa were estimated based on the age determination of 1034 opercula obtained from 34,969 organisms sampled in five fishing areas off the west coast of Baja California Sur (Mexico), during 1997 and 1998. No significant differences were detected in the sizes of each sex and age groups of 0 to 12 years were determined. To describe the growth pattern, the von Bertalanffy growth model was fitted to size-age data per fishing area and the following growth parameters were obtained: L_∞ = 167.8 to 175.1 mm basal diameter, K = 0.08 to 0.10 mm/year and t₀ = -1.7 to -1.2 years. The growth pattern was similar among areas in agreement with the performance index, φ'. However, a north-south size-age latitudinal gradient was observed; the largest sizes per age were observed at Isla Natividad. The natural mortality was 0.29 per year. The total mortality rate per area varied from 0.43 to 0.90 per year and the exploitation rate from 0.11 to 0.40 per year. The results indicate that the fishery sustains appropriate exploitation levels.