Long-Term Changes in the Fraction of Mature Brown Shrimp Farfantepenaeus californiensis (Holmes, 1900) Females and Their Impact on Length at First Maturity

This study analyzed the interannual changes in the fraction of female brown shrimp hufantepenaeus californiensis that were mature by assessing the performance of a 3-parameter versus a 2-parameter logistic model of maturity at length and the effect on the magnitude of length at first maturity (L-50). Shrimp biological data were registered monthly from 1995 through 2015, off the southwestern coast of the Baja California Peninsula, Mexico. The model was fitted to the data by assuming two conditions for the asymptote, which represents the proportion of mature females: (1) asymptote equal to 1 (2-parameter), and (2) asymptote less than 1(3-parameter). On the basis of Akaike's information criterion, the logistic model with asymptote less than 1 was selected as the best model. Therefore, the asymptote varied from 0.34 to 0.92, and the L-50 ranged between 138 and 172 nun in total length. The estimates of the L-50 for the 3-parameter model were lower than those for the 2-parameter model, avoiding misinterpretation of this quantity used in management. The results show a decline in the proportion of mature females, indicating that not all the female shrimp in the population spawn every year. The use of the 3-parameter model provided a better representation of the observed data and reliable parameter estimation.