Agustin Hernández Herrera

Improving estimates of recruitment and catchability of Jumbo squid Dosidicus gigas in the Gulf of California

Abstract We analyzed the effect of outliers of the catch-per-unit effort on the catchability coefficient estimated by using a depletion model. When we used catch-per-unit effort in the Delury model, we observed a curve in the regression of depletion against time. When we then solved the model with a normal probability distribution, the catchability coefficient was poorly estimated. We improved the estimation of catchability using an algorithm that used a two-component-mixture probability distribution. The estimations for catchability (q) and recruitment (N 0) were q = 0.41 × 10−3, N 0 = 9.13 × 106, and the estimated likelihood was 2.65 × 104 using an algorithm of the normal probability distribution, whereas the estimations made using the algorithm of a two-component-mixture probability distribution were q = 0.23 × 10−3, N 0 = 18.07 × 106, and the estimated likelihood was 4.89 × 106. The maximum likelihood estimated with the mixture-distribution algorithm was greater than the maximum likelihood estimated w...We analyzed the effect of outliers of the catch-per-unit effort on the catchability coefficient estimated by using a depletion model. When we used catch-per-unit effort in the Delury model, we observed a curve in the regression of depletion against time. When we then solved the model with a normal probability distribution, the catchability coefficient was poorly estimated. We improved the estimation of catchability using an algorithm that used a two-component-mixture probability distribution. The estimations for catchability (q) and recruitment (N0) were q1⁄4 0.41 3 10,N01⁄4 9.13 3 10, and the estimated likelihood was 2.65 3 10 using an algorithm of the normal probability distribution, whereas the estimations made using the algorithm of a two-component-mixture probability distribution were q 1⁄4 0.23 3 10, N0 1⁄4 18.07 3 10, and the estimated likelihood was 4.89 3 10. The maximum likelihood estimated with the mixture-distribution algorithm was greater than the maximum likelihood estimated with the normal-distribution algorithm. We believe the two-component-mixture probability distribution fit the data better than the normal probability distribution. From this we determined the consequences on management when overestimations or underestimations of catchability are estimated.

Maturation, Age, and Growth Estimation of the Jumbo Squid Dosidicus gigas (Cephalopoda: Ommastrephidae) in the Central Region of the Gulf of California

ABSTRACT In this study, the statolith microstructure of the jumbo squid Dosidicus gigas was used to determine age, individual growth, and changes in sexual maturity off the west coast of the central region of the Gulf of California during 2000 and 2002. The number of individuals sampled was 3,369 with a sex ratio of 1.8:1 (female to male). The size at first maturity (ML50%) in males varied between 46 cm and 56 cm, which was less than that seen in females (76–79 cm). The age of 251 squid was analyzed, and the growth of each sex was described by fitting the Gompertz and logistic models to the age-mantle length (ML) data. The Gompertz model best described the growth of the jumbo squid, and no significant differences were detected between sexes (ARSS, F = 0.73, P = 0.54). The parameters estimated for the combined data were ML∞ = 143.3 cm and g (growth coefficient at inflection point) = 0.004/y and t0 (age at inflection point) = 259.5 days. From the hatch date frequency distribution, a permanent incorporation of small individuals (ML, <55 cm) was identified in the fishing zone with 2 maximum values, one in May and another in November, suggesting that there are at least 2 cohorts in the population.