Implementation of catch-at-age model for the jumbo squid Dosidicus gigas

Abstract

The knowledge of the population dynamics and changes of biomass of harvested marine species is relevant for fisheries management. In this study, a catch-at-age analysis for jumbo squid Dosidicus gigas called CAGEAN-JS model was implemented. So, for illustrative purposes and based on the best biological and fishery data available, the advantages of the catch-at-age model are described and modeled as an alternative statistical method useful for stock assessment in jumbo squid fishery, improving the biomass and recruitment estimations in the population. A matrix was implemented that included catch-at-age data using a time step of the matrix of 30days with a fishing period or time expressed in months. Numbers of squid caught at time (age) and fishing period (months) were estimated from the commercial catch using an age-length key and weight-at-length relationship. Catch and catch rate data for 2001 and 2002 fishing seasons from three different fleets were used to provide extra structure to the CAGEAN-JS model. The model estimated a total biomass of 798,084t (C.I. 781,435–837,679t, P<0.05) and 638,792t (C.I. 622,281–678,400t, P<0.05) of vulnerable biomass during the 2001–2002 fishing seasons. The monthly total biomass varied from 19,704t (October 2001) to 55,164t (November 2001), and monthly vulnerable biomass showed a minimum value during November 2001 (13,232t) and a maximum during September 2002 (45,372t). Three peaks of recruitment were observed in the time series, high abundance of squid at an age class of 5 months was estimated during May 2001, November 2001, and April 2002, previously recruitment in the month of November had not been reported for this species in the Gulf of California. The monthly fishing mortality reached a maximum value of 0.260, while during summer months of every year the harvest diminished. The advantages of CAGEAN-JS model proposed is that it estimates monthly changes in total and vulnerable biomass, fishing mortality and recruitment; these quantities are based on the best available data of the fishery, such as catch-at-age, selectivity, and fishery dependent-data (catch rate). Thus, the CAGEAN-JS model is very inclusive, thus providing stakeholders with a great deal of quantitative information useful for decision making in order to fish the Mexican jumbo squid in the Gulf of California in a sustainable manner.