Movement patterns determine the availability of Argentine shortfin squid Illex argentinus to fisheries

In this study, we found that dynamic movements of squid in its feeding phase have profound effects on its abundance and thus affect its availability to fisheries. The Argentine shortfin squid Illex argentinus is one of the world's important economic invertebrate species, with annual fisheries production exceeding one million tons in some years, but the value drastically fluctuates by more than 20-fold. Using catch per unit effort (CPUE) data from the Taiwanese squid jigging fleets during the years 2004-2013, we evaluated its variability in abundance, and the most possible relationships to migration patterns. Results from the statistical analysis using a generalized additive model (GAM) showed that within a specific year, the CPUE was linearly related to latitude (between 46°S and 50°S) and sea surface temperature (SST; of between 10 and 14 °C) components, corresponding to the squid's dynamic movement during a fishing season. Two distinctive movement patterns for low- and high-abundance years were recognized. In low-abundance years (2004 and 2010), negative cross-correlations between the CPUE and the latitudinal component of the fishing position were found in a time-lagged analyses, suggesting a decoupling of the CPUE from latitude; while in high-abundance years (2007 and 2013), a positive correlation was found, signifying a strong coupling between the CPUE and latitude. A spectral analysis identified one significant long-period (low frequency) coherency between the CPUE and the latitudinal component in 2007, while no significant coherency was found in 2004, suggesting a feasible matchup of squid abundance and its southern feeding movement for an expected high annual production.