Abundance, distribution and population dynamics of the short fin squid illex argentinus in southeastern and southern Brazil

Abstract

Surveys and commercial fishing landings data of the short fin squid Illex argentinus were analyzed to address three related issues: the seasonal and spatial pattern of abundance; seasonal and regional variation of growth and maturation; and the interannual variation in the size at maturity and growth from Southern Brazil (SB, 28◦–34◦S) and Southeastern Brazil (SEB, 23◦–28◦S). Overall, 2455 specimens were examined for maturity and 337 specimens had their daily increments in the statoliths recorded. Aged specimens from SB ranged from 51 to 275 days, 55 to 354 mm ML and 2.4 to 1098 g. It was observed that (1) I. argentinus is a common component of the nekton on all the outer shelf and slope and appears to be more abundant south of Santa Marta Grande Cape, where the largest catches were obtained in the autumn survey. (2) Spawning and hatching occurs year round along all the region. (3) In SB growth was faster and maturity was attained at larger sizes in the cold season (June to November) and no differences between seasons were observed in the mean age of mature specimens. (4) In 2001/2002, growth was faster, mature squids were in mean 159 days old and most were under 210 days, in 2007/2008, growth was slower, mean mature age was 191 days and most were 250 days. (5) In SEB, maturity was attained at smaller sizes and it is likely that maturity is attained at a lower age and the lifespan is shorter. In the northern range of its distribution I. argentinus is characterized by a decreasing adult size toward lower latitudes, a short and variable lifespan with hatching and spawning in all seasons