Surface oceanography of the inferred hatching grounds of Illex argentinus (Cephalopoda: Ommastrephidae) and influences on recruitment variability

Interannual variability in the mesoscale oceanography of the inferred hatching area of winter-spawned Illex argentinus (i.e. those belonging to the Southern Patagonic Stock) was examined during the hatching months of June and July. The hatching area was defined as the region 32°-39°S, 49°-61° W, and indicators of the surface oceanography in this area were derived from remotely sensed advanced very high resolution radiometer (AVHRR) sea-surface temperature (SST) data. Interannual variability in the mesoscale oceanic circulation in the inferred hatching area was examined in terms of (1) the area occupied by "frontal" waters (defined as areas with SST gradients of ́°C over an area of 15 km by 15 km), and (2) the area occupied by waters of "favourable" SST (defined as those with temperatures in the range 16-18°C). Oceanographic indicators were compared with an index of I. argentinus recruitment to the Falkland Islands (Malvinas) fishery (catch per licensed vessel) for the period 1987 to 1999. The two oceanographic indicators were seen to co-vary, with a decrease in the proportion of the inferred hatching area occupied by frontal waters corresponding to an increase in the proportion of water of favourable SST. High squid abundance was found to be associated with a lower proportion of frontal waters or a higher proportion of favourable-SST waters within the inferred hatching area in the year preceding the fishery. Interannual variability in the interaction of the Brazil and Falkland Currents in the inferred hatching area during the early life stages is shown to be important in influencing the population size of I, argentinus, and mechanisms influencing squid recruitment in this highly dynamic region are discussed.