Physical oceanographic processes play a major role in influencing the distribution of many species of ommastrephid squid. In this study the distribution of Illex argentinus (Cephalopoda: Ommastrephidae) was examined in relation to mesoscale oceanographic processes around the Falkland (Malvinas) Islands, Southwest Atlantic.

Daily fishery data were obtained from the Falkland Islands Government Fisheries department for the area defined by the Falkland Islands Interim Conservation and Management Zone (FICZ) and Falkland Islands Outer Conservation Zone (FOCZ) [Fig 1]. Spatially referenced fishery data and satellite-derived Advanced Very High Resolution Radiometry (AVHRR) sea surface temperature (SST) data were examined using Geographic Information System (GIS) techniques.

The distribution and relative abundance of Illex argentinus in the Falkland Islands fishery was examined for the period 1989 to 1996 [Fig 2]. Three consistent areas of high catch were observed to the northwest (shelf region) and northeast (shelf-break region) of the islands, and close to the northern coast of East Falkland. Data on fishing effort showed a similar pattern suggesting these three regions are favourable fishing areas for Illex argentinus.

Areas of high sea surface temperature gradients were extracted from remotely-sensed satellite SST images [Fig 3]. Areas exhibiting temperature ranges of 0.4-1 degree C over an area of 10.9 Km2 were defined as 'thermal gradients' [Fig 4] and used as an indicator of mesoscale oceanographic activity in Falkland Island waters.

Thermal gradient features were seen to be persistent throughout the year, especially near the shelf break (200m contour) region [Fig 5]. Gradients appear to break down towards the end of the season (May) due to the onset of seasonal cooling in winter.

The location of thermal gradient areas were superimposed onto spatially-referenced fishery data [Fig 6]. Data were analysed to test for differences between the number of vessels and catch rates (catch per unit effort [CPUE]) occurring in fishery cells falling within and outside thermal gradient regions.

Illex argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used allow the overlay and analysis of physical oceanographic and fishery data and have potential applications in operational fisheries oceanography and the management of commercially important ommastrephid squid.