Interactions between oceanography, ecology and fishery biology of the ommastrephid squid Martialia hyadesi in the South Atlantic
The seven star flying squid Martialia hyadesi is an oceanic slope ommastrephid with a circumpolar distribution associated with the Antarctic Polar Frontal Zone (APFZ) and is a minor, variable catch in the South Atlantic Illex argentinus fishery. There have been occasional unusually large catches of M. hyadesi, the latest being in 1995. Because of the importance of understanding the influence of the physical environment on fisheries for oceanic squid, and interest in developing a new fishery for M. hyadesi in the CCAMLR area, we examined specimens and data from the 1995 season and analysed 10 yr fisheries and remotely sensed oceanographic data sets from the area. The 1995 data show that M. hyadesi remains in the cool APFZ waters of the Falkland Current where it preys on oceanic fish and crustaceans and its distribution rarely extends over the Patagonian Shelf. The squid exploited by the fishery in 1995 were 6 to 12 mo old; females were immature but some males were fully mature. A remotely sensed sea surface temperature (SST) image revealed mesoscale features at the shelf break front between Patagonian Shelf water and APFZ water where the squid were caught. The appearance of M. hyadesi in the fishery over the last decade, including 1995, has been related to SST anomalies. Teleconnections probably exist between these anomalies, El Niño/Southern Oscillation (ENSO) events in the Pacific and sub-decadal oceanographic instability in the Antarctic. Squid are short-lived and populations are likely to be able to respond rapidly to environmental change. However, it is not clear at what stage in the life cycle of M. hyadesi these oceanographic events exert their effect. We propose 2 alternative, but not mutually exclusive, hypotheses. Warm events prior to the appearance of M. hyadesi may favour reproductive success of the parent generation giving rise to a strong recruitment, or alternatively this cool water species may extend its range to the edge of the Patagonian Shelf early in the development of cold oceanographic events. In either case oceanographic effects are probably mediated via the squid's prey.