CEPHALOPODS AND MESOSCALE OCEANOGRAPHY AT THE ANTARCTIC POLAR FRONT -SATELLITE TRACKED PREDATORS LOCATE PELAGIC TROPHIC INTERACTIONS

Predator data and exploratory fishing in the Scotia Sea have revealed the presence of cephalopod stocks in the Antarctic Polar Frontal Zone (PFZ). This is a vast, remote region where large epipelagic cephalopod s aggregate into highly mobile schools making them difficult to locate and sample. We used satellite tagged predators and shipboard acoustic s for coarse and fine scale location of cephalopod concentrations, and sampled them with commercial and scientific nets to determine the rel ationship between cephalopod distribution and mesoscale oceanographic features at the PFZ. Satellite tags were attached to 9 grey-headed alb atrosses Diomedea chrysostoma, breeding at Bird Island, South Georgia, to monitor foraging at sea in January-March 1994. A foraging area at the PFZ, north of South Georgia, was located, an acoustic survey under taken and a fixed station established where acoustic targets were foun d. A net survey was carried out with a commercial pelagic trawl, a rec tangular midwater trawl 25 m(2) (RMT25), a horizontal multiple plankto n sampler and a neuston net. Acoustic layers were targeted and the RMT 25 sampled 200 m layers to 1000 m in daylight and darkness. Cephalopod s were simultaneously recovered from food samples fed to D. chrysostom a chicks at Bird Island. Two CTD transects, approximately normal to th e major current flow, were undertaken across the PFZ and remote-sensed sea-surface temperature images from NOAA polar orbiting satellites we re obtained aboard ship. The pelagic trawl sampled a cephalopod commun ity that closely resembled that exploited by D. chrysostoma. The large st and most conspicuous species was the ommastrephid squid Martialia h yadesi which is the most important cephalopod prey species. Net-sample d M. hyadesi had been feeding on crustaceans and mesopelagic fish. The cephalopod community was sampled in a feature, interpreted as a warm core ring, in an area characterised by mesoscale features associated w ith the bathymetry of the northern end of the Northeast Georgia Rise a nd near a gap in the Falkland Ridge. The association of these mesoscal e features with the bathymetry suggests that they may be predictable f oraging locations for the cephalopods and their predators.