Cephalopods and mesoscale oceanography at the Antarctic Polar Front: satellite tracked predators locate pelagic trophic interactions

• Published in: Marine Ecology Progress Series
• Main Authors: Rodhouse, P.G., Prince, P.A., Trathan, P.N., Hatfield, E.M.C., Watkins, J.L., Bone , D.G., Murphy, E.J., White, M.G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Inter Research 1996
• Subjects: Antarctic; Bird Island; Falkland Ridge; Georgia Rise; Northeast Georgia Rise; Scotia Sea; The Antarctic; Antarc*
• Online Access: https://oceanrep.geomar.de/id/eprint/50734/; https://oceanrep.geomar.de/id/eprint/50734/1/2969.pdf; https://doi.org/10.3354/meps136037

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 cephalopods aggregate into highly mobile schools making them difficult to locate and sample. We used satellite tagged predators and shipboard acoustics for coarse and fine scale location of cephalopods concentrations, and sampled them with commercial and scientific nets to determine the relationship between cephalopod distribution and mesoscale oceanographic features at the PFZ. Saltellite tags were attached to 9 grey-headed albatrosses 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 undertaken and a fixed situation established where gular midwater trawl 25m² (RTM25), a horizontal multiple plankton sampler and a neuston net. Acoustic layers were targeted and the RMT25 sampled 200m layers to 1000m in daylight and darkness. Cephalopods were simultaneously recovered from food samples fed to D. chrysostoma chicks at Bird Island. Two CTD transects, approximately normal to the major current flow, were undertaken across the PFZ and remote-sensed-sea-surface temperature images from NOAA polar orbiting satellites that exploited by D. chrysostoma. The largest and most conspicious species was the ommastrphid squid Martialia hyadesi which is the most important cephalopod prey species. Net-sampled 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 with the bathymetry of the northern end of the Northeast Georgia Rise and near a gap in the Falkland Ridge. The association of these mesoscale features with the bathymetry suggests that they may be predictable foraging locations for the cephalopods and their predators.