CCAMLR

The changing nature of marine fisheries requires management approaches that recognize and include ecosystem and environmental effects. Therefore, we review some examples of exploited fishery stocks in which environmental control is a major contributor to structuring the abundance and distribution of the stock. Four examples, ranging from Antarctic krill to oysters, are given that clearly illustrate environmental control on the fishery. From these examples, we argue that future management strategies for exploited fisheries must include effects of environmental variability. In particular, management strategies must be flexible enough to include delayed responses to environmental variations that result from the transfer of perturbations from larger to smaller scales and vice versa. This capability requires an understanding of where linkages between the physical environment and the species of interest occur. Development of this knowledge requires input from a variety of disciplines, coordinated research programs, and considerable cooperation at national and international levels.

The transport of secondary production in the Southern Ocean food-web was investigated using a combination of physical model data and ship based biological data. The physical current velocity dataset was from FRAM and was used to derive a mean velocity field for the upper 250m of the water column. These have been combined with estimates of krill density and standing stocks to consider the flux of krill through the South Georgia area and estimate residence times. These data have been considered with estimates of local predator demand to consider the implications for calculating the precautionary catch levels suitable for the region. The study suggests that catch levels in this area have in the past being of the same order as the calculated potential yield. The work highlights the need for improved infomation the spatial food web connections, the flux of krill and residence times.

The foraging behaviour of Adélie Penguins Pygoscelis adeliae was studied simultaneously at Shirley Island (SI) near Casey Station and at Petrel Island (PI) at Dumont D'Urville during the 1995/96 breeding season. The study took place in conjunction with a ship-based krill survey in the CCAMLR Division 58.4.1 (south of 55 °S, 80 - 150 ° E) to determine the extent of overlap between penguin foraging areas and krill distribution. The maximal distances travelled by penguins from Shirley Island were significantly greater than those by penguins from Petrel Island (SI 68 - 113 km; Petrel Island about 37 km). Foraging trip durations and total distances travelled were also significantly different between colonies (duration: SI 55 - 113 h, PI 25 - 32 h; total distance: SI 182 - 352 km, PI 86 - 100 km). All penguins foraged over the continental shelf and not in oceanic waters. The percentage distribution of dive depths were similar at both colonies; nearly 70 % of all dives were to

The accuracy of correction factors estimated to compensate the digestion and loss through the gastrointestinal tract of the otoliths of fish represented in pellets of the Antarctic Shag Phalacrocorax bransfieldensis was tested at two localities of the South Shetland Islands. F or such purpose, the results from the analysis of 226 and 115 pellets collected at Harmony Point and at Duthoit Point, respectively, throughout the breeding season were compensated with the mentioned factors. The estimations indicated that the daily food intake increased from November to January (pre-laying to late-rearing) and slightly decreased in February. These estimations, in general, are in line with those previously obtained for other colonies and/or shags by different methods, which suggests that the use pellets is an acceptable method to quantify the diet of the Antarctic Shag.

The diet of juvenile and non-breeding male Antarctic fur seals Arctocephalus gazella was investigated at Harmony Point, Nelson Island, South Shetland Islands, by the analysis of 18 and 33 scats collected during the 1995/96 and 1996/97 summer seasons respectively. Overall, fish were the most frequent prey (74,5%) and predominated by mass (54,4%), whereas krill did by number (94.2%). This pattern coincides well with the observed in 1996/97, but in 1995/96 krill was the most important prey also by mass (50.2%). The importance of the remaining taxa represented in the samples (octopods, hyperiids and bivalves) was negligible. Among fish, Myctophiids represented 85 .2% of the fish mass, being Gymnoscopelus nicholsi and Electrona antarctica the main prey. These two species also predominated in 1996/97, whereas Cryodraco antarcticus and Gobionotothen gibberifrons did in 1995/96. The importance of the Myctophiids as prey of the Antarctic fur seal is discussed.

The diet of the Antarctic petrel Thalassoica antarctica was studied during two years at Svarthamaren, an inland colony situated in Dronning Maud Land, Antarctica and in the pack-ice outside Svarthamaren. The analyses showed that the most important food (wet weight) at Svarthamaren was Crustaceans (68%), followed by fish (29%) and squid (3%), whereas individuals collected in the pack ice took mostly fish (95%), followed by Crustaceans (5%). The prey composition and length found in this study is comparable to what is found in other diet studies. Estimates of food consumption for birds breeding at Svarthamaren (c. 250,000 pairs) indicate that the take approximately 6,600 tons of Crustaceans, 2,600 tons of fish and 485 tons of squid during the breeding season. Furthermore, their annual consumption is estimated to 34,800 tons of Crustaceans, 13,800 tons of fish, and 2,600 tons of squid. Satellite telemetry studies indicate at Antarctic petrels from Svarthamaren may fly more than 3,000 km during one foraging trip and may thus, cover a huge ocean area.