CCAMLR

Krill (Euphausia superba) provide a direct link between primary producers and higher trophic levels in the Antarctic marine food web. The pelagic tunicate Salpa thompsoni can also be important during spring and summer through the formation of extensive and dense blooms. Although salps are not a major dietary item for Antarctic vertebrate predators, their blooms can affect adult krill reproduction and survival of krill larvae. Here we provide data from 1995 and 1996 that support hypothesized relationships between krill, salps and region-wide sea-ice conditions. We have assessed salp consumption as a proportion of net primary production, and found correlations between herbivore densities and integrated chlorophyll-a that indicate that there is a degree of competition between krill and salps. Our analysis of the relationship between annual sea-ice cover and a longer time series of air temperature measurements indicates a decreased frequency of winters with extensive sea-ice development over the last five decades. Our data suggest that decreased krill availability may affect the levels of their vertebrate predators. Regional warming and reduced krill abundance therefore affect the marine food web and krill resource management.

Scientific observations on fishes incidentally caught during krill fisheries by F/V Niitaka Maru were made from 1 to 23 February, 1997 to the north of the South Shetland Islands. Among 80 hauls examined, a total of 61 specimens belonging to 4 families and 7 species, Electrona antarctica (50 specimens), Electrona carlsbergi (4), Protomyctophum tenisoni (1), Gymnoscopelus opisthopterus (1), Notolepis coatsi (3), Benthalbella elongata (1) and Neopagetopsis ionah (1), were captured as by-catch in 16 hauls. Except for one channichthyid juvenile of Neopagetopsis ionah, by-catch fishes were referred to the bathypelagic families, the Myctophidae, Paralepididae and Scopelarchidae. Among by-catch fishes, Electrona antarctica of the Myctophidae was the most abundant. This species was found in 12 hauls, and its estimated value was 20 to 380 ind./t. The present by-catch data did not provide clear relationship between the abundance of by-catch fish and the krill CPUE. This observation is different from by-catch data made in previous studies. In the present survey, the abundance of by-catch was well correlated to the time zone of trawling, which is thought to depend on a large amount of bathypelagic fishes in the catches.

Thomson and Butterworth (1996) developed a krill-predator model and applied this to an Antarctic fur seal dataset. These calculations are extended here. The level of krill fishing intensity required to halve the fur seal population (γhalf) is between 0.08 and 0.09, slightly lower than that estimated previously. Tests of the estimation procedure indicate that γhalf estimates are likely to be biased upwards. The estimator is not robust to incorrect specification of the form of the functional relationship assumed between krill availability and survival rates, and especially not to the assumption of the size of the maximum growth rate which the population can achieve. Refinements are introduced to the process of applying this approach to the black-browed albatross dataset, but calculations to estimate γhalf for this species have yet to be completed. The results quoted above are for the deterministic models; stochastic calculations await finalisation.

Polynyas accelerate oceanic and atmospheric processes. We additionally think polynyas influence biological activity. We pursued daily transition of coastal polynyas in the Antarctic Peninsula area from 1978 through 1995 using images of sea ice concentrations by the satellite microwave observations. A typical polynya existed off the tip of the Peninsula in 1987 and 1991. In the such years, sea ice cover developed extensively. Inversely, the years of the narrow sea ice cover were 1988, 1989,1990 and 1993. In the such years, polynyas did not existed. The typical polynya (nearly 500 x 200 km) in 1987 was pursed from beginning on August 1 to end on October 20. The shape of the polynya changed remarkably in several days. We speculated that annual variability of sea ice cover and consequently polynyas is mainly caused by the Westerly winds.

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