CCAMLR

A U.S. flagged commercial factory trawler, the Top Ocean, started fishing operations for krill (Euphausia superba) in Area 48 in July, 2000. This fishery has continued and expanded each year since the initial fishing trials. This paper presents information on the development, yields, and decision making processes involved in harvesting krill by the U.S. fishery. Because the Captain of the Top Ocean had no prior experience fishing for krill, anecdotal and historical information served as the initial basis for decision making. Initial fishing trials in 2000 were conducted in Bransfield Strait and north of South Georgia; in 2001, all fishing was conducted off the South Shetland Islands and Bransfield Strait. In 2002, fishing operations were carried out off the Antarctic Peninsula, west of Elephant Island; and northwest of the South Orkney Islands. Information on set locations, effort, yield, catch rates, and the decision making processes involved in prosecuting the U.S. commercial fishery for krill by each month and region fished are summarized. The decision making processes involved during fishing operations were based on several factors, including krill abundance, weather, ice conditions, condition of krill in relation to the target product, and ad hoc information from nearby fishing fleets. High concentrations of krill were found in Bransfield Strait in 2001 while fishing inside the ice edge. The success of the fishery has increased each year due to factors related to the experience of the Top Ocean. Increasing catch rates with time are likely related to the experience of the Captain, as opposed to indices of krill abundance.

Satellite monitoring of sea surface temperatures (SST) off South Georgia (Subarea 48.3) which includes both analysis of real-time data from vessels and buoy stations provides constant information on the temperature conditions of the area. Weekly SST maps constructed from GOES-E and Meteosat-7 daily satellite data are used to develop maps of mean monthly SST and SST anomalies. For quantitative monthly analysis of variations in temperature distribution and SST anomalies in the South Georgia waters in 12.1989/03.1991 and 11.1999/04.2002 we have selected Cells 1 and 2 (2°x2° resolution, centered at 54°S 41°W and 53°S 37°W, respectively). Temperature values of monthly trends of mean SST and SST anomalies in Cell 1 and 2 are calculated with precision of 0.01°C.

Understanding the demographics of Antarctic krill over large scales may be complicated by regional differences in the 11 processes that govern population structure. The influence of regional differences in growth and mortality on population size 12 structure was examined using data on the length–frequency distribution of krill in the Scotia Sea using samples from the South 13 Shetland Islands and South Georgia collected annually from 1991 to 2000. A correction function, which took account of the 14 higher growth rate at South Georgia, produced a consistent similarity in the position of the modal size classes that was not present 15 in the raw data. Optimising the mortality rate, to minimise the differences in the growth corrected length–frequency distribution, 16 suggested a higher mortality rate at South Georgia that the South Shetlands. The intra-specific variations in growth and mortality 17 rates are consistent with published values and with other Euphausiids species. Having accounted for the demographic plasticity, it 18 is apparent that strong recruitment of the smallest size class of krill is represented in both populations simultaneously. It appears 19 that first-year krill are advected into different regions of the Scotia Sea where the resultant population size structure is determined 20 by regional differences in growth and mortality. The majority of the commercial harvest of krill in the Antarctic occurs in a 21 relatively small number of regional fisheries within the Scotia Sea and is managed using population models based on a single set 22 of demographic parameters. Where substantial differences in these parameters exist between fishing areas, the calculation of 23 catch limits should take these differences into account.

Adélie (Pygoscelis adeliae) and chinstrap penguins (P. antarctica) are morphologically and ecologically very similar, have very similar diet and breed sympatrically in the Scotia Arc from the South Sandwich Islands to the Antarctic Peninsula. To investigate how these two species co-exist, their foraging distribution and diet were studied during the chick-rearing period at Signy Island, South Orkney Islands during the breeding seasons of 2000 and 2001. Satellite tracking data from of 19 Adélie penguins and 24 chinstrap penguins were used to compare foraging distributions. In both years the diet of both species was exclusively Antarctic krill (Euphausia superba) of the same size range. In a year of low prey availability (2000), there was a statistically significant segregation of foraging areas between the two species, however, in a year of normal resource availability (2001) there was no such segregation. There was a significant difference in the foraging areas used by Adélie penguins between years but not for chinstrap penguins. Adélie penguins foraged significantly farther (mean 100 km) from the colony than chinstrap penguins (mean 58 km) in 2000 but not in 2001 (mean 58 km and 35 km respectively). In 2000, the breeding success of Adélie penguins was 51% lower than the long-term mean compared to 15% lower in chinstrap penguins. Both species achieved above average breeding success in 2001. The changes in foraging distribution and breeding success suggest that in years of low resource availability, chinstrap penguins may be able to competitively exclude Adélie penguins from potential inshore foraging areas. Current trends in climatic change and possible effects on ice distribution and krill abundance suggest that conditions could become less favourable for Adélie penguins than chinstrap penguins in areas where both species occur.

The measurement of spatial overlap between predators and fisheries exploiting a common prey source is dependent upon the measurement scale used and the use of inappropriate scales may provide misleading results. Previous assessments of the level of overlap between predators and fisheries for Antarctic krill Euphausia superba in the South Shetland Islands have used different measurement scales and arrives at contradictory conclusions. At-sea data from observations of krill predators during the CCAMLR 2000 krill survey were used to identify the areas of potential overlap with fisheries in the Scotia Sea and to determine the scale at which such overlap should be measured. The relationship between auto-correlation and sampling distance was used to identify the characteristic scales of the distribution of predators, krill and krill fisheries and an effort-corrected index of relative abundance as a function of distance from land was used to identify the characteristics of areas of high potential for overlap. Despite distinct differences in foraging ecology a group of krill-dependent species including chinstrap penguin Pygoscelis antarctica, (Antarctic) fur seal Arctocephalus sp. (gazella) and white-chinned petrel Procellaria aequinoctialis showed similar patterns of distribution; the relative abundances were highest at 60 - 120 and decreased sharply t distances greater than 150 km from land. There was more inter-specific differences in the characteristic scales which were of the order of 50 - 100 km. Antarctic krill had a characteristic scale of c 200 km and the relationship with distance from land showed a log-linear decline. Krill fisheries operated at a scale of 150 km and almost all of this operation took place within 100 km of land. The requirement of land for breeding and the biological and oceanographic conditions that produce high concentrations of krill associated with those islands produce a system in which the demand for Antarctic krill from fisheries and predators is essentially co-extensive. The areas of greatest potential overlap are within 150 - 200 km of land and the extent of any such overlap in these areas should be assessed at scales of 70 - 100 km to accommodate the scales of operation of the predators involved.

In the north-eastern part of South Georgia Island shelf (Subarea 48.3) on 30 July 2001 for the first time we found out young and mature antarctic krill Euphasia superba individuals affected by the disease that had not been described earlier. In the period of winter and spring some males and females Euphasia superba of all size groups - from 27 to 52 cm - were affected. From winter to spring the percentage of krill invasion increased 2.3 times. In shelf zone and on the continental slope of the South Georgia Island northern part, where definite currents provided for isolation of krill aggregations, affected individuals occurred everywhere.

A history of development and completion of tasks put forward by WG-EMM is summarised for the period 1995-2001.

The diet of non-breeding male Antarctic fur seals Arctocephalus gazella was investigated at Harmony Point, Nelson Island, South Shetland Islands, by the analysis of 523 scats collected from January to March 2001 and 2002. The composition of the diet was diverse and both, pelagic and benthic-demersal preys were represented in the samples. Overall, the Antarctic Krill Euphausia superba and fish were the most frequent and numerous preys, followed by penguins (presumably Pygoscelis antarctica), cephalopods (mainly squids) and gastropods. Among fish, Myctophids represented 86.5% and 65.8% of the fish mass in both seasons, with Gymnoscopelus nicholsi being the main prey. Interestingly, penguins were represented in the 39.0% and 31.9% of the samples in 2001 and 2002 and, as reflected by the reconstructed diet, was the main prey by mass (74.0% and 76.1%). The occurrence of penguins in the diet of A. gazella at Harmony Point is discussed and analysed in relation to the foraging strategy used by seals and to the temporal prey availability.

The diet of non-breeding male Antarctic fur seals Arctocephalus gazella was investigated at different localities of the Antarctic Peninsula (Cierva Point and Hope Bay), South Shetland (Deception Island and Potter Peninsula) and South Orkney (Laurie Island) islands, by the analysis of 438 scats collected from January to March 2000. The composition of the diet was diverse and both, pelagic and benthic-demersal preys were represented in the samples. The Antarctic krill Euphausia superba was the most frequent (except at Cierva Point) and numerous prey at all the study sites, being followed by fish, penguins and cephalopods. The Antarctic krill also predominated by mass being followed by fish or penguins. Fish were the second most important prey by mass at the Antarctic Peninsula whereas penguins were at the South Shetland and South Orkney islands. Among fish, Pleuragramma antarcticum was the species that most contributed to the diet of the Antarctic fur seals at the Antarctic Peninsula whereas Gymnoscopelus nicholsi was at the South Shetland and South Orkney islands. The results are compared with previous studies and the possibility of implement monitoring studies on the distribution/abundance of Myctophids and P. antarcticum based in the analysis of the diet of the Antarctic fur seal is considered.

The diet of non-breeding male Antarctic fur seals Arctocephalus gazella was investigated at the Danco Coast, Antarctic Peninsula, by the analysis of 31 and 149 scats collected from January to March 1998 and 2000 respectively. Overall fish and krill, followed by penguins and squids, were the most frequent prey and constituted the bulk of the diet. The importance of the remaining taxa represented in the samples (octopods, gastropods, bivalves, isopods, polychaetes and porifera) was negligible. Among fish, Channichthyids constituted the bulk of the diet with Chionodraco rastrospinosus and Chaenodraco wilsoni, followed by the Nototheniid Pleuragramma antarcticum, being the main prey. The Myctophid Electrona antarctica was the most frequent and numerous fish prey. The results are discussed and compared with those reported for the South Shetland Islands, the closest area from where similar information is available.