CCAMLR

A census of the breeding population of Antarctic fur seals (Arctocephalus gazella) at South Georgia was carried out during the 1990/91 breeding season. Using counts of adult females ashore at the breeding grounds during the pupping period, together with corrections for the likelihood of a female being ashore at a census and for pregnancy rate (71 % in 1990/91), pup production was estimated as 269,000 (95% confidence intervals 188,000 - 350,000). The breeding population in 1990/91 was reduced at long-term study sites probably because of a short term reduction in food availability. Data from these sites were used to estimate the pup production of the population had 1990/91 been a typical year. Based on values from 1983/84 to 1990/91, pup production in 1990/91 would have been 378,000 (S.E. = 19,100) if it had been an average year. The annual increase from 1976/17 to 1990/91 was 9.8% which shows that the rate of increase in pup production has declined since the initial period of population expansion in the 1950s and 1960s. Increased population size has led to an expansion of the breeding range at South Georgia.

We studied diving patterns and performance (dive depth, duration, frequency and organization during the foraging trip) in relation to diet in nonbreeding Gentoo Penguins (Pygoscelis papua) over 59 days (involving 5,469 dives) in winter. We estimated foraging ranges and prey capture rates, and compared foraging behavior with that of breeding (chick-rearing) birds. Foraging was highly diurnal with 98% of foraging trips completed during the same day. Foraging-trip frequency was 0.8/day, trip duration was 6-8 h, and birds spent 51-62% of the foraging trip diving. Dive depth and duration were bimodal. Shallow dives (30 m; 55% of total number and 81% of dive time) averaged 74-105 m and 2.7-3.5 min, respectively. Deep-dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals two to three times dive duration. Deep dives showed clear diel patterns, averaging 10-20 m at dawn and dusk and 70-90 m at midday. These results are consistent with the patchy vertical and horizontal distribution and diel movements of Antarctic krill, the main winter prey of Gentoo Penguins (including study birds). We suggest that shallow dives are mainly searching dives, and deep dives mainly for feeding. Foraging activity of non breeding Gentoo Penguins in winter is similar to that of chick-rearing birds. The only major differences are that foraging-trip frequency is 20% less and stomach-content mass on return ashore 30% less in winter. We conclude that foraging activity in Gentoo Penguins is changed by varying the frequency and duration of foraging trips, rather than by changing the pattern and rate of diving.

The foraging ranges of six female and four male Adélie penguins breeding at Bechervaise Island near Mawson Station (Mac. Robertson Land) were determined by satellite tracking, using the ARGOS system. Birds were tracked over four foraging trips (by 2 females and 4 males) during the incubation period (November-December 1991) and 17 trips (by 4 females and 2 males) throughout January 1992 when birds were feeding chicks. Most birds made foraging trips to the continental shelf break (1000m isobath) approximately 110 km distant at its closest point. Birds feeding chicks also made journeys of 1-2 days ranging up to 12 km after 17 January when the sea became ice free to the coast. Concentrations of krill Euphausia superba which have in the past been the subject of a fishery occur along the shelf break zone where the birds were foraging. There is potential therefore for overlap between the foraging range of Adélie penguins breeding along the Mac. Robertson Land Coast (approximately 150000 pairs) and any future harvest of krill in the region. The foraging range of the birds at Bechervaise Island considerably exceeds the 15-50 km determined for birds in the South Shetland and South Orkney Islands and reflects the distance offshore of krill one of their major food sources.

Temporal and spatial variability of krill distribution features was investigated at the micropolygon of 8 x 6 miles, where eight consecutive hydroacoustic stations were carried out. Krill aggregations occurred as fields of small swarms of spatial distribution features (size and density of swarms, swarm field density, number of swarms per one mile) varied considerably from tack to tack within each survey. Horizontal extension of swarms amounted to 120 m, however about 70% of swarms were of 30 m in length, with density up to 200 g/m3. About 75% of all swarms revealed bad biomass of less 1 t. Average statistical parameters of swarms at polygon varied insignificantly from survey to survey, while the swarm number varied within the broad range from 1918 to 7000 and further to 1554 units. Krill biomass at polygon varied spasmodically within the range from 1091 to 6085 t. Krill distribution variability revealed at polygon suggests the impulsive nature of krill enter and exit out of the polygon due to its transport by the current. Besides, in the upper layer of 0-50 m the swarm number was a almost constant, and krill redistribution due to transport and diurnal migrations occurred in the layer of 5-150 m. Estimated velocity of krill swarms displacement corresponds to the estimated water transport velocity at the polygon, suggesting the passive krill transport occurred. Krill biomass transported across different tacks also varied spasmodically from survey to survey.

From 18 to 23 April hydroacoustic, oceanological and trawling surveys were carried out within the square of 30 x 30 miles northwestwards of Coronation Island in the fishing fleet operation area. The krill biomass was estimated within the square at the start and the end of works. It amounted to 56.1 thous. t and 61.2 thous. t respectively. During the period remained the hydroacoustic assessment of krill density and oceanological stations were carried out along the square perimeter. Four dublicates of perimeter were made. Control hauls with midwater trawl were made on the regular basis. The average estimates of krill density were obtained by 15-miles intercepts of the perimeter, along with mean water flow and geostrophic currents. The balance of krill input and output for the square was calculated based on these values. In the .first two dublicates the aggregation of krill was observed within the contour and in the second two - loss of krill. The aggregation was 52 thous. t greater than the loss. The researches show that the fishing aggregation stability depends essentially on the heterogeneity of the current's field. The researches were carried out by R/V "Dmitriy Stefanov" owned by PPO "Yugrybpoisk" (Ukraine).

The oceanological, hydroacoustic and trawling surveys were carried out within the polygon of 30 x 30 miles in the fishing area northwestward of Coronation Island in 18-22 April,1992. The krill biomass was estimated in the beginning and at the end of surveys. It amounted to 56.1 and 61.2 thous. t respectively. During the rest of the period the hydroacoustic assessment of krill aggregation density and oceanological stations were carried out along the square perimeter. There were four dublicates of perimeter. The midwater trawl hauls were made periodically. The average estimates of krill aggregation density by 15-mile perimeter sections, average water flow and scheme of geostro-phycal currents were obtained. The balance of krill transport from and into the polygon was calculated. The first two dublicates revealed the krill accumulation in the contour, and the second two showed the loss. The accumulation was 52 thous. t as high as the loss. The researches pointed out that fishing aggregation stability is mainly determined by the water dynamics, such as the availability and duration of heterogenity in the current fields. From 25 to 27 April 1992 three hauls with fishing bottom trawl were made to collect data on size and age composition of icefish, champsocephalus gunnari, green notothenia and yellowfin notothenia over the shelf of South Georgia and Shague rocks. The researches were carried out by H/V "Dmitriy Stefanov" ovmed by PPO "Yugrybpoisk" (Ukraine).