CCAMLR

1. This study examined the costs of reproduction in terms of future survival and reproduction in female Antarctic fur seals from Bird Island, South Georgia. It used mark-recapture data from 11 consecutive years, including 3 years when several indices showed that food availability was well below average.
2. Population age structures were used, in conjuction with the measured age-specific survival rates, to estimate the rate of increase of the population as 10•7% per annum.
3. The average annual survival rate was 0•83 (SD = 0•10) with a range from 0•65 to 0•93. Survival rate showed no trend through time but was weakly correlated with pup growth rate, suggesting that it may be influenced by availability of food. Survival rate was unrelated to any other environmental or demographic parameter including population size.
4. There was no evidence of senescence. Survival rate was not related to year of birth or age, after accounting for variation due to pregnancy and calendar year. Survival was reduced as a result of pregnancy which accounted for 40–50% of adult female mortality. This effect was greatest in the age classes with the highest reproductive output (ages 5-8 years).
5. Mean pregnancy rate was 0•70 (SD = 0•11) with an interannual range of 0•59–0•88. Although females normally produced their first pups at age 3–4 years, pregnancy rate peaked at age 8 years and declined thereafter. Otherwise pregnancy rate was unrelated to the environmental or demographic variables we tested. Food availability during the pup-rearing period had no effect on pregnancy rate. 40–50% of failures to become pregnant related to animals having been pregnant in the previous year.
6. Reproduction incurs costs to females, in terms of reduced survival and future fecundity, and consequently, on average, females which survive longest tend to do so because they have lower fecundity.

During sustained bouts of diving, predators like fur seals may adjust the time they spend diving to maximise the time they can spend foraging and minimise the time spent at the surface between dives. To examine this, swimming speeds and the time allocated to different parts of the dive cycle were measured in 10 adult female Antarctic fur seals (Arctocephalus gazella) while they were foraging at sea. Mean swimming speeds during diving ranged from 1.32 to 1.99 ms-1 and 90% of diving swimming speeds within individuals were between 1 and 2.5 ms-1. This represented a narrower range of speed than was exhibited by animals when swimming at the surface. Swimming speeds were fastest during the descent and ascent phases of dives with a reduction in speed near the bottom of the dive, when the seals were assumed to be feeding on krill. Surface interval increased as a curvilinear function of dive duration and was influenced by diving swimming speed. This relationship was, on average, close to that predicted by a model (Houston & Carbone, Behav. Ecol., 3, 255-265) which suggested that the metabolic rate was greatest during the foraging phase of dives (5.9 times predicted BMR) than during the ascent or descent (3.6 time predicted BMR). Deep diving (>30 m) and high swim speeds also incurred costs in terms of reduced foraging time and may explain why mean dive depths for individuals were within the range of 12-33 m. These data broadly support the predictions of models of diving behaviour based on balancing the supply of, and demand for, oxygen and the principles that fur seals are attempting to maximise the time they spend within the foraging area.

The pattern of prey distribution can profoundly affect the foraging behavior and success of a predator. In pelagic marine ecosystems, where prey is often patchily distributed, predators must be able to adapt quickly to changes in the spatial patterning of prey. Antarctic fur seals feed primarily on krill, which is patchily distributed. When combined with information about swimming speed on the surface, the time taken for a fur seal to locate a new patch after leaving an old one is an indication of the distance between patches. The frequency distribution of intervals between bouts of foraging showed that fur seals foraged at two spatial distributions: (1) a fine-scale (median distance 0.18 - 0.27 km) represented by short (5 rain) travel durations. In a study lasting 5 years, the distributions of travel durations between bouts of feeding changed between years. These changes suggested either that the structure and/or the spatial distribution of krill swarms varied between years. The behavior of fur seals suggested that there was overall clumping of prey at the fine-scale but there was a more even spacing of prey patches at the meso-scale level. Only in one year of the study (1990/91) were there indications that fur seals had difficulty in finding enough food. Fur seal behavior suggested that there was no reduction in the number of prey patches available in that year but that prey patches were of poorer quality. The study showed how predator behavior can provide valuable information about the functional relationship between prey dispersion and predator performance.

An attempt was made to develop simple, inexpensive, rapid means of determining body composition in Antarctic fur seals (Arctocephalus gazella). Measurements of total body water (TBW) and total body lipid (TBL), obtained by hydrogen isotope dilution, were compared to the results of bioelectrical impedance analysis (BIA) and morphometric indices of body condition in 52 adult females. TBW was weakly correlated with BIA measurements of resistance (r = -0.30, P

In connection with future calculation of volume of krill immigration/emigration (flux) in the choosen polygones, the proves of active long-distance migrations of krill are considered. These proves are not undoubted. The most difficult problem, which nevertheless should determine the results of calculations, is the valuation of krill retention time. To make it more correct and natural it is necessary to take into account the biological characteristics of krill, especially for the regions outside the shelf and slope areas of investigating regions.

Krill sampling was carried out onboard RV ‘Polarstem’ from January 25 to March 11, 1994 south of 66°S, between 68°W and 120°W. Krill Euphausia superba abundance and biomass was in the lower range of values generally found in the Antarctic Peninsula and Elephant Island region. A distinct spatial separation for size groups was observed for krill, with small size groups being more abundant in the East Wind Drift zone and larger ones further north under the influence of West Wind Drift waters. The overall krill length frequency distribution was similar to the composition reported from the South Shetland Island region for the same summer period. The recruitment index for krill indicated a poor recruitment success of the 1992/93 year-class in the region (R1 = 0.076). Both results indicate large scale effects on the krill stock. Spawning was late during the studied season, no larvae were found in the area. These findings were discussed in the light of recently described correlations between winter sea-ice conditions, krill spawning and recruitment success and let to the conclusion that recruitment of the 1993/94 kri11 year-class will be poor.