CCAMLR

Antarctic fur seal, Arctocephalus gazella, pup growth rates were measured using CEMP Standard Methods (C2 - Procedure B) over four consecutive Austral summer season (1994/95-1997/98) at CEMP Site and SSSI N°32 Cape Shirreff, Livingston Island, South Shetlands. Every fortnight (15 days) 100 pups (50 of each sex) were weighed by cross-sectional sampling. Pup growth rates were determined from least square linear regression of weight against age. Strong correlation was found between variables for both sexes, and assumptions of linearity and homogeneity of variance proved to be adequate (? =0.05).
For comparison purposes we contrasted our data with values reported for Bird Island, South Georgia (1973-1987). From this comparison, Cape Shirreff's male pups resulted to have a faster growth with less deviation from the mean, while females on both sites had very similar growth rates. If these growth rate patterns remain similar for equal time series, it could make sense to suggest that Cape Shirreff's male pups grow faster in order to undergo with better body conditions higher latitude associated problems, although female data would not support this hipothesis.
Highest growth rate for males was attained in 1995, and females in 1994. Conversely, lowest growth rate for males was attained in 1994, and females in 1995 and 1996. This could be explained by differential maternal expenditure between pup sexes, although this hipothesis has been suggested as invalid by Lunn and Arnould (1997). Further conclusions will have to be tested with larger data sets in order to establish possible differences on reproductive strategies between populations of A. gazella.
An important decrease in A. gazella's population was observed during 1997/98. No evidence for an ENSO phenomenon influence is explained by pup growth rates until present.
Pup growth rates might be influenced indirectly by sea-ice extent, and directly by krill or salp dominance, since the highest value of male growth rate (1995/96) was attained when large sea-ice extent was reported, while the two lowest growth rates for males (1994/95 and 1996/97) were attained when less sea-ice was evidenced. This pattern is surprisingly not followed by females, which appear to have no relation with sea-ice variation.
Four years of data is apparently not enough to sustain all hipotheses described due to some incoherence between sexes, and conclusions drawn are necessarily tentative, but could serve to expose limitations of particular schemes and to give a first insight into variation of Antarctic fur seal reproductive performance in the CEMP site with relation to the local marine environment.

Variability in the reproductive performance of marine predators may be a result of physical forcing by large-scale oceanographic variability. Time lags, remoteness from the epicentre of a physical process and the simultaneous action of multiple physical processes often mean that it is difficult to link variability in predator performance with specific measurements of oceanographic variability. This study examined variation in the foraging behavior of lactating Antarctic fur seals (Arctocephalus gazella) over 15 years at the island of South Georgia in relation to major indices of southern hemisphere climate variation. Fur seal foraging trip duration was transformed into a normally distributed index of environmental variation. In a multiple regression analysis, the El Niño/southern oscillation index (ENSO) and a measure of the annual sea ice extent both had significant effects on the fur seal foraging index but both had the greatest effect when entered into regression models together. There was also a significant effect of the interaction between the ENSO and sea ice indices on the fur seal foraging index. There was little effect of a krill recruitment index upon the fur seal foraging index, either alone or when in combination with ENSO or sea ice indices. Lagged cross-correlations showed that the ENSO and sea ice indices had strong effects when lagged by one year. This was supported by bivariate correlation between the monthly ENSO means and the fur seal foraging index. These results show that the foraging behavior of fur seals in the Atlantic domain of the Southern Ocean is sensitive to the proximate physical forcing by a combination of physical variability occurring in the central tropical Pacific as well as in the Antarctic.

Central to understanding krill population dynamics is knowledge of their population structure. To examine this we used length-frequency distributions from 142 weeks of sampling (n= 23996 krill) of 3 predator species breeding at South Georgia and 12 weeks of sampling (n = 10 252 krill) from scientific nets from the same area over the summers of 1991-1997. In comparing the 5 years with both predator and net samples, despite differing selectivities and spatio-temporal circumscriptions, both were sampling the same overall krill population. Greatest similarity results from comparing net samples with samples from Antarctic fur seal and macaroni penguin combined; least temporal variation occurs in predator samples from late summer (March). From the 7-year predator time-series, within-year variation was greatest in 1991 and 1994, both years of low krill biomass at South Georgia. In both of these years large krill dominated during December but were completely replaced by small krill by February. The mean length of the March krill population showed a regular increase from 1991 to 1993, fell to a minimum in 1994 and thereafter increased steadily to 1997. Using these data in conjunction with putative size/age-group cohorts in the length-frequency distribution, we suggest that year's of high mean krill length reflect failure of small krill to recruit into the population, producing a period of low krill biomass in the following year. Similar recruitment failure in the same years is evident in krill populations in the Antarctic Peninsula region to the south, indicating large-scale events. This supports suggestions of periodic fluctuations in krill production and recruitment which may relate directly to physical phenomena such as cycles in the distribution and extent of sea-ice.