CCAMLR

1. We examine the spatial distributions of pelagic seabirds and. fur seals near South Georgia, and asked to what extent the distributions of these predators were influenced by the spatial distribution of their principal prey, Antarctic krill Euphausia superba Dana. One novel aspect of our analysis is an explicit consideration of the separation in space between swarms of krill and aggregations of predators that feed upon krill.
2. Our data were collected in February 1986, during a systematic shipboard survey of the waters surrounding Bird Island, South. Georgia. Predator abundance was estimated visually using strip transects, and krill abundance was simultaneously estimated using a hull-mounted echosounder.
3. We approached the difficult analytical problems associated with spatial distributions of organisms by using spatial autocorrelation and cross-correlation analysis, regression models with spatial terms, and randomization tests. The randomization tests involved repeated simulations of predator distributions, and subsequent estimation of spatial association between predators and prey.
4. Pelagic birds and seals were distributed in a strikingly non-random fashion at sea near South Georgia; their distributional patterns were strongly influenced by the distribution of krill swarms.
5. Differences between predators in their spatial distribution and in their response to krill swarms suggest interspecific differences in foraging strategies.

Published in Journal of Animal Ecology (1993) 62, 000-000

We studied the distributions, abundances and interactions of macaroni penguins Eudyptes chrysolophus, Antarctic fur seals Arctocephalus gazella, and their zooplankton prey, in particular Antarctic hill Euphausia superba, near Bird Island, South Georgia, South Atlantic Ocean, in February 1986. Simultaneous surveys of marine birds, Antarctic fur seals and Antarctic krill were conducted along a series of transects radiating from the breeding colonies of the vertebrate predators. We examined the relationships between the distributions of predators and their prey with respect to the abundance of krill in the water column and marine habitats near the colonies. Antarctic fur seals and macaroni penguins showed positive correlations with Antarctic krill density across a wide range of spatial scales. Because krill was abundant dose to the colony and predator densities decreased with distance due to geometry, distance from colony was a confounding variable. When the influences of distance and direction on predator abundance were factored out, we were able to demonstrate an additional influence of Antarctic krill abundance at measurement scales between 10 and 100 km for Antarctic fur seals and for macaroni penguins at the scale of 70 to 100 km. Water depth was an important correlate of Antarctic krill and Antarctic fur seal abundances but not of the abundance of macaroni penguins. 'We found no evidence that the fur seals or macaroni penguins were concentrating their foraging for krill in the vicinity of the shelf-break.

Growth of upper canine teeth of male Antarctic fur seals (Arctocephalus gazella) which died of natural causes at Bird Island. South Georgia, was quantified from measurements of annual layers in longitudinal sections of teeth. Mean age at death was 7∙69 ± 0∙07 years and this showed a small but significant increase through the period when samples were collected (l972/73–1988/89). There were significant correlations between morphometrics of teeth and those of seals, suggesting that tooth growth provided an indication of body growth, Tooth growth rate was lowest in seals which died early (age 4 years) and increased with age at death. Changes in the growth pattern of teeth suggested that fur seals which became sexually mature early also died early. Tooth growth layers deposited in each calendar year were compared with the expected layer depth based on a linear relationship between layer depth and age at which each layer was deposited. There was significant variation in the depth of tooth growth layers deposited in different years, suggesting that growth was greater in some years than others. No trends in cohort strengths were detected, but particularly poor years for growth were closely related to years in which reproductive performance was also observed to be low, Variations in growth from 1967/68 to 1987/88 were correlated significantly (P

We studied the influence of sex of pup, maternal age, birth date of pup, number of foraging trips, and the mean duration of both foraging trips at sea and nursing visits ashore on the growth and mass at weaning of pups of Antarctic fur seals (Arctocephalus gazella) during the austral summers from 1988 to 1990. Although growth and mass at weaning were highly correlated, they were not related to maternal characteristics in 1988 or 1989. However in 1990 there was a negative relationship between growth of pup and mean duration of foraging trips. Growth rates of male and female pups varied considerably between 1972 and 1991 and appeared to decline from 1984 through 1990. Methods used to collect and weigh the pups influenced the nature and magnitude of sex differences in estimated growth rates. Growth rates of male and female pups did not differ when weighed serially (same individuals weighed throughout lactation), but males grew faster than females when weighed cross-sectionally (different individuals weighed throughout lactation). Based on our results of pairs of mothers and pups followed over the lactation period, maternal investment was greater in sons than daughters because males were heavier at birth and older at weaning than females and not because of any differential growth between the sexes. Mothers appear to have to work longer but not harder to wean male pups than female pups. Under the favorable feeding conditions that normally exist, individual differences in the growth of pups are most likely influenced by variation in foraging efficiency of mothers.

Data on breeding population size and breeding success in gentoo penguins at Bird Island, South Georgia from 1977-1992 are used, in conjunction with empirical (and some hypothetical) data on survival and recruitment rates, to model the fluctuations in breeding populations, taking account of variations introduced by good and bad years (as classified on the basis of breeding success). There is generally good agreement between observed and predicted breeding populations, except in four years, when major population changes (large decreases followed by substantial increases) occurred. Three of these years were associated with reduced availability of krill, one with very cold winter and spring conditions. Comparing model and reality indicates that deferred breeding could account for the discrepancy in one year, and for part of the differences in two other years, when mortality rates must also have been higher. In the remaining year, when the increase in population greatly exceeded the preceding decrease, it is likely that some immigration occurred. Detailed field studies from 1987-1991 established that the population decline in 1988 was indeed attributable to substantial deferred breeding coupled with higher rates of adult mortality. Emigration was most unlikely to be involved; no data are available on immigration. Gentoo penguin population dynamics are disproportionately effected by the consequences of infrequent bad years; any increase, natural or artificial, in the frequency of such events might have serious consequences for population trends.

An activity recorder weighing 24 g with on-board data storage, designed to record data relating to seabird activity and behaviour at sea, is described. The principles, the design specification and the circuit description of the device are presented, together with data from field tests on Wandering Albatrosses Diomedea exulans to illustrate performance.

Published in Ornis Scandinavica 00-0 (1992) Ornis 23795/1433

Population dynamics of Black-browed and Grey-headed Albatrosses were studied at Bird Island, South Georgia for 17 consecutive years (1975-1991). Over this period almost all the Grey-headed Albatross colonies decreased, at an average rate of 1.8% per annum. Although the total Black-browed Albatross population increased (at 0.8% p.a.), 14 of the 23 colonies (including both study colonies) decreased. Black-browed Albatrosses follow an annual breeding cycle, with over 80% of birds successful in rearing a chick and 75% of those failing to do so returning to breed the next year, 5- 10% of both categories delaying one further year (even when still paired). Grey-headed Albatrosses are essentially biennial,

Estimates are provided for crabeater seal life-history parameters, to be incorporated into a simple model of the functional relationships between krill escapement and crabeater seal demographic performance. The crabeater seal parameters were estimated from seals collected near the Antarctic Peninsula between 1964 and 1990. Average annual survival rate of adults was estimated to be 0.93. Age at sexual maturity was estimated to be 3.8 years. Of 44 annual estimates of historical cohort strength, 16 were judged to represent “ good" years for demographic performance, 18 as "poor" years, and 10 as "bad" years.