The distribution of foraging activity for female Antarctic fur seals was investigated at Cap Noir (49°07' S, 70°45' E), Kerguelen Island in February 1998. Eleven females were fitted with a satellite transmitter and time-depth recorder. The 2 data sets were combined in order to locate diving activity of the seals. The occurrence of fish in the diet of the seals was investigated by the identification of otoliths in 55 scats collected at the breeding colony during the study period. Oceanographic variables were measured simultaneously by direct sampling and satellite remote sensing. The mesopelagic fish community was sampled at 20 stations along 4 transects, where epipelagic trawls were conducted at night at 50 m depth. We then investigated, using geographic information systems, the relationship between the spatial distribution of diving activity of the seals and oceanographic variables (sea surface temperature, surface chlorophyll concentration, prey distribution and bathymetry) at the same spatio-temporal scale. An inverse relationship was found between the main fish species preyed on by the fur seals and those sampled in trawl nets. However, diving activity of the seals was significantly related to oceanographic conditions, forage fish distribution and distance from the colony, although these relationships changed with the spatial scale investigated. A probabilistic model was developed for the distribution of diving activity, which predicted where females should concentrate their foraging activity according to the oceanographic conditions of the year, and where breeding colonies should be located.

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Whereas it is accepted that the population dynamics of higher organisms is strongly grounded in life history processes, such as the time taken to mature and reproduce, regulation in the abundance of aquatic protists is generally attributed to proximate properties of the environment in which they grow. We used 10 yr of data from the Gulf of Naples to determine the life history of a planktonic diatom, Pseudo-nitzschia multistriata, through the analysis of cell abundances and cell size patterns. Asexual and sexual phases recurred with remarkable regularity. Maximum abundance occurred annually, between the end of summer and the beginning of autumn, but cohorts of large cells, derived from sexual events, were found only every second year. We developed a model of population growth, based on parameters determined from laboratory cultures, with further tuning using information from natural populations. The model simulated the birth, maturation, and disappearance of age classes like those in natural populations, but only when we imposed seasonal variation in the rate of cell division and timed sexual reproduction during the stationary phase of a bloom. The model predicts that P. multistriata will become locally extinct if sexual reproduction does not occur within 4 yr. Our data and model show that coherent life cycle properties can emerge in natural populations of unicellular organisms, analogous to those in multicellular organisms, as a result of finely tuned regulation of cell division and sexual competence.

The large temporal and spatial variability in marine productivity encountered by marine predators may negatively influence breeding success. The Antarctic fur seal Arctocephalus gazella (AFS), a marine predator in the Southern Ocean (SO) ecosystem with a circumpolar distribution, exhibits a short, 4 mo lactation coinciding with increased summer marine productivity. The diet of AFS, and the distance to significant and productive oceanographic features, such as the Antarctic Polar Frontal Zone (PFZ), varies considerably between populations. We studied the foraging activity, foraging efficiency and the pup provisioning strategies of lactating AFS at a key breeding site in the southern Indian Ocean, the Kerguelen Archipelago. Foraging parameters were examined in relation to interannual variability in oceanographic conditions and prey availability in the PFZ over 3 consecutive breeding seasons (1998 to 2000). The location of foraging zones, diving activity, diet and foraging efficiency varied significantly between years, concurrently with annual changes in seasurface temperature (SST) and prey availability. The strongest recorded El Niño Southern Oscillation event in 1997-1998 coincided with anomalously warm waters in the vicinity of the Archipelago. Deeper diving by females, reduced maternal and pup body condition, and minimal pup growth rates and low catch per unit effort of the primary prey species, lanternfishes (Myctophidae) were all recorded in this period. Maternal size was positively related to the growth performance of pups only in this period, indicating the importance of age/size and/or experience in mediating environmental fluctuations. Foraging efficiency over a foraging cycle and variability in mean provisioning rates (trip duration), were identified as proxies of prey availability within the foraging range of seals, emphasising the effectiveness of the use of AFS foraging behaviour as an indicator of both food and oceanographic variability and climatic anomalies. The increasing frequency of anomalously warm SST events in sectors of the SO, however, may elicit specific behavioural responses from 'central place foragers' (i.e. species that return to breeding sites to feed their young) to avoid sustained poor body condition of females and their weaned offspring.