CCAMLR

The cephalopod diet of the Gentoo penguin, Pygoscelis papua and the Antarctic fur seal, Arctocephalus gazella was comparatively analyzed at Laurie Island, South Orkney Islands. A total of 125 stomach samples were collected by the water off-loading method from Gentoo penguins during the autumns of 1993, 1995 and 1996, and 39 fur seal scats were collected from mid March to April 1988. Cephalopods preyed upon by Gentoo penguins were represented by 1974 beaks (1628 lower, 346 upper) which occurred in 50.4% of the samples. Lower beaks identified belonged exclusively to the squid Psychroteuthis glacialis. The mean lower rostral length (LRL) of these beaks was 1.1 mm (range 0.4 - 1.8 mm). From the Antarctic fur seal scats 103 beaks (41 lower, 62 upper) were removed from 60.6% of scats which contained prey remains. The cephalopod species identified were Slosarczykovia circumantarctica and P. glacialis which constituted 78.8% and 21.1% in terms of numbers, respectively. The mean lower rostral length for S. circumantarctica was 2.7 mm (range 2.0 - 3.5 mm), while that of P. glacialis was 1.6 mm (range 1.0 - 2.5 mm). The foraging behaviour of the two top predators was analyzed and discussed according to the composition and size of their cephalopod prey.

An ecosystem approach for the management of human activities in the Southern Ocean is enshrined in the principles of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The implementation of such an approach requires an understanding of the wider dynamics of the ecosystem, which is best achieved through the development of ecosystem models. However, not all models will be suitable for developing an ecosystem approach to management. To facilitate the development of ecosystem models appropriate for CCAMLR, we review the existing models of Southern Ocean ecosystems that include krill and the higher trophic levels. We also briefly consider modelling approaches from elsewhere in the world. The main categories we consider are models of krill populations and life cycles, predator-prey models and models of ecosystems. A range of approaches has been developed in each of these categories and we review the major results of each approach. Finally, we discuss the issues highlighted by the studies that are still relevant today, and we note where major requirements for model development were identified.

Results of acoustic surveys carried out in winter months of 2000 and 2002 demonstrate significant distinctions in spatial distribution patterns of krill in the northwestern and the northeastern parts of South Georgia area. The boundary between two areas is located at about 37°30/ W. It is shown that in winter months in the northwestern part where foraging areas of dependent predators are located is non-attractive to fishery . The observed grounds with krill density exceeding the threshold value 100 g/m2 determined as potential fishing grounds were located in the northeastern part of South Georgia.
Comparison of krill aggregations structure in the northwestern and the northeastern parts of South Georgia area allows to assume that dispersed aggregation (layer and irregular forms) much more suits to the foraging tactics of dependent predators than krill distribution in the form of dense swarms or patches, which on the contrary are attractive to the fishing fleet. The considered results show that not only krill biomass density, but also its availability determined by krill aggregations distribution, will be very important both to fishery and to dependent species,

The Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) is currently considering plausible models of the Southern Ocean ecosystem within the Working Group on Ecosystem Monitoring and Management (WG-EMM). This paper describes properties for two groups of marine mammals that may be included in future ecosystem models of the Southern Ocean: cetaceans and pack-ice breeding seals. Important ecological differences exist among and between these groups, which should be considered in the development such models.

The extent to which the assumptions underlying line transect sampling are satisfied in shipboard surveys of crabeater seals hauled-out on the Antarctic pack-ice is examined. Crabeater seals showed little movement in response to the approaching ship. Movement away from the ship by seals close to the ship’s track was partially responsible for a relative lack of sightings close to the transect-line, but otherwise had little effect on the sighting histogram. Minor deviations from the transect direction to avoid running over seals violated the assumption of uniform distribution of groups, and contributed to a relative lack of sightings, close to (

Variability in the Southern Ocean is often characterised by fluctuations in the distribution and abundance of a single dominant zooplankton species, Antarctic krill Euphausia superba. At South Georgia interannual variability in the krill-based marine ecosystem has historically been most frequently detected in the response of upper-trophic level predators. Analysis of the changes in the population size structure of krill in the diet of Antarctic fur seals Arctocephalus gazella, particularly associated with periods of low krill biomass, has shown that the population dynamics of krill is a major factor in driving the inter-annual variability in its abundance. The ability to sample krill in the diet of predators at temporal scales not available using conventional (i.e. ship based) sampling methods has provided the basis for a re-evaluation of the role of recruitment variability and high rates of growth and mortality in generating the high amplitude of variability in krill abundance at South Georgia. Furthermore the production of a consistent index of krill population size composition from the diet of predators at Bird Island over the past decade has provided evidence for a relationship between sea-surface temperature and the level of krill recruitment. Krill-dependent predators not only show distinct behavioural responses to changes in krill abundance but also provide critical dietary data with which to elucidate the mechanisms underlying those changes. Using predators as samplers of commercial prey species can provide information on the key life-history parameters of prey species that are fundamental to reducing uncertainty in fisheries management models.

We present an initial analysis of the fishing locations, fishing depth and length-frequency distribution of krill at South Georgia during the winter of 2002 and 2003 and compare these with the length-frequency distribution and frequency of occurrence of krill in the diet of Antarctic fur seals. There were significant differences in the mean size of krill taken by vessels/measured by observers that should be addressed prior to more detailed analysis, nevertheless there was considerable overlap in the size composition of krill in the fishery and the diet of Antarctic fur seals. During the period of the winter when there was a reduction in the frequency of occurrence of krill in the diet of seals the fishery appeared to operate at greater depth suggesting a possible depth change of krill during winter. It may be appropriate to review the number of krill measured by observers in order to ensure that other sufficient time can be allocated to other activities, especially the assessment of by-catch.

The current approach to providing advice on the status of the krill-centric ecosystem relies on the evaluation of statistical anomalies in the CEMP database. A new approach based on the ordination of variables according to functional groupings is suggested. This approach uses the methodology developed within WG EMM to produce composite standardised indices (CSIs) from matrices containing missing data to summarise the variability in CEMP parameters.

The methods and presentation of CEMP parameters A1, A5 and A7 where evaluated using simulated time-series data. The effects of sampling timing and intensity during five-day periods for measures of arrival and fledging mass suggested that situations where sampling is distributed unevenly around the peak arrival/fledging date may introduce substantial bias in CEMP parameters A1and A7. The description of foraging trip duration using the mean arising from a bimodal distribution of trip durations may provide a useful index of foraging performance, however, the use of the 90th percentile of the cumulative foraging effort may provide a more sensitive measure of changes arising from changes in foraging strategies of penguins.

The Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) is currently considering plausible models of the Southern Ocean ecosystem within the Working Group on Ecosystem Monitoring and Management (WG-EMM). The icefish, Champsocephalus gunnari, is one of the key components in the subantarctic marine ecosystem in the Scotia Sea and northern Kerguelen Plateau areas, as well as supporting commercial fisheries. Data on the species’ distribution, biology, ecological interactions and susceptibility to environmental change are summarised for use in ecological modelling work.