CCAMLR

This paper presents a summary of the foraging locations of the Ad6lie penguin at 7 widely spaced locations along the coast of Eastern Antarctica between 55°E near Enderby Land and 175°E in the Ross Sea region. Birds feeding chicks regularly travel 100-120km offshore to the continental shelf and return with krill. The pattern of foraging is similar between sites. The potential for overlap with the krill fishery occurs where ice conditions permit the fishing fleet to cross onto the continental shelf. Observations at Casey and Dumont D'Urville from one season suggest such an overlap may not occur at these sites in normal ice years. It is suggested that an understanding of the potential for over lap between the areas of foraging of the birds and fishing be established by tracking before a decision is taken to establish new CEMP sites.

A time-dependent, size-structured, bioenergetically-based model was developed to examine the growth dynamics of Antarctic krill, Euphausia superba. A system of coupled, ordinary differential equations was developed to describe the growth of krill between 2 and 60 mm. The metabolic processes included in the model were ingestion, assimilation efficiency, a baseline respiration. respiratory losses due to feeding and digestion, and an activity-based respiration factor. Positive net production resulted in the transfer of individuals to the next highest size class (growth), whereas negative net production resulted in transfer to the next smallest size class (shrinkage). Size-dependent parameterizations of model coefficients were constructed from an analysis of field and laboratory measurements provided in the current literature. The model was forced with an environmental time series of food (pelagic phytoplankton concentration) that was derived from data sets collected west of the Antarctic Peninsula. Three time series were created to represent high, low, and intermediate food conditions with the high and low conditions representative of phytoplankton concentrations observed on the inner and outer shelf, respectively. Simulated growth rates during the spring and summer for all size classes were consistent with published growth rates; however, winter shrinkage rates were too large. Although the use of a seasonally-varying respiration activity factor (reduced winter respiration rates) resulted in winter shrinkage rates of adults that were consistent with observations of experimentally starved individuals. the annual change in length of specific size classes was still inconsistent with observations. Subsequent simulations were designed to examine the effect of the ingestion of sea-ice algae in the late winter and early spring. The annual growth cycle best matched observations with reduced winter respiration rates and ingestion of sea ice algae, particularly for larval and subadult krill (

The krill-predator modelling calculations of Thomson and Butterworth (1995) are extended to take account of a number of the suggestions made at the 1995 meeting of the CCAMLR Working Group on Ecosystem Monitoring and Management. The resilience of the Antarctic fur seal population to krill harvesting is found to be strongly dependent on the estimate of the maximum annual growth rate (R) which the population can achieve. For R=10%, it is estimated that a krill harvesting intensity rate γ of slightly more than 0.1 would be required to reduce the seal population to half its pre-exploitation level. Similar calculations are initiated for the black-browed albatross, but require the separation of fishery-related mortality effects from overall survival rate data before they can be taken further.

Hatching season and larval growth of Pleuragramma antacticum in the water off Antarctic Peninsula were determined by the examination of growth increments in otoliths. The samples were collected by Bongo plankton net or MOCNESS from December 1993 through January 1994. P. antacticum was predominated (54 inds. out of 77 fish larvae) in ichthyoplankton samples, and occurred mainly in cold water of the Weddell Sea. Body length of P. antacticum ranged from 12.0 to 67.3 mm. Otolith radii (R) ranged from 150 to 260 μm, and linearly related to body size (L); R = - 43.6 + 5.99 L (r2=0.79). The mean size of otolith cores was about 50 μm in diameter. The width of the growth increments was narrow near the core, but it became broader at around 50 - 100th increments (ca. 1.3 μm). However, it decreased thereafter toward the edge maintaining the size of ca. 0.5 μm. Assuming that a growth increment was deposited daily after hatching, P. antacticum seems to be hatched during June - July, because the mean number of increments was 178.3 (standard deviation = 12.8). With the samples we examined, we speculate that there exist two hatching periods for P. antacticum: The large larvae (40-50 mm) hatched in winter (June - July), while the small ones in early summer (December) .

The distribution of kri!! harvesting effort and associated catch rates has previously only been available to the scientific community in the form of sub-area or fine-scale(0.5 ° latitude by 1 ° longitude) recorded statistics. Earlier analyses of these data have shown this was a shelf-break fishery over much of the Scotia Sea. Although these statistics give a general idea of where the fishery has operated they do not reveal the localised nature of the fishing operation. In particular they give little ecological insight into how the fishable aggregations relate to the local environmental conditions. Over the last three winter fishing seasons (1993-1995) haul by haul statistics have been recorded in the South Georgia area. Analyses of these data show marked interannual variability and indications of a seasonal pattern. In 1994 the fishery was almost totally based over a large shallow bank area on the north-east shelf edge. During 1995 the fishery was still predominantly in this area but also operated further west on a range of banks associated with submarine canyons. The data for 1993 were only available from August but the fishery was restricted in that period to an area on the western edge of the shelf break where negligible fishing occurred in the following two seasons. The results are discussed in relation to the ecology of krill and the fishery interaction with the local predator colonies.