CCAMLR

The CCAMLR Secretariat has been requested to provide annual calculations of the catch of krill within the critical period-distance of land-based predators in Subareas 48.1 and 48.2 (100km from colonies, December - March). This index of the overlap of predators and the fishery is unsuitable for a number of reasons. An alternative method of calculating an index of fishery-predator interaction is developed, which is based on a detailed model of the supposed functional interaction between these two utilisers of the krill resource.

Being prepared by a collective of authors, this paper demonstrates some approaches to mathematical modelling of Antarctic krill population in the Cooperation Sea. The choice of investigation area is not casual since there are data on YugNIRO long-term observations over kri11 biological state here, its stocks, other pelagic system components, inhabitancy conditions, landing by FVs for the period from 1978 to 1984 and 1988.
The objective of the researches was to reveal causes of sharp fluctuations in krill abundance in the Cooperation Sea basing on mathematical modelling. The main task was to assess variations in parameters of the ecosystem and its staunchness against their impact.
A possibility is shown to apply logical-information modelling for future creation of a prognostic model of functioning of Antarctic krill population.

Preliminary analyses of this topic identified some problems with the data originally submitted. To clarify these problems and to provide additional data to enhance the accuracy and relevance of the overall model, this paper provides quantitative information on potential biases associated with estimation of survival rate, observed rates of population increase (both maxima and at study colonies from which the data derived) and diet for black-browed albatross, gentoo penguin and Antarctic fur seal at Bird Island, South Georgia. In addition, year-specific data for a) black-browed albatross breeding population size and success and adult survival (1976-1992); b) gentoo penguin breeding population size and success (1977-1993) and c) Antarctic fur seal adult female survival (1984-1993, including allowance for tag loss), pregnancy rate, pup production, pup growth rates and mortality rates and foraging trip duration (1984-1993) are presented.

The model of the krill fishery presented in 1993 (wg-Krill-93/14) refined and applied to both Japanese and Chilean krill fishing fleets in Subarea 48.1. A stochastic element is introduced to account for variability in catch rates. The most successful management regime is found to be one which restricts fishing within 75 km of breeding penguins during January and February. For this regime the model predicts a 90% reduction in overlap with foraging predators, and a 15 to 20% reduction in catch. Closure of Livingston Island for the breeding period resulted in a 60% reduction in overlap with predators and 0 to 15% reduction in catches.

We present data on sexual dimorphism in some morphological measurements (wing length, head length, bill depth and bill length) in the Antarctic Petrel Thalassoica antarctica. Males were on average larger than females for all measurements. Sexual dimorphism was on average largest for bill depths whereas wing lengths discriminated least between the sexes. A discriminant function including bill depth, head length and wing length correctly sexed 92% of the sample. Due to between-measurer variation it is recommended that morphometric measurements obtained by others on sexed birds are compared with ours before proceeding with the use of the discriminant function on unsexed individuals.