CCAMLR

Distribution and abundance of salps were studied near the South Shetland Islands during summer 1990/1991. Total salp biomass ranged between 0.1 and 2021.3 mg WW∙m-3 and was nearly equal to krill biomass in the area. Two species; Salpa thompsoni and Ihlea racovitzai were found, and the former was dominant. Horizontal distribution of salps and krill did not overlap. Krill occurred abundantly at the high-chlorophyll a area, in contrast, salps exhibited high biomass in the area of low chlorophyll a concentration

Food habits of the southern baleen whales were reviewed being based on the published and unpublished data since 1946. Past geographical distributions of the krill in the whales stomach revealed that the frequency occurrence by krill size showed that the large krill(>50mm) occurs more frequently in the whaling Areas II and III, then the size comes medium (40-50mm) in the Areas IV and V, and finally small krill (

A simple deterministic model is described which models the behaviour of the krill fishery in Subarea 48.1 and estimates the effort applied and the catch of krill in fine-scale squares. Parameters for the model are calculated from data reported to CCAMLR by Chile over the period 1989 to 1992. The distribution of catches predicted by the model, which is restricted to the months December to March, compare favourably with the general distribution of catches in Subarea 48.1. A number of management scenarios are considered, which involve closures (i) of a zone 50 km offshore from the South Shetland Islands, and (ii) of zones 100 km around Livingston and Elephant Islands. The model predicts that the management option of closing the zones around Livingston and Elephant Islands in alternate years would result in an average yearly catch similar to that at present, although the catch is much more concentrated in foraging areas of land-based predators in alternate years under this scenario.

A method is developed for using observed values of the mean proportion of recruits and its variance to model recruitment in a krill population in terms of numbers of recruits. The method includes the calculation of natural mortality and other parameters consistent with the observed proportional recruitment parameters. A procedure is given for generating families of recruitment functions which are consistent with the statistical uncertainty in the observed recruitment parameters.

A maximum likelihood method is developed for the decomposition of krill density at length data into the proportion of recruits in population sampled in a net haul survey. Preliminary results from a series of 5 net haul surveys in the South Atlantic and the Indian Ocean sectors of the Southern Ocean give a mean recruitment rate for one year old krill of 0.339 with a standard deviation of 0.100. The corresponding results for two year old krill from 9 surveys are 0.552 and standard deviation 0.074. A number of the assumptions needed for reliable results are discussed.

The distribution of krill catches in relation to land-based predator colonies, calculated from CCAMLR fine-scale data, is shown for Subareas 48.1 and 48.2. The pattern of catches in 1992 is similar to that seen for other years, with 70% of the total catch from Subarea 48.1 being taken within 100 km of colonies and between the months of December to March inclusive (the ‘critical period-distance’). Although data reporting was not complete for Subarea 48.2 in 1992, it was estimated that 38% of the total catch from this subarea was taken in the critical period distance, compared to 5 to 78% in previous years. It is estimated that the catch in the critical period-distance was equal to 12% and 15% of the total exploitation of krill in these two subareas respectively.

Krill stock composition and distribution patterns in the vicinity of Elephant Island during austral summer 1991/92 and 1992/93 are described and compared with information from previous years. The general distribution of krill length and maturity classes conformed to previous descriptions and appears to be a recurring and predictable aspect of the krill stocks in the Antarctic Peninsula region. The length frequency distributions and maturity stage composition reflected relatively good year class success from the 1990/91 spawning season but poor success from 1991/92. Year class success from these and other years appears to be associated with female maturity development and spawning during early summer months. The overall abundance, maturity stage composition and reproductive activity of krill appeared to be affected by dense salp concentrations during 1992/93 and 1989/90.