USING ECOSYSTEM STRUCTURE TO IDENTIFY FINER-SCALE SSMUS FOR OCEANIC AREAS IN SUBAREAS 48.1 TO 48.3

One of the main issues in the management of the krill fishery is finding a spatial subdivision of catches that allows CCAMLR to achieve its objectives for both the fishery and the ecosystem. This requires a framework of spatial areas over which catches can be subdivided. WG-EMM has devised an initial framework of small scale management units (SSMUs) in subareas 48.1 to 48.4 based on the spatial structure of the ecosystem. This framework is hierarchical. It recognises a distinction between coastal (shelf and shelf-break) areas and oceanic areas. WG-EMM devised thirteen coastal SSMUs with an average area of 34,690 km2, separating discrete concentrations of land-based predator colonies. WG-EMM also devised just four SSMUs, with an average area of 758,809 km2, to cover the remaining 87% of the four subareas. The oceanic SSMUs are the location of 72% of the estimated krill biomass, 61% of the estimated consumption of krill by predators and 10% of the cumulative total fishery catch in the three subareas (48.1 to 48.3) where the fishery operates.

There is ample evidence of structure in oceanic areas from both ecological and oceanographic studies, and from the concentration of krill catches in limited parts of the oceanic SSMUs. A more detailed application of knowledge about ecological structure is likely to allow more, finer-scale SSMUs to be devised for oceanic areas. This would: (i) allow a greater range of options for the subdivision of catches; (ii) afford oceanic predators a greater level of protection from localised fishery impacts; and (iii) allow more realistic evaluation of management strategies in terms of consequences for both the fishery and the ecosystem.

Krill distribution during the CCAMLR 2000 synoptic survey is an indicator of ecosystem structure. Relationships between krill distribution and physical environmental characteristics could be used to identify units of coherent structure in oceanic areas. British Antarctic Survey scientists are currently conducting this analysis. Because the synoptic survey only provides a single snapshot of structure it will be necessary to further investigate the consistency in this structure over intra- and inter- annual timescales by (a) testing for such consistency in longer time series of data on physical characteristics which have spatial relationships with the distribution of krill and (b) directed survey or fishing effort to test hypotheses about where concentrations of krill are likely to occur in oceanic areas. The fact that the physical influences on this structure are often dynamic (e.g. frontal systems), presents an additional challenge. Nonetheless, it is important to address the disparity between the scales of coastal and oceanic SSMUs to provide CCAMLR with the tools necessary to manage these habitats in a consistent way.