CCAMLR

Data of repeated operation recorded on Japanese log book were examined the validity of identifying the same patch and the resulting change in CPUE. While no change was detected in CPUE some difficulties were thought in identification of krill patch(es).

Annual summary of Japanese krill fishery in the Antarctic was updated with delineation of two different type of operation. Operated areas in 1983/84 and 1984/85 seasons were illustrated and three historical main fishing grounds were identified.

The characteristics of Japanese krill fishery were reviewed in several examples based on the information recorded on log book. While searching behaviour seems to be the basis of this fishery, CPUE in terms of catch per minute of towing was thought to be an useful index of patch density and possibly of local abundance.

A crude mathematical framework is developed to describe krill abundance in terms of selected parameters of various aggregation behaviours exhibited by krill (Euphausia superba Dana). The relationship of combinations of these parameters to various possible measures of catch-per-unit-effort (CPUE) for the Antarctic krill fishery is considered. The combined index of catch-per-hour of trawling divided by average inter-concentration search time is suggested as a possible measure of krill abundance; such an index should be stratified both spatially and by krill aggregation type - this has implications for routine data collection. Models should be constructed to investigate how substantial non-linearities in the relationship between the index and krill abundance might be.