Analysis of trends in Japanese krill fishery CPUE data, and its possible use as a krill abundance index
Haul-by-haul logbook catch and effort data from the Japanese krill fishery for the 1980/81 to 2003/04 fishing seasons were analysed. For a number of definitions of effort and catch-per-unit-effort (CPUE), variables were modelled using linear mixed models in order to obtain time series of predicted intra- and interannual trends of standardised fishery indices. The results strongly suggest that the krill fishery in the South Georgia area is operating at a critical level of krill availability which is just enough to maintain the best factory performance. In this analysis the status of fishing in Subareas 48.1 and 48.2 was not clear. A linear correlation was observed between ‘catch per searching time’ and ‘catch per day’ within their lower ranges, suggesting these may have some value as abundance indices. Standardised CPUE for the pelagic areas showed significant correlations with previously published interannual series of acoustic density estimates from scientific surveys. To refine these CPUE indices, it will be necessary to collect more detailed information from fishing vessels. It is also mportant to undertake the same kind of analysis for fleets from other fishing nations.