Estimates of global krill abundance based on recent acoustic density measurements and their implications for the calculation of precautionary catch limits and the designation of management areas

The global abundance of krill is estimated using recent estimates of krill density from acoustic surveys and historical information on the overall range of krill. The biomass estimates fall between 64 and 137 million tonnes - at the low end of values that have been suggested in the past. The differences between our estimates and others can be explained by a number of factors such as: an underestimation of the range, or of the acoustic biomass estimates, the possibility of a large, undetected krill population, and the overestimation of the demand for krill by predators. Even if these low global krill biomass estimates are correct, regional and global precautionary limits are still likely to rise as a result of new surveys because the method used to calculate precautionary limits uses a value of 11 % of the biomass. Additionally, the current precautionary catch limits in the South Atlantic are set using the old target strength which has effectively underestimated the krill biomass by a factor of three so the new survey of the South Atlantic is likely to result in an effective biomass which is greater than that used in the past. The seasonal and local consequences of elevated catch limits will have to be taken into account when managing an expanded krill fishery and the appropriateness of using the existing statistical divisions as management areas will have to be considered.