The use of predator-derived length-frequency distributions to calculate krill target strength

The relationship between krill abundance and predator performance is fundamental to an ecosystem-based approach to resource management. We propose a method using krill sampled from the diet of predators to provide a length-frequency distribution of krill at times when it is possible to run automated shipboard acoustic systems but not to conduct scientific netting, i.e during logistic/resupply operations. This will allow a robust estimate of krill abundance to be calculated from acoustic data. Changes in the lengthfrequency distribution of krill over a period of a few weeks produced a 10% difference in TS, whereas simultaneous samples from predators and nets produced only a 1% difference, illustrating the need for simultaneous length-frequency data. By integrating data from land-based predators directly with automated on-board data collection systems it will be possible to gain important estimates of krill biomass at times of the season hitherto unavailable from shipboard scientific surveys.