The use of predator-derived krill 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 ship-board acoustic systems but not to conduct scientific netting, i.e during logistic/re-supply operations. This will allow a robust estimate of krill abundance to be estimated from acoustic data. Changes in the length-frequency distribution of krill over a period of 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 ship-board scientific surveys.