Revised estimates of yield for Electrona carlsbergi based on a generalised version of the CCAMLR krill yield model

Traditional methods for estimating yield per recruit as a function of fishing mortality can result in inappropriate high estimates of yield that could lead to depletion of stocks because of widely varying recruitment patterns, overestimation of the abundance of the stock and age of the most recent survey. These problems are addressed in this paper by using stock projections to assess the probabilities of the stock of Electrona carlsbergi becoming depleted over a 20 year period. These projections have been undertaken using a generalised version of the CCAMLR Krill Yield Model. This is appropriate because this species has a number of similar attributes to krill, including population dynamics, behaviour and its importance as prey in the Antarctic ecosystem. The decision rules for determining yield adopted by Working Group on Krill were adopted for this analysis (where yield = γ.median pre-exploitation biomass): (i) choose γ1, so that the probability of the spawning biomass dropping below 20% of its pre-exploitation median level over a 20-year harvesting period is 10%; (ii) choose γ2, so that the median escapement over a 20-year period is 75%; (iii) select the lower of γ1 and γ2 as the level of γ for calculation of yield. The estimate of γ for a fishery targetting juvenile fish was 0.091.