Thomson and Butterworth (1996) developed a krill-predator model and applied this to an Antarctic fur seal dataset. These calculations are extended here. The level of krill fishing intensity required to halve the fur seal population (γhalf) is between 0.08 and 0.09, slightly lower than that estimated previously. Tests of the estimation procedure indicate that γhalf estimates are likely to be biased upwards. The estimator is not robust to incorrect specification of the form of the functional relationship assumed between krill availability and survival rates, and especially not to the assumption of the size of the maximum growth rate which the population can achieve. Refinements are introduced to the process of applying this approach to the black-browed albatross dataset, but calculations to estimate γhalf for this species have yet to be completed. The results quoted above are for the deterministic models; stochastic calculations await finalisation.
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