On the consequences of differentiating between adult and sub-adult survival rates in the krill-predators model

The krill-predators model is generalised by splitting post-first-year animals into adults and sub-adults, with different survival rates for these two groups. Broadly speaking, the sub-adult survival rate can be adjusted to ensure that the modelled predator population reflects observed growth rates, thus solving problems of lack of self-sustainability encountered in earlier model analyses. This solution brings with it new problems, however, in that two further parameters need to be specified: one reflects the difference between adult and sub-adult survival rates, while the other relates to the split of the overall density dependence effect between the first year and following sub-adult years of life. Since evaluations of the level of resilience of a predator to krill fishing depend on the values for both these parameters, consideration needs to be given to the possibilities for qualitatively inferring these values or estimating them from data. The generalised model is applied, for illustrative purposes only, to the Bird Island blackbrowed albatross population. However, even as generalised, the model is unable to achieve compatibility with survival rate data for the Antarctic fur seal coupled to an annual population growth rate of 10%.