Abstract
A numeric model for the life history of the mesopelagic planktivore Maurolicus muelleri is tested for sensitivity to different parameter values. The model is based on stochastic dynamic programming with decision variables for habitat choice (depth) and energy allocation (between somatic or reproductive growth). The model includes sub-models to represent the foraging, mortality and growth processes. The parameters that induce large changes in most variables are those related to foraging and visual predation risk. By inducing changes in the strategic habitat choices, they have a large impact on other processes like growth, survival and reproduction. The other parameters tested generally have local impact (e.g. on weight or survival), with less impact on other variables of the model. Seasonality in prey abundance and larval survival both have to be present for the model to predict the seasonal strategies observed for M. muelleri in Norwegian fjords. Size dependent factors in the prey encounter, predation and growth processes may explain the observed differences amongst different sized groups of the fish. The strategies predicted for different seasons and size groups of fish, however, are very dependent on the ratio between food abundance and visual predation risk. Size dependent processes in general seem important to understand the selective forces that shape the observed life history patterns of the fish.