A model simulating the impact of habitat supply limits on northern pike, Esox lucius, in Hamilton harbour, Lake Ontario

The effects of life-stage habitat supply limits on fish populations are examined using a simple model of northern pike (Esox lucius). The model has submodels for spawning, fry, and juveniles + adults (1+). The modelling approach assumes the habitat supply for life stages can be estimated and the key population processes in each life stage are controlled by a saturation function of habitat supply. Only one life stage can limit the population at a time. Baseline simulations show that fry and juvenile-adult habitat supplies are more limiting than spawning habitat, contrary to conventional wisdom. Paradoxically, spawning habitat may be rarer in absolute terms but other life stages need more of the total lake ecosystem area to be suitable for the population to succeed. Simulations based on a simple depth-based model of suitable habitat show how lake depth and hypsographic shape can affect population size and structure. Population sizes generated with various habitat supply scenarios overlap the reported range of values. The application to Hamilton Harbour shows how a dynamic model with habitat supply limitations can guide restoration efforts. Habitat management and conservation assessments must consider the dynamic population responses to varying life-stage habitat supplies.