A life history approach to understanding marine exit timing of a sockeye salmon population from Haida Gwaii.

This thesis examines the individual variation of marine exit strategies within a population of sockeye salmon known to have early marine exit timing and long delays before spawning. Mean delay was 134 days and represents some the longest known wait times of any sockeye salmon population. Thermal limit avoidance hypotheses were not able to explain this behaviour, as the thermal regime of the stream was moderate. Marine exit date was not correlated to spawning date, as fish were able to spawn at any time (early or late) regardless of their marine exit strategy. Individuals with early marine exit strategies had higher growth, greater somatic energy density, smaller gonads, and greater fecundity. In addition, males and older fish migrated earlier than females and younger fish. These data are explained using a simple life history model and support the hypothesis that marine exit timing is a condition-dependent life history decision.