Survival, Movement and Growth of Juvenile Chinook ( Oncorhynchus tshawytscha) Salmon Over-wintering in Twitter Creek, South-central, Alaska

I investigated aspects of winter ecology of juvenile stream-type Chinook Salmon (Oncorhynchus tshawytscha) in Twitter Creek, a small tributary of the Anchor River, South-Central Alaska. A multistate modeling approach utilizing passive integrated transponder (PIT) technology to consider both live recaptures of individuals during discrete sampling occasions, and continuous data collected by monitoring movements of PIT-tagged fish was used to characterize both movement and survival. Juveniles emigrated from the stream throughout the winter peaking in the late fall and spring. Survival rates were eight times higher for juvenile Chinook that maintained stream fidelity during the entire winter period. The probability of emigration and survival were strongly size-dependent, where larger fish tended to remain resident and survive better than smaller fish which tended to migrate and experience higher mortality. The deceleration of growth of Pre-smolt (age 0+) Chinook Salmon during winter was accurately characterized by an asymtotic relationship between fish size and time-at-large during periods of low water temperatures. These results suggest that the increased growth and lower survival and tributary fidelity for a smaller juvenile Chinook could be a result of size-mediated, metaboloic rates and energy stores. The conflicts between maintaining energy stores and foraging require smaller individual to engage in risky energetically favorable behavior. These differences in physiological scaling result in size-dependent responses to winter induced food and space limitations. I suggest that tributary streams provide important winter habitats for dominate juvenile stream-type Chinook Salmon in the Anchor River drainage