Long-term survival of adult Arctic grayling (Thymallus arcticus) in the Kuparuk River, Alaska

Abstract

In many long-lived species such as Arctic grayling (Thymallus arcticus), population growth rate is most sensitive to changes in adult survival probabilities. Understanding the factors that regulate adult survival in this species should provide insight into the population dynamics of this and other long-lived Arctic species. Using the program MARK, we analyzed 17 years of mark–recapture data to estimate survival rates for Arctic grayling in the Kuparuk River, Alaska, from 1985 to 2000. Mean annual survival rates overall ranged from 0.39 to 1.0 and averaged 0.71 ± 0.05 for resident and 0.75 ± 0.05 for nonresident fish. Spending the summer in the more productive fertilized zone of the experimental reach had no influence on survival despite higher productivity on all trophic levels and consistently higher growth rates in Arctic grayling. None of the environmental (stream temperature, discharge, winter severity, and incidence of drought) or population parameters (growth, condition factor, and mean fish size) that we examined explained significant amounts of variance in survival rates. The lack of responsiveness of survival to annual environmental conditions was unexpected and suggests that multiyear factors or life history tactics that maintain survival at the expense of growth and fecundity likely determine survival.