Trends in Annual Survival of Steller’s Eiders Molting at Izembek Lagoon on the Alaska Peninsula, 1993–2006

Abstract

Izembek Lagoon, located on the Alaska Peninsula, is an important molting area for the Pacific population of Steller’s Eiders (Polysticta stelleri) and was the site of consistent banding effort during 1993–2006. We used Pradel mark-recapture models to estimate annual survival and population growth rates for adult Steller’s Eiders molting at Izembek Lagoon. We designed 32 models that included effects of sex and year on survival, recapture rate, and seniority, as well as potential trends in survival and seniority. The top model incorporated a two-phase trend (1993–98, 1999–2003) in survival and seniority for each sex and fully sex- and year-specific recapture rates. Average annual adult survival was estimated at 0.86 (SE = 0.030) for females and 0.87 (SE = 0.018) for males. Average annual population growth rates since 1998 were estimated to be approximately 1.0 for both sexes. A brief warming event in the Pacific Decadal Oscillation (1997–98) coincided with the lowest estimates of annual survival, while a subsequent return to cooler conditions in the Bering Sea coincided with the highest estimates and an increasing trend in annual survival.