The value of herring spawning events to spring conditioning of scoters in the Puget Sound Georgia Basin

Anderson, Eric M.
Lovvorn, James R.
Esler, Daniel
Boyd W. Sean
Nysewander, David R.
Evenson, Joseph R.
University of Wyoming, Department of Zoology
Centre for Wildlife Ecology, Simon Fraser University
Canadian Wildlife Service - Pacific and Yukon Region
Washington Dept of Fish and Wildlife
Proceedings of the 2005 Puget Sound Georgia Basin Research Conference
Publication Date: 

PSAMP Marine Bird Component

Like many sea ducks, scoters have declined throughout their ranges, including dramatic declines in the
Puget Sound Georgia Basin (PSGB). A potential limiting factor is the availability of herring spawn in late
winter and spring. Scoters and other marine birds congregate in dramatic numbers to consume spawn
along much of the North American Pacific Coast. However, spawning stocks in the PSGB, an important
wintering and staging area for scoters, have declined substantially over the past several decades. To
determine whether spawn is critical to spring conditioning of scoters, we address two questions: (1) How
does variation in spawning activity affect acquisition of fat by scoters?; and (2) In years when spawn is
less available, are alternative foods in key winter foraging sites adequate to meet the needs of scoters?
Preliminary tissue analyses (stable isotopes, fatty acids) indicate that when spawn is available, scoters
consume little else. Further, our captures of over 850 scoters in 2003-04 indicate spawn availability and
scoter fattening rates are correlated. Preliminary data from 2003-04 indicate that in some winter foraging
sites, prey alternative to spawn decline seasonally. Thus, spawn is likely important to spring conditioning
of scoters, although multiple factors suggest that Surf Scoters may be more sensitive to variation in
spawning activity than White-winged Scoters.