Above the dam: salmon colonization of new habitat
Joseph
H. Anderson
Fisheries and Aquatic Sciences
Freshwater habitat destruction is a primary cause for declining salmon abundances,
as fish make extensive use of rivers and streams for migration, reproduction,
and rearing. In many areas, dam construction has blocked adult salmon migration,
denying fish access to large stretches of high quality habitat. Fish ladders,
a series of step-pools navigable by migrating salmon, are gaining in popularity
as a means to increase the habitat available to anadromous fish. However,
relatively little is known about the ultimate success or failure of these
restoration efforts. The construction of a fish ladder at Landsburg Diversion
Dam on the Cedar River, WA provides an incredible opportunity to investigate
salmon colonization.
My research investigates the colonization process as adult salmon migrate
above the dam and utilize the new habitat. In fall 2003, Seattle Public Utilities
began passing migrating chinook salmon (Oncorhynchus tshawytscha), coho salmon
(O. kisutch) and steelhead trout (O. mykiss) above the dam. With access to
over 27 kilometers of habitat above Landsburg, anadromous fish will be allowed
to naturally re-colonize an area closed to them for over 100 years. At the
dam, all fish are identified by species and sex, measured, sampled for DNA,
and checked for hatchery marks on the adipose fin. Coho salmon are the focus
of research efforts and receive radio transmitters, allowing an investigation
of fish movement patterns. A combination of remote listening stations and
mobile tracking by vehicle, foot and inflatable raft tracks salmon behavior.
The objectives of coho salmon tracking are to (1) determine the extent of
colonist exploration and (2) identify reach scale patterns in coho spawn
site selection. In particular, research seeks to identify whether coho salmon
utilize the mainstem Cedar River or tributaries for spawning.