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Juvenile Chinook salmon. See slideshow.
Chinook and coho salmon are now recolonizing the Cedar River above Landsburg Diversion Dam, which was a passage barrier from 1901 to 2003.
Chinook and coho salmon have an anadromous life cycle (spending part of their life in freshwater and part in saltwater). Young salmon emerge from eggs in the gravel of streams, migrate to the ocean to grow and become adults, and then return to their native streams to spawn and die. Their offspring develop in the streambed gravels to begin the cycle over again.
In 1901 completion of the Landsburg Diversion Dam, which diverts water from the Cedar River for the City’s water supply, blocked passage to the Cedar River and its tributaries above the dam. As a result, Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon and steelhead trout (O. mykiss) returning to spawn no longer had access to habitat above the dam.
A fish passage facility was opened in 2003 at Landsburg, allowing salmon and steelhead to return upstream for the first time in over 100 years. The fish passage is one of the City’s commitments under the Cedar River Watershed Habitat Conservation Plan.
Seattle Public Utilities (SPU), NOAA Fisheries, and the University of Washington are collaborating on studies to monitor the process of salmon recolonization in the 12.6 miles of mainstem river habitat and 8.0 miles of tributary habitat that were made accessible in 2003. These studies include:
The following sections cover some of the results of these studies.
Above Landsburg, SPU scientists have found most of the Chinook and coho salmon spawning downstream of Taylor Creek. Spawning has been documented almost 12 miles upstream of Landsburg, near Cedar Falls. See map of Chinook Salmon Spawning Locations (pdf).
Although it was expected that coho salmon would spawn in Rock Creek, which provides abundant potential coho habitat, no evidence of spawning in the creek was documented until 2009, six years after passage was reinitiated. In spawning seasons for 2003 through 2009, a total of 1,062 Chinook and 1,573 coho salmon have passed the Landsburg Diversion Dam (See fish counts related to Landsburg mitigation efforts).
Most Chinook salmon fry in the Cedar River migrate downstream out of the river soon after they emerge from the gravel. In contrast, coho salmon fry typically remain in stream habitat for one to two years.
Studies by NOAA Fisheries showed juvenile coho salmon moving progressively further up Rock Creek in 2004, the first year after fish passage. Numbers of juvenile coho in the creek have steadily increased each year since. In 2007, juvenile coho were documented moving further upstream into an extensive beaver-pond system that provides high quality coho rearing habitat and by summer 2010 there were abundant juvenile coho throughout Rock Creek produced from numerous redds in the creek the previous fall/winter.
Scientists expected Rock Creek to become very productive coho rearing habitat. As salmon recolonize above Landsburg, the mainstem Cedar River is also becoming an important coho rearing area.
Scientists from NOAA Fisheries have been implanting juvenile coho with small devices called PIT tags, which can then be detected as they move through an antenna installed in the stream. PIT stands for “passive integrated transponder.”
PIT tag antenna arrays are installed at the mouth of Rock Creek, in the Cedar River above Landsburg, and at the Ballard Locks in Seattle (through which fish from the Cedar River must pass as they go to and from marine waters). The PIT tag technology provides a way to track fish from the time they are a few months old until they return to spawn three to four years later.
PIT tag data show that young coho migrate out of Rock Creek from fall through the following spring, with most migrating to saltwater in mid-May. Initial data on juvenile coho migrating out of Rock Creek to the Ballard Locks shows about 50 percent survival rates.
In 2003, all the spawning salmon moving up through the Landsburg fish ladder were strays from the lower river or elsewhere. As time goes on, scientists expect more and more salmon passing upstream through Landsburg during spawning season to have been born in the Cedar River Watershed.
To document the number of returning progeny, they must be distinguished from strays that continue to pass upstream. University of Washington scientists are using genetic analysis to determine not only which fish are strays and which are not, but also which fish sampled in previous years were their parents!
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Other fish species in the watershed: