Modelling Shows Upper Columbia Spring Chinook Remain Among Most “At-Risk”
- October 19, 2020
- John Harrison
Less than 1 percent of the juvenile wild Upper Columbia Spring Chinook that migrate down the Columbia River to the ocean past seven to nine dams return to three upper Columbia tributaries in north central Washington to spawn. This helps explain why the species continues to be listed as endangered, a fish biologist who has studied the species extensively reported to the Council’s Fish and Wildlife Committee at its October meeting.
The fish were listed under the Endangered Species Act in 1998, and a recovery plan was developed and implemented. But while the recovery plan has made good progress protecting the fish and improving their spawning habitat in the Methow, Entiat, and Wenatchee rivers, “on the scale of at-risk, these are among the most at-risk populations we have in the Columbia River Basin,” said Dan Rawding, Columbia River Salmon Recovery Coordinator for the Washington Department of Fish and Wildlife.
In 2017, the Council’s Independent Scientific Advisory Board reviewed the status of recovery efforts and research of Upper Columbia Spring Chinook and recommended, among other things, additional life-cycle modeling to identify things that were limiting recovery and to assist with restoration planning. In response, a multistate model was developed to estimate reach-specific survival using the extensive Columbia River Passive Integrated Transponder (PIT) tag detection network at dams and in tributaries where the fish spawn. Juvenile spring Chinook were PIT-tagged at fish traps on the Methow, Entitat, and Wenatchee Rivers from 2009 to 2013 and their movements recorded.
Rawding, who conducted the modeling, said a total of 93,000 PIT tags were inserted in Upper Columbia Spring Chinook smolts, including 8,000 tags in Methow River Fish, 23,000 in fish in the Entiat, and 62,000 in the Wenatchee. The difference in the number of tags represents the number of fish in the rivers and the comparative difficulty in capturing juvenile fish to tag – most difficult in the Methow, easiest in the Wenatchee. The tags are detected as the fish migrate downstream from the tributaries and at dams, and again as they return as adults.
Survivals from the tributaries to Bonneville Dam, the last where juvenile fish can be detected, are about 30 percent for Methow and Entiat fish and a little less for fish from the Wenatchee, Rawding said. Ocean survival for all three populations is about 2 percent, and the upriver survival of adult fish from Bonneville Dam to the home tributaries is between 50 and 75 percent. But few fish return, and so the all-important measurement, smolt to adult return, or SAR, is “close to 1 percent” of the fish that migrated to the ocean, Rawding said. The SAR for Methow fish is lowest, perhaps because the Methow fish pass two more dams, Rawding said. The SAR goal in the Council’s Columbia River Basin Fish and Wildlife Program is 4-6 percent.
“The SARs are well less than the Council’s goal, and this probably explains why the fish are still classified as endangered,” he said. “The SARs should be approaching 2 percent to be considered on the way to recovery.”
Rawding said the analysis only considered wild fish and not hatchery fish, which are being introduced into the rivers to help boost the populations. He said assessing hatchery fish survivals could be among his next steps as he continues the analytical work. Others include comparisons of hatchery and wild fish survival; additional brood year and juvenile fish data; electroshock data, the impacts of factors that affect survival including spill; overwinter survival for Entiat fish; and the development of separate models for each population in this specific evolutionary group of fish.
“Your information reinforces that there is a long way to go as we trend toward recovery,” Committee Chair Guy Norman said.