Category: Fish/Shellfish Research
Published: June 2009
Publication number: FPA 09-09
Author(s): Joseph D. Bumgarner and Jerry Dedloff
This annual report is one in a continuing series describing WDFWâ€™s progress toward meeting summer steelhead and rainbow trout mitigation goals established in the LSRCP.
Stocking of LSRCP-produced rainbow trout within Washington, and transfers to the State of Idaho generally went as planned, though in 2007 and 2008 there was a shortfall in rainbow trout production and not all LSRCP goals were met. Hatchery survival and smolt release goals for summer steelhead were met for both years. Adjustments were made to the marks and tags applied to the summer steelhead over the reporting period.
We continued smolt trapping on the Tucannon River to estimate the number of migrant steelhead. In the 2006/2007 and 2007/2008 we estimated 11,546, and 26,099 total migrants, respectively. Mean smolt size and peak of out-migration for both years was similar to previous years. Average smolt-to-adult survival of wild origin summer steelhead from the Tucannon River (based on the PIT tags) was 2.25% back to Bonneville Dam, and 1.75% to McNary Dam. PIT tag detections of naturally produced Tucannon River steelhead exhibited a disturbing migration pattern, with about 50% returning to and remaining above Lower Granite Dam. This same migration pattern has also been observed in the Lyons Ferry stock fish and the Tucannon River hatchery endemic stock steelhead.
As part of our ongoing annual broodstock collection and research activities, WDFW hatchery and evaluation staff operate a series of traps in southeast Washington. We reported the number of fish captured and released at all trap locations, composition of hatchery and wild origin fish, coded-wire tag recoveries (where appropriate) age composition, eggtake and fecundity estimates from spawning activities, and historical spawn timing for each steelhead stock.
WDFW staff surveyed steelhead sport anglers during the 2006/2007 and 2007/2008 sport fishing season within the LSRCP area of Washington to recover CWTs from tagged steelhead. In 2007/2008, creel surveys, on the Tucannon, Touchet or Walla Walla rivers were limited or not conducted. This was done to increase our sample rate in the mainstem of the Snake River to achieve at least a 20% sample of what is eventually reported on Washingtonâ€™s catch record cards.
During the springs of 2007 and 2008, evaluation staff conducted spawning ground surveys to estimate the number of redds in index areas of the Tucannon and Touchet rivers and Asotin Creek. Stream flows were favorable in 2007, but were high and turbid during 2008 which greatly affected our ability to estimate redds in the Tucannon River. Evaluation staff standardized all spawning ground survey estimates for summer steelhead in the Touchet River and Asotin Creek.
Coded-wire tag recoveries from fisheries, hatcheries, or from traps in river have provided the basic data to estimate minimum smolt-to-adult return rates on LFH and Wallowa stock summer steelhead from the program. Due to a variety of factors, smolt-to-adult survivals back to the project area have generally been nearly 3 times the assumed rate. The LFC summer steelhead program (LFH and Wallowa stock only) continues to meet and/or exceed its original mitigation goals by supplying large returns of hatchery steelhead for harvest to the Snake River area. This is mainly due to the fact that harvest rates in the lower Columbia River fisheries have declined substantially since the program was initiated. Hence more fish are returning to the project area even though hatchery production has been reduced in recent years.
As in previous years, WDFW electrofished using either a multiple or a single pass removal method at index sties to estimate Age 0 and Age 1+ juvenile steelhead densities and derive population estimates for specific river reaches. During the summer of 2005 and 2006, we tested estimator bias (multiple pass estimate vs. mark/recapture estimate) at 44 sites in SE Washington. For both years on average, we found that multiple pass underestimated Age 0 and Age 1+ summer steelhead by 29.9% and 22.7%, respectively, compared to the mark/recapture estimate. Based on these results, and other factors such as high confidence intervals around the electrofishing estimates, we have discontinued electrofishing surveys for juveniles.