Summary of Pacific Lamprey Salvage Efforts from Dryden Diversion Maintenance Operations (Wenatchee River, Dryden, WA)
Dates
Publication Date
2016-04
Summary
Dryden Diversion is an irrigation diversion on the Wenatchee River (river km 27.8, 1.75 mm mesh-size fish screens) which entrains many thousands of larval/juvenile Pacific Lamprey each year. The Yakama Nation (YNPLP) assisted with Pacific Lamprey salvage operations 1) when the canal was dewatered (October 12 and 13, 2015) and 2) during dredging operations in the canal forebay area upstream of the headgate (March 4, 2015). Part I: Dryden Diversion was dewatered on October 12, 2015 and lamprey salvage efforts in the canal occurred on October 12, 13, and 14, 2015, by Chelan County PUD (CCPUD), the YNPLP, US Fish and Wildlife Service (USFWS), and Washington Department of Fish and Wildlife (WDFW). Through our collective efforts between [...]
Summary
Dryden Diversion is an irrigation diversion on the Wenatchee River (river km 27.8, 1.75 mm mesh-size fish screens) which entrains many thousands of larval/juvenile Pacific Lamprey each year. The Yakama Nation (YNPLP) assisted with Pacific Lamprey salvage operations 1) when the canal was dewatered (October 12 and 13, 2015) and 2) during dredging operations in the canal forebay area upstream of the headgate (March 4, 2015).
Part I: Dryden Diversion was dewatered on October 12, 2015 and lamprey salvage efforts in the canal occurred on October 12, 13, and 14, 2015, by Chelan County PUD (CCPUD), the YNPLP, US Fish and Wildlife Service (USFWS), and Washington Department of Fish and Wildlife (WDFW). Through our collective efforts between October 12, 2015, and October 14, 2015, a total of 8999 lamprey (8408 larvae and 591 macrophthalmia) were captured and released back to the Wenatchee River into a small side channel with Type I and II habitat. Macrophthalmia composed 6.6% of the overall number salvaged. Collective electrofishing efforts (between YNPLP and USFWS) captured a total of 6,750 larval lamprey (79.4% of the total lamprey capture) and 395 macrophthalmia (5.5% of total capture through electrofishing) in 21.5 hours of sample time (332 lamprey/hour). CCPUD primarily salvaged lamprey from dewatered banks (collecting exposed lamprey and digging with shovels), collecting a total of 1,658 larval lamprey and 196 macrophthalmia (20.6% of all life stages) in 15.5 hours of sample time (120 lamprey/hour). Although efforts were made to capture all lamprey we observed, a large number of the lamprey, especially smaller ones, escaped our nets due to high density (missed between 2~4 fish for every fish captured).
To estimate the number of entrained lamprey in Dryden Diversion, we used electrofishing densities from October 12 and 13, 2015. Although on average 2-4 lamprey were missed for every lamprey captured, observed lamprey numbers for each survey (captured and missed) were estimated at twice the number of captured fish to provide a more conservative estimate of lamprey numbers. The resulting densities were used in extrapolating to the overall area within each section.
On October 12, 2015 (the first day of salvage), the highest estimate of lamprey was 47,038 for Section 2 (the high density section within the area upstream of the fish screens). On October 13, 2015 (the second day of salvage), the highest estimate of lamprey was 36,953 within this same section, yet decreased to 15,106 later in the day. Using the combined estimate from the two days of salvage, we estimate the total number of lamprey entrained within Dryden Diversion to be approximately 50,619. Number of lamprey estimated downstream of the fish screens were low (~619), but this estimate only covered a small section immediately below the fish screens.
Part II: Dredging of fine sediment (primarily silt) occurred in the Dryden Diversion forebay between March 3 and March 11, 2016. The slow water and fine sediment in the forebay area provides refuge to tens of thousands of larval and juvenile lamprey. The YNPLP aided in lamprey salvage operations on March 4, 2015. The dredged material was immediately placed into a custom dump truck designed to hold water as well as lamprey. The dredged material was then laid out on a large dirt parking lot and the salvage crew searched through the sediment for lamprey. To salvage the lamprey, the salvage crew used fine mesh nets, hands, fire hoses (for breaking up the sediment), and a backpack electrofisher. All lamprey were counted separately by life stage (larvae or macrophthalmia) and approximately 13% of the lamprey were tallied by three size class categories. In total, 18,746 larval lamprey and 21 macrophthalmia (0.11% of the total) were recovered from approximately 244.5 cubic yards of dredged material.
In addition to aiding with the salvage operation, the YNPLP provided several recommendations to improve fish health and salvage efficiency. These recommendations include placement of a large tarp between dredged material and dirt parking lot, improved temperature monitoring between holding buckets and river water (+/- 1°C before release), and using the salvage as a means for public outreach and education. Mortalities and injuries were also noted during the diversion dewatering and forebay dredging salvage operations by the YNPLP crew; for instance, during the last release of the day on October 13, 2015, approximately 3.9-7.7% of the larvae/juvenile salvaged were estimated to be dead at the release site. In addition, approximately 24% (62 out of 274) of the larvae salvaged from the forebay dredging operation and transported to Prosser Hatchery died over a period of 11 days after the transfer - majority of these dead lamprey had various levels of visible bruises on its body. There may also be impacts from rapid changes in water temperature during the salvage operations.
This report was funded in part by the Bonneville Power Administration (BPA), U.S. Department of Energy, as part of BPA's program to protect, mitigate, and enhance fish and wildlife affected by the development and operation of hydroelectric facilities on the Columbia River and its tributaries. The views in this report are the author's and do not necessarily represent the views of BPA.
