The Eel River Recovery Project (ERRP) is non-profit grassroots group that employs citizen assisted monitoring to take the pulse of the Eel River ecosystem, including assessing fish populations. ERRP was formed after community scoping meetings in September 2011 all over the Eel River basin and there was universal concern about the non-native, highly predatory Sacramento pikeminnow, formerly known as the squawfish. People were concerned about their impacts on native salmon and steelhead and thought they needed to be controlled, if possible.
It wasn’t until 2016 ERRP received a grant from the Salmon Restoration Association (SRA) in Ft Bragg to do a pikeminnow census. SRA holds the annual World’s Largest Salmon Festival on the 4th of July weekend annually and gives out grants from proceeds for salmon monitoring, restoration and outdoor education. The study design for the South Fork Eel River pikeminnow monitoring was created in cooperation with Dr. Bret Harvey of U.S. Forest Service Redwood Sciences Lab in Arcata, who has studied the species extensively. The reach chosen, which is from Rattlesnake Creek to Standish Hickey State Park, is where Dr. Harvey found predation in fall by large adult pikeminnow on juvenile steelhead.
ERRP uses a dive team of six that walk and swim six miles a day for two days. Day 1 the team covers from the Hermitage at the mouth of Rattlesnake Creek to the Gomde Monastery at the mouth of Cedar Creek, then Cedar Creek to Standish Hickey on day 2. Dive teams have been comprised of seasoned ERRP volunteers who also count salmon, professional fish biologists who volunteer, agency staff and University of California graduate students affiliated with the Angelo Reserve.
The biggest surprise of both survey years was the abundance of steelhead trout juveniles in the survey reach, which was not as dominated by pikeminnow as anticipated. Findings in 2016 were that there were 1408 total pikeminnow counted, with 132 large adult pikeminnow over 18” long, 80% of which were concentrated in deeper pools and around large woody debris jams. Evidence from 5 years of observation suggests this is due to intensive otter predation. In 2017, there were slightly fewer large adults (90) and slightly fewer pikeminnow overall (1173). There was also a substantial reduction in 4-8” fish counted, likely as a result of poor recruitment in recent wet years. Interestingly, the number of fish in the 14-18” size class increased, reflecting high recruitment during the 2013-2015 drought.
A major difference in 2017 was that large adult pikeminnow were not only in pools, but also in runs and ambush locations like at the base of cascade. This was likely due to the very late high-water conditions due to one of the wettest years in the last 100 years.
Otter chowing down on very large adult pikeminnow on the SF Eel. Photo by Ann Constantino, 7/1/17.
Since many of the largest pikeminnow are concentrated in just a few deep pools, it would be easy to remove them using highly trained scuba divers with spear guns during low flow periods in late summer. The large adults consume very large numbers of juvenile salmonids and have also decimated native fish species like the Sacramento sucker and three sculpin species. Large adult pikeminnow also tend to be females and the most fecund in terms of producing eggs and offspring. Therefore, large adult removal would also depress the population resilience of the pikeminnow, particularly if removal is conducted for ten years, which is equivalent to the life span of a pikeminnow. Scientists call this prolonged selective pressure a “press disturbance” on the population, from which it will not likely rebound for a long time.
ERRP will be seeking a permit for pikeminnow removal from the California Department of Fish and Wildlife after one more year of trend data collection in 2018. Annual dive counts in 2019 would be carried out in early summer prior to removal of adults later in the year. Repeating this cycle will supply trend data to show effectiveness and can be used for adaptive management.
Virtually every fisheries study and restoration or recovery plan about the Eel River since the 1979 introduction of the pikeminnow has called for their removal or management. ERRP has highly skilled divers ready to volunteer and active interest from the science community to help support the project. You can help fund these efforts by joining the Eel River Recovery Project on-line at www.eelriverrecovery.org or by sending your donations to PO Box 214, Loleta, CA 95551. Call Pat Higgins at 223-7200 or Eric Stockwell at 845-0400 if you have questions or want to join the dive team next summer.