TABLE OF CONTENTS
Fall Chinook Rebound in 2010
Fisheries biologist Patrick Higgins conducted an Eel River fall Chinook salmon survey for Friends of the Eel River from September through the end of December 2010. His field reports and final report can be viewed at eelriver.org/fish-monitor. Instead of finding just a few hundred fish and very low flows, as anticipated, Higgins documented one of the largest Chinook salmon returns in recent time; and the flows were unusually high due to early rains. An estimated 10,000 to 30,000 Chinook salmon spawned in the Eel River basin in 2010. Higgins' report, "Fall Chinook Monitoring Studies," recommends speedy action to help sustain this level of return and maybe increase it to 100,000 fish.
FOER sponsored the Fall Chinook Monitoring Studies as part of our continuing inquiry into the health of the watershed. Pat's enthusiasm for the task’Äîin addition to his depth of knowledge’Äîis why we engaged him. His voice is heard throughout his writing, and his own opinions come to light in the conclusion, which we are content to let stand as part of this particular study and its author's conclusions at the time. FOER sees this as a starting point for discussion rather than a confirmed solution. The health and efficient management of this impaired watershed requires ongoing studies like this in order to inform the decisions we make.
By Pat Higgins
At the beginning of the Friends of Eel River (FOER) fall Chinook monitoring project, I expected to see only a few hundred fish and very impaired habitat conditions. Instead I found a resurgent population in the tens of thousands and positive signs that extensive reaches of the main Eel River are healing. The high returns should not cause complacency, however, because climate and ocean cycles that have fostered recovery will not remain favorable, and serious water pollution problems still need to be remedied.
How Big Was the 2010 Chinook Salmon Run?
Chinook salmon entered the lower Eel River in September 2010 and their numbers grew to more than 2,000 just prior to the inception of torrential rains on October 23. Less than a week later the Chinook salmon arrived at the Van Arsdale Fish Station 150 miles from the ocean. The 2010 total there of 2,315 Chinook salmon was the highest since counts began in 1946, but there were many more fish spawning in Eel River reaches outside the Potter Valley Project area.
When I visited the upper Eel River between Outlet Creek and Dos Rios and above and below Hearst during November, virtually every riffle had active Chinook salmon spawning. These reaches had been healed from past flood damage as a result of watershed rest and recent high-flow years. Similar recovery is occurring in the Middle Fork Eel, upper South Fork Eel, and a reach of the upper Van Duzen River above Bridgeville. These recovered areas in aggregate are largely responsible for the large fall Chinook salmon return in 2010’Äîhaving increasingly provided more and better salmonid habitat conditions for young Chinook fry over the past decade’Äîand why I estimate that the total run was between 10,000 and 30,000 fish. This return is comparable to runs during the last upswing in 1985-1988 or possibly 1955’Äì1958, when the last comprehensive survey found a three-year average of 24,361 Chinook salmon.
The rebound of the salmon is extremely good news, but we need more data to properly manage the fish and to gauge population trends. The report Fall Chinook Monitoring Studies recommends installation of a dual-frequency radar device (DIDSON) to get an accurate count, and continuation of fall dive surveys as an index until there is an automated counting system in place.
What Other Factors Allowed the Chinook Salmon Rebound?
In addition to mainstem Eel River spawning habitat recovery, other factors that helped create such a robust 2010 run are high spring flows and good ocean conditions for recent brood years, low fishing pressure, and a cycle of reduced pikeminnow abundance. (The pikeminnow is an accidentally introduced species that preys upon young salmonids in the river system.)
The Pacific decadal oscillation (PDO) cycle causes variability in precipitation as well as ocean productivity on the West Coast. Since 1995 we have enjoyed mostly favorable ocean conditions for Chinook salmon and many years with high rainfall. Sustained high flows helped flush fine sediment from gravel beds but also improved juvenile Chinook salmon survival by maintaining cool water temperatures and helping them avoid pikeminnow predation. Chinook salmon return to spawn after one to five years in the ocean, which accounts for their variability in size. The 2010 run was comprised of year classes or broods spanning from 2004 to 2008, and high spring flow and ocean conditions favored their survival.
Chinook salmon harvest in the Eel River has not been allowed for more than a decade, and ocean fishing has been closed or very restricted since 2007; this too has helped the fish population rebound. Furthermore, high-flow years reduce pikeminnow reproductive success, thereby diminishing predation on Chinook salmon. I found evidence that otters may control pikeminnow locally, and that fishing pressure is likely also reducing the number of large adults. The National Marine Fisheries Service (NMFS) required that PG&E control pikeminnow between Scott Dam and Cape Horn Dam, but that effort failed. The FOER report recommends that as an alternative control technique, NMFS require PG&E to fund suppression efforts elsewhere in the basin, such as paying a bounty for pikeminnow.
Major Habitat and Water Quality Improvements Needed
The pools in the lower Eel River remain at a fraction of their historic depth due to excess sediment transport and continuing gravel mining, resulting in few places where Chinook salmon can hold without stress. This problem is compounded when river flows are deflected by sand bars away from existing pools.
A recommendation offered for improving salmon holding habitat is that the lower Eel River channel be excavated so that flow is directed through existing pools. Bank stabilization in the Worswick Hole upstream of Fernbridge using living vegetation (bioengineering) is also recommended to create a hole suitable for 500 holding Chinook adults. The most ambitious recommendation is that the lower Van Duzen River from Yager Creek downstream to the Eel River be fully restored to create a major salmon refuge area.
Nutrient pollution and associated algae blooms are also a significant threat to fish. During the day algae produces oxygen while photosynthesizing but then can depress oxygen levels at night when it respires. If a large number of Chinook salmon crowded into confined pools choked with algae, this has the potential to cause an adult fish kill similar to the Klamath River in 2002. These same low-oxygen conditions foster toxic algae species that can threaten fish and human health.
Reducing algae blooms and nutrient pollution will require a basin-wide effort to conserve water and eliminate excess nutrient contributions from rural development.
More Water Needed Over the Dams to Prevent Fish Kills
During the monitoring project, FOER obtained photos of a November 2, 2002, Chinook salmon fish kill below Fernbridge. The flow of the main Eel River at Scotia at that time was 87 cubic feet per second (cfs), and releases from the Potter Valley dams were only 28 cfs, so it is clear that low flows caused the event. Low fall flows from 2006 to 2009 impeded Chinook migrations and delayed spawn timing. This causes diminished survival of adult fish and also a reduction in the size and fertility of eggs, which together constitute a "take" of this threatened species.¬† To avoid future Chinook salmon fish kills and ongoing take, it is recommended in th FOER report that NMFS require PG&E to increase the "block water" set aside for Chinook salmon to 7,500 acre-feet (AF) to provide for 30 days of flows of 100 cfs. This would allow fish access to the entire main stem up to Scott Dam and still only constitute less than 5% of the average 166,000 AF diverted annually to the Russian River.
The Chinook salmon is actually not the best indicator species for Eel River health because it does not use the river during the summer when water quality problems are most acute. Coho salmon are showing a much weaker rebound than fall Chinook, although there is a functional population in the upper South Fork Eel River from which the stock could be rebuilt. From what little information I was able to gather, steelhead are also experiencing a rebound, likely in response to recent wet years. If we work with nature expeditiously at this point, we can restore all three of these magnificent species, but if we wait until climate and ocean cycles become less favorable, chances for success will be substantially less.
Patrick Higgins is a consulting fisheries biologist with an office in Arcata, CA. (www.pathiggins.org)