by Peter Moyle and Robert Lusardi

Image source: Fisheries 42(9)

Removing Shasta Dam is the single best action we can take to save California’s wild salmon.  Not possible, you say?

Then there are two alternatives.

One is to provide plenty of cold water and diverse, highly managed habitat below dams. The other is to transport fish to now-inaccessible habitat above dams.

(A third option might be improved management of hatcheries; however, to avoid the pitfalls of domestication that come with hatchery production, our focus is on wild, naturally spawning fish.)

The focus of management today involves regulating dam releases to manage flow and temperature, as well as creating new habitat for spawning and rearing, such as floodplains.  Central Valley salmon are so far not doing well under this option.

The second option is being proposed by fisheries agencies (mainly NMFS), moving fish above the dams. Seventy percent of all salmon habitat is now above impassible dams.  Given that it is nearly impossible to construct fish ladders over California’s large dams, current management proposals involve what we call “two-way trap and haul”.

Basically, adult fish are trapped below dams, then trucked and released in rivers above dams.  If the transported fish spawn successfully, juveniles are then trapped as they move downstream to lower sections of river or into a reservoir.  After trapping, juveniles are trucked for release below dams, allowing them to migrate to sea.

Sound good?  Well, there are some problems to overcome.

First, many adult fish die after being transported, due to stress and other factors. This issue has largely been resolved, however, and there are many success stories of transporting adult salmon over barriers.

Second, habitat conditions above dams are different from historical conditions. In California, most of these upstream rivers have been without salmon, and the influx of ocean nutrients they provide, for 60-70 years.  Besides water quality, other changes to upstream habitat can include stream flow, temperature, channel morphology, and  potentially competing resident fishes (including introduced species such as brown trout).

Third is the difficulty of capturing out-migrating juveniles before they reach the reservoir. Juvenile traps must work under a wide range of reservoir surface elevations and during sudden high flow events, when most juveniles move downstream.  Juvenile capture is among the most difficult hurdles to overcome and capture rates are low. The current favored proposal for the McCloud River is a trap at the mouth of the McCloud River.  To keep the water cool enough for salmon, a temperature curtain is proposed, based on modeling, which will prevent cool water from sinking until it is past the collector.

Fourth is the problem of releasing captured juvenile salmon after transport and expecting them to survive in the river after the stress of capture and transport.  These fish also must face all the below-dam problems that non-transported fish face during outmigration, including passage through the Delta, degraded water quality, and predation.

Overcoming these problems is essential to making two-way trap and haul work.  NMFS proposes this technique to establish above-dam populations of Central Valley steelhead, spring-run Chinook salmon, and winter-run Chinook salmon, all listed under state and federal endangered species acts (ESAs).

Steelhead should not be included in this list because they do not need the protection of the ESAs for complex reasons.  Also, most reservoirs support steelhead-like rainbow trout that live in the reservoirs and migrate up tributaries to spawn, likely making it more difficult for introduced steelhead to establish.  Some reservoirs also have land-locked populations of Chinook salmon.

Spring-run and winter-run Chinook need additional protection at all life history stages, including the need to have multiple populations across the landscape. Thus, two-way trap and haul seems to have potential to aid that aspect of recovery.  The requirements of the two runs are somewhat different, so we focus on winter-run Chinook salmon because it is also the main focus of NMFS efforts.

The urgency of developing new approaches for winter-run conservation increased during the 2012-2015 drought, when low flows, combined with mismanagement of the coldwater pool in Shasta Reservoir, resulted in the near-extirpation of naturally spawned fish in the Sacramento River.  The run was saved mainly by a hatchery program at the Livingston Stone facility below Shasta Dam.

Of all the Chinook salmon runs in California, Sacramento winter-run is the most distinctive by genetics and habitat requirements.  Here is a salmon that lives at the southern end of the range of the species, yet it incubates its eggs, the most temperature-sensitive life stage, during the hot days of summer. Originally, it accomplished this amazing feat by spawning in the McCloud River. Historically, the McCloud was a good-sized, cascading river, fed by giant cold-water (7-8°C) springs  all year around. Winter-run spawned in the McCloud so their young would hatch during late summer when there would be little competition from the young from other salmon runs.  Eventually they would migrate downstream to the productive Pit River, which in turn flowed into the Sacramento River.  Small juveniles likely reached the Sacramento Valley in time to catch the annual flooding of riparian lands and forests, where food and cover were abundant so fish could grow fast and fat.  As floods receded, winter-run moved off the floodplains, down the river, and out to sea.

Of course, winter-run Chinook were not alone. The McCloud River in the 19^th Century was regarded as the most productive salmon stream in California and was the site of the first fish hatchery in the state.   All four runs of Chinook salmon spawned there, as did steelhead.  There was almost a continuous influx of spawners, with juveniles of many ages and sizes rearing and then moving out as conditions permitted.  One indication of the unique nature of the McCloud is that it was the only river (as far as we know) to support bull trout, a cold-water loving trout that preyed upon abundant juvenile salmon.  It is now extirpated from the river and the state.

The McCloud River, July 2014 (Photo credit: Peter Moyle)

But the historic McCloud River is no more.  Over 80% of the cold spring water flowing into McCloud Reservoir is diverted for hydropower production, making the river below the dam smaller and the water somewhat warmer. Below-dam tributaries increase flows in the main river and create a more natural river flow regime, including flood events.  Shasta Reservoir covers the lowest and presumably once-most productive reaches.  The Pit River is a staircase of hydropower dams.  Winter-run Chinook have survived by establishing a population in non-historical habitat immediately below Shasta Dam, where cold water releases from the reservoir are managed for their continued existence.

Today, winter-run Chinook depend on these flows and on gravel dumped in the river below Keswick Dam and Red Bluff to improve spawning. As a backup, a few are reared through their entire life cycle at the Livingston Stone Hatchery at the base of the dam; the hatchery has chillers to keep the water cold.

Winter run Chinook are in a desperate situation; they are on the brink of extinction, especially as wild fish.   Hence, they are NMFS’ prime candidates for two-way trap and haul, between the Sacramento and McCloud rivers. Presumably, the operation will be conducted initially as an experiment, to see if a back-up population can be established that can persist through years of severe drought.  This will not be easy.

Here are a few of the problems that must be dealt with in tandem:

• The McCloud of today is a smaller, shorter river than the original river and it has not been fertilized by salmon for 70 years.
• The McCloud River supports substantial populations of potentially competing rainbow and brown trout.
• Capture of out-migrating juveniles will require a trap in or just above the reservoir that can work during rapid reservoir fluctuations and during all flows, including high flows.
• The release program for captured juveniles must result in survival rates as high or higher than naturally spawned fish in the Sacramento River.
• The trap and haul program should not take funds and effort away from improving habitats for rearing and migration in the Sacramento River corridor.

Despite these problems, it is likely that a two-way trap and haul program for winter-run Chinook salmon will be established soon.   A pilot study is a top priority action for NMFS in California. We recommend that such a program not be tried on other runs of salmon until it can be demonstrated that the winter-run Chinook program works successfully.  Success should be clearly defined and measured against objective and quantifiable pre-determined criteria.   Ultimately, the recovery of winter run Chinook, and other fishes, will depend on improved/expanded riverine and floodplain habitats, such as proposed in the salmon resiliency strategy of the California Natural Resources Agency.  The alternative is either extinction or maintaining winter-run Chinook salmon as a domesticated oddity.

Peter B. Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences. Robert A. Lusardi is a researcher at the Center for Watershed Sciences and is the CaliforniaTrout-UC Davis Wild and Coldwater Fish Scientist.

Further reading

Lusardi, R. A and P. B. Moyle 2017. Two-way trap and haul as a conservation strategy for anadromous salmonids.

Baumsteiger, J. and P.B. Moyle 2017. Assessing extinction.

California Natural Resources Agency. 2017.  Sacramento Valley Salmon Resiliency Strategy, June 2017.

Clancey, K., L. Saito, K. Hellmann, C. Svoboda, J. Hannon and R. Beckwith 2017. Evaluating head-of-reservoir water temperature for juvenile Chinook salmon and Steelhead at Shasta Lake with modeled temperature curtains.

Moyle, P., R. Lusardi, P. Samuel, and J. Katz. 2017. State of the Salmonids: Status of California’s Emblematic Fishes 2017.

Opperman, J.J, P.B. Moyle, E.W. Larsen, J.L. Florsheim, and A.D. Manfree. 2017 Floodplains: Processes, Ecosystems, and Services in Temperate Regions.

Perales, K.M., J. Rowan, and P.B. Moyle. 2015. Evidence of landlocked Chinook Salmon populations in California.