Science Spotlight

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  • April 30, 2020

Upper Independence creek. Water from the creek flowing through brush and trees with snow capped mountains in the background
Upper Independence Creek provides vital spawning habitat for the Lahontan cutthroat trout in Independence Lake.

Man holding a large cutthroat trout. Very large green fish with a colorful rainbow stripe running along the flank
State and federal agencies, joined by conservation groups such as Trout Unlimited, have worked for decades to safeguard the wild Lahontan cutthroat trout population at Independence Lake, the only self-sustaining lake population of the native species left in California. Trout Unlimited’s Brandon Reeder shows off a hefty Lahontan cutthroat captured at a temporary weir to count spawning fish.

Cutthroat trout fish spawning in a creek. Shallow water creek with rocks on the bottom, perfect location for fish to lay eggs
Lahontan cutthroat trout spawn in upper Independence Creek, where biologists have worked for years to remove non-native brook trout.

Biologist in Independence creek removing non native brook trout. Men wading in the creek hand removing non native fish
Each spring, biologists and volunteers set up a weir at upper Independence Creek to trap spawning Lahontan cutthroat trout and assess the population.

The news out of UC Davis last spring knocked California native fish biologists for a loop.

Genetic testing of native Lahontan cutthroat trout from Independence Lake in the Tahoe National Forest near Truckee found evidence of hybridization with non-native rainbow trout.

To understand the magnitude of that news you have to understand that Independence Lake is the only lake in California – and just one of two lakes in the world – to support a self-sustaining lake population of Lahontan cutthroat trout, a trout native to the eastern Sierra range and the Lahontan basin of Nevada.

And you have to understand that for decades, California Department of Fish and Wildlife (CDFW) biologists – joined by colleagues at the U.S. Geological Survey, U.S. Forest Service, the U.S. Fish and Wildlife Service and conservation groups including The Nature Conservancy and Trout Unlimited – have worked to safeguard these fish, enhance their habitat, and reduce competition from non-native brook trout, brown trout and Kokanee salmon introduced over the years into Independence Lake.

Lahontan cutthroat trout are listed as a threatened species under the federal Endangered Species Act. Their original listing in 1970 predates the modern act itself, which was passed in 1973.


Each fall, as part of species recovery efforts, biologists from CDFW and partner organizations electrofish upper Independence Creek, which feeds into Independence Lake, to remove brook trout from the creek that the Lahontan cutthroat trout depend on to spawn. Also in the fall, biologists set up a weir on the creek to block any of the lake’s resident brown and brook trout from moving up the creek to spawn. Non-native trout staging for a fall spawning run at the mouth of Independence Creek are stunned to the surface through electrofishing and removed from the lake.

“For the past 20 years at Independence Lake, we’ve been trying to give the cutthroat a helping hand by removing the non-native trout. It’s not a done deal but we’ve been pretty successful at reducing brown and brook trout down to very low numbers,” explained Dave Lentz, CDFW’s native trout conservation coordinator. “Lahontan cutthroat trout did not evolve with brook trout or brown trout on the landscape and they have been out-competed and displaced by these and other non-native species throughout much of the cutthroat’s historic range.”

Each spring, when the Lahontan cutthroat trout move up to spawn in upper Independence Creek, biologists and volunteers return with their weir to capture and count the numbers of spawning fish to assess population trends.

This spring, however, the spawning surveys will take on a new sense of urgency. After last year’s disheartening news from genetics experts, CDFW staff and partners captured some 170 Lahontan cutthroat trout from Independence Lake, took genetic samples and outfitted each trout with an identifying Passive Integrated Transponder (PIT) tag before releasing the fish back to the lake.

The tissue samples were sent to two labs for genetic testing. The results indicate that some 20 percent of the cutthroats captured and tagged last year show evidence of hybridization with rainbow trout. Biologists are now discussing plans and options for the spring spawn. Cutthroat trout returning to upper Independence Creek will be trapped and scanned with a PIT reader. Unmarked fish will be given a PIT tag, genetic samples will be taken for later testing, and the fish will be returned to the lake.

“We want to prevent further spawning by hybridized trout. We’re using some emerging science and the latest genetics information to manage this fishery,” said Lentz. “The situation is dire for Independence Lake cutthroat trout but we hope to improve their status by taking these measures.”

There are no known populations of rainbow trout within Independence Lake that could account for the hybridization but they are present in lower portions of Independence Creek below the lake. The outlet of the lake, however, is controlled by a dam that does not allow for fish passage into the lake. CDFW and partners will continue to investigate how rainbow trout gained access to the lake. It is thought that the rainbow invasion and hybridization are recent events, likely in the last 10 years.

The effort to remove hybridized cutthroat trout from Independence Lake takes place as state and federal officials in California, Nevada and Oregon step up collaborative efforts to increase Lahontan cutthroat trout awareness and recovery across their native range. Among those efforts:

  • A genetic assessment of Lahontan cutthroat trout across their historic range has been underway for the past several years. That process resulted in the UC Davis findings of hybridization within the Independence Lake cutthroat population.
  • In May 2019, the U.S. Fish and Wildlife Service released a document that updates recovery goals and objectives from its 1995 Lahontan cutthroat trout recovery plan using current science and a new conservation framework for species recovery.
  • In October 2019, the U.S. Fish and Wildlife Service released 5,000 Pilot Peak strain Lahontan cutthroat trout back into Lake Tahoe, returning the native, fast-growing strain to Lake Tahoe for the first time in nearly 90 years.
  • This coming May, state and federal fisheries biologists are scheduled to begin planning Lahontan cutthroat trout recovery and outreach efforts within the Carson River drainage.
  • CDFW’s Hot Creek Trout Hatchery in the eastern Sierra is preparing facilities to establish a new rearing program for the Walker River strain of Lahontan cutthroat trout native to the Walker River drainage and Nevada’s Walker Lake.

CDFW Photo. Top Photo: A windy day at Independence Lake in the Tahoe National Forest.

Media Contact:
Peter Tira, CDFW Communications, (916) 215-3858

 

Categories: Science Spotlight
  • September 11, 2019

Black and white image of a man crouched in front of truck, holding a large fish in one hand and measuring stick in other hand. Man is wearing plaid collared shirt and pants.
Faded black and white photos are all that’s left of the Owens River Gorge’s glory days as a trophy brown trout fishery. Biologists expect the fish to make a comeback following near-annual pulse flows that begin in September to improve habitat.

Sepia colored image of young man and older man sitting behind table covered in nearly 100 fish. A sign in front reads Harry Smith, 23 years 1953 74 browns, from the owens river gorge, limit 25 trout per day.

Two men in waders standing in river. One man has a large machine backpack on and holds a long, yellow stick in the water. Other man holds a net. Rocks and rough river in background.
CDFW crews electrofish the Owens River Gorge two times per year to assess the health of the river’s brown trout.

From boom to bust to decades of angler indifference, few California fisheries have experienced such wild swings of fortune as Mono County’s Owens River Gorge.

The latest chapter in the long saga of the Gorge unfolds this month when the Los Angeles Department of Water and Power (LADWP) sends a relatively brief burst of water known as a “Channel Maintenance Flow” down the 10-mile stretch of river between the Upper Gorge Power Plant and Pleasant Valley Reservoir to benefit fish habitat.

From Sept. 9 to Sept. 17, water flows will rise from the relatively placid 35 to 55 cubic feet per second (cfs) typical in the Gorge to 680 cfs before gradually ramping back down. link opens in new tab or windowAccess to the Gorge will be closed by LADWP during the nine-day “pulse flow” event for public safety.

The temporary boost in water flow represents the successful resolution of decades of legal battles involving LADWP, Mono County and CDFW. The high flows are expected to breathe new life into the Owens River Gorge ecosystem and its once-storied brown trout fishery. Court settlements mandate the pulse flows continue almost annually -- 18 out of every 20 years.

The flows are intended to replicate seasonal scouring that occurred naturally in the Gorge long before dams, power plants and water diversions were constructed in the last century. In fact, these alterations dried up the Owens River Gorge from 1953 to 1991 until years of litigation restored some minimal flows and attempts to restart a once-fabled brown trout fishery.

The Owens River Gorge is paradoxical – so close yet so far away. Just northwest of Bishop and within sight of Highway 395, it is difficult to access with limited and steep trails to reach its waters 500 to 900 feet below the rim. Since water returned to the Owens River Gorge in 1991, it has been more popular with hikers and rock climbers than trout anglers.

It was a much different story prior to the construction of the Long Valley Dam in 1941, which created Crowley Lake, and the subsequent addition of a number of power plants along the stretch of river. Before then, the Owens River Gorge was a destination brown trout fishery with a worldwide reputation. So good was the fishing it was one of the few waters in California with limits based on weight – 25 pounds plus one fish per angler per day.

CDFW Environmental Scientist Nick Buckmaster is based in Bishop and conducts twice-yearly electrofishing surveys in the Gorge along with macroinvertebrate sampling.
“Right now, the fish populations are pretty stunted,” Buckmaster said. “We just don’t have large brown trout in the Gorge anymore.”"

The Gorge is home almost exclusively to wild brown trout and the populations are high. Buckmaster estimates between 1,500 to 5,000 trout per mile, numbers that compare favorably to many blue-ribbon trout fisheries in the state.

“The problem is they are all small. Their growth really slows down around 5 inches, and most of the fish in the Gorge are less than 8-inches long. Their growth really plateaus,” he said. “By the time they get to 8 inches, they are geriatric fish.”

Buckmaster explained that brown trout undergo an important life change once they reach between 8 and 14 inches in size. They mostly stop eating aquatic insects and transition into apex predators, preying on other fish and just about anything else of substance they can eat. The diet change leads to rapid growth and turns them into a prize for any trout angler skilled enough to catch them.

Plateauing at 5 inches, however, most of the brown trout in the Owens River Gorge never reach that important developmental milestone or achieve it only toward the end of their lives.

“If you want big brown trout, they need something to eat,” Buckmaster said. “And they usually need a lot of something to eat.”

CDFW fisheries biologists expect the pulse flows to provide just that by dramatically altering the ecosystem. The big burst of water will scour pools and restore the deep-water holding and ambush habitat needed by large brown trout. The flows will flush out years of accumulated sediment, exposing gravel beds critical for trout breeding while fostering a broader diversity of aquatic life than what’s present in the Gorge today.

Mayflies and stoneflies are largely absent from the ecosystem, and caddisflies – safely encased and underneath rocks in their larval stages – provide a limited food source. Small populations of native Owens suckers exist in the Gorge. Their numbers are expected to grow with an increase in aquatic insect life following the pulse flows, incidentally providing important forage for growing brown trout.

The high waters will inundate and benefit riverside riparian growth, offering shade and cover and additional insect habitat. The flows also are expected to flush out invasive  New Zealand mud snails that have infested the Gorge over time. The snails provide little benefit to fish and are a source of competition for other macroinvertebrate life.

Buckmaster said biologists could see positive changes in the Gorge as quickly as three months after the flows. And bigger brown trout could start turning up in Buckmaster’s electrofishing surveys – and at the end of anglers’ lines – as early as next year.

CDFW Photos. Top Photo: CDFW scientific aids Christi Kruse and Emma Hewitt identify some of the macroinvertebrate life taken from the Owens River Gorge.

Categories: General