Science Spotlight

A new egg mat prior to deployment (CDFW photo by Marc Beccio)


Sturgeon egg mats deployed in a local waterway (CDFW photo by Marc Beccio)


Egg mats with Green Sturgeon eggs (CDFW photo by Marc Beccio)

CDFW biologists have been taking a new approach to looking at reproduction in one of the oldest fish species in existence.

Green sturgeon, which are listed as threatened under the Federal Endangered Species Act, are in effect a living fossil, having swam in both the fresh and ocean waters from California to Alaska for more than 200 million years.

They are a very slow-growing fish, typically living 60 to 70 years and reaching lengths of seven feet and weights of up to 350 pounds. Little is known about where they spawn in the Central Valley and how successful they are when they spawn.

In the spring of 2017, CDFW biologists began deploying egg mats in various rivers in the Sacramento Valley. In 2018, they documented green sturgeon spawning in the Yuba River for the first time, finding approximately 270 green sturgeon eggs on an egg mat deployed immediately below Daguerre Point Dam in Yuba County.

The egg mats consist of 3.5-foot by 2.5-foot metal frames that weigh about 20 pounds and are filled with a material similar to that used for a furnace filter. Mats are deployed by being gradually lowered to the river bottom from the bow of a boat. They are then retrieved by slowly hauling in the float line to avoid dislodging eggs stuck on the mat.

Unlike salmon and trout which dig redds and cover their eggs with gravel, green sturgeon females “broadcast” (release) their eggs into the water, which then sink to the river bottom, where their sticky surfaces adhere to various objects. Of eight egg mats deployed in the pool below Daguerre Point Dam, the biologists collected 270 eggs from just a single mat. As spawning locations can be difficult to identify, and eggs can be distributed broadly by the current within individual locations, documenting this spawning event was important.

A subsample of 33 eggs was retained to determine the developmental stage which will be used to calculate a spawning date. The mat was then lowered back to the river bottom. The 33 eggs collected represent about 0.02 percent of the total produced by a female green sturgeon of average size.

After confirming the presence of adult green sturgeon in the Yuba River, CDFW biologists believe the river may be important habitat for the species. Further research using these egg mats over the next several years will help fisheries managers identify critical spawning locations and habitat requirements for the future protection and enhancement of the species.

CDFW Photos. Top Photo: Green Sturgeon underwater. CDFW photo by Mike Healey.

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Media Contact:
Kyle Orr, CDFW Communications, (916) 322-8958

Joe Millosovich, an environmental scientist who specializes in lake and fisheries management in the Central Valley, came all the way from Fresno to captain one of the electrofishing boats collecting bass in the Delta Jan. 16. Several of CDFW’s biologists participating in the outing called it one of their favorite days of the year.


Max Fish, an environmental scientist with CDFW’s Inland Fisheries Program, captained the electrofishing boat that collected the largest largemouth bass of the morning – a 10-pound-plus whopper.


Kyle Murphy, a senior environmental scientist with CDFW’s Inland Fisheries Program, shows off two of the larger Delta largemouth bass headed for the International Sportsmen’s Exposition demonstration tank in Sacramento.

Among the more popular attractions at the Sacramento International Sportsmen’s Expo each January is the Western Bass Aquarium Demo Tank. The 6,000-gallon aquarium displays dozens of trophy largemouth bass collected by CDFW biologists from the Sacramento-San Joaquin Delta. The aquarium demo tank, with bleachers on both sides, is where professional bass anglers lead seminars demonstrating the latest techniques and can’t-miss lures – all without hooks attached so as not to injure the fish.

“This is the best display of largemouth bass anywhere in the country,” said Kent Brown, the longtime host of the ISE demonstration tank. “And that’s not just me talking. That’s from tournament bass fishermen who travel all over the country. There’s just no bass anywhere that can rival these Delta bass.”

The tank is also a tremendous source of pride for the CDFW fisheries biologists tasked with collecting the fish.

“It’s great for people to see the kind of fish they can catch here in their own backyard,” says Ben Ewing, a CDFW district fisheries biologist who headed the ISE collection effort this year. “All the fish get released back into the Delta immediately after the show and literally are available for anyone with a fishing license to catch.”

A mix of 16 fisheries biologists and volunteers assembled along the Delta near Stockton the morning of Jan. 16, the day before the opening of the four-day ISE show at Sacramento’s Cal Expo. They climbed onto four electrofishing boats to probe likely largemouth hideouts – tule stands, rip-rap shoreline, sunken boats, submerged tree limbs and other structure.

“We all come together to try and make a good display for the public,” Ewing said.

Over the years, a friendly competition has developed. A trophy and bragging rights go to the CDFW boat captain who collects the largest bass for the show. Each of the four captains took off with their crews in different directions searching for a largemouth bass that might not only win the day but one that might top their all-time ISE show record fish of more than 13 pounds.

The boats sent targeted currents of electricity through the water while crew members standing on the bow were ready with nets to scoop up the stunned fish for deposit into the live wells for safekeeping. In more than 20 years of providing Delta largemouth bass for the Sacramento ISE show, CDFW biologists have refined their methods and strategies.

In addition to looking for the largest fish, a mix of sizes is collected. Smaller bass add perspective in the tank and make the biggest fish look even bigger. Suckers, catfish and large sunfish add some fun diversity to the display. Striped bass are a no-go – they don’t do so well in transport and they’ve been known to jump out of the aquarium.

Max Fish, an environmental scientist with CDFW’s Inland Fisheries Program, piloted one of the electrofishing boats. He explained how these vessels are important research tools that allows CDFW scientists to survey fish populations and assess health in the state’s lakes and reservoirs. CDFW puts one of the boats on display at the ISE show each year and points out the connection between the boat and the bass in the tank.

On that overcast January morning with major winter storms looming in the forecast, Fish sent 340 volts of electric current through the shallow Delta waters. The conditions for electrofishing were nearly ideal – the plentiful organic material in the Delta helps conduct electricity while the overcast skies were unlikely to spook fish and send them deep beyond the boat’s effective reach.

Fish said the boat’s electric current ranges about 10 feet deep and about 20 feet wide – roughly the span between the two sets of anodes extending from the boat’s bow into the water.

Fish’s efforts were rewarded with the largest bass of the day – a 10.3-pound lunker among others in the 9- and 8-pound class. After congratulations, photos and good-natured ribbing from his colleagues back at the dock, the 60 or so fish collected by all the boats were shuttled directly to Sacramento’s ISE show in an aerated live well.

Meeting them there was CDFW veterinarian and fish pathologist Keven Kwak, who tested and treated the aquarium’s water to make sure it was safe for what would be the fish’s short, but celebrated stay in Sacramento.

CDFW Photos. Top Photo: CDFW biologists stand ready with nets in hand to scoop up temporarily stunned fish for the ISE’s bass fishing demonstration tank in Sacramento. Biologists look for the biggest and best specimens to showcase the Delta fishery. While the biologists are targeting largemouth bass primarily, the electric current brings up carp, catfish, suckers, striped bass and all manner of sunfish. Within a minute or two, the stunned fish come to and swim off.

Media Contact:
Peter Tira, CDFW Communications, (916) 322-8908

CDFW staff and volunteers set a one-day record of 1.5 million eggs collected on the Little Truckee River earlier this month.


CDFW staff and volunteers use seine nets and electric fishing techniques to corral and capture adult Kokanee salmon.


Volunteers from the California Inland Fisheries Foundation, Inc. and Kokanee Power help CDFW personnel capture Kokanee salmon.

Each October, conditions permitting, CDFW staff and volunteers from the California Inland Fisheries Foundation, Inc. and Kokanee Power descend on the Little Truckee River, just upstream from Stampede Reservoir near Truckee, and get to work on the annual Kokanee Egg Take.

Using seine nets and electrofishing techniques to corral and capture adult Kokanee Salmon, staff and volunteers then collect eggs and milt (fish semen) add them together in specific ratios to complete the spawning process. The fertilized eggs are carried to an egg care station on the side of river where they are measured, enumerated, disinfected and finally placed in containers to be transferred to the San Joaquin Hatchery.

Staff at San Joaquin Hatchery incubate, hatch and care for the early-life stages of the resulting baby salmon. Some fertilized eggs are shipped to other CFDW hatcheries for hatching and rearing. Resulting fingerling fish are stocked to several approved waters in the state to provide recreational angling opportunities.

“By all accounts, this year set the one-day egg take record of 1.5 million eggs,” said Roger Bloom, CDFW’s Inland Fisheries Program Manager. “This was a collective effort from our scientists, hatchery staff and stakeholders that culminated into actions in support of fisheries across the state. Given the magnitude of eggs taken on that record day, it took a non-stop effort of over 23 straight hours to get the job done, which highlights the dedication and resolve CDFW personnel have -- especially the hatchery staff who now will care for these eggs that will eventually grow to be little salmon!”

Kokanee Salmon were introduced into California waters to provide diverse recreational angling opportunities for anglers and have become an extremely popular sport fish. They are typically smaller than the landlocked Chinook Salmon, with an average size of about 12 inches. This summer, CDFW will release the Kokanee Salmon fingerlings that emerge from this collection effort into lakes and reservoirs throughout the state.

The landlocked version of the Sockeye Salmon, the Kokanee (pronounced coke-a-nee) Salmon spends its entire life in fresh water. Instead of migrating to the ocean, adult Kokanee Salmon inhabit large lakes before returning to their natal streams or gravelly shorelines to spawn. Like all Pacific salmon, Kokanee die after spawning, the whole life cycle taking from two to four years.

CDFW Photos. Top Photo: Volunteer holds a Kokanee salmon during work on the Little Truckee River.

Brush habitats were created and put into Lake Perris to provide fish with habitat to feed and reproduce. The habitats will be completely submersed when the lake is filled to capacity.


The exposed lakebed gave CDFW fisheries biologists the opportunity to safely construct different kinds of habitat for the fish in Lake Perris.


Rock Reefs and Spawning gravel areas have been created and placed in more than 100 places around Lake Perris that will be utilized once the lake is returned to full capacity.


Rock Reefs constructed along the shore of Lake Perris, most about 1,000 square feet provide cover for juvenile fish and forage species.


135 Pipe Caves were constructed from PVC pipe and will provide spawning habitat for catfish.


Biologists created about 1,500 brush habitats in hundreds of locations on the banks of Lake Perris and in accessible locations further into the lake.


Biologists created about 1,500 brush habitats in hundreds of locations on the banks of Lake Perris and in accessible locations further into the lake.

More than a decade ago, Southern California freshwater anglers were disappointed to see a tried-and-true fishing spot dramatically affected by an emergency lake drawdown. Due to seismic concerns with the Perris Dam, California Department of Water Resources (DWR) officials deemed it necessary to reduce the water level at Lake Perris near Riverside by several thousands of acre-feet.

The drawdown exposed about 25 feet of bank around the perimeter of the lake. Since water was not going to be available for years while the dam was assessed and repaired, CDFW embarked upon a fisheries habitat mitigation project (funded by DWR) to create new fish habitat in the remaining water and the now exposed lakebed.

The project had two phases. The first was to immediately create fisheries habitat in the drawn-down portion of the lake in order to maximize use of the remaining water. The second was to build new habitats on the temporarily exposed areas, with the hope of benefitting both sport-fish species and anglers when the lake is eventually refilled. 

After 12 years, both phases are nearly completed.

After the initial water level reduction, teams from CDFW and DWR began working to prevent the immediate collapse of the lake’s fishery. The initial work, which took three years, involved the creation and placement of about 400 fish habitats made of recycled Christmas trees and citrus limbs. The man-made shelters ensured the fish would have places to hide and reproduce.

After the initial triage, CDFW biologists began to place additional habitats into the remaining water of Lake Perris. These habitats, made of thousands of tree trunks, citrus limbs and whole tree stumps would eventually give the lake’s fish an additional 1,500 refuges for safety. 

The citrus limbs were drilled with a ½” hole in the base and multiple limbs were tied together as compactly as possible and attached to a concrete block with polypropylene ropes to weigh them down. They were then placed strategically in different parts of the lake. These citrus habitats should provide cover for the warm water fish for at least 10 - 15 years.

Due to their bulk, increased buoyancy and weight, the single tree stumps were placed individually around the lake and weighted down with concrete blocks to keep them anchored.

Because the lake will be refilled to capacity once dam repairs are complete, it is important that the scientists are able to carefully track each habitat location. They worked in quadrants, placing 20 - 60 bundles into each to create “communities.” The grouped communities increase localized productivity of the warm water fish native to the lake and contribute to maintaining the warm water fisheries while the lake is in its reduced capacity. Each of the quadrant’s corners was marked with GPS, enabling scientists to record and monitor data specific to each location. 

The second phase of the project was the implementation of a Fishery Habitat Plan for the exposed lakebed above the drawn-down area. The implementation of the plan is a requirement of the Lake and Streambed Alteration Agreement between CDFW and DWR.

As with the below-water work that had already been completed, CDFW scientists carefully planned what kinds of habitat to create, what materials to use and where to place them in the open, exposed lakebed in order to provide the best environments for fish when the lake was fully restored. Areas were selected for habitat placement based on accessibility, proximity to existing natural habitat directly affected by the water reduction, avoidance of areas utilized for construction activities, distance from swimming areas and consideration of boating hazards.

Multiple types of habitats were designed and installed in Lake Perris, including:

• Brush habitats. Similar to the citrus branch habitats already placed in phase one, these brush habitats add to the terrestrial vegetation growth that has thrived in the lakebed since initial triage efforts began in 2006.
• Pipe caves constructed from 12” diameter PVC pipes. Approximately 4 feet long and capped at one end with concrete, these will provide spawning habitat for catfish that was lost when the lake was drawn down. A total of 135 pipe caves were placed around the rock reefs and terrestrial vegetation and will allow the young catfish to disperse into favored rearing habitat.
• Rock reefs were created from 226 dump truck loads of material stockpiled by DWR from a nearby rock quarry. These rock piles cover about 110,000 square feet of the lakebed -- about the size of two football fields. Staff created 109 rock reefs, each about 1,000 square feet (about the size of an average home lot). These provide cover for juvenile fish and forage species (such as crayfish) as well as spawning habitat and foraging areas for adult fish. Their placement is designed to allow fish to transition from deeper waters to shallower waters -- and vice-versa -- when the lake returns to normal operating levels.
• Spawning gravel areas. Thirty of these were created from suitable bottom composition for sunfish, bass, bluegill, etc. to spawn on and around. Almost 200,000 square feet of gravel bed habitat are now in the shallowest areas of the lake, adjacent to rock reefs or terrestrial vegetation that will be covered once the lake refills.
  
  After years of cooperative work Lake Perris is nearly ready to be refilled and with the thousands of new and improved habitats local anglers will be shouting “fish on” for decades to come. 

CDFW Photos. Top Photo: Citrus tree stumps, weighted down with concrete blocks to keep them anchored were placed individually around Lake Perris to create small habitats called communities.

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Since 1959 the California Department of Fish and Wildlife (CDFW) has used a combination of scientific techniques to better understand fish populations and the general health of Northern California waterways. Examples include tagging sturgeon, trawling the Delta for smelt, and counting salmon carcasses. CDFW uses data from these strategies and others to help influence operations of the State Water Project and Central Valley Project, ultimately helping decision makers determine water flows. This short video highlights these operations along the Sacramento River and into the Delta, including a smelt survey conducted by Environmental Scientist Felipe la Luz.