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Creating Habitat in a Drawn-Down Lake

Creating Habitat in a Drawn-Down Lake

Bow of kayak floating on calm lake with foggy mountains in background
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.

Barren earth with large piles of large rocks distributed throughout
The exposed lakebed gave CDFW fisheries biologists the opportunity to safely construct different kinds of habitat for the fish in Lake Perris.

Landscape covered in gravel and piles of large rocks
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.

Calm lake facing a pile of large rocks partially submerged with mountains in the background
Rock Reefs constructed along the shore of Lake Perris, most about 1,000 square feet provide cover for juvenile fish and forage species.

Lake with partially submerged pile of rocks with trees and mountain in the background
135 Pipe Caves were constructed from PVC pipe and will provide spawning habitat for catfish.

Landscape of lake with overgrown vegetation in foreground, land peninsula with piles of large rocks in midground, and trees and mountains in background
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.

lake with partially submerged vegetation and mountain in the background
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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California Fish and Game, Issue 103(4)

California Fish and Game, Issue 103(4)

The latest issue of California Fish and Game, the California Department of Fish and Wildlife’s scientific journal, is now available online! Issue 103(4) features articles that add to the knowledge base for three marine species, all of which face potential threats from overharvesting, incidental take and loss of habitat: Thorny stingray, Chinook salmon and green abalone. 

The link opens in new windowThorny stingray (Urotrygon rogersi) (PDF) is common in the eastern Pacific, from the Gulf of California south to Ecuador, and is frequently a by-catch of commercial shrimp trawlers. Little is known about its life history and movements. It was thought to occupy relatively shallow depths ranging from two to 15 meters, with a maximum recorded depth of 30 meters. In their published research, Acevedo-Cervantes et al. report the discovery of specimens at a depth of 235 meters—an indicator that the Thorny stingray has the capacity to survive beneath the disturbance of commercial shrimping activity. According to the authors, this new information is “of vital relevance” for the management of the species.

Adams et al. examined the effects of link opens in new windowEl Niño on adult Chinook salmon as they migrate through the Gulf of the Farallones (PDF). Researchers found that the dressed weight of commercial landed Chinook was lower during El Niño compared to non-El Niño years, a reduction attributed to a disruption in the normal feeding cycle in the Gulf of the Farallones. The analysis suggests that management agencies need to give more consideration to ocean conditions as risk factors in planning the recovery of endangered and at-risk Chinook salmon spawning runs.

link opens in new windowGreen abalone (Haliotis fulgens; Philippi) (PDF) were once part of a large recreational and commercial fishery, but are now estimated to be at less than 1% of their baseline density. Past attempts at restocking wild populations using juvenile farm-raised green abalone have resulted in high mortality rates. In “Outplanting large adult green abalone (Haliotis fulgens) as a strategy for population restoration,” author Caruso explores the efficacy of using adult specimens—at least 10 years old—to augment wild populations. The resulting 40 percent survival rate is much higher than the survival rates of previous projects that used juveniles. Although it is costly to raise green abalone to adult size, it may be the best method, given the decades of past unsuccessful restocking attempts.

These articles provide information useful to fisheries managers and should be helpful for future recovery efforts.

Cover photo © Peter Hemming



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