The Lahontan National Fish Hatchery Complex
Pacific Southwest Region

Fishery Improvement Program

In 2005 the passage of Public Law 109-103 under the Desert Terminal Lakes Program provided funding for fishery improvements in the State of Nevada with an emphasis on the Walker River Basin. As a result, the Walker Lake Fishery Improvement Program (FIP) was formed. The goals of this comprehensive, partnership-based program are to improve the survival of the Lahontan cutthroat trout (LCT) and other native fish in Walker Lake, the lower Walker River, and to investigate ecosystem response to decreased fresh water inflow and changing levels of total dissolved solids (TDS).

Named after Joseph Walker, a guide on the 1845 John Fremont expedition, Walker Lake is defined as a terminal lake because it has no outlet. Water flowing into Walker Lake exits only by evaporation, leaving behind naturally occurring salts that increase in concentration as the water level declines. Walker Lake is one of the last remaining lakes descendent from the ancient Pleistocene Lake Lahontan that once covered much of western and northern Nevada. From its high point about 12,000 years ago, the lake has slowly decreased in size; leaving Pyramid and Walker Lakes as the final remnants. The current accelerated water loss is a result of agricultural water diversion, which began in the late 1800’s. Research indicates that if Walker River had not been diverted, Walker Lake would currently have a lake level near the pre-agricultural development level and would have retained its full range of native fish.

Historically Walker Lake supported populations native fish including tui chub, Tahoe sucker, Lahontan redside shiner, speckled dace, and a thriving, naturally reproducing population of Lahontan cutthroat trout. The largest of the cutthroat trout, LCT evolved to be the apex predator in Lake Lahontan reaching sizes of more than 40 pounds. In 1885 a significant commercial fishery existed for LCT, as witnessed by Indian Agent W.D.C. Gibson who reported that the lake “abounded with trout.” However, water levels have dropped over 150 feet in the past 100 years, resulting in an increase in total dissolved solids (salts), which threaten the lake’s ecosystem, including the native wildlife, and the fishery.

The Fishery Improvement Team (Team), which was formed under the FIP, includes representatives from the Service, the Walker River Paiute Tribe, and the Nevada Department of Wildlife. To help achieve FIP goals, the Team developed a fisheries improvement plan which has been used to identify and implement research, monitoring, and fisheries management actions needed to advance knowledge of the Walker Lake ecosystem and improve its native fishery.

The Team has been successful in accomplishing many of its goals and continues to work cooperatively on a number of projects aimed at understanding how the lake’s ecosystem and the native fishery are responding to changes in water level, river flows into the lake, and salinity. We will provide updates on our research and findings on this website, and provide links to all reports when they become available.

Acclimation of stocked LCT

The Team has investigated a variety of methods to improve acclimation of LCT prior to stocking. These actions include testing and improving acclimation methods in a laboratory setting (Bigelow 2010) and using river inflow to allow for self-acclimation in the freshwater area at the confluence of the Walker River and Walker Lake. Prior to stocking, the Service works with the Walker River Paiute Tribe and the Bureau of Indian Affairs to procure water releases from Weber Reservoir. LCT are stocked into the river just upstream of the lake during these increased flows. Monitoring of tagged, recaptured LCT that are stocked on separate dates help us to understand which conditions are most favorable for successful acclimation.

Survival and growth of stocked LCT

The Team worked with scientists on a 5-year mark-recapture study using stocked, tagged fish to assess survivorship and growth of LCT in Walker Lake. Beginning in 2006, all LCT stocked in Walker Lake were measured and tagged with individually numbered Floy tags prior to release. The Team employed a variety of methods to recapture the tagged fish: these included netting, hook and line sampling, an expanded creel survey to gather information from anglers, and encouraging self-reporting of recaptured fish by installing additional drop boxes near lake access points. In addition, a hotline telephone number is printed on the tags so that anglers can call in their catch. Measurements of recaptured fish are used to ascertain growth, and tag information is used to determine survival rates of stocked LCT (Sedinger et al. 2012).

By studying how LCT stocked from the Lahontan National Fish Hatchery and Mason Valley Hatchery are surviving, the team is ascertaining what management actions to take to improve the long-term survivorship of LCT in the lake. Monitoring growth gives us information on whether an adequate prey base is available and whether lake water quality imposes limitations on the performance of stocked LCT.

Understanding LCT survivorship and growth under variable lake, river flow, and salinity levels will assist us in developing strategies to achieve the goal of restoring a self-sustaining lake population of LCT.

Limnological monitoring

Concurrent with other projects the Team is monitoring physical, nutrient, phytoplankton and zooplankton in Walker Lake. Limnological conditions at Walker Lake have been measured by state and federal agencies and other organizations over many years prior to initiation of the Desert Terminal Lakes Program. Using this information as a baseline, the Team expanded limnological monitoring in 2007. This 5 year project documented changes in the planktonic community as well as physical and chemical properties of Walker Lake water under variable lake, river flow, and salinity levels (Jellison and Rose 2012). The results of limnological monitoring will help interpret other changes in the lake, such as variations in the LCT prey base and LCT survival. Understanding relationships between the limnological conditions and the LCT fishery will help us predict how changes in Walker Lake surface elevation will affect the fishery, allowing better management.

Biogeochemical analysis

Changing lake levels in a terminal saline lake alter the complex interactions between the bacteria, chemicals and nutrients in the lake. In 2013, the FWS initiated a study of these interactions that will assist in management of the lake under a variety of inflow rates and as lake levels decline and eventually increase.

LCT prey items

Tui chub, which are native to Walker Lake, are the most abundant fish in the lake. They are an important food resource for LCT as well as piscivorous migratory birds such as loons, pelicans and grebes. Current and previous monitoring of the tui chub population suggests that reproduction has decreased with the increase in salinity. Learning how the LCT prey base responds to fluctuating lake levels and salinity will help us improve the LCT fishery in Walker Lake.

Three projects initiated by the Team have studied LCT prey items in Walker Lake. The first study, which began in 2007, documented the current distribution and abundance of benthic invertebrates in the lake (Herbst et al. 2013). Invertebrates are a critical resource to LCT both as direct prey items and indirectly as a food resource to tui chub, which are a preferred food item of LCT.

The second project analyzed tui chub reproductive success, physiological response and changes in abundance as TDS levels increased (Wright 2012).

The third project utilized hydroacoustic technology to estimate tui chub densities and population parameters, such as age distribution and population size over time. This project documented the condition of the tui chub population from 2009 to 20012, (Jellison and Herbst, 2012) which has been a critical time in lake’s ecological health.

Migratory Bird Surveys

Walker Lake is a historically important site for migratory and wintering birds. Stopping sites for water bird migrating along the Pacific Flyway through the Great Basin are limited and Walker Lake is the first available lake for fish eating birds migrating to their northern breeding grounds. With a healthy fishery, common loons, white pelicans, western and Clark’s grebes and double crested cormorants utilize the lake. However surveys by the Great Basin Bird Observatory indicate that the loon population has declined markedly, while salt tolerant insect eating fish such as phalaropes are becoming more common.

 

 

Distribution of Macrophytes

In addition to assessing tui chub populations, the Team is using hydroacoustic technology to map the distribution and monitor changes in Walker Lake macrophytes (aquatic plants). Macrophyte beds are a prominent feature in the lake and serve as both shelter and food for invertebrates and tui chub (Herbst et al. 2013). Macrophytes, like other Walker Lake inhabitants, are affected by changes in lake elevation and salinity. Documenting changes in macrophyte distribution in relation to fluctuating lake levels will give us further information on how the lake ecosystem as a whole responds to varying river inflow.

Creel census

With the long-term goal of improving the native LCT fishery at Walker Lake, the Team expanded the creel census to determine seasonal catch rates and assess angler satisfaction. In addition, information gathered during creel surveys is used to support ongoing monitoring of survival and growth. Looking at trends in creel data is another means by which the team can assess changes in the LCT fishery and assess appropriate management actions. Angler information is vital to these ongoing studies. The Team expanded contact with anglers not only through creel surveys but through installation of additional self-reporting drop boxes and informational signs. The Angler Information page on this website provides additional information on how to report a tagged fish.

For more information on Walker River and Walker Lake, visit these sites:
http://walkerlakenv.org/index.htm external link
http://water.nv.gov/mapping/chronologies/walker/ a detailed chronology

Last updated: April 22, 2015