The Deshka River hosts five species of Pacific salmon and is home to one of the most productive fisheries in the Matanuska-Susitna (Mat-Su) basin. It is also among the warmest salmon systems in the Mat-Su with summer water temperatures regularly exceeding thresholds considered stressful for rearing juvenile and spawning adult salmon. Based on available data, the Mat-Su has some of the warmest streams in Alaska.

Water temperature affects all phases of the salmon lifecycle; egg/embryo survival, juvenile growth, timing of seaward migration and migration rate of returning adults. Warm water temperature induces stress in salmon and makes them more vulnerable to pollution, predation and disease. Research indicates that warm summer temperatures negatively impact the survival of juvenile Chinook salmon rearing in the Deshka and other streams around the region (Mauger et al. 2017; Jones et al. 2020). In 2019, warm stream temperatures blocked adult migration and had negative effects on juvenile growth.

Management actions to minimize the effects of warming on Deshka River salmon have been limited by a poor understanding of both their thermal requirements and the extent and distribution of thermally suitable habitats.

To help close these gaps, partners from the U.S. Fish and Wildlife Service (USFWS), University of Alaska Anchorage (UAA), and Cook Inletkeeper have been:

• Monitoring water temperature, streamflow and the distribution of juvenile Chinook and Coho salmon throughout the growing season across the Deshka River watershed. These data, when combined with output from the spatially explicit watershed temperature model (based on data from the Deshka River temperature monitoring and flow measurements), will allow partners to define the temperature range used by juvenile Chinook and Coho salmon rearing in the Deshka River watershed (i.e., their thermal niches; see Isaak et al. 2017).

• Conducting long term stream temperature monitoring, coupled with remote sensing data to enable partners to identify cold-water refugia in the Deshka River system, which may be critical habitat for salmon in a warming climate.

• Modeling to estimate how the extent and distribution of thermally suitable habitat has changed over time, how it will change in the future, and the degree to which it has affected the size of past salmon runs. This information can guide conservation and fishery management actions by identifying key rearing areas for juvenile salmon, prioritizing areas for conservation actions that maintain cool water and habitat connectivity, predicting the effects of warming on future salmon production, and reserving instream flow in key tributaries. This work can feed directly into fishery management by informing pre-season forecasts and spawning escapement goals.

These same partners are mirroring efforts underway on the Deshka and initiating a multi-year effort to understand thermal needs of salmon life stages and model changing temperatures across the Little Susitna watershed - another top producing salmon stream in the Mat-Su basin. Partners will continue to monitor water temperature, streamflow, and summer distribution of juvenile Chinook and Coho salmon in each of these historically productive salmon streams that differ in terms of watershed topography and temperature regimes. This information will guide conservation efforts by identifying areas that will remain cool enough to function as salmon habitat well into the future and highlighting stream segments that are key to maintaining connectivity among these areas.

Human Interest/Community Benefit:

The Deshka River hosts five species of Pacific salmon, and often produces the largest Chinook salmon returns in upper Cook Inlet and contributes to subsistence resources for the residents of Tyonek. It’s home to a popular salmon sport fishery – which has waned in recent years due to lower returns and subsequent fishing restrictions.

In an economic analysis commissioned by the Mat-Su Borough in 2007 and again in 2017, the economic benefits of sportfishing in the Mat-Su, including angler days, direct spending, and employment were reduced by approximately half during this time period. These findings underscored both sportfishing as an important component of the Mat-Su Borough’s economy and the importance of healthy salmon returns while maintaining fishing opportunities for both residents and visitors.

Although largely inaccessible by road, the Deshka faces potential changes in habitat protections and new potential development pressures. The Deshka River is one of six rivers in the Susitna River basin designated as a “Recreational River” under the Recreational Rivers Act, which was passed by the Alaska State Legislature in 1988. The subsequent Susitna Basin Recreational Rivers Management Plan was created in 1991 to ensure recreational access and maintain cultural and ecological characteristics of these rivers. During the 2021 Legislative Session, Senate Bill 97 was introduced to repeal the Susitna Basin Recreational Rivers Management Plan. The bill has not been voted on by both chambers, however, a governor-appointed Advisory Board has been formed to review the Management Plan. The state is separately considering approval of natural gas exploration licenses that would cover a large portion of the Deshka River in an area of potential coal bed methane deposits.

Additional partner efforts:

USFWS/Alaska Department of Fish & Game/United States Geological Survey: Reserving water for fish. Partners collected necessary data to secure water rights on Kroto, Moose and Trapper Creeks and other small Deshka River drainage streams as supplemental sites. Partners have been completing water reservations like these, on important salmon streams vulnerable to development, so that as the region grows and demand for water resources increases or climatic conditions change, water will be reserved to remain in the stream for the benefit of fish and aquatic life.

Cook Inletkeeper: Real time temperature monitoring on the Deshka. Since 2013, Cook Inletkeeper has maintained an online, real time temperature monitoring station below the Deshka River weir operated by ADFG. Learn more here.

Alaska Department of Fish and Game: Monitoring salmon returns and genetic identification: ADFG operates a weir at mile 7 on the Deshka River, and provides daily counts of migrating adult salmon. These data will be used to overlap timing of warm events with habitat use of salmon by life stage. Among other benefits, ADFG is collecting tissue samples to provide genetic identification of migrating fish.

University of Alaska Fairbanks: Invasive species research. The Deshka River is home to an invasive population of Northern Pike. A UAF graduate student is assessing how invasive Northern Pike predation on juvenile salmon in the Deshka River may change in response to warming water temperatures.

Publications:

Cook Inletkeeper monitored the mainstems of 48 salmon streams in the Mat-Su Basin and elsewhere around Cook Inlet. Collaborations with other partners, including the University of Alaska and the U.S. Fish and Wildlife Service, have produced three journal articles that analyze how ongoing warming may be affecting salmon:

Lowland salmon streams in the Mat-Su Basin are warming rapidly and parts of these watersheds have already reached temperatures that are considered harmful to salmon during warm summers. Read the article: bit.ly/warmingmatsustreams

Mat-Su Basin salmon streams are predominantly cold, but temperature regimes will be warmer, more variable, and less diverse in the coming decades. Read the article: bit.ly/thermaldiversity

Recent declines in Cook Inlet’s Chinook salmon populations can be attributed in part to climate-driven changes in temperature and streamflow in freshwater habitats. Read the article: bit.ly/climateandchinook

Project Timeline: 

2017-2022

Partners:

Core partners in this work are Cook Inletkeeper, U.S. Fish and Wildlife Service,
University of Alaska Anchorage. Additional partners and supporters include (but are not limited to) ADFG, USGS, Mat-Su Salmon Partnership.