Anadromous Fish Stressors

Man-made barriers to fish passage include road/stream crossings, irrigation diversions and dams.  Passage impediments and delays in migration affect both adult and juvenile fish. Given the magnitude and severity of the problem, reconnecting isolated stream habitat has become an important priority in restoring anadromous fish populations.  Common factors that adversely impact fish populations in California’s anadromous waters include:

  • changes in runoff patterns and water storage

  • land-use and natural resource extraction activities

  • spatial and temporal changes in connectivity

  • non-native species introductions

  • increased predator populations

  • commercial and recreational fishing

  • hatchery operations

  • natural environmental variations

Anadromous Fish Species Affected by Passage Barriers in California

California streams and rivers have historically been home to several native anadromous fish species. These include Chinook salmon, Coho salmon, Steelhead/rainbow trout, Coastal Cutthroat trout, Green sturgeon and White sturgeon, Pacific lamprey, Eulachon, and Threespine stickleback.  Historically, anadromous fish passage efforts in California have focused on Chinook salmon, Coho salmon, and Steelhead. Pink salmon have only occurred rarely in California since the latter half of the 20th century. Chum salmon are slightly more common than pink salmon, but are still highly limited in California. 

Chinook Salmon

Oncorhynchus tshawytscha

Chinook salmon are a major focus of fish passage restoration efforts. Regional populations of Chinook are either listed as endangered or threatened, in part due to greatly reduced habitat connectivity.

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Coho Salmon

Oncorhynchus kisutch

Coho salmon are a major focus of fish passage restoration efforts. Regional populations of Coho are either listed as endangered or threatened, in part due to greatly reduced habitat connectivity.

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Steelhead/Rainbow Trout

Oncorhynchus mykiss

California Steelhead are a major focus of fish passage restoration efforts. Regional populations of Steelhead are either listed as endangered or threatened, in part due to greatly reduced habitat connectivity.

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Pacific Lamprey

Entosphenus tridentatus

Currently, there are efforts across the Pacific Northwest to analyze and mediate the impact of barriers on lampreys. These efforts are often linked to passage projects associated with salmon and steelhead and once refined, will likely consist of additions or alterations to traditional salmonid passage designs.

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Coastal Cutthroat Trout

Oncorhynchus clarkii clarkii

Coastal cutthroat trout are a State of California Species of Special Concern, but have no federal status and have generally not been the focus of fish passage efforts.

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White Sturgeon

Acipenser transmontanus

Passage impacts on white sturgeon are almost exclusively limited to large dams and therefore, passage improvement projects for sturgeon are complex, expensive, and not common. 

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Green Sturgeon

Acipenser medirostris

Passage impacts on green sturgeon are almost exclusively limited to large dams and therefore, passage improvement projects for sturgeon are complex, expensive, and not common.

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Eulachon (Pacific Smelt)

Thaleichthys pacificus

Passage does not likely have a major impact on eulachon as they are found in the lower reaches of coastal rivers and streams and spend very little time in freshwater.

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Threespine Stickleback

Gasterosteus aculeatus

Threespine sticklebacks are highly adaptable and show a wide variety of life history strategies that likely greatly reduce the impact of barriers.

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Explore the Status of Population and Range of Salmon in California

Why Address Connectivity? Removing Barriers to Connectivity Improves…

Economics

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Ecosystem Function

  • Improves floodplain function—Floodplains are critical for maintaining river productivity and biotic diversity. 

  • Improves resilience to climate change—Eliminating the barriers to fish passage in California’s coastal river systems results in ecosystems that are more resilient to sea-level rise, while opening habitat upstream of a barrier provides access to cooler refugia as well as ensuring migration corridors are intact.

  • Enhances connectivity—Reconnects Fragmented Habitats.  Without ecosystem connectivity, areas could remain void of species diversity, as new populations cannot move in to mitigate a local extirpation.

  • Improves upstream nutrient quality—Anadromous fish whose movements are impeded upstream contribute less to upstream nutrient quality through carcass deposition.

  • Invasive species deterrent—Healthy watersheds are less likely to become infested with invasive species because naturally functioning ecosystems favor colonization by indigenous species. Invasive species cost the United States millions of dollars annually in lost food production, tourism and trade.

  • Improves access to more and better quality habitats—Fish passage barriers impede fish and other aquatic life from accessing existing higher quality habitats (size, distribution, and connectivity) upstream and freshwater habitat for spawning and juvenile rearing.

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Fisheries Health

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