Threats to Salmon Populations

Major Threats Facing Salmon in the PNW

There are four major causes to salmon declines in the past couple decades and can be remembered as the 4 H's.

Habitat degradation- Human induced land use change has severely reduced viable salmon habitat. Historically common occurrences such as mining, ranching, farming and logging have all played a hand in this degradation process. 

Pollution added to salmon habitat due to mining.

Young fry with Sea Lice infestation

Hatchery Operations/Hybridization- When salmon from a farm or sea pen escape into the wild, many times it will negatively affect the natives. If the farm raised salmon is a different species than the wild salmon, the farm raised will compete (many times outcompetting) with wild salmon. If the farm raised salmon is of the same species as the wild salmon, it will be able to interbred. This reduces the overall genetic diversity of the population and hurts the population health by reducing adaptability and resistance of the native salmon*. Farm raised salmon also can be a place of high concentration of parasites such as Sea Lice.  Large escape events such as the 500,000 individuals who escaped off the coast of Norwayin 2005, or the 600,000 individuals released off the coast of Scotland in 2004, can greatly harm wild salmon populations and reduce genetic diversity.

***Interesting Fact***
A single salmon farm of 200,000 individuals can  produce as much fecal matter as a city of 62,000 people** (this fecal matter is deposited directly into the surrounding water, untreated).

Over harvest- Virtually all commercial fish stocks across the globe have already begun to suffer from over harvestation, especially PNW salmon. Due to the immense conservation pressures of the last decade, salmon harvests have begun to decline***. This action can be the result of both purposeful and accidental motives. In the Puget Sound area of Washington State, salmon stocks have suffered from over harvest effects. To attain sustainable fishing levels, conservation plans were drawn up that appropriated quotas to certain groups. In this example, the policy drawn up forgot to account for all the parties that relied on salmon. Orca whales in the South Puget Sound prey on salmon and rely on them as 95% of their diet.  

Hydroelectric Dam- Dams obstruct migration of salmon and other fish both up and down river. Dams also prove hazardous traps for young smolts and can be easily swept up in the power turbines. Fragmented populations of fish lose genetic diversity and are more susceptible to widespread diseases because of this impediment.

Grand Coulee Dam, Grand Coulee, Washington

Dams across Washington States's Columbia and Snake rivers.

There are many, many dams across the Columbia and Snake rivers in Washington State. The Grand Coulee is a hydroelectric dam that is so large that it generates the most power of any dam in the entire United States^.   

Although the above reasons are the likely major players in salmon declines, other influences such as  climate, exotic invasive species and pollution lead to declines in salmon populations also.

References:

*Gardner J and DL Peterson (2003) "Making sense of the aquaculture debate: analysis of the issues related to netcage salmon farming and wild salmon in British Columbia", Pacific Fisheries Resource Conservation Council, Vancouver, BC.

 **All About Salmon Quarterly Update (http://www.seafoodchoices.com)

***www.oregon-anglers.org

  ^www.americanrivers.org