Dept of Biology, Lewis and Clark College
Dr Kenneth Clifton
 
Biology 141 Lecture Outline

Salmon in the Pacific NW as case study of ecology and human impacts

Salmon and trout in the Pacific Northwest... an important natural resource to many organisms

salmon species

Numerous species to think about

Their basic life-cycle.
Most are anadromous, i.e. they spend part of their life in freshwater, part in saltwater.

Eggs laid in a freshwater stream, in a gravel depression called a redd.

Eggs hatch, young feed on benthic invertebrates when young, later small fish.

After several months to a yr (depending on species), they migrate downstream to the ocean.

More information on juvenile life history

This involves physiological adaptation to saltwater.

Growth to maturity in the Pacific Ocean over several years.

Return to their natal stream to spawn

Salmon die after spawning (semelparity).  Sea-going trout (Steelhead and Cutthroat) return to the ocean after spawning (iteroparity)

Steelhead and Cutthroat as well as Atlantic salmon (not native to Pacific NW) return to the sea and may breed again another year (iteroparity)

Changes in salmon abundance over the last century.... not a pretty picture

salmon abundance

Given their biology, think about genetics and species concepts

The introduction of Evolutionarily Significant Units (ESU's)

Current listings of salmon stocks identify many stocks as threatened or endangered

Click here to learn more about Pacific salmon and efforts at recovery

MANY reasons for their decline.

Biggest contributor-- most biologists think -- is dams.

History of dam-building in PNW and a map

Contributions of dams to salmon decline.

Adult fish returning upstream.
Some dams have no fish ladders.

Navigating fish ladders causes mortality.

Dams change habitat (silt accumulation), causing declining conditions for spawning.

Juvenile fish going downstream.

Dams slow water down and make it warmer, increasing mortality.

Dams make the journey to saltwater take longer, thus fish transform physiologically too quickly.

Irrigation diversions cause some mortality.

Turbines and (more likely) spillways cause mortality.

Dams attract predators.

Attempted solutions and their shortcomings:

Fish hatcheries.

Barging fish around dams.

Drawdowns of reservoirs to increase flows during spring migration.

New spillway engineering

Dam breaching

Favored by scientists

Some lobbies suggest such strategies are not necessary

The political players:

The Army Corps of Engineers.

Bonneville Power Administration.

The National Marine Fisheries Service.

The State of Oregon.

Coastal salmon runs: not affected by large dams.. but the also show declines.

 

What other factors may influence the health of salmon populations?

 

 

An overview of salmon issues here

A question about salmon conservation

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