What's depleting salmon populations?

Habitat and Hydropower

Without modifications, hydropower dams block salmon from accessing vital habitats.
Without modifications, hydropower dams block salmon from accessing vital habitats.
Joel Sartore/National Geographic/Getty Images

The health of salmon populat­ions depends a lot on the health of their living environment. The fact that salmon live in a variety of habitats throughout their lives makes them especially vulnerable to the next H -- habitat degradation. Even small disturbances can make a big difference, since spawning is highly sensitive to things like increased sedimentation. Logging, agricultural practices, trash dumping and oil spills all contribute to poor water quality.

Another factor that can disrupt habitat is the final H, hydropower dams. The Clearwater coho salmon, once abundant in the Snake River Basin of Oregon, Washington and Idaho, became extinct in the early 1960s largely due to the construction of a dam that blocked the fish's passage to and from its birthing grounds [source: Northwest Power & Conservation Council]. Besides potentially blocking access to salmons' habitats, dams may cause changes to water flows and temperatures that can devastate local populations.

Dams aren't necessarily a death knell for salmon, however. Researchers tracking salmon on the dam-laden Columbia River concluded it wasn't the dams impeding their survival but challenges they face at sea including predation, ocean warming and alterations to their prey distribution [source: Owen]. The study showed that with proper modifications to assist the salmon in their migration, dams and salmon can coexist.

The four Hs -- harvests, hatcheries, habitat and hydropower -- aren't problematic in and of themselves. It's only when they're mismanaged that things start to go downhill. While some populations have dropped so low they will take years to restore, if at all, others can be saved from following the path of the Clearwater coho.


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  • Briggs, Helen. "Extinction threat to wild salmon." BBC News. Dec. 13, 2007. (Nov. 6, 2008)http://news.bbc.co.uk/2/hi/science/nature/7142053.stm
  • "Extinction." Northwest Power & Conservation Council. (Nov. 6, 2008)http://www.nwcouncil.org/history/Extinction.asp
  • "Fish for thought." BBC News. (Nov. 6, 2008)http://www.bbc.co.uk/food/food_matters/eatingfish.shtml
  • Hume, Mark. "We're killing too many salmon, and it's time to take the blame." Globeandmail.com. Sept. 3, 2008. (Nov. 6, 2008)http://www.watershed-watch.org/Salmon-GlobeMail-Sept2_2008.pdf
  • Hunt, Ed. "Ecosystem Keystone: Salmon Support 137 Other Species." Environment News Service. July 6, 2000. (Nov. 6, 2008)http://www.bluefish.org/keystone.htm
  • Kettlewell, Jo. "Wild salmon face numbers crisis: WWF." BBC News Online. June 1, 2001. (Nov. 6, 2008)http://news.bbc.co.uk/2/low/science/nature/1362144.stm
  • Kirby, Alex. "Salmon farms 'threaten wild fish.'" BBC News. May 30, 2002. (Nov. 6, 2008)http://news.bbc.co.uk/2/low/science/nature/2016319.stm
  • "Late spawning seen as climate change calamity." Vancouver Island News Group. Nov. 22, 2006. (Nov. 6, 2008)http://www.watershed-watch.org/publications/files/LateSpawning-Nov22- 2006.pdf
  • Levy, David. "BC Sockeye Salmon Population Declines: Probable Causes and Recommended Response Strategies." Sierra Club of Canada. BC Chapter. February 2006. (Nov. 6, 2008)http://www.watershed-watch.org/publications/file/SCBC_sockeye_review.pdf
  • McGrath, Susan. "Spawning Hope." Audobon Magazine. September 2003. (Nov. 6, 2008)http://www.audubonmagazine.org/features0309/hope.html
  • "Northwest Regional Office." NOAA's National Marine Fisheries Service. (Nov. 6, 2008)http://www.nwr.noaa.gov/
  • Owen, James. "Dams Not Main Cause of Salmon Collapse, Study Says." National Geographic News. Oct. 27, 2008. (Nov. 6, 2008)http://news.nationalgeographic.com/news/2008/10/081027-salmon-dams.html
  • Owen, James. "Farmed Salmon Decimating Wild Salmon Worldwide." National Geographic News. Feb. 12, 2008. (Nov. 6, 2008)http://news.nationalgeographic.com/news/2008/02/080212-salmon-lice.html
  • "Salmon: Keystone of the Coast." Conservation Areas Design. (Nov. 6, 2008)http://www.savethegreatbear.org/CAD/Salmon.htm
  • "Salmon Population Crash Shuts Down West Coast Fishery." Environment News Service. April 10, 2008. (Nov. 6, 2008)http://www.ens-newswire.com/ens/apr2008/2008-04-10-092.asp
  • "Salmon Facts." Washington Department of Fish and Wildlife. (Nov. 6, 2008)http://www.wdfw.wa.gov/outreach/fishing/salmon.htm
  • "Wild salmon 'threatened.'" BBC News. July 16, 2002. (Nov. 6, 2008)http://news.bbc.co.uk/2/low/uk_news/scotland/2130469.stm
  • Young, Emma. "Plunging Salmon." New Scientist. May 31, 2001. (Nov. 3, 2008)http://www.newscientist.com/channel/life/endangered-species/dn817