Editing Salmon (section)

===Beavers===
[[File:Sockeye salmon jumping over beaver dam Lake Aleknagik, AK Kristina Ramstad 1997.jpg|thumb|upright|Sockeye salmon jumping over beaver dam]]

[[Beaver]]s also function as ecosystem engineers; in the process of tree-cutting and [[beaver dam|dam]]ming, beavers alter the local ecosystems extensively. Beaver ponds can provide critical habitat for [[juvenile salmon]].

An example of this was seen in the years following 1818 in the [[Columbia River]] Basin. In 1818, the British government made an agreement with the U.S. government to allow U.S. citizens access to the Columbia catchment (see [[Treaty of 1818]]). At the time, the [[Hudson's Bay Company]] sent word to [[fur trapping|trappers]] to extirpate all furbearers from the area in an effort to make the area less attractive to U.S. fur traders. In response to the elimination of beavers from large parts of the river system, [[salmon run]]s plummeted, even in the absence of many of the factors usually associated with the demise of salmon runs. Salmon recruitment can be affected by beavers' dams because dams can:<ref>{{cite web | url = http://www.nwcouncil.org/history/Extinction.asp | title = Extinction | publisher = Northwest Power and Conservation Council | access-date = 21 December 2007 | archive-url = https://web.archive.org/web/20180101173222/https://www.nwcouncil.org/history/Extinction | archive-date = 1 January 2018 | url-status = live}}</ref><ref>{{cite journal | title=Sockeye salmon (''Oncorhynchus nerka'') nursery lake fertilization: Review and summary of results |journal=Environmental Reviews|volume=12|issue=3|pages=133–162|doi=10.1139/a04-008|year=2004|last1=Hyatt|first1=K D|last2=McQueen|first2=D J|last3=Shortreed|first3=K S|last4=Rankin|first4=D P|bibcode=2004EnvRv..12..133H |s2cid=12930576| url=http://pdfs.semanticscholar.org/0cfb/39999bce91178a1091a58a6f8f9d090570cb.pdf | archive-url=https://web.archive.org/web/20200807012439/http://pdfs.semanticscholar.org/0cfb/39999bce91178a1091a58a6f8f9d090570cb.pdf | url-status=dead | archive-date=7 August 2020 }}</ref><ref>{{cite web | url = http://rocky.ess.washington.edu/grg/publications/pdfs/Pollock.pdf | title = The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA | last1 = Pollock | first1 = M. M. | last2 = Pess | first2 = G. R. | last3 = Beechie | first3 = T. J. | access-date = 21 December 2007 | archive-url = https://web.archive.org/web/20060901185801/http://rocky.ess.washington.edu/grg/publications/pdfs/Pollock.pdf | archive-date = 1 September 2006 | url-status = live}}</ref>
*Slow the rate at which nutrients are flushed from the water system; nutrients provided by adult salmon dying throughout the fall and winter remain available in the spring to newly hatched juveniles
*Provide deeper [[salmon pool]]s where young salmon can avoid avian predators
*Increase productivity through [[algal]] [[photosynthesis]] and by enhancing the conversion efficiency of the [[cellulose]]-powered [[detritus cycle]]{{Clarify | date = May 2019 | reason = Not directly clear how it's related to Salmon; also, only one of the references seem to posit a question that the photosynthesis increase due to fertilizers related to Salmon may help juvenile salmons. }}
*Create slow-water environments where juvenile salmon put the food they ingest into growth rather than into fighting currents
*Increase structural complexity with many physical niches where salmon can avoid predators

Beaver dams are able to nurture salmon juveniles in estuarine [[tidal marsh]]es where the salinity is less than 10&nbsp;ppm. Beavers build small dams of generally less than {{convert|2|ft|cm|sigfig=1|abbr=on|order=flip}} high in channels in the [[myrtle zone]]{{Clarify | date = May 2019 | reason = What's a 'myrtle zone'}}. These dams can be overtopped at high tide and hold water at low tide. This provides refuges for juvenile salmon so they do not have to swim into large channels where they are subject to predation by larger fish.<ref>{{cite web | last1 = Hood | first1 = W Gregory  | title = AN OVERLOOKED ECOLOGICAL WEB | url = http://www.skagitwatershed.org/rpapers_overlooked.html | archive-url = https://web.archive.org/web/20080724000846/http://www.skagitwatershed.org/rpapers_overlooked.html | archive-date = 24 July 2008 | url-status = dead }}</ref>