Editing Rainbow trout (section)

==Conservation==
[[File:Rainbow Trout US Range.JPG|thumb|alt=Map of U.S. range for rainbow trout|U.S. range map for ''O.&nbsp;mykiss''; native (light brown) and introduced (dark brown and pink)<ref>{{cite web |url=https://nas.er.usgs.gov//queries/FactSheet.aspx?speciesID=910 |author1=Fuller, P. |author2=Larson, J. |author3=Fusaro, A. |author4=Neilson, M. |title=Fact Sheet-''Oncorhynchus mykiss'' |work=USGS Nonindigenous Aquatic Species Database, Gainesville, FL. |publisher=U.S. Geological Survey |date=2013-11-04 |access-date=2013-11-30}}</ref>]]
Populations of many rainbow trout subspecies, including anadromous forms (steelhead) of {{nowrap|''O. m. irideus''}} (coastal rainbow trout) and {{nowrap|''O. m. gairdneri''}} (Columbia River redband trout), have declined in their native ranges due to over-harvest, habitat loss, disease, [[invasive species]], pollution and hybridization with other subspecies, and some introduced populations, once healthy, have declined for the same reasons. As a consequence, some rainbow populations, particularly anadromous forms within their native range, have been classified as [[Endangered species|endangered]], [[Threatened species|threatened]] or species of special concern by federal or state agencies.<ref>{{cite web |url=http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=E08D |title=Species Profile: Steelhead |publisher=U.S. Fish and Wildlife Service |access-date=2013-11-29 |url-status=dead |archive-url=https://web.archive.org/web/20131203031938/http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=E08D |archive-date=2013-12-03 }}</ref> Rainbow trout, and subspecies thereof, are currently a [[United States Environmental Protection Agency|U.S. Environmental Protection Agency]]-approved indicator species for acute freshwater [[toxicity]] testing.<ref>{{cite web |url=http://water.epa.gov/scitech/methods/cwa/wet/index.cfm |title=Whole Effluent Toxicity |publisher=Environmental Protection Agency|date=2013-09-12 |access-date=2013-11-29}}</ref>

Many non-profit organizations have formed to protect, conserve and restore native rainbow trout and steelhead populations. Generally, in partnership with various universities, state, federal and tribal agencies, and private interests, these organizations sponsor projects to restore habitat, prevent habitat loss and promote awareness of threats to native trout populations. [[File:Two pairs adult Steelhead trout and 2 redds March 2013 Stevens Creek.jpg|thumb|left|Two pairs of steelhead spawning in the lower reaches of [[Stevens Creek (California)|Stevens Creek]] in [[Mountain View, California]], in 2013]]
[[Trout Unlimited]] (TU) is a non-profit organization dedicated to the conservation of North American freshwater streams, rivers, and associated upland habitats for trout, salmon, other aquatic species, and people.<ref>{{cite book |author1=Washabaugh, William |author2=Washabaugh, Catherine |title=Deep Trout: Angling in Popular Culture |publisher=Berg |location=Oxford, United Kingdom |isbn=978-1-85973-393-6 |year=2000 |page=119 }}</ref> A typical TU project is the Circle Creek Fish Passage Project, in which access to a spawning stream is being improved for steelhead and other salmonid species.<ref>{{cite web |url=http://www.tu.org/tu-projects/circle-creek-fish-passage-project |title=Circle Creek Fish Passage Project |publisher=Trout Unlimited |access-date=2014-01-04 |archive-date=2015-12-23 |archive-url=https://web.archive.org/web/20151223045552/http://www.tu.org/tu-projects/circle-creek-fish-passage-project |url-status=dead }}</ref> The [[Wild Salmon Center]], an international coalition of Russian, Canadian and U.S. scientists, sponsors the Kamchatka Steelhead Project, a 20-year (1994–2014) scientific program to study and conserve the present condition of Kamchatkan steelhead ("mikizha"), a species listed in the [[Red Data Book of the Russian Federation|''Red Data Book of Russia'']].<ref>{{cite web |url=http://www.wildsalmoncenter.org/programs/kamchatka/steelhead_project_report.php |title=Steelhead Project Report |publisher=Wild Salmon Center |date=November 2004 |access-date=2013-12-01 |url-status=dead |archive-url=https://web.archive.org/web/20140306070614/http://www.wildsalmoncenter.org/programs/kamchatka/steelhead_project_report.php/ |archive-date=2014-03-06 }}</ref> Other high-profile organizations involved in rainbow trout conservation include [[California Trout]], which protects wild trout and other salmonids in the waters of California.<ref>{{cite web |url=http://caltrout.org/about/ |title=About Us |publisher=California Trout |access-date=2013-12-01 |archive-date=2013-12-03 |archive-url=https://web.archive.org/web/20131203040651/http://caltrout.org/about/ |url-status=dead }}</ref> The Steelhead Society of British Columbia promotes the wellbeing of wild salmonids in British Columbia.<ref>{{cite web |url=http://www.steelheadsociety.org/about-us |title=About Us |publisher=The Steelhead Society of British Columbia |access-date=2013-12-01}}</ref> In 1997, a group of approximately 40 ichthyologists, biologists and naturalists from several U.S. and Mexican institutions formed a collaborative group—Truchas Mexicanas—to study the diversity of [[Mexican native trout]], most of which are considered subspecies of {{nowrap|''O. mykiss''}}.<ref>{{cite web |url=http://truchasmexicanas.org/ |title=Truchas Mexicanas |access-date=2014-02-12}}</ref>

===Hybridization and habitat loss===
Rainbow trout, primarily hatchery-raised fish of the coastal rainbow trout subspecies {{nowrap|(''O. m. irideus'')}} introduced into waters inhabited with cutthroat trout, will breed with cutthroats and produce fertile hybrids called [[Cutbow|cutbows]].<ref>{{cite journal |title=Weight, Length, and Growth in Cutbow Trout (''O. m. x clarkii'') |journal=Nature Precedings |url=http://precedings.nature.com/documents/6432/version/1/files/npre20116432-1.pdf |year=2011 |last=Parker|first=David|author2=Avers, Thomas |author3=Courtney, Michael  |access-date=2014-01-04 | doi = 10.1038/npre.2011.6432.1|doi-access=free }}</ref> In the case of the [[westslope cutthroat trout]] (''O.&nbsp;clarki lewisi''), hybridization with introduced rainbow and [[Yellowstone cutthroat trout]] (''O.&nbsp;clarki bouvieri'') is threatening the westslope cutthroat trout with [[Genomics|genomic]] [[extinction]].<ref>{{cite journal |url=http://academic.regis.edu/ckleier/Conservation%20Biology/IntercrossesandUSEndangered.pdf |title=Intercrosses and the U.S. Endangered Species Act: Should Hybridized Populations be Included as Westslope Cutthroat Trout? |journal=Conservation Biology |volume=18 |date=October 2004 |location=Washington, D.C. |pages=1203–1213 |author1=Allendorf, Fred W. |author2=Leary, Robb F. |author3=Hitt, Nathaniel P. |author4=Knudsen, Kathy L. |author5=Lundquist, Laura L. |author6=Spruell, Paul |name-list-style=amp |issue=5 |doi=10.1111/j.1523-1739.2004.00305.x |bibcode=2004ConBi..18.1203A |s2cid=9574838 |access-date=2014-01-12 |archive-date=2014-01-12 |archive-url=https://web.archive.org/web/20140112162500/http://academic.regis.edu/ckleier/Conservation%20Biology/IntercrossesandUSEndangered.pdf |url-status=dead }}</ref> Such introductions into the ranges of redband trout {{nowrap|(''O. m. gairdneri''}}, ''newberrii'', and ''stonei'') have severely reduced the range of pure stocks of these subspecies, making them "species of concern" in their respective ranges.<ref>{{cite journal|last=Dickson|first=Tom|url=http://fwp.mt.gov/mtoutdoors/HTML/articles/2011/RedbandTrout.htm|title=Montana's Redband Trout|journal=Montana Outdoors|publisher=Montana Fish, Wildlife & Parks|issue=May–June 2011|access-date=2013-11-29|archive-date=2013-09-28|archive-url=https://web.archive.org/web/20130928223503/http://fwp.mt.gov/mtoutdoors/HTML/articles/2011/RedbandTrout.htm|url-status=dead}}</ref>
[[File:Gulf of Alaska cutbow trout.jpg|thumb|A cutbow from the Gulf of Alaska]]
Within the range of the Kern River golden trout of Southern California, hatchery-bred rainbows introduced into the Kern River have diluted the genetic purity of the [[Kern River rainbow trout]] {{nowrap|''(O. m. gilberti)''}} and [[golden trout]] {{nowrap|''(O. m. aguabonita)''}} through intraspecific breeding.<ref>{{cite journal|title=Trouts of the Upper Kern River Basin, California, with Reference to Systematics and Evolution of Western North American Salmo|journal=Journal of the Fisheries Research Board of Canada |last=Shreck|first=Carl B.|author2=Behnke, Robert J.  |doi=10.1139/f71-143|year=1971|volume=28|issue=7|pages=987–998}}</ref><ref>{{cite web |url=http://caltrout.org/pdf/Kern%20River%20Rainbow%20Trout.pdf |title=Kern River Rainbow Trout |publisher=Cal Trout |access-date=2014-03-03}}</ref><ref>{{cite web |url=http://caltrout.org/pdf/California%20Golden%20Trout.pdf |title=California Golden Trout |publisher=Cal Trout |access-date=2014-03-03}}</ref> The [[Beardslee trout]] {{nowrap|(''O. m. irideus'' var. ''beardsleei'')}}, a genetically unique lake-dwelling variety of the coastal rainbow trout that is isolated in [[Lake Crescent]] (Washington), is threatened by the loss of its only spawning grounds in the [[Lyre River]] to [[siltation]] and other types of habitat degradation.<ref name=Meyer>{{cite journal |last=Meyer |first=J. |author2=Fradkin, S.  |title=Summary of Fisheries and Limnological Data for Lake Crescent, Washington |journal=Olympic National Park Report |location=Port Angeles, Washington |year=2002}}</ref>

===Invasive species and disease===
====Whirling disease====
{{see also|Salmonid susceptibility to whirling disease}}
{{nowrap|''[[Myxobolus cerebralis]]''}} is a [[myxosporea]]n [[parasite]] of [[Salmonidae|salmonids]] (salmon, trout, and their allies) that causes whirling disease in pen [[Aquaculture of salmonids|farmed salmon]] and trout and also in [[Wild fisheries|wild fish populations]].<ref name=whirlingdiseaseinitiative2009>{{cite web |url=http://whirlingdisease.montana.edu/pdfs/wdi_final_2009.pdf |title=Whirling Disease Initiative: Final Report |date=October 2009 |publisher=Montana Water Center, Montana State University |page=1 |access-date=2013-12-30 |url-status=dead |archive-url=https://web.archive.org/web/20120717065507/http://whirlingdisease.montana.edu/pdfs/wdi_final_2009.pdf |archive-date=2012-07-17 }}</ref> It was first described in rainbow trout introduced to Germany a century ago, but its range has spread and it has appeared in most of Europe, northern Asia, the U.S., South Africa<ref name="S-Afr-CIB">{{cite web | title=Trout impact on distributional patterns of native fish species | website=[[Centre for Invasion Biology]] | date=2021-09-20 | url=http://blogs.sun.ac.za/cib/trout-impact-on-distributional-patterns-of-native-fish-species/ | access-date=2021-09-25 | first=Lerato | last=Maimela}}</ref> and other countries.<ref name=TUWD2009>{{cite web |url=http://fwp.mt.gov/fwpDoc.html?id=40473 |title=Whirling Disease in the United States – A Summary of Progress in Research and Management 2009 |publisher=Whirling Disease Foundation, Trout Unlimited |access-date=2013-12-31 |author1=Elwell, Leah C. Steinbach |author2=Stromberg, Kajsa Eagle |author3=Ryce, Eileen K.N. |author4=Bartholomew, Jerri L. |archive-date=2013-08-28 |archive-url=https://web.archive.org/web/20130828195623/http://fwp.mt.gov/fwpDoc.html?id=40473 |url-status=dead }}</ref> In the 1980s, {{nowrap|''M. cerebralis''}} was found to require ''[[Tubifex tubifex]]'' (a kind of [[Annelid|segmented worm]]) to complete its [[Biological life cycle|life cycle]]. The parasite infects its hosts with its cells after piercing them with [[polar filament]]s ejected from [[cnidocyte|nematocyst]]-like capsules.<ref name=wddescription/>
[[File:Worldwide distribution of Mcerebralis.png|right|thumb|300px|alt=Map of worldwide distribution of Whirling Disease|''M. cerebralis'' has been reported in Germany (1893), Italy (1954), [[USSR]] (1955), including [[Sakhalin]] Island (1960), U.S. (1958), [[Bulgaria]] (1960), [[Socialist Federal Republic of Yugoslavia|Yugoslavia]] (1960), Sweden (1966), South Africa (1966), Scotland (1968), New Zealand (1971), [[Ecuador]] (1971), Norway (1971), [[Colombia]] (1972), [[Lebanon]] (1973), Ireland (1974), Spain (1981) and England (1981).]]
This parasite was originally a mild pathogen of brown trout in central Europe and other salmonids in northeast Asia, and the spread of the rainbow trout has greatly increased its impact. Having no innate [[Immunity (medicine)|immunity]] to {{nowrap|''M. cerebralis''}}, rainbow trout are particularly susceptible, and can release so many spores that even more resistant species in the same area, such as {{nowrap|''Salmo trutta''}}, can become overloaded with parasites and incur mortalities of 80 to 90&nbsp;percent. Where {{nowrap|''M. cerebralis''}} has become well-established, it has caused a decline or even elimination of whole [[Taxonomic rank#All ranks|cohorts]] of fish.<ref>Nehring, R. B. "Whirling Disease in Feral Trout Populations in Colorado". In Bergersen, E. P., and Knopf, B. A. (1996). ''Proceedings, Whirling Disease Workshop, Denver, Colorado, February 6–8, 1996: Where Do We Go from Here?'' Fort Collins, Colorado: Colorado Cooperative Fish and Wildlife Research Unit, pp. 126–144. {{OCLC|37379539}}</ref><ref>Vincent, E. R. "Whirling Disease – the Montana Experience, Madison River". In Bergersen, E. P., and Knopf, B. A. (1996). ''Proceedings, Whirling Disease Workshop, Denver, Colorado, February 6–8, 1996: Where Do We Go from Here?'' Fort Collins, Colorado: Colorado Cooperative Fish and Wildlife Research Unit, p. 159. {{OCLC| 37379539}}</ref>

The parasite {{nowrap|''M. cerebralis''}} was first recorded in North America in 1956 in Pennsylvania,<ref name=wddescription>{{cite web |url=http://www.ncrac.org/NR/rdonlyres/3CBECF1E-2AE0-4661-9C08-29A0A15DE403/26267/Whirling2.pdf |title=What Is Whirling Disease? |publisher=North Central Regional Aquaculture Center and Michigan State University Extension |date=December 2004 |access-date=2013-12-31 |author1=Faisal, Mohamed |author2=Garling, Donald |url-status=dead |archive-url=https://web.archive.org/web/20140101073322/http://www.ncrac.org/NR/rdonlyres/3CBECF1E-2AE0-4661-9C08-29A0A15DE403/26267/Whirling2.pdf |archive-date=2014-01-01 }}</ref> but until the 1990s, whirling disease was considered a manageable problem affecting only rainbow trout in hatcheries. It eventually became established in the natural waters of the Rocky Mountain states ([[Colorado]], Wyoming, [[Utah]], [[Montana]], [[Idaho]], [[New Mexico]]), where it is damaging several sport fishing rivers. Some streams in the western U.S. lost 90&nbsp;percent of their trout.<ref>{{cite web |date=January 13, 1997 |title=Scientific Breakthrough Helps Combat Trout Disease |publisher=U.S. Fish and Wildlife Service Whirling Disease Foundation News Release| url=http://www.fws.gov/mountain-prairie/pressrel/97-01.HTM |author1=Tennyson, J. |author2=Anacker, T. |author3=Higgins, S. |access-date=2014-01-05}}</ref> Whirling disease threatens recreational fishing, which is important for the tourism industry, a key component of the economies of some U.S. western states. For example, in 2005 anglers in Montana spent approximately $196,000,000 in activities directly related to trout fishing in the state.<ref>{{cite web |url=http://www.montanatrout.org/native.html |title=Montana's Wild Trout |publisher=The Trout Conservancy |archive-url=https://web.archive.org/web/20140101135600/http://www.montanatrout.org/native.html |archive-date=2014-01-01}}</ref> Some of the salmonids that {{nowrap|''M. cerebralis''}} infects ([[bull trout]], [[cutthroat trout]], and anadromous forms of rainbow trout—steelhead) are already threatened or endangered, and the parasite could worsen their population decline.<ref name="Gilbert">{{cite journal |last1=Gilbert |first1=M. A. |last2=Granath |first2=W. O. Jr. |year=2003 |title=Whirling Disease and Salmonid Fish: Life Cycle, Biology, and Disease |journal=Journal of Parasitology |volume=89 |issue=4 |pages=658–667 |doi= 10.1645/GE-82R|jstor=3285855 |pmid=14533670 |s2cid=8950955 }}</ref>

====New Zealand mud snail====
[[File:Potamopyrgus antipodarum map.png|thumb|alt=Map of U.S. distribution of New Zealand mud snail|Distribution of New Zealand mud snail within the U.S. in 2009]]
The [[New Zealand mud snail]] {{nowrap|(''Potamopyrgus antipodarum'')}}, once [[endemism|endemic]] to New Zealand, has spread widely and has become [[Naturalisation (biology)|naturalised]] and an invasive species in many areas including Australia,<ref>{{cite journal |url=https://www.cabi.org/isc/datasheet/43672 |title=Datasheet: Potamopyrgus antipodarum (New Zealand mudsnail) |author=<!--Not stated--> |website=Invasive Species Compendium |date=2013 |publisher=[[Centre for Agriculture and Bioscience International]] |doi=10.1079/cabicompendium.43672 |access-date=2012-12-04|doi-access=free }}</ref> Asia (Japan,<ref name="Davidson"/> in the Garmat Ali River in Iraq since 2008<ref>{{cite journal  |year=2009 |url=http://www.aquaticinvasions.net/2009/AI_2009_4_2_Naser_Son.pdf |title=First Record of the New Zealand Mud Snail ''Potamopyrgus antipodarum'' (Gray 1843) from Iraq: the Start of Expansion to Western Asia? |journal=Aquatic Invasions |volume=4 |pages=369–372 |author1=Naser, Murtada D. |author2=Son, Mikhail O. |issue=2 |doi=10.3391/ai.2009.4.2.11|doi-access=free }}</ref>), Europe (since 1859 in England), and North America (U.S. and Canada: [[Thunder Bay (Ontario landform)|Thunder Bay]] in Ontario since 2001, British Columbia since July 2007<ref name="Davidson">{{cite journal |url=https://www.researchgate.net/publication/236342603 |title=Northern Range Expansion and Coastal Occurrences of the New Zealand Mud Snail ''Potamopyrgus antipodarum'' (Gray, 1843) in the Northeast Pacific |journal=Aquatic Invasions |year=2008 |volume=3 |pages=349–353 |author1=Davidson, Timothy M. |author2=Brenneis, Valance E. F. |author3=de Rivera, Catherine |author4=Draheim, Robyn |author5=Gillespie, Graham E. |issue=3 |format=PDF |doi=10.3391/ai.2008.3.3.12|doi-access=free }}</ref>), most likely inadvertently during human activity.<ref name=usgs/> It can reach concentrations greater than {{convert|500000|/m2|/sqft}}, endangering the [[food chain]] by outcompeting native snails and water insects for food, leading to sharp declines in native populations.<ref>{{cite web| author=Benson, Amy| year=2006| title=New Zealand Mudsnail: Potamopyrgus antipodarum| work=Florida Integrated Science Center| url=http://cars.er.usgs.gov/Nonindigenous_Species/New_Zealand_Mudsnail/new_zealand_mudsnail.html| access-date=2006-05-04| url-status=dead| archive-url=https://web.archive.org/web/20060219142324/http://cars.er.usgs.gov/Nonindigenous_Species/New_Zealand_Mudsnail/new_zealand_mudsnail.html| archive-date=2006-02-19}}</ref> There is evidence North American fishes are unable to digest the tiny but hard shells of the mud snail, and that their presence may result in poor growth outcomes for rainbow trout.<ref>{{cite journal |last1=Vinson |first1=M. R. |last2=Baker |first2=M. A. |date=2008 |title=Poor growth of rainbow trout fed New Zealand mud snails ''Potamopyrgus antipodarum'' |journal=North American Journal of Fisheries Management |volume=28 |issue=3 |pages=701–709 |doi=10.1577/M06-039.1|bibcode=2008NAJFM..28..701V }}</ref>

The mud snail was first detected in the U.S. in Idaho's Snake River in 1987. Since then, the snail has spread to the [[Madison River]], Firehole River, and other watercourses around Yellowstone National Park, and has been discovered throughout the western U.S.<ref name=usgs>{{cite web | url = https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=1008 | title = ''Potamopyrgus antipodarum'' | access-date = 2013-05-25 |author1=Benson, A. J. |author2=Kipp, R. M. |author3=Larson, J. |author4=Fusaro, A. | year = 2013 | work = USGS Nonindigenous Aquatic Species Database | publisher = U.S. Geological Survey}}</ref> The exact means of transmission is unknown, but it is likely that it was introduced in water transferred with live [[game fish]] and has been spread by [[ship ballast]] or contaminated recreational equipment such as [[Waders (footwear)|wading gear]].<ref name="Montana">{{cite web| title=Aquatic Nuisance Project Fact Sheet: New Zealand Mudsnail (''Potamopyrgus antipodarum'')| publisher=Aquatic Nuisance Species Project| url=http://www.aquaticnuisance.org/fact-sheets/new-zealand-mudsnail| access-date=2014-01-03| archive-date=2013-12-12| archive-url=https://web.archive.org/web/20131212164937/http://www.aquaticnuisance.org/fact-sheets/new-zealand-mudsnail| url-status=dead}}</ref>

====Didymo====
{{nowrap|''[[Didymosphenia geminata]]''}}, commonly known as didymo or rock snot, is a species of [[diatom]] that produces nuisance growths in freshwater rivers and streams with consistently cold water temperatures.<ref name=dpiw-tassie>{{cite web | url=http://dpipwe.tas.gov.au/biosecurity/aquatic-pests-and-diseases/aquatic-biosecurity-threats/didymo-%28rock-snot%29 | title=DPIPWE - Didymo (Rock Snot) | publisher=Tasmania Department of Primary Industries, Parks, Water and Environment | access-date=2014-08-12 | url-status=dead | archive-url=https://web.archive.org/web/20150308142725/http://dpipwe.tas.gov.au/biosecurity/aquatic-pests-and-diseases/aquatic-biosecurity-threats/didymo-(rock-snot) | archive-date=2015-03-08 }}</ref> In New Zealand, invasive didymo can form large mats on the bottom of rivers and streams in late winter. It is not considered a significant human health risk, but it can affect stream habitats and sources of food for fish, including rainbow trout, and make recreational activities unpleasant.<ref name="biosec-nz">{{cite web |url=http://www.biosecurity.govt.nz/faq/term/907/didymo-11.htm |title=Is Didymo an Exotic Species? |access-date=2013-12-01 |last=Biosecurity New Zealand |date=August 2007 |publisher=Biosecurity New Zealand |archive-url=https://web.archive.org/web/20131203005603/http://www.biosecurity.govt.nz/faq/term/907/didymo-11.htm |archive-date=2013-12-03 |url-status=dead }}</ref> Even though it is native in North America, it is considered a nuisance organism or invasive species.<ref>{{cite web |url=https://www.invasivespeciesinfo.gov/profile/didymo |title=Invasive Aquatic Species-Didymo |publisher=U.S. Department of Agriculture |access-date=2013-12-16}}</ref>

====Redmouth disease====
Enteric redmouth disease is a [[bacterial infection]] of freshwater and marine fish caused by the pathogen {{nowrap|''[[Yersinia ruckeri]]''}}. It is primarily found in rainbow trout and other cultured [[salmonids]]. The disease is characterized by [[Subcutaneous tissue|subcutaneous]] hemorrhaging of the mouth, fins, and eyes. It is most commonly seen in fish farms with poor water quality. Redmouth disease was first discovered in Idaho rainbow trout in the 1950s.<ref>{{cite journal |last=Busch |first=R. A. |url=http://spo.nmfs.noaa.gov/mfr403/mfr40311.pdf |title=MFR Paper 1296 Enteric Redmouth Disease (Haggerman Strain) |journal=Marine Fisheries Review |volume=40 |date=March 1978 |issue=3 |access-date=2014-01-05 |archive-date=2017-05-25 |archive-url=https://web.archive.org/web/20170525110624/http://spo.nmfs.noaa.gov/mfr403/mfr40311.pdf |url-status=dead }}</ref>

=== Removal methods ===
Some fisheries are focused on removing rainbow trout in order to reestablish native trout populations. This can be done by poisoning rivers with chemicals such as [[antimycin]] or [[rotenone]] which have been declared safe in the U.S. by the [[United States Environmental Protection Agency|Environmental Protection Agency]]. Once the chemicals have dissipated, native trout are released into the river. Another method is to use [[electrofishing]] which enables the fish to be caught alive and harvested or re-located. This technique has been used in the Great Smokey Mountains National Park to rid it of rainbow trout that were introduced in the 1930s and have thrived ever since. They are hoping to re-establish native brook trout in at least some of the {{convert|2100|mi|km|order=flip|abbr=on}} river system.<ref>{{Cite web|url=http://www.smithsonianmag.com/science-nature/native-trout-are-returning-to-americas-rivers-160317057/?no-ist|title=Native Trout Are Returning to America's Rivers|website=Smithsonian|access-date=2016-05-03}}</ref> Neither method of control is 100% effective and are best regarded as methods to change the relative population sizes of fish species.

===Steelhead declines===
[[File:Zymoetz (Copper) River Steelhead.jpg|thumb|A large Steelhead caught on the [[Zymoetz River|Zymoetz (Copper) River]] in British Columbia]]
{{see also|Steelhead and salmon distinct population segments|Conservation status of British Columbia salmonids}}
Steelhead populations in parts of its native range have declined due to a variety of human and natural causes. While populations in Alaska and along the British Columbia coast are considered healthy, populations in Kamchatka and some populations along the U.S. West Coast are in decline. The U.S. [[National Marine Fisheries Service]] has 15 identified [[distinct population segment]]s, in [[Washington (state)|Washington]], [[Oregon]], and California. Eleven of these populations are listed under the U.S. [[Endangered Species Act]], ten as threatened and one as endangered.<ref name=noaa>{{cite web |url=http://www.nmfs.noaa.gov/pr/species/fish/steelheadtrout.htm |title=Steelhead Trout (''Oncorhynchus mykiss'') |publisher=NOAA Fisheries, Office of Protected Resources |access-date=2013-11-28}}</ref> One distinct population segment on the Oregon coast is designated a U.S. [[Species of Concern]].<ref name=noaa/><ref>{{cite web |url=http://www.water.ca.gov/fishpassage/docs/b250/B250_app_D.pdf |title=Appendix D Evolutionarily Significant Units, Critical Habitat, and Essential Fish Habitat |publisher=California Department of Water Resources |access-date=2013-11-29 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304053253/http://www.water.ca.gov/fishpassage/docs/b250/B250_app_D.pdf |url-status=dead }}</ref>

The [[Southern California Steelhead DPS|Southern California distinct population segment]], which was listed as endangered in 2011, has been affected by habitat loss due to dams, confinement of streams in concrete channels, [[water pollution]], groundwater pumping, [[urban heat island]] effects, and other byproducts of urbanization.<ref>{{cite web |url=http://www.westcoast.fisheries.noaa.gov/publications/status_reviews/salmon_steelhead/steelhead/2001_status_review_southern_california_coast_steelhead.pdf |title=South-Central/Southern California Coast Steelhead Recovery Planning Domain 5-Year Review: Summary and Evaluation of Southern California Coast Steelhead Distinct Population Segment |publisher=National Oceanic and Atmospheric Administration |year=2011|access-date=2013-12-03}}</ref> Steelhead in the Kamchatka Peninsula are threatened by over-harvest, particularly from [[poaching]] and potential development, and are listed in the ''Red Data Book of Russia'' that documents rare and endangered species.<ref>{{cite web |url= https://www.pbs.org/edens/kamchatka/bountiful.html |title=Bountiful Breed: Kamchatka Siberia's Forbidden Wilderness |author=Rahr III, Guido |publisher=Public Broadcasting System (PBS)|access-date=2013-12-04}}</ref>

====Hatchery stocking influence====
[[File:Lower-elwha-klallam-steelhead-broodstock-spawning-keith-lauderback-melanie-roed-0277.jpg|thumb|left|alt=Photo of man inspecting steelhead broodstock in hatchery|Steelhead hatchery broodstock inspection]]
Several studies have shown that almost all California coastal steelhead are of native origin, despite over a century of hatchery stocking. Genetic analysis shows that the South Central California Coast and Southern California populations from [[Malibu Creek]] north, including the [[San Gabriel River (California)|San Gabriel River]], [[Santa Ana River]], and [[San Mateo Creek (Southern California)|San Mateo Creek]], are not hatchery strains. Steelhead from [[Topanga, California#Topanga Canyon|Topanga Creek]] and the [[Sweetwater River (California)|Sweetwater River]] were partly, and those from [[San Juan Creek]] completely, of hatchery origin.<ref name=Clemento>{{cite journal |title=Population Genetic Structure and Ancestry of ''Oncorhynchus mykiss'' Populations Above and Below Dams in South-central California |journal=Conservation Genetics |year=2009 |pages=1321–1336 |url=http://www.westcoast.fisheries.noaa.gov/publications/recovery_planning/salmon_steelhead/domains/south_central_southern_california/clemento_et_al_conserv_genetic_population_genetic_structure_ancestry.pdf |access-date=2014-01-03 |author1=Clemento, Anthony J. |author2=Anderson, Eric C. |author3=Boughton, David |author4=Girman, Derek |author5=Garza, John Carlos |doi=10.1007/s10592-008-9712-0 |volume=10 |issue=5|bibcode=2009ConG...10.1321C |s2cid=32490944 }}</ref> Genetic analysis has also shown that the steelhead in the streams of the [[Santa Clara County, California|Santa Clara County]] and [[Monterey Bay]] basins are not of hatchery origin, including the [[Coyote Creek (Santa Clara County)|Coyote Creek]], [[Guadalupe River (California)|Guadalupe River]], [[Pajaro River]], [[Permanente Creek]], [[Stevens Creek (California)|Stevens Creek]], [[San Francisquito Creek]], [[San Lorenzo River]], and [[San Tomas Aquino Creek]] basins.<ref>{{cite report |title=Population Genetics of ''Oncorhynchus mykiss'' in the Santa Clara Valley Region, Final Report to the Santa Clara Valley Water District |author1=Garza, John Carlos |author2=Pearse, Devon |date=March 2008 |pages=1–54 |publisher=Santa Clara Valley Water District }}</ref> Natural waterfalls and two major dams have isolated [[Russian River (California)|Russian River]] steelhead from freshwater rainbow trout forms above the impassable barriers; a 2007 genetic study of fin samples collected from steelhead at 20 different sites both above and below passage barriers in the watershed found that although 30&nbsp;million hatchery trout were stocked in the river from 1911 to 1925, the steelhead remain of native and not hatchery origin.<ref>{{cite journal |title=Population Structure and Genetic Diversity of Trout (''Oncorhynchus mykiss'') Above and Below Natural and Man-made Barriers in the Russian River, California |journal=Conservation Genetics |year=2007 |pages=437–454 |url=http://cahatcheryreview.com/wp-content/uploads/2012/08/Garza-2008.pdf |access-date=2011-06-12 |author=Deiner, Kristy; Garza, John Carlos, Coey, Robert, Girman, Derek J. |doi=10.1007/s10592-006-9183-0 |volume=8 |issue=2 |bibcode=2007ConG....8..437D |hdl=10211.1/1550 |s2cid=6159852 |hdl-access=free |archive-date=2014-01-04 |archive-url=https://web.archive.org/web/20140104032713/http://cahatcheryreview.com/wp-content/uploads/2012/08/Garza-2008.pdf |url-status=dead }}</ref>

Releases of conventionally reared hatchery steelhead pose ecological risks to wild steelhead populations. Hatchery steelhead are typically larger than the wild forms and can displace wild-form juveniles from optimal habitats. The dominance of hatchery steelhead for optimal microhabitats within streams may reduce wild steelhead survival as a result of reduced foraging opportunities and increased rates of predation.<ref>{{cite journal |year=1999 |title=Behavioral Interactions Among Hatchery-reared Steelhead Smolts and Wild ''Oncorhynchus mykiss'' in Natural Streams |journal=North American Journal of Fisheries Management  |pages=948–956 |author1=McMichael, G. A. |author2=Pearsons, T. N. |author3=Leider, S. A. |doi=10.1577/1548-8675(1999)019<0948:BIAHRS>2.0.CO;2 |volume=19 |issue=4|bibcode=1999NAJFM..19..948M }}</ref>