Life-History And Ecology Of The Greenback Cutthroat Trout

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Life-History and Ecology of theGreenback Cutthroat TroutBy Mark A. ColemanIllustration Copyright 2007 by Tim Gunther. All Rights Reserved.

Life-History and Ecology of theGreenback Cutthroat TroutByMark A. ColemanColeman Ecological, Inc.1019 Boltz DriveFort Collins, CO 80525(970) 225-3948andThe Colorado Natural Heritage ProgramColorado State University8002 Campus DeliveryFort Collins, CO 80523-8002ForThe Greenback Cutthroat Trout Recovery Teamc/o Bruce RosenlundU.S. Fish and Wildlife Service755 Parfet, Suite 496Lakewood, CO 80215April 26, 2007Cover Illustration: Cover Illustration by Gunther Graphics (www.guthergraphics.biz)Photos: Some photos provided by Freshwaters Illustrated (www.freshwatersillustrated.org)ii

ACKNOWLEDGEMENTSDevelopment of this report was supported by funding from the U.S. Fish and Wildlife Service(USFWS). The author thanks Bruce Rosenlund (USFWS) for administering this funding. BruceRosenlund and Chris Kennedy (USFWS) provided a large collection of information that was used inresearching this report. Doug Krieger, Phil Schler, Tom Nesler, and Greg Gerlich (ColoradoDivision of Wildlife), Dave Winters and Mike Young (U.S. Forest Service) contributed additionalinformation either directly or through their contributions to the body of research on greenbackcutthroat trout. Kurt Fausch and Bob Behnke (Colorado State University) have also contributed tothe author’s knowledge of greenback cutthroat trout. Cecelia Coleman provided editorial assistanceduring report preparation. The text was also improved by comments and suggestions of threereviewers: Doug Krieger, Kevin Rogers, and Bruce Rosenlund.Greenback Cutthroat Trout. Copyright 2004 by Mark Coleman. All Rights Reserved.iii

TABLE OF CONTENTSINTRODUCTION . 1HABITAT REQUIREMENTS . 1Elevation .2Physical and thermal requirements .3Spawning habitat.5Rearing habitat .5Water Quality.6LIFE-HISTORY . 7Migration and movement.7Spawning and Reproduction .8Size and Growth.9POPULATION ECOLOGY. 10Spatial patterns in populations .10Variation in populations over time .10Metapopulations.11COMMUNITY ECOLOGY. 11Greenback cutthroat trout as predators .11Disease and Parasites .12RESEARCH NEEDS. 13REFERENCES . 14iv

ColemanGreenback Life-History and Ecologyresulted in 20 stable populations by 1998(USFWS 1998). The greenback cutthroat troutwas believed to be poised for delisting by 2006,when efforts to prepare a long-rangemanagement plan for the subspecies began.This report summarizes what is known, orcan be gleaned, from research and recordedobservations on the life-history and ecology ofgreenback cutthroat trout. It is organized intofour major interrelated sections that reviewHabitat Requirements, Life-History, PopulationEcology, and Community Ecology. Each ofthese is further subdivided into topics toorganize the information presented inmeaningful ways, as the report is intended to beadapted for use in the final version of thegreenback cutthroat trout long-rangemanagement plan. An effort has been made tofocus as much as possible on results fromstudies and observations specifically ongreenback cutthroat trout, but in places thegreenback-specific information is supplementedwith information on other salmonids that areeither closely related or have ecologicalsimilarities to greenback cutthroat trout. Whenresults from studies on other salmonids wereincluded, it was noted, and further research tofill gaps in the collective knowledge ofgreenback cutthroat trout life-history andecology was recommended.West Creek Falls is a natural barrier to upstream migration.Copyright 2004 by Mark Coleman. All Rights Reserved.INTRODUCTIONThe greenback cutthroat trout is one of fourcutthroat trout subspecies native to Colorado,one of which (the yellowfin cutthroat) isassumed to be extinct. The only salmonidnative to the South Platte and Arkansas Riverbasins, the greenback cutthroat trout wasthreatened by habitat loss, unregulated fishing,and invasions by introduced nonnativesalmonids by the early 1900’s, and was thoughtto be extinct by 1937. However, two purepopulations were discovered in the 1950’s and60’s, with the subspecies listed as “Endangered”under the Endangered Species Act when enactedin 1973. In 1978, their status was changed to“Threatened” with discovery of additionalhistorical populations and successfultranslocations above barriers to upstreammigration that prevent invasion by nonnativesalmonids. Management and recovery hadHABITAT REQUIREMENTSSuitable habitat for self-sustaining salmonidpopulations must contain sufficient physicalcomplexity to meet the requirements of all lifehistory stages, from embryo to adult. In thisregard, the habitat requirements of greenbackcutthroat trout are similar to those of othersalmonids confined to fresh waters. Availablephysical habitats must provide temperatureswithin the range tolerated by the fish, spawninghabitat, small backwater or shallow pockethabitats for newly emerged fry to find prey andrefuge from the stream’s current, and poolhabitat for overwintering of fry and adults.1

ColemanGreenback Life-History and EcologyThe turbulent habitat of the greenback cutthroat trout . Copyright 2002 by Jeremy Monroe, Freshwaters Illustrated. All Rights ReservedUpper Hutcheson Lake greenback cutthroattrout population is the highest known. Researchstocking in other high elevation lakes hasresulted in mixed success. For example,greenback cutthroat trout stocked in LakeOdessa (3,048 m) spawned and established areproducing population, whereas greenbackcutthroat trout stocked in Crystal Lake (3,511m) do not appear to be reproducing at a ratesufficient to maintain this population.Based on the known historic presence ofgreenback cutthroat trout in headwaters of boththe South Platte and Cache la Poudre Riverbasins, at one time the lower elevational rangeof greenback cutthroat trout may have extendeddown to 1,420 m to the confluence of the SouthPlatte and Cache la Poudre rivers near presentday Greeley, Colorado (Behnke 1992, 2002).Indeed, greenback cutthroat trout stocked in alow elevation lake (1,889 m) at Fort Carson,Habitats that provide adequate complexity arealso generally productive and provide a foodbase of terrestrial and aquatic invertebrates withthe range of sizes needed to sustain fish at eachlife stage. The water quality must also besuitable, having a tolerable pH and containinglow levels of contaminants such as heavy metalsand other substances which interfere withphysiology and development and threaten theviability of populations.ElevationThe original elevational distribution ofgreenback cutthroat trout is unknown, but theupper and lower elevation limits at whichgreenback cutthroat trout can establishreproducing populations can be estimated basedon the results of experimental stockings in bothhigh and low-elevation lakes, and from thehistorical record. At 3,402 m elevation, the2

ColemanGreenback Life-History and EcologyManagement for the species is therefore“sandwiched” between lower and upperelevations.Regardless, the studies described aboveprovide valuable tools for identifying habitatsthat are probably suitable, probably unsuitable,or may require further investigation to judgesuitability. For example, based on the abovestudies, stream segments that have a watershedarea of at least 14.7 km2, a minimum occupiedlength of between 2.9 and 3.8 km, mean Julytemperatures 7.8ºC, mean bankfull pool width 3.4 m, and 69 pools more than 30 cm inresidual depth can be assumed to providesufficient habitat to sustain greenback cutthroattrout populations. Streams that fail to meetmost of these criteria can most likely be ruledout as suitable sites for translocations.However, streams that fall short in only one or afew of these criteria should not be ruled outbefore more detailed assessments have beenconducted.Environmental temperature is a variable thatinfluences nearly every physiological andecological process necessary for survival of allsalmonids. Where habitat is marginal due tocold temperatures and the short growing seasonstypical in high elevation streams and lakes,greenback cutthroat trout and other cutthroattrout subspecies that spawn in the spring maynot be able to incubate successfully, or growlarge enough to insure survival over their firstwinter (Coleman and Fausch in press a, in pressb). In a two-year laboratory study, ColoradoRiver cutthroat trout survived poorly throughthe start of their first winter in temperatureregimes in which fewer than 800 degree-daysaccumulated between spawning and the start ofwinter (Coleman and Fausch in press a).Growing season degree-days can be estimatedby summing the average daily temperaturesduring the period each year when temperaturesare suitable for growth (e.g., 30 days 10ºCaverage daily temperature 300 degree-days).In a companion field study, young-of-yeargreenback or Colorado River cutthroat trout frydensities were very low in stream reaches withfewer than 800 growing season degree-days andColorado, survived and reached sizes of up to2.0 kg.Physical and thermal requirementsStable and reproducing populations arerarely found above timberline, and thepreponderance of evidence suggests that variousphysical factors, including temperature andhabitat structure, constrain the upper elevationlimits for greenback cutthroat trout today(USFWS 1998; Harig and Fausch 2002;Coleman and Fausch in press a). Field studieshave indicated that temperature and physicalhabitat characteristics in stream segments atmultiple scales are all related to greenbackcutthroat trout abundance or the probability ofestablishing stable populations during recoveryefforts (Harig and Fausch 2002). In 27translocated or reintroduced greenback and RioGrande cutthroat trout populations, one fieldstudy indicated that cold summer temperaturesand the number and width of deep pools werecorrelated with fish abundance at the streamscale (Harig and Fausch 2002), while at a largerscale watershed area was also correlated withfish abundance. Further, Young et al (2005)found that occupied stream length waspositively correlated with electrofishingabundance estimates for 31 stream populationsof greenback and Colorado River cutthroattrout.Specific threshold values for habitatcharacteristics derived from correlative studieslike these should be regarded with caution, andnot applied as “rules of thumb” because someself-sustaining populations occur in streams thatfail to meet some or all of the criteria derivedfrom these studies. Furthermore, managementof greenback cutthroat trout can be difficult atlower elevation habitats due to complexity ofhabitat, water management operations, orpresence of structures that prevent successfulelimination of non-native salmonids. Althoughthese lower elevation habitats provide thebenefits of warmer temperatures and preferredlarge river habitats relative to headwaterstreams, other factors often prevent their use forrecovery of greenback cutthroat trout.3

ColemanGreenback Life-History and EcologyAdult greenback cutthroat trout during spawning season. Copyright 2005 by Cecelia Coleman. All Rights Reservedinvestigation to determine the extent ofthermally suitable habitat if thermal suitabilitycriteria are to be applied with the greatestcertainty.It is important to note that the thermalcriteria above are derived from studies ofpredominantly stream resident populations.Greenback cutthroat trout populations in lakesor ponds with inlet or outlet streams that areotherwise too cold to sustain them maynonetheless be stable and reproducing due to thethermal and velocity refugia available in theselakes or ponds. Further research on lakepopulations should be conducted to furtherrefine our understanding of greenback cutthroattrout physical habitat requirements in a greatervariety of physical habitat types.Despite the apparent limitation of greenbackcutthroat trout recruitment by cold temperatures,fry length was 30 mm. Thus, the mean Julytemperature criteria ( 7.8 C) for predictingsalmonid abundance and stable streampopulations reported by Harig and Fausch(2002) may be further refined when sufficienttemperature data are available to calculatedegree-days during the growing season. Theresults of these studies indicate that the “5-8ºCby early July” criteria (USFWS 1998) forselecting candidate habitats for greenbackcutthroat trout recovery may be adequate whenapplied to streams that are not otherwise limitedby poor physical habitat conditions. One caveatis that temperatures vary along stream segmentsdue to the influence of groundwater, springseeps, shading, natural and human-madeimpoundments, and tributaries that can serve toeither warm or cool the stream. This spatialvariation in temperature requires more detailed4

ColemanGreenback Life-History and Ecologyobserved near the shore of the lake during 2004.Loomis Lake has no inlet stream, althoughsignificant water does trickle into the lake underrocks on the shore of the lake. Furtherinvestigations are required to determine thelifespan of fish and the success rate of spawningand recruitment within the lake.there is some evidence for cold-temperatureadaptation in at least one greenback cutthroattrout population in the Little South Fork of theCache la Poudre River. Eggs from thispopulation required only 256 degree-days tohatch compared to those from a greenbackcutthroat trout population in the Arkansas RiverBasin. The Arkansas River Basin populationrequired 312 degree-days, a value more typicalfor trout species in general (Dwyer andRosenlund 1988).Rearing habitatSpecific habitat requirements or preferencesof young-of-year greenback cutthroat trout havenot been widely reported in the scientificliterature. However, Cummings (1987)indicated that young-of-year greenbackcutthroat trout in Hidden Valley Creek occupiedmicrohabitats along the margins of the stream,characterized by low velocities and fine (silt)substrate. Similar habitat associations weredescribed for coastal cutthroat trout fry less than30 mm long, which are noted to be weakswimmers and are confined to backwaters,isolated pools, or small shallow sheltereddepressions with very low water velocity(Moore and Gregory 1988). This was consistentwith microhabitat observations made in highelevation Colorado streams where eithergreenback or Colorado River cutthroat trout frywere surveyed by Coleman and Fausch (in pressb).In the southern Rocky Mountain region, thevolume of these nursery habitats decreases asflows drop during the summer. This may forceyoung-of-year greenback cutthroat trout, whichin many streams do not emerge from redds untillate in the summer, to occupy higher-velocitypositions in the stream that are moreenergetically demanding (Cummings 1987).Further studies are needed to determine theextent to which recruitment of young-of-yearfish depends on the types of rearing habitatpreviously described (Moore and Gregory 1988;Coleman and Fausch in press b), and developmethods to better describe and quantify rearinghabitat.Invading brook trout may compound theproblem of shrinking lateral habitats for rearingof cutthroat trout. Brook trout spawn during falland their fry emerge well before cutthroat trout,Spawning habitatNo studies have been conducted to identifyspawning habitat requirements specific togreenback cutthroat trout, although Scarnecchiaand Bergersen (1986) reported that among threestreams they studied that contained eithergreenback or Colorado River cutthroat troutduring 1979-1980, more young fish were foundby electrofishing in the stream with a greaterproportion of fine to coarse gravel substrate (215 mm and 15-63 mm particle sizes,respectively). Others have reported that Gilatrout (Rinne 1980) and Apache trout (Harper1978) of sizes similar to the adult trout reportedby Scarnecchia and Bergersen (1986) spawn ina range of gravel sizes that overlap the fine andcoarse gravel size classes they used.Recent evidence suggests that at least onegreenback cutthroat trout population maysuccessfully spawn in a lake in Rocky MountainNational Park (Bruce Rosenlund and ChrisKennedy, US Fish and Wildlife Service,unpublished data). Brook trout were removedfrom Loomis Lake (3,110 m) in 1990, andgreenback cutthroat trout were stocked in 1992,and the area has been open to catch-and-releasefishing since 1993. There is no spawning inletor outlet habitat, and it is believed that fish areunable to migrate into the lake fromdownstream due to a barrier at the outlet of thelake. Periodic fish surveys conducted through2006 indicate that the population is stable andfish have ranged in size from 155-378 mm sincestocking. Greenback cutthroat trout have beenobserved to exhibit spawning behavior on shoalsin the lake, and one young-of-year fry was5

ColemanGreenback Life-History and EcologyYoung-of-year greenback cutthroat trout in rearing habitat along stream margin. Copyright 2006 by Mark Coleman. All Rights Reservedanthropogenic processes. In general, salmonidsrequire cold, clean waters and usually do notpersist in waters contaminated by thermal orchemical effluents. Of the water qualityparameters that may influence the viability ofgreenback cutthroat trout populations,temperature has been studied most thoroughlyand is best understood. Less understood are theeffects of chemicals.Only two laboratory toxicity studies havebeen published for greenback cutthroat trout.They describe the effects of low (acidic) pH andaluminum (Woodward and others 1991), andfive other chemicals commonly found in theenvironment due to domestic, industrial, oragricultural uses (Sappington and others 2001).These studies show that larval greenbackcutthroat trout are more sensitive to low pH andelevated aluminum than eggs and embryos. Thewhen rearing habitat volume is greater. Brooktrout fry are thus larger and better able todominate the best of the dwindling rearinghabitat in late summer, when greenbackcutthroat trout fry emerge. There is someevidence that the negative effects of brook trouton cutthroat trout populations are strongestduring early life-history stages, and theinteraction between early life stage brook troutand cutthroat trout may explain why brook troutoften completely displace or extirpate cutthroattrout populations in headwater streams in thesouthern Rocky Mountains (Peterson andFausch 2004).Water QualityLike other salmonids, greenba

Apr 26, 2007 · Life-History and Ecology of the Greenback Cutthroat Trout By Mark A. Coleman Coleman Ecological, Inc. 1019 Boltz Drive Fort Collins, CO 80525 (970) 225-3948 and The Colorado Natural Heritage Program Colorado State University 8002 Campus Delivery Fort Collins, CO 80523-8002 For The Greenback C

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