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Last modified
7/14/2009 5:02:36 PM
Creation date
5/20/2009 9:28:09 AM
Metadata
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UCREFRP
UCREFRP Catalog Number
9557
Author
Jackson, J. A. and J. M. Hudson.
Title
Population Estimate for Humpback Chub (Gila cypha) in Desolation and Gray Canyons, Green River, Utah 2001-2003.
USFW Year
2005.
USFW - Doc Type
22k,
Copyright Material
NO
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0 <br />INTRODUCTION <br />The humpback chub (Gila cypha) is a large-bodied cyprinid endemic to the Colorado <br />River Basin. It is a canyon-dweller that evolved in seasonally warm and turbid water, <br />adapting to variable hydrologic conditions typical to an unregulated river system. The <br />canyons where humpback chub are found are characterized by swift deep water and <br />rocky substrates (Valdez 1990). Humpback chub are believed to presently inhabit <br />approximately 68% of their original range. Factors that may have contributed to the <br />decline of this species include: stream alteration, (dams, irrigation, dewatering, and <br />channelization); habitat modification; competition with and predation by introduced, <br />nonnative fish species; parasitism; hybridization with other Gila spp.; and pesticides and <br />pollutants. <br />Humpback chub were first reported in Desolation and Gray canyons (Deso/Gray) on the <br />Green River in 1975 as a result of investigations conducted from 1967-1971 (Holden and <br />Stalnaker 1975). This population has been monitored nearly annually for approximately <br />25 years. The Utah Division of Wildlife Resources has been responsible for this <br />monitoring since 1985. Currently, there are six self-sustaining populations that exist, one <br />within the lower basin in the Grand Canyon on the Colorado River and five within the <br />upper basin in the Colorado River and Green River sub-basin. The population of <br />humpback chub in Deso/Gray is considered the third largest in the upper basin, following <br />the Black Rocks and Westwater populations on the Colorado River. <br />The humpback chub is currently protected under the Endangered Species Act of 1973, as <br />amended (ESA; 16 U.S.C. 1531 et. seq). In 1990, a recovery plan for humpback chub <br />was completed (USFWS 1990) and in 2002, an amendment and supplement to the <br />recovery plan was approved (USFWS 2002). Objective and measurable recovery criteria <br />were identified in the amendment and supplement for the downlisting and delisting of <br />humpback chub. Recovery criteria were developed for the upper and lower Colorado <br />River basins that outlined the goals that must be met for downlisting and delisting to be <br />considered. To downlist humpback chub, the following criteria must be met for a five- <br />year period: 1) The trend in adult (age-4+; > 200 mm TL) point estimates for each of the <br />six populations does not decline significantly; 2) Mean estimated recruitment of age-3 <br />(150-199 mm TL) naturally produced fish equals or exceeds mean annual adult mortality <br />for each of the six populations; 3) Two of the genetically and demographically viable, <br />self-sustaining core populations are maintained, such that each point estimate for each <br />core population exceeds 2,100 adults; 4) Certain site-specific management tasks to <br />minimize or remove threats have been identified, developed, and implemented. Delisting <br />can occur, if over a three-year period beyond downlisting: see 1 and 2 above; 3) three <br />genetically and demographically viable, self-sustaining core populations are maintained, <br />such that each point estimate for each core population exceeds 2,100 adults; 4) certain <br />site-specific management tasks to minimize or remove threats have been identified, <br />developed, and attained. <br />Population estimates generated by mark-recapture sampling and analysis were conducted <br />from 2001 to 2003 for the Deso/Gray humpback chub population. The. specific <br />5
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