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Gila trout

The Gila trout (Oncorhynchus gilae gilae) had an historic range that included the headwaters of the Gila River drainage in New Mexico, the Gila River, and possibly the San Francisco Drainage, and the Verde and Agua Fria drainages of Arizona [1]. By the time the species was formerly described in 1950 its distribution had been dramatically reduced to as few as 20 stream miles [1]. A survey conducted in 1975 (two years after the Gila trout was listed as endangered under the current Endangered Species act) found that five relict populations remained [1] and estimated the population at less than 7,600 [2]. These five populations (Main Diamond Creek, South Diamond Creek, McKenna Creek, Spruce Creek and Iron Creek) were restricted to headwater stream habitats in the upper Gila River drainage in New Mexico [1]

Historic declines in Gila trout populations were associated with habitat degradation and competition and hybridization with exotic fish species, most notably rainbow and brown trout [1]. Mining, logging, and cattle-grazing activities altered habitat through increased erosion and sedimentation as well as by causing changes in water levels, increased water temperatures, and reduced bank cover [1]. Overfishing was also problematic [1]. Forest fires (that now burn more severely that they did historically) and associated fire suppression activities also pose a threat to Gila trout populations [1].

By 1985, the total Gila trout population was estimated to have increased to between 18,000 and 26,000 [3]. By 1987 recovery and reintroduction efforts had resulted in the establishment of Gila trout populations at nine localities (eight in New Mexico and one in Arizona) and the USFWS proposed downlisting the species [4]. Shortly after this proposal however, a flood eliminated more than 80% of the Gila trout population from McKnight Creek (a reintroduced population), a forest fire and subsequent flooding eliminated the Main Diamond Creek population (this population was ultimately saved through the removal and subsequent repatriation of Apache trout), and drought and forest fire eliminated more than 90% of the South Diamond Creek population [4]. This demonstrated the fragility of the species status and in 1991 the downlisting proposal was withdrawn [4]. In 1992, a sixth relict population in Whiskey Creek was discovered [1], but despite this, total population size was estimated to be less than 10,000 [2]. In 1996-97 two of the relict populations (McKenna and Iron Creek) were found to have hybridized with rainbow trout, reducing the number of genetically pure relict populations to four [5].

Continuing captive propagation and reintroduction efforts, aimed not only at increasing population numbers but also at preserving and replicating genetic lineages at new locations [5], resulted in increasing Gila trout numbers through the 1990s and by 1998 the total wild population had increased to around 37,000 [2]. There are now 14 populations of Gila trout in the wild and they are known to inhabit approximately 65 miles of habitat [1]. The four pure relict populations are self-sustaining in the wild [1] and three of these four (Main Diamond, South Diamond, and Spruce Creeks) are replicated at least once [5]. Replicated populations in New Mexico are now reproducing in the wild [5]. It is also thought that a small pure population remains in Whiskey Creek and replication of this population may be possible [5]. Additionally, the Mora National Fish Health and Technology Center maintains a captive population of Gila trout that represents the Main Diamond lineage [1]. Currently, the total population of Gila trout in the wild is unknown [5]. In 2005, the USFWS stated their belief that the viability of the Gila trout was sufficiently protected and proposed downlisting the Gila tout to threatened [5]. The proposed rule to downlist also proposes a special rule that will allow for some recreational fishing of the species [5].

Although populations have increased since listing, threats to the Gila trout still exist and over the past decade, declines due to forest fire and hybridization have taken place [6]. Since 1989, seven populations of Gila trout have been extirpated by high-severity wildfires and subsequent flooding and ash-flows; two of these have been reestablished [5]. Grazing, which still occurs on eight of 14 streams occupied by Gila trout, may also adversely affect some populations [1]. Illegal angling could also pose a threat at some sites [1]. Although non-native salmonids currently do not occur in streams supporting Gila trout, management of these non-native species will need to continue for this to remain the case [5]. Whirling disease, caused by the metazoan parasite Myxobolus cerebralis, could also possibly pose a threat to the Gila trout [1].

NEW MEXICO: Grant County: Main and South Diamond Creeks support relict lineages of Gila trout. A census conducted from 1974-1976 estimated the population in Main Diamond Creek at 4,750 [2]. In 1989, however, a wildfire and subsequent erosion, runoff, and sedimentation threatened the population with eradication and caused extensive destruction of Gila trout habitat [1]. The population was saved by removing 566 trout from the stream and keeping them in captivity until conditions improved [1]. Gila trout were repatriated to the site in 1994 [1]. On South Diamond Creek, a high severity wildfire in 1995 resulted in the removal of trout from this stream, but in 1997 Gila trout were repatriated to the site [1]. Gila trout from the Main Diamond Creek lineage were introduced into Black Canyon, Sheep Corral Canyon, and McKnight Creek [1].

Catron County: Spruce Creek and Whiskey Creek support relict lineage populations [1]. Gila trout from pure lineages have been stocked in Big Dry Creek, Upper Mogollon, White Creek, and Upper Little Creek [1]. In 2002, a fire near Whiskey Creek (the “cub” fire) resulted in the implementation of an emergency plan to evacuate Gila trout from the lower portion of the stream, but upper Whiskey Creek where the majority of the fish occur, was not affected [5]. In 2003 a fire forced the removal of fish from Mogollon Creek [5].

ARIZONA: Gap Creek: Gap Creek was the site of the 1st translocation of Gila trout into Arizona [1]. In 1974, 65 Gila trout from Main Diamond Creek were moved into Gap Creek [1]. Initially, the population grew to about 150 [7], but by 1990, only six trout were detected and the population is now considered extirpated [1].

Dude Creek: In 1999, Gila trout were introduced into Dude Creek Arizona [1], but unknown factors seem to be limiting reproduction at this site [5].

Raspberry Creek: In 2000, young of the year were planted in Raspberry Creek [1]. In 2004, Gila trout were found in mixed size classes indicating that the fish spawned and successfully recruited [5]. Although some fish were removed in 2004 due to a wildfire, they were restocked the same year and it appears the creek will still support the trout [5].

Chitty Creek: An introduction into Chitty creek in planned, possibly for 2005 [1].

[1] U.S. Fish and Wildlife Service. 2003. Gila trout recovery plan (third revision). Albuquerque, New
Mexico. i-vii + 78 pp.
[2] U.S. Fish and Wildlife Service. 2002. Region 2 Regional News and Recovery Updates. Endangered Species Bulletin XXVII(2):38.
[3] New Mexico Game and Fish. 2004. Gila Trout Species Account. Biota Information System of New Mexico BISON version 1/2004. Website <http://fwie.fw.vt.edu/states/nmex_main/species/010600.htm> accessed Aprill, 2006.
[4] Platania, S.P. Perils Facing the Gila Trout. Our living resources: a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. U.S. Department of the Interior, National Biological Service, Washington, DC. 530 pp. Available at <http://biology.usgs.gov/s+t/SNT/noframe/sw157.htm>.
[5] U.S. Fish and Wildlife Service. 2005. Reclassification of the Gila Trout (Oncorhynchus gilae) from Endangered to Threatened with Regulations. Federal Register 70:24750-24764.
[6] New Mexico Game and Fish. 2004 Biennial Review of threatened and Endangered Species of New Mexico, Final Draft Recommendation. Available at <http://www.wildlife.state.nm.us/conservation/threatened_endangered_species/documents/2004biennial_review_fulltext.pdf>.
[7] Arizona Game and Fish Department. Animal abstract, Gila Trout. Heritage Data Management System. Available at <http://www.azgfd.gov/w_c/edits/documents/Oncogila.fo.pdf>.

Banner photo © Phillip Colla