The nonnative Iowa darter (Etheostoma exile) established in the Yampa River, Colorado, and Green River, Utah.
The Yampa River is a tributary to the Green River, and the Green River is the largest tributary of the Colorado River in the Upper Colorado River Basin. Sampling of the Yampa River occurred in three areas. The most upstream reach, Little Yampa Canyon (river km 161-200, just downstream of Craig, Colorado), and the intermediate reach, Lily Park (river km 80-89), were sampled with an electric seine (10 m long, 2 kW generator). The most downstream site on Yampa River at Echo Park (river km 1) was just upstream of the confluence of the Green River and sampling was conducted with drift nets (4 m long, 0.5 [m.sup.2], 560-[micro]m mesh). The sampling site on the Green River, 68 river km downstream of the confluence of Yampa River near Jensen, Utah (backwater of Cliff Creek confluence, river km 487 of Green River, and other backwaters downstream of there), was with light traps (quatrefoil design, slits were 4 or 6 mm wide) set overnight. Results reported here are from portions of several studies with differing research objectives, which is why different types of gear were used at most locations.
In 2003, we collected one adult Iowa darter in the Yampa River, in Little Yampa Canyon, from a low-velocity, shallow, channel margin (Table 1). Abundance of the Iowa darter in Little Yampa Canyon increased in subsequent years; we collected 40, 148, 166, and 108 specimens in 2004, 2005, 2006, and 2007, respectively. Relative abundance of Iowa darters in those same electric-seine samples increased in a similar fashion and represented ca. 1% of fishes collected during 2004-2007. We also collected two Iowa darters from Milk Creek in 2007, a tributary of the Yampa River in Little Yampa Canyon. We identified juvenile and adult Iowa darters using presence of a frenum, two anal-fin spines, an incomplete lateral line (usually extending posterior to between the origin of the soft dorsal and the midpoint of soft-dorsal base), dark saddles or other pigment on the lateral surface, and a terminal mouth and snout. These are characteristics that distinguish them from other darters, including those native to eastern Colorado. We identified early life stages of the Iowa darter using characteristics from Auer (1982). No other species of darter was collected. We preserved voucher specimens in 10% formalin and those are deposited in the collection at the Larval Fish Laboratory, Colorado State University.
Iowa darters were captured in the Yampa River at Lily Park in 2005 and 2006. No Iowa darter was collected at Lily Park in 2007, but effort was comparatively low and turbid water inhibited efficiency of sampling with an electric seine. In 2005, we also captured one juvenile Iowa darter in the Yampa River at Echo Park. No Iowa darter was captured there in 2006 and 2007, but drift nets set in summer and designed for capture of larvae are a relatively inefficient gear for Iowa darters that are in juvenile life stage or larger by then. Additional Iowa darters were captured in spring in the Green River near Jensen, Utah, at Cliff Creek; 11 in 2005, 42 in 2006, and 214 in 2007. Only early life stages, 3-14 mm total length, were captured with this size-selective gear (K. R. Bestgen, unpublished data). Extensive sampling of backwater by seine in the Green River upstream and downstream of Cliff Creek and light-trap sampling downstream from there in 2003-2007 did not yield the Iowa darter, which suggested a localized distribution (K. R. Bestgen, unpublished data; T. Hedrick, pers. comm.).
Specimens from the Yampa River and Green River that were captured in our study area during 2003-2007 must have resulted from a relatively recent introduction or colonization from upstream because extensive sampling in Little Yampa Canyon and Lily Park during 1999-2001 (R. Anderson, pers. comm.), and sampling at Echo Park and Cliff Creek since the early 1990s (Bestgen et al., 2006; K. R. Bestgen, unpublished data) failed to detect the species. Iowa darters spawn in spring at water temperatures of 12-16[degrees]C Uaffa, 1917; Becker, 1983), so specimens in early life stage captured in Green River initially might have dispersed as larvae from Little Yampa Canyon during high spring-snowmelt-runoff in late May and early June. Persistence of the Iowa darter at Little Yampa Canyon and Lily Park and colonization of tributary Milk Creek suggested the species is established in that area. Presence of early life stages of the Iowa darter in 3 consecutive years at Cliff Creek, and increasing abundance over time, suggested it also was established there, although no adult specimen has been reported in seine sampling upstream and downstream of that vicinity during 2005-2007.
Iowa darters in samples collected using electric seines from Little Yampa Canyon and Lily Park were from relatively shallow near-shore runs, pools, or backwaters over sand, gravel, and cobble substrate. Rooted macrophytes, a common habitat attribute of the Iowa darter, were uncommon in the Yampa River, where flows are fluctuating and erosive. However, Iowa darters were found commonly among algae-covered substrate. The most common species associates of the Iowa darter in our samples from Yampa River were, in descending order of abundance, smallmouth bass Microptems dolomieu, sand shiner Notropis stramineus, white sucker Catostomus commersonii, and fathead minnow Pimephales promelas (all nonnative taxa). A recent population expansion of smallmouth bass in the Yampa River (33% of fish in our electric-seine samples, 2003-2007) occurred prior to our sampling and was concurrent with decline of small-bodied or juvenile native fishes including roundtail chub Gila robusta, speckled dace Rhinichthys osculus, bluehead sucker Catostomus discobolus, and flannelmouth sucker Catostomus latipinnis since 2001 (R. Anderson, pers. comm.). Thus, establishment of the Iowa darter, a small-bodied species with a maximum total length of ca. 60 mm, concurrent with population expansion of piscivorous smallmouth bass and abundant age-0 life stages that occurred in the same habitat as darters, was something of a conundrum.
Proliferation of nonnative fishes is considered a primary reason for demise of the highly endemic and endangered native-fish assemblage in the Colorado River Basin (Carlson and Muth, 1989; Valdez and Muth, 2005; Olden et al., 2006). Although generally not considered to be a problematic species, darters (not the Iowa darter) prey upon newly stocked larvae of American shad Alosa sapidissima (Johnson and Dropkin, 1992). Other small-bodied fishes, such as red shiner Cyprinella lutrensis that are not considered traditional piscivores, also have been implicated in decline of native fishes in the Colorado River Basin (Ruppert et al., 1993; Bestgen et al., 2006). The Iowa darter might be particularly problematic if populations expand in backwaters of the Green River because they may compete for food resources or prey upon larvae of the endangered Colorado pikeminnow Ptychocheilus lucius or razorback sucker Xyrauchen texanus. It seems likely that introduction of the Iowa darter to the Yampa River was from a bait-bucket release, in spite of state regulations prohibiting use of live bait there since 1986. More stringent regulations and deterrents may be needed to prevent further illicit introductions of nonnative fishes and subsequent negative effects on native and endangered fishes in the Colorado River Basin.
This study was funded by the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin. The Recovery Program is a joint effort of the United States Fish and Wildlife Service, United States Bureau of Reclamation, Western Area Power Administration, states of Colorado, Utah, and Wyoming, Upper Basin water users, environmental organizations, Colorado River Energy Distributors Association, and the National Park Service. Funding for this research was administered by the United States Bureau of Reclamation under cooperative agreements with Colorado State University and the Larval Fish Laboratory. Administration was facilitated by T. Chart, D. Speas, V. Romero, M. Olivas, J. Frantz, A. Nielsen, and C. Morales. Field assistance was provided by R. Compton, G. DeKleva, G. Fox, M. Gruszczynski, A. Hill, C. McNerney, M. Sullivan, T. Sorensen, R Streater, K. Terry, C. Wilcox, G. B. Haines, and others who have escaped memory but also deserve thanks. Identification of specimens was provided by D. E. Snyder and S. Seal. Collecting permits were provided by the state of Colorado and the United States Fish and Wildlife Service. Reviews by J. Hawkins, A. Hill, and anonymous reviewers are appreciated. This is contribution 151 of the Larval Fish Laboratory.
Submitted 24 August 2007. Accepted 8 February 2008. Associate Editor was Gary P. Garrett.
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CAMERON D. WALFORD * AND KEVIN R. BESTGEN
Larval Fish Laboratory, Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, CO 80523
* Correspondent: firstname.lastname@example.org
TABLE 1--Location, date, number of specimens (total length, mm), sampling gear, and sampling effort for Iowa darters (Etheostoma exile) captured in the Yampa River, Colorado, and Green River, Utah, 2003-2007. Relative abundance is the percent composition of Iowa darters among all fishes captured; relative abundance of Iowa darters at sites other than Little Yampa Canyon was not calculated because of few captures (Lily Park) or differences in sampling gear. Number of specimens (range of total Location Date length, mm) Yampa River, Autumn 1 (60) Little Yampa 2003 Canyon, River Autumn 40 (41-61) km 161-200 2004 Autumn 148 (38-65) 2005 Autumn 166 (34-61) 2006 Autumn 108 (28-65) 2007 Yampa River, Lily Autumn 1 (58) Park, River 2005 km 80-89 Summer 2 (46,50) 2006 Autumn 0 2007 Yampa River, Summer 1 (24) Echo Park, 2005 River km 1 Summer 0 2006 Summer 0 2007 Green River, Spring 11 (3-14) confluence 2005 of Cliff Creek, Spring 42 (3-11) River km 487 2006 Spring 214 (3-16) 2007 Sampling Location Date gear Yampa River, Autumn Backpack, seine, Little Yampa 2003 bankshocker Canyon, River Autumn Electric seine km 161-200 2004 Autumn Electric seine 2005 Autumn Electric seine 2006 Autumn Electric seine 2007 Yampa River, Lily Autumn Electric seine Park, River 2005 km 80-89 Summer Electric seine 2006 Autumn Electric seine 2007 Yampa River, Summer Drift net Echo Park, 2005 River km 1 Summer Drift net 2006 Summer Drift net 2007 Green River, Spring Light trap confluence 2005 of Cliff Creek, Spring Light trap River km 487 2006 Spring Light trap 2007 Relative Number abundance of samples Location Date (%) Yampa River, Autumn 0.03 64 Little Yampa 2003 Canyon, River Autumn 1.0 20 km 161-200 2004 Autumn 1.1 86 2005 Autumn 1.4 72 2006 Autumn 1.0 54 2007 Yampa River, Lily Autumn -- 11 Park, River 2005 km 80-89 Summer -- 5 2006 Autumn -- 8 2007 Yampa River, Summer -- 207 Echo Park, 2005 River km 1 Summer -- 201 2006 Summer -- 222 2007 Green River, Spring -- 192 confluence 2005 of Cliff Creek, Spring -- 155 River km 487 2006 Spring -- 144 2007
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|Author:||Walford, Cameron D.; Bestgen, Kevin R.|
|Date:||Dec 1, 2008|
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