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December 2008 Notes 531 TABLE I-Location, date, number of specimens (total length, mm), sampling gear, and sampling effort for Iowa darters (EtheostO'lna eJo.ile) 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 Relative (range of total Sampling abundance Number Location Date length, mm) gear (%) of samples Yampa River, Little Yarnpa Autumn 1 (60) Backpack, seine, 0.03 64 Canyon, River km 161-200 2003 bankshocker Autumn 40 (41-61) Electric seine 1.0 20 2004 Autumn 148 (38-65) Electric seine 1.1 86 2005 Autumn 166 (34-61) Electric seine 1.4 72 2006 Autumn 108 (28-65) Electric seine 1.0 54 2007 Yarnpa River, Lily Park, Autumn 1 (58) Electric seine 11 River km 80-89 2005 Summer 2 (46,50) Electric seine 5 2006 Autumn 0 Electric seine 8 2007 Yampa River, Echo Park, Summer 1 (24) Drift net 207 River km 1 2005 Summer 0 Drift net 201 2006 Summer 0 Drift net 222 2007 Green River, confluence Spring 11 (3-14) Light trap 192 of Cliff Creek, River km 487 2005 Spring 42 (3-11) Light trap 155 2006 Spring 214 (3-16) Light trap 144 2007 NotTapis stramineus, white sucker Catostom-us com- mersonii, and fathead minnow Pimephales prornelas (all nonnative taxa), A recent population expan- sion 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 OSC-UlU5, bluehead sucker Catostomus discobolus, and flan- nelmonth sucker Catostomus latipinnis since 2001 (R. Anderson, pers. comm.), Thus, establish- ment of the Iowa darter, a small-bodied species with a maximum total length of ca, 60 mm, concurrent with population expansion of pisciv- orous smallmouth bass and abundant age-O 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 aI., 20(6). 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