David L. Propst

Responses of Native and Nonnative Fishes to Natural Flow Regime Mimicry in the San Juan River

Abstract The maintenance or restoration of natural flow regimes has been proposed as one means of conserving native fishes. Native fish conservation is enhanced either through the restoration of natural fluvial geomorphic processes (and thus the maintenance of essential habitats) or by the suppression of nonnative fishes. The San Juan River of Colorado, New Mexico, and Utah was dammed in 1962 and its natural flow regime was lost. Beginning in 1993, the river was regulated to mimic a natural flow regime by increasing reservoir releases to mimic timing, but only partially to mimic amplitude, volume, and duration of spring snowmelt discharge. We evaluated the responses of native and nonnative fishes to this natural flow regime mimicry by comparing their autumn densities (number/m2) in San Juan River secondary channels to those during spring runoff and summer base flow over a 9-year period. Densities of native speckled dace Rhinichthys osculus, bluehead sucker Catostomus discobolus, and flannelmouth sucker C....

NATURAL FLOW REGIMES, NONNATIVE FISHES, AND NATIVE FISH PERSISTENCE IN ARID-LAND RIVER SYSTEMS

Escalating demands for water have led to substantial modifications of river systems in arid regions, which coupled with the widespread invasion of nonnative organisms, have increased the vulnerability of native aquatic species to extirpation. Whereas a number of studies have evaluated the role of modified flow regimes and nonnative species on native aquatic assemblages, few have been conducted where the compounding effects of modified flow regimes and established nonnatives do not confound interpretations, particularly at spatial and temporal scales that are relevant to conservation of species at a range-wide level. By evaluating a 19-year data set across six sites in the relatively unaltered upper Gila River basin, New Mexico, USA, we tested how natural flow regimes and presence of nonnative species affected long-term stability of native fish assemblages. Overall, we found that native fish density was greatest during a wet period at the beginning of our study and declined during a dry period near the end of the study. Nonnative fishes, particularly predators, generally responded in opposite directions to these climatic cycles. Our data suggested that chronic presence of nonnative fishes, coupled with naturally low flows reduced abundance of individual species and compromised persistence of native fish assemblages. We also found that a natural flow regime alone was unlikely to ensure persistence of native fish assemblages. Rather, active management that maintains natural flow regimes while concurrently suppressing or excluding nonnative fishes from remaining native fish strongholds is critical to conservation of native fish assemblages in a system, such as the upper Gila River drainage, with comparatively little anthropogenic modification.

Dispersal and Life History Traits of Notropis girardi (Cypriniformes: Cyprinidae), Introduced into the Pecos River, New Mexico

-The Arkansas River shiner Notropis girardi was introduced into the Pecos River, New Mexico, in 1978 and was common in collections made in 1986-1987. From collections made since 1978 in the Pecos River drainage, we analyzed patterns of dispersal and abundance, and compared life history traits with a native population of N. girardi from Revuelto Creek, New Mexico. Notropis girardi dispersed downstream, presumably from a single introduction, colonizing much of the mainstream Pecos River (260 km) by 1981. Since 1981, the distribution and abundance of introduced N. girardi has expanded slightly. Age structure, growth and mortality rates of the Pecos River population are similar to those reported in the literature and to a native population of N. girardi in New Mexico. Timing of reproduction was similar for non-native and native populations, and both may exhibit multiple spawning peaks. Notropis girardi reproduction in the Pecos River coincided with large increases in flow. High discharge presumably initiates spawning and promotes downstream dispersal. Similarity of flow regimes of the Pecos River to those formerly found in lotic systems in the native range of N. girardi (e.g., Cimarron River, Kansas and Oklahoma) may account for the relative success of this introduced population.

Spatial and temporal variation of fish communities in secondary channels of the San Juan River, New Mexico and Utah

Spatial and temporal variation of fish communities in four secondary channels of the San Juan River between Shiprock, NM and Bluff, UT were investigated from July 1993 through November 1994. Fish abundance and habitat availability data were collected to determine if physical attributes of sites influenced spatial and temporal variation in their fish communities. Stability of habitat was shown to positively influence the stability of the fish community. Analysis of variance revealed greater spatial than temporal variation in the abundance of red shiner, Cyprinella lutrensis, fathead minnow, Pimephales promelas, and flannelmouth sucker Catostomus latipinnis, while speckled dace, Rhinichthys osculus showed greater temporal variation. Ordination, using detrended correspondence analysis, revealed variation in fish communities by site, date, and sample year. Spatial variation was greatest during low-flow periods when the greatest differences in habitat among the four sites occurred. Spring runoff had the greatest temporal effect on the fish communities in secondary channels and appeared to ‘reset’ the communities by displacing those species that were less resistant to increased current velocities. This annual event may help maintain native fish species adapted to these conditions in the San Juan River while moderating the abundance of nonnative fish species.

Habitat Use and Association of Native and Nonnative Fishes in the San Juan River, New Mexico and Utah

Habitat use and associations of native and nonnative fish species in secondary channels of the San Juan River, New Mexico and Utah were investigated. Most species and age classes within species (larvae, juveniles, subadults, and adults) used low velocity habitats with silt substrata. Discriminant function analysis revealed broad overlap in habitat use among species, with a trend of older age classes occurring in deeper habitats with faster current velocities. Overall, discriminant function analysis was able to correctly classify species and age classes, based on habitat use, 23.4% of the time. Native juvenile fishes exhibited the greatest interspecific association with nonnative fishes, whereas adult and subadult native fishes showed the least. Depending on the availability of resources, overlap in habitat use may result in negative interactions among native and nonnative fishes.

Native Inland Trout Restoration on National Forests in the Western United States: Time for Improvement?

Abstract The piscicides rotenone and antimycin are integral to successful restoration of native inland trout populations on public lands in the western United States by removing nonnative fishes that compete and hybridize with 13 species and subspecies of native trout. The U.S. Forest Service administers the greatest portion of native inland trout habitat on public lands. Piscicide use by state and federal agencies on national forests has become encumbered by redundant processes, uneven and irregular application of policies and regulations, and overlapping authorities. This has culminated in project delays and cancellations, placing native trout at continued, if not heightened, extinction risks. We reviewed the status of native trout restoration efforts on national forests in the western United States and considered issues associated with piscicide use. Central to the issue is whether piscicide applications by states require a permit from the Forest Service; those that required a permit usually invoked a ...

STATUS OF COLORADO SQUAWFISH AND RAZORBACK SUCKER IN THE SAN JUAN RIVER, COLORADO, NEW MEXICO, AND UTAH

growth, and provide further support for a winter breeding season in northwestern Louisiana. Dundee and Rossman (1989) reported that the probable time of hatching of sirens in Louisiana is midwinter. Courtship activity preceding a winter breeding season may explain the higher fall captures reported here. I thank L. M. Hardy for assistance and encouragement throughout the study. S. P. Ly ch provided assistance with the statistical anal ses, and A. C. Raymond prepared Fig. 1.

Long-Term Dynamics of Native and Nonnative Fishes in the San Juan River, New Mexico and Utah, under a Partially Managed Flow Regime

Abstract Nonnative fishes and flow alteration are primary threats to native fish persistence in lotic systems. We used several flow regime attributes and fish sampling data obtained from the San Juan River, New Mexico and Utah, during 1993–2010 to evaluate the potential use of flow manipulations to increase recruitment of native fishes that must cope with nonnative species. During this period, discharge in the river was partially manipulated by reservoir releases that augmented naturally high spring flows in this snowmelt-driven system. An information theoretic approach was used to rank candidate models that predicted species densities based upon selected combinations of flow attributes and abundances of nonnative species. Autumn density of age-0 fishes in secondary channels was the main response variable. The main predictor variables included flow attributes associated with interannual variation in daily discharge and water temperature; densities of nonnative competitors; and catch rates of a numerically...

Allozymic divergence and systematics of the Rio Grande silvery minnow, Hybognathus amarus (Teleostei: Cyprinidae)

Hybognathus amarus, a cyprinid endemic to the Rio Grande drainage, has had a confused taxonomic and systematic history. We examined allozymic variation for 22 presumptive gene loci for two populations each of H. amarus, H. hankinsoni, and H. placitus and one population of H. nuchalis. Dionda episcopa, Pimephales promelas, and Campostoma anomalum were included as outgroups. Neis (1978) genetic distance values were greater than 0.111 for all species pairwise comparisons in this study; intraspecific comparisons yielded genetic distances less than 0.005. Phenetic and phylogenetic analyses corroborated the hypothesis that H. amarus is a valid taxon, separate from H. nuchalis and H. placitus with which it was previously included.

THE DISTRIBUTION AND STATUS OF WARMWATER FISHES IN THE PLATTE RIVER DRAINAGE, COLORADO

r-In a 2.5 year (1978-1980) study of the lotic warmwater fish communities of the Platte River Basin, Colorado, 25 native and 9 non-native species were collected. Three natives (Nocomis biguttatus, Couesius plumbeus, and Notropis heterolepis) have been extirpated. Salmo clarki stomias was not collected, nor were the provisional natives, Stizostedion vitreum and Carpiodes cyprinus. Eleven native species were rare in the basin. The rarity of each was strongly correlated with their limited historic distributions, rather special habitat requirements, and intolerance of environmental stresses. Six native species were historically more common and widespread, but habitat deterioration associated with European settlement has caused their decline. The remaining native species (8) were common and widely distributed. The common carp (Cyprinus carpio) was the only common non-native fish. Lack of suitable habitat is believed responsible for the rarity of other non-native species. The Platte River arises in the Rocky Mountains of central and northern Colorado; the river system is comprised of two major basins: the North and South Platte. The North Platte River System in Colorado is limited to its headwaters area, a broad intermountain basin (3,706 km2). In its warmwater reaches, coalescing streams are small (<15 m wide and <1 m deep) but have a mixture of flow patterns. The relative isolation and high elevation (2,250 m) of the basin have restricted human activities primarily to ranching. In contrast, the South Platte River basin is 59,927 km2 and has a greater diversity of stream morphologies. Upon emerging from the mountains, the streams are in transition from montane to plains streams. Stream dimensions vary, but streams exhibit a commonality of heterogeneous flow patterns and substrate types. As the system progresses eastward and anastomoses, streams evolve from ones characterized by variable gradients and substrate types but stable, sinuous thalwegs to broad, shallow, sand- bottomed rivers. Except for the South Platte River, the eastern portion of the basin is drained only by intermittent streams. Peak discharge in the basins normally occurs from late spring to mid summer (May-July). Mean discharge of the South Platte River varies greatly, but decade means have remained fairly constant since 1900 (Williams, 1978) (Fig. 1). The South Platte River System has been significantly altered by human activities. As the streams flow eastward, they are deleteriously affected by industrial, municipal, and agricultural effluents. Irrigation, flood control, and municipal water supply reservoirs control the pulse of water through the streams. Transmountain diversions and ground-water pumping supplement natural discharge. The North Platte System in Colorado remains comparatively unmodified. Because this research was funded by the Colorado Division of Wildlife, political rather than ecosystem boundaries defined the limits of the study