Gordon Mueller

A Conservation Plan for Native Fishes of the Lower Colorado River

Abstract The native fish fauna of the lower Colorado River, in the western United States, includes four “big-river” fishes that are federally listed as endangered. Existing recovery implementation plans are inadequate for these critically imperiled species. We describe a realistic, proactive management program founded on demographic and genetic principles and crafted to avoid potential conflicts with nonnative sport fisheries. In this program, native species would breed and their progeny grow in isolated, protected, off-channel habitats in the absence of nonnative fishes. Panmictic adult populations would reside in the main channel and connected waters, exchanging reproductive adults and repatriated subadults with populations occupying isolated habitats. Implementation of the plan would greatly enhance recovery potential of the four listed fishes.

Predatory Fish Removal and Native Fish Recovery in the Colorado River Mainstem

Abstract Mechanical predator removal programs have gained popularity in the United States and have benefited the recovery of several native trout and spring fish. These successes have been limited to headwater streams and small, isolated ponds or springs. Nevertheless, these same approaches are being applied to large river systems on the belief that any degree of predator removal will somehow benefit natives. This attitude is prevalent in the Colorado River mainstem where recovery and conservation programs are struggling to reverse the decline of four endangered fish species. Predator removal and prevention are major thrusts of that work but unfortunately, after 10 years and the removal of >1.5 million predators, we have yet to see a positive response from the native fish community. This leads to the obvious question: is mechanical removal or control in large (>100 cfs base flow) western streams technically or politically feasible? If not, recovery for some mainstem fishes may not be practical in the conv...

BULLFROG TADPOLE (RANA CATESBEIANA) AND RED SWAMP CRAYFISH (PROCAMBARUS CLARKII) PREDATION ON EARLY LIFE STAGES OF ENDANGERED RAZORBACK SUCKER (XYRAUCHEN TEXANUS)

Abstract Bullfrog tadpoles (Rana catesbeiana) and red swamp crayfish (Procambarus clarkii) are widespread introduced taxa that are problematic throughout the western United States. Their impact on native amphibians and crustaceans is well documented, but less is known regarding their influence on native fishes. Predator-prey tank tests showed both species consumed eggs and larvae of the endangered razorback sucker (Xyrauchen texanus) in a laboratory setting. Tadpoles consumed 2.2 razorback sucker eggs/d and 1.4 razorback sucker larvae/d, while crayfish ate 6.0 eggs/d and 3.5 larvae/d. Relatively high densities of bullfrog tadpoles and crayfish in razorback sucker spawning areas suggest that these nonnative taxa might pose a threat to the recruitment success of this and other imperiled native fish.

Reintroduction of the Flannelmouth Sucker in the Lower Colorado River

Abstract A single stocking of 611 wild flannelmouth suckers Catostomus latipinnis in 1976 represented the first successful reintroduction of a native fish in the lower Colorado River. Flannelmouth suckers ranging in age from young of the year to 24 years were captured during 1999–2001; their population was estimated as at least 2,286 (95% confidence interval, 1,847–2,998). Recruitment appeared sporadic, consisting of consecutive years of low recruitment (<10%) supplemented by a stronger (31%) year-class. Historically, this native fish was rare and was believed extirpated from the lower river by 1975, but it now reproduces naturally in a reach dramatically altered by water development. This successful reintroduction indicates that one native fish can successfully tolerate environmental alterations whereas another, the razorback sucker Xyrauchen texanus, apparently cannot. Other opportunities may exist in altered rivers to benefit native fishes where they were absent or historically rare.

SMALL NONNATIVE FISHES AS PREDATORS OF LARVAL RAZORBACK SUCKERS

Abstract The razorback sucker (Xyrauchen texanus), an endangered big-river fish of the Colorado River basin, has demonstrated no sustainable recruitment in 4 decades, despite presence of spawning adults and larvae. Lack of adequate recruitment has been attributed to several factors, including predation by nonnative fishes. Substantial funding and effort has been expended on mechanically removing nonnative game fishes, typically targeting large predators. As a result, abundance of larger predators has declined, but the abundance of small nonnative fishes has increased in some areas. We conducted laboratory experiments to determine if small nonnative fishes would consume larval razorback suckers. We tested adults of three small species (threadfin shad, Dorosoma petenense; red shiner, Cyprinella lutrensis; fathead minnow, Pimephales promelas) and juveniles of six larger species (common carp, Cyprinus carpio; yellow bullhead, Ameiurus natalis; channel catfish, Ictalurus punctatus; rainbow trout, Oncorhynchus mykiss; green sunfish, Lepomis cyanellus; bluegill, L. macrochirus). These nonnative fishes span a broad ecological range and are abundant within the historical range of the razorback sucker. All nine species fed on larval razorback suckers (total length, 9–16 mm). Our results suggest that predation by small nonnative fishes could be responsible for limiting recovery of this endangered species.

Factors Influencing Poststocking Dispersal of Razorback Sucker

Abstract Efforts to reintroduce razorback suckers Xyrauchen texanus to specific river reaches have been plagued by downstream drift and poor survival, which have been attributed to stress, disorientation, predation, and poor conditioning. Poststocking dispersal of eight test groups (15 fish each) of razorback suckers was examined for 28 d with telemetry equipment. Fish were released in three different locations in the Colorado River basin of Utah, Arizona, and Nevada: (1) a 65,000-ha reservoir, (2) a small (<1-ha) backwater, and (3) a large (30-ha) backwater on the mainstem river. At each location, subgroups were released immediately (reference) or held to acclimate them to the site (3–7 d) before release. Two of four subgroups for the large-backwater test were preconditioned to flow. Dispersal from the stocking sites was rapid and declined with time for all tests, as fish appeared to seek and find cover. Downstream drift was most pronounced (x = 69.5 km) from the small backwater and significantly (Kruska...

Evaluation of Tire Reefs for Enhancing Aquatic Communities in Concrete-Lined Canals

Abstract Large earthen canals in the and southwest are being lined with concrete to reduce seepage and conserve limited water supplies. Lining reduces habitat and increases operational velocities (relative to unaltered streams), which are detrimental to aquatic communities. Fish communities that become reestablished in these waterways exhibit lower species diversity, densities, and biomass than they did in the former earthen canals. Placement of low-profile tire reefs in the Coachella Canal, California, and the Hayden–Rhodes Aqueduct, Arizona, reversed these trends. Comparative sampling revealed that invertebrate and fish densities were 3 and 20 times higher, respectively, in reef areas than in typical canal sections without reefs. Tire reefs are recommended as an effective means of enhancing aquatic communities in concrete canals.

Establishment of a Fish Community in the Hayden-Rhodes and Salt-Gila Aqueducts, Arizona

Abstract Fish populations were studied in the Central Arizona Projects canal system during the first 4 years of aqueduct operation (1986–1989). Ichthyoplankton entering the canal from Lake Havasu averaged 1 larva/m3 during April–June 1987 and 1988. Larval fish densities increased significantly in downstream samples, substantiating diver observations that fish were spawning in the canal system. Of the 16 fish species collected, 14 were assumed to have originated from Lake Havasu and 2 were introduced by anglers from their bait buckets. Initially, the fish community was dominated numerically by threadfin shad Dorosoma petenense (>88%), centrarchids (< 10%), cyprinids (<2%), and striped bass Morone saxatilis (<I%). However, as annual water diversions increased from 1.3 × 108 m3 in 1986 to 9.4 × 108 m3 in 1989, community composition shifted from clupeids to centrarchids (70%). Fish densities dropped from an estimated 1,260 fish/ha in 1986 to 17 fish/ha in 1989, and biomass dropped from 116 to 73 kg/ha. Decli...

Diel Cover use and Local Site Fidelity of a Large Southwestern Cyprinid, Bonytail Gila elegans, in a Lower Colorado River Backwater

ABSTRACT. Sonic transmitters were affixed to 10 large (40.4–51.4 cm TL) adult bonytail Gila elegans in 2003 from Cibola High Levee Pond, a small, isolated backwater adjacent to the lower Colorado River in Arizona and California, Point and paired directional observations showed that all marked adult bonytail occupied interstices of large riprap during daytime and used open water areas during darkness, presumably to feed. There were 2 spatial patterns of nighttime distribution by adult fish; 70% of fish exhibited mesohabitat site fidelity to a particular area of the pond, while others appeared to move about at random. Selection or design of bonytail management areas including grow-out and refuge sites should consider cover requirements for larger fish, as this may be a limiting factor if lack of cover subjects some individuals to higher predation risk.

Springtime Foods of Bonytail (Cyprinidae: Gila elegans) In A Lower Colorado River Backwater

Abstract Bonytail, Gila elegans, in Cibola High Levee Pond, an isolated lower Colorado River backwater, fed more during evening and after dark than during daylight. Fish were omnivorous, and contents of stomachs (n = 72) included amorphous organic matter (materials digested beyond visual identification), aquatic macrophytes, invertebrates (micro-crustaceans, insects, and crayfish), bullfrog, and fish. Proportion of plants decreased while that of invertebrates increased with increased size of fish. Remains of fish were found only in the largest specimens. Asian tapeworm, Bothriocephalus acheilognathi, was in 11% of the sample and represents the first report for this parasite from open waters of the lower Colorado River system.