Dennis M. Stone

Ecology of spawning humpback chub, Gila cypha, in the Little Colorado River near Grand Canyon, Arizona

The morphologically unique and endangered humpback chub, Gila cypha, is found in canyon-bound reaches of the Colorado River and its tributaries. Now limited to six isolated reproducing populations, this species is believed to have been once distributed over a large portion of the mainstem river. Because the species inhabits remote canyon areas, little is known about its spawning ecology. The largest remaining population occurs in the lower Little Colorado River (LCR) near Grand Canyon, where we conducted a three-year study of spawning ecology during spring (March-June) 1993–1995. We analyzed seasonal patterns of movement, population density, relative condition, spawning scores, and frequency of ripe condition and fin abrasions and compared these data with seasonal discharge and water temperature to determine spawning phenology and ecology. Spawning commenced in late March, peaked in mid-April, and waned in mid-May. A high proportion of males remained ripe over this period, whereas ripe females were relatively abundant only in April. Increased densities of adult fish in March-April and rapid declines in May-June coupled with recaptures of 18.4% of these adults in the Colorado River suggest that a portion of the population migrated from the Colorado River into the LCR to spawn and then returned. Ripe males aggregated in areas of complex habitat structure with high angular variation in bottom profiles (matrix of large boulders, travertine masses combined with chutes, runs and eddies, 0.5–2.0 m deep) and were associated with deposits of clean gravel. Ripe females appeared to move to these male aggregations to spawn. Near-spawning (including gravid) females and non-spawning fish used similar habitats and were segregated but close (< 50 m) to habitats occupied by aggregations of ripe males. Abrasions on anal and lower caudal fins of males and females suggest that spawning involves contact with gravel substrates, where semi-adhesive eggs are deposited and fertilized. The findings of this study should aid recovery efforts for humpback chub by identifying spawning habitat within the historic distributional range where additional spawning stocks could be established.

Ontogenesis of Endangered Humpback Chub (Gila cypha) in the Little Colorado River, Arizona

Abstract The largest population of endangered humpback chub Gila cypha inhabits the Colorado River below Glen Canyon Dam and the lower 14 km of the Little Colorado River (LCR), Arizona. Currently, adults from both rivers spawn and their progenies grow and recruit to adulthood primarily within the LCR, where we studied G. cyphas life history using hoop net capture data. Humpback chub undergo an ontogenesis from diurnally active, vulnerable, nearshore-reliant young-of-the-year (YOY; 30–90 mm total length) into nocturnally active, large-bodied adults (≥180 mm TL). During the day, adults primarily resided in deep midchannel pools; however, at night they dispersed inshore amongst the higher densities of YOY conspecifics. Many YOY G. cypha shifted to nocturnal habitats that provided greater cover, possibly, to avoid inshore invading adults. These findings mirror predator-prey scenarios described in other freshwater assemblages, but do not refute other plausible hypotheses. Gila cypha piscivorous activity may escalate in hoop nets, which can confine fish of disparate sizes together; adults were significantly associated with YOY conspecifics and small dead fish in hoop nets at night and eight G. cypha (156–372 mm TL) regurgitated and/or defecated other fish body parts during handling following capture. Gila cypha can definitely be piscivorous given the opportunity, but the magnitude of their piscivorous activity in the wild is debatable.

Overriding Effects of Species-Specific Turbidity Thresholds on Hoop-Net Catch Rates of Native Fishes in the Little Colorado River, Arizona

Abstract I examined the effects of turbidity, discharge, and temperature on hoop-net catch rates of native humpback chub Gila cypha, speckled dace Rhinichthys osculus, flannelmouth suckers Catostomus latipinnis, and bluehead suckers C. discobolus in the Little Colorado River, Arizona. Results indicated that native fish catch rates were primarily influenced by whether turbidity levels were below or above species-specific thresholds of approximately 545 nephelometric turbidity units (NTU) for humpback chub, 221 NTU for speckled dace, 846 NTU for flannelmouth suckers, and 70 NTU for bluehead suckers. The effects of discharge were negligible, but discharge did dictate the turbidity level. Turbidity levels at hoop-net deployment relative to the turbidity thresholds predetermined much of the catchability of fish. Catch rates were highest in a high-catch zone consisting of the lowermost turbidities, which ranged up to the start of a transition zone for each species (humpback chub, ≤54 NTU; speckled dace, ≤29 NTU...

Dispersal of nonnative fishes and parasites in the intermittent Little Colorado River, Arizona.

Abstract We sampled nonnative fishes stranded in isolated pools near Grand Falls in the Little Colorado River (LCR), Arizona, after the river ceased flowing (21 June and 12 July 2005) to evaluate whether nonnative fishes can invade the perennial, lower 21 km of the LCR from upriver sources. The encroachment of nonnative fishes could jeopardize resident populations of endangered humpback chub, Gila cypha, and other native fishes in the lower LCR. We captured red shiner, Cyprinella lutrensis; common carp, Cyprinus carpio; fathead minnow, Pimephales promelas; black bullhead, Ameiurus melas; and plains killifish, Fundulus zebrinus, all of which have been captured >132 km downriver in the lower LCR and >127 km upriver in the closest perennial sources. Moreover, we detected Asian tapeworm, Bothriocephalus acheilognathi, in 9 of 30 common carp examined. Our findings suggest that nonnative fishes, including those hosting parasites, can invade the lower LCR from upriver sources >250 km away during freshets and provide a mechanism for the dispersal of invasive aquatic species in intermittent river systems.

Effect of Baiting on Hoop Net Catch Rates of Endangered Humpback Chub

Abstract The effects of unbaited, scented (odor emitted by inaccessible hatchery feed), and baited (accessible feed) single-throated hoop nets on the catch rates of the federally endangered humpback chub Gila cypha (≥100 mm total length) were assessed in the Little Colorado River, Arizona, to determine how baiting affected the catch of these fish. Of a total of 1,297 unique humpback chub captured, 262 (20%) were caught in 179 unbaited nets, 330 (25%) in 179 scented nets, and 705 (54%) in 178 baited nets. Humpback chub retention in unbaited nets did not differ from a 50:50 chance event (P = 0.075) but probably peaked in baited nets where these fish were preoccupied with feeding (i.e., gorging themselves), which would explain the higher catch rates in baited than in scented or unbaited nets (P ≤ 0.001). Moreover, humpback chub catch rates were not significantly higher in scented than in unbaited nets (P = 0.779), which suggests that elevating both “fish attraction” and “fish retention” are essential to subs...

An Individual-Based Model for Population Viability Analysis of Humpback Chub in Grand Canyon

Abstract We developed an individual-based population viability analysis model (females only) for evaluating risk to populations from catastrophic events or conservation and research actions. This model tracks attributes (size, weight, viability, etc.) for individual fish through time and then compiles this information to assess the extinction risk of the population across large numbers of simulation trials. Using a case history for the Little Colorado River population of Humpback Chub Gila cypha in Grand Canyon, Arizona, we assessed extinction risk and resiliency to a catastrophic event for this population and then assessed a series of conservation actions related to removing specific numbers of Humpback Chub at different sizes for conservation purposes, such as translocating individuals to establish other spawning populations or hatchery refuge development. Our results suggested that the Little Colorado River population is generally resilient to a single catastrophic event and also to removals of larvae ...

Differential Detection of Ingested Items Evacuated from Genus Gila Cyprinids by Two Nonlethal Alimentary Tract Lavage Techniques

ABSTRACT Two nonlethal alimentary tract lavage techniques were conducted on ten bonytail chub (Gila elegans, 211–241 mm TL) that had previously ingested 2–4 rainbow trout (Onchorynchus mykiss, ∼40 mm TL) to evaluate their capabilities of detecting piscivory in the field. Each fish was initially lavaged with water down its buccal cavity and out its anal vent using the Wasowicz and Valdez (W-V) technique and then immediately flushed in the opposite direction with the Baker and Fraser (B-F) method. Microscopic examination of evacuated material revealed only three identifiable rainbow trout scales and other assorted clumps of presumably well-digested body material. Overall, 30% of bonytail chub expelled rainbow trout scales andlor other body material during the initial W-V lavage, and 60% expelled material during the B-F flush. Dissections of four bonytail, seven humpback (G. cypha), and four roundtail chubs (G. robusta) revealed that their intestines were similarly curved and tapered to ≤50% of the anterior widths. Whereas the B-F method pushes ingested items backwards through the increasingly larger intestinal circumferences in these Gila fishes, it is more apt to retrieve greater quantities of food items. Food preference studies based on findings from a highly size-selective lavage technique will likely be biased in favor of smaller, less-digestible prey items, such as invertebrates with chitinous exoskeletons. Use of the B-F rather than W-V technique should lessen this bias.

Abiotic Controls of Invasive Nonnative Fishes in the Little Colorado River, Arizona

Abstract We examined why the lower Little Colorado River (LCR), Arizona continues to be dominated by four native fish species despite decades of encroachment by nine nonnative species. Most perennial flow begins at Blue Spring, located at river kilometer (RKM) 20.74 above the LCRs mouth, which is supplemented downriver by other springs. Blue Springs water is extremely supersaturated with dissolved CO2 (658 mg/L), and at baseflow the CO2 concentrations apparently functioned as a fish-barrier for about 1 km further downriver until it outgassed to 288 mg/L. Thereafter, CO2 outgassed to 202 mg/L by the top of Chute Falls (RKM 14.20) and 76 mg/L near the rivers mouth. Chute Falls, and high CO2 levels above it, obstruct upriver, but not downriver, fish movements; however, we still captured fishes from eight nonnative species above this falls. Our findings indicate most warmwater nonnative fishes in the LCR were immigrants from upriver sources within and bordering the intermittent corridor that invaded the system during floods, while most coldwater trout invaded from the Colorado River. Most nonnative species failed or were severely limited at reproducing progeny in the LCR, except occasionally by channel catfish Ictalurus punctatus and fathead minnow Pimephales promelas in the lower 13.57 km corridor, which was likely related to CO2. Correlation tests suggested severe flood and/or suspended sediment regimes reduced populations of fathead minnows, red shiners Cyprinella lutrensis, and plains killifish Fundulus zebrinus in the LCR. Conversely, severe suspended sediment regimes (especially ≥60,000 mg/L) increased channel catfish, black bullhead Ameiurus melas, and common carp Cyprinus carpio, hypothetically by paralyzing these fishes upriver, whereby many drifted downstream and recovered in the lower LCR; however, their abundances decreased after prolonged periods of high CO2. Nonnative fishes are controlled in the LCR by the systems endemic abiotic conditions.

Population Expansion of Humpback Chub In Western Grand Canyon and Hypothesized Mechanisms

Abstract— Humpback chub, Gila cypha, is an endangered warm water fish endemic to the Colorado River basin of southwestern North America. In Grand Canyon National Park, cold hypolimnetic water-release temperatures from Glen Canyon Dam have largely precluded successful spawning and recruitment of humpback chub in the mainstem Colorado River. Therefore, the species has utilized the warmer, more saline, and free-flowing Little Colorado River for its primary spawning habitat and continued existence. Based on long-term fish sampling efforts, we document local recruitment and population expansion of humpback chub in the western Grand Canyon and hypothesize that this is a result of recent warmer mainstem water temperatures. Continued recruitment and population expansion of humpback chub in the western Grand Canyon could potentially reduce extinction risk by providing population redundancy and less reliance upon the Little Colorado River for the species survival in the Grand Canyon.