Anthony T. Robinson

Dispersal of Larval Fishes in a Regulated River Tributary

Abstract We investigated longitudinal distributions, nearshore movements, and drift of larval native fishes (humpback chub Gila cypha, speckled dace Rhinichthys osculus, bluehead sucker Catostomus discobolus, and flannelmouth sucker Catostomus latipinnis) in the Little Colorado River, a tributary to the regulated Colorado River in Grand Canyon, Arizona, to determine spawning sites, larval dispersal patterns, and amount of drift into the mainstem Colorado River. Larval distributions and drift indicated native fishes spawned throughout the terminal 14.2 km of the Little Colorado River. In addition, distribution, drift, and trap data suggest an active component to dispersal for all four native species. Drift of larval native fish was greater near shore than midchannel, and except for speckled dace larvae, which were prone to drift at night, larval native fish did not exhibit diel periodicity in drift. During a 46-d period in 1993, we estimated that over 370,000 native fish larvae drifted out of the Little Co...

Juvenile Growth of Native Fishes in the Little Colorado River and in a Thermally Modified Portion of the Colorado River

Abstract We estimated juvenile growth rates of four native fish species using the von Bertalanffy growth equation and length data from fish captured during 1991–1994 in the Little Colorado River, a tributary to the Colorado River in Arizona in the Grand Canyon. We compared growth rates to water temperatures for all four species and modeled the effects of warming the Colorado River (through a proposed retrofit of Glen Canyon Dam) on the growth of age-0 emigrants from the tributary. Juvenile growth rates in the Little Colorado River were fastest for flannelmouth sucker Catostomus latipinnis, slowest for speckled dace Rhinichthys osculus, and intermediate for humpback chub Gila cypha and bluehead sucker Catostomus discobolus. Growth rates for each species were positively correlated with water temperature; flannelmouth sucker exhibited the strongest relationship, followed by speckled dace, humpback chub, and bluehead sucker. Our model indicates that native fish immigrating into the cold Colorado River (8–12°C...

Resource Use by Larval and Early Juvenile Native Fishes in the Little Colorado River, Grand Canyon, Arizona

Abstract We investigated resource use by early life stage (≤30 mm, total length) humpback chub Gila cypha, speckled dace Rhinichthys osculus, bluehead suckers Catostomus discobolus, and flannelmouth suckers C. latipinnis in the Little Colorado River, a tributary to the Colorado River in Grand Canyon, Arizona. Significant logistic regression models for habitat use were developed for all species pairwise combinations except flannelmouth sucker–humpback chub and flannelmouth sucker–speckled dace; correct classification probabilities ranged from 54% to 81%. Parameters used in discriminating among habitat use included depth, distance from shore, cover, and substrate. Logistic models were also developed to compare habitat use among larval stages within species, and most combinations produced significant models. Classification probabilities ranged from 60% to 95% in these models with the variables of depth, distance from shore, current velocity, cover, and substrate contributing to the various models. Behavioral...

Behavioral Responses of a Small Native Fish to Multiple Introduced Predators

Rainbow trout, Oncorhynchus mykiss, and crayfish, Orconectes virilis, have been introduced for the last century into North American streams inhabited by native fishes. We sought to determine the behavioral response of a federally threatened cyprinid, Little Colorado spinedace, Lepidomeda vittata, in the concurrent presence of multiple nonnative predators (rainbow trout and crayfish), as well as the response to the presence of a combination of native (Apache trout, Oncorhynchus apache) and nonnative (crayfish) predators. We held spinedace in artificial streams and exposed them to four treatments: (1) control, (2) crayfish added, (3) trout added, and (4) both crayfish and trout added. Only a single spinedace was consumed over the course of the experiments; it was captured and preyed upon by a crayfish. When both crayfish and Apache trout were present, spinedace response was similar to what it was when only Apache trout were present (decreased movement in and out of refuge), suggesting that crayfish and Apache trout did not mutually influence spinedace behavior. However, when both rainbow trout and crayfish were present, spinedace not only decreased movements in and out of refuge, but also decreased activity rates. We suggest that crayfish and rainbow trout mutually influence spinedace behavior and recommend control or elimination of crayfish and rainbow trout from spinedace critical habitat or potential reintroduction sites. In addition, potential reintroduction sites for Apache trout should be evaluated based on presence of crayfish and spinedace to avoid potential multiple predator interactions and negative effects on spinedace.

Parasites and Fish Health in a Desert Stream, and Management Implications for Two Endangered Fishes

Abstract Reintroductions of the endangered razorback sucker Xyrauchen texanus and Colorado squawfish Ptychocheilus lucius into the Verde River, Arizona, have failed to establish self-sustaining populations. The failure of these reintroductions is often attributed to predation and competition by nonnative fishes and habitat loss, but parasite infestations (particularly a copepod, Lernaea cyprinacea) also have been implicated. We assessed the relationships among fish health, eukaryotic parasites, and bacterial and viral infections of these endangered fishes collected from two locations (Perkinsville and Childs) on the Verde River, Arizona, during February and June 1996. We also examined surrogate nonendangered native fishes (Sonora sucker Catostomus insignis, desert sucker Catostomus clarki, and roundtail chub Gila robusta) and nonnative species (common carp Cyprinus carpio and smallmouth bass Micropterus dolomieu) to determine if there were any systemwide patterns in parasite infestation and health of fish...

Short-term effectiveness of constructed barriers at protecting apache trout

Abstract Placement of fish migration barriers (primarily of gabion construction) on select streams is one of the major recovery actions used to isolate and protect upstream populations of Apache trout Oncorhynchus gilae apache from downstream populations of nonnative salmonids. However, the effectiveness of the recovery action has not been evaluated. We evaluated the success of constructed barriers at preventing upstream movement of nonnative salmonids into areas occupied by native Apache trout. We collected and marked salmonids downstream of six barriers on six streams in the White Mountains of east-central Arizona and subsequently electrofished upstream of the barriers to determine whether marked fish had moved past them. Only 1 of 1,436 marked salmonids was collected upstream of one of the six barriers evaluated over a 3-year period. Our results showed that the barriers evaluated in our study are effective for a short term; however, long-term evaluation is needed, as these failure rates represent minim...

Habitat Selection by Apache Trout in Six East-Central Arizona Streams

Abstract Information on habitat selection by Apache trout Oncorhynchus gilae apache is needed to help recovery efforts for this federally threatened species. We investigated Apache trout habitat selection in six White Mountain streams in east-central Arizona. We measured environmental characteristics at used sites and randomly selected available sites and modeled habitat selection using forward step-wise logistic regression, for two size-classes of Apache trout (≤100 mm and >100 mm total length [TL]). We also compared overall habitat type selection using contingency table analysis and G-tests. Our logistic regression models correctly predicted habitat selection by 100-mm TL or smaller Apache trout for 62.8% of sites over all streams surveyed and that by Apache trout larger than 100 mm TL for 75% of sites. Logistic regression models determined that larger width, lower width: Depth ratio, more eddy flows, and more cover in the form of overhanging vegetation, debris, and boulders were significant predictors ...

Interactions between Desert Pupfish and Gila Topminnow Can Affect Reintroduction Success

Abstract In fisheries, recovery actions for species of concern sometimes involve reintroductions of multiple species. As an example, desert pupfish Cyprinodon macularius and Gila topminnow Poeciliopsis occidentalis historically had sympatric distributions and inhabited similar environments, and they are often reintroduced into the same waters. Success of these stockings has varied greatly, and a hypothesis developed among conservationists that desert pupfish populations were more likely to establish and persist if they were stocked first and allowed to establish before Gila topminnow were stocked. We examined historical records of desert pupfish reintroductions and conducted laboratory experiments to evaluate this hypothesis. For the reintroductions, we evaluated 29 ponds where four general stocking strategies (treatments) were implemented: (1) only desert pupfish were stocked, (2) desert pupfish were stocked first and allowed to establish and then Gila topminnow were stocked, (3) both desert pupfish and ...

Comparison of American Fisheries Society (AFS) Standard Fish Sampling Techniques and Environmental DNA for Characterizing Fish Communities in a Large Reservoir

AbstractRecently, methods involving examination of environmental DNA (eDNA) have shown promise for characterizing fish species presence and distribution in waterbodies. We evaluated the use of eDNA for standard fish monitoring surveys in a large reservoir. Specifically, we compared the presence, relative abundance, biomass, and relative percent composition of Largemouth Bass Micropterus salmoides and Gizzard Shad Dorosoma cepedianum measured through eDNA methods and established American Fisheries Society standard sampling methods for Theodore Roosevelt Lake, Arizona. Catches at electrofishing and gillnetting sites were compared with eDNA water samples at sites, within spatial strata, and over the entire reservoir. Gizzard Shad were detected at a higher percentage of sites with eDNA methods than with boat electrofishing in both spring and fall. In contrast, spring and fall gillnetting detected Gizzard Shad at more sites than eDNA. Boat electrofishing and gillnetting detected Largemouth Bass at more sites t...

Health Assessment, Associated Metrics, and Nematode Parasitism of Rainbow Trout in the Colorado River below Glen Canyon Dam, Arizona

Abstract We captured rainbow trout Oncorhynchus mykiss in the Colorado River below Glen Canyon Dam, Arizona, between 1995 and 1997 to develop baseline data for a modified health assessment index (mHAI) and to determine relationships among mHAI, parasite burden, relative condition, mesenteric fat index, and diet. We also examined effects of a simulated flood on these variables during 1996. There were no significant effects of the flood on variables measured in the fish. Total stomach volume increased during spring and summer following the flood and reflected an expected trend. Health of fish, based on the mHAI, remained good throughout the study but declined with increasing burden of the nematode Truttaedacnitis truttae and with trout size. Increasing relative condition and greater mesenteric fat levels and stomach volumes of macroinvertebrates were associated with reduced mHAI. Larger trout also ate more Cladophora glomerata than did smaller fish, and nematode burden was related negatively to volumes of t...