Red Shiner Eradication from the Virgin River, Arizona-Nevada-Utah: Background, Impacts, and Needs for Future Studies

W. L. Minckley

Professor of Zooloay. Arizona State University. Tempe. Arizona 85287-1501

Contents

Introduction ...... 1 Background Information: Description of the Area and its Fauna ...... 1 Events Leading to Management Efforts of 1988 ...... 3 Proposed Remedial Actions ...... 4 Ichthyocide Application ...... 4 Actual and Potential Impacts ...... 5 Recommendations for Post-eradication Actions ...... 8 Significance of the proposed program ...... 8

Introduction

Historic information in the following summary of data on the Virgin River basin, Arizona-Nevada-Utah, Is from the research files of J. E. Deacon, P. C. Marsh, W. L. Minckley, and their students and associates, some of which is unpublished, and from open literature or agency reports. Information on intent of agencies relative to application of rotenone to the Virgin River Is mostly from a U. S. Fish and Wildlife Service (Service) Environmental Assessment, and from a Service-Utah Department of Wildlife Resources briefing held at Arizona Game and Fish Department offices in Phoenix, Arizona, on 21 October 1988. Data on field activities, actions, and impacts of the operation are from first-hand field notes and written and verbal reports of personnel who participated or who observed operations in the field. Extensive literature or report citations are not included in the present document; a thorough review, with citations, will be accomplished as written summaries become available and specific proposals are prepared.

Background Information: Description of the Area and its Fauna

The Virgin River drains extreme southwestern Utah, flows through northwestern Arizona, and enters Lake Mead in southern Nevada. The region is chronically arid, and, under natural conditions, most streams (including the Virgin River mainstream) are intermittent in their lower reaches. Normal low flows have been exacerbated by irrigational, domestic, and other water-use demands of increasing human populations.

This system may be quite old, a headwater remnant of a stream that flowed south or west before formation of the Grand Canyon. It drains the page 2

southwestern margin of the Colorado Plateau. flowing through a rugged, mountainous region formed by parts of the plateau that collapsed toward extension zones to the west and south. Runoff from montane rain and snow i s augmented by springs along faults in this highly fractured region. These enter the mainstream (1.g., Pah Tempe Spring), as well as feeding tributaries (Beaver Dam and Meadow Valley washes, and the Moapa River). which contribute significant discharge plus unique habitats and fishes to the system. The lowermost Virgin River Is now drowned by Lake Mead, which also excludes the Moapa and Pluvial White rivers from the system.

Native fishes of the system (Table 1) reflect its age, habitat diversity, and Isolation. Excluding Moapa and pluvial White rivers, six native taxa are present, with evidence that at least three of them exist as two or more

TABLE 1. Common and scientific names of native fishes of the Virgin River system, Arizona-Nevada-Utah.

Scientific Name Common Name Habitat

Rhinichthvs oscutus Speckled dace R. Q. varrowi Virgin River channel and largest tributaries R. osculus subspecies(?) Springs and spring-fed tributaries Plummterus arPentissimus Woundfin Virgin River channel, downstream from Pah Tempe Spring gill robusta g. L. seminuda Virgin River Virgin River channel, chub downstream from Pah Tempe Spring Loidomeda mollispinis L. m. mollisPinis Virgin spinedace Virgin River tributaries, rare in channel, where associated with springs

Catostomus latiPinnis Flannelmouth Virgin River mainstream, sucker precise ecologic distribution undefined Catostomus species(?) Virgin River largest tributaries, precise ecologic distribution undefined Pantosteus "clarkii Desert sucker Virgin River mainstream, precise ecologic distribution undefined Pantosteus species(?) Virgin River tributaries, Including small, spring- fed systems; precise ecologic distribution undefined Page 3

"forms" that are not yet taxonomically defined. The "forms" are segregated into channel habitats versus those in tributary streams or springs, as is the pattern in many such systems.

Historically, the first known collections of fishes from the Virgin River were during the Wheeler Expedition of 1871-74. Carl L. Hubbs and Robert R. Miller sampled extensively between 1934 and 1959, and Deacon and his students commenced work in the area In the 1960s, continuing to the present. Federal listing of woundfin as Endangered stimulated detailed sampling of the mainstream habitat of this species, which has resulted In accumulation of an invaluable, long-term, quantitative data-base.

Events Leading to Management Efforts of 1988

The Virgin River mainstream is a severe environment, hot in summer, violent In flood, and nearly dry In drought. Mainstream native fishes appear adapted to such vagaries, and although their populations fluctuate dramatically year-to-year, they have persisted under such conditions for millenia. Man's development of the Virgin River basin commenced about a century ago, consisting of clearing and irrigation of floodplains for subsistence agriculture and production of foodstuffs and livestock feeds for export, mostly to adjacent areas of colder climate and shorter growing seasons. The moderate climate also attracted winter visitors, which, with burgeoning "sun belt" trends, has become a major industry. St. George, Utah, the major population center, is growing rapidly, with vast influxes of retirees and development of winter homes.

This combination of expanding agriculture and human populations resulted In increased demands for water, and planning for expanded use brought the Endangered Species Act of 1973 (as amended) to bear to protect the Endangered woundfin. Negotiations too complex to relate here resulted In agreements that may have helped the fish and local people, alike, but in the meantime, changes in the Virgin River created new problems for the woundf in.

The non-native red shiner (Notropis lutrensis) had long been in the lower Virgin River, below the "Narrows" (the uppermost part of the reach within Arizona, often dry in drought, which flows in a precipitous canyon), where it had presumably invaded from Lake Mead. The species was first introduced In the lower Colorado River basin In the 1950s.

Red shiners co-occurred with woundfin in the lower Virgin River for at least 25 years. It was abundant downstream from Mesquite, Nevada, to the apparent detriment of woundf in, but remained at relatively low population levels between Littlefield, Arizona, and the Narrows; woundfin remained common there. In the early 1980s, an irrigation reservoir was completed on Quail Creek. upstream from the Narrows, which allowed more constant delivery of water to downstream agriculturists. This, and perhaps other factors such as unusually high runoff in the early 1980s, stabilized flow from Utah into Arizona, and red shiners attained and densely populated the Utah segment upstream to the Washington Fields Diversion (WFD), a man-enhanced, natural barrier that prevented further upstream invasion. Page 4

With establishment and explosive expansion of red shiner populations upstream from the Narrows, those In the reach downstream (between the Narrows and Mesquite, Nevada) had a source of continuous repopulation against environmental stresses. Red shiners became Increasingly abundant, were not evidently reduced after flood or drought as had been the case before, and woundfin populations began to decline in relative and absolute abundance. Red shiners had before been implicated in decline of the related spikedace (Meda fulaida) and other species in Arizona, so managers quickly became concerned. In addition, an exotic, Asiatic tapeworm was discovered to infect red shiners, and soon invaded native fishes, including woundf in.

Proposed Remedial Actions

The woundfin recovery team and its advisors concluded that eradication of red shiners from below WFD was necessary to stop its potential Invasion further upstream. Opportunities existed for construction of one or more additional barriers downstream, upstream from the narrows, then to apply rotenone to the reach between barriers and maintain it in the future as a shiner-free zone. The scheme decided upon Included two barriers, one -10 km below WFD and a second -24 km below that. Rotenone applied at WFD was to be detoxified at the most downstream barrier. Arrangements were made for barrier construction, which commenced in September 1988. It was assumed that recolonization of the -34-km reach would be from movement of native fishes downstream, over WFD, and that adequate repopulation would occur In a relatively brief period of time, to re-establish the original fauna. An Environmental Assessment (EA) of this preferred alternative was prepared, comparing it to other possible, but unlikely-to-succeed alternatives. The EA was circulated for review and comment and approved with a finding of no significant impact.

Ichthyocide Application

In early September 1988, substantial numbers of woundfin (the major target species because of its Endangered status) and Virgin River chub (a secondary target because of Candidate-for-listing status) were removed and placed in holding facilities. A sample of the former was transferred to Dexter National Fish Hatchery, New Mexico, and another large number was moved below the lowermost barrier-site, and released. A number of chubs were placed in a holding pond near Quail Creek Dam. No attempt was made to salvage or otherwise protect other native species.

A series of small floods occurred In mid-September. However, by late September the Virgin River had declined in flow and rotenone was applied to the mainstream and appropriate irrigation canals and drains at and near WFD to remove fish from between that point and the first barrier. Discharge was reduced by turnout of water into canals. Water levels were low, and drip stations were augmented by direct spraying of isolated backwaters. No attempt was made to detoxify at the lower end of this reach. In anticipation of other studies, Arizona State University (ASU) personnel preserved large series of native and non-native fishes and froze substantial numbers of other specimens for projected genetic analyses. Page 5

The second segment (first to second barrier and associated off-river habitats) was treated in October using the same combination of drip stations and sprayer application of rotenone. Detoxification was to occur downstream of the second (lowermost) barrier site. Due to a combination of factors, e.g., the rotenone carried far more rapidly and at higher cumulative concentration than anticipated and the start of detoxification was delayed, fish died downstream at least as far as Mesquite, Nevada, and perhaps farther. Substantial numbers of dead and dying fish at the Bureau of Land Management campgound in the Virgin River Narrows, downstream at Littlefield, Arizona, and at Mesquite Diversion. Nevada, were recorded by observations and limited sampling by Service and other personnel. It must be concluded that an unknown percentage of the total fauna was destroyed, and seems likely that rotenone-sensitive, channel inhabiting species, unfortunately the native fishes, were selectively removed. However, at this writing (24 October 1988), no quantitative data are available on the magnitude or selectivity (or lack of same) of fish mortality in the reach below the second barrier.

Pick-up of dead and moribund fishes by ASU personnel Indicated that the first (September) treatment had also carried farther than at least those personnel anticipated, likely throughout the 34-km reach between barriers, although not as far as Littlefield, Arizona. This conclusion was based on the essentially-exclusive presence of rotenone-resistant, non-native fishes (red shiner and bullhead catfish [Ameiurus spp.]) and essential absence of rotenone-sensitive, native species in the reach during the second ichthyocide application. Native species had remained common at Littlefield, Arizona, based on observations made during the accidental poisoning.

Actual and Potential Impacts

Potential impacts of these events, subject to changes in interpretation when quantitative data become available, may be divided into short- and long-term problems. On the short term, questions that must be answered include the magnitude and geographic extent of damage. which I understand is to be assessed during a Woundfin Recovery Team monitoring effort that is soon to occur. It is important to stress that monitoring for Woundfin recovery efforts has accumulated a remarkable data-base, which will serve to allow direct and objective interpretation of impacts of this accident. Among streams in the American Southwest, the Virgin River stands as one of the few for which such an historic and up-to-date data-base exists. Once we know these facts, longer-term problems can be evaluated, and herein lies an unprecedented opportunity--no matter what results derive from the accident in the Virgin River, we will:

1) obtain data that will serve to guide future management of Virgin River fishes from a solid baseline of community ecology and genetics: and

2) obtain answers to questions being asked about managed fish populations, pertaining not only to impacts of in situ population manipulations, but also to the propagation and reintroduction in recovery of Endangered and Threatened species. Page 6

If a complete or at least substantial kill was realized in Arizona and Nevada, which seems to be the case based on preliminary data, some concerns may be summarized as follows:

1) Overall, potential losses of the Federally-listed woundfin and candidate Virgin River chub include not only the anticipated -34 km of target area, but 70 km or more of the river downstream. Habitat not so affected includes -15 km. from WFD upstream to a variable distance below Pah Tempe Spring. Neither species is known to inhabit tributary streams in any numbers, although chubs are reportedly common in some Irrigation diversions not affected by ichthyocide. Downstream populations that may have been destroyed or decimated were furthermore those which had succeeded in surviving in syntopy with red shiners for a number of years, the significance of which is unknown.

2) The flannelmouth sucker, although remaining common in the upper Colorado River basin, has been extirpated from the entire lower Colorado River basin downstream from Lake Mead. The last known populations inhabit the Virgin River basin and the Colorado River in Grand Canyon. However, there is evidence that fish in Grand Canyon are morphologically different from those which occupied that originally reach of the Colorado River. It has been suggested that fish from the Little Colorado River (see below) invaded Grand Canyon after closure of Glen Canyon Dam, hybridizing with the native population and resulting In alteration of their phenotype.

Flannelmouth sucker once occupied the Gila River drainage from the San Pedro River near the U.S.-Mexican line (the type locality) throughout southern Arizona, and the mainstream Colorado River at least to Yuma (and perhaps into Mexico). It, like some other species to be discussed below, further exists as more than one "kind" based on body shape. There are elongate, thin-bodied "forms" in larger streams such as the mainstream Virgin River, and shorter, thicker-bodied "forms" In tributaries (termed an undescribed form, the Little Colorado River sucker [Catostomus sp.], In the tributary of that same name by Minckley, 1973, Fishes of Arizona [AZ Game Fish Dept., Phoenix], which has been accepted by many later workers). Possible destruction of a mainstream population (or even part of that population) of this fish in the Virgin River will therefore be an Important loss to the lower Colorado River basin fauna.

3) The desert sucker population presents similar, unresolved taxonomic problems. Smith (1966, Distribution and evolution of the North American catostomid fishes of the subgenus Pantosteus, genus Catostomus. Misc. Publ. Mus. Zool. Univ. MI 29: 1-132) synonymized Virgin River populations with E. clarki, which was originally considered to be restricted to the Gila River system. Minckley (1973) challenged this action, and summarized his Page 7 observations (and unpublished, earlier observations of Carl L. Hubbs and Robert R. Miller) as follows:

The Virgin River basin (including Meadow Valley Wash in Nevada) is inhabited by two "forms' of Pantosteus. A swift-water kind, with large fins and a thin caudal peduncle, lives in the mainstream, and a thicker-bodied, shorter-finned form is in tributary streams. Intergradation or hybridization of these two kinds is Indicated in the mouth of Beaver Dam Creek, Arizona, but the two kinds also occur together, Infrequently, in the mainstream of the Virgin River near Littlefield, a kilometer or so up- and downstream from that tributary. The populations persisting In remnants of the Pluvial White River, Nevada (a Pleistocene contributor to the Virgin River basin), were formerly known as Pantosteus intermedius Tanner (1942). These are separated from the remainder of the iciarkie complex by a distinct break in a number of characters (Smith 1966), and would best be retained as a distinct taxon until the complexities of the problem are further resolved.

No one has yet carefully analysed this problem, and If mainstream populations have been eradicated from the Virgin River, questions must certainly be raised as to the status of these various kinds and the ecological, management, and scientific results of such losses.

4) Similar arguments and problems occur with speckled dace; tributary versus mainstream populations exist, and loss of the mainstream form might well be a substantial deletion from the fauna; the situation will not be recounted here.

5) Repopulation/recolonization of the Virgin River mainstream by native species, now Involving far more than a -34-km reach, may occur from:

a)in sitg reproduction of survivors of the accidental kill;

b) from above WFD, as anticipated in the original project;

C) from tributary (or Irrigation diversion) populations unaffected by rotenone application; or

d) from any combination of a-c.

Some potential problems developing from these unknowns may Involve populational or genetic changes. such as:

a) Community changes may involve loss of one or more species, or replacement of channel 'forms," with tributary 'forms" that are ill-adjusted to the system. Assuming that native fish communities are tightly integrated, loss of species or alteration of species composition may result in changes in population structure, abundance, or survival potential of either listed or unlisted species, and thus in their recovery Page 8

potential. A 'worst-case scenario' will involve explosive population increases by a non-native species, most likely the targeted red shiner, which would present insurmountable obstacles to repopulation/ recolonization by native species.

b) Channel-inhabiting species surviving the rotenone application may persist in such small numbers that genetic bottlenecking may ensue. That is, remaining individuals of woundfin and other native species alike may be so few in number that they represent a sample of the gene pool substantially different In qualitative or quantitative factors that characterized the original population.

C) So few individuals of channel-inhabiting 'forms' may exist that tributary 'forms' will invade and reproduce to Influence the community and/or genetic makeup of a newly-formed channel-inhabiting fish population.

Recommendations for Post-eradication Actions

The most Important single aspect of post-eradication action will be sampling of the mainstream for evaluation of success, with regards red shiner, and impacts, with regards native species. Such sampling should follow the timing and protocols already in place for woundfin monitoring, in continuing and remphasizing assessment of population structure, reproduction, and changes in time and space of the other native and non-native components of the fauna. On-going monitoring will provide data for definition of answers to potential questions (or problems) arising from Item "5a," immediately above.

With regards opportunities afforded by accidental treatment of the lower Virgin River, downstream from the target area, additional sampling should immediately include the major tributaries, both in their mouths and upstream, so that genetic, morphological, and populational data will be available with which to assess patterns of repopulation/recolonization. This will afford materials to compare with samples secured during treatment of the first (upper 10-km) segment of the target area, allowing development of a baseline for future interpretation of population development. Samples of survivors should be obtained from the reach subjected to accidental treatment in order to assess the genetics of parents of those fishes that presumably will repopulate the reach (from in situ reproduction) during the next spawning season. Sampling for genetic analysis will be of each succeeding year class, for two or more generation-times per native species, to determine the development of genetic features of the population, and compare it with known sources of genetic material (i.g., in situ survivors or tributary dispersants).

Significance of the Proposed Program

Due to the broad ecological data-base already accumulated for the Virgin River, the sequence of events described above provides an unparalleled opportunity to obtain accurate assessments of the ecological and genetic processes which shape fish communities in desert streams. The proposed studies will allow us to address questions of fisheries management Page 9 personnel, as well as those of ecologists and evolutionary biologists. In particular:

1) How heterogenous is the river system? Is there evidence for considerable gene flow among tributary and channel populations, or does each comprise a distinct genetic unit? Morphological evidence suggests that three of the species in the Virgin River exhibit distinct tributary and channel "forms" (Table 1). Are they taxonomic units, or simply variants of a single species? Analyses of allozymic and mitochondrial DNA data will provide estimates of relatedness among tributary and channel populations for each species, answering long-standing questions of the taxonomic, population, and genetic status of tributary versus channel "forms," as well as providing estimation of gene flow among regions. From the manager's viewpoint, can the Virgin River (and similar systems) be dealt with as a single unit, or must it be considered a series of discrete units, each with special problems?

2) If the system is heterogenous, as suggested by the morphological data, will the fishes recover by repopulation (i.g., reproduction by survivors of the accident) or recolonization (i.g., dispersal from tributaries or other refugia into the channel)? If they are to primarily re-established by repopulation, one might hypothesize that selection against tributary "forms" in the channel must be extremely severe, or that dispersal from tributaries to the channel is minimal. On the other hand, if channel populations re-establish by recolonization, the original system may well have been maintained by competitive exclusion. Genetic data gathered from specimens collected prior to the accident, and from tributaries as outlined above, should make it possible to assess these alternatives and determine the relative contributions of particular populations to re-establishment of the fauna.

3) How distinct are populations of woundfin and Virgin River chub in hatchery or refugium stocks from those originally present in the mainstream Virgin River? It Is possible that stocks now at Dexter National Fish Hatchery (woundfin) or surviving In a pond below Quail Creek reservoir (or in irrigation diversions) (chubs) contain far more genetic variability than extant, native populations, especially if those subjected to accidental poisoning were forced to extremely low population levels. Genetic assessment of parental stocks and subsequently-produced hatchery (or otherwise captive) fish will determine the extent of differentiation among broodfish and evaluation of the advisability for restocking as a management tool. Page 10

In summary, key needs are for additional and immediate sampling, not only to evaluate success of the program in removal of the target red shiner, but also to assess impacts of the accidental release of rotenone to the lower Virgin River and to obtain research materials to accompany those already collected during early parts of the eradication program. Detailed documentation of the entire operation will also be required, so that post- eradication events may be placed In accurate perspective.

I urge that a long-term program be put in place to evaluate this accident, so that positive information, useful In further management of this, and other, desert systems, may accrue. The Virgin River eradication program merits full and careful analysis and disclosure, since It may well prove to be a pivotal event In the sorely-needed accumulation of information toward recovery of native fishes there and in other Southwestern streams.

Department of Zoology Arizona State University Tempe, Arizona 85287-1501 25 October 1988