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Recovery goals for the large river endangered fishes of the Colorado River Basin were finalized this summer and the notice of their availability will be posted shortly in the Federal Register. Flow recommendations are being developed for the two tributaries to the Green River, the White and Duchesne Rivers. Negotiations between the Fish and Wildlife Service and the Upper Basin Recovery Program continue on the Gunnison River flow recommendations. The Bureau of Reclamation will have a draft Environmental Impact Statement regarding the reoperation of Flaming Gorge Dam in September. The reoperation is based on Green River flow recommendations provided by the Upper Basin Recovery Implementation Program. Population estimates of Colorado Pikeminnow in the Green River have been obtained for the entire Green River system for two complete years. The initial estimate was encouraging, estimates for the second year have not been calculated at this time. In addition, population estimates for three consecutive years were also completed for humpback chub Gila cypha in Black Rocks, Westwater and Yampa canyons. The Upper Basin experienced a severe drought in 2002, and nonnatives, particularly smallmouth bass Micropterus dolomieu numbers seem to be increasing in the Yampa River. Northern pike Esox lucius removal efforts are continuing in the Green and Yampa Rivers. Fewer numbers of northern pike were observed in the Green River, while no difference was observed in the Yampa River. Some encouraging experimental results were observed in applying the ‘reset’ approach to management of off-channel wetlands to enhance survival of larval and juvenile razorback sucker and bonytail G. elegans. Experimental pens were stocked with nonnative densities consistent with expected numbers following initial connection of the river. Larval razorback sucker and bonytail were stocked with nonnatives and survival was encouraging.

Harvest of hatchery-produced razorback sucker from grow-out ponds in Grand Junction has begun. About 3,000 fish (300 + mm TL) have been stocked to date in the Upper Colorado River. An additional 7,000 fish will be harvested and stocked this fall. Stocking plans call for three stocking sites — Colorado River near Rulison, Gunnison River near Delta, and Colorado River near Grand Junction. Because the first two sites are upstream from large diversion canals taking most of the river flow, all fish have been stocked near Grand Junction to prevent their entrainment in the canals. Larval razorback sucker were collected this spring and are believed to be offspring of stocked fish.

In the San Juan River, augmentation of Colorado pikeminnow and razorback sucker is continuing and results to date are very encouraging. The San Juan River Recovery Implementation Program continues to make significant progress towards recovery.known only from Whitmore Pond remains abundant but has a high infection rate of both the monogenean Gyrodactylus sp and trematode Clinostomum sp.

In April 2002, NatureServe, the umbrella organization for Natural Heritage Programs, published "States of the Union: Ranking America's Biodiversity". This document ranked all 50 states in terms of species diversity, risk, endemism, and extinctions. Nevada ranked third highest in percentage of species at risk, with the fourth highest percentage of fishes and third highest percentage of amphibians at risk in the U.S.

Ash Meadows

Restoration efforts continued at Point of Rocks Springs system. The spring outflows were restored in 2001 to enhance habitats for the Ash Meadows naucorid (Ambrysus amargosus) and Ash Meadows Amargosa pupfish (Cyprinodon nevadensis mionectes). Re-vegetation efforts continued during 2002. Introduction of Ash Meadows speckled dace into the lower stream will occur once instream habitat enhancement is completed. No green sunfish have been observed in recently treated waters, although they are still present in Crystal Reservoir. With refuge personnel vacancies, NDOW will be providing cooperative assistance to insure that monitoring for Ash Meadows pupfish and other key species continues on schedule.

Devils Hole pupfish

Devils Hole pupfish (Cyprinodon diabolis) summer counts at Devil’s Hole have been declining since 1996; the summer 2002 counts through October are extremely low compared to the historical record, although the winter counts show some stability in 2000-2002. It is uncertain if the population in Devils Hole may show some stability at a lower than previous level. The Death Valley National Park has hosted a workshop to discuss future management actions. Three separate refugia, Point of Rocks, School Springs, and Hoover Dam, contain populations of 103 (stable), 19 (decrease), and 80 (increase) Devils Hole pupfish, respectively.

Muddy River

Blue tilapia (Oreochromis aurea) in the Muddy River system continue to have a negative effect on native fishes. All chemical treatments of tributaries in the headwaters have been successful in tilapia eradication. Moapa dace (Moapa coriacea) numbers have responded accordingly, with 1085 dace counted in intra-agency dive counts completed in February 2002, 150 more than in 2001 surveys.

The first phase of spring and stream restoration at the Pederson Unit of the Moapa Valley NWR was completed in April 2002. Native fish populations have responded positively. Future plans include implementing a re-vegetation plan and continuing stream restoration throughout the entire Refuge.

Virgin River chub numbers in the middle Muddy River continue to decline based on 2002 survey efforts to date. A Memorandum of Understanding is being developed between Nevada Power Company, NDOW, and the U.S. Fish and Wildlife Service to establish a refugium for Virgin River chub (Gila seminuda) utilizing the raw water ponds at Reid Gardner Power plant next to the Muddy River at Moapa.

Pahranagat Valley

November 2001 Paharanagat River snorkel surveys detected 14 Pahranagat roundtail chub (Gila robusta jordani), indicating a severe decline in the population. Since this census, the landowner has denied access to the property for additional surveys. NDOW is drafting a safe harbor agreement for the entire Valley, which could be used to manage habitat for listed species on private land. Dexter National Fish Hatchery and Technology Center maintains a refugium population of approximately 100 individuals. Additional refugia for the chub are being developed at Pahranagat National Wildlife Refuge and Key Pittman WMA, which would be stocked with fish from Dexter NFH&TC as well as wild fish if found.

Hiko Spring was surveyed in June 2002. The population estimate for Hiko River springfish is down from 6277, in 2000, to 1291; exotic species increased to 64% of the total species composition compared to 44% in 2000.

The refuge population of Hiko WR springfish at Blue Link Spring was surveyed in August 2002. The population was estimated to be 6991.

Crystal Spring springfish numbers have been high for two years in a row; the proposed development at Ash Spring has not occurred and habitat and numbers of springfish have maintained some stability, but the future of the private land part of the outflow is uncertain.

Pahrump poolfish

The Shoshone Ponds and Spring Mountain Ranch State Park refugia populations of Pahrump poolfish (Empetrichthys latos) are self-sustaining, containing in excess of 50,000 individuals. A new refugium at Corn Creek Springs on the Desert National Wildlife Range will be completed in fall of 2002, and will replace the population previously lost at this site due to the infestation of predatory non-native species.

White River Valley–

White River spinedace estimates declined from 1600 in 1999 to 538 in fall 2000 but increased to 914 in March 2002 and 1264 by September 2002 following implementation of cormorant control efforts. Speckled dace and desert suckers also became more abundant throughout the surveyed reaches. Cormorant activity in the area will continue to be monitored.

A rehabilitation project, initiated by the USFWS as a Partners for Fish and Wildlife project at Indian Spring in Preston, is being completed in October 2002 primarily to benefit White River springfish.

A new pipeline to provide water for livestock on adjacent federal lands from South Flag Spring will be constructed in fall 2002. Water will no longer be transported via an old ditch, leaving more water in the main channel for spinedace.

Railroad Valley

Monitoring of Railroad Valley springfish was completed in July 2002 at Hay Corral, Big, North, Reynolds and Chimney Springs All numbers were consistent with previous years with the exception of Hay Corral. Habitat at Hay Corral was significantly disturbed in 2001, which may have affected fish numbers and distribution. Springfish were seen in the outflow ditch and pond, but were not common; a combination of factors may be present, although no other habitat changes and/or threats were observed. The landowner at Lockes Ranch, which contains all or part of three key RRV springfish habitats, is willing to sell the property for conservation purposes but has not been able to agree on a price with BLM.

Once again, the Duckwater populations of Railroad Valley springfish were not sampled, due to a lack of permission from the tribe. However, recent negotiations have taken place and a more positive relationship is expected soon.

Big Springs spinedace densities were higher in 2002 than in 2001. Between 280 and 4000 spinedace per kilometer were estimated in August 2002. In August 2001, between 280 and 1920 spinedace per kilometer were estimated. Rainbow trout continue to be found in a few locations in Condor Canyon in very low numbers, but do not appear to represent a significant threat.

Spinedace were only detected in 3 transects in 2002 compared to 4 in 2001, but flows have been reduced because of drought conditions.

Meadow Valley Wash

The lower reaches of Meadow Valley Wash were surveyed in March 2002 to determine baseline distribution of native fish in this system in response to projected development in this area. Surveys indicated that distribution of the native fish species was similar to previous monitoring. Meadow Valley speckled dace (Rhinichthys osculus spp.) were found near Hoya/Leith, and Meadow Valley desert sucker (Catostomus clarki ssp.) were found only in the vicinity of Elgin. Several specimens of southwestern toads (Bufo microscaphus microscaphus) were collected from this reach and positively identified by biologists at the University of Nevada, Las Vegas.

Razorback sucker

In April 2002, 35 Lake Mead larval sucker (Xyrauchen texanus) were successfully taken from Echo Bay and reared at the Lake Mead Hatchery. Similar numbers of the 1999 and 2001 cohort are being held for future release into Lake Mead. In 2002, 5,000 Lake Mohave sucker were reared at this facility, destined for Beal Lake/Imperial ponds. Larval razorback sucker from Lake Mohave were reared at the Boulder City Golf Course and Veterans Park ponds in cooperation with the Bureau of Reclamation.

Amargosa toad

This year 666 more toads were tagged, for a total of 3461 over the past five years at 15 survey sites. Given ongoing drought conditions, toad populations in Oasis Valley are maintaining and doing fairly well. Annual monitoring surveys will be continued in the future on a more limited basis. A species management plan is being developed utilizing long-term monitoring data.

Other Species

A conservation agreement for management of the Toiyabe population of spotted frog in Nye County should be completed by the end of 2002.

Efforts to re-establish Virgin spinedace in upper Beaver Dam Wash, below Schroeder Reservoir in Nevada, have not been particularly successful. The strategy and future options are being assessed.

NDOW has received grant funding to develop private land CCAA agreements for tui chub in central Nevada and springfish in upper White River Valley. A new biologist position in Tonopah to be filled this fall will have responsibility for this project along with bird projects.
 

Recovery goals for the large river endangered fishes of the Colorado River Basin were finalized this summer and the notice of their availability will be posted shortly in the Federal Register. Flow recommendations are being developed for the two tributaries to the Green River, the White and Duchesne Rivers. Negotiations between the Fish and Wildlife Service and the Upper Basin Recovery Program continue on the Gunnison River flow recommendations. The Bureau of Reclamation will have a draft Environmental Impact Statement regarding the reoperation of Flaming Gorge Dam in September. The reoperation is based on Green River flow recommendations provided by the Upper Basin Recovery Implementation Program. Population estimates of Colorado Pikeminnow in the Green River have been obtained for the entire Green River system for two complete years. The initial estimate was encouraging, estimates for the second year have not been calculated at this time. In addition, population estimates for three consecutive years were also completed for humpback chub Gila cypha in Black Rocks, Westwater and Yampa canyons. The Upper Basin experienced a severe drought in 2002, and nonnatives, particularly smallmouth bass Micropterus dolomieu numbers seem to be increasing in the Yampa River. Northern pike Esox lucius removal efforts are continuing in the Green and Yampa Rivers. Fewer numbers of northern pike were observed in the Green River, while no difference was observed in the Yampa River. Some encouraging experimental results were observed in applying the ‘reset’ approach to management of off-channel wetlands to enhance survival of larval and juvenile razorback sucker and bonytail G. elegans. Experimental pens were stocked with nonnative densities consistent with expected numbers following initial connection of the river. Larval razorback sucker and bonytail were stocked with nonnatives and survival was encouraging.

Harvest of hatchery-produced razorback sucker from grow-out ponds in Grand Junction has begun. About 3,000 fish (300 + mm TL) have been stocked to date in the Upper Colorado River. An additional 7,000 fish will be harvested and stocked this fall. Stocking plans call for three stocking sites — Colorado River near Rulison, Gunnison River near Delta, and Colorado River near Grand Junction. Because the first two sites are upstream from large diversion canals taking most of the river flow, all fish have been stocked near Grand Junction to prevent their entrainment in the canals. Larval razorback sucker were collected this spring and are believed to be offspring of stocked fish.

In the San Juan River, augmentation of Colorado pikeminnow and razorback sucker is continuing and results to date are very encouraging. The San Juan River Recovery Implementation Program continues to make significant progress towards recovery.known only from Whitmore Pond remains abundant but has a high infection rate of both the monogenean Gyrodactylus sp and trematode Clinostomum sp.

In the Virgin River basin, a five-year effort to repatriate Virgin spinedace Lepidomeda mollispinis mollispinis in upper Beaver Dam Wash in Nevada does not appear to have been successful and additional repatriation alternatives are being considered.

In the Virgin River, spring and fall sampling by the Virgin River Recovery Team at three sites in Nevada produced no woundfin Plagopterus argentissimus and only a single Virgin River chub Gila seminuda, at the Bunkerville Diversion in fall. Mask and snorkel surveys were completed along several mainstem Virgin River segments in Arizona and Nevada to provide baseline inventories for chub. In Arizona, the July survey counted 33 adults and 147 juvenile chub. In Nevada no chub were recorded during the August survey. Most striking was the high number of large channel catfish Ictalurus punctatus found throughout the mainstem river. In all 2002 surveys, Tilapia Tilapia sp.. the most recent nonnative to invade, was not found along any of the reaches until September 25 when small numbers were found at Halfway Wash. Upstream, red shiner Cyprinella lutrensis was found above Washington Fields Diversion in the only area of the river previously free of this species. They are thought to have come from a bait pond. Efforts to propagate woundfin at Utah’s Wahweap Hatchery have met with setbacks, but stocks still are held at Dexter National Fish Hatchery.

In the Little Colorado River basin, drought conditions forced salvage operations for Little Colorado spinedace Lepidomeda vittata in Yeager, Leonard, and West Leonard Canyons in the East Clear Creek drainage. Less than 46 spinedace (8 from Yeager, 38 from Dines Tank in Leonard Canyon) were placed into the refugia pond at the Flagstaff Arboretum. From West Leonard Canyon, 363 spinedace were captured, of which 200 were placed at the Arboretum and 57 were stocked into Dane Canyon in the East Clear Creek watershed.

No reports were received regarding the Bill Williams River basin. No reports were received regarding the upper Gila River basin in New Mexico.

Within the Gila River basin work has been conducted for a variety of species.

It was a big year for Gila chub Gila intermedia. The species was proposed for listing as endangered with critical habitat on August 9, 2002. O’Donnell Creek, a tributary of the Babocomari River in southern Arizona was successfully renovated with antimycin in June 2002 to remove green sunfish Lepomis cyanellus. Gila chub and desert sucker Pantosteus clarki were restocked in August. Sabino Canyon, a Gila chub habitat was successfully renovated for green sunfish in 1999, reached critically low water levels in lower canyon pools in July 2002. Gila chub were salvaged and held at the Forest Service Ranger Station. A September 2002 survey of Turkey Creek, in the Babocomari River basin failed to find Gila chub, which have not been seen there since 1991, but other surveys confirmed continued existence of Gila chub at Williamson Valley Wash in the upper Verde basin and found new locations in two Verde mid-basin tributaries.

A status report for roundtail chub Gila robusta and headwater chub Gila nigra was completed and a final report issued in January 2002. That report finds that there are significant declines in both species and substantial threats to most of their habitat.

For spikedace Meda fulgida and loach minnow Tiaroga cobitis, a survey of Verde River tributaries specifically looking for loach minnow failed to find any remnant populations. Construction plans, site investigations, and planning documents are under way for a fish barrier on the lower Blue River in eastern Arizona. Construction is scheduled to begin in September 2003. The Blue River, which has been identified by the Forest Service for native fish restoration, supports loach minnow and several other native fishes and frogs, is critical habitat for spikedace, and historic habitat for Gila chub.

The recent appearance of Asian tapeworm Bothriocephalus acheilognathi in the Verde River has been documented during research that is ongoing on native and nonnative species interactions.

For longfin dace Agosia chrysogaster a repatriation stocking was conducted in Martinez Canyon, a tributary of the middle Gila River near Florence. An ongoing crayfish removal project is also taking place in Martinez Canyon by a couple of dedicated volunteers.

Stocking of razorback sucker Xyrauchen texanus into the Verde River continues. No successful recruitment has yet been documented from this 15-year program.

A new population of desert pupfish Cyprindon maculariuswas initiated in Lousy Canyon, a tributary of the Agua Fria River. That stocking occurred in October 2001 and appears to have been succesful.

The first sighting of Gila topminnow Poeciliopsis occidentalis since 1994 in Sonoita Creek above Patagonia Lake occurred in July 2002. At Sharp Spring on the upper Santa Cruz River, fall surveys found Gila topminnow to still persist, although only 1 topminnow was found to 397 mosquitofish Gambusia affinis. In the Redrock Canyon drainage near Patagonia, an additional exclosure to livestock grazing was built to restore Gila topminnow habitat in Oak Grove Canyon. Original exclosure plans included habitat below and above a barrier, with repopulation to occur naturally below the barrier from movement from the main canyon. Above the barrier, repopulation would require stocking. The exclosure as-built does not include any below-barrier habitat, thus substantially reducing recovery value. The Forest Service has declined to rebuild the exclosure.

For Apache trout Oncorhynchus apache a renovation project to remove nonnative trouts was conducted in October 2002 on Snake Creek on the Apache-Sitgreaves National Forest.

In the Rio Sonoyta basin, verbal reports indicate the Rio Sonoyta had very little water this summer. Apparently staff of the Pinacate Biosphere Preserve conducted a salvage operation for the Quitobaquito pupfish Cyprinodon eremus to hold pending better water conditions.

At Quitobaquito Springs, the fall survey of Quitobaquito pupfish showed that population to be doing well. In this year’s survey 2,100 individuals were sampled. The mean of this 10-year effort is 2,280 individuals. Water level is down at the pond, but not enough to cause concern. Of more concern is the increasingly heavy traffic of illegal immigration at Quitobaquito, where even the border fence walk-through has been crushed by vehicle traffic.

In the lower Colorado River itself, a number of efforts are ongoing.

Efforts to rear bonytail chub at Niland Fish Hatchery have been temporarily suspended due to lack of success and severe infestation of the nonnative parasitic anchor worm Lernea cyprinacea. Efforts are concentrated at Achii Hanyo Hatchery near Parker. Achii Hanyo success rates have been good and parasite problems have been negligible. As of August 13, 2002, 7,728 bonytail chub have been augmented into Lake Havasu. Ongoing stocking efforts have also placed 30,000 razorack sucker into Lake Havasu.

Giant salvinia Salvinia molesta continues to be present in the lower Colorado River and irrigation canals downstream of Blythe. Efforts to eradicate it have been limited.

Beal Lake along the lower Colorado, was treated with rotenone in December 2001 to remove a variety of nonnative fish. It was restocked with 10,000 razorback sucker in April 2002. Mosquitofish Gambusia affinis were recently discovered to have either survived the treatment or reinvaded from nearby waters. Another 40 acres, at the Imperial Duck Ponds, was renovated in October 2002. Restocking of razorbacks has not yet occurred, but 5,000 are planned.

Recent population census on Lake Mohave estimate a razorback sucker population of 3,000 to 4,000 fish. That is compared to the 6-figure estimates of 20-30 years ago.

Research continues in the Imperial Division of the lower Colorado on habitat selection and overlap between razorback sucker and flathead catfish. Razorback sucker have been found to use off-channel backwaters newly reconnected as part of restoration activities. Flathead catfish Pylodictus olivarus, on the other hand, have been found to inhabit main and side-channel habitats and rarely co-occur with razorback sucker. Collection of razorback larvae in Senator Wash has begun with a purpose of quantifying reproduction, determining if it has led to recruitment, and how predation affects that particular area.

Gizzard shad Dorosoma cepediianum have now been confirmed as an established population in Lake Powell. This nonnative species was introduced as a contaminant in a shipment of sport fish from Inks Dam National Fish Hatchery to an upstream site on the Navajo Indian Reservation.

The USGS Branch of Biological Survey Fish Control Lab in LaCrosse, Wisconsin has undertaken a major study, through Central Arizona Project mitigation funding, to research and develop innovative techniques and integrated management for nonnative fish control in the Gila basin.

As previously discussed for 2000-2001, the declining status and distribution of the Rio Grande silvery minnow continued in 2002, with all-time low estimates of density recorded. Diminishing flow caused by water management activities and exacerbated by dry climatic conditions remained the primary threat to persistence of the species. Monitoring efforts continued to illustrate uneven distributional patterns, with Rio Grande silvery minnow occurring primarily downstream of the Albuquerque area, a reach that suffers frequent flow intermittency. Short-term measures that have been implemented to stave off extinction of the species include captive propagation and rescue/salvage/transplant from drying downstream reaches to upstream reaches of continuous flow, but poor habitat quality. Recent genetics work indicated that captive propagation stocks had lower genetic diversity and fewer alleles at all loci studied than those individuals sampled from the wild. Because of chronic mortality and lower genetic diversity of propagated fish and lack of demonstrable survival of salvaged individuals, questions remain regarding the efficacy of these measures.

In the New Mexico portion of the Pecos River Basin, a research report detailing flow/habitat relationships and habitat use patterns of resident fishes continued to drive interagency deliberations. The revised report continued to identify similar base flow requirements for providing the array of depths and velocities utilized by Pecos bluntnose shiner. While avoiding channel intermittency through manipulation of reservoir releases 1992-2000, such was not the case in 2001-2002. Monitoring of fish community structure in 2002 suggested a significant decline from 2001 results in density for Pecos bluntnose shiner at monitoring sites . Unlike the Rio Grande silvery minnow, Pecos bluntnose shiner primarily occur within the upper portion of the occupied reach and, coupled with more natural stream channel conditions, may be able to better withstand anthropogenic modification of habitat and thus far deficient species conservation measures.

Rio Grande cutthroat trout were the subject of a candidate status review under the Endangered Species Act of 1973, as amended. It was determined that, after review of all relevant information, listing of the species was not warranted. Eighteen streams in Colorado and New Mexico were considered to harbor genetically pure, stable, and secure populations of Rio Grande cutthroat trout. Stability and security of populations was related to large population size (generally > 2500 individuals), sufficient stream length (generally > 8 km), absence of non-native species, and stable habitat conditions. With updated population survey data and genetic analyses, the number of stable and secure populations could rise by five. Field conservation activities for Rio Grande cutthroat trout continued to center around antimycin application to stream segments above barriers to remove non-native salmonids and introduction of hatchery-reared fish. Public opposition to use of antimycin, a piscicide, through attempted implementation of regulatory functions of the New Mexico Surface Water Quality Control Bureau were unsuccessful in halting proposed renovation projects. Current emphasis by management agencies is on development of a range-wide conservation plan for Rio Grande cutthroat trout.

Conservation of native fishes in the upper/middle Rio Grande Basin of New Mexico and southern Colorado faces continually growing challenge. It is becoming more commonplace, in spite of the call for ‘good science’, to avoid and minimize objective data that support change to resource use patterns. While native species biologists have been consumed by the aspect of using intelligence to further resource protection, the conviction of those same biologists remains largely invisible. The lack of recognition by proponents of resource extraction that human life needs are also at risk continues to relegate native species management to the back of the bus.

During the study, two significant flood events impacted the San Marcos River and three affected the Comal River; these events resulted in significant short-term reductions in vegetation coverage and density. In both rivers, the vegetation types that provide the greatest habitat for fountain darters were generally the most significantly impacted; however, the impact to fountain darters differed between rivers. In the San Marcos River, estimates of fountain darter abundance decreased in the two reaches after each event. In the Comal system, estimates of fountain darter abundance did not differ dramatically before and after flooding in most instances. This suggests that fountain darters in the Comal River may have a greater “buffering” capacity to flooding effects than populations in the San Marcos River. One significant factor is the substantial area in the impounded headwaters of the Comal River (Landa Lake) compared to the remaining portion of the range in that system. Fountain darters are numerous in this habitat and it was virtually unimpacted from intense flooding. There is a similar protected pool in the headwaters of the San Marcos River (Spring Lake) which was not sampled using the same methods, but which visually appeared unimpacted following flooding. Snorkeling has shown that fountain darter densities are extremely high in Spring Lake, however, the lake constitutes a much smaller portion of the fountain darter range in the San Marcos River than Landa Lake in the Comal River. Recovery of vegetation following each flood event was rapid and suggests that flushing flows followed by a recovery period does not effectively reduce fountain darter habitat, and may stimulate growth and increase overall habitat availability.

Norogachi se localiza en la Sierra Madre Occidental, por su posicion geografica contiene elementos nearticos y neotropicales, que se conjugan con una topografia muy accidentada que va desde la zona desertica hasta el bosque de pino-encino, con elevaciones entre 200 y 3,000 msnm. Estos factores dan como resultado una diversidad biológica con características unicas, especialmente en los dos principales sistemas hidricos de la region: el rio Fuerte y el rio Conchos. Paradojicamente, esta es una de las regiones menos estudiadas del pais desde el punto de vista biologico, no obstante que la dinamica economica del area ha causado altos niveles de deterioro ambiental, al igual que el cambio climatico caracterizado por largas sequias. Con el proposito de hacer un reconocimiento de la diversidad de la ictiofauna, dentro de esta region prioritaria terrestre y dulceacuicola, se desarrolla un inventario por medio de un proyecto con la CONABIO, en el cual se han realizado recolectas y se trabaja en la revision critica de las bases de datos de las colecciones, donde se ha depositado material ictico de la region. Hasta el momento se tienen como resultados, la presencia de 14 familias, 28 géneros y 46 especies. Destacan por su abundancia las familias Cyprinidae con 15 especies, Poeciliidae con ocho e Ictaluridae con cinco. Ademas de los impactos reconocidos en la zona, se ha identificado la presencia de cinco especies introducidas.

Research activities for the 2001-2002 study year were conducted as lake elevation was declining to levels not encountered since the late 1970's. Reservoir elevations decreased 20 feet during the 2001-2002 study year, 31 feet since the beginning of the study in October 1996, and 55 feet since the highest elevation was reached during the study in October 1998. Numbers of larval razorback sucker captured at the Echo Bay and Las Vegas Bay study areas were similar to previous years; however, razorback sucker at Echo Bay utilized a new spawning area because of decreased lake levels. Spawning at Las Vegas Bay probably occurred at a location similar to previous years because of the increased depths at this location. No razorback sucker larvae were collected during spring sampling at the Colorado River inflow area.

Four sonic tagged, impoundment reared, razorback sucker were released at the Colorado River inflow area with the anticipation that these fish would lead us to wild spawning razorback sucker in the area. After nearly two months of tracking these tagged razorback sucker, they apparently left the area and were not relocated either up-river in the lower 40 miles of the Grand Canyon or down-lake in Gregg or Virgin Basin. The migration of these fish out of the Colorado River inflow area, combined with the fact that no razorback sucker larvae were found in the area this year, suggests that decreasing lake levels negatively affected spawning in this area and may have caused wild razorback sucker to move out of this vicinity.

An additional eighteen razorback sucker were aged during the 2001-2002 study year. These fish had ages ranging from six years, for a juvenile razorback sucker, to 35+ years for the oldest razorback sucker that we have aged during the study. Comparing the years spawned for all aged razorback sucker to historical Lake Mead water elevations provides some evidence that a combination of small annual lake level fluctuations, and larger multi-year changes in lake elevation may influence razorback sucker recruitment. The long tern lake level changes may promote the growth of litoral vegetation which could provide increased habitat for larval and juvenile razorback sucker, resulting in the limited recruitment documented in Lake Mead.

The distribution and recapture rate of approximately 2,000 subadult/adult razorback sucker (>250 mm) stocked directly into the river between 1997 and 2001 were compared with fish that were stocked as age-1 fingerlings (~ 100 mm) in a natural wetland in the spring of 1999 and accessed the Green River the following spring (approximately 1,100 fish in excess of 300 mm). The entire reach of the Green River between Split Mountain Canyon (rkm 352) and the confluence with the Colorado River was sampled with electrofishing boats during the spring of 2001. Three complete passes were made. Despite the fewer fish accessing the river from the floodplain, nearly three times (74) as many acclimated fish (i.e., floodplain stocked fish) were recaptured than those stocked into the river directly from the hatchery (29). Despite the differences in apparent capture rates the distribution of fish downstream from the stocking area was approximately equal between the two groups. As expected, the majority of post-stocking movement occurred downstream of the stocking site.

Larval razorback sucker were stocked into two 0.1 hectare pens with adult nonnative fishes. The numbers of nonnative fishes were similar to those observed during the first year of inundation following complete drying of the wetland. Each pen was stocked with a different density of larvae (~60,000 = low density, and 450,000 = high density). Larvae and nonnative adult fishes were stocked May and harvested in August. Zooplankton and water chemistry were monitored through out the study period. Following harvesting, 359 and 1,709 age-0 razorback sucker were harvested averaging 70mm and 58mm, respectively from the high and low density ponds. In addition to razorback sucker survival, large numbers of age-0 nonnative fishes were present in the study pens. Although survival was low, the potential for razorback sucker in offchannel wetlands following drought conditions offers management options that may improve natural recruitment.

A proposal to remove trout populations from the Sixth and Seventh lake complex to benefit native fauna was incorporated into a California Department of Fish and Game resurce management plan for the Big Pine Creek Basin and was accomplished using only intensive gill netting and electrofishing techniques. Approximately 10,000 trout were removed from 1999 through 2001. During this time amphibian numbers increased dramatically, and successful Rana muscosa reproduction was documented in both Sixth and Seventh lakes in 2002.

All three reaches represented distinct fish communities with different factors most likely affecting each reach. The San Acacia Reach fish community was most distinct, with highest Rio Grande silvery minnow densities. Red shiner, Cyprinella lutrensis, was also abundant in this reach, accounting for 23.7% of fish collected. Isleta Reach had the highest fish community stability with a majority of individuals represented by non-fluvial species red shiner, western mosquitofish, Gambusia affinis, and fathead minnow, Pimephales promelas. Angostura Reach had low fish community and flow regime stability and was dominated by white sucker, Catostomus commersoni. Non-fluvial species thrived in all three reaches while fluvial species such as Rio Grande silvery minnow, flathead chub, Platygobio gracilis, and longnose dace, Rhinichthys cataractae, declined.