Southwest Biological Science Center
Fish and Wildlife
Just below Glen Canyon Dam on the Colorado River is a very popular Blue Ribbon trout fishery known for its rainbow trout. However, approximately 78 miles downstream, near were the Little Colorado River flows into the Colorado River, is a population of endangered humpback chub. The introduced rainbow trout can negatively affect native humpback chub by competing with them for food (immature black flies and midges) and by preying on humpback chub. Therefore, it is important to understand rainbow trout movement and the abundance of these trout in the stretch of river directly below Glen Canyon Dam and the Little Colorado River. That information can help with maintaining the trout fishery while protecting humpback chub.
Renewable energy development is expanding in southwestern deserts, including in Arizona. Energy developers look to resource management agencies to provide siting guidance on public lands where there might be conflicts with wildlife. Often, agency guidance considers species of conservation concern and economic importance, but information on comprehensive vertebrate biodiversity has been hard to incorporate. In this project, USGS researchers illustrate how biodiversity richness metrics for most vertebrate wildlife that can use an area and for sensitive guilds of wildlife such as bats, raptors, and migratory land birds can be incorporated into renewable energy siting decisions.
Aquatic invertebrates are critical food for fish and other species that inhabit large rivers. In the Colorado River Basin, invertebrates that get transported down the river (“in the drift”) are particularly important to rainbow trout and other species of interest to recreational users. This research seeks to compare rivers downstream of large dams throughout the Colorado River Basin in order to understand how dam operations and the local environment may be affecting differences in drift concentrations, and thus higher levels of the food chain as well.
Algae, phytoplankton, and rooted macrophytes represent the base of many aquatic food webs and are known as primary producers. Through photosynthesis, these organisms convert sunlight energy into chemical energy (i.e., carbon) that in turn fuels the growth of animals such as macroinvertebrates and fish. This project uses high frequency measurements of dissolved oxygen, which is a by-product of photosynthesis, to estimate rates of primary production at six locations in the Colorado River downstream of Glen Canyon Dam. Quantifying time series of primary production is used to identify the environmental factors that control primary production. Additionally, trends in primary production may be a leading indicator of changes in fish populations and the ecosystem as a whole.
Construction of Glen Canyon Dam has led to large changes in environmental conditions of the downriver Colorado River. Whereas the pre-dam Colorado River experienced large seasonal variation in temperature and discharge and was highly turbid, the post-dam Colorado River is far less variable in terms of temperature and discharge and is frequently clear. Many nonnative fish species had already been introduced to the Colorado River or its tributary prior to dam completion, and some thrive in this altered environment. The federally endangered humpback chub is a native fish of the Colorado River that evolved in the pre-dam environment over millions of years and has been able to persist for a half-century in the post-dam environment, alongside introduced non-native species including rainbow trout. The goal of this project is to monitor all life stages of humpback chub (juvenile, subadult, and adult), estimate survival, growth, movement and abundances for various life stages and develop population models to predict responses to potential management strategies focused on either controlling non-native invasive species or restoring aspects of the physical environment.
Rainbow trout is a desirable sport fish that has been introduced in many locations around the world. Although introductions of rainbow trout and other nonnative fishes provide recreational fishing opportunities, they also pose threats to native fish populations. The Glen Canyon Dam Adaptive Management Program has tasked scientists and managers with identifying management options that allow rainbow trout to thrive from Glen Canyon Dam downstream to Lees Ferry, while minimizing impacts to downstream populations of native fish, especially the endangered humpback chub. This project aims to identify factors that drive rainbow trout growth through a combination of approaches. A synthesis of tailwaters (river segments just downstream of dams) across the Western US has elucidated larger scale patterns, relating river flows to the size of adult rainbow trout. Ultimately, this project aims to guide adaptive management of rainbow trout, balancing recreational interests within the tailwater with downstream native fish conservation.
Introduced rainbow trout and brown trout are considered a threat to the endangered humpback chub in the Colorado River in Grand Canyon. These introduced species eat native fish, but impacts are difficult to assess because predation vulnerability depends on the physical conditions under which predation takes place. We studied how predation vulnerability of juvenile humpback chub changes in response to turbidity. We exposed hatchery-reared juvenile humpback chub and bonytail (a surrogate for humpback chub) to adult rainbow and brown trout at turbidities ranging from 0 (clear water) to 1,000 formazin nephlometric units (FNU). Turbidity as low as 25 FNU reduced predation of bonytail to rainbow trout and led to a 36% increase in survival compared to trials conducted in clear water. Predation vulnerability of bonytail to brown trout at 25 FNU also decreased with increasing turbidity and resulted in a 25% increase in survival. This research suggests that relatively small changes in turbidity may be sufficient to alter predation dynamics of trout on humpback chub in the Colorado River, and that turbidity manipulation may warrant further investigation as a fisheries management tool.
Although it is not listed on the Federal Endangered Species list, there is considerable concern over northern leopard frog declines in western North America. It is listed as a “special concern” species by some state wildlife agencies (e.g., Arizona Game and Fish Department 1996) and declines have been reported in Arizona, Colorado, New Mexico, and other areas across the west. Leopard frogs have become very rare in the northern Arizona and southern Utah region, but their current status is poorly known. A major aim of this work is to determine the present distribution, population status, and habitat occurrence of the northern leopard frog in Glen Canyon, Grand Canyon, and surrounding areas. Careful surveys of the distribution and numbers of leopard frogs in the region provide important information on long-term population trends, and the effects of population fragmentation and isolation on leopard frog populations in the southwestern part of their range.
The Island Night Lizard was removed from the Federal list of "Threatened" species in May 2014. This rare and unique species represents an ancient lineage whose members are now sparsely distributed across parts of the Southwest North America, south through Mexico to the New World Tropics. The Island Night Lizard has a very small world range, occurring only on three of the southern California Channel Islands—San Clemente, San Nicolas, and Santa Barbara. Suitable habitat for island night lizards is extensive on San Clemente Island, and the species is quite abundant there. However, habitat is much more limited and fragmented on San Nicolas Island and small Santa Barbara Island. The U.S. Fish and Wildlife Service requires a post-delisting program for "monitoring the overall health of the island night lizard..." to assure the continued long-term viability of the species in its restricted distribution. This project fulfills that requirement for the Night Lizard on San Nicolas Island. The information on population size and habitat presented here will help inform and guide conservation and management efforts by the U.S. Navy on San Nicolas Island over the coming years.
Economic research at Grand Canyon Monitoring and Research Center is used to determine economic benefits of outdoor recreation in Glen Canyon National Recreation Area below Glen Canyon Dam and in Grand Canyon National Park, as affected by operation of Glen Canyon Dam. This research identifies recreationists’ preferences for attributes associated with their trips, spending that occurs regionally, and the net economic benefit to recreationists. To accomplish this research objective, surveys of recreationists are used to collect information. This material is necessary for the Glen Canyon Dam Adaptive Management Program, federal, and state decision-makers to make informed choices about the economic tradeoffs that occur, with regard to recreation, when evaluating resource management actions in Glen Canyon National Recreation Area and Grand Canyon National Park.
Managing a species with intensive tools like reintroduction may focus on single sites or entire landscapes. For mobile species like the federally-threatened Chiricahua leopard frog (Lithobates chiricahuensis [CLF]), both suitable colonization sites and suitable dispersal corridors between sites are needed. Following the eradication of the invasive American bullfrog (Lithobates catesbeianus) from most of Buenos Aires National Wildlife Refuge in AZ, captive CLF tadpoles were reintroduced into three stocks ponds on the refuge. Populations became established at all three reintroduction sites, followed by colonization of neighboring ponds in subsequent years. Based on this initial post-reintroduction colonization of neighboring ponds, we developed a habitat connectivity model to identify potential dispersal corridors. Next, using data on pond occupancy between 2007 and 2016, habitat characteristics, and pond isolation, we modeled predicted colonization of ponds through the valley as well as the long-term extinction risk for the metapopulation. Collectively, these efforts should provide insight into the security of CLF in the refuge and help inform other reintroduction efforts.
All aquatic invertebrates drift downstream at some point in their life cycle. Invertebrates may drift to find more preferable habitats, to leave the water during their transition from aquatic larvae to terrestrial adults, or accidentally such as when swept off the river bed by a flood. Regardless, when they enter the drift, invertebrates become particularly susceptible to predation by several groups of drift-feeding fish. In Glen, Marble, and Grand Canyons, these fish include rainbow trout (Oncorhynchus mykiss) that sustain the Lees Ferry a Blue Ribbon trout fishery, and the native, federally-endangered humpback chub (Gila cypha). By researching and monitoring invertebrate drift, our group can better understand the health of these fish populations, and how they interact with one another.