Electrofishing, a valuable sampling technique in North America for over half a century, involves a very dynamic and complex mix of physics, physiology, and behavior that remains poorly understood. New hypotheses have been advanced regarding "power transfer" to fish and the epileptic nature of their responses to electric fields, but these too need to be more fully explored and validated.
Fishery researchers and managers in the Colorado River Basin, and elsewhere, are particularly concerned about the harmful effects of electrofishing on fish, especially endangered species. Although often not externally obvious or fatal, spinal injuries and associated hemorrhages sometimes have been documented in over 50% of fish examined internally. Such injuries can occur anywhere in the electrofishing field at or above the intensity threshold for twitch. These injuries are believed to result from powerful convulsions of body musculature (possibly epileptic seizures) caused mostly by sudden changes in voltage as when electricity is pulsed or switched on or off. Significantly fewer spinal injuries are reported when direct current, low-frequency pulsed direct current (<30 Hz), or specially designed pulse trains are used. Salmoniae are especially susceptible. Endangered cyprinids of the Colorado River Basin are generally much less susceptible, enough so to allow cautious use of less harmful currents for most recovery monitoring and research. However, the endangered catostomid Xyrauchen texanus appears sufficiently susceptible to warrant a continued minimal-use policy.
Other harmful effects, such as bleeding at gills or vent and excessive physiological stress, are also of concern. Mortality, usually by asphyxiation, is a common result of excessive exposure to tetanizing intensities near electrodes or poor handling of captured specimens. Reported effects on reproduction are contradictory, but electrofishing over spawning grounds can harm embryos. Electrofishing is often considered the most effective and benign technique for capturing moderate- to large-size fish, but when adverse effects are problematic and cannot be sufficiently reduced, its use should be severely restricted.
Effects of an introduced crayfish on native Arizona fishes: Final Report
Bonytail (Gila elegans) and razorback sucker (Xyrauchen texanus) are large river fish found only in western North America’s Colorado River basin. The bonytail in nearly extinct and the razorback sucker is becoming rare…
Colorado River Basin Riparian Ecology
Colorado River Basin
Fully functional riverine ecosystems that traverse North American deserts provide a variety of ecosystem services. However, these landscapes have been altered significantly since the 1800s, and the processes responsible for their structure and function remain poorly understood. Information on community structure, nutrient dynamics, plant-animal interactions, floodplain soil processes, and linkages between riverine aquatic/riparian/upland ecosystems is needed before key research questions (e.g., “To what extent have ecosystem services in the Colorado River Basin been lost or degraded due to altered streamflows?”) can be answered. The overall objectives of this research are to describe the effects of streamflow regulation on key riparian species and processes, and to elucidate the mechanisms responsible for those effects. This work will provide species- and site-specific information of immediate benefit to water resource managers and managers of floodplain lands in the Colorado River Basin. The primary products will bear on specific management questions pertaining to streamflow alteration, vegetation-restoration issues, and grazing management.
Native Fish Sanctuary Evaluation
Bonytail (Gila elegans) and razorback sucker (Xyrauchen texanus) are endemic to the Colorado River and represent two of the four endangered, large-river fishes. Recovery programs have focused on predator removal, stocking of native fish into the mainstem river, and more recently, creation of off-channel habitats, or fish sanctuaries, dedicated to raising native fish. This study is evaluating the feasibility and success of using smaller (<5 acre), more manageable ponds as sanctuaries for these species. (Young fish are raised to a size more likely to survive in the mainstem Colorado River.) Sanctuary evaluation involves several phases: (1) examining existing small ponds for suitability; (2) working with management agencies and other partners to salvage, renovate, and stock native fish into potential sanctuaries; (3) developing and initiating monitoring plans for each sanctuary; and (4) initiating new research to fill information gaps that may be impeding effective sanctuary management. For example, this study examines whether conditioning in a controlled environment, through various levels of physical activity and exposure to predation threats, improves the ability of recently stocked, warm-water native fish to avoid and escape predators. Increased survivorship would result in economic savings by reducing the number of fish required to reach reintroduction goals. A second related study is evaluating remote fish-censusing techniques, including high-resolution aerial photography and systematic counts by observers in boats to estimate population sizes. Effective remote censusing techniques may reduce handling stress on rare fish. Partners include biologists and natural resource managers from the Bureau of Reclamation, U.S. Fish and Wildlife Service, Bureau of Land Management, National Park Service, Arizona Game and Fish Department, California Department of Fish and Game, The Nature Conservancy, and Arizona State University.
Interactions between Native and Non-native Aquatic Species in the Southwestern United States
Fish from the Colorado River Basin
Recovery efforts for native fish within the Southwest have included native fish stocking and repatriation, stream-barrier construction to prevent invasion of non-natives, habitat restoration, and chemical and mechanical removal of non-native predators. The effectiveness of these techniques over extended time periods is a function of both the engineering effectiveness of construction and mechanical removal practices, and ecological interactions that occur over multiple spatial scales. In order to improve the effectiveness of restoration efforts and assist State and Federal agencies responsible for implementing management actions, FORT scientists are working with these agencies to conduct research to identify the life histories, habitat requirements, and ecological roles of native fish as well as their interactions with introduced species. Recent studies have examined the role of introduced fish predation on native fish recovery and investigated the impacts of crayfish on habitat characteristics, such as in-stream vegetative cover and the population structure of southwestern native fish. The long-term effectiveness of various combinations of different barrier designs and chemical renovation approaches is being compared across a multistate area. Cooperators include the U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, University of Arizona, and several State game and fish departments.