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Razorback Sucker

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The Razorback Sucker

In the early 1900s, the razorback sucker could be found in abundance within the Colorado River and its major tributaries. A fish native to the Colorado River Basin, the razorback sucker gained its name from the sharp-edged hump on its back, between the head and dorsal fin which acts as a keel to assist swimming in strong river currents. The fish can measure up to 2.5 feet in length, and is also known as the “humpback sucker,” not to be confused with the humpback chub.

For the last 50 years, the razorback sucker has suffered substantial population declines due to the construction of large dams throughout the basin, as well as an influx of non-native species. Its range now consists of a few small populations throughout the Colorado River and several tributaries as far north as Colorado, with the largest population concentrated in Lake Mohave of an estimated 25,000 fish. But even there, due to predatory, non-native fish, the number of young fish maturing to adulthood requires an intensive multi-agency effort of collecting larvae, rearing them in a hatchery and repatriating them back into the lake once they’ve reached a specific length in size.

Razorback Sucker

The U.S. Fish and Wildlife Service (FWS) listed the razorback sucker as endangered in 1991 and designated critical habitat in 1994 in an effort to protect it from extinction. Lake Mead is included in the razorback sucker’s federally-designated critical habitat, where the Southern Nevada Water Authority, and in recent years the Bureau of Reclamation, have funded comprehensive monitoring since 1996. The study is conducted cooperatively with the Nevada Department of Wildlife, National Park Service, Arizona Game and Fish Department and the FWS. BIO-WEST, an environmental research firm, was tasked with monitoring efforts and maintaining a decade-plus database.

The Las Vegas Wash Coordination Committee (LVWCC) consults with partnering agencies on monitoring the razorback population because that data indicates effectiveness of the erosion control programs along the Las Vegas Wash. In recent years, the Lake Mead populations have proven to be the most successful, and possibly the only naturally recruiting populations throughout the whole system. Although spawning seems to occur throughout the whole basin, recruitment refers to the ability of larvae to develop into sexually mature adults. The working hypothesis is that vegetative cover, water turbidity, and food accessibility is essential to young razorback suckers to avoid predation, and that these necessities are affected by fluctuations in Lake Mead water elevation.

The fact that there is a spawning population in the Las Vegas Bay indicates the success of wetlands along the Las Vegas Wash, i.e., if the population increases, the LVWCC goals for weirs affecting water quality are being accomplished. Current efforts, assisted by Las Vegas Wash Project Coordination Team member and Environmental Biologist Tim Ricks, include attempting to determine which environmental conditions are contributing to this success, monitoring the seasonal behavioral dynamics of the two populations as well as monitoring how the lowering lake levels are affecting spawning success. Trammel netting is used to collect adults, night lighting to capture larvae, and sonic-telemetry techniques to determine movements and habitat selection. Water quality measurements will provide a better perspective of how environmental conditions and opportunities change with the fluctuating levels of Lake Mead. By using fin ray sections, a non-lethal technique, researchers are able to determine the age of a fish and this allows them to identify recruiting classes and compare lake conditions from those classes. Past monitoring efforts have compared vegetative cover, nutrients, and plankton populations at three sites in Lake Mead and two sites in Lake Mohave. The overall goal of this comprehensive effort is to expand Lake Mead’s unique recruitment trend elsewhere.

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Las Vegas Wash Project Coordination Team • 100 City Parkway, Suite 700 • Las Vegas, NV 89106 • (702) 822-3300