Razorback Sucker

The razorback sucker (Xyrauchen texanus) is a unique fish native to the Colorado River Basin.

In the early 1900s, this fish was abundant in the main stem of the Colorado River and its major tributaries. Following the introduction of non-native species and construction of dams in the basin, the razorback sucker suffered substantial population declines across its range.

Presently, this species exists mostly in small remnant populations scattered across the Colorado River Basin. The only population that has any substantial size is in Lake Mojave where there lives an estimated 25,000. But even there, recruitment of young fish to the adult population is virtually nonexistent due to predatory, non-native fish.

An endangered species

In an effort to protect the razorback sucker from extinction, the U.S. Fish & Wildlife Service listed this species as endangered in 1991 and designated critical habitat for it in 1994. In addition, the Lower Colorado River Multi-Species Conservation Program was initiated in 1993 by the states of Arizona, California, Nevada and federal agencies in a cooperative effort to aid in the recovery of the razorback sucker.

Lake Mead comprises a portion of the razorback sucker's federally-designated critical habitat. Little is known about the Lake Mead population of razorback sucker. Between the years of 1990 and 1993, the Nevada Department of Wildlife conducted a small-scale population survey and captured, tagged and released 50 adult fish. Although this effort did produce some valuable information, it was not conclusive enough upon which to base sound resource management decisions.

Information like total population size, number of females in the population, age structure of the population, seasonal habitat use, location of spawning sites and spawning success is extremely important to resource managers. Without this information, management decisions regarding this population would be based upon limited data.

In an effort to gain valuable information, the Southern Nevada Water Authority initiated an extensive study on the razorback sucker in Lake Mead in 1996. This study is a cooperative effort between the Water Authority, Colorado River Commission, Nevada Department of Wildlife, National Park Service and U.S. Bureau of Reclamation. Various resources, including labor, equipment and money, have been pooled together by these agencies so as to maximize the scope of the study.

The study includes three primary components:

• Trammel netting
• Sonic tagging and tracking
• Larva sampling

The trammel netting effort involves running trammel nets in Las Vegas Bay and Echo Bay for one to three weeks per month, depending on the expected activity of the razorback sucker. These locations were selected as starting points for the study due to a high probability of contacting these elusive fish.

Once individuals are captured, a passive integrated transponder (PIT) tag is injected into those fish that do not already have one. A sonic tag is surgically placed in the body cavity of selected fish. Following their return to the point of capture, the movements of each fish with a sonic tag are tracked by a team of biologists for the life of the tag, which spans 14 to 48 months.

We conduct larva sampling during the spawning season by setting light traps in potential spawning sites at night. The larva are attracted to the light source, where they are counted.

As of July 2005, we have captured a total of 300 adult razorback suckers. We sonic-tagged 56 fish and counted 7,808 larva. In addition, we have aged 77 razorback suckers using pectoral fin ray sections.

Information gained from this study will benefit the various agencies involved, as well as the razorback sucker, by providing a strong scientific base of knowledge from which resource management decisions can be made. In addition, future environmental compliance regarding the razorback sucker in Lake Mead will be facilitated by the availability of information gained from this contemporary study.