By: Mike Demlong
It is difficult to inspire people to care about fish - unless they are in sticks, steaks or fillets. The Phoenix Zoo, however, is doing just that with a comprehensive conservation and education program designed to help imperiled Arizona fish.
Within the boundaries of The Phoenix Zoo is a series of artificial lakes originally created as a bass hatchery for the Arizona Game and Fish Department. The hatchery closed in the early 1960's, but the lakes and surrounding land were leased to the new Phoenix Zoo.
In the fall of 1995, the living collections staff at the zoo proposed to convert this underutilized area into a refugium for endangered native fish. To ensure the success of this project, the zoo enlisted experts from Arizona State University (ASU), U.S. Fish and Wildlife Service (FWS), Arizona Game and Fish Department, Dexter National Fish Hatchery, Willow Beach National Fish Hatchery, American Zoo and Aquarium Association Freshwater Fish Advisory Group, Arizona Zoological Society Conservation Committee, Salt River Project, and City of Phoenix Parks, Recreation, and Library Department. Our objectives were to create a long-term refugium for endangered native fish and headstart juveniles for potential reintroduction projects. The decision to use the zoo-held fish for either reintroduction, brood stock, or as a genetic refugium will be determined by the FWS.
The FWS's biological assessment determined the 15-acre lake to be suitable habitat and offered to introduce endangered bonytail chub (Gila elegans) and razorback sucker (Xyrauchen texanus) once non-native game fish were removed. These native species were appropriate because both once thrived in the rivers that dissect Phoenix. However, numerous species, including the bonytail chub and razorback sucker, have been pushed toward extinction by dams, exotic fish, water diversion for residential and farming use, pollution from agricultural run-off, river channelization, loss of wetland nurseries, and dewatering. Approximately 40 species of North American freshwater fish have become extinct this century, and approximately 80% of fish in the arid Southwest states are imperiled.
Bonytail chub historically ranged from Wyoming to Mexico, throughout the Colorado River and many of its tributaries. Today, bonytail are seldom found in the upper Colorado River and are instead restricted to two artificial lakes along the Arizona/California border. The temperature, physical and chemical composition of these lakes are very different from those in which the fish evolved. For example, the Colorado, once a warm, heavy silted, swift river, is now a cold, clear series of artificial impoundments.
Since the damming of the Colorado River in 1954, there has been no recruitment in wild populations. The few bonytail recovered are geriatric adults of 40 years of age or more. Failure of this fish species to maintain a self-supporting population in the wild is attributed to habitat alteration from dams and the introduction of exotic fish species for sport fishing. Consequently, the bonytail chub is the most endangered fish in the Colorado River Basin, perhaps in the entire United States. Fortunately, between 1979 and 1981, 18 adult bonytail were captured to establish a captive propagation population at the Dexter National Fish Hatchery. Eleven of these fish became the genetic founders of the entire captive hatchery population used for reintroduction efforts.
The second species of native fish released in the zoo refugium were razorback suckers. Like the bonytail chub, they ranged throughout the Colorado River Basin in Wyoming, Colorado, Utah, Arizona, and Mexico. In the early 1900's, the species was so abundant that it supported a commercial fishery in central Arizona, providing human food, animal food, and fertilizer. The largest population of razorback suckers (approximately 23,000) is restricted to Lake Mojave, however a smaller population of about 1,000 fish remains in the middle Green River. Unfortunately, little or no recruitment has been documented in either population.
Since non-native fish compete with native species for resources, zoo staff removed as many adult gamefish from the zoo lake as possible. With the assistance of Arizona Game and Fish Department, hundreds of largemouth bass (Micropterus salmoides), bluegill (Lepomis machrochirus), and green sunfish (Lepomis cyanellus) were translocated using fishing poles, electroshock boats, drift nets, and various other traps over a two month period. Captured fish were relocated to other lakes on the zoo grounds or to city parks within the metropolitan Phoenix area.
Once the majority of non-native fish were removed from the lake, the drain valve was opened and within seven days the lake was empty. The lake bed was allowed to dry for the entire month of June to kill any remaining fish and embryos. Small pools of water were treated with ichthyocide on three separate occasions to be sure no fish survived.
In early July, the lake was refilled with canal water from the mountain watersheds northeast of Phoenix. Ironically, the water used to fill the fish refugium was from the same watersheds that once fed the rivers the fish historically inhabited. Since canal water is also contaminated with game fish, it had to be filtered before entering the renovated lake. Zoo staff members, biologists from ASU, and engineers from Salt River Project, collaborated to design a fish excluder where canal water entered the grounds. The filter is a 12 foot long concrete trough partially filled with 3/16 inch crushed aggregate. All canal water flowing in the zoo lakes falls on top of a raised gravel bed, impeding non-native fish and ideally their larvae and eggs. Dead and live fish, crayfish, and inorganic and organic debris are removed daily from the gravel bed to improve filtration. Daily cleaning takes about five minutes and approximately every two months the gravel bed is replaced with new aggregate. Some juvenile non-native fish have reappeared in the lake. They either passed through the excluder device or were missed in the initial treatments. Fortunately, the native fish have grown large enough to avoid predation by non-natives.
The lake took two weeks to refill and was aged for several more weeks to allow reestablishment of aquatic invertebrates and phytoplankton. In August 1997, approximately 200 bonytail chub were released, followed by 5,000 razorback suckers in November. The bonytail chub originated from a captive population maintained at the Dexter National Fish Hatchery in New Mexico. The razorback suckers were wild caught as larvae at Lake Mojave, and head-started at Willow Beach National Fish Hatchery in Parker, Arizona before release in The Phoenix Zoo lake.
Fishermen, boats, and a smelly lake bed are hard things to hide at a city zoo. So instead of hiding the activities, they were publicized. The arrival of the endangered fish was announced to the community via local television stations and major newspapers. To interpret the project to zoo visitors, The Phoenix Zoo incorporated temporary script into guided tram tours and installed temporary interpretive signs around the lake. Informal surveys of zoo visitors revealed general support for the project and associated inconveniences (e.g., no monkeys on the lake islands, the strong offensive odor, dead fish).
Eventually, temporary graphics were replaced with permanent interpretive stations around the lake's perimeter. At each station, visitors were provided with information about the endangered fish project, the animals' natural history, and reasons for their decline. Each interpretive station includes two life-size "touchable" cement sculptures of an adult razorback and bonytail chub. The three-dimensional sculptures attract visitors to the interpretive station and help them visualize an otherwise invisible animal.
Zoos and aquariums cannot provide what endangered native fish need most to survive: clean water, unaltered habitat and absence of non-native species. What we can provide are captive refugia for imperiled species, and an opportunity to motivate over 120 million people a year to minimize their impact on the aquatic natural world. The Phoenix Zoo is providing low cost, low maintenance refugia for three species of endangered native fish (the third is the desert pupfish (Cyprinodon macularius)). Yearly maintenance of this project costs less than the monthly food bill for one tiger! Depending on the success of this project and FWS needs, The Phoenix Zoo hopes to eventually convert three more artificial lakes on zoo grounds to endangered fish refugia.
For more information on this project contact Mike Demlong, The Phoenix Zoo, 455 North Galvin Parkway, Phoenix, AZ 85008, phone (602) 273-1341, ext. 7624 or e-mail at firstname.lastname@example.org.
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