FISHERIES REPORT OF THE LOWER COLORADO RIVER by The Fisheries Task Group Colorado River Great Basin Field Committee September, 1951 Printing and Distribution by Arizona Game and Fish Commission Phoenix, Arizona FISHERIES REPORT OF TBE LOWER COLORADO RIVER by The Fisheries Task Group Colorado River Great Basin Field Committee INTRODUCTION At the request of the Colorado River Great Basin Field Committee, a report on the fishery of the Lower Colorado River was prepared by Fisheries Task Group composed of fisheries biologists from the State fish and game departments of Nevada, Arizona and California, and a representative of the Fish and Wildlife Service. The report divides the Colorado River into seven sections, each river sec- tion being considered individually. The purpose of the report is to describe the present and potential aspects. of the fishery and of fishing recreation in the area, and to point the way for future fisheries research and management programs. However, some definite recommendations, based on the results of field surveys and research carried out to this date, have been made. The entire Colorado River area from Hoover Dam to the Mexican border has been covered by the field crews during the past year. The following individuals are accredited with undertaking the field survey End preparation of their compiled data as follows: Section I - Al Jonez, Nevada Fish and Game Commission and Jack Hemphill, Arizona Game and Fish Commission; Section II - Al Jonez and Jack Hemphill; Section III - Richard D. Beland, California Division of Fish and Game; Section IV - Richard D. Beland; Section V - Richard D. Beland; Section VI - Gerald Duncan, U. S. Fish and Wildlife Service; Section VII - Richard A. Wagner, Arizona Game and Fish Commission. The Lower Colorado River Fishery is a diversified one and with minor exceptions one that is not being utilized to its fullest extent. As a result of serious drought conditions and the subsequent drying up of many lakes and reservoirs throughout the Southwest, the Lower Colorado River repre- sents the last frontier for the ever increasing number of fresh water resident anglers. There has been, and no doubt will continue to be, an ever increasing recre- ational use made of the Lower Colorado River, and with wise management, the fishery will continue to provide good angling. The fishes referred to in the report are as follows: * Rainbow trout, Salmo gairdnerii, (Richardson) Largemouth black bass, Micropterus salmoides (Lapcepede) Smallmouth black bass, Micropterus dolomieu (Lacepede) Black crappie, Pomoxis nigro - mactifiEW-(Ee Sueur) White crappie, Pomoxir, -nnularis (Rafinesque) Bluegill, Lepomis macOodEgag,—(Rafinesque) Green sunfish, Lepomis cyanellus (Rafinesque) Redear sunfish, Lepomis microlophus (Gather) Brown bullhead, Ameriurus nebulosus (Le Sueur) Yellow bullhead, Ameriurus natalis (Le Sueur) Channel catfish, ICtalurus lacustris (Walbaum) Carp, Cyprinus cti5157(-Eanaeus) Bonytail, Gila robusta elegans, (Baird & Girard) Colorado squawfish, Ptychocheilus lUcius (Girard) Razorback sucker, Xyrauchen texanus (Abbott) Striped mullet, Mugil cephalTIT(EEnaeus) Ten Pounder, flops affinis (Began) Gambusia, Gambusia affinis (Baird & Girard) The aquatic plants referred to in the report are as follows: ** Sago pondweed, Potamogetonlaectinatus Spiny naiad, Najas marina Widgeon grass, Ruppia maratima Horned pondweed, Zannichel iajm. Cattail, Typha domingensis Rush, Juncus torreyi Tale, Scirpus californicus Spike rush, Eleocharis parishii SECTION I - MOHAVE LAKE I. Physical Inventory This segment of the river is bordered on the north by Hoover Dam and on the south by Davis Dam. The reservoir itself is contained in Black and Eldorado Canyons, with the lower portion in Pyramid Canyon. High water elevation of the lake is 647 feet above sea level, and the operating level is 643 feet. During June and July, the lake level will drop (because of the requirements of the Mexican Water Treaty), and by August, will be approximately 627 feet. Lake Mohave is 67.5 miles long with a maximum width of four miles near Cottonwood Landing. All land use and concessions are under the jurisdiction of the * Common and scientific names of fishes used in the sectional reports are taken from the American Fisheries Society Special Publication No. 1, A List of the Common and Scientific Names of the Better Known Fishes of the United States and Canada. **Aquatic plant names were taken fromFlowering Plants and Ferns of Arizona by Kearney and Peebles. National Park Service and Bureau of Reclamation. Fish and wildlife are administered by the states concerned. The upper lake is a canyon-type lake, with sheer vertical rock sides broken occasionally by sandy washes that wind down from the surrounding mountains. Upper and lower Lake Mohave are arbitrarily separated at Emery's Landing in Eldorado Canyon. All roads leading into the lake follow these large washes in their gen- eral descent into the canyons. Near the center of the lake, long, sloping foot- hills extend back to the high mountain ranges on either side. These foothills contain many wide washes that have formed long fingers of water extending inland. These fingers have furnished excellent bass spawning areas during this fi year of inundation. Lower Lake Mohave is characterized by rough, rocky shores with numerous in- lets and coves. The lake is subject to strong winds at various seasons. In Summer, these winds are from the south and southwest; in winter, they are from the north. Occasional waves of oceanic proportions occur on the open portions of the lake during periods of strong winds. To date, this rough water is one of the main limiting factors to good fishing. The present policy of the Bureau of Reclamation is to operate the lake with a four foot maximum fluctuation. How- ever, emergency action in operational procedure may alter this policy. II- Biological Inventory The -species of fish present in Lake Mohave are: A. Game Fish: 1. Rainbow trout 2. Largemouth bass 3. Crappie 4. Channel catfish 5. Bluegill sunfish 6. Brown bullhead . Rough Fish: 1. Carp 2. ponytail 3. L,...mpback sucker 4. Colorado squawfish C. Rainbow Trout Most angling on Lake Mohave has been for rainbow trout, which comprises about 95 percent of the total catch. The game commissions of Nevada and Arizona maintain this trout population by plants of young fry and fingerling. Many millions of fry have been planted over the past several years ) and many age classes are present in the lake today. The record rainbow for 1950 weighed 18 pounds. Thus far, for 1951, an 18i pound rainbow caught near Willow Beach holds this season's record. From observations maa,. on the limited spawning beds a mile below Hoover Dam, it is known that many more of these large fish are present in the lake. Asa result of observations over the past year, it is definitely known that trout can and will spawn in the upper portion of the lake. It was thought that rainbow did not spawn in the old river; but these recent observations prove beyond a doubt that rainbow did spawn in suitable areas as far down as Cotton- wood Landing. The fluctuation of water that occurred in the old river undodlt- edly damaged the redds of the rainbow. The deeper redds would not have been affected; these would have hatched. This conclusion was borne out by observa- tions made among the spawning beds in and below the tailrace of Hoover Dam. With the filling of Lake Mohave, and subsequent deepening of the water, spawning is now confined to the area above Ringbolt Rapids. There the current . has become slower and the water somewhat deeper. The increaied depth of the water should make the upper area of the lake a better spawning area in the future. The growth rate of rainbow trout has decreased somewhat during the period of filling the lake. Now, however, growths of filamentous algae, widgeon grass, horned pondweed and sago pondweed are becoming established in shallow areas of the upper lake. With the establishment of aquatic vegetation, a proportionate increase of aquatic insect life is expected, along with the continuance of the fresh-water shrimp (Gammarus fasciatus) and snail (Limnaces E2.). This ex- pected increase in available food should restore the previous growth rate. D. Largemouth Black Bass: A sizeable population of largemouth bass existed in the river area that has since been inundated to form lower Lake Mohave. This population had a very successful spawn in April and May, 1951, and promises to furnish some of the best bass fishing in the Southwest. This body of water is unique in that a sizeable population of trout and largemouth bass exist together. From studies complikted to date, it is believed that the shore areas of the lower lake will be excellent bass waters and the upper lake more suitable0 to trout. Water re- leased from Hocver Dam has a constant temperature of 53 F. when released from the lower level of0 the dam. (In 1951, the temperatures from the lower level have been near 56 F. because of the low level of Lake Mead.) This gives the0 upper ten miles of the lake cool water, even when the air temperature is 115 F. in 0summer. The surface temperature of the lower lake is expected to rise to 80 to 85° F. in late August, driving the trout upstream or to greater depths. In winter, this lake will become almost uniform in temperature, allowing a mixing of trout and bass populations. The extent of this mixing of species is not known, but it is hoped that the trout will occupy the open lake waters and the bass the rocky shoreline. In early summer, the trout will either migrate upstream into cool waters or live in the lake depths near bottom. Bass did not migrate into the cool upper lake water to any great extent In past years, unless.