Assessment of a Forage Fish Introduction Into Lake Powell
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ASSESSMENT OF A FORAGE FISH INTRODUCTION INTO LAKE POWELL Prepared by: A. Wayne Gustaveson Henry R. Maddux and Bruce L. Bonebrake Lake Powell Fisheries Project Utah Department of Natural Resources Division of Wildlife Resources 1596 West North Temple Salt Lake City, Utah 84116 Timothy H. Provan Director March 1990 TABLE OF CONTENTS Page List of Tables ....... vi List of Figures .....viii Purpose and Need ........ 1 Description of Affected Environment ........2- Location ........ 2 Fishery Resources 4 Threadfin Shad ........ 7 Other Forage Organisms ........ 9 Largemouth Bass 9 Smallmouth Bass 9 Black Crappie 11 Walleye 11 Catfish 12 Threatened and Endangered Species 12 Striped Bass ....... 12 Environmental Components Not Affected 14 Commercial Concerns 14 Recreation ....... 14 Alternatives ....... 15 Introduction ....... 15 Lake Powell Management Objectives 15 Economic Benefits 16 Alternatives Evaluated ....... 16 Proposed Action - Rainbow Smelt Introduction ....... 17 Pygmy Smelt 17 Multi-Species Forage Complex ....... 17 Commercial Fishery ....... 17 Regulation Changes ....... 17 No Action 17 Discussion of Alternatives ....... 18 Rainbow Smelt Introduction ....... 18 Pygmy Smelt 19 Multi-Species Forage Complex ....... 19 Commercial Fishery ....... 20 Regulation Changes ....... 21 No Action 22 Comparative Analysis ....... 23 Selection Standards 23 Alternatives Considered But Dismissed 24 Increasing Reservoir Productivity 24 Stocking Additional Threadfin Shad ....... 24 TABLE OF CONTENTS (Continued) Page Introducing Some Form of Sterile Striped Bass 25 Stripercides .......25 Limit or Disrupt Spawning 25 Introduce Predator for Striped Bass 25 Create Large Protected Shad Nursery Areas 25 Other Candidate Species Considered But Dismissed .......26 Analysis of Environmental Consequences .......27 Expected Benefits 27 Lake Powell Productivity and Plankton Abundance 28 Life History and Ecology of Rainbow Smelt 28 Description 28 Distribution .......29 Habitat 30 Spawning .......30 Food Habits 31 Disease Potential 32 Hybridization 33 Smelt as Forage 33 Expected Behavior of Smelt in Lake Powell 33 Threatened and Endangered Species 35 Humpback Chub 35 Bonytail Chub 37 Razorback Sucker .......37 Other Environmental Components .......37 Summary and Conclusions .......39 Documentation of Consultations .......40 Public Meetings 40 Colorado River Fish and Wildlife Council 41 Other Public Meetings 41 Federal Agency Consultation 42 Literature Cited .......43 -iv- LIST OF TABLES Table Page 1. Stocking history of Lake Powell, Utah-Arizona, 1963-86 . 5 2. Alternatives comparison matrix of selection standards . 24 3. Species considered for introduction into Lake Powell . 26 -vi- LIST OF FIGURES Figure Page 1. Indices of total recreational boat use and angling pressure Lake Powell, 1965-88 3 2. Mean number of threadfin shad collected per trawl tow July-September, Lake Powell, 1977-89 ........ 8 3. Catch rates (fish/net day) for walleye and largemouth bass during annual trend gillnetting at Lake Powell, 1972-88 10 4. Mean condition factor (Kfl) of adult and juvenile striped bass at Lake Powell, 1975-89 ....... 13 i PURPOSE AND NEED The purpose of this action is to enhance forage conditions for all fish species currently established in Lake Powell by introducing a deep, cold water planktivorous forage fish, such as rainbow smelt (Osmerus mordax). Once established, rainbow smelt could increase forage species diversity, provide forage for fish occupying the cool water zone, more efficiently utilize plankton in the pelagic zone and expand escape habitat utilized by forage species. An over population of piscivorous predators resulting from unlimited striped bass (Morone saxatilis) reproduction has placed extreme predatory pressure on threadfin shad (Dorosoma petenense), the only pelagic forage fish present in Lake Powell. The shad population has been impacted by predation to the point that it no longer provides adequate forage for pelagic or deep water predators. The striped bass population has become stunted with few fish attaining a length in excess of 500 mm (20 in). Adult striped bass move into the deep cooler water as they mature. They are not able to successfully compete with juvenile striped bass which forage on the annual shad crop in the warmer shallow water areas. Both walleye (Stizostedion vitreum) and striped bass populations suffer recurring periodic declines in physical condition which is attributable to the separation of predator and prey and the lack of sufficient shad forage. Juvenile and some adult striped bass are having to forage directly on large zooplankton to maintain body condition, indicating an inadequate forage base for a major part of the predator population. Over the past 25 years, fishing at Lake Powell has been good enough to attract anglers from all over the world. When the reservoir was young and filling, largemouth bass (Micropterus salmoides) and black crappie (Pomoxis nigromaculatus) fishing was outstanding. Angler catch rates in 1979 for largemouth bass and black crappie were 0.22 and 0.16 fish/h; by 1984 catch rates had declined to 0.05 and 0.03 fish/h and by 1988 had declined to 0.04 and 0.00 fish/h, respectively. More recently the fisheries have been dominated by walleye and striped bass. Over the life of the reservoir, anglers have been able to catch a mixed bag of fish at an average rate near 0.4 fish per hour (Scott and Gustaveson 1989). Fishing pressure has steadily increased throughout the life of the reservoir until recently (Figure 1). The striped bass sport fishery gained wide public recognition from 1979-1985. The fish were large and easy to catch. Many people came to the lake just to fish for striped bass. The average size of sport caught fish harvested between 1979 and 1984 was 620 mm (24.4 in). This was easily the largest fish that the average Lake Powell angler had caught in a lifetime. As striped bass predation depleted shad stocks from the pelagic zone condition of adult striped bass dramatically declined. During 1982-1983 most anglers were happy with their trophies despite their poor physical condition of some fish. During 1985 the average length of all striped bass sampled declined from 620 mm to 555 mm (21.8 in) and condition factor fell to near 0.90. Anglers began to become dissatisfied at this point. By the spring of 1986 striped bass averaged 497 mm (19.5 in). They further declined in size to 423 mm (16.5 in) by the fall of 1986, and 393 mm (15 in) in 1987. During the winter of 1987 a massive die-off eliminated most striped bass between 500-800 mm (20-31 inches) from the population. Total length declined to 348 mm (13.7 in) in 1988 and -1- rebounded slightly to 355 mm (14 in) in 1989. Smaller striped bass typically have better condition factors (Kfl) than larger fish. Condition is currently averaging near 1.0 to 1.1. A Kfl factor greater than 1.1 is the value where striped bass become acceptable to anglers. DESCRIPTION OF AFFECTED ENVIRONMENT LOCATION Lake Powell was impounded by Glen Canyon Dam on the Colorado River, 9.7 km (6 mi) south of the Utah-Arizona border. The lake's main purpose was water storage and regulation as well as hydroelectric power generation within the Colorado River Storage Project (CRSP). The 300 km-long (186 mi) reservoir is confined to the deep narrow canyon of the Colorado River and its tributaries. Most of the 2,930 km (1,820 mi) of shoreline is comprised of sandstone cliffs and talus slopes. Only a few side bays offer relief from the vertical canyon walls. Average depth of the reservoir is 50.9 m (167 ft) and the maximum capacity is 3.32 x 108 m3 and 160,000 surface acres (Johnson and Merritt 1979). Lake Powell is an oligotrophic, warm monomictic, canyon reservoir (Johnson and Merritt 1979). Stratification generally begins in April and often persists into December. Surface temperatures range between extremes of 6.7 and 29.4 C. Secchi readings are typically 3-9 m, although readings as high as 13 m have been recorded (unpublished data, Utah Division of Wildlife Resources, Page, AZ). Lake Powell, within Glen Canyon National Recreation Area, has become a popular tourist attraction with an annual visitation of over 3 million per year. It offers boating, fishing, hiking and associated recreational opportunities. The regulated Colorado River below Lake Powell flows through Grand Canyon National Park 445 km (277 mi) from Glen Canyon Dam to Lake Mead. Lake Mead, formed by Hoover Dam, supplies most of the storage and regulation in the lower Colorado River Basin, providing for irrigation, municipal and industrial uses, power generation, flood control, and recreation. Lake Mohave, formed by Davis Dam, backs water about 100 km (67 mi) upstream to Hoover Dam. Storage in Lake Mohave is used for reregulation of releases from Hoover Dam, for meeting treaty requirements with Mexico, and for power generation. The river then flows through a natural channel for about 16 km (10 mi) below Davis Dam at which point the river enters Mohave Valley 53 km (33 mi) above the upper end of Lake Havasu. Lake Havasu behind Parker Dam impounds 72 km (45 mi) of river and serves as a forebay from which the Metropolitan Water District of Southern California pumps water into the Colorado River Aqueduct. Lake Havasu also serves as forebay for the Central Arizona Project pumping plants and aqueducts. Lake Havasu is used to control floods originating below Davis Dam and above Parker Dam. -2- 450 400 350 300 0 c 250 CO 0 00 _1= 700 150 100 50 65 67 69 71 73 75 77 79 81 83 85 87 66 68 70 72 74 76 78 80 82 84 86 88 Year figure 1. indices of total recreational boat use and angling pressure, Lake Powell, 1965-1988. The river then flows 444 km (276 mi) below Davis Dam to the Mexican border. Important structures within this reach include Headgate Rock Dam, Palo Verde Diversion Dam, and Imperial Dam which serve as diversionary structures with practically no storage.