American Fisheries Society Symposium 80:15–23, 2013 © 2013 by the American Fisheries Society History of Striped Bass Management in the Colorado River WAYNE GUSTAVESON* AND GEORG BLOMMER Utah Division of Wildlife Resources Post Office Box 1446, Page, Arizona 86040, USA Abstract.—The discovery of landlocked populations of striped bass Morone saxatilis in Santee–Cooper Reservoir, South Carolina and Kerr Reservoir, Vir- ginia prompted a rush to stock striped bass in other inland waters of the United States, including impoundments in the Colorado River. Fisheries managers re- sponsible for Colorado River waters studied existing literature and predicted that it would be unlikely for successful natural reproduction of striped bass in these systems. Striped bass population development proved unique in the Colorado River system, which is marked by nutrient-poor, well-oxygenated waters with limited forage. Natural reproduction did occur in these reservoirs despite the lack of current previously thought to be essential for successful reproduction, resulting in high survival. Developing populations were sometimes overabundant to the point of forage elimination from pelagic zones. Lack of prey limited growth and temporarily reduced reproduction. Eventually forage returned, increasing striped bass growth and maturity, which led to more reproduction (a “boom and bust” cycle). Planned low-impact, low-abundance adult trophy fisheries produced by managed stocking were replaced by high-abundance juvenile fisheries with high catch rates produced by natural reproduction. In most years, juvenile striped bass living in warm surface waters proved to have the competitive advantage over adults for limited forage. Colorado River Historical Overview and Burrell 2013, this volume). The last im- poundment was completed in 1963 when Glen The preimpoundment Colorado River was Canyon Dam was closed, forming Lake Powell characterized by harsh environmental condi- (Utah and Arizona), which is 300 km long with tions ranging from muddy spring floods ex- 3 3 a surface area of 65,000 ha when full. ceeding 8,495 m /s to flows less than 8 m /s in The Colorado River watershed is mostly drought plagued summer months. Hoover Dam devoid of agricultural and commercial devel- was completed in 1935, creating Lake Mead, opment, which has been the main cause of the first impoundment on the river and one of nutrient enrichment in many of the nation’s the largest reservoirs by volume in the United impoundments and river systems. Colorado States (Figure 1). At full pool, Lake Mead is River impoundments are characterized by low 63,900 ha with a maximum depth of 177 m phosphorus and nitrogen levels. The new lakes and maximum length of approximately 184 filled deep canyons carved out by the Colorado km. Two smaller but significant reservoirs fol- River with limited littoral zones. Seven native lowed. Lake Havasu (1938) and Lake Mohave fish species that thrived in the river prior to (1952) were constructed downstream (Stewart impoundment were poorly suited for life in the * Corresponding author: [email protected] new lake environment. Introduced nonnative 15 16 gustaveson and blommer FIGURE 1. Map of Colorado River drainage with large reservoirs included. history of striped bass management in the colorado river 17 sport and forage fish species dominate the fish tion would not be sufficient to maintain a sport communities that developed in these reservoirs. fishery” (R. Stone, Utah Division of Wildlife Resources, personal communication). Hatchery Striped Bass History rearing ponds were built near Lake Powell to meet the anticipated annual stocking require- Many new impoundments were constructed ment. The initial 1974 stocking in Lake Pow- in the United States between 1930 and 1970. ell came from Virginia, California, and North Striped bass Morone saxatilis trapped in Santee– Carolina genetic stock (May and Hepworth Cooper Reservoir (South Carolina) impound- 1975). Over time, most of the fish stocked in ments and Kerr Reservoir (Virginia–North Car- Lake Powell came from North Carolina and olina) survived and reproduced (Van Horn 2013, the California Delta stock (Hepworth et al. this volume). Land-locked striped bass provided 1976; Gustaveson et al. 1979). fisheries managers a top-level predator that pro- duced charismatic trophy fish for anglers while Natural Reproduction controlling overabundant forage fish popula- tions. A nationwide rush to stock striped bass in Based on the literature (Bailey 1975), biologists reservoirs ensued as fish managers hoped to reap stocking Colorado River reservoirs believed the biological and recreational rewards. Biolo- that most reservoir striped bass populations gists in the Southeast quickly determined that were not self-sustaining. Most thought that most striped bass populations in reservoirs failed fingerling introductions would be required to to reproduce because the semibuoyant eggs support a continuing sport fishery. However, in would settle to the bottom without supporting the late 1970s, reports from Arizona and Ne- water currents and die due to siltation or lack of vada suggested that evidence of striped bass dissolved oxygen. Barkuloo (1970) proclaimed natural reproduction had been found. Striped that “striped bass eggs and larvae must be sus- bass reproduction in Lake Mead was first pended by current to prevent settling and death noted in 1973 and in every year since (Allan by suffocation.” This finding guided managers in and Roden 1978). Possible spawning sites in- the Colorado River basin who contemplated in- cluded areas where river current could suspend troduction of striped bass. eggs and larvae, as the literature suggested, but Biologists at the California Department of spawning sites were also suspected in reservoir Fish and Game stocked the first striped bass into locations with minimal current. The Lake Mead the Colorado River in 1959 (St. Amant 1959). analysis by Allan and Roden (1978) referenced Young-of-year striped bass were seined from the an important but overlooked hatchery experi- San Joaquin River Delta and transported over- ment conducted by Bayless (1968) confirming land to the Colorado River near Blythe, Califor- that “suspension of striped bass eggs by water nia. All stocked striped bass were descendants of current is not necessary for a successful hatch fish that were transported from the East Coast in provided eggs are not subjected to suffocation 1879 and stocked in the delta near San Francisco by silt or water quality.” Bay. Collaborative stocking efforts from 1962 to Evidence of striped bass natural reproduc- 1969 by state wildlife agencies in Arizona, Cali- tion in Lake Powell was first discovered in 1979 fornia, and Nevada created thriving striped bass and annually thereafter. Initially, it was thought populations in Lake Mead, Lake Havasu, and that reproduction was confined to the Colorado the connecting river reaches (Edwards 1974). River above the lake where river current could Popular striped bass sport fisheries developed, suspend eggs and larvae. The spawning site was which included trophy-sized adults. in or below Cataract Canyon, a 19-km gorge Striped bass were stocked by the Utah Di- containing 23 sets of rapids. Striped bass ap- vision of Wildlife Resources in Lake Powell in parently used less than 20 km of river above the 1974. It was initially thought that “reproduc- reservoir because ripe striped bass adults were 18 gustaveson and blommer collected below but not above Cataract Canyon density current in the reservoir that could not during spawning season (Persons and Bulkley have assisted in moving larvae from the inflow 1982). any closer to the dam than 190 km (D. Mer- During spring 1979, striped bass spawn- ritt, U.S. Bureau of Reclamation, personal com- ing was discovered in the lower reservoir near munication). Instead, striped bass larvae were the dam. In spring of most years, prespawn- captured 295 km downstream from the inflow. ing striped bass aggregated near Glen Canyon If spawning occurred only at inflow areas and Dam. These fish seemed attracted to the cur- larval fish were distributed by reservoir cur- rent created as water was drawn through the rents, then larval fish should have been found dam penstocks. With time and warming, the throughout the reservoir. In contrast, there was aggregation left the 165-m-deep dam forebay a preponderance of young striped bass at two and moved to nearby coves where spawning oc- distinct locations, the inflow and again at the curred. Most fish left the prespawning staging dam. It was evident from these analyses that area simultaneously during early May as water these young striped bass found near the dam surface temperature reached 16–19°C, which were the result of successful in-reservoir spawn- is the generally accepted peak spawning tem- ing (Gustaveson et al. 1984). perature range (Setzler et al. 1980). Spawning Over the years, it has been confirmed that sites were located near the dam where floating striped bass spawning occurs annually in Lake masses of dead (unfertilized) eggs were clearly Powell, Lake Mead, Lake Mohave (Liles 1985), visible. J. D. Bayless (South Carolina Wildlife and Lake Havasu. Eggs and larval striped bass and Marine Resources Department, personal also pass through the dams to provide addi- communication) found that unfertilized eggs tional recruits to downstream lakes and canals would float but that immediately after fertiliza- as water is delivered from the Colorado River tion, eggs would sink 0.3 m in 27 s. Settling to locations in California, Nevada and Arizona rate slowed with time, but eggs still descended (Stewart and Burrell 2013). 0.3 m every 60 s some 24 h after fertilization (Gustaveson et al. 1984). Population Dynamics An oxygen-temperature profile taken in spawning coves near the dam showed oxygen Initial growth of Lake Powell and Lake Mo- levels of 8.4 mg/L near the surface and 13.2 have striped bass was comparable to other fast mg/L on the substrate in 9 m of water. Siltation growing cohorts in the United States (Liles was insignificant in these coves on the rock and 1985; Gustaveson 1999).