Larry J. Paulson

Fish aid — the lake mead fertilization project

ABSTRACT Sport fishing at Lake Mead in Nevada and Arizona is a resource valued at nearly

Movement and Dipersal of Tournament-Caught Largemouth Bass in Lake Mead, Arizona-Nevada

100 million per year to southern Nevada. During the past two decades, salmonids, mostly trout, have disappeared entirely, the largemouth bass catch has drastically declined despite greater fishing pressure, and the condition factors for striped bass have steadily deteriorated. It appears that a major reduction in phosphorus loading caused by the upstream impoundment of the Colorado River to form Lake Powell in 1963 and advanced wastewater treatment removal of phosphorus from domestic wastewater inflows in 1981 are the principal factors responsible for decreased production at all levels of the food chain. The Lake Mead Fertilization Project is an attempt to reverse these declining fisheries. The first large-scale test of fertilization occurred on May 30, 1987. More than 300 boats and 1,000 volunteers helped spread 20,000 gallons (75.7 m3) of liquid ammonium polyphosphate over 19,000 acres (7700 ha) of lake surface. Hi...

Effects of ambient Lake Mohave temperatures on development, oxygen consumption, and hatching success of the razorback sucker

ABSTRACT We used ultrasonic telemetry to study post-release movement and dispersal of tournament-caught largemouth bass (Micropterus salmoides) in Lake Mead, Arizona-Nevada. Among 19 fish that survived for more than one week after release, none returned to its site of capture during a 43-day observation period. Dispersal was limited; twelve (63%) fish were last located less than 0.5 km from the tournament release site.

Spawning Season of the Razorback Sucker, Xyrauchen texanus in Lake Mohave, Arizona and Nevada

SynopsisSpawning of razorback suckers,Xyrauchen texanus, in Lake Mohave occurred from 10–22°C and larvae were collected at water temperatures from 10–15°C in 1982 and 1983. In the laboratory, hatching success was similar from 12–20°C, but reduced hatching success was found at 10°C while none hatched a 8°C. Development rate and oxygen consumption were positively related to incubation temperature. Direct effects of ambient Lake Mohave water temperatures on hatching success of razorback sucker embryos are considered minimal. Historical spawning temperatures for the species are hypothesized based upon successful incubation temperatures and comparison to the white sucker,Catostomus commersoni.

The water quality implications of artificially fertilizing a large desert reservoir for fisheries enhancement

ABSTRACT Spawning of the razorback sucker, (Xyrauchen texanus), in Lake Mohave was assessed by visual surveys, trammel netting, and larval sampling in 1982 and 1983. Collections of ripe fish (n=546) and larvae (n=1,205) indicated that razorback suckers spawned from November to May, but larvae were collected only from spawning activity occurring from December through March. Water temperature was 13°C in November as spawning commenced, dropped to 9.5°C during January and February, then increased to 22°C as the spawning season ended in May. Peak spawning, indicated by ripeness, spawning activity, and larval collections, occurred from January through March when water temperatures ranged from 10 to 15°C.

Littoral and limnetic zooplankton communities in Lake Mead, Nevada-Arizona, USA

Multiple use management of aquatic systems frequently involves conflicting demands from the various user groups. A 4-year program designed to evaluate large-scale artificial fertilization as a potential management tool for enhancing the forage and game fish populations of Lake Mead, a large Colorado River reservoir, generated considerable attention from both on-lake and downstream water users. An extensive water-quality monitoring program, undertaken as part of the fertilization experiment, demonstrated that the nutrient additions did not produce significant negative impacts on Lake Mead water quality from either a public health (that is, drinking water) or environmental perspective. One set of parameters, for example, hypolimnetic oxygen depletion and the relative abundance of blue-green algae, exhibited no consistent response to the fertilizer. A second group of parameters did respond to fertilizer addition, but changes were both moderate and relatively short-term. Examples in this group include chlorophyll, threshold odor number, and trihalomethane formation potentials

Use of Gizzard Weights to Determine Total Length and Weight of Threadfin Shad Eaten by Predators

Zooplankton were collected from adjacent littoral and limnetic sites in Lake Mead, Nevada-Arizona, USA. Limnetic species dominated both littoral and limnetic zooplankton communities; littoral species rarely exceeded 2% of monthly total zooplankton densities. Low species richness of littoral taxa and high similarity in species composition between littoral and limnetic habitats appeared to result from uniform horizontal physical and chemical environments, due to horizontal mixing, and from the absence aquatic macrophytes.Significant differences in spatial distribution occurred in phytoplankton biomass, total zooplankton density, and fish abundances; highest concentrations of these factors occurred nearest an inflow high in nutrients and progressively declined farther below the inflow. These factors generally showed no significant difference between adjacent littoral and limnetic sites. Large variation also occurred in seasonal zooplankton community structure among some sites.

A desert wetland created by wastewater flows: current trends and problems

Abstract Threadfin shad gizzard weights were used to determine the total length and total weight of threadfin shad. It was found that a high degree of correlation existed among the parameters tested and that the best relationship was between body weight to gizzard weight empty. Using this information it is possible to estimate the weights of threadfin shad eaten by predatory fish.

Nutrient interactions among reservoirs on the Colorado River

Las Vegas Wash is an artificial wetland supported mostly by discharges of wastewaters from sewage treatment plants. Conflicting interests among municipal, recreational, and down-river users make the Las Vegas Wash a focal point in current management disputes regarding the need for advanced wastewater treatment, desert wetland habitat for wildlife, and salinity control measures. Water quality investigations were performed from July 1979 to December 1980 to characterize nutrient loads and flow regimes within the lower 18 kilometers of the Las Vegas Wash which discharges into the receiving waters of Lake Mead (Colorado River). Although wastewaters were retained for less than 20 hours, this ecosystem behaved as a nitrogen and phosphorus sink. Total nitrogen and phosphorus removal rates averaged 723 kg N day−1 and 124 kg P day−1, respectively. This represented a 20% removal of nutrient loads discharged from the sewage treatment plants. Nutrient removal rates have declined in recent years. Stormwater runoff and higher wastewater discharges have caused extensive channel erosion in downstream reaches. This has decreased the wetlands area by about 90% over the last 5 years. Stabilization of erosion would improve nutrient removal, but uncertainty exists concerning future management of this unique ecosystem.