Lake Mead Science Symposium Concurrent Sessions

Tuesday Afternoon Emerging Issues Abstracts Limnology and Water Quality Abstracts

Wednesday Morning Aquatic Biota and Fisheries Abstracts Riparian and Shoreline Resources Abstracts

Wednesday Afternoon Environmental Contaminants Lake Management

RIPARIAN AND SHORELINE RESOURCES
Session Chairs:
Jef Jaeger and Scott Abella
Wednesday, January 14, 2009 * 8:30 am to 11:45 am * Room 208

8:35 – 8:55 am
Revegetation Efforts along the Las Vegas Wash, Nevada
Eckberg, Jason R. and Shanahan, Seth A., Southern Nevada Water Authority

The Las Vegas Wash is the most substantial riparian area in the Las Vegas Valley and it is the primary drainage channel for this 1,600 square-mile watershed that drains to Lake Mead. During the last few hundred years, the most significant flows in the Las Vegas Wash came from periodic stormwater runoff from the valley. Currently, the Las Vegas Wash has a consistent base flow of more than 150 million gallons per day which comes from a combination of highly treated wastewater discharge, urban runoff, and groundwater seepage. Exponentially increasing base flows in the Las Vegas Wash created approximately 2000 acres of wetlands by the 1970s. These wetlands, however, have been reduced substantially by erosion. In 1998, the Las Vegas Wash Coordination Committee was formed to address stabilization and enhancement activities along the Las Vegas Wash. Over the past 10 years, extensive revegetation projects have been implemented to complement mechanical stabilization initiatives. These projects have enhanced ecosystem services such that wildlife habitat and aesthetic values have improved substantially. Nearly 200 acres have been actively planted along the Las Vegas Wash. Planning efforts, procedures, monitoring results and planned future revegetation activities will be presented.

9:00 – 9:20 am
Monitoring Wintering Bald Eagles at Lakes Mead and Mohave:  Assessing Historic Data, Improving Counts, and Modeling Habitat Use       
Jaeger, Jef R.1; Raskin, Morgan2; Fletcher, Dawn M.1; Sappington, J. Mark2, (1) University of Nevada, Las Vegas and (2) NPS Lake Mead National Recreation Area

Lakes Mead and Mohave are favored stop-over areas during bald eagle winter migrations in the western United States. Each January since 1985, personnel from Lake Mead National Recreation Area have participated in a Midwinter Bald Eagle Count in support of a national effort to measure population size and distribution. Unfortunately, count methods have varied over the years resulting in data which are inconsistent and potentially misleading. Since 2001, efforts have been made to standardize count methodologies and to better train personnel in both identification and recording techniques. Herein we describe what meaningful information can be derived from the historical data, how these counts were improved by standardizing protocols, and what can now be derived from more recent data. To better understand habitat use on Lake Mead, we used location and activity data collected during counts in 2007 and 2008 to create distribution maps and habitat use models. We evaluated habitat variables representing food availability, shelter, and human disturbance. Results indicate that distribution and habitat use varied between the two years, probably in response to differences in weather conditions during the counts. Bald eagles appear to have selected habitat which provided greater shelter from inclement weather during the count in 2007, whereas during good weather in 2008 eagles appear to have selected habitat which provided greater foraging potential along shorelines. By improving our count data, we hope to better understand temporal variation in numbers and to gain insight into distribution and habitat use on Lakes Mead and Mojave.

9:25 – 9:45 am
Assessing the Potential for Noxious Aquatic Plant Invasions of Lake Mead
Schlickeisen, Erica1; Dibble, Eric1; and Tietjen, Todd E.2 (1) Mississippi State University and (2) Southern Nevada Water Authority

Lake Mead has recently been colonized by the invasive quagga mussel and the impacts of this species are only now becoming apparent. It is likely that these mussels were accidentally introduced to the lake by recreational boaters or by passive transport through the Colorado River system. It is important to consider the vulnerability of the Lake Mead ecosystem to other potential invaders; already found in the region are a wide variety of invasive aquatic plants that can have profound impacts. Among the common invasive plants currently impacting lakes of the western United States, Lake Mead is susceptible to invasion by Giant Reed (Arundo donax) Hydrilla (Hydrilla verticillata), Eurasian Water Millfoil and Parrotfeather (Myriophyllum sp.), Alligator Weed (Alternanthera philoxeroides), Curly leaf pondweed (Potamogeton crispus), and Giant Salvinia (Salvinia molesta). A review of conditions in Lake Mead suggest that while extensive colonization of the lake is unlikely given the extremely steep shorelines, deep water column, fluctuating water levels, and relatively low nutrient concentrations; several popular bays and beaches have the potential to be invaded. The accumulation of sediments, nutrient inputs from inflows, wind conditions, relatively shallow depths, deep light penetration and the high potential for local introductions (boat ramps) in these areas may lead to invasive plant issues. We will review limnological and morphometric conditions in conjunction with data related to recreational use in order to develop a framework for assessing the potential risk of invasion.

10:05 – 10:25 am
Inventory and Temporal Variation of Aquatic Birds Using Lakes Mead and Mohave
Barnes, Joseph, G. and Jaeger, Jef, R., University of Nevada, Las Vegas

The creation of Lakes Mead and Mohave in the 1930s and 1950s impounded water along 140 river miles of the Colorado and Virgin Rivers. These large reservoirs substantially changed aquatic and shoreline habitats which subsequently attracted aquatic birds not previously known to frequent the region in large numbers. We report here on a multiyear inventory of aquatic bird species on these two reservoirs and on temporal variation in species composition and numbers over a five-year period. In 2004, we began monthly surveys at four sites on Lake Mead and three sites on Lake Mohave that represented areas of high aquatic bird activity. We tallied 93 aquatic bird species and 17 species of raptor. For summary, we classified species into nine foraging guilds: aerialists, diving carnivores, diving omnivores, herbivores, marsh birds, raptors, shorebirds, and waders. Both reservoirs show high seasonal variation in overall abundance, species and guild assemblages, and include regionally substantial numbers of wintering and migrating birds. Overall, more than 112,000 birds of 103 species were tallied on Lake Mead during the monthly surveys. On this reservoir, herbivores and diving carnivores were the most abundant guilds, and the top five most abundant species accounted for over 53% of all records. In contrast, Lake Mohave was dominated by one herbivore species, the American coot, which accounted for over 81% of the more than 32,000 recorded birds of 66 species. These data establish a baseline of aquatic bird use on these lakes, which will be critical in evaluating future trends.  

10:30 – 10:50 am
Modeling Habitat for Gila Monster (Heloderma suspectum) Over Large Landscapes
Boykin, Kenneth G.1 and Conrad, Paulette M.2 (1) Cooperative Fish & Wildlife Research Unit (2) Nevada Department of Wildlife

Conservation of species is dependent on fine and coarse-scale assessments with habitat modeling often providing the coarser scale. The Gila monster (Heloderma suspectum) is protected in every U.S. state in which it resides but is losing considerable amounts of habitat in rapidly expanding areas such as southern Nevada, southwestern Utah and throughout Arizona. Given the difficulty in observing this elusive species in the field, a habitat model can identify potentially suitable H. suspectum habitat that can inform mitigation actions, especially where significant habitat loss would result from proposed land development or use activities. Inductive (species occurrence based) and deductive (knowledge based) models have strengths and weaknesses. We created an inductive habitat model for H. suspectum using species occurrence points obtained from state wildlife agencies in Arizona, Nevada, New Mexico and Utah, and online museum databases. We used regional environmental variables of meso-scale and relative fine resolution (30m). We ran six model iterations and identified a model consisting of elevation, distance to springs, land cover, and landform as providing the best model based on Area Under the Curve (AUC) and omission rates. We then compared our model with the Southwest Regional Gap Analysis Project deductive model. Though both models identified much of the same habitat, the inductive model was more limited and provided more detailed habitat information that could be useful to managers and researchers interested in the conservation of H. suspectum.

10:55 – 11:15 am
Long-term Monitoring of Bat Populations Associated with Extensive Riparian Restoration in Las Vegas Wash, Clark County, Nevada
O'Farrell, Michael J.1; Shanahan, Seth2; Foster, Marissa2, (1) O'Farrell Biological Consulting (2) Southern Nevada Water Authority

This is a progress report of a long-term continuous monitoring program that was initiated in January 2004 to establish baseline inventory and habitat use of bats in Las Vegas Wash. This study provides baseline conditions in a currently highly disturbed riparian corridor, which is in the beginning stages of an extensive riparian restoration project. Continued monitoring through the restoration process will be able to document the effects of restoration process on the resident and transitory bat community. Three acoustic monitoring stations were established at approximately 1.6 km intervals in the wash allowing collection of data all night every night. Locations were selected to reflect the variations in habitat composition and structure found within the wash. A total of 17 species of bats have been recorded; three species were previously known from a single historic record and six species were not known to occur within Las Vegas Valley, including a species new to the State. Patterns of occurrence and intensity of use are forming. Marked differences of use by various species have been found among the three monitoring sites. Continued monitoring will allow determination of annual variations in occurrence and use due to changing weather patterns as well as the effects of riparian restoration.

11:20 – 11:40 am

Southwestern Willow Flycatcher Habitat and Demographic Studies along the Virgin and Muddy Rivers, Lake Mead, and Lower Colorado River Regions: 2003 to 2007
Koronkiewicz, Thomas J. and McLeod, Mary Anne, SWCA Environmental Consultants

From 2003 to 2007, we have been conducting habitat and demographic studies of the Southwestern Willow Flycatcher at Pahranagat NWR, along the Virgin and Muddy Rivers, within Lake Mead NRA and Grand Canyon, and along the Colorado River and tributaries south to the Mexico border. We found resident and breeding flycatchers in eight study areas. Nest sites had taller canopy, greater canopy closure, and greater vertical foliage density above the nest layer compared to non-use locations. Nests were closer to water/saturated soil than were non-use locations, and were located in areas exhibiting higher humidity and a smaller daily temperature range when compared to non-use locations. Of the flycatchers banded as juveniles and detected as adults, 59% returned to the same study area and 41% returned to a different study area. For adults that were detected in multiple years, 92% returned to the same study area while 8% returned to a different study area. Movement data indicate juvenile dispersal among local populations is largely limited to within river drainages, and most dispersal distances are 30 km or less. Adult survivorship varied by geographical area but not by year. Juvenile survival was lower than that for adults, but models did not indicate that juvenile survival varied significantly between geographic areas. Results of this long-term study have been successful in providing restoration practitioners goals for creating flycatcher breeding habitat.

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