Funding Program: Contaminant Biology

Statement of Problem: The razorback sucker (Xyrauchen texanus) once flourished in the Colorado River basin. Habitat alterations, dam construction, predation/competition with non-native fishes, and water quality degradation are believed to have contributed to population declines. As a result, the U.S. Fish and Wildlife Service (FWS) has listed the razorback sucker as an endangered species and designated critical habitat in the Colorado River and many of its tributaries. Razorback sucker are currently monitored by the FWS to assess the health of the remaining populations. In the lower Colorado River basin, razorback sucker continue to spawn and reproduce at a low level in Lake Mead, spawning without documented recruitment in Lake Mohave and Lake Havasu (USFWS 2002). Researchers have already documented how selenium in the lower Colorado River may adversely affect razorback sucker survival and reproduction (Hamilton et al. 2005a,b). Deterioration of water quality with environmental estrogens could also limit recovery efforts for the razorback sucker. Urban runoff and wastewater effluent from large metropolitan areas such as Las Vegas are potential sources of estrogenic compounds that can affect the reproductive systems of aquatic organisms (Arnold et al. 2004, Folmar et al. 1996). The FWS is specifically concerned about the viable razorback sucker population in the Las Vegas Wash because it is one of two sites in Lake Mead where recruitment has been documented and where high anthropogenic inputs are problematic to water quality and aquatic organisms (Bevans et al. 1996, Tuttle and Orsak 2002, Gross et al. 2004, Snyder et al. 2004). Estrogenic responses to environmental conditions in male carp, bass, and channel catfish from the Colorado River basin were documented in a 2003 USGS study (Hinck et al. 2006), and in razorback suckers from Las Vegas Wash (Tuttle and Orsak 2002). The Clean Water Coalition (CWC), which is made up of the City of Las Vegas, the City of Henderson, and the Clark County Water Reclamation District, will begin releasing effluent from Las Vegas into Lake Mead closer to Hoover Dam if a new disposal location is approved through a NEPA process starting with the release of the 2005 Draft Environmental Impact Statement (NPS 2005). The existing effluent disposal site into Las Vegas Wash is no longer a preferred alternative due to low dilution capability and erosion of the wash during drought conditions (lowered lake levels). By discharging deeper in the lake and closer to the center of the lake, the CWC hopes to maintain a constant source of water for effluent dilution and will remove an obvious point source out of the public-eye. Concentrations of metals, pesticides, organochlorine compounds, dioxins, furans, polycyclic aromatic hydrocarbons, phthalates, phenolic compounds, and ethinylestradiol that are high in Las Vegas Wash and Las Vegas Bay water and/or sediment (Tuttle and Orsak 2002) are likely to increase in the main body of Lake Mead near the new discharge location. Leiker et al. (1997) attributed the pollution in Las Vegas Wash to the effluent discharge. Although Las Vegas Wash receives both treated effluent in addition to urban stormwater runoff, moving the discharge outfall is likely to only move the source of the contamination from Las Vegas Wash to the new discharge location (likely to be near the Boulder Islands). Although Marr (2006) did not find any evidence of endocrine disruption in carp or razorback suckers in Lake Mohave, Lake Havasu, or below Parker Dam, it will be important to continue monitoring at these sites. Monitoring in the future will be more meaningful if we can measure vitellogenic responses in male razorback suckers directly.

Objectives:  Our objective is to measure vtg and steroid hormones in sexually mature, adult razorback sucker over one annual -estradiol,ß reproductive cycle. We will measure vtg and steroid hormones (17 11-ketotestosterone, and testosterone) in blood plasma of razorback suckers once a month for one year to document concentrations throughout the reproductive cycle. These data will document the variation in vtg and hormones during the reproductive cycle and determine typical concentrations during the various seasons. Because the vtg assay is normally species specific, we will need to screen antibodies currently available for various fish species for cross reactivity with the razorback sucker. If currently available antibodies do not cross-react with razorback sucker vtg, we will develop species-specific monoclonal antibodies to measure vtg in razorback sucker.