Environmental Contaminants in Piscivorous Birds at the Salton Sea, 1992-1993

The Carlsbad Fish and Wildlife Office (CFWO) and the Salton Sea National Wildlife Refuge (SSNWR) jointly conducted this study to evaluate the role of environmental contaminants in the decline of reproduction in piscivorous birds at the Salton Sea. This included the collection of tissue samples for chemical analysis and nest monitoring activities in the first year of the study. The second year of the study focused on the Black Skimmer as this species was believed to best represent the exposure to contaminants experience by the Brown Pelican.

Information gathered in this study forms a baseline against which data collected under current inflow conditions (100,000 acre-feet/year of water has been transferred out of the watershed to the Metropolitan Water District since these samples were collected) or future inflow conditions (there is a water transfer of 200,000 acre-feet/year or more pending between Imperial Irrigation District and San Diego County Water Authority) may be compared.

Because the reduction in inflows are anticipated to occur largely as a result of reduction and/or reuse of surface run-off from agricultural fields, we anticipate increases in the aquatic concentrations and bioavailability of some contaminants. This will ultimately affect the exposures of the apex predators in the system, piscivorous birds. This information, in combination with data gathered in the future, should enhance our ability to implement adaptive management in the restoration of the Salton Sea.

In 1992 specific focus was given to the issue of differences in exposure to organic contaminants in different developmental stages. This was carried out by sampling Black-crowned Night-herons (Nycticorax nycticorax) at three stages of development: eggs collected early in the incubation period (early embryo exposure), embryos near pipping (embryo exposure as it relates to eggs that survive to hatching), and approximately 10 day old chicks that have consumed locally available prey.

The eggs collected early in incubation were analyzed for inorganics, the others were only analyzed for organochlorine compounds.