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

Annual colonial nesting bird surveys conducted at the Salton Sea from 1987-1991
(U.S. Fish and Wildlife Service (USFWS)( unpublished)) data documents a sharp
decline in many nesting species known to use the Salton Sea including the
Black Skimmer (Rhyncops niger), Great Egret (Casmerodius Alba), and Snowy
Egret (Egretta thula). Although double-crested cormorants (Phalacrocorax
auritus) were previously documented nesting at the Salton Sea, none nested
there from 1989 through 1991. A smaller scale study in 1991 (Audet et al,
1997 indicated that these species were exposed to contaminants (e.g., selenium
and
p,p DDE) and that additional studies fo this situation were warranted. We
hypothesize that this exposure may be contributing to changes in reproduction.
Of particular concern was the fact that Brown Pelicans (Pelecanus
occidentalis), a federally listed endangered species, were beginning to use
the Salton Sea in much greater numbers and may be exposed to the same
contaminants that may have been affecting other piscivorous birds.

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.