Environmental Engineering Reference
In-Depth Information
Blus et al. (
1979a
) reported on a program to transplant brown pelicans from
Florida to Louisiana. A total of 765 young pelicans were transplanted in 1971 and
began breeding and increasing in numbers until a severe die-off in 1975. The die-off
was attributed to endrin. Eggshell thickness gradually decreased to 14% below
pre-DDT era thickness by 1974 and then began to increase thereafter. Endrin use
was curtailed in 1976 and breeding improved to 1.47 fl edged per nest. The authors
considered fl edgling rates of 1.2-1.5 to be necessary to maintain a stable population.
DDE residues in eggs peaked at 1.36 ppm in 1972 and decreased to 0.92 ppm by
1976. The authors concluded that DDE-induced eggshell thinning was not high
enough to interfere with reproductive success.
Blus et al. (
1979b
) reported on DDT residues, eggshell thinning and reproduction
in brown pelicans in South Carolina and Florida. Samples of the primary food item
of the breeding colonies, the Atlantic menhaden, were collected in 1974 and 1975
from regurgitated stomach contents in South Carolina and analyzed for DDT. From
1969 to 1975, the trend in total DDT residues in eggs from South Carolina was
steadily downward from 7.81 to 1.80 ppm. DDE decreased from 5.45 to 1.40 ppm
during the same period. By 1975, residues of parent DDT were barely measureable.
Menhaden DDE residues were 0.016 ppm in 1974 and 0.014 ppm in 1975. Egg shells
increased in thickness from 17% thinner to 10% thinner than pre- DDT era eggshells.
Florida populations had been stable for several years. South Carolina populations
were increasing. Fledgling rates in the South Carolina populations in 1975 were
adequate to maintain a stable population.
Blus (
1982
) provided further interpretation of the relationship of DDT residues
in brown pelican eggs to reproductive success. By collecting single eggs from a
marked nest and following productivity in the same nest, residues of DDE could be
associated directly with reproductive success. The critical level of DDE residues in
eggs was 3 ppm. Residues below this level generally produced, at most, a slight
reproductive effect. Residues in excess of this level were associated with a substan-
tial effect on reproduction. A residue of 4 ppm in eggs was associated with total
reproductive failure.
An overall decline in organochlorine residues in brown pelican eggs is illustrated
in data from Blus et al. (
1979b
), which is plotted in Fig.
21
below.
I n
1983
, Anderson and Gress published an update on the status of populations
of brown pelicans in the Southern California Bight. DDE residues in eggs and
eggshell thinning were not measured. Fledgling rates were closely associated with
stocks of northern anchovies since about 1974. The population of brown pelicans on
Anacapa Island continued to increase even though fl edgling rates were below one;
“…1980 was the fi rst year when reproduction was probably not drastically affected
by pollution…”.
Blus (
1984
) reported a comparison of regression and sample egg methods for
predicting the reproductive effects threshold for DDE. Brown pelican eggs from
California, Florida, Louisiana, and South Carolina were analyzed for DDE residue,
eggshell thinning, and these were then compared to reproductive success. Eggshell
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