Environmental Engineering Reference
In-Depth Information
Table 23
Early recovery of brown pelican reproduction off Baja and California coasts. Table 1 in
Anderson et al. (
1975
) reproduced with permission from the author and from AAAS
taken from each of 93 marked nests. In this way, residue level and shell thinning
could be related directly to nest success. The effects of DDE on eggshell thinning
and reproductive success were confounded by dieldrin. Reproductive success was
normal in those nests in which a sample egg contained less than 2.5 ppm DDE.
Anderson et al. (
1975
) published the fi rst report of the recovery of the brown
pelican following the ban of DDT in 1972. The major source of DDT for the study
populations was the wastes of the DDT manufacturer being released into the ocean
by way of the Los Angeles County Sanitation District's waste water outfall at
White's Point. Releases were greatly reduced after April, 1970. Recovery of brown
pelican reproduction on offshore islands to the north and south improved quickly
during the period 1971-1974 (Table
23
).
Fledging rates increased from 0.004 to 0.922. Thicker shelled eggs and fewer
broken eggs were observed over time during this period. The recovery was not com-
plete, as a fl edging rate of 1.2-1.5 is needed to achieve a stable population.
Direct observation confi rmed that the northern anchovy was the major food item
for this breeding colony of brown pelicans. The authors (Anderson et al.
1975
)
stated: “During banding at Anacapa from 1972 to 1974, we examined stomach
contents regurgitated by young pelicans; the material consisted almost exclusively
of anchovies. Our observations of feeding adults before and during the breeding
season also indicated a heavy reliance on anchovies.”
Residues of DDE in northern anchovies decreased 27-fold from 1969 to 1974
while during the same period, DDE in brown pelican eggs decreased ninefold
(Table
24
). The slower decline in egg compared to fi sh residues suggests that at a
steady-state, the 150 ppb total DDT measured in northern anchovies in 1974 would
result in an egg residue that is below the threshold for a reproductive effect.
Anderson et al. (
1977
) continued to study brown pelicans on Anacapa Island in
1975. The only breeding colonies in California observed by these investigators were
on Anacapa Island and nearby scorpion rock. Only four eggs were collected and
three of these were putrifi ed. Lipid content of eggs was assumed to be 5%. DDE egg
residue analysis, shell thickness and productivity appeared to have leveled off in 1975,
following the recovery from 1969 to 1974. PCB egg residues were 5-10 ppm during
this period. The data are summarized in Fig.
19
. PCBs may have affected reproduction,
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