Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
Table 2.4. Densities of Gray Whales (no./km2) Estimated From Aerial Surveys
in the Chirikof Basin.
Spr ing Summer - Fall Winter
Mar-May June- Aug Sep t-Nov Dec-Feb
Gray whale 0.01' 0.04~ 0.0.1~9~ 0
'~orthward migrating gray whales arrive at St. Lawrence Island in May and
June. Here we have arbitrarily assumed that one quarter of the gray whales
that are present in the summer in the Chirikof Basin have arrived by the end
of May.
2~rom Miller (1986). Densities are corrected for submerged whales, but not
for whales at the surface that were missed by the observer.
3~rom ~iller ( 1986). Densities observed on aerial surveys in September were
unexpectedly lower than summer densities. Migration out of the Bering Sea
begins in October and is completed by the end of December.
The Bering Sea walrus population has been estimated to be as large as
200,000-300,000 individuals. There are two major breeding populations, one in
the northcentral Bering Sea, the other in the southeastern Bering Sea. Most
females and young migrate from April-June to the Chukchi Sea. During this
period large numbers of walruses would be passing through the Chirikof
Basin. These walruses would be returning through the area from October-
December. Actual densities are not available for the Chirikof Basin, but
would clearly be extremely variable depending on ice concentrations and
movements. There would be few walruses in the Chirikof Basin in late winter,
except in the immediate vicinity of St. Lawrence Island. In summer the
walruses remaining in the Chirikof Basin would be present primarily at haulout
sites.
Alaskan Beaufort Sea/Corona Site
Several marine mammal species occur in this area. Table 2.5 summarizes
information available on densities of bowheads and ringed seals, especially
with regard to the "Corona" drillsite.
Chukchi Sea, Unimak Pass, Norton Sound*
Observed numbers and estimated densities of selected marine mammal
species are shown in Table 2.6 for selected seasons. Numbers of marine
mammals in these areas are variable within seasons and between years and are
difficult to summarize, being dependent on such factors as ice conditions.
For example, gray whales generally migrate south through Unimak Pass from
October to early January, but the exact timing of this migration varies from