Twice each year, from December to May, the population of the California, or eastern
North Pacific, gray whale passes through southern California on its migration between
breeding and calving lagoons in Mexico and summer feeding grounds off Alaska. During this
journey, most gray whales stay close to the coastline and pass through the Santa Barbara
Channel and the Santa Maria Basin--areas where most of the offshore gas and oil
development activities in southern California are concentrated.
Recently removed from the Federal list of endangered species, the gray whale is an
important component of California marine mammal wildlife. The possible effects of outer
continental shelf (OCS) activities on this population are of particular concern. Gray
whales may be vulnerable to potentially adverse impacts from both routine offshore
activities and accidental events such as oil spills.
Routine OCS activities that may affect gray whales include operational discharges,
geological seismic surveys, drilling, vessel and air traffic, and pipeline and platform
construction. Produced waters and drilling muds and cuttings are routinely discharged into
offshore marine waters during operations. These discharges are regulated by the
Environmental Protection Agency. Drilling discharges might cause eye irritation to a gray
whale if the animal were in the immediate vicinity, but the settling of large particles
and the dilution of fine particles and soluble compounds are probably rapid enough that
this potential exists only within a few hundred meters of the source.
Many of the sounds produced by OCS activities are within the frequency range of sounds
produced by and, thus, probably heard by the California gray whale. The acoustical pulses
used in seismic surveys off California are generated by airguns or waterguns. If
seismic-generated sound waves exceed the "background" noise, they could
interfere with gray whale communication or disturb behavior.
In controlled experiments, gray whales have exhibited startle
responses, avoidance reactions, and other behavioral changes when exposed to seismic
pulses at sound levels corresponding to a distance of 2 to 3 miles from an airgun setup
off the California coast. In recent biological opinions issued for OCS activities, the
National Marine Fisheries Service, the Federal agency responsible for protecting the gray
whale, has concluded that geophysical seismic activities may create a stressful situation
for gray whales, but are not likely to inhibit their migration.
In experiments conducted off central California, migrating gray whales have been
exposed to underwater playbacks of drillship, semi-submersible, drilling platform, and
production platform sounds. Avoidance reactions to all sounds were observed at levels
corresponding to distances of about 3,300 feet from a drillship and only 12 to 65 feet
from the other three sources.
Noise from helicopter and service-vessel traffic may startle gray whales or interfere
with their sound reception. The reactions of gray whales to aircraft and/or certain
aircraft noises have been examined in several studies. Although sensitivity varies with
whale activity, reactions including hasty dives, turns, and other altered behaviors have
been observed. There is no evidence that single or occasional aircraft overflights cause
long-term displacement. Service vessels comprise the greatest amount of marine traffic
associated with OCS activities. Although gray whales seem to ignore most low-amplitude
vessel sounds, avoidance and approach responses have been observed in field studies. There
is little information on the sound levels involved. Migrating gray whales have been
observed to avoid the approach of vessels to within 650-1,000 feet.
In one study, wintering grays were observed to become less sensitive to boats as the
winter progressed. There also seems to have been a tendency for wintering gray whales to
approach rather than flee from vessels in recent years. However, gray whales reportedly
did abandon one wintering lagoon when ship traffic became heavy.
During the winter of 1991-1992, a gray whale monitoring study was conducted in
conjunction with offshore pipeline and cable-laying activities in the Santa Barbara
Channel. Although no entanglement, physical contact, or obvious startle reactions were
recorded, gray whales were observed to change course in apparent reaction to construction
activities. Relatively few gray whales passed through the construction area itself, but
there was no evidence that the construction activities interfered with their migration.
Oil spills pose a number of risks to cetaceans such as gray whales. Recent studies on
the possible effects of oil on marine mammals have focused on the animals' ability to
detect and avoid oil, behavioral effects, thermal effects, and physiological effects due
to contact, inhalation, and ingestion of oil.
Experiments have shown that dolphins can detect and will avoid a surface layer of oil.
Baleen whales, such as the gray whale, also appear to be capable of detecting oil. A field
study of the reactions of migrating gray whales to naturally occurring oil slicks from
seeps in the Santa Barbara Channel recorded mainly subtle and short-term responses like
changes in direction.During the 1969 oil spill in the Santa Barbara Channel, gray whales
were beginning to arrive in the Channel on their northward migration. By April, as much as
70,000 barrels of oil had been released, and as much as 800 square miles of water surface
may have been contaminated. Gray whales were observed moving northward through the slick
during this period. Although six dead gray whales were recovered from the area during the
2 months following the spill, no link was established between oil contamination and
mortality, and no effects on the gray whale population or migration were observed.
Studies have shown that cetacean skin is nearly impenetrable to even the highly
volatile components in oil. This indicates that contact with oil probably would be less
harmful to an animal such as a gray whale than previously believed. However, the toxic,
volatile fractions in fresh crude oils could irritate and damage cetacean soft tissues,
such as the mucous membranes of the eyes and airways. The effects could be as severe as
death in extreme cases. A gray whale unable to leave the area during the first few hours
after a spill, when vapor concentrations are still high, would inhale vapors and might be
harmed in this way. The extent of injury would depend on the health of the animal and its
response to stress.
Oil could also adhere to the fringed baleen plates that gray whales use to filter their
food, blocking the flow of water and interfering with feeding. A study of the fouling
effects of oil on the baleen of several species, including gray whales, concluded that a
spill of heavy oil or residual patches of weathered oil could foul plates enough to
interfere with feeding efficiency for several days, and that such effects would probably
be cumulative in heavily fouled areas like the center of a spill or a contaminated bay.
Gray whales could also ingest oil-contaminated prey or bottom sediments. Gray whales,
which are mainly bottom feeders, are among the most vulnerable of the baleen whales to
these effects. However, most of this risk would occur on the species' Alaskan feeding
grounds. Migrating gray whales, which generally do not feed, are probably much less
vulnerable to the effects of spilled oil. Thus, as indicated by the 1969 spill, a spill
offshore California would likely present a much smaller risk to gray whales than one
occurring in Alaskan waters.
Selected Readings
Bonnell, M.L., and M.D. Dailey. 1993. Marine mammals of the Southern California Bight.
Pp. 604-681, in, M.D. Dailey, D.J. Reish, and J.W. Anderson (eds.), Ecology of the
Southern California Bight: A Synthesis and Interpretation. University of California Press,
Berkeley/Los Angeles
Geraci, J.R., and D.J. St. Aubin (eds.). 1990. Sea mammals and oil: confronting the
risks. Academic Press, Inc., San Diego. 282 pp.
Jones, M.L., S.L. Swartz, and S. Leatherwood (eds.). 1984. The gray whale, Eschrichtius
robustus. Academic Press, Inc., Orlando, Florida. 600 pp.
Richardson,W.J., C.R. Greene,Jr., C.I. Malme, and D.H. Thomson. 1995. Marine Mammals
and Noise. Academic Press Inc., San Diego. 576 pp.
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