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.

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