Cetaceans—mammals of the sea, a group including whales, dolphins, and porpoises—have auditory systems similar to man, though much more sensitive. Because of poor visibility conditions underwater, hearing is much more important than seeing. Hearing, interpreting, and acting on auditory information is an oceanic matter of life and death.
In water, the velocity of sound is 4.3 times greater than in air. Sounds are intensified, and marine mammals today are being increasingly stressed by noise pollution in the sea. The sources are many: shipping, oil and gas development, seismic surveys, marine construction, and military operations. Each of those noise sources is increasing, further intensifying their damage to life in the sea.
Of the cetaceans, whales are the most affected by noise pollution. They must vocally communicate over long distances to locate mates, food, friend, and foe, as well as to mark their territory. Scientists even have recorded songs of specific whales. In addition to vocalizing, whales also have highly sophisticated sound-ranging systems. In short, their lives depend on their uses of sound in the sea. But that cetaceous communication channel is often drowned out by man-made noise.
Interaction between mankind and animals of the sea is a classic example of multiple-use conflicts. And the animals seem to be losing. This is especially true in the coastal ocean from shoreline to a few miles seaward. Here are the fishermen, merchant ships, oil and gas production, and many military-operation areas. This also is often a region where whales congregate to feed and mate. And their migratory tracks frequently run through these coastal areas.
Background noise level in a calm sea is about the same as a sound source of 100 decibels three feet distant. Whale vocalizations would be about 120 decibels; by comparison, a large tanker would radiate noise in the range of 190–200 decibels. This means that ship noise can interfere with a whale’s hearing and communicating abilities. If the ship is close, the animal may become disoriented and get run over before it can take evasive action.
The National Marine Fisheries Service of the National Oceanic and Atmospheric Administration (NOAA) reports that in U.S. waters 292 whales were struck by ships from 1975 to 2002. About 68 percenet were mortally injured. Two species, fin and humpback, accounted for 40 percent of the strikes.
The majority of those incidents were off the East Coast, followed in frequency by the West Coast and then Alaska. The data are somewhat old, but given the rapid annual growth in coastal-ocean activities, the current situation is considerably worse today. Many of the whales reported as injured undoubtedly will succumb later to their injuries. In addition, we occasionally see images in the media of dead whales impaled on the bows of ships, while the crew knew nothing about it until entering port. Therefore, the NOAA numbers may be considered very conservative.
NOAA and the U.S. Coast Guard are working to set up “whale-safe” rules and routes along parts of the U.S. coastline where most mishaps have occurred. Mandated speed reductions for shipping seem an effective measure. A ship speed of 10 knots gives a survival rate 40 percent greater than for a vessel moving at 20–25 knots. Also, coastal traffic corridors near ports are being set up to avoid traditional coastal whale-migration routes. Better knowledge of timing and location of migrations also will reduce marine mammal/ship encounters.
A much more difficult situation is the conflict related to the U.S. Navy’s need to use its high-powered sonars in routine training operations. Acoustically speaking, the more power (noise) you can jam into the water, the greater the detection range. Considerable hard evidence indicates that these activities have resulted in injuries and deaths of whales.
Most deaths seem to have been the result of strandings along shorelines. The animals appear to have lost their sense of direction, and autopsies often show serious internal injuries. Mass strandings of marine mammals have been correlated to nearby naval operations.
Environmental groups have undertaken various legal actions to have the Navy greatly reduce or stop the use of high-powered sonar systems. They have had some early victories in the lower federal courts, and the issue was heard by the Supreme Court in late 2008. It ruled in favor of the Navy. Few people disputed the Navy’s need to fully exercise its seagoing systems in peacetime. The legal challenges were more intended to sharply reduce the “when,” “where,” and “how much.”
The Navy has taken aboard the concerns of the environmental groups and realizes it must do more to mitigate harm to our mammalian cousins in the sea. A significant amount of Navy research funding has gone into marine-mammal studies to ascertain how whales and navies can coexist at sea.