Pollution poses a threat to marine mammals in many forms.
Plastic debris, including the ubiquitous beverage six-pack
rings, can become entangled around the snouts and necks of
seals and sea lions, preventing proper breathing and feeding.
Razor-thin nylon fishing lines slice off flukes and fins of
whales and dolphins who have become entangled in them.
Oil spills, such as the horrific 1989 Exxon Valdez spill in
Prince William Sound, Alaska, and the even more massive 2002
Prestige spill off the coast of Spain, may kill and injure
hundreds or even thousands of marine mammals and birds. Direct
damage includes the oiling of fur and feathers, which destroys
their insulating properties; injury to internal organs through
ingesting oil, especially as a result of cleaning it off fur or
feathers; and pneumonia from inhaling it, especially in the
case of whales and dolphins, who may inhale air through the oil
slick at the surface of the water. Finally, a frequently
overlooked threat to marine mammal populations is habitat
destruction from oil spills that occur as side effects of other
events; for example, acres of sea-grass beds vital to dugongs
(relatives of the manatee) were destroyed in the Persian Gulf
after the U.S. military operation Desert Storm.
Bottlenose dolphins, beluga whales, manatees, polar bears,
and other marine mammals are threatened by industrial pollution
(from sources such as heavy metals, PCBs and other organic
pollutants) and the destruction of coastal habitats by
agricultural runoff and other forms of environmental
degradation. The large-scale die-off of bottlenose dolphins
along the mid-Atlantic coast of the United States in the
mid-1980s may have been the direct or indirect result of
increasing levels of toxic waste from industrial sources in
these waters. Such pollutants can depress the immune system of
marine mammals, making the animals susceptible to diseases they
could normally fight off. Polar bears in Svalbard, Norway, are
exhibiting serious congenital abnormalities, the result of
exposure to toxic pollutants in their otherwise pristine
environment. These pollutants have apparently circulated to the
Arctic from distant sources in Europe.
Marine mammals are also threatened by increasing vessel
traffic. A prime example is the threat facing manatees in
Florida as growing numbers of high-speed boats take to coastal
waterways. These vessels often strike these slow-moving,
surface-dwelling herbivores, scarring them for life or killing
them. Right whales, the most endangered great whale species in
the ocean, are also threatened by ship strikes. Their slow,
surface-foraging behavior makes them highly susceptible to
collisions in the busy shipping lanes of the North American
Atlantic coast, their preferred habitat.
