WHALES
P1618
By Tony Corey
They are the largest animals on the planet. They are mammals but they are completely aquatic, feeding, mating, calving, and suckling their young in the water. They are thousands of years old and ubiquitous throughout the world, but they remain elusive and mysterious.
Whales are among the oldest, most diverse group of marine mammals, dating back 40 to 50 million years, according to fossil evidence. They share with dolphins and porpoises the taxonomic order cetacea. Within this order, they fall into two suborders, according to their feeding habits: mysticeti and odontoceti. Mysticetes are baleen whales, which feed by filtering animal plankton and small schooling fish from the water through bristlelike baleen plates growing from the upper jaw. Odontocetes are toothed whales, whose conical teeth grasp prey consisting primarily of squid and fish.
Defined in large part by their size, whales exhibit considerable variation among species. The blue whale, the largest animal ever to exist, can grow to 90 ft (27 m) and 125 tons. At the other end of the range, the dwarf sperm whale may be only 7 to 9 ft (2.5 m) and just over 600 pounds (280 kg).
Huge size suits these creatures to life in the ocean. With their massive bulk supported by water, they take maximum advantage of evolutionary adaptations for specialized swimming. With body shape streamlined to reduce drag, limbs tapered into powerful flippers, and horizontally flattened tails, or flukes, propelling them, they can sustain speeds up to 25 mph. Moving through the water at different depths, they may stay submerged anywhere from one minute to two hours.
Their respiratory systems are specially adapted for diving. Highly efficient lungs allow exchange of 80 to 90 percent of air with each breath. The additional capacity to draw on oxygen reserves chemically stored in blood and muscles and to work muscles anaerobically (without oxygen) permits maximum locomotion during long dives. As whales surface, they forcefully expel moist air through a blowhole on top of the head. The blowhole differs from one species to another—single, divided, off-center—and the blow itself can be distinctive enough for identification. The Northern right whale, for example, has a divided blowhole and a unique V-shaped blow; the sperm whale has a blow that angles forward at 45 degrees; and the blue whale exhibits a tall, dense blow that can shoot up to 30 feet (9 m).
Along with the blow, the dorsal fin can characterize a specific whale species. Triangular to falcate (sickle-shaped) in shape and varied in size from the low hump of the sperm whale to the 6-foot fin of the male killer whale, the dorsal fin helps stabilize the animal as it swims. The right whale, alone among the North Atlantic baleen whales, has no dorsal fin.
Environment and society
As mammals living in the cold ocean waters, whales have evolved adaptations for maintaining body temperature and water/salt balance. Their immense bodies present a small surface-to-volume ratio that combines with the insulation of a subcutaneous blubber layer to conserve heat. Blubber also provides a reservoir of freshwater which, along with water ingested in food and inspired air, maintains the mammals' freshwater balance against a saltwater environment. In addition, they excrete excess salt via their kidneys.
Such evolutionary progress would seem to give these leviathans free reign of the oceans, but like other marine animals, whales delineate their habitat primarily by food and reproductive needs. Many Atlantic whale species migrate north in spring to feed in productive New England waters. But for breeding and calving they seek out warm waters farther south. Females typically bear one calf every two to three years after gestation periods of 10-14 months, with lactation continuing for a few months to a year. Some species produce young less frequently: The sperm whale may go six years between births. Depending on species, these long-lived creatures may live 40, 70, even 90 years.
For the most part, whales are social creatures, swimming in pods made up of two or three to more than 50 (killer whales) or even 100 (pilot whales) individuals. Some species, including the minke whale, are often solitary, but most species form aggregations of varying sizes for feeding. Female-calf pairs also tend to aggregate in the protective waters of nursery areas.
The human factor
Their sociability sometimes gets these creatures in trouble. Mass strandings, according to one theory, stem from the social cohesion that causes a whole group of whales to follow when one—distracted by illness, disruption of its "sonar," or interference with its ability to navigate by the earth's magnetic field—heads into the beach.
More positive social behaviors earn whales particularly fond attention among humans. Their use of sound, or echolocation, both to locate prey and to communicate, becomes "singing" for human purposes. Songs of the humpback whale, for example, are available as recordings for relaxation tapes and other "musical" uses.
Whales' acrobatic behaviors also engage humans through whale watches and marine life exhibits. Breaching (leaping into the air), bowriding (swimming in the wave made by a moving boat, often at the bow), lobtailing (forcefully slapping the water with the tail), and spyhopping (poking the head vertically out of the water) are common behaviors among many species. The killer whale, also called orca, is especially acrobatic and therefore very popular in marine life attractions.
These benign human associations with whales cap a history of much more aggressive interactions. Even 1,000 years ago, humans hunted whales in the North Atlantic, according to Robert Kenney, University of Rhode Island marine biologist and right whale expert. The Basques, the world's first commercial whalers, were hunting whales from their settlements in Labrador by 1530. By the time the Yankee whaling industry got under way, the Northern right whale was commercially extinct. Today, the right whale is the most endangered species in the world, numbering fewer than 300 individuals in the western North Atlantic.
No longer widely hunted for food, oil, or whalebone, whales are nonetheless susceptible to injury from humans. Entanglement in fishing gear is a hazard that now draws stringent management intervention, with regulations ranging from gear modifications to fishing area closures. More deadly, though, are ship strikes that account for a significant number of whale deaths. Solving this problem requires international initiative and cooperation because of the international nature of marine commerce and the economic disruption of rerouting shipping traffic.
Many whale species are now federally protected, with a number of initiatives in effect to minimize harmful whale-human interactions. Breakaway fishing gear, 500-yard buffer areas, early warning systems to alert commercial and military vessels about whale sightings, disentanglement response teams, and ongoing public education efforts help keep these marine mammals protected in reality as well as in regulatory status.
Information for this article drawn from Guide to Marine Mammals & Turtles of the U.S. Atlantic and Gulf of Mexico, written by Kate Wynne and Malia Schwartz, illustrated by Garth Mix. Available from Rhode Island Sea Grant; also from http://www.cetacea.org/; and from personal communication with Robert Kenney.
posted 5/01