Marine biologists are alarmed by the recent deaths of four North Atlantic right whales, one of the most endangered cetaceans on the planet. Only 325 to 350 of the mammoth whales remain, due largely to the ravages of 19th-century hunters. Still, the population has rebounded slightly over the past few years; in 2000, it was estimated that the population numbered just 300 individuals. How do scientists make such an accurate right whale count?
Partly with the assistance of generous shutterbugs, and partly by keeping aerial tabs on the species' annual birth-giving practices. Fortunately for the marine biologists who track the right whale, the animals bear unique calluses on their heads. These areas of thickened skin are present at birth and are hued white, yellow, or pink as whale lice make their home there. (The lice are actually tiny crustaceans rather than insects.) Scientists are therefore able to use photographic evidence to differentiate one individual from another.
Over the years, the New England Aquarium, which spearheads the efforts to accurately count the North Atlantic right whale, has examined and catalogued hundreds of thousands of pictures from its own researchers, other marine biologists, wildlife officials, Coast Guard patrols, and even amateur whale watchers. These pictures are almost exclusively snapped in areas known to be the species' favorite haunts, such as the Bay of Fundy off Nova Scotia, Cape Cod Bay, and the coastal border between Florida and Georgia, where calves are born each winter.
In addition to analyzing photographs for evidence of uniquely marked whales, the New England Aquarium researchers and their affiliates also conduct an annual aerial survey of the species' southern birthing grounds. They spend about four months swooping over the area, covering about 1,000 square miles per day and taking pictures of the 18-foot-long newborns. The number of calves born varies widely from year to year; in 2000, for example, the surveyors recorded just one birth, compared to a record 31 the following year. No one's quite sure why the birth rate swings so dramatically, but it probably has something to do with the fluctuating amounts of scrumptious plankton in the whale's habitat.
Marine biologists generally assume that a quarter of the calves will never reach adulthood. Predation by sharks and orcas plays a small role, but the lion's share of the unfortunate right whale deaths are caused by either ships or fishing nets. The speed of today's vessels means that the slow-moving whales have scant opportunity to get away; at least 60 percent of North Atlantic right whales bear scars from run-ins with either boats or fishing equipment. The calving surveyors do their best to warn fishermen and freighter captains to steer clear of the birthing grounds.
The New England Aquarium also collects information on any right-whale carcasses that turn up, either washed ashore or out at sea. Sometimes, however, a deceased right whale's body escapes notice, especially when the death takes place in deep northern waters. The rule of thumb is that, if an individual isn't spotted or photographed for six years, it's judged to have passed away.
Explainer thanks Tony LaCasse of the New England Aquarium.