Northern right whales are some of the world's rarest mammals. No more than 300 of these spectacular animals, which ply coastal waters from Florida to the Bay of Fundy, in Canada, are thought to exist, the population down because of hunting from several thousand a century ago.
The whale, Eubalaena glacialis, has been a protected species for about 65 years, and its numbers were thought to be growing. Yet they went into slow decline in the 1990s, according to research published today in Nature by specialists from the Woods Hole Oceanographic Institution, in Massachusetts.
This is the worst of news, but also possibly the best for the embattled species. The researchers, Dr Masami Fujiwara and Dr Hal Caswell, believe they may have come up with a plan to reverse the decline and prevent the northern right whale's extinction.
They took information from 10,000 sightings of identifiable individuals and processed it using computer models. The goal was to identify what was behind the decline - an inability to find mates in the vast Atlantic Ocean, known as the Allee effect, perhaps, or injuries caused by fishing tackle or ships.
They discovered that the fall in numbers was occurring because an unexpectedly high number of female right whales were dying.
"Increased mortality of mother whales can explain the declining population size, suggesting that the population is not doomed to extinction as a result of the Allee effect," they write.
They go even farther, suggesting that saving only two or three females from early death "would increase the population growth rate to replacement level", and so save the species.
These medium-sized baleen whales - baleen means their mouths contain plates of whalebone, to strain plankton - are between 14 and 17 metres long and have a distinctive black body, with no dorsal fin and a large head.
Females take about nine years to reach sexual maturity, after which they produce calves only every three to five years. In 1980, their life expectancy was more than 50 years, but by 1995 this had fallen dramatically, to fewer than 15. Pregnancies showed the whales could find mates despite their low numbers, ruling out the Allee effect.
The much shorter life expectancy means, however, that the number of opportunities to give birth fell from about five to little more than one by 1995. The females are not living long enough to allow the population to increase.
"Right whale conservation efforts are directed towards reducing mortality due to entanglement and ship collisions. Because the population is so small, a single death represents a significant mortality rate," the authors write.
The key to conservation is making sure that female whales are saved. Entanglement is a significant problem, with surveys showing that more than 60 per cent of right whales have scars from lobster pots, gill nets and other fishing gear. Their work also seems to show that changes in food supply, due to climate change, may also be having an impact on survival.
It remains unclear whether directing conservation resources towards protecting the females in particular will be enough to save the species. "There are now fewer than 300 individuals, and the species may already be functionally extinct."
A central element of the research is that just a few individuals are, apparently, enough to tip the balance. Focusing on the females may represent a lifeline for the northern right whale and help prevent the loss of yet another species through the depredations of humankind.