In a recent 10-year study of their population, only 30 blue whales were spotted even though they need to surface often, taking breaths every two minutes on average, he said. It's very difficult to find out if whale stocks are increasing or decreasing. The rarer and more dispersed whales are, the less accurately they can be counted. The large whales have been protected from hunters for three decades. Pollution, depletion of the ozone layer and ultraviolet radiation pose the biggest threats today.
Ozone depletion is just as deadly as the whaler's harpoon.
But some scientists say the anecdotal evidence on whales is encouraging. Cooke said Icelandic data on whale sightings suggest the blue whale is on the increase in the northern hemisphere. He said there may be more than 1,000 in northern waters. The IWC's chairman Peter Bridgewater said signals picked up by national defence monitoring systems may also suggest a rise in the blue whale population. The blue is a member of the balleen, or toothless, whale family.