When a particular species is decimated by centuries of hunting, it's often difficult to accurately say what a "normal," fully recovered population might number.

When it comes to whales, that guess has become even more complex thanks to DNA research that shows numbers of pre-hunt populations may be vastly underestimated. It's only been since 1986 that a ban on whaling has allowed populations to slowly recover — but already discussions are underway to potentially allow some whaling to continue. Such a decision would be based on old estimates of population, mostly conducted by people working for the International Whaling Commission. Rules in place say that certain species may be considered for hunting again once their levels climb back to 54 percent of pre-hunting populations.

However, the controversial genetic research published in 2003 by Stephen Palumbi and Joe Roman of Stanford University's Hopkins Marine Station calls the IWC's numbers into question. From New Scientist,

The IWC believed that before large-scale whaling began, the North Atlantic was home to about 20,000 humpback whales. With a current population of about 10,000 and rising, this meant that under the 54-percent rule, hunting could soon resume. But Roman and Palumbi estimated the pre-exploitation population was more than 20 times as great, at 240,000. Globally, they suggested, there may have once been 1.5 million humpbacks, rather than the 100,000 estimated by the IWC.
Obviously, those numbers blow the IWC's estimates out of the water and would mean recovery is the extremely early stages — something pro-whaling nations are not so interested in hearing. Further adding scrutiny to the IWC's science has been the discovery of "cooked" logbooks from nations like the Soviet Union. According to New Scientist, from 1959 to 1961, Soviet whaling fleets killed 25,000 humpback whales in the Southern Ocean, while reporting a catch of just 2,710 to the IWC. The number of whales brought home also probably does not equal the number killed at sea, says Roman. Many often escape from whalers only to die of their harpoon injuries later — or are hit by ships, snagged in nets, etc. 

All of this points to the scenario that whales, at one point, were the dominant species in the oceans. Mass-scale harvesting not only decimated their populations, but also shifted entire ecosystems. Continued research on what is healthy for the sea in terms of numbers — and not just hunting — will be crucial for these gentle giants going forward.

via New Scientist