North Atlantic humpback whales have recovered from years of whaling, but a precise pre-whaling number estimate is key to defining that recovery, scientists say.

To that end, researchers from Stanford University, the Wildlife Conservation Society, the American Museum of Natural History and other organizations are using genetic analysis to estimate the pre-whaling population of North Atlantic humpback whales.

They estimate humpbacks existed in numbers of more than 100,000, a figure lower than previously calculated but still two to three times higher than pre-whaling estimates based on catch data from whaling records, a WCS release said Thursday.

"We're certain that humpback whales in the North Atlantic have significantly recovered from commercial whaling over the past several decades of protection, but without an accurate size estimate of the pre-whaling population, the threshold of recovery remains unknown," Stanford researcher Kristen Ruegg said. "We now have a solid, genetically generated estimate upon which future work on this important issue can be based."

Humpbacks, which can reach 50 feet in length, were hunted for centuries by commercial whaling fleets in all the world's oceans, with their numbers in the North Atlantic eventually being reduced to just hundreds before whaling bans went into effect and the creatures began a remarkable comeback.

"We have spent a great deal of effort refining the techniques and approaches that give us this pre-whaling number," Steve Palumbi of Stanford said. "It's worth the trouble because genetic tools give one of the only glimpses into the past we have for whales."