Pre-Whaling Humpback Population Estimates Could Help Recovery Measures
February 14, 2013

Pre-Whaling Humpback Population Estimates Could Help Recovery Measures

Brett Smith for - Your Universe Online

For over 50 years, conservationists have been championing the protection of humpback whales–and as the population begins to recover from decades of whaling, scientists are starting to ask about the size of the whale population before they were hunted en masse.

Using a refined genetic analysis, a group of American scientists has estimated the humpback´s historical population size at more than 100,000 whales, according to their report in the journal Conservation Genetics. The new estimate is lower than a previous genetic analysis, but two to three times higher than estimates that are based on historical whaling records.

"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," said lead author Kristen Ruegg of Stanford University. "We now have a solid, genetically generated estimate upon which future work on this important issue can be based."

Whaling fleets in the 19th and 20th centuries decimated the humpback population by about 90 percent, according to some estimates. The precipitous drop in population led to the marine mammals receiving protection status from the International Whaling Commission (IWC) for North Atlantic waters in 1955.

Since then, North Atlantic humpbacks have made a remarkable comeback, with some estimates pegging the current population at over 17,000 animals. The encouraging signs have conservation scientists shifting their focus when studying the majestic creatures.

"Our current challenge is to explain the remaining discrepancy between the historical catch data and the population estimate generated by genetic analyses," said Howard Rosenbaum, study co-author and Director of the Wildlife Conservation Society's (WCS) Ocean Giants Program. "The gap highlights the need for continued evaluations of whale populations, and presents new information informing the debate and challenges associated with recovery goals."

Historical whaling data suggests a previous population size between 20,000 and 46,000 whales, and a previous study that analyzed the mitochondrial DNA of North Atlantic humpbacks suggested an average population of about 240,000 individuals.

In the latest study, the team increased the accuracy of their genetic analysis by measuring nine segments in the DNA sequences, instead of just the one DNA segment used in the previous study. The more refined process suggested that the North Atlantic once held between 45,000 and 235,000 humpback whales, translating to an average estimate of 112,000 animals.

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

"The International Whaling Commission reviewed the results of the first study and recommended we improve the method in six specific ways,” he added. “We've done that now and have the best-ever estimate of ancient humpback populations."

“These genetic estimates greatly improve our understanding of the genetic diversity of humpback whales, something we need to understand the impact of past hunting and to manage whales in the uncertain future,” said co-author Scott Baker, Associate Director of Oregon State University's Marine Mammal Institute.