It’s All in the Genes – Have Humpbacks Really Recovered?

I was concerned to read today that the World Conservation Union (IUCN) has downgraded the status of the majority of the world’s humpback whale populations. They have been reclassified from the status of “vulnerable” to that of “least concern”. Exempt are small population in the South Pacific and the Arabian Sea, which maintain their endangered status. To my surprise, Southern Right Whales have also been down listed. Of course it is encouraging to see that these species once hunted to the brink of extinction are making a slow recovery, what concerns me is the baseline we are using to suggest that they are well on their way to approaching pre-exploitation levels.

Two reasons underlie my skepticism. Firstly, to suggest any species of great whale may be ‘bouncing back’ is an undeniable win for whalers who are quick to advocate a renewed kill, citing that populations can now afford to lose a few animals to the harpoon.

Perhaps what is most disturbing and rarely considered, is how we decide a species has recovered to the point where there are enough animals in relation to historic levels, that they are viewed as recovering sufficiently.

In 2003, a paper published in the journal Science entitled Whales before whaling in the North Atlantic, by US marine ecologists Steve Palumbi and Joe Roman, highlights why we may be making a diabolical error when it comes to estimating safe population levels for great whale species based on what we think we know about historic population levels.

It is the role of scientific experts at the International Whaling Commission (IWC) to attempt to estimate the number of whales before whaling began in earnest in the seventeenth century. Based on whaling logbooks and other historical records, the commission for example calculated that there were probably around twenty thousand humpback whales in the North Atlantic. Therefore this is the baseline we now use to measure the recovery of this species in that region.

However, Palumbi and Roman have challenged these conclusions for humpbacks, and other great whale species, suggesting that early populations were far larger than IWC estimates. Their findings published in Science are summarized by Professor Callum Roberts in his book "The Unnatural History of the Sea":

“Genetic variability increases with the size of a breeding population. This enables population size to be estimated from analysis of genetic material in tissue samples. Because whales have a long generation time, it takes a very long time for genetic variability in their populations to equilibrate after a change in population size. The genetic heterogeneity of today’s whale populations still reflects population sizes from days before large-scale commercial whaling. Genetic estimates by Roman and Palumbi put the pre-whaling population size for humpback whales at 240 million, nine to twelve times the estimate from whaling records.”

As a keen student of whaling history and literature, these numbers seem far more in line with the kind of whale numbers seen and described by early travelers. In addition, relying on whaling records is notoriously dangerous as many records have been lost, while those that remain are fraught with inaccuracies and omissions. Furthermore, whalers in the twentieth century often failed to record or declare their kills.

Whatever the reason for the difference suggested by genetic data and historical accounts, it remains that we may be greatly overestimating the recovery of whale populations. According to IWC estimates, humpbacks among other species are well on their way to recovery, yet, the truth could be very, very different, and such a false assumption may only imperil whales once more.