To gear up for Discover Science Weekend, November 11–13, we’ve put together a guest blog series featuring some of the researchers who will be joining us for the event. Our second post comes to us from Trevor A. Branch, associate professor at the School of Aquatic and Fishery Sciences at the University of Washington, writing on the topic of “Antarctic blue whales: nearly whaled to extinction, now there is some hope.”
Blue whales are the largest animals ever to have lived on the Earth—larger than any dinosaur—and no blue whales are as big or used to be as numerous as those that feed in the krill-rich waters of the Antarctic. Some may have exceeded 100 feet (30.t m) in length, with the tongue alone weighing more than an adult elephant. Initially, Antarctic blue whales escaped the whaling plunder of the Yankee whalers’ Moby Dick era because they were too fast to catch, and sank upon death, but the industrial whaling era came upon them with a vengeance starting in 1904. These developments included fast boats, explosive-tipped harpoons, stern slipways that allowed on-board processing, air pumps to keep them afloat, and eventually floating fleets of catcher vessels, supply vessels and processing motherships that left no refuge for blue whales anywhere in the world.
In one year, these massive southern ocean whaling fleets caught more than 31,000 blue whales—twice today’s global population of blue whales. By the 1960s Antarctic blue whales had been reduced to less than a half percent of their original population size of 239,000. Worse was to come: despite a global ban on blue whales, Soviet whalers continued hunting them—illegally—using the biggest whaling fleets yet assembled, and the population collapsed further to just 360 individuals, a mere 0.15 percent of their pre-whaling levels.
Since 1973 though, whaling has ended, and the population has grown over time, reaching 2,280 in 1998, and likely increasing at seven percent per year since then. How do we know their trends in numbers over time? I used mathematics and computer models and applied these to data from expensive ship-based sighting surveys around the Antarctic. It’s surprisingly difficult and expensive to count blue whales since the ocean is vast and it’s hard to find a small number of gigantic yet elusive whales. Newer methods rely on taking photos of individuals and seeing how often you identify the same whales again from their splotch patterns. Such mark-recapture methods have suggested Antarctic blue whale numbers may have increased to 3,000–4,000: a remarkable tenfold increase from their lowest point.
The main threats to blue whales worldwide are deaths from being hit by ships and entanglement in fishing gear, with other concerns including loud noise from navy sonar and oil and gas exploration, pollution, and the harder-to-pin-down, long-term effects of global warming and ocean acidification on their main prey. All of these factors are minor, though, compared to the enormous toll that whaling took on blue whales during the 20th century.
Branch TA, Matsuoka K, Miyashita T (2004) Evidence for increases in Antarctic blue whales based on Bayesian modelling. Marine Mammal Science 20:726-754
Branch TA et al. (2007) Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean. Mammal Review 37:116-175
Trevor Branch is an associate professor in the School of Aquatic and Fishery Sciences at the University of Washington. He uses mathematical models and synthesis of available data to help conserve and manage large whale populations and fisheries. Among his scientific papers are 14 on blue whales including their status, distribution, subspecies separation, catches and trends over time.