Blue Whales are in the news just now, with a few feeding off the coast of California and around Sri Lanka where enthused whale watchers can see them. An adult that weighs 200 tons and is 30 meters long, twice the size of the largest dinosaur, is an extraordinary sight, and a rare one.
They were hunted almost to extinction in the 20th Century. In the Southern Ocean, 200-300 thousand of them once fed on the huge schools of krill feeding along the Antarctic ice edge. By the time the International Whaling Commission agreed 1n 1973 on a moratorium on hunting the Great Whales, perhaps 700 were left in the Southern Ocean. That’s very close to the edge.
Though the Southern Ocean population was by far the largest, smaller populations roamed elsewhere. In fact, three subspecies probably exist, varying a little in size at maturity and maximum size, isolated from each other in different oceans. One lives in the North Atlantic and the North Pacific, with 1-2,000 whales in each region, genetically connected by migrants through the Arctic ocean. Another population of about 2000 is the remnant of the slaughter of the last century in the Southern Ocean. The third, known as Pygmy Blue Whales because they only grow to about 24 meters long instead of 30, lives in the Indian Ocean, with somewhere between 2 and 10 thousand individuals.
So some recovery has occurred – about 7% increase overall per year. That sounds pretty good, but remember where they started. The population in the Southern Ocean is currently about 1% of its size before the whalers hunted them, and is still considered ‘Endangered’.
So what lies ahead for the Blue Whales? They turn up where krill become most abundant, even if only temporarily – this is what has brought some this year to the coast of California. An adult Blue needs a lot of food, and may eat about 4 tons of krill (40 million krill!) per day.
But we are also fishing for more krill in the Antarctic now. As well, as climate change continues to warm parts of the Antarctic, particularly around the West Antarctic Peninsula, krill competitors like salps are doing well. They are too low in food value to nourish whales, or humans for that matter.
An adult female Blue whale should reproduce every 2-3 years when she is well fed. When she is not, she is unlikely to reproduce at all. When krill supplies are diminished, further population growth of the Blue whales will be very limited.
Blue whales call when they are not actively feeding. The calls sound like very low, down-sweeping moans, and males probably do all the moaning, trying to attract females, and perhaps warn other males of their presence. We don’t know much about this.
A moan typically lasts about 30 seconds, at a very low frequency of 10-40 Hz. That is really low – we can’t hear anything below 20 Hz, and 40 Hz is still a rumbling base we find barely audible. Such low frequencies travel far in the ocean, but at the same time they can get lost in the background of the noises our ships produce.
Living in such relatively small and dispersed populations, calling to each other in a noisy sea, Blue Whales have a huge challenge of finding one another.
Still, it is tantalizing to think we might again share the oceans with this amazing beast. We are generally attracted to things that are very big and we tolerate other animals that don’t compete directly with us.
But there isn’t a whole lot left in the sea for us to eat. A large and hungry competitor for that food we want to have instead has is playing a hand it cannot win.
The Age of the Great Whales ended when they were hunted out of all the oceans. Remnant populations may continue to exist. But the Age of Great Whales will not return. We can’t afford it.