Minke Whale

For decades, people listening to the ocean off Australia’s east coast kept recording a sound they could not identify. It was a repeating mechanical pulse, and researchers nicknamed it the Star Wars sound, because that is genuinely what it resembles.

It turned out to be the dwarf minke whale. The call is loud, around 150 to 165 decibels underwater, structured in precise repeating units, and used almost entirely during the winter breeding season, which strongly suggests it is a male advertising himself.

The minke is the whale nobody looks at twice, and it was the last great whale left alone by the whaling industry because it was too small to be worth the effort. Then the big ones ran out.

There are two species. The common minke whale is Balaenoptera acutorostrata, found mainly in the northern hemisphere, and the Antarctic minke whale is Balaenoptera bonaerensis, recognized as separate in the 1990s.

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia
• Order: Artiodactyla
• Family: Balaenopteridae
• Species: Balaenoptera acutorostrata

Minkes are rorquals, the same family as the blue, fin and humpback whales, and the minke is the smallest of them. They are baleen whales, filtering food from the water rather than catching it with teeth like the sperm whale.

The name is an accident of reputation. It comes from Meincke, a Norwegian whaling gunner who, the story goes, mistook a small minke for a blue whale, and his colleagues attached his name to the small ones afterward as a joke. Whether or not the detail is exact, the whale is named for somebody’s error.

A minke has no teeth. Instead it has 230 to 360 baleen plates hanging from the upper jaw, made of keratin, the same material as fingernails, fringed into a dense mat on the inner edge.

It feeds by lunging. The whale accelerates into a school of fish or krill with its mouth open, and the pleated grooves along its throat expand enormously to take in a volume of water comparable to its own body. Then it closes its mouth, pushes the water out through the baleen with its tongue, and swallows what is left.

The engineering is remarkable. A lunge happens in seconds and the drag is immense, and rorquals have a sensory organ in the chin, found in the 2010s, that appears to coordinate the whole movement by sensing how far the mouth has opened.

Being small has an advantage here. A blue whale needs dense krill swarms to make a lunge worthwhile; a minke can profit from smaller, patchier food, which is part of why minkes are found in far more places than the giant rorquals.

Minkes are 23 to 35 feet long and weigh 9,000 to 22,000 pounds (4 to 10 metric tons), with females slightly larger than males, as in most baleen whales.

• Snout. Sharply pointed, with a single ridge running from the blowholes forward, which is the quickest way to identify one at sea.
• Flipper band. Common minkes have a bright white band across each flipper, visible underwater and diagnostic. Antarctic minkes do not.
• Throat pleats. 50 to 70 grooves that expand during a lunge.
• Dorsal fin. Tall and curved, appearing almost at the same moment as the blow, which is another field mark.

The blow is small and often invisible, which is a large part of why minkes are easy to miss and hard to survey.

Minke whales live in every ocean, from the tropics to the ice edge at both poles, which makes them the most widely distributed of the rorquals.

They use coastal waters far more than their larger relatives, entering bays, fjords and inshore channels, and this is why minkes are the whale most people on a whale-watching boat in Scotland, Iceland or New England actually see.

They migrate between cold feeding grounds in summer and warmer waters in winter, though the pattern is loose and some individuals stay put. Antarctic minkes go right into the pack ice, working the gaps between floes, which is a habitat almost no other whale of that size uses.

Dwarf minkes gather predictably on the northern Great Barrier Reef in winter, which has produced the only place in the world with a regulated swim-with-minke-whales industry.

Minkes are carnivores and generalists by baleen whale standards, which is unusual and useful.

In the north they eat sand eels, herring, capelin, cod, sprat and krill, switching according to what is locally abundant. Antarctic minkes eat almost entirely krill.

They often feed with seabirds, driving fish to the surface, and a flock of diving gannets or shearwaters is a reliable sign of a minke working below.

An adult eats several hundred pounds of food a day during the feeding season and lives substantially on stored blubber the rest of the year.

Minkes are usually alone or in twos and threes, gathering in numbers only where food is concentrated.

They are fast and maneuverable for baleen whales, reaching around 20 miles an hour, and they breach, which is startling in an animal usually described as inconspicuous.

Dwarf minkes on the Great Barrier Reef are notably curious, approaching boats and divers repeatedly and circling them, which is the opposite of what the species does almost everywhere else and is the basis of that swim-with industry.

Beyond the Star Wars sound, minkes produce downsweeps, pulse trains and a thump that carries for miles, and acoustic monitoring has become the main way of tracking them, precisely because the blow is so hard to spot.

Females mature at around six to eight years, which is early for a baleen whale, and breed more often than their larger relatives.

Gestation lasts about ten months and a single calf is born, 8 to 10 feet long and roughly 700 pounds.

The calf nurses for four to six months, which is short for a whale, and separates from its mother within the first year.

A female may produce a calf every one to two years, and that relatively fast reproduction is the main reason minkes came through the whaling era in far better shape than the blue or right whales, which breed far more slowly.

Minkes live 30 to 50 years, with some individuals aged past 60 using earplug growth layers.

Orcas are the main natural predator, and minkes are a favored target. A hunted minke runs in a straight line rather than turning, which is effective against a short chase and fatal against orcas willing to pursue for an hour, and such hunts have been filmed lasting far longer than that.

Whaling is the human issue, and the minke’s position is unusual. It was ignored in the industrial era for being too small, and after the large whales were depleted it became the main commercial target. It remains the principal species hunted today, by Norway, Iceland and Japan, under objections to or exemptions from the 1986 moratorium, including the scientific-permit whaling that Japan conducted in the Antarctic for decades.

Beyond hunting: entanglement in fishing gear, which kills minkes worldwide; ship strikes; underwater noise; and, for Antarctic minkes, the long-term question of what happens to krill as sea ice declines.

The common minke whale is listed as Least Concern, with a global population usually estimated around 200,000, making it the most numerous baleen whale.

The Antarctic minke is listed as Near Threatened, and the honest point here is uncertainty: estimates of the Antarctic population dropped substantially between survey periods, and whether that reflects a real decline or whales moving into the pack ice where surveys cannot see them has never been resolved.

Some regional populations are in genuine trouble, notably the J-stock minke whales of the Sea of Japan, which are depleted and still taken in nets.

There is an irony worth naming. The minke is the great whale in the best condition, and it is in the best condition because it was not worth killing during the century when the others were destroyed. It is now hunted for the same reason: it is what is left.

Minkes are significant predators of krill and schooling fish, and because they are the most numerous baleen whale they move a great deal of energy through the system.

They contribute to the whale pump, feeding at depth and releasing nutrients near the surface where plankton can use them, which fertilizes the water they swim in.

Their surface feeding helps seabirds, by driving fish up within reach of birds that cannot dive deep.

And they are the whale that taught a generation of people to care about whales, simply by being the one they could actually see. A minke in a Scottish sea loch or off Cape Cod is most people’s only encounter with a great whale, and it is worth knowing that the modest animal surfacing beside the boat is the smallest member of the family that contains the largest animal that has ever lived, and that it makes a noise like a spacecraft.