New Zealand is a nice place to be during the austral summer. I’m not the only one that thinks so. While the sole native land mammals are bats, around half the world’s marine mammal species are found in kiwi waters. Everything from the endemic New Zealand dolphin, the world’s smallest, to enormous blue whales frequent our long coastline.
The best place to see marine life in New Zealand is off Kaikoura, a small town in the northeast South Island. The Kaikoura Canyon, just offshore, has been described as “the most productive non-chemosynthetic habitat recorded to date in the deep sea.” A multitude of animals call Kaikoura home, from the world’s smallest penguins to the largest of all predators: the sperm whale.
The latter are a major focus of marine ecotourism in the town. Sperm whales are huge, smart, and formidable. Males grow to 18-21 m in length, and can weigh 60 tons. Adults dive to over 2000 m, and hold their breath for at least 138 minutes. They can eat massive prey, including squid over 13 m long (and weighing over half a ton). Their teeth, on the lower jaw, measure up to 27 cm high. BADASS.
My friend Tamzin Henderson has a whale curse, so she drove down from Picton to exorcise the affliction. We booked an afternoon trip with Whale Watch Kaikoura, expertly guided by Heleen Middel. On the way out to find said whales, Heleen casually mentioned that Kaikoura sperm whales occasionally hunt mako sharks.
I know, I know. Sperm whales eat squid. It’s true. They’re estimated to eat 110-320 million tons of squid per year, with each individual eating up to 1.5 tons per day. Nom.
But they eat sharks, too. It’s totally a thing.
Whale watching is a big deal in Kaikoura. You can see whales from a boat, helicopter, or small plane. I’ve done flights with Wings Over Whales a couple of times. They’re absolutely brilliant; it’s how I got the photo above. Chatting before a trip, one of the pilots also mentioned that he’d watched a sperm whale hunt down a blue shark.
That settled it. I had to know more. To the library! And by library I mean the internet!
A 1980 study used historical whaling data to investigate sperm whale diet. Several large (1-3 m) sharks were found in the whales’ stomachs, including a 2.5 m basking shark and large, deepwater sleeper sharks (the genus that includes Greenland sharks). In 1998, a group of three sperm whales were also observed ‘attacking’ a megamouth shark, one of the most enigmatic sharks on the planet, off Sulawesi in Indonesia. Pelagic sharks, such as blues and makos, are entirely within their capabilities.
Sperm whale superpowers
Sperm whales live in a world of sound. Sunlight only penetrates the top couple of hundred metres of ocean. Underneath, it’s permanent darkness. Sperm whales spend more than half their lives at 500 m deep or more, so vision isn’t particularly useful when hunting.
The whale’s species name, macrocephalus, means “big head”. Bit rude, but – to be fair – their head is around a third of their body length. A large part of this real estate is occupied by the junk, a mass of oil-saturated fatty tissue, which acts as a component of their sound production and bio-sonar system.
That has no direct relevance to the story. I just wanted to point out that they have a lot of junk in their trunk.
Anyway, the whales use this organ to make extremely loud ‘clicks’, the loudest noise produced by any animal. Scientists even put forward a ‘biological big bang hypothesis’, suggesting that the whales’ powerful clicks could be used to stun their prey. (I prefer to call it the ‘mind-bullet hypothesis’.)
The regular loud clicks, which the whales use to locate prey at depth, rapidly speed up to create a “buzz” when they’re actively pursuing prey. Sadly for all concerned, a recent study found that the loudest clicks are probably for longer-range echolocation. The buzzes used to zero in on their prey are quieter, and used for quick updates on the location of a fleeing snack. (No mind-bullets then? Curses.)
Last year, a study at Kaikoura found that buzzes were rarely recorded between the surface to 300 m depth. Of course, the top few metres are well-lit, so echolocation may not be so vital to hunting success. In the darkness of the deep sea though, sharks are clearly a routine snack. Researchers examined 133 sperm whale stomachs from New Zealand between 1963-64, when there was commercial whaling. Half of their diet was fishes, including a lot of deepwater sharks.
Food webs are complicated. Even apex predators can sometimes be prey.