The whales that eat sharks
Dr Simon J Pierce is a marine conservation biologist and underwater photographer from New Zealand. He is a co-founder and Principal Scientist at the Marine Megafauna Foundation, where he leads the global whale shark research programme, and a regional Co-Chair for the IUCN Shark Specialist Group.
New Zealand is a nice place to be during the Southern summer. I’m not the only one that thinks so. While the only 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 this long coastline.
The best place to see marine life in New Zealand is a small town named Kaikoura 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, from the world’s smallest penguins to the world’s largest predator, the sperm whale, call Kaikoura home.
The latter was the focus of my latest visit. Sperm whales are huge, smart, and formidable. Males grow to 18-21 metres in length, and can weigh 60 tons. Adults dive to more than two kilometres, and hold their breath for more than two hours. They can eat massive prey, such as 13-metre-long squid. Their teeth, on the lower jaw, measure up to 27cm high.
On the way out to find said whales, our guide mentioned as an aside 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.
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 the flights a couple of times. They’re brilliant. 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.
A 1980 study used historical whaling data to investigate sperm whale diet. Several large sharks (up to 3m long) were found in the whales’ stomachs, including a 2.5m 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 therefore entirely within their capabilities.
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 depths of 500m 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 much quieter, and used for quick updates on the location of a fleeing snack. Not mind bullets then. Curses.
Last year, a study at Kaikoura found that buzzes were rarely recorded between the surface to 300m deep. Of course, the surface is well-lit, so echolocation may not be required. In the darkness of the deep sea, 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.
If there’s a lesson here, I guess it’s that food webs are complicated. Apex predators can be prey themselves. Also, you should probably visit Kaikoura. It’s very nice. Lots of seafood.
This column appears in ISSUE 1: Saving the Arctic of Oceanographic Magazine
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