Scientists on our research vessel (RV) Investigator recently had a surprise visitor when a curious fur seal suddenly appeared on the video feed from their deep-water camera. At the time, the scientists were off the west coast of Tasmania doing a seafloor survey at a depth of 155 metres.
The fur seal was most likely attracted by the camera’s spotlights, and perhaps the opportunity to find an easy meal in the light. However, this isn’t the first time a seal has been spotted by our deep tow camera.
Here's a highlight reel showing our seal visitors during camera surveys from 2015 and 2023.
The recent chance encounter with our pinniped friend (seals belong to the taxonomic group Pinnipedia) led us to ask: what are the ocean’s deepest diving animals?
Let’s dive in.
Fur seals: deepest dive 300 metres
While fur seals like our surprise underwater visitor are common in the waters of southern Australia, catching them on camera in the deep sea is rare. Why? Well, it’s a big ocean and there aren't many cameras down there!
There are two main types of seals – those with external ears and those without. Fur seals belong to the family Otariidae, which do have ears. Most species of fur seal, and their sea lion cousins, are thought of as the shallow divers of the seal world. Their dives are generally less than 100 metres deep and last less than 10 minutes.
However, fur seals can dive to depths of more than 300 metres. So, our fur seal friend spotted on our deep tow camera was probably taking it easy at 155 metres below the surface.
Penguins: deepest dive 500 metres
Despite their small size, penguins are impressive divers. And in the penguin world, size matters! Perhaps not surprisingly, smaller penguins like Australia’s little penguin are usually restricted to the upper 20 metres of the ocean. However, in 2006, one female was recorded diving to 67 metres! A mighty impressive effort for a bird that weighs only 1.5 kilograms.
However, the deepest diving penguin is the world’s largest penguin, the 45 kilogram emperor penguin. These majestic flightless birds can dive to depths of more than 500 metres in search of food in the icy waters of the Southern Ocean.
Turtles: deepest dive 1200 metres
We often think of turtles splashing about in the azure waters of the tropics. But these reptiles aren’t content with handing over all the deep-diving glory to the mammals and birds. Leatherback turtles can dive to more than 1000 metres in search of their favourite prey - jellyfish.
Turtles aren’t necessarily the quickest of marine animals. It takes a lot of time and energy just to reach that depth. To make the most of it, leatherback turtles can stay down for up to 85 minutes.
These turtles are the only species of turtle that doesn’t have a hard shell. Instead, they have soft, leathery skin. This forms a flexible shell that can cope with the changes in pressure experienced on long, deep dives.
Whale shark: deepest dive 1800 metres
Whale sharks are the gentle giants of the shark world and a much-loved resident of tropical waters.
The diet of a whale shark is mostly plankton, which is readily available in the photic zone. This is the uppermost part of the ocean, which receives sunlight and is generally the top 200 metres of the ocean. Despite this, whale sharks have been recorded diving to almost 1800 metres deep in recent years.
Why? Well, that remains a mystery!
Sperm whale: deepest dive 2250 metres
Whales are often thought of as master divers. Yet many species of large baleen whales, such as humpback whales, and some of the toothed whales, such as orcas, don’t venture much beyond 1000 metres.
Enter the sperm whale.
Reaching lengths of up to 20 metres, sperm whales are the largest of the toothed whales. They regularly dive to depths of 1000 metres in search of deep-sea prey such as squid. But when they need to, they’re capable of exceeding depths of 2200 metres.
Southern elephant seal: deepest dive 2388 metres
Everything the southern elephant seal does is extreme!
First, they are the biggest seal on the planet. Males weigh in at close to four tonnes.
Second, they exhibit one of the most pronounced examples of sexual dimorphism (males and females look different) in the animal kingdom. Males are up to 10 times larger than females.
Third, they have a truly astonishing mating system. Males fight each other to be crowned the ’beach master.’ After receiving their crown, they will then mate with over 100 females in their harem in just a couple of weeks.
Unsurprisingly, elephant seals are also extreme divers. They can stay underwater for close to two hours. To do this, elephant seals have a large volume of blood for their size. Importantly, this enables them to hold lots of oxygen when diving. Elephant seals also have a very thick blubber layer to help keep them warm in the cold, deep ocean.
The deepest recorded dive by an elephant seal is a staggering 2388 metres. Very few animals can reach such a depth. There’s certainly no other that can then swim back to the surface and haul themselves out onto the beach for a nap!
Cuvier's beaked whale: deepest dive 2992 metres
Finally, amid some serious competition, we reach our winner.
Meet the Cuvier’s beaked whale! This is by far the ocean’s deep-diving champion. This obscure, sausage-shaped whale grows up to seven metres long. Don’t be surprised if you’ve never heard of it. As a result of their pelagic (open ocean) life, reclusive behaviour and low abundance, beaked whales are one of the least understood groups of mammals on Earth.
However, what we do know is that they are extraordinary divers!
In 2014, researchers off the coast of California tracked a Cuvier’s beaked whale diving to 2992 metres! This is the world record for diving animals. Equally extraordinary, its dive lasted two hours and 17 minutes. Another world record! Not to be outdone, a few years later another Cuvier’s beaked whale was recorded on a dive that lasted an astonishing three hours and 42 minutes.
Whale, whale, whale, you might say these deep diving records will take some b(r)eaking!