If you’ve seen Finding Nemo, you’ll be familiar with the surprisingly small prey consumed by some of the world’s biggest sea creatures (swim away!). To be fair, as a whale, you’re hard pushed to find prey items bigger than yourself so it stands to reason they have opted for gorging on bitesize snacks. Some feed on krill and plankton while others dine on fish, and dependent on their diet these animals have evolved to have teeth or plates that can filter tiny organisms from seawater.
An episode of David Attenborough’s new BBC series, A Perfect Planet, last week showed for the first time a bizarre and ingenious new feeding strategy employed by Eden's whales in the Gulf of Thailand. Pollution from the land has begun to suffocate the waters here and it's driven fish species to the surface where the oxygen concentration is naturally higher. Eden's whales (Balaenoptera edeni edeni) lunge feed to scoop up these fish but they have to swallow lots of water to catch prey this way and when numbers are low it's hardly worth the effort. Tired, it seems, of actively pursuing lunch, they’ve opted for an alternative approach called trap feeding which leaves the heavy lifting to its prey.
By opening their mouths at the surface like a giant basketball hoop, the whales can spook the fish making them leap into the air and straight into their mouth. During the making of the program, the team witnessed the behavior being practiced by lone whales and even mothers and calves, who benefited from having a partner to swim around and scare more fish into jumping into their gaping mouth. Amazingly, birds will even cash in on the feeding events by swooping down and grabbing fish from inside the whale’s mouth. It's a rough deal for the oxygen-starved fish but a breathtaking example of how wild animals can learn to overcome anthropogenic-driven changes in the environment.
An incredible example of wildlife videography but as Daniel Rasmussen, an associate producer on the shoot, told IFLScience, it was a far from easy sequence to film. Even finding the animals proved tricky as murky water meant it was hard to locate them using drones and the whales’ sensitivity to noise meant they couldn't use speedy boats.
“We were cursed with a very slow boat which made even finding the whales near impossible, and when you did spot them in the distance, you could pretty much set your direction and then lie down for a nap for two hours before you got there and even then they were inevitably gone,” said Rasmussen. The frustrating piece of kit was however a conscious choice, he explained, as most modern boats with exhausts in the water would cause too much of a din and scare off any whales they were tracking.
Armed with an older, more traditional Thai boat that exhausted into the air, the team's progress was slow and while it was whisper-quiet below deck it was terribly noisy for those up top. As such, despite working two 3-week shoots over 2 years, the team saw just a handful of feeding events suitable for filming.
Reports from members of A Perfect Planet’s huge production team certainly give an idea of the difficulties faced in wildlife filmmaking, including this harrowing account from Matt Aeberhard who tackled the caustic soda flats of Lake Natron to film its flamingos. However, it seems all is forgiven of the natural world when you finally land that perfect shot – even if your means of celebration is limited.
“We were all incredibly excited to be eating Thai food on this trip, but on day one, we realised we had been given the same food for lunch as we had for breakfast, and then again the same for dinner,” said Rasmussen. “The next day was a repeat, and the next, and so it continued. By week three we had barely seen a whale, couldn't talk to each other because the boat was so loud, and none of us wanted to eat anymore. So, when we finally filmed a successful trap feeding moment it was euphoric and we celebrated in the only way we could, by eating lunch.”