Orcas in the Gulf of California have been hunting juvenile great white sharks using a clever tactic: flipping them upside down to render them immobile. The discovery suggests there may be a previously unrecognised group of orcas in the region that specialises in hunting sharks.

Only a few orca populations are known to , and even fewer have been found to eat great whites (Carcharodon carcharias). For example, orcas (Orcinus orca) off the coast of San Francisco were , and a great white carcass near Australia showed signs of an orca attack in . But until recently, there had only been one known instance, recorded in South Africa, of the animals preying on juvenile great white sharks.

, an independent marine biologist in Mexico, and his colleagues captured video footage of orcas in the Gulf of California hunting juvenile great white sharks on two separate occasions. The first, recorded in August 2020, showed five female orcas working together to push a young great white to the surface. “The orcas were ramming the great white to flip it upside down,” says Higuera.

The manoeuvre forced the shark into a state of temporary paralysis, called tonic immobility. It also allowed the orcas to get at the shark’s energy-rich liver, which they shared amongst themselves. A few minutes later, the pod repeated the attack on a different adolescent great white. In August 2022, the research team recorded another group of five orcas using the same technique to hunt a young great white around the same location at the same time of year.

The researchers identified some of the orcas in the first incident as those previously spotted hunting whale sharks and bull sharks. Footage from the second incident wasn’t clear enough to determine whether these orcas belonged to the same pod. “But it is highly possible,” says Higuera.

Orca populations drastically differ depending on where they are located. “Orcas are hunting machines. They are like snipers – they use specific hunting strategies, very specific ones depending on their prey,” says Higuera. These findings suggest the orcas belong to a previously unrecognised shark-eating group, he says.

“So now we have an example of another unique feeding strategy that probably isn’t shared by any other group of [orcas] in the world,” says at the University of British Columbia in Canada. However, more research is needed to know for sure, as the orcas could be an offshoot of those from the Pacific Northwest that hunt other types of sharks, he says.

A giant crustacean that resembles a large white shrimp may be far more common across the deep sea than thought, with potential habitat extending over much of the ocean floor.

“We have called this species rare for so long. We call everything in the deep sea rare,” says at the University of Western Australia. “But in actual fact these species are probably more connected than we would have ever expected.”

The crustacean, known as Alicella gigantea, has the distinction of being the world’s largest amphipod, growing up to 34 centimetres in length. But this “supergiant”, living on the floor of the deep ocean, hasn’t been easy to find. “Because [the deep sea] is so hard to get to, it’s been undersampled for so long, and we’re finally playing catch up,” says Maroni.

She and her colleagues collected 75 records of A. gigantea, stretching back to the first collection of a specimen in 1899. These included finds in the Pacific, Atlantic and Indian oceans. They also used DNA sequences from specimens across all three oceans to reconstruct genetic relationships among different populations.

They found the specimens had been collected from depths ranging from 3890 to 8931 metres. They estimate that about 59 per cent of the sea floor falls within this range. The genetic data also suggested the specimens, although distributed across this vast area, all represented one genetically similar species.

Maroni says this implies the crustaceans could live across far more of the ocean floor than sparse collections would suggest. The 59 per cent figure based only on depth is a maximum habitat extent, but is the best available based on the little we know about these creatures.

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Brainwave testing of two young baleen whales has revealed they can hear higher frequency sounds than previously thought, forcing researchers to rethink how the ocean’s largest animals respond to predators and human noises.

“This is truly groundbreaking work,” says at Syracuse University in New York, who wasn’t involved in the new study. “Directly measuring the hearing of a wild baleen whale is something the researchers in the field have been working towards for decades… This is, to my knowledge, the first successful test of this method with a baleen whale.”

But baleen whales include the largest animals on Earth, and the study method of temporarily restraining them for a hearing test isn’t easy. “The body size of most baleen whales is too large for the approach to be effective,” says at the National Marine Mammal Foundation, a nonprofit organisation based in California. So Houser and his colleagues turned to a relatively small baleen species called the minke whale.

The researchers examined the migratory route of minke whales along the coast of Norway and found a natural channel between two islands, where they used net barriers and boats to guide two whales – each about 3 to 5 metres in length – into a fish farm enclosure with a drop-down net door. Researchers then used a roller system to pull up a net and hold the teenage animals partially submerged at the water’s surface.

The hearing test involved placing two gold-plated electrodes with silicone suction cups on each whale’s skin near its blowhole and dorsal fin, which enabled the researchers to record brainwave signals. They measured how the whales’ brains responded to sounds played from an underwater speaker for about 30 minutes for one whale and 90 minutes for the other.

Such experiments revealed that the whales’ auditory brainstems respond to ultrasonic sounds, which are beyond those the human ear can detect, at frequencies as high as 45 to 90 kilohertz – a much broader hearing range than previously believed possible based on ear anatomy and vocalisations.

The corralling and restraining of wild marine mammals is “quite controversial” because of the potential for “significant stress” in the animals, says at Marine Conservation Research, a nonprofit organisation based in the UK. But he described the findings as “very important” in helping understand how baleen whales may evade predators such as killer whales, which hunt using high-frequency echolocation clicks.

Researchers should also rethink how baleen whales are affected by military sonar and commercially available echo sounders used for mapping the seafloor, says Boisseau. “It seems the more we study the hearing of marine mammals, the more we confound our initial assumptions,” he says.