During a whale-watching trip last week, wildlife photographer Chase Dekker stared in awe as a humpback surfaced and engulfed a sea lion in its mouth.

The humpback whale, the largest of the three the group was observing—likely measuring around 50 feet long—opened its mouth to consume fish and accidentally “lifted the male sea lion like it was nothing,” says Dekker, who works as a naturalist for the whale-watching outfit, Sanctuary Cruises.

“As soon as I saw this photograph, I knew it may be one of the rarest shots I’ve ever taken,” Dekker says. “Not the most beautiful, not the most artistic, but probably something I would never see again.”

This time of year is prime for humpback sightings in Monterey Bay: The hungry leviathans stop in the area each summer to snack on schooling anchovies. The fish attract other predators as well, resulting in spectacular feeding frenzies.

Usually, the predators avoid each other, and sea lions typically swim out of the way as the humpbacks prepare to eat. This process, called lunge-feeding, constists of charging toward and engulfing food in a huge mouthful. The whales then push out the water and strain the fish through flexible comb-like structures in their mouths called baleen.

Taking turns

“You start to notice this pattern around bait balls,” Dekker explains, referring to swirling masses of fish. “The whales dive down, and the sea lions generally [move in] shortly after. When the sea lions pop back up, the whales are typically 10 to 30 seconds behind them.”

Sea lions do occasionally wind up close to whales, sometimes even close enough for a nudge, but mealtime mishaps of this magnitude are few. Dekker’s sighting piqued the interest of Christie McMillan, a biologist with the Marine Education and Research Society in British Columbia, who studies humpback feeding behavior.

“The photo blew our minds,” says McMillan, noting that most documented cases like this involve small seabirds.

It doesn't take much to whet a humpback whale's appetite—just a thousand pounds or so a day of fish, krill, plankton, and the like.

“Our colleague once watched a very lucky common murre swim out after a whale opened its mouth twice at the surface to let the bird out,” she adds. The researchers have also seen whales release gulls, both alive and dead, which were accidentally engulfed.

Close calls with larger species, from pelicans, to harbor seals, to the odd human diver crop up from time to time, but these events are exceptionally rare.

“I have never seen this happen with a sea lion,” says McMillan. “Nor have I ever heard of it.”

Exactly what caused the underwater collision is anyone’s guess, but reports that the sea lion was “gobbled up” are sensational. Neither party was likely in any danger.

No harm, no foul

Despite their impressive size, humpback whales are filter feeders who gulp down krill and other plankton, as well as small fish like sardines, juvenile salmon, and herring. That preference for small prey means the whales’ bodies aren’t suited to swallowing bigger animals. At rest, a humpback’s throat is about as wide as a human fist. And while the esophagus can stretch to accommodate slightly larger meals, it maxes out between 12 and 15 inches in diameter.

Even birds rarely make it down a whale’s gullet, although sometimes they do, according to an analysis of whale poop in Alaska’s Glacier Bay and Icy Strait. When this happens, the birds pass through mostly undigested, and emerge as what McMillan terms “bird bricks.”

Once at the surface, a lunge-feeding whale will typically close its mouth almost immediately to trap the fish inside. But in this case, the humpback stayed at the surface with its mouth open for 10 seconds, likely the result of the animal feeling the “the odd sensation of the sea lion,” says anatomist Joy Reidenberg, who specializes in whales.

Though the whale-watchers couldn’t see what happened after the whale engulfed the sea lion, it likely quickly escaped during this pause.

“I don’t think this would be any bother for a large sea lion,” says Robert Delong, leader of NOAA’s California Current Ecosystem Program. “These are very hardy animals, and to a sea lion, hanging out in a whale’s mouth would be like hanging out in a swimming pool.”

Experts similarly agree the sea lion was unlikely to hurt the whale. Humpback jaws are incredibly strong, built to withstand the immense force of rushing water during feeding. The whales also breathe through their blowholes, which are separate from their mouths, and very rarely blocked by debris.

As for the whale’s bristly baleen, these fibers and plates are flexible and resistant to fracture thanks to high levels of keratin. Much like our fingernails, baleen will bend long before it breaks, even under a sea lion’s 400- to 600-pound bulk. What’s more, baleen regrows over time.

“We didn’t see any injured sea lions that day, so we assume it just escaped without any trouble,” says Dekker. “About five minutes later, the whales were all feeding as though nothing had happened at all.”