Chase Dekker gripped his camera with anticipation. A couple hundred feet from his seat on a whale-watching boat, the waters of Monterey Bay in California teemed with activity.

A group of California sea lions had just come up for air after feeding on a school of anchovies, and following close behind them was the main event: humpback whales.

But as a whale burst from the waves, the wildlife photographer told The Washington Post, he instantly noticed something was off. A sizable sea lion, weighing about 400 to 600 pounds (180 to 270 kilograms), was teetering precariously above the whale's gaping mouth.

"I was like, 'Oh my goodness'," the 27-year-old said, "and I lifted my camera."

Dekker, who was guiding the tour on July 22, didn't know it at the time, but he ended up capturing an occurrence so unusual that many marine mammal researchers had never seen it before. The photo shows the surprised-looking sea lion, its mouth wide open, appearing moments away from being engulfed by the roughly 50-foot-long (15-metre-long) surfacing humpback whale.

"It was capturing this perfect moment when nature kind of backfires a little bit," Ari Friedlaender, an ecologist at the University of California at Santa Cruz who studies the foraging behavior of marine mammals, told The Post.

"It's so anomalous to see something like this because the animals are so well-adapted and so good at what they do."

The unlucky sea lion was likely just in "the wrong place at the wrong time," Friedlaender said.

"This was a once-in-a-million time that the sea lion zigged when it should have zagged and kind of got taken for a ride," he said, noting that there was "no intent by the whale to eat the sea lion."

When the Sanctuary Cruises tour set out last week, Dekker said he knew chances were good of seeing enormous humpback whales, sea lions and sea birds engaged in "feeding frenzies." Between late spring and fall, ravenous whales, along with other predators, are often drawn to the bay by the masses of schooling fish.

Though the group of animals that Dekker's tour came across was on the smaller side with only three humpback whales and about 200 sea lions, he said there was still an abundance of activity at the water's surface. As the boat pulled up to the action, Dekker said he grabbed his camera.

"I always have it ready for any lunge feed," he said, referencing an eating technique used by humpbacks and other baleen whales in which they rapidly move toward their prey, jaws agape, and take in mouthfuls of food. They later use flexible structures in their mouths to filter out the water, leaving behind small fish and krill or plankton.

First, Dekker saw the sea lions pop up. After years of observing whales, he knew that meant the massive creatures were about "10 to 30 seconds" behind, so he got into position.

But unlike the countless other times he's watched a lunge-feeding whale surface, this time, one sea lion couldn't get out of the way fast enough. Dekker said he reflexively snapped a few shots, but was so excited that he initially didn't even bother checking his camera.

"I just ran around the boat going, 'Did everyone see that?'" he said. "I was screaming at the other boats that I know next to us."

A short while later, Dekker returned to the camera and clicked through the images to find, much to his surprise, that he had somehow managed to capture the fleeting moment.

"I was just ecstatic," he said. "I had actually taken it, gotten it."

(Courtesy of Chase Dekker)(Courtesy of Chase Dekker)

This isn't the first time animals other than fish and krill have had the misfortune of accidentally ending up in the mouth of a humpback whale. Researchers have found evidence of small seabirds getting swallowed, while larger creatures such as pelicans and harbor seals have had close encounters.

In March, a Bryde's whale, part of the same group as humpback whales, even reportedly scooped up a person.

The fate of the sea lion captured in this photo isn't clear, but Dekker said he's "almost 100 percent confident" that it escaped unharmed.

A humpback whale's esophagus is "only about the size of maybe a big grapefruit or small melon," he said, meaning the chances of a sea lion that weighs hundreds of pounds getting swallowed and eaten are slim. He added that an injured or dead sea lion wasn't spotted in the water and the whale seemed to be behaving normally a few minutes later, which would not be the case if it still had the mammal in its mouth.

"If you had the equivalent of a little field mouse inside your mouth, you'd probably be a little concerned," he said. "You would notice."

It's likely that the sea lion just swam away and continued feeding, Dekker said.

Friedlaender said he also believes the sea lion emerged from the ordeal unscathed, given that the species is known to be "pretty physical" with each other on shore.

"I suspect the animal was probably pretty scared, but hopefully it had a soft landing," he said.

While the photo may be rare, John Calambokidis, a research biologist who has studied humpback whales along the West Coast for more than 30 years, told The Post he wasn't shocked to hear about the sea lion's close call.

Underwater recordings of feedings often show sea lions and humpback whales going after the same prey in "very close proximity," said Calambokidis, one of the founders of the Cascadia Research Collective in Washington state.

The event of a sea lion getting accidentally caught in a lunging whale's mouth may only seem unheard of because people usually can't see beneath the surface where most of the action takes place, he said.

Calambokidis was, however, surprised by Dekker's photo.

"I thought it was an amazing photo," he said, later adding, "I've not seen a photo myself like that before."

For Dekker, the picture represents "a true once in a lifetime moment" that he was able to "immortalize so everyone can see it forever."

"It's something I may never witness and most likely will never capture ever again," he said.

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