As if life weren't hard enough for Hawai'i's monk seals, unprecedented camera footage has caught reef sharks, snapper and ulua in the act of stealing prey from the endangered marine mammals.

Scientists say this competition for food could be one reason the monk seal population is declining at a rate of 4 percent per year, despite the fact the animals inhabit the protected waters of the Papahanaumokuakea Marine National Monument.

There are only about 1,200 Hawaiian monk seals in the wild.

NOAA Fisheries research biologist Frank Parrish said studies using other tools have tracked how deep the seals were diving, but "Crittercams" allowed researchers to see the animal's underwater habitat and observe their foraging behavior and interactions with fish.

"This is exciting stuff. We knew that seals, sharks and jacks share the same prey, but now we have evidence that they go after the same individual fish," he said.

Crittercam is a National Geographic Society-patented research instrument with a video camera and other information-gathering equipment. The instrument is attached to wild animals and has been used to study emperor penguins, killer whales, lions, tigers and bears.

The research with monk seals took place over an eight-year period during which Crittercams were attached to 42 seals in French Frigate Shoals for short periods. The cameras collected 69 hours of footage, including scenes of sharks, snapper and ulua, also known as jack fish, accompanying seals to foraging areas.

Parrish said that without additional study, it's difficult to know whether the competition for food is contributing to the seal's decline, but it's likely one of a number of factors.

Unlike their rivals, the seals have the skills to flip rocks and dig in the sand to find fish, eels or octopi, and when they flushed out prey, the sharks, snapper and ulua tried to snatch it away.

In one instance, a shark appeared to bump a seal in an apparent attempt to get it to drop a fish.

Parrish said the shark's action bordered on "kleptoparasitism," behavior commonly seen in seabirds such as frigates, or 'iwa, that harass other seabirds so they'll surrender their food.

"They were following the seals around ... You can really see that they're looking at the seal and paying attention to what it's feeding on and looking for an opportunity to get something out of it," Parrish said. "Typically these sharks and jacks don't have the ability to flush prey from cover like these seals do."

In most cases, the adult seals were able to gobble their prey first, but Parrish said such competition may be more difficult for young seals to deal with, since they are less experienced and are about the same size as the 3- to 5-foot ulua that tag along on foraging missions.

Fewer than one in five Hawaiian monk seal pups survive to maturity. Other threats to their survival include tiger sharks and marine debris.

The Crittercam footage also provided new information on where seals feed and the kind of prey they go after, Parrish said.

"When we started work on this project, we were thinking we would see a lot of feeding inside the atolls, in the shallows," he said. "In fact, we saw the opposite, with most of the feeding taking place outside the atolls" in the neighboring banks.

Parrish called the computer-controlled Crittercam "a high-tech Post-It." The camera, which is about the size of a water bottle, is glued onto the seal's back and activated in 90-second intervals. It is removed three days later without pulling any of the animal's fur with it, he said.

Researchers hope to use the instruments on some of the few monk seals that visit the main Hawaiian Islands to see if similar competition is occurring.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.

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