PORTLAND, Ore. -- Josh Robb was crabbing on the Columbia River west of Astoria on Saturday when his father-in-law saw an injured seal and blood in the water. Then they noticed something else swimming nearby trying to get at the seal.

Robb pulled out a camera and started recording the action about 15 yards away.

“Finally you could see the fin come out of the water. I said, ‘holy cow, it’s a shark!’” Robb said.

Watch: Shark attacking seal

Robb’s video shows a shark come out of the water to finish off the seal. He estimates the shark was between 12-15 feet long.

“It was almost as big as our boat,” Robb said. “Once we saw that we got the heck out of dodge.”

Robb said the seal attack happened fairly close to shore near the Hammond boat launch. That’s about eight miles west of Astoria, not far from the mouth of the Columbia River.

He suspected it was a great white shark. Biologists from the Oregon Department of Fish and Wildlife reviewed the video and say that might be the case; however, they argue it could also be a salmon shark.

“I am pretty sure it is a salmon shark, the closest living relative to the great white shark,” said Lynn Mattes with the Oregon Department of Fish and Wildlife. “There is a chance it could be a small great white shark.”

Mattes said the size, brownish coloration on the dorsal fin and general tail shape lead her to believe it’s likely a salmon shark.

Both kinds of sharks live off the Oregon coast, according to ODFW spokesman Rick Hargrave. He said both species are also known to swim into fresh water when looking for food.

Hargrave said it was a great white shark that recently attacked a surfer north of Cannon Beach.