The boat’s journey likely began four years ago, across the Pacific, in the wake of devastation. A big piece of the vessel is believed to have broken off in a tsunami and traveled thousands of miles from Japan before it arrived off the central coast of Oregon.

Some passengers were still aboard when the ship’s remains were found this week: About 20 yellowtail jack fish, representing a species usually found in the waters off Japan.

Police from Oregon inspecting fishing licenses a couple of miles off-shore on Thursday came across the 25- to 30-foot piece of what appears to have once been a 50-foot commercial fishing vessel, said Chris Havel, spokesman for the Oregon Parks and Recreation Department. The boat — or at least what’s left of it — has been hauled into a port and will be checked for any sort of markers or numbers that could help officials conclusively deduce the boat’s origins, Havel said.

This has been happening quite a bit since 2011, when a 9.0-magnitude earthquake sparked 30-foot waves. The tsunami killed more than 15,000 people and caused $300 billion worth of damage.

The tsunami also swept about 5 million tons of debris into the ocean, with 70 percent of it quickly sinking, the Japanese government estimated three years ago. Much of the debris that’s still floating is widely dispersed, according to the National Oceanic and Atmospheric Administration.

About three or four boat-sized pieces of debris wash up on the Oregon coast or in its waters every year, Havel told The Post. Many of those have been light and shallow boats, the kinds you spot on a lake. But the debris discovered this week came from a fishing trawler, Havel said.

“Trawlers are designed to go into deeper water, and they’re designed to haul a load of fish in, so it may have been a commercial fishing boat,” Havel said. “It’s deeper and more substantial, but still it’s not like a boat designed to go across the ocean.”

The boat was successfully intercepted before it washed ashore, which would have made the recovery operation messier and more costly. While it was still at sea, biologists inspected it and determined the debris to be low-risk for carrying invasive species.

The yellowtail jack fish that were discovered in the vessel’s remains will be taken to the Oregon Coast Aquarium. They could have been caught and stored aboard the boat before the tsunami, or they could have hatched from larvae that were aboard when the boat was set adrift. “We may never know the complete answer,” Havel said.

Fish and other live creatures have been found aboard pieces of tsunami-related debris before. Those creatures ate other organisms aboard, or they would leave to find food and come back to the debris as a refuge in open waters, Havel said.

Six live fish stowed on a bait box were found on a 20-foot Japanese boat that washed up in Washington State in 2013. Although other animals clinging to debris had been previously found, researchers at the time said they hadn’t yet encountered live fish from Asia that had drifted to the waters off America’s West Coast.

“This comes out there on the far end of the bell curve, I think,” John Chapman of Oregon State University’s Hatfield Marine Science Center told the Los Angeles Times. “We know that it does happen that things disperse like that, but it’s on a million-year scale, not within a century or anything like that.”

Small pieces of debris, such as wood, plastic and Styrofoam, wash up on Oregon beaches all the time, Havel said. But the mother lode came in 2012 when a 200-ton dock — yes, an actual dock — floated in during a morning tide and landed on Agate Beach. The dock came from Misawa and remained on the Oregon beach for months before workers broke it apart and threw it away, bit by bit.

“The dock is sort of this big turning point,” Havel said at the time. “It was like a 200-ton alarm clock.”