CALAIS – The sight this week was one that hadn’t been witnessed for decades, as hundreds of sea-run Atlantic salmon migrated down the St. Croix River on their way to the ocean.

Last year, 750 of the 15-pound salmon were placed at various locations along the river as part of a pilot project, according to Lee Sochasky, director of the St. Croix Waterway Commission whose agency oversaw the program.

“We used adult fish to spawn in the river rather than stocking young fish and waiting for them to grow,” she said.

The St. Croix River is the border between Calais and St. Stephen, New Brunswick. The commission is an international group made up of representatives from both sides of the border, and is responsible for overseeing the ecology of the river.

After being placed in the river last year, some salmon spawned and wintered as far north as Spednic Lake near Vanceboro. “They were placed in locations all along the river from Baring to the Little Falls,” she said. “We tried to put them close to where they would find good spawning places.”

Now they are engaged in their spring outward migration. It is uncertain where they will spend their summer. Historically, Atlantic salmon migrate to waters off Greenland where they will find rich ocean feeding grounds.

On Thursday, Sochasky and fisheries technician Amanda Keddy were at the Milltown dam, north of the Calais downtown area, to make certain the salmon did not get hung up against the grates.

The restoration project was a combined effort of Sochasky’s group, the Maine Atlantic Salmon Commission, National Marine Fisheries Service, and the Atlantic Salmon Commission.

As part of the two-year project, Sochasky said more salmon would be placed in the river in September. She said salmon also were stocked in the Machias and Dennys rivers. The fish were raised in sea cages in Washington and Hancock counties.

Sochasky said some of the salmon might return to the St. Croix.

“Pacific salmon only have one spawning cycle, and they die right after they spawn. But Atlantic salmon can live to spawn again,” she said. “In fact some rivers are noted for their multiple spawning. They come back two or three times.”

At the same time the adult salmon were migrating, Sochasky said, smolt, young salmon that had been raised by the waterway commission, also were part of the migration pattern. The majority of smolt in the out-migration trip were put into the river about two years ago. If they survive their ocean trek, the smolt will return to the river in one to two years.

Sochasky warned anglers that sea-run salmon are protected.

“You can neither take or keep sea-run salmon,” she said. The small thumb-sized fin that should be located on top of the fish between the large fin and tail has been removed so that the salmon can be easily identified.