As the Center for Sea Mammals Rehabilitation of the Leningrad region said, the intruders were captured by divers from the Russian National Guard (Rosgvardiya).
Most likely, the seals entered the canal on a block of ice. When animal rights activists arrived at the scene, the crafty seals were sitting on the shore surrounded by the military.
Visual inspection showed that the mammal were absolutely healthy and highly tallowy. Therefore, the staff of the rehabilitation center brought animals from the territory of the nuclear power plant and released in the Gulf of Finland.