Yes, you need to check when you get there. The tours stop when the number of whales decreases to the point that it is questionable whether whales will be seen. There may still be whales in the area, but not enough to ensure a sighting.
Many of the whales are already on their way back to the northern waters where they feed. They don't eat during the winter but live off the blubber accumulated during the summer feeding season.
Among the last to leave are mothers with new calves. They linger longer to give the calf an opportunity to build up strength and blubber for the long migration to colder waters.
When you get to your hotel, call Victoria Marine/Whale Samana (538-2494) for a status report.
One of the problems for the tour companies is the fact the whales are wild animals. They follow their own schedule, and it isn't known by humans.