Whale watching in these waters is regulated, and the numbers are worth knowing because they explain why a captain will refuse to move closer.
North Atlantic right whales are critically endangered, and federal law requires vessels to stay 500 yards away anywhere in United States waters. There is no discretion in this, no exception for whale-watch boats, and a captain who spots one will back off and tell you why. If a right whale surfaces near the boat, the vessel must move away at a safe, slow speed.
For other large whales — humpback, fin, minke — NOAA's Northeast guidance sets a minimum of 100 feet, with 100 to 600 feet advised as the operating range. The rule applies to the vessel approaching the whale. A humpback that chooses to swim under the boat is a different matter entirely and is the reason people talk about these trips for years.
Seals carry their own guidance: stay at least 150 feet away, on the water and on the beach.
The practical effect is that a good operator will sometimes hold position and wait rather than chase. That is the trip working correctly. An operator who runs at animals is breaking the rules and giving you a worse experience, because whales approached hard dive and leave.