On a whale watch, you might only catch a quick glimpse of a harbor porpoise - just a small, triangular dorsal fin on a dark gray body. Harbor porpoises are small toothed whales (Odontocetes) that grow to 4-6 feet and up to about 130 pounds.
The name porpoise comes from the Latin word porcus - "pig," and harbor porpoises are sometimes called the "puffing pig".
Where do harbor porpoises live? Primarily cold water - they can be found in temperate and sub-arctic waters in the North Pacific and North Atlantic Oceans, and the Black Sea. One of the largest harbor porpoise "stocks," according to NOAA is in the Gulf of Maine/Bay of Fundy region.
Image: Harbor porpoises in the Gulf of Maine / Jennifer Kennedy, Blue Ocean Society for Marine Conservation