Want to see the largest mammals on earth? Take a whale watching cruise this summer. From May through December, the West Coast is prime territory for summer sightings of blue whales, 80-foot long behemoths that can weigh up to 100 tons. You might also spot humpback whales, which can grow to 50 feet and weigh upwards of 40 tons. Humpbacks, as well as minke and finback whales, are also found off the coast of New England from May through October.