Description & Fascinating Facts. The Harbor porpoise, Phocoena phocoena, (a.k.a. Common porpoise), is a small cetacean with a rotund, stocky body that tapers toward the tailstock. This porpoise reaches a maximum length of 1.9m (6ft) and maximum weight of 90kg (198lbs). On average, Harbor porpoises are smaller, and do not exceed 1.5m (5ft) or weigh more than 60kg (132lbs).