Natural History Harbour porpoises are one of the world's smallest cetaceans, growing to an average length of 1.55 meters and a mass of 55 kilograms. Female porpoises are usually larger than males. It is believed that porpoises can live as long as 20 years. Harbour porpoises become sexually mature between 3 and 5 years of age. After that time, female porpoises usually produce one calf every year.
Porpoises also eat squid.
Recently weaned porpoises eat euphausiid shrimp. Harbour porpoises are deep divers, capable of reaching depths in excess of 200 meters. Status and Protection Many harbour porpoise populations around the world have been depleted through bycatch in fisheries. This has led some countries to afford them special status. A similar listing under the U.S. Endangered Species Act is under consideration.