Gray whales are mysticetes, or baleen whales, that can grow up to 16 metres (49 feet) in length and weigh approximately 30 to 40 tonnes (66,000 to 90,000 pounds). Females are usually slightly larger than males and both sexes become lighter and more mottled as they age, also acquiring whale lice and barnacles. They have a tapered head, arched jaw and paddle-shaped pectoral fins with pointed tips. Rather than a dorsal fin, gray whales have a dorsal hump and a series of knuckles running from the dorsal hump to their broad tail fluke. Their two blowholes produce a distinctive heart-shaped blow.
Unlike other baleen whales, gray whales are benthic feeders consuming mysids, isopods and anthropods found in, or close to, sediment on the seafloor. They catch their prey by swimming along the seafloor on their side, sucking in sediment that they filter through their coarse baleen plates. Worn baleen and extensive scarring shows that most gray whales turn onto their right side when feeding, but left-‘handed’ whales have also been observed. This feeding technique limits gray whales to fairly shallow, coastal waters. The majority of gray whales spend their summers feeding in the Bering, Chukchi and Beaufort Seas although some feed off Kamchatka and Sakhalin in Russia.
As summer ends and the sea ice returns, gray whales begin one of the longest migrations of any mammal with some whales travelling over 10,000 miles per round trip. The eastern North Pacific population – the biggest of the two populations – begins travelling south along the western coast of North America around October, reaching the warm waters of Baja California two to three months later. Here, the heavily pregnant females give birth and nurse their calves before the whales begin the return journey, ready to reach their northern feeding grounds as the sea ice retreats once more.
Commercial hunting of gray whales in the North Pacific in the mid-19th century dramatically reduced their stock almost to the point of extinction. Since then the eastern population has recovered and is now thought to have reached carrying capacity at approximately 27,000 animals. The western population, however, remains endangered with the population estimated to number between 102 and 144 mature individuals. The anthropogenic threats faced by gray whales today include entanglement in fishing gear, vessel strikes, ocean noise, disturbance from whale-watching activities, energy production and pollution.