Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, and short, thick hair. Together with the fur seals, they comprise the family Otariidae, eared seals and there are six extant and one extinct species (the Japanese sea lion) in five genera. Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, with the notable exception of the northern Atlantic Ocean. They have an average life span of 20-0 years. A male California sea lion weighs on an average about 300 kg (660 lb) and is about 8 ft (2.4 m) long, while the female sea lion weighs 100 kg (220 lb) and is 6 ft (1.8 m) long. The largest sea lion is the Steller's sea lion which can weigh 1,000 kg (2,200 lb) and grow to a length of 10 ft (3.0 m). Sea lions consume large quantities of food at a time and are known to eat about 5-8% of their body weight (about 15--35 lb (6.8-16 kg)) at a single feeding. Together with the fur seals, they constitute the Otariidae family, collectively known as eared seals. Until recently, sea lions were grouped under a single subfamily called Otariinae, whereas fur seals were grouped in the subfamily Arcocephalinae. This division was based on the most prominent common feature shared by the fur seals and absent in the sea lions, namely the dense underfur characteristic of the latter. Recent genetic evidence, however, strongly suggests Callorhinus, the genus of the northern fur seal, is more closely related to some sea lion species than to the other fur seal genus, Arctocephalus. Therefore, the fur seal/sea lion subfamily distinction has been eliminated from many taxonomies. Sea lions are related to the walrus and the seal. Nonetheless, all fur seals have certain features in common: the fur, generally smaller sizes, farther and longer foraging trips, smaller and more abundant prey items and greater sexual dimorphism. All sea lions have certain features in common, in particular their coarse, short fur, greater bulk and larger prey than fur seals. For these reasons, the distinction remains useful. Some species of sea lion are readily trainable and are often a popular attraction at zoos and aquariums. The archetypal circus "seal" performing behaviors such as throwing and catching balls on its nose and clapping is almost always a sea lion. The U.S. Navy's Marine Mammal Program, based in San Diego, has trained sea lions to detain scuba divers. Sea lion attacks on humans are rare. In a highly unusual attack in 2007 in Western Australia, a sea lion leapt from the water and seriously mauled a 13-year-old girl surfing behind a speedboat. The sea lion appeared to be preparing for a second attack when the girl was rescued. An Australian marine biologist opined the sea lion may have viewed the girl "like a rag doll toy" to be played with. In San Francisco, where an increasingly large population of California sea lion crowds dock along San Francisco Bay, there have been incidents in recent years of swimmers being bitten on the legs by large, aggressive males, possibly as territorial acts. The Moche people of ancient Peru worshipped the sea and its animals. They often depicted sea lions in their art. Sea lions have also been reported to assist or save humans who show signs of distress in the open waters. In June 2000, Kevin Hines leaped into San Francisco Bay; he reportedly was saved by a sea lion that kept him afloat and breathing until the paramedics arrived.