Beginning in the 18th century, northern elephant seals were hunted extensively, almost to extinction by the end of the 19th century, being prized for oil made from their blubber, and the population may have fallen as low as only 20-40 individuals. In 1874, Charles Melville Scammon recorded in "Marine Mammals of the Northwestern Coast of America", that an 18-ft-long bull caught on Santa Barbara Island yielded 210 gallons of oil. They were thought to be extinct in 1884 until a remnant population of eight individuals was discovered on Guadalupe Island in 1892 by a Smithsonian expedition, who promptly killed several for their collections. The elephant seals managed to survive, and were finally protected by the Mexican government in 1922. Since the early 20th century, they have been protected by law in both Mexico and in the United States. Subsequently, the U.S. protection was strengthened after passage of the Marine Mammal Protection Act of 1972, and numbers have now recovered to over 100,000.