During the nineteenth century, Hooker's sea lion was killed for its hide and oil. Since 1893, however, killing this species has been illegal (2). Rabbits, which were introduced into the breeding islands of Hooker's sea lion, caused a problem as pups were falling into the rabbit burrows, resulting in high pup mortality (4) (2). Rabbits have since been eradicated and their burrows have been filled in (2). Currently, the most serious current threat is accidental by-catch in the nets of the squid fishing industry (2). This fishery has operated in the range of this sea lion since the 1970s, and has been a serious problem since then (2). In January 1998 the Hooker's sea lion population suffered a catastrophic mass mortality event, which is thought to have killed 53 percent of pups and a high percentage of adults that year (7) (2). The cause of this mass mortality is unknown (2). Before this event there were an estimated 12,000 to 14,000 individuals (7). This species is exceptionally vulnerable because its breeding range is so restricted (2).