3. Steller’s sea cow

4. Figuring out why a species became extinct is often a tricky business, especially in distinguishing direct and indirect causes. In the case of Steller’s sea cow, it did not take long for the last remaining population of Steller’s sea cow to be driven into extinction. Discovered by the German naturalist George Steller around the Bering Sea’s Commander Islands in 1741, this enormous and peculiar creature became vulnerable to ecological change and human predation. By 1768, it was gone. First, sea cows seem to have been quickly wiped out by the overhunt of Siberians that followed Bering's route past the islands to Alaska, who hunted them both for food. In cold regions like Siberia, people have difficulty maintaining their body temperature, and one of the methods to do so is to eat fat. Thus, it is presumed that sea cows were hunted for their valuable subcutaneous fat ( 피하 지방 ), which was used for food (usually as a butter substitute) because it could be kept for a long time in warm weather without spoiling. Second, decreases among sea otter populations may have played an indirect role. Sea otters have long been highly prized for their thick pelts, and as they were killed (by both aboriginal people and Russian fur hunters) populations of sea urchins – among their most regular prey – exploded. The inflated sea urchin populations then fed on shallow-water kelp unhindered, and since Steller’s sea cow relied upon kelp for sustenance their decline may have been at least partly caused by these changes. It is hypothesized that they were easy targets for hunters and extirpated ( 종족 따 위를 멸종 시키다 ) from most of their range. The hunters came from Russia and they caught Steller’s sea cows for their fur because their fur could be sold at a high price. Hence hunting by humans obviously played a critical role in the extinction of Steller’s sea cows.