sea cow

The reading claims that in 1768 a marine mammal known as Steller's sea cow became extinct and the article provides three theories of the extinction. In contrast, the professor states that we have problem in each theory about extinction and we just don't know and he refutes each of the author's reasons.

First, the article avers that the sea cows may have been overhunted by groups of native Siberian people. However, the lecturer opposes this point by saying that the sea cow is a massive creature that is very long and it weighs about 10 tons so it could feed a small group of people and the Siberian people were not large. In fact, he says that they didn't need to hunt a lot for food. This point disputes the information made in the passage.

Second, the passage asserts that the sea cow population may have become extinct because of ecosystem disturbances that caused a decline in their main source of food, kelp. On the other hand, the professor counters this point by stating that if severe ecosystem disturbances happaned before 1768, it should affect the other ecosystem such as decline in whales, but there was no report about declining in whales population. As a result, he mentions that the sea cow didn't experience food shortage.

Third, the article posits that the main cause of extinction could have been European fur traders who came to the island after 1741 and they caught the last sea cow in 1768. Conversely, the professor casts doubt on this theory by explaining that when the traders arrived, it already was small amount of sea cow. Actually, he says that the evidence of decreasing the sea cow population occurred before 1700 that means before arriving of traders, so there were other causes and not the European traders.