TPO 34 Integrated TOEFL Writing

Both the author and the lecturer are talking about a sea marine mammal, named sea cow which became extinct in 1768. The author believes that this happened for three possible reasons and provides some evidence for his hypothesis. However, the lecturer considers these reasons to be problematic and supports his idea by reasoning.
First of all, the author insists that the main reason for the extinction of the sea cow was the huge amount of hunting done by Siberian people. The lecturer conflicts with this idea. He states that first of all, sea cows were really huge animals and they could supply food for a great deal of time. Moreover, he demonstrates that the Siberian population was not great at that time. Hence, hunting small numbers of sea cows would provide food for people for about a month or so and there were no needs to hunt many of these animals.
Secondly, it has been mentioned in the text that due to some ecosystem disturbances, sea cows might have faced a strict shortage in the population of Kelp which was their main food resource. The lecturer totally disagrees with this idea and describes that there are no reports admitting that there were shortages in other food supplies and therefore if there were any environmental disturbances, they should have been a whole decline in other resources.
Finally, the author insists that the main cause for the extinction of these animals is the advent of European fur traders who were probably hunting them. The lecturer, however, states that the number of sea cows started to demolish for about hundred of years before the arrival of European traders. So, when these traders arrived, there were actually a limited number of sea cows existing in the area. Hence, the reduction in the number of sea cows has nothing to do with the appearance of European traders.
To sum it up, the author has counted three main reasons for the extinction of sea cows. But the lecturer conflicts with all the mentioned reasons and provides support to reject the hypothesis.