Answer:
(E) To maintain their current income, manatee hunters who switched to guiding tourists would have to use far larger boats and make many more trips into the manatees’ fragile habitat than they currently do.
Explanation:
The twin goal is to generate income to the hunters and at the same time ensure the manatee's survival. The option that threatens the achievement of these twin goals is option E. For the hunters to make their current income they need larger boats and need to make more frequent trips which could be harmful to the manatees. Income and the survival of the manatees is threatened here.
Option A is wrong because the text clearly indicates that there is a high interest among tourists to see the manatee.
Options B, C, and D are irrelevant.