Here is how I deal with this problem:

Answer choice A uses heaving wording while pointing at technology - OUT!
Answer choice B is not mentioned in the argument - OUT!
Answer choice C is not mentioned in the argument - OUT!
Answer choice D uses heaving wording while pointing at technology - OUT!
Answer choice E is the only thing that has to be true based on the argument.

Avoid extreme and heavy assumptions that are not supported within the argument. This simple rule is the key to solve majority of Inference questions.

There is a conclusion already in the text of the problem itself. We just have to reword it a little to get the correct answer.

Let's analyze the argument. We have:
1) a fact that the number of fish caught increased
2) an argument (=reasoning) of the commissioner of the Fish and Game Authority
3) a claim that the conclusion of the commissioner's argument isn't sound
4) an analogy with the rain forests that supports the claim
5) an alternative explanation of the fact at hand (that fish-catch increased), which also supports the claim

Let's look closer at the claim so supported by an environmentalist. It is in fact the conclusion we're looking for. He says, "This is a specious argument", referring to the commissioner's argument.
What was the conclusion of that argument? - the commissioner claims that the number of fish caught demonstrates that this source is no longer endangered. So, fish are no longer endangered.
And the environmentalist claims that this is not true. Basically, he says that fish ARE in danger, which coincides with the answer choice E.