We can make a prediction: "Perplexingly" is an important word, because it allows us to parse the prompt into two parts. The second, shorter part is that sharks must be protected from overfishing. Why is that perplexing? Because of whatever the main point of the first part is: sharks live longer than expected. We'll look for something that connects logically to both parts: 1) sharks live longer than expected, and 2) they must be protected.
Testing this prediction, (A) doesn't connect to the sharks' age. Choice (B) just restates part of the prompt. Choice (C) just restates the other part of the prompt. Choice (D) doesn't connect to either portion of the discrepancy. Choice (E) touches on both parts: it says that if sharks are older than we thought, there are fewer of them than we thought. That's a good reason to protect them from overfishing.
We can look for logical confirmation of the correct answer: A logical proof is not always possible on "explain" questions, but we can use the negation test to confirm (E), in this case. Suppose that sharks reproduced more quickly than had previously been assumed: that would lessen the need to protect sharks. Since the negation would add to the mystery and contradict the opinion of "some parties," we have confirmation the non-negated (E) would, indeed, resolve the mystery.
The correct answer is (E).