E is the answer.

This conclusion is: CPUE number same -> shark numbers are same

To weakedn the conclusion, we need to establish that the way to reach CPUE somehow has changed since 1973.

This question defines the CPUE carefully.

E is the only answer that could address catches 'per hour' and the other answers are not relevant.

E: (Technology improvement -> sharks still easy to find EVEN THOUGH numbers have dropped -> maybe shark numbers not equal)