Thanks for the question! For the evidence for this one, take a look at the last paragraph starting on line 48. We’re told here that the extent to which ocean fisheries are fished can depend on certain forces like the price of farmed salmon and investment in fishing fleets. The introduction of substitute goods like farmed fish, for example, may cause a decrease in demand of wild fish. We’re also told that niche markets are increasing demand for certain species of wild-caught fish. These are all market forces that affect how much the ocean fisheries are fished, which is what (D) tells us.
(C), on the other hand, is incorrect because the passage never compares the amount of damage caused by overfishing versus pollution, and so we can’t make that inference from the passage.
Hope this helps! Feel free to ask any other questions that you might have.