Which of the following contributed most to fish population dying during the 1970's?

Question

is it salt, toxic waste, predators, mercury, or iodine.

Answer 1

It would depend upon the part of the world  you are talking about. The near extinction of the North Atlantic cod stock can be attributed to over-fishing and to an abounding population of seals - both predatory activities. I believe that polution, per se, played very little part in that tragedy. Elsewhere, different story. As to over-all numbers, who's doing the counting, and how?

Answer 2

Do you mean fresh water fish or salt water?

Answer 3

Most likely over fishing. Predator = Mankind