Answer:
C) The main predator of these fish is another species of fish on which alligators also prey
Explanation:
The only reasonable explanation as to why the species of fish experiences decline in number despite the fishing being the same, and the number of alligators that preyed on the fish going down, is another species of fish which preyed upon the fishes that are fished, but the alligators were also preying on them. Since the alligators have been mostly removed from the ecosystem, the fish that preyed on the other fishes experienced significant increase in its numbers, and since it feeds upon the other fish, that resulted in constant decline in the population of those fishes. The decline in number will only stop when the carrying capacity is reached for the predatory fish in the ecosystem.