Your copious amount of fish destruction was overshadowed by the sudden appearance of a mysterious fisherman. He apparently went about slaughtering the fish with an amazing spearing display.
Ancient myths state that the killer fish committed the sin of gluttony and were duly punished by the sea god. Whenever the sea god isn't nearby, they take advantage of the opportunity and eat everything in the water.
The mysterious fisherman's identity is unknown, but his shell horn leads people to speculate that he is a form of the sea god.