Depends on what you mean by far away and what kind of fish you're talking about. Big fish like tuna are often caught far out at sea, but they're also caught by the same small boats that do charter fishing an hour or two out from the shore. There's plenty of inshore fishing that would be at risk, especially in bays where the salt would be less easily dispersed. I used to work at a fish market, and offhand I can think of multiple fishing industries that would be put at risk by carelessly dumping salt back in the ocean. The majority of shellfish, for example, is caught within sight of the beach. I don't know if it's still the case, but there used to be a ton of fishing done in Boston Harbor, and I've heard stories of crates of lobsters being opened only to find the lobsters carrying pieces of bodies dumped by the mob off the docks and into the harbor.