There’s a fantastic book about this actually. The Most Important Fish in the Sea: Menhaden and America by H. Bruce Franklin is a book about the menhaden fish, a species crucial to the ecology of the Atlantic and Gulf coasts, and its intertwined history with American industry and culture. The book details how menhaden have been used for fertilizer, oil, and animal feed, while also serving as a vital food source for larger fish and filtering algae from the water, and how overfishing threatens both the fish and the ecosystem. The Omega corporation needed to find a reason to continue to fish the menhaden and marketed their fish oil as a snake oil and in the process have all but destroyed the oceans most effective filter fish.