Oceans - 4 free documentaries about fishing & overfishing.
Start with Backbreaking work: Deep-sea fishing in the Arctic Ocean (55 min, DW Documentary), then The Broken Economics of the Oceans (25 min, Wendover Productions). All 4 documentaries here are free to watch from their makers' official uploads. To read deeper, the top-rated book on fishing & overfishing is Four Fish by Paul Greenberg.