To get one pound of salmon, you need three pounds of fish meal. To get a pound of fish meal, you need to grind up five pounds of fish. Thus, each pound of cage-raised salmon “costs” fifteen pounds of fish from the ocean. At present, about one-third of the total catch fished out of the ocean is ground up into fish meal and then fed to fish that live in pens. Anchovies, herring, and sardines are the most fished fish in the world, and almost all of the catch is used as fish meal for aquaculture. These small fish are also foragers, which means that they survive on plankton—the tiniest plants and animals of the ocean. Foragers are near the base of the ocean’s food web, where they serve as a staple food source for more charismatic species, including dolphins, sea lions, and humpback whales. More small fish diverted into aquaculture to feed us means less food left in the ocean to feed them.

— The Story of More by Hope Jahren