Why does the fishing industry watch for upwellings eagerly?

Most ocean waters are depleted of nutrients - plankton gets eaten by larger creatures, the larger creatures export nutrients in their wastes out of the lighted zone, where plants can grow, into the deep ocean. Where upwelling occurs, as in the Peru Current, these deep waters come to the surface carrying nutrients. This yields a phytoplankton boom, which gives fish a rich source of food. The anchovy fishery of Peru, one of the richest fisheries in the world, is directly fed by upwelling. During an el Nino event the upwelling fails - so does the fishery.