How can El Niño negatively affect fishing?
The water can be too warm off of the coast of South America.
El Nino is the warm phase of what is called ENSO (El Nino Southern Oscillation) which is a phenomenon affecting the climate at regional and global scale.
During El Nino water warmer than usual is pushed along the Pacific coast of Peru. This usually happens around December from where the name "El Nino" that means "the baby boy" in Spanish.
These warmer waters push the thermocline (a sharp boundary between warm and cold water within the water column) deeper than usual. Moreover the upwelling (rising) of deep cold and nutrients-rich water is strongly reduced.
The consequence is that fish, mostly anchovies, moves deeper and farther from the coast affecting the local fishery activity.