Question

why do fisheries off the coast of south america often collapse during an el niño year?○ the fish migrate to the arctic to stay cool.○ warm water blocks the upwelling of nutrient-rich deep water.○ increased upwelling brings toxic minerals to the surface.○ the water becomes too salty for fish to survive.

Explanation:

El Niño events cause warm surface waters to accumulate off the South American coast, which stops the normal upwelling of cold, nutrient-rich deep ocean water. These nutrients support the phytoplankton that form the base of the marine food web; without them, fish populations decline, leading to fishery collapses. The other options are incorrect: fish do not migrate to the Arctic, upwelling decreases (not increases) during El Niño, and salinity changes are not the primary driver of fishery collapse here.

Answer:

Warm water blocks the upwelling of nutrient-rich deep water.