Why would upwelling zones have large schools of fish?

Upwelling zones are regions in the ocean where nutrient-rich water from the deep ocean rises to the surface. This process brings essential nutrients, such as nitrogen and phosphorus, into the photic zone, which is the layer of the ocean where sunlight can penetrate. These nutrients are used by phytoplankton, microscopic plants that form the base of the marine food web.

Phytoplankton are eaten by zooplankton, small animals that drift through the water column. Zooplankton are in turn eaten by fish, which are preyed upon by larger fish, seabirds, and marine mammals. As a result, upwelling zones are often home to large schools of fish, including sardines, anchovies, tuna, and mackerel.

In addition to providing nutrients, upwelling zones also create ideal conditions for fish to reproduce. The cooler, nutrient-rich water is often more oxygenated than the surrounding surface water, which can be beneficial for fish eggs and larvae. Additionally, the currents associated with upwelling zones can help to distribute fish eggs and larvae over a wide area, increasing their chances of survival.

For these reasons, upwelling zones are considered to be important areas for marine biodiversity and fisheries production.