productivity of the Humboldt current. Upwelling within the current is not uniform across the entire system. Three notable upwelling subsystems are produced by this current: seasonal upwelling in Chile only during the spring and summer, because of the displacement of the subtropical center of high pressure during the period January–March, upwelling "shadow" that is less productive, but still large in northern Chile and Southern Peru, and highly productive year-round upwelling in Peru. The upwelling shadow identified between 35°S and 15°S is caused by the oligotrophic subtropical gyre impinging on the coast. This creates a narrow, but highly productive, upwelling zone. Biological productivity Due to the upwelling zones within the Humboldt current, biological diversity is extremely high. The Humboldt Current is considered a Class I, highly productive (>300 gC/m2/yr) ecosystem. The current hosts a wide range of organisms including multiple species of plankton, mollusks, sea urchins, crustaceans, fish, and marine mammals. The food web starts with the phytoplankton. The conditions of the Humboldt current are prime for these organisms to thrive. This causes a cascade effect in which larger and larger organisms are drawn to the area. Fisheries The Humboldt current produces some of the most successful commercial fisheries in the world. The major catches include: sardines, anchovies, mackerel, hake, and squid. Three major stocks of anchoveta are distributed between 4°S and 42°S within the Humboldt Current System. North-central Peru's fishery is primarily composed of one stock of anchoveta. Sardines, chub mackerel, and bonito are also common catches, but not as prominent, in Peru. Southern Peru and Northern Chile host a major sardine fishery. Other common stocks include: a second anchoveta stock, jack mackerel, tuna, and swordfish. Anchoveta, jack mackerel, and sardines are the primary commercial stocks in central Chile. Anchoveta are found in more recently upwelled waters, close to the coast. Sardines, on the other hand, are typically found farther offshore. Seasonal upwelling plays a major role in the spawning behaviors of both sardines and anchoveta. By spawning at the end of winter, egg and larval survival is greatly enhanced. This is due to the moderate upwelling, which causes lower turbulence, as well as a weakened Ekman drift offshore. These two species experience population shifts related to climate changes and environmental events such as El Niño. This is due to changes in the availability of each species habitat. Anchoveta are an important component in the diets of marine mammals, seabirds,