and larger fish. Shifts in these populations ultimately cause a shift in the energy processing within the Humboldt Current System. Jack mackerel (jurel) is the second largest fishery in the Humboldt Current System. As with the anchoveta in Peru, this species is believed to be composed of a single stock. Jurel are a straddling species. This means the species is found both within and outside of the 200-mile economic exclusive zone. Jurel became an important fishery in the 1970s to alleviate the pressure put on the anchoveta stock. During the 1980s, however, the jurel decreased in population size due to poor recruitment and overfishing. Restrictions of jurel fishing were imposed in 1998 which led to regrowth of the population. Since 2002, the jurel population is now under full exploitation. Between 1993 and 2008, the hake fishery in Peru declined significantly. This was due to overfishing, environmental stress, and decreased reproductive capacity. The Chilean hake population in central-south Chile catch exceeded 100,000 tons, and dropped to 40,000 tons in 2007. Influence of El Niño The productivity of the Humboldt Current System is strongly affected by El Niño and La Niña events. During an El Niño event, the thermocline and upper region of the OMZ deepen to greater than 600 m. This causes a loss of nitrogen and decrease in export of carbon. El Niño also causes poleward currents to increase in velocity. During non-El Niño years, productivity is very high due to the high nutrient contents, nitrogen recycling through processes such as denitrification, increased carbon export, and remineralization During El Nino events, fish abundance and distribution are significantly affected, often leading to stock crashes and cascading social and economic impacts. These events have led to sequential changes, where sardines and anchovies have replaced each other periodically as the dominant species in the ecosystem. These species changes can have negative consequences for the fishing industry and the economies of the countries that fish the system. The anchoveta fishery in Peru was booming during the 1960s. In 1970, catches were reported to exceed 12 million tons per year. This accounted for 20% of the world's catches. An El Niño event occurred during 1972 and caused the anchoveta population to collapse. However, sardine populations saw a dramatic increase in the next 15–20 years. Consequently, sardine fisheries grew in this "regime shift". See also Gulf Stream Humboldt squid Ocean current Oceanic gyres Physical oceanography South