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examBoard: Cambridge
examType: IGCSE
lessonTitle: Effects of ENSO on South American Fisheries
The waters off the western coast of South America are home to some of the world's most productive fisheries. However, these fisheries experience dramatic changes every few years due to a natural climate pattern called El Niño-Southern Oscillation (ENSO). Understanding how ENSO affects these fisheries is crucial for managing marine resources sustainably and supporting the communities that depend on them.
Key Definitions:
During El Niño events, trade winds weaken or reverse direction. This causes warm water to flow eastward across the Pacific, raising sea surface temperatures along the South American coast. The warm water creates a barrier that prevents nutrient-rich deep water from rising to the surface (upwelling). Without these nutrients, phytoplankton populations decline dramatically, affecting the entire marine food web.
During La Niña events, trade winds strengthen, pushing more warm water westward and allowing colder, nutrient-rich water to upwell along the South American coast. These conditions typically enhance marine productivity, creating favourable conditions for fish populations to thrive. La Niña often brings a boom to fisheries after the disruption of El Niño.
The Humboldt Current flows northward along the western coast of South America and is one of the most productive marine ecosystems on Earth. This cold-water current supports an abundance of marine life due to its high nutrient content from upwelling. ENSO events significantly disrupt this ecosystem.
Under normal conditions, the Humboldt Current ecosystem supports massive populations of small pelagic fish, particularly anchoveta (Peruvian anchovy). These fish feed on the abundant phytoplankton and zooplankton that thrive in the nutrient-rich waters. The anchoveta then become food for larger predators, including humans, making them a critical link in both the marine food web and the human economy.
During El Niño, anchoveta populations crash as they either die off or migrate to deeper, cooler waters. Some species like sardines and jack mackerel may temporarily increase. During La Niña, anchoveta populations typically boom, sometimes increasing tenfold from El Niño lows.
Sea lions, fur seals and other marine mammals that feed on anchoveta suffer during El Niño events. Breeding success drops and mortality rates increase. Some may change their feeding habits or migrate to find food.
Seabird populations like cormorants and boobies experience mass mortality during strong El Niño events. Breeding colonies may be completely abandoned as adult birds search for food elsewhere, leading to failed reproduction for entire seasons.
Peru's fishing industry, which is heavily dependent on the anchoveta, experiences dramatic boom-and-bust cycles linked to ENSO events. The Peruvian anchoveta fishery is typically the largest single-species fishery in the world, but it becomes highly vulnerable during El Niño events.
The 1972-73 El Niño event caused one of the most dramatic fishery collapses in history. Before this event, Peru's anchoveta catch reached a peak of 12 million tonnes in 1970 (about 20% of the world's total fish catch). During the El Niño, the catch plummeted by over 80%. This collapse was worsened by overfishing in the preceding years, which had already stressed the population. The Peruvian fishing industry, which had become the world's largest, was devastated. Thousands of workers lost their jobs, processing plants closed and the national economy suffered significantly. This event highlighted the vulnerability of single-species fisheries to climate variability.
Chile's fisheries are also affected by ENSO events, though sometimes in different ways than Peru. Chile's fishing industry is more diversified, targeting species like jack mackerel, sardines and hake in addition to anchoveta.
During El Niño events, while anchoveta populations decline, some other commercially valuable species may temporarily increase in Chilean waters. Tropical and subtropical species may move southward into Chilean waters, creating opportunities to catch different species. However, these shifts require fishers to adapt their equipment and techniques, which can be costly and challenging.
The economic consequences of ENSO events on South American fisheries are substantial:
ENSO events create significant social challenges in fishing communities:
Over decades of experiencing ENSO events, South American countries have developed various strategies to manage fisheries during these climate fluctuations:
Advanced monitoring of ocean temperatures and conditions helps predict ENSO events months in advance. This early warning allows fisheries managers and fishers to prepare for changing conditions.
Fishing quotas that can be quickly adjusted based on fish population assessments help prevent overfishing during vulnerable periods. Peru now uses a system where fishing is paused when juvenile fish make up too large a percentage of catches.
Encouraging fishers to target multiple species and develop alternative livelihoods (like tourism or aquaculture) reduces vulnerability to single-species collapses during El Niño events.
Climate change may be altering the frequency, intensity and impacts of ENSO events. Some research suggests that extreme El Niño events may become more common in a warming world. This could mean more frequent and severe disruptions to South American fisheries in the future. Additionally, ocean acidification (caused by increased CO₂ absorption) may further stress marine ecosystems already dealing with ENSO fluctuations. Developing robust management systems that can adapt to these changing conditions will be crucial for the sustainability of South American fisheries.
ENSO events create a natural cycle of boom and bust for South American fisheries, particularly those dependent on anchoveta and other small pelagic fish. These cycles have profound ecological, economic and social consequences for coastal communities and national economies. While these natural climate variations cannot be prevented, improved understanding, monitoring and management strategies can help reduce their negative impacts and build more resilient fishing communities and industries. As climate change potentially alters ENSO patterns, adaptive management will become even more important for sustainable fisheries in South America.
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