EarthLabs > Fisheries > Lab 8: Hot Topic: Effects of Climate Variability on Fisheries > 8A: Short-Term Variability: El Nio

Hot Topic: Effects of Climate Variability on Fisheries

Part A: Short Term Variability: El Niño

Satellite image showing global sea surface temperatures. Warmer areas are red. The red band moving east across the equator shows El Niño conditions. Image courtesy of NASA.

El Niño is an abnormal warming of surface ocean waters in the eastern tropical Pacific that occurs approximately every 3 to 7 years. The phenomenon was named El Niño (meaning "The Boy Child" or "The Christ Child") by South American fishermen because it typically arrives around Christmastime.

Under normal conditions, east-to-west winds drag warm waters westward. This results in a pile-up of warm water in the western Pacific, just east of Indonesia, and northeast of Australia. At the same time, cold water from deep in the ocean rises to the surface along the South American Coast.

Every few years, the trade winds change direction. This allows the pool of warm water to move eastward, where it blocks the rising cold water. These changes help trigger the global weather changes associated with El Niño. The images below show the direction of trade winds (yellow arrows) and the location of warm ocean waters (red) under normal ocean conditions (left) and during an El Niño event (right).

Image Source: NOAA (via USA Today. Graphic by John Herne.
Image Source: NOAA (via USA Today. Graphic by John Herne.



  1. Read more about ocean conditions during a non-El Niño year and during an El Niño year.

    Checking In

    Answer the following questions to check your understanding of conditions affected by El Niño.

    • What is the role of upwelling along the South American coast?
      Upwelling is when deeper colder water from the bottom of the ocean moves up toward the surface away from the shore. This water is nutrient-rich and is responsible for supporting the large fish population commonly found in this area.
    • Why are the waters warmer and deeper in the western Pacific than they are in the eastern Pacific during a non-El Niño year?
      Trade winds push surface water westward toward Indonesia, causing the sea level to be roughly half a meter higher in the western Pacific than in the east. Thus you have warmer, deeper waters in the western Pacific and cooler, shallower waters in the east near the coast of South America.
    • How does El Niño alter weather patterns?
      Tropical thunderstorms are fueled by hot, humid air over the oceans. As the Pacific's warmest water spreads eastward, the biggest thunderstorms move with it. Rains that normally would fall over the tropical rain forests of Indonesia fall over the deserts of Peru, causing forest fires and drought in the western Pacific and flooding in South America. The atmosphere also responds to El-Niño by producing patterns of high and low pressure that can impact weather far away from the equatorial Pacific (e.g., higher temperatures in western Canada and the upper plains of the United States, and colder temperatures in the southern United States). The east coast of southern Africa often experiences drought during El Niño.


  2. Examine the graph below of California squid landings from 1940-2000. The blue bars show the years in which particularly strong El Niño events occurred.
    • 1965-1966
    • 1972-1973
    • 1987-1988
    • 1992-1993
    • 1994-1995


    Image courtesy of NOAA.


    Checking In

    Answer the following questions to check your understanding of the information provided in the graph of California squid landings.

    • How were squid catches affected by El Niño between 1950 and 2000?
      Squid catches were typically lower during El Niño years than non-El Niño years.
    • Do the effects of El Niño on California squid appear to be permanent?
      According to the data shown in the graph above, the squid fishing areas appear to always bounce back after El Niño events.


    Reduced Catches of Squid During El Niño Warming Events

    Squid has become an increasingly important product in California. Landings have been increasing since the 1960s; however, we don't know if the population has actually been increasing in the warm period since 1976, or if the increased landings reflect increased fishing effort and markets for squid. This increase has been interrupted several times by major El Niño events that raise ocean surface temperatures along the California coast. Landings dropped markedly during the 1958, 1983-84, 1992, and 1998 El Niños. Squid are short lived, reproducing and then dying within 1 year. During El Niño events they are not found on their normal spawning grounds or farther north. They may be spawning in deeper colder water during these years. So far, the population has always recovered after the El Niño has passed.



    Stop and Think


    1: Squid has only recently become a commercially important seafood. Explain how other species with long histories of commercial fishing and economic importance might be affected by an El Niño event.


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