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?
    • Why are the waters warmer and deeper in the western Pacific than they are in the eastern Pacific during a non-El Niño year?
    • How does El Niño alter weather patterns?
  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.

    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?
    • Do the effects of El Niño on California squid appear to be permanent?

    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.