Activity: Find the Break! Searching for Steelhead

Summary: Students use surface water temperature data to find fish, in the same way that commercial, subsistence and recreational fishermen use them.

You Need:


Use surface water temperature contour maps to answer questions.

Part 1

Working as a whole class:

  • Locate Lake Michigan, Ludington and Big Sable Point on charts.
  • Explore CoastWatch surface water temperature maps (Figure: St Joseph).
  • Point out:
    • Image location, date and time.
    • City names, latitude and longitude.
    • CoastWatch uses contour lines to represent isotherms. Each contour line represents a 1 degree Fahrenheit (F) change in temperature.
    • Grey and black shading indicate the presence of clouds or other possible errors in data.
  • Identify warmest and coldest regions.
  • Discuss steelhead natural history and optimal fish habitat.
  • Fish prefer habitats that:
    • Are within the fish’s optimal temperature range.
    • Have access to food.

Part 2

Discuss thermal fronts:

Thermal fronts are the interface between water masses with significantly different temperatures. This interface is a region where water temperatures rapidly change and are often abundant with aquatic life. Temperatures can range 3 to 10 degrees F over a short distance. Thermal fronts with the rapid temperature change tend to be the most productive fishing areas.

  • Discuss upwelling and how physical factors in eastern central Lake Michigan contribute to upwelling at Big Sable Point (Figure: Big Sable Point).
    • The bathymetry and coastline at Big Sable Point contribute to upwelling and availability of terrestrial insects at thermal fronts.

Part 3

In groups of two:

  • Complete the data sheet.
  • Communicate conclusions to class.
  • Ask students where they would expect to find steelhead on Maps A, B and C from the data sheet, based on what they’ve learned about steelhead life history and upwelling.

Activity Extension

Use a computer with internet access to explore real-time surface water temperature contour maps and weather data.

  • Navigate to surface water temperature maps:
    • Go to: Great Lakes Observation System
      • In the pull-down menu: data mapping / offsite data, select: surface water temps.
      • Select one of the Great Lakes (or Lake St Clair) from the satellite image on the CoastWatch Great Lakes Surface Water Temperature page.
  • Explore real-time weather data:
    • Go to: Great Lakes Observation System
      • Select: Harborview
      • Select: Harbor to get started (upper middle of the page)
      • Select: Layers (modeled winds, water surface temperatures, latest observations) from the right column.