Hitchhikers: No Ballast on Board (NOBOB)

Many ships enter the Great Lakes from the St. Lawrence Seaway that connects the Great Lakes to the Atlantic Ocean. Scientists collected data from ships to determine the threat that water and sediment in the ballast area of ocean-going ships poses to the Great Lakes. These ships coming from around the globe may contain aquatic non-native (invasive) plants and animal species.

Hitchhikers: No Ballast On Board

View the Data: NOBOB Data Set

Sample Inquiry Questions

  • What body of water had the highest (ind/kg -¹) for freshwater animals? Which had the lowest?
  • Which two oceans had the lowest total animals in residual water?
  • Do ballast tanks typically carry more freshwater/brackish animals or marine animals?
  • How many organisms are carried in an average NOBOB ship?

Using this data:

  • Graph the percentage of salinity in the residual sediment data.
  • Graph the percentage of salinity in the residual water data.
  • Observe if there are more organisms in residual water or residual sediment.
  • Is there a correlation to  the number of organisms in the residual sediment and the number in the water?

About the Data

This data, collected from 2000-2002 shows percentage of salinity, the number of plants and animals found in sediment and water of the ballast tanks of 42 vessels that entered the St. Lawrence Seaway and Great Lakes from the following areas: Great Lakes, North Sea, Baltic, Mediterranean and Black Sea, Northwest Pacific, West-Central Atlantic Ocean. Data calculations:

  • The units for the total animal count in residual sediment are individuals per kilogram (ind/kg -¹), which indicates the total number of animals per kilogram of sediment.
  • Likewise, the units for the total animal count in residual water are (ind/L -¹), which indicates the total animal count per liter of water.
  • Because a liter of water weighs one kilogram, these units are directly comparable.
  • Values reported here are the median values for all the samples (from multiple ships) of a particular type.


Left: A ballast tank is a compartment within a ship that holds water.

Right: Scientists enter the ballast hatch to take samples of the water and sediment in the ballast tank.

Fig 1_Ballast Tank Diagram2a Researcher in Ballast Hatch2b InsideTank

Figure 1, Ballast Tank Diagram (left).  Figures 2a, 2b, scientist in ballast hatch and ballast tank with scientist inside

How water is loaded and discharged from the ballast.

Ballast water loading

Figure 3a, Ballast loading

Ballast water discharge

Figure 3b, Ballast discharge


Data Source: NOAA Great Lakes Environmental Research Laboratory, Tom Johengen