The Study

Rivers in North Carolina contain small concentrations of mercury which can accumulate in fish over their lifetimes. Because mercury cannot be excreted from the body, it builds up in the tissues. The concentration of mercury in fish tissue can be obtained at considerable expense by catching fish and sending samples to a lab for analysis. Directly measuring the mercury concentration in the water is impossible since it is almost always below detectable limits.

A study was recently conducted in the Wacamaw and Lumber Rivers to investigate mercury levels in tissues of large mouth bass. At several stations along each river, a group of fish were caught, weighed, and measured. In addition a filet from each fish caught was sent to the lab so that the tissue concentration of mercury could be determined for each fish. Here are the data. Each fish caught corresponds to a single row of the file. In order, the recorded information for each fish is

river

station

length in cm

weight in grams

mercury concentration in parts per million

Data analysis

Questions:

• Is there a relationship between mercury concentration and size (weight and/or length) of a fish? Is this relationship the same for the two rivers?
• A concentration over 1 part per million (0 on the log scale) is considered unsafe for human consumption. In light of this, what recommendations can you make for fish caught from these rivers?