Powerboats and Manatees

Since this post is for a school assignment, it may be a little different from usual. I hope you enjoy it anyway!


I’m studying the correlation between registered powerboats and manatees killed. The independent variable is the registered powerboats, and the dependent variable is the manatees killed. I chose these variables to answer the question, “Do powerboats pose a risk to manatees in the sea?” This is interesting to me because I’m an animal lover, and am interested in the well-being of sea creatures. My hypothesis about the relationship between my variables is a strong positive correlation.


I got my data from Sharyn O’Halloran’s PowerPoint presentation on the subject. It contains 18 data points. I used a TI-83 Plus to analyze my data and find a linear regression for it.


  • Graphs and tables: powerboats-and-manatees.xlsx
    • Figure 1 is a table with the data from the aforementioned PowerPoint. The last column is interactive; it gives approximate values for each value as a function of the year.
    • Figure 2 is a scatter plot comparing the two values.
    • Figure 3 is a line plot comparing each value to the year
  • Linear regression: y=0.1127x-35.1785
    • This means that if no powerboats are registered, -35.18 manatees will be killed. It also means that for every 1000 powerboats, 0.11 manatees are killed.
  • X-intercept: 312.15
    • This means that if 312,150 powerboats are registered, 0 manatees will be killed. In this scenario, the x-intercept is useful because it shows an “okay” number of powerboat registries.


Correlation coefficient: 0.9127

The correlation between registered powerboats and manatees killed is strong and positive. I can be rather confident about using my trend line to make predictions and draw conclusions. An example of extrapolationg using my equation is that if there are 800,000 registered powerboats, 53 manatees will be killed. An example of interpolating with my equation is that if there are 600,000 registered powerboats, 31 manatees will be killed.

There is causation between my two variables because reckless powerboat drivers are the ones who kill the manatees. People can use these results to determine how safe powerboats for manatees, and adjust regulations as necessary.

Image credit: Chris Muenzer, Flickr CC BY-SA 2.0


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