Someone Call for a PI?

By: Caroline Fazzio

I went through a phase in middle school where I devoured mystery stories. I scoured library shelves for authors like Agatha Christie, Sir Arthur Conan Doyle, and Mary Higgins Clark, and passed hours reveling in the adventures of their sleuthing heroes and heroines. For the briefest moment, I even considered pursuing a career in law enforcement and detective work. Little did I know that years later I’d be involved in my own PI work—tracking down aquatic plants for the MN DNR.

PI (point-intercept) surveys are the PI (private investigator) work of the invasive species program. Point-intercept surveys investigate all the vegetation in an entire lake, revealing where certain species occur, and in what abundance they exist. These surveys inform us about changes in lake vegetation across years and after treatments for invasive species.

Conducting a PI survey is fairly straightforward. We assign a grid of points across the lake and upload them to a GPS. Once out on the water, we navigate to each point and toss a throw rake into the water (a throw rake is simply a double-sided rake head attached to a rope). We let the rake drag along the bottom, then pull it up along with all the plants it caught on the way. We identify the plants on the rake and note their abundance. Then we clean the rake, drive to the next point, and repeat the process.

July was a busy month for PI surveys, and I’ve spent many days out on a lake pulling up plants and practicing my aquatic plant-ID skills. Seeing what kinds of plants we pull up is always interesting, but even more intriguing is trying to explain the presence or absence of a plant we weren’t expecting, or comparing surveys to understand treatment effects on lake vegetation. Aquatic invasive species management requires striking a balance between curbing invasive species and interfering as little as possible with native aquatic ecosystems. Achieving this balance requires thoughtful planning, careful monitoring, creative thinking, and a little investigative work along the way.

*Photos curtesy of the MN Department of Natural Resources