Great Lakes Fishing

This week’s Tidy Tuesday deals with commercial fishing on the Great Lakes. While exploring the data, I was struck by a rapid increase followed by a rapid decline in commercial fish hauls. I was further struck by how much of this rise and fall occurred entirely due to one species (alewife) in one lake (Michigan).

It turns out that alewife are an invasive species that were first found in Lake Michigan in 1949. Salmon were introduced in 1966 as a predator in an effort to control alewife populations. They were only moderately successful at this goal, but they became a popular sport fish.

What did eventually control and then devastate alewife populations were other invasive species, namely zebra and quagga mussels. These mussels have out competed alewife and other forage fish, depriving them of a food supply and creating a a ripple effect throughout the food chain.

Salmon continue to be stocked in the Great Lakes but without a source of prey, sport fishing on the Great Lakes is likely to decline

Line chart showing salmon stocking and alewife production in Lake Michigan. The introduction of salmon had only a modest impact on alewife production, but invasive mussels later caused alewife production to collapse

My source code is available on GitHub.