Big lake, small mussels: estimating size and distribution of zebra mussel populations
The first field season of a project developing underwater survey methods for zebra mussels is complete. The project will develop recommendations for using underwater surveys to estimate zebra mussel population abundance and distribution. Researchers sampled seven infested lakes using two different survey methods – distance sampling and double-observer – that will allow them to quantify zebra mussel populations and estimate detection probabilities.
Without estimates of detection probabilities, it’s extremely difficult to know the extent of a zebra mussel population in a newly infested lake, to determine appropriate rapid-response treatment options, or to evaluate the effectiveness of the treatments over time. This project will create, test, and standardize sampling methods, leading to estimates of zebra mussel population size and distribution that can be compared across lakes and over time (for example, before and after treatment efforts).
Researchers visited twelve lakes this summer, and conducted SCUBA operations in seven of them. To verify their efforts, they also collected data from two SCUBA teams (the double-observer method) at two lakes. Survey efforts were concentrated around the area of infestation, with efforts decreasing as they moved farther around the lake. To conduct the surveys, divers set up 30-meter-long transects and counted the zebra mussels they could see within one meter on each side. They also recorded factors such as water clarity, percent cover, and depth. Check out an underwater video of what setting the transect and counting the mussels looks like here.
Members of the research team gave attendees of the 2017 AIS Research and Management Showcase a peek into how difficult it is to assess distribution of such small organisms by attaching pistachio shells to rocks and logs and having observers search for them. The attendees found fewer than half of the shells!
Going forward, this project is forming a partnership with students at Carleton College who will be exploring sampling methods and their utility for monitoring zebra mussels for their senior comprehensive project. Next summer, researchers will sample roughly a dozen more infested lakes to further test survey methods and provide enough data to make these methods applicable to many other lakes.