We are working to understand the population status of River Herring spawning runs in tributaries of Chesapeake Bay. To do this, we are counting fish in spawning streams using Dual-frequency Identification Sonar (DIDSON), also known as imaging sonar, to determine population size. This cutting-edge technology allows us to record and count adult fish in both clear and turbid water as they swim past a sonar station during their spawning runs. It also allows us to sample throughout the day and night without having to be present on site. See below for an example of what a DIDSON video looks like.

What are you seeing in the DIDSON video above? You are essentially looking down on the stream from above. The brightest spots that you see, if you notice, are not moving. Those are rocks on the bottom of the river bed. Each of the moving, short, bright lines is a fish. Dark spots that are moving are shadows cast by the fish. The fish moving from right to left are swimming upstream. We know that these fish are Alewife because we caught several and visually identified them at the site.

We also sample for fish using fyke nets or electrofishing to determine which species we are counting in DIDSON videos and to study the sex and age distributions of the population.

Our work on River Herring will help contribute to an important body of research needed to direct efforts to restore herring populations to what they once were.