March 31, 2017 — Scientists have a powerful new tool to help them “see” fish in the Chesapeake Bay’s murky tributaries, and it’s yielding some surprisingly good news about two of the estuary’s most troubled species. “Imaging sonar” uses sound to help them view, and count, passing fish in dark or cloudy water. For the past few years, scientists with the Smithsonian Environmental Research Center have been deploying one of these underwater sound cameras in some of the Bay’s rivers to monitor spawning runs of alewife and blueback herring, collectively known as river herring.
No one knows for sure how many river herring are in the Bay, as fisheries managers lack the staff and resources to do a comprehensive assessment. But a SERC-led team of scientists deployed an imaging sonar device in the Choptank River in 2014 that captured images of the fish as they swam by. Based on the rate at which scientists saw the shadowy blips cross their computer screens, they estimated that as many as 1.3 million river herring swam upriver that spring to spawn. That’s more than expected, and way more than state biologists had figured were there in the early 1970s, the last time anyone looked intensively at the Choptank’s herring runs.