Restoring Rivers, Reviving Species: Our Work to Help River Herring

Fish Monitoring and Ecosystem Resiliency in Long Island Sound

Alewife is a small fish—but it’s incredibly important to the Sound ecosystem because it’s at the bottom of the food chain and feeds other fish, mammals, and birds. A type of river herring, alewife must migrate from the Sound into river habitats to reproduce. Dams that block their way can cause alewife populations to crash (along with populations of other Sound species that also need access to rivers for parts of their life cycles).

Since 2005, Save the Sound has opened 107 river miles through dam removal and fishway installation projects in the Long Island Sound region. But the true measure of ecological impact comes from fish monitoring before and after a restoration project, a task that falls into the hands of Fish Biologist Jon Vander Werff.

“We need to understand how fish are using a system before we change the system,” says Jon. “We trap and release fish to estimate the number of species and of fish that are using the river as a highway—traveling upstream and downstream—or as a home. If the numbers are lower than expected, those findings can help initiate and guide restoration efforts.”

Monitoring after the removal of a dam is important too. “After our removal of Pond Lily Dam on New Haven’s West River in 2016, our monitoring efforts have shown alewife, sea lamprey, and gizzard shad migrating into spawning habitat upstream of the former dam site,” says Jon. So far this year, our fish trap has caught more than 57 alewives, indicating another year of habitat utilization since we removed the Pond Lily Dam. “This river has made a remarkable recovery and is a terrific example of ecosystem resiliency."