Volunteer River Herring Monitoring at Beaver Dam Brook and Manomet Brook

River Herring are anadromous (migratory) fish that consist of two species —alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis). They live in the ocean for most of their lives, but each spring the adults (3+ years) swim up rivers to spawn. In April and May, the adult herring enter the streams along the Massachusetts coast, including Beaver Dam Brook where the alewife swim up to Fresh Pond and the blueback herring, who arrive somewhat later, spawn in the riverine system. Once they spawn, the adults head back to the ocean. Once the eggs hatch, the juveniles will spend a few months in the freshwater habitat before they too head to the ocean to live as adults.

Brook Trout (Salvelinus fontinalis) are Massachusetts's only native trout species, and they require clear, cold, well-oxygenated water year-round. They are threatened by development, pollution, and climate change impacts that alter and remove suitable habitat. Manomet Brook and Foothills Preserve restorations provide potentially suitable cold-water habitat.

The Tidmarsh Herring Count Project is focused on documenting the number of fish that make it up Beaver Dam Brook en route to Fresh Pond or to elsewhere in the riverine system to spawn. The counts are reported to the Massachusetts Department of Marine Fisheries and become part of the Massachusetts state count. The project also contributes important information to research about the return of biodiversity to the Tidmarsh Headwaters and Manomet Brook restoration projects. The annual count typically occurs throughout April and May.

The Tidmarsh Herring Count is a collaboration between Mass Audubon, Living Observatory, and the Town of Plymouth. The lead scientist on the project is Dr. Sara Grady, Mass Audubon Senior Coastal Ecologist.

This group of over 20 herring sped under the Beaver Dam Brook bridge on May 7, 2017.

Recent Updates

Herring Count Summary, May 9 - fish at both bridges!

By Sara P. Grady on May 9, 2024
Hooray! We have fish! So far 36 river herring have been seen at Bridge #2 and what's even more amazing, 2 fish have been seen at Bridge #1. This is the first year that we've seen herring there so that's very exciting. Right now our number of fish per week is tracking along with 2018, which was a relatively low year, but there's still 2/3 of a month to go as well. In 2018, the issue was likely the inability of river herring to get through the entrance to Beaver Dam Brook at White Horse Beach. We have talked to the town and they recently cleared the culvert and brook entrance so that's not a concern this year. That said, the structure of the beach and location of the sand on it means that passage into Beaver Dam Brook is difficult except at high tide, so fish passage is limited through part of the tidal cycle. It is a testament to the restoration of Tidmarsh that there are river herring traveling through the system at all. Keep collecting that data so we can have a valid population estimate at the end of the season. Happy May!

Herring Count Summary, April 16, 2024 - this could be the week!

By Sara P. Grady on April 16, 2024
This could be the week that we see herring! Here's why that seems very possible:


Sara P. Grady
Robert Vincent
Glorianna Davenport
Kimberly Snyder