Herring are an integral part of the river ecosystem. They are anadromous, meaning they spend part of their lives in the ocean and part in the river. By moving between the two as both predator and prey, they distribute energy and nutrients among the ecosystems along the way. Herring were also an important fishery, and play a central role in Wampanoag food and ceremony. The precipitous drop in their population was therefore of great concern and a big motivator for restoring the river and the herring run in it.
CRT has been tagging herring since 2015. Tagging can tell us many things about the fine-scale movements of these fish: where they go to spawn in the watershed, where they get hung up, and what we might be able to do to improve their freshwater habitats.
We catch the fish in nets, make a small incision in their abdomen, and insert a tiny "PIT" tag. The tags send a radio signal to antennae we have set up along the river when the fish passes by. If a tag "pings" repeatedly on one antenna, we know the fish is "stuck" there, perhaps because of a dam or culvert. If that happens a lot, then we prioritize that obstacle for removal or improvement.
Note: Fish tagging and counting have been suspended during the Corona virus emergency.
Photo: Alison Leschen
What have we learned by tagging?
The tagging work was critical in demonstrating that we needed to remove the dams and culverts. We found that the many culverts and dams (over 26 along the river!) blocked or slowed fish migration, preventing them from reaching spawning ponds and making them more vulnerable to predation. For instance, we found that the culverts under John Parker Rd. caused fish to remain in the pool below the road for several days and we watched birds pluck them out of the water as they milled around. Because of this information, removing dams and culverts and replacing them walkways and improving passages under road crossings is a major effort in the restoration.
This work also demonstrated that, in contrast to other rivers, in the Coonamessett herring move at night. This is probably because there are no trees along the river to protect them from bird predators, like gulls and ospreys, during the day. This told us that we needed to make the river deeper and create hiding places and to plant trees along the river to create shade to keep the river cool and protect the fish.