Third Herring Brook: Dam removal will restore habitat -10/8/14

Third Herring Brook: Dam removal will restore habitat

Wicked Local Marshfield

By Erin Tiernan
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Updated Oct 8, 2014 at 4:29 PM

NORWELL
The first of three dams in the Third Herring Brook Watershed is coming down.
The removal of the Mill Pond dam behind the South Shore YMCA will allow the brook to flow freely, creating a larger and more viable habitat for native fish populations.
The Mill Pond dam is centrally located within the watershed, and although the dam removal will not reopen the brook's gateways to the ocean, it will free up habitat for fish such as the native wild brook trout to nest and spawn in more areas.
"Our vision for Third Herring Brook is to restore the free-flowing rivers," Samantha Woods, executive director to the North and South Rivers Watershed Association, said.
Four dams clog the brook and the tributaries that trickle through the watershed, cutting off miles of habitat for native aquatic animals.
As suggested by the name, herring once filled the streams that make up the watershep all the way up to Jacob's Pond in Norwell, when they returned to the fresh waters to spawn. After the four dams went in, the fish lost nearly 10 miles of streams. This and other factors has resulted in smaller populations, Woods said.
"These are keystone species and they are important to the larger ecological system," she said.
If herring populations along with wild brook trout and American eel, which also live in the rivers, are given expanded habitat, the increases in populations could have a positive impact on the South Shore's coastal fisheries. While there are many factors playing into the decimation of the fisheries on the Eastern seaboard, both Woods and state Department of Ecological Restoration Priority Projects Manager Nick Wildman agree that more brook fish could help revitalize populations of striped bass and other sport fish in the nearby ocean.
"These migratory fish are river herring and American eel mainly and are food for striped bass and even sport fish, as well as commercial fish," Wildman said. "They are under threat from overfishing just like cod and haddock."
The implications of the dam project could be far-reaching. Under the supervision of the North and South Rivers Watershed Association and the DER, the Peterson Pond dam at the Hanover Mall and the Tack Factory dam, located behind the Cardinal Cushing Centers, will also be removed. This will free up more that 9.7 miles of free-flowing rivers and tributaries for the ecosystem.
Free of dams, scientists hope the native aquatic animal populations will reclaim the habitat and revitalize the ecosystem.
"Where these dams don't serve a purpose anymore, it makes sense to take them down and also take away the liability and maintenance issues for the owner," Woods said.
Across the commonwealth there are more than 3,000 dams, nearly all of which are nonfunctioning reminders of the hydraulic power they generated during the Industrial Revolution. Now, the dams isolate habitat and impede the growth of native fish populations. The dams, many of which are more than 200 years old, also present a liability issue for owners. The owner – whether private or public – would assume responsibility for any injury to person or property as a result of a breach or fall.

In Hanover, the Mill Pond dam removal will not reconnect the watershed with the ocean, but it will augment the amount of habitat available to wild brook trout, which have been trapped in tributaries for up to 200 years due to river fragmentation by dams.
"When species cannot migrate, we get a population with isolated genetics, they are not as robust or resilient," Woods said.
The pond environments created by the dams within the watershed have also adversely impacted native fish populations. Ponds are naturally much warmer and species cannot survive in the tepid waters of Jacobs and other area ponds.
"It's not that the pond habitat is bad, it's that it is not supposed to be here. This is supposed to be a river," Woods said.
By next fall, the NSRWA and its partner, the DER, hope to take down the Tack Factory dam at the Cardinal Cushing Centers. This dam removal will open the watershed up to the mouth of the North River, allowing herring, American eel and other species to reclaim miles of habitat.
"The more stream they have to spawn in, the more successful the spawn will be," Woods said. "The more complex the habitat is and the better off the fish will be. We are restoring that connectivity and having that complexity is critical to our fisheries."
One dam will remain once the connectivity project is completed, Wildman said. The dam that holds the waters of Jacobs Pond will not be removed.
"Jacobs pond is such a huge community resource. To lose that would be a huge loss for the community," Wildman said. "Our charge at the DER is to restore habitat for fish and wildlife, but also for people. We certainly take the public into consideration and see what the public benefits and the ecological benefits are."
There are, however, some drawbacks to dam removal. It can be expensive. Wildman said the Mill Pond dam removal will cost $411,000 once completed this week. Much of the funding, with the exception of grants, is paid for by the dam owner, which in this case is the South Shore YMCA.
Wildman said there could also be implications for Hanover's and Norwell's public drinking water. Both towns pull water from wells in the Third Herring Brook watershed.
"We will remove all of these barriers, but if there is not enough water, that could be a problem," he said. "It is something we will have to watch carefully."
Follow Erin Tiernan on Twitter @ErinTiernan.