Brewster Works To Keep Alewife Flowing Through Low Waters

By: Bronwen Walsh

Topics: Herring

Baby alewife migrate from their forever home in Slough Pond to Walkers Pond and out to sea, returning every three years to spawn. JANICE RILEY PHOTO

BREWSTER – The Alewife Committee on Feb. 23 chose to continue aiding the herring that migrate between Walkers and Slough ponds despite drought-induced low water levels that made last year especially challenging for juvenile herring.

“There’s been an alewife committee since 1788, when the town, what was then Harwich, bought the stream,” said member Doug Erickson. “We have made many efforts over the years to improve our ability to control the water, so we’d have optimal water for the herring migration, for both the adults going up to spawn and the juvenile herring to return to the ocean.”

Because of last summer’s drought, a screen was put at the top of the run at the dam to keep the juvenile herring from going down the stream between Walkers and Slough ponds because the water levels were so low, Erickson said.

In partnership with the Massachusetts Division of Marine Fisheries, “we built the water up, and we would flush the juvenile herring out for a while, and then we’d put the screen back,” he said. “I think we’ve been doing a good job of managing the water levels.”

The southwest winds also tend to dry the sand in the ditch between the two ponds, Erickson said, so plans this year include continued water level maintenance, digging a one-foot-deep ditch along the stream, and repairing concrete weirs (or fish ladders) north of Stony Brook that date back to 1945.

Alewives and blueback herring share the common name of river herring that annually use the Cape’s 20-some river systems to migrate between fresh and saltwater to complete their lifecycle. Females spawn in the spring and can lay up to 30,000 eggs, which hatch in a few days. Over the summer, the juvenile herring, or fry, occupy the same pond where they were born before emigrating to the sea and returning every three years to spawn.

Due to an overall decline along the East Coast, alewives and river herring are considered “species of concern.” In 2006, the state placed a moratorium on the harvest, possession or sale of river herring in Massachusetts. In 2020, Harwich counted 1.2 million herring through its runs, marking the largest count in the state.
Stephen Spear, a conservation specialist with Natural Resources Conservation Service who lives in town, said other herring runs on the Cape are having the same problem as Brewster.

“There’s just some years the juveniles can’t get out when they’re ready to get out,” Spear said. “Sometimes they go out early before the water levels drop. Sometimes they leave late in the fall.”

If the fry are allowed to overwinter, they’re more vulnerable to predators, Erickson said. Their food source disappears as the water gets colder and there’s less sun.
Other alternatives, suggested by Brad Chase of Marine Fisheries’ New Bedford South Coast Field Station, would be placing a weighted line net where the ditch enters Walkers Pond, or installing a water gate at the culvert, Erickson said. “That way, any herring that would want to get up there, they would still be in the ponds in deeper water, where there’s plenty of habitat,” he said.

“Is it better to have the fish spawn in the other ponds, where we know they can get out?” Erickson asked aloud, noting that last summer, the narrows between Upper and Lower Mill Pond completely dried up, and the water got so low, “we couldn’t run the mill.” Then September rains produced “an incredible run” in October and November.

Janice Riley, who lives on Slough Pond, thanked the committee for its hard work over many years.

“It’s a long stretch through the woods that requires attention,” said Riley, who also thanked Brewster Natural Resources Director Chris Miller for partnering with AmeriCorps to provide additional help. “It varies every year, but I’d hate to see us making decisions after this drastic year we’ve had. [Fry] are very persistent, and that’s how they survive.”

Marcia Kielb and Ron Essig, board members of the Brewster Ponds Coalition, also supported the committee’s efforts. “It’s very important to us to not disrupt the health of the ponds,” Kielb said, noting that the fry eat zooplankton, thereby removing excess phosphorus.

Brewster Natural Resources Advisory Committee is monitoring a University of New Hampshire study of herring, plankton and pond health, Miller said.

“It does alter a pond by having a herring population in it,” Miller testified. “Often it leads to increased amounts of algae.” At the same time, “baby alewife eat the zooplankton, and zooplankton act as the grazers who eat phytoplankton.”