DMF To Assess Herring Spawning Ponds With Help From Town Officials

BREWSTER – It’s perhaps the most celebrated herring run on the Cape, and soon the fish will be making their way up Stony Brook to Upper Mill Pond and Slough Pond for their annual spawning. Water levels there, and the state of the passage between the two ponds, have a big impact on how many fish are able to reproduce successfully, and state and local officials will be giving that a closer look.

At a recent meeting of the alewife committee, Chair Doug Erickson said the town signed on with the state Division of Marine Fisheries last year to conduct a river herring spawning and nursery habitat assessment, which will likely include Upper Mill Pond and Slough Pond, as well as Walker’s and Elbow ponds. Each spring, river herring including alewives swim up Paine’s Creek, through the weirs at Stony Brook and into the pond complex to reproduce. The habitat assessment will analyze the challenges and obstructions the fish encounter on their journey.

“That will be going on for a couple years. There’s going to be all sorts of testing of water, everything that grows in the water and lives in the water and the amount of oxygen in the water,” Erickson said.

The connection between Upper Mill and Slough ponds is through a ditch that becomes very shallow in dry weather, and Erickson said by his observations, the ditch had lost its water by around April 6 last year. At that stage in the migration, some fish had successfully passed through, and many others could not do so.

“They were trying to get up there [but] were getting pretty much slaughtered by the otters and the raccoons and stuff,” he said. “The fish struggle real hard to try to get up the pond, and they get eaten on the way.”

When water levels dropped, many of the adult herring were trapped in Slough Pond, though the juvenile herring, known as brit, were largely able to escape. Volunteers did some digging in late October and early November and were able to get more of the fish out of the pond, he said.

Committee member Gary Kaser said he looked into the phenomenon.

“I think one of the biggest fears people have is that herring would all die in Slough Pond. I found that there are some landlocked ponds with herring in them that live year-round,” he said. While they are more vulnerable to predation, they can survive until water levels rise again and they can escape. “There was a lot of emotion. People thought if they didn’t all get out, it was a death sentence. And that’s not the case,” Kaser said.

Volunteers have installed sandbags at one end of the ditch between the ponds to try and conserve water in Slough Pond, and current conditions would allow herring to pass, Erickson said. Hopefully the habitat assessment will determine whether that management strategy is sufficient, he said. Alternatively, the town might need to install netting or fencing to keep herring in Upper Mill Pond.

The habitat assessment will also likely evaluate the culverts that lead from Slough Pond to Walker’s and Elbow ponds. The Elbow Pond culvert has metal mesh screening, likely designed to keep herring from entering the cranberry bog upstream. Some herring squeeze through, Erickson said, but the water flow from Elbow Pond appeared to be very weak when observed recently.

Kaser said the challenge in Brewster is not unique; silting threatens many fishways in the region.

“The situation is almost identical to Seymour’s Pond,” he said. There, improvements were made that kept the passage clear for fish but also allowed control of the water levels.