Alewife Runs Continue in St. Croix River

The number of sea-run fish returning to the St. Croix River to spawn continues its recovery, according to on-going tracking efforts.

From approximately 2015-2022 the IJC funded fish counts at the Milltown Dam through its International Watersheds Initiative. These fish counts are primarily focused on alewives and blueback herring, collectively known as river herring, two species native to the river system that are vital as a food source for other species, lobster bait, and traditionally for human consumption. Milltown Dam, formerly located near the head of tide for the river, was decommissioned and removal work wrapped up in 2024, which required changes to where the monitoring takes place.

As of the 2024 spawning season, the traditional fish counts are now conducted by the St. Croix International Waterway Commission (SCIWC) at the Woodland Dam, the next dam upriver from where Milltown Dam was located, as well as at Grand Falls Dam by the Sipayik Environmental Department. 

“With the Woodland Dam now the first dam along the St. Croix River following the Milltown Dam decommissioning, the SCIWC reviewed daily underwater footage of the river-herring migration from the Woodland dam’s fish ladder from late April - early July,” said Neal Berry, director of the waterway commission. “560,334 river herring were counted during the 2025 season."

The Maine Department of Marine Resources (MDMR) is currently taking bids to construct a new fish passage system at Woodland Dam to replace the decades-old fish ladder. This old fish ladder was originally designed for Atlantic salmon and is therefore difficult for other species to cross, according to a 2021 report conducted by the International St. Croix River Watershed Board and its partners. An estimated 25 percent of fish that attempt to cross the existing fish ladder successfully make it, according to a 2024 study funded by the IJC.

At Grand Falls Dam, the Sipayik Environmental Department counted approximately 456,463 fish crossing the fish passage system, said Chris Soctomah, fisheries biologist with the department. This was down from the roughly 504,942 counted in 2024, he said, but still an increase over the 189,852 seen at the dam in 2022 prior to the removal of the Milltown Dam downriver. 

Counts at Grand Falls are conducted using a camera system that records the fishway for 10 minutes every hour for about 14 hours a day during the spawning season, according to Soctomah. The number of fish caught on camera are counted at that time, and the numbers are multiplied to get a general figure for the whole day.

“We saw a small increase before the (Milltown) Dam was decommissioned, and after the dam removal we saw the number of alewives more than double since 2022 at Grand Falls,” Soctomah said. “Now, those numbers are starting to level off this year. This may be due to colder temperatures in spring with lots of high flows from precipitation events.

Separately, Soctomah added, the Sipayik Environmental Department is collecting eDNA samples from the St. Croix River. These can be analyzed and used to learn about the biodiversity of the river and how it is changing with the recent changes to fish passage that have taken place or are being proposed. To date an analysis has been done on the samples collected in 2023, and Soctomah said they are interested in comparing those with the results from 2024 and 2025 now that the Milltown Dam has been decommissioned.

But the Milltown Dam site is still the focus of an ongoing study as well. New Brunswick Power funded a fish tagging study as part of the Canadian Fisheries Act Authorization, tracking fish passage at the former Milltown Dam site, now known by its original name of Salmon Falls, using radio tags and a receiver array along the Canadian shoreline. This study is expected to last about five years, with 2025 being the first full year undertaken. 

Since Milltown Dam had been partially removed in 2024 to the extent that fish could move past it, that now represents a partial year “zero” according to Philip Harrison, a research scientist with the Canadian Rivers Institute at the University of New Brunswick and one of the study leads. 

While data for the 2025 spawning season is still being analyzed as of this writing, in 2024 the effort found that 72 percent of fish that entered Salmon Falls successfully passed upstream within 24 hours.

“A successful passage rate of 65 percent over the next five years (is our target),” Harrison said. “So 2024 was slightly higher.”

The Milltown effort is primarily interested in the river herring species, which are considered keystone species to the ecology of the St. Croix River, said Alexa Meyer, an environmental biologist and conservation manager with the Passamaquoddy Recognition Group. As such those were the species tagged most frequently, along with American shad and other species as they are caught, such as brook trout and striped and smallmouth bass. Approximately 176 fish were tagged in 2024, with another 226 in 2025.

Shortnose sturgeon and elver (young eel) are all of interest too, but the eels are too small for the tags the effort uses, and sturgeon are difficult to tag, she said. 

“We don’t expect elver to have much difficulty ascending the newly constructed channel, but we have plans in the future to see if they’re making it upstream,” Meyer said.

The project is expected to run through the 2029 spawning season, though Meyer expressed interest in expanding the effort to cover areas upstream in the future through additional partnerships and funding.

According to Soctomah, the MDMR estimates that the St. Croix River watershed could support around 27 million fish, adding that estimates from Fisheries and Oceans Canada and the US National Oceanic and Atmospheric Administration are both higher than that relatively conservative one.