One Small, Man-Made Leap for Herring...One Large Leap Forward for the Mystic River

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One Small, Man-Made Leap for Herring...One Large Leap Forward for the Mystic River
By Todd Callaghan, CZM

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Color photo of a man and woman standing in the Mystic River. The man is smoking a pipe and they are both holding a net full of herring.

On May 25, 2007, dozens of volunteers and state employees joined together in the Third Annual Herring Bucket Brigade to manually lift migrating river herring above the Mystic Lakes dam to their desired spawning grounds in Upper Mystic Lake. The bucket brigade arose as an outreach effort to help make people aware of the river herring’s plight, and to create momentum to expedite a long-overdue reconstruction of the dam between Upper and Lower Mystic Lakes. The dam poses a particularly difficult problem for the migrating herring because they are drawn to the rushing water spilling over it in the spring, but there is no way for them to access the lake on the other side. In the two previous years, a few thousand fish were lifted over the dam by a handful of volunteers. The fish were caught in nets by quick-handed volunteers standing among concrete fragments at the dam’s toe. The netted fish were then transferred to water-filled five gallon pails, hoisted by rope up to the top of the dam, and poured down a chute to the lake on the upstream side of the dam. Biologists from the state’s Division of Marine Fisheries oversaw the event and counted the fish as they were poured into the chute.

The 2007 event, hosted by the Medford Boat Club, saw a total of 19,358 fish lifted over the dam, greatly surpassing the number transferred in the previous two years combined. While the number lifted over the dam is only a fraction of the fish that are estimated to spawn in the Mystic River, the effort furthered the visibility of their plight to state representatives, the head of the Department of Fish and Game, the head of the Executive Office of Energy and Environmental Affairs, and many local people who live around the lake.

Color photo of herring being dumped out of a plastic bucket down a metal chute leading into the Mystic River.

But what happens to the fish once they get to the other side? While the herring bucket brigade began as an outreach event, the sheer number of spawning-crazed herring that were lifted over the dam begged the question: Were the herring spawning on the other side? Was all of this effort for naught?

Between June and August of 200, I teamed up with Brad Chase, a state anadromous fish biologist, and Mary Beth Dechant, the monitoring coordinator for the Mystic River Watershed Association, to determine if Upper Mystic Lake was suitable for the development of young herring. Chase had just developed a standard operating procedure for performing river herring spawning assessments that the team applied monthly from June to September. The team collected data on dissolved oxygen, temperature, pH, water quality, and other measures. They also made visual observations of fish passage barriers at the dam and the types of sediments available for egg-laying along the shores (e.g., sand, gravel, cobble, and presence or absence of algal sheets). Three sites, one adjacent to shore, one in the middle of the lake, and one in between the other two, were monitored, while an additional site or two somewhere else in the lake was chosen each time monitoring was conducted.

Upper Mystic Lake has been studied extensively over the years, so it was known that the lake was deep (up to 80 feet) and that it harbored toxic metals, such as arsenic, in its cold and silty depths. But relatively little was known about the condition of the water column at the surface and edges, areas where juvenile river herring might feed. Data from this effort confirmed that there was a region of low dissolved oxygen in the lake. What was surprising was the extent of this low oxygen area.

Color photo of volunteers with nets and prodders, helping the herring get to their destination.

Todd Callaghan from the Massachusetts Office of Coastal Zone Management (and author of this article) and Priscilla Geigis (Director of State Parks and Recreation, Department of Conservation and Recreation), along with a group of volunteers net river herring at the base of Upper Mystic Lake Dam. Water and herring-filled buckets are hoisted to the top of this dam, where the fish are then poured into a chute that delivers them safely to their intended spawning area in the lake.

At depths past 15-25 feet, the amount of oxygen dissolved in the water column was less than that which can support river herring, or any creature needing oxygen for that matter. In fact, on several instances when the calibration drift caused by the extreme change in temperature and pressure between the surface and the bottom of the water occurred, the dissolved oxygen meter gave readings of less than zero! This area of low dissolved oxygen spread out to lake’s edges, up to 30 feet from shoreline. While the uninhabitable depths seemed daunting, the team’s data indicated that the lake did have areas of good habitat for river herring, especially along the edges of the lake, within 30 feet of shore.

Visual inspection of the lake’s edge identified sediments that were deemed suitable for egg laying and development, according to Chase. As validation that Upper Mystic Lake does in fact offer suitable river herring spawning habitat, the study team noticed schools of several hundred to thousands of juvenile herring in Upper Mystic Lake, some of which were leaping out of the water.

While it was good news that the herring that were lifted by the volunteers were spawning in Upper Mystic Lake, the bad news was that no water was flowing over the dam in August and September, when the juvenile herring needed to get back downstream. A bucket brigade for the juveniles would have been futile because their bodies are so fragile that handling them would likely induce massive mortality. Chase decided that it would be best to wait for an October rain to wash the fish over the dam and downstream so they can venture out to the ocean. To address this outward migration challenge, the Department of Conservation and Recreation has made a commitment to rehabilitate the dam and hopes to implement the plan by the 2010 spawning season. The new dam will include a fishway that has been designed so that the bucket brigade can retire and the young-of-the-year river herring can happily swim downstream to the ocean.

	*Thanks for the lift!*

Photos: Bob Greco