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Citizen scientists document dramatic increase herring at Mystic Lakes Dam

Mystic River logoCommenters early in June expressed fear on the Arlington email list that river herring were dying in great numbers at the Mystic Lakes Dam.

Best to fight fear with facts. Whether the number of dying herring seen recently was greater than usual is not known, but the number of herring successfully using the fish ladder to spawn has increased significantly.

Ask the Mystic River Watershed Association (MyRWA), which has been working with hundreds of volunteers.

Since 2012, the volunteers have counted river herring passing through the fish ladder at Mystic Lakes Dam to spawn in Upper Mystic Lake. In 2015, the citizen scientists were able to document that an estimated nearly half a million river herring swam through the fish ladder to spawn -- a 100-percent increase over the counts in the previous three years, a news release from the watershed says.

River herring collectively refer to two species of herring, Blueback (Alosa aestivilis) and Alewife (Alosa pseudoharengus). These two species are "anadromous" fish; they live the majority of their lives in saltwater but lay eggs (spawn) in fresh water.

The billions of river herring eggs that are produced in Upper Mystic Lake will develop into juvenile herring within just a few days. These juveniles will stay in the fresh water for as long as four months, before swimming downstream to live in estuarine waters. The river herring that survive will reach an age to reproduce after three to four years and usually return to the same waters where they were born.

The Mystic River is one of 78 river herring runs in Massachusetts. River herring are an important component of ocean fisheries, and they need access to freshwater systems to survive. Over the past several decades, populations of river herring have dramatically declined.

The watershed association works each year to train a set of volunteers to perform visual counts at the fish ladder Mystic Lakes Dam. The volunteers agree to perform at least one 10-minute observation each week. Volunteers in the 2015 program performed 680 10-minute observations and counted 57,617 fish. The observations and counted fish are plugged into a sophisticated model developed by the Division of Marine Fisheries that yields the population estimate of 477,827 (plus or minus 40,674) for 2015.

Why the increase?

So what is the reason for the dramatic increase in the number of fish observed in 2015?

The watershed group and the state Division of Marine Fisheries are exploring this question.

One explanation might be that since large numbers of river herring were not able to access the additional habitat in Upper Mystic Lake before 2011, when the new dam and fish ladder were completed, we might be witnessing a true increase in the adult population that results from providing additional quality habitat for spawning.

The fish count in 2016 will contribute to an understanding of this year’s numbers. If the numbers stay high, it may be evidence that the population has increased in a sustainable way.

"The scale of this herring migration shows the Mystic River to be a living, breathing ecosystem, filled with life," said MyRWA Executive Director EkOngKar Singh Khalsa in a news release.

"It may be hard to see that life from Interstate I-93, and it is easy to take this urban river for granted. But the herring run speaks to the importance of treating natural spaces in urban areas with great respect and care. We can live alongside nature, if we are thoughtful."

Work is underway to build on the successes of the 2012-2015 counting programs. The watrershed group is working with the state and local river-herring advocates to see a fish ladder installed at the Center Falls Dam in Winchester center to allow herring access to Wedge Pond and potentially Horn Pond.

The watershed is a vital natural resource for the more than 500,000 people who live in 22 Mystic River communities.

For more information about the association, click here >>

This report was published Tuesday, July 21, 2015.

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