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Herring - a keystone fish in the Coonamessett

On Cape Cod, the return of the herring is a welcome sign of Spring. Each year, herring return from the sea to spawn in their natal freshwater streams and ponds. Visual counting tells us how many fish migrate up the Coonamessett to their spawning grounds each year. It gives us a sense of the health of this herring population.

River herring populations are suffering up and down the Eastern Seaboard. Knowing how to help our local herring populations will contribute to restoring the threatened stocks and provide food to local gamefish such as stripers, bluefish and largemouth bass.

Starting in 2005, volunteers have counted the number of fish swimming up the river.  We now have over 30 volunteers who count fish every evening between April 1st and June 1st. We also have volunteers do random daytime counts. Many thanks to our wonderful volunteers who stand in the rain or cold or wind to watch the silver fish flash by daytime counts. Many thanks to our wonderful volunteers who stand in the rain or cold or wind to watch the silver fish flash by!

The visual data is used by the MA Division of Marine Fisheries to estimate the total population for the Coonamessett.  The graphs below show how the herring population can fluctuate each year.


herring counts.jpg

Herring swim over a white board, which makes it easier for counters to see them.

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These numbers are far from the estimated historical populations of a million fish in the river in the early 1900s. Longtime residents recall the river being “black with fish” or so numerous you could “cross the river on their backs” in the early 1960s. We hope that the restoration will bring the population closer to these numbers as trees grow to cover the water and culverts and other obstructions are removed, smoothing their way to their spawning grounds.

 Herring Life Cycle

Two species of river herring use the Coonamessett River system for their spawning grounds. Alewives (Alosa pseudoharengus)are the first to show up in early to mid April.  They spawn in the freshwater ponds. Bluebacks (Alosa aestivalis) migrate in mid May and spawn in the river itself near cold water springs.


These species share a similar anadromous life history, meaning they are born in freshwater and spend approximately 6-8 months in freshwater and then migrate to the ocean where they spend 3-5 years growing and maturing. They return to their natal rivers and lakes again to spawn. They can spawn multiple times before dying.

Herring Life Cycle.jpg

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