Town Brook Herring & Eel Run Information

River Herring Run

Town Brook Herring RunTown Brook is one of over 100 riverine systems across the state that are host to an annual migration of river herring each spring. Two species of river herring, Alewife (Alosa pseudoharangus) and Blueback Herring (Alosa aestivalis), are anadromous species. They migrate from their maturing habitat in the Atlantic Ocean, up these fresh-water rivers to spawn every year. The fish seen in Town Brook are migrating to Billington Sea, approximately 1.6 miles inland. Fish queue below the Jenney Grist Mill dam off Spring Lane; during peak days of the migration, ten-of-thousands of fish can be seen waiting their turn to move through the fish ladder and make it over the dam. Benches and an observation platform are located here and open to the public to enjoy the migration. Plymouth also sees herring migrating up other rivers in town: Eel River, Bartlett Brook, Red Brook, Agawam River, and Monument River (in Bourne but leads to Great Herring Pond in Plymouth). Herring aren't the only fish that can be seen migrating in the spring- rainbow smelt (Osmerus mordax) and American eels (Anguilla rostrata) make their way up the Brook each spring as well.


The Town Brook herring have been an important part of Plymouth history since the Pilgrims arrived in 1620. The stories in history books that tell of Patuxet tribe member Squanto showing pilgrims how to use herring to fertilize corn seeds is referring to these very Town Brook fish! (Or at least their great-great-great-great-... great-grandparents). Herring populations in Town Brook during this time have been estimated at 1 to 2 million fish! Due to damming and industrialization, herring populations nationwide began to plummet to dangerous levels, as fish were unable to circumvent the dams to get to spawning grounds. Over 3,000 dams currently exist in Massachusetts, and it wasn't until 2002 that the first coastal dam in Massachusetts, located on Town Brook, was removed and began a sort of coastal dam-busting revolution in the state. Since 2002, over 40 dams have been removed in Massachusetts, restoring hundreds of miles of river; 5 dams have been removed on Town Brook alone! With every dam removal, fish are able to reach sections of river that have been inaccessible for hundreds of years, reaching more spawning grounds, and giving migrating fish an increased chance of successfully spawning and bolstering the population. It is hoped that populations will reach pre-industrialization levels, and allow for harvest to resume.


Town Brook Herring CounterIn 2008 the Department of Marine and Environmental Affairs (DMEA), formerly the Environmental Management Division (EMD), undertook as a project the task of establishing baseline population estimates for the number of river herring migrating upstream at Town Brook. EMD partnered with the University of Massachusetts - Amherst and the Massachusetts Division of Marine Fisheries (DMF) to complete this project. EMD utilized three different methodologies to Herring swimming through the Smith-Root counter establish the population: a video counting system that ran 24 hours a day over the course of 70 days, 3 daily ten-minute counts every day for 70 days along with subsequent algorithmic analysis of the data, and the Smith-Root electronic fish counter. Both the video counting system and the Smith-Root system provided counting coverage 24 hours a day over the entire herring run season.

Since 2008, visual counts have provided the most consistent and accurate data as accepted by DMF, and continue to be the primary means of data collection. This data is collected solely by volunteers, and the Town is always looking for help. People of all ages are welcome to assist with counting, and no prior training or education is necessary. Please scroll to the bottom of this page for more information.

Beginning in 2018, DMEA partnered with NOAA, Cape Cod Cooperative Extension, Woods Hole Sea Grant, and the United State Geological Survey (USGS) Conte Anadromous Fish Research Center to track herring during the migration. Each year, fish are netted and have a small transmitter affixed to them. In numerous locations along the river, antennae are installed that log when a tagged fish swims past it- sort of like 'EZ Pass' for fish, except in this case the Mass Pike is Town Brook. This data allows the project partners to calculate how long the migration takes and identify where there are constrictions in passage, and address those issues. Many of those problematic areas were dams, and this quantitative data was invaluable in acquiring funding to have the dams removed. It will take several years after each dam removal to retrieve data indicating how successful the dam removal was. While data can quickly show that significantly more fish are moving through the areas of formerly located dams, newly hatched fish do not reach sexual maturity for several years, so there is a delay in their return. However, all data that has been analyzed since 2018 is showing wildly positive results!

In 2019, DMEA, DMF, and NOAA installed a pilot video counting system and underwater camera to remotely count and view the migration. The camera is available for viewing on our website during the normal migration period of March to June. This data is also saved for crowdsourcing. If you'd like to help us collect data on the herring virtually, please visit the Town Brook Herring Run website to help count fish! This data doesn't contribute to the size estimate for the Town Brook run, but it helps provide quantitative data that could someday soon help other rivers that don't have large volunteer groups collect important information!

Population Estimates

The population of migrating river herring at Town Brook in:

  • 2008 was estimated at 168,996 for the spring
  • 2009 was estimated at 155,015 for the spring
  • 2010 was estimated at 195,091 for the spring
  • 2011 was estimated at 142,633 for the spring (plus or minus 11,487)
  • 2012 was estimated at 171,141 for the spring (plus or minus 50,404)
  • 2013 was estimated at 107,413 for the spring
  • 2014 was estimated at 135,737 for the spring
  • 2015 was estimated at 173,567 for the spring (plus or minus 14,627)
  • 2016 was estimated at 199,368 for the spring (plus or minus 17,441)
  • 2017 was estimated at 160,668 for the spring (plus or minus 16,336)
  • 2018 was estimated at 185,071 for the spring (plus or minus 15,131)
  • 2019 was estimated at 230,860 for the spring (plus or minus 18,299)
  • 2020 was estimated at 190,810 for the spring (plus or minus 17,589)
  • 2021 was estimated at 136,626 for the spring (plus or minus 16,407)
  • 2022 was estimated at 169,462 for the spring (plus or minus 19,906)
  • 2023 was estimated at 235,291 for the spring (plus or minus 21,915)

Yearly Herring Run Totals

What Plymouth Is Doing to Help the Town Brook Fish Thrive

The Town's Division of Natural Resources (DNR), which comes under DMEA, conducts annual maintenance to Town Brook each spring to ensure fish passage is as clear as possible. These tasks include removal of trash and major river obstructions such as woody or man-made debris, cleaning the fish ladder, installing guide blocks, brushing back overgrown vegetation, and replacing/upgrading aging equipment. During the migration, roughly between mid-March and early June, DNR staff performs daily maintenance and monitoring of Town Brook, checking on water levels, flow rates, and mitigating any hazards that could adversely affect the run. Below is a timeline of larger projects and events that have helped to directly impact the success of the species.

  • 1620s - (it started a while ago) the Herring Warden job position is created to help manage the population when numbers began to decline.
  • 2002 - the Billington Street dam is removed, becoming the first coastal dam to be removed in Massachusetts.
  • 2005 - the Water Street dam is lowered by 18 inches to allow greater passage with less tidal dependence.
  • 2006 - Massachusetts issues a state-wide moratorium on the possession and sale of river herring.
  • 2007 - the Town creates the Department of Marine and Environmental Affairs tasked with preserving and protecting the Town's natural resources.
  • 2007 - a modern fish ladder is installed next to the Jenney Grist Mill to increase passage rates.
  • 2008 - volunteers begin collecting consistent, scientifically recognized herring passage data.
  • 2013 - the Off Billington Street dam is removed.
  • 2013 - the Town of Plymouth creates the Natural Resources Warden position; among the responsibilities is enforcing state freshwater fishing laws and the 2006 moratorium.
  • 2014 - a rock-ramp is installed below the former Water Street dam to allow fish passage during all tides.
  • 2014 - volunteers organize the annual Herring Festival in Plymouth that helps bring awareness to the need to protect river herring. The festivals draws hundreds of people annually.
  • 2015 - the Plymco dam is removed.
  • 2017 - a plunge pool is installed below the Jenney Grist Mill dam to decrease outmigration mortality.
  • 2017 - concrete modifications are made to the Jenney Grist Mill fish ladder to decrease likelihood of fish jumping out of the ladder.
  • 2018 - the Town of Plymouth and project partners begin a multi-year a PIT tagging research project to track the migration.
  • 2018 - the Holmes Playground dam on Newfield Street is removed and 2,000ft. of river is restored.
  • 2019 - an exclusionary board is installed that guides fish away from the grist mill water wheel to decrease outmigrBlueback and Alewife Herringsation mortality.
  • 2019 - a migration monitoring underwater camera is installed.
  • 2020 - an underwater inspection of the Spring Lane fish ladder culvert identifies blockages slowing passage, and several large tree roots are cut and removed.
  • 2021 - a modified temporary crowding board was fabricated to help guide fish to the plunge pool and decrease outmigration mortality of fish falling onto rocks by the grist mill wheel.

Please visit the NOAA story map for a visual history of the projects on Town Brook to help protect these fish. Pictures of both species of Herring

Volunteers are always needed to conduct 10-minute counts from the end of March through the first week in June. The above data is all collected by volunteers, so we depend highly upon citizen science. No experience or education is required, and any training and materials will be provided. Data collection requires the volunteer to stand for approximately 10 minutes, and may require some stooping or bending. Should you be available to volunteer, or would like additional information, please email Nate Cristofori.

American Eel Run

American eels (Anguilla rostrata) are a catadromous species, meaning they mature in fresh-water and spawn in salt water. They are also North America's only catadromous species! (And no, they're not electric). While adult herring are migrating upstream to spawn, swimming next to them are juvenile American eels making their way upstream to live out their lives. These small 2- to 3-inch-long 'baby' eels are called elvers, young-of-the-year (as they are only about 1 to 1.5 years old), or glass eels for their nearly translucent appearance. They are born in the Sargasso Sea, and as larvae float with the Atlantic Currents up the east coast. As they grow, they begin to make their way inland to the nearest riverine habitat which they'll call home for the next 20 to 30 years! When fully matured they'll reach lengths of up to 5 feet! Towards the end of their life, they'll outmigrate back to the Sargasso Sea to spawn.

Eel RampEach spring since 2019, Natural Resources staff have installed an eel ramp at the Jenney Grist Mill. This structure, engineered and built by the Massachusetts Division of Marine Fisheries, allows American eels (Anguilla rostrata) to migrate over the dam, which similar to herring, would otherwise act as a migration passage barrier. Unlike herring, eels are unable to swim against rapid currents and thus cannot use the fish ladder. An eel's primary way of circumventing a barrier like a dam comes from their unique ability to climb vertical surfaces that are wet and textured. It is not unheard of to see eels squirming their way across wet roads in order to make their way past a dam- that's how strong their drive to migrate is! In order to avoid the mortality that comes with this option, Natural Resources worked with DMF to install an eel ramp.

The eel ramp is a simple structure; a 16-foot-long aluminum ramp (the longest in the state!) with pumped water flowing down it, extends down into the Brook at the base of the dam. It's this attraction flow that brings the eels to the ramp. When they reach the ramp, a 3/4-inch-thick filamentous substrate inside the ramp housing provides the eels with a means to grip the slope, and they very literally climb their way up the ramp. Upon reaching the top, they fall into a water-filled holding tank that is constantly circulating. Natural Resources Wardens empty the tank once a day for over 5 months, counting each eel to collect population data. The number of eels to enter the tank each day varies greatly- some days see single digits, while others will have over 10,000! On days when numbers are extremely high, DNR staff will use volumetric analysis to count the number of eels. In a graduated cylinder, it is known how many eels constitute a given volume, so this method speeds up the counting process. However, this methodology is only used when daily eels approach 1,000 or more; counting each eel one-by-one is as exact as data collection can get and DNR strives for that accuracy. Plymouth is very fortunate to once again partner with DMF to install a ramp, as the Town is one of only a handful of communities around the state to be assisting with eel migration.

Because the Jenney eel ramp has only been in place for four years, it's not known exactly how many eels should be expected in Town Brook each year.

The population of glass eels in Town Brook in:

  • 2019 was 63,960
  • 2020 was 7,796
  • 2021 was 44,894
  • 2022 was 45,058
  • 2023 was 4,483

EelsIf DNR staff are emptying the tank while you're nearby, be sure to come check out the eels! If not, there's even a viewing window in the holding tank, so you just might catch a glimpse of Town Brook's other protected species.

Like river herring, it is illegal to harvest or possess glass eels or elvers (eels under 9 inches in length) in Massachusetts, and violations come with heavy fines and even jail time. The ramp and tank are padlocked and further secured to the deck - only DNR staff have the ability to unlock the tank to gain access to the eels. No one should be accessing the eel tank without staff present. Multiple local, state, and federal law enforcement agencies are aware of the eel ramp and partner to monitor its security around the clock for the duration of its deployment. If you see any suspicious activity around the eel ramp, please contact the Massachusetts Environmental Police at 800-632-8075, or the Plymouth Police at 508-830-4218.


For Town Brook Volunteer Herring Counters

The information below will be useful to our volunteer herring counters who collect data for us on Town Brook. All of the documents that are sent out annually in the February email blast can be found here, as well as our volunteer instruction video. If you're interested in volunteering to collecting herring data please email Nate Cristofori.

Looking for a little more information on being a volunteer herring counter? Check out the following video - former Warden Cristofori, (now reclassified as Natural Resources Specialist), who coordinates the volunteer counters, explains some of the background, importance, and methodology of being a citizen scientist on Town Brook! DNR is always looking for volunteers please contact our office if you'd like to participate- training and materials will be provided.