Fish and Habitat Monitoring

Tyson Bottenus, a local volunteer, and Olivia Bourque, summer intern with the North and South Rivers Watershed Association, drill a small hole on the side of the crab shell to set a tag in place for research on the bay side of Duxbury beach on Thursday, May 21, 2015. Photo by Lauren Owens

Horseshoe Crab Monitoring

Our horseshoe crab surveys are completed for 2016. We will be posting the results as soon as we have analyzed the data.

Marine Invasive Species Monitoring

During the summer we explore docks and the intertidal rocks looking for creatures that don’t belong. This is a great way to get outside and get your feet wet while you learn a little bit of species identification.

River Herring Monitoring


A river herring is a type of fish. The North and South Rivers support two species of river herring: Alewife (Alosa psuedoharengus) and Blueback Herring (Alosa aestivalis). Both species, collectively called river herring, are anadromous. This means they spend most of their lives at sea and return to rivers – like the North and South Rivers – to spawn (lay eggs).  Herring are a vital component of the marine food chain. These fish are prey for a wide variety of fish, birds, and marine mammals.


In colonial times, herring in the North and South Rivers and their tributaries were extraordinarily abundant.  But from the 1900’s until today a much smaller population of river herring is present.

According to the Herring Alliance some river herring runs on the Atlantic Coast have declined by 95% or more over the past 20 years. In 2006 the National Marine Fisheries Service designated river herring as a species of concern. Population decline may be associated with numerous factors including by-catch, habitat loss and degradation, water pollution, poaching, access to spawning habitat, and natural predators.


The NSRWA and Massachusetts Bays Program recruited and trained 68 citizen scientist volunteers this year to count river herring migrating into First Herring Brook in Scituate, Third Herring Brook in Norwell and Hanover, Herring Brook in Pembroke, and the South River in Marshfield. From March 28th to May 31st volunteers spent over 193 hours in 10-minute intervals counting over 9,516 fish.

Cumulative Herring Observed 2016
Counts at First Herring Brook in Scituate were low, similar to recent years since flow was restored to the Old Oaken Bucket fish ladder in 2012. Only four fish were seen this year in the fish ladder. The first fish was seen on March 29th while the peak sighting of 2 fish was also the last sighting on April 19th.  NSRWA is working closely with the Town of Scituate to continue to provide flows for herring and instream habitat.

The herring at Third Herring Brook were late compared to previous years with the first sighting (43 fish) being May 9th , the peak (1,340 fish) on May 11th, and the final sighting (12 fish) May 14th.  Still, Third Herring Brook managed to have its highest herring count yet, reaching over 2,599 fish. It is important to note that the count at this location is somewhat unofficial, since the fish are counted below the River/Broadway St. culvert and not at the top of a ladder. When the Tack Factory Dam is removed, a statistically sound count can be conducted at the former Mill Pond Dam site.

Herring Brook is certainly our most robust population, reaching 6,906 herring observed by counters (the second highest year, behind 2012’s 10,449 count). The first sighting (86 fish) at Herring Brook was April 1st, counts then peaked (191 fish) on April 17th, and the final sighting (75 fish) was May 30th. Herring Brook is the only location where substantial counts and the presence of a fish ladder allow a provisional population estimate to be made. This year the population of Herring Brook is estimated at 89,712 +/-11,292 based on volunteer counts. This is lower than the counts from the electronic counter on Herring Brook, due to missed fish that passed before 7am or after 7pm, when volunteers are not counting.

herring brook cumulative data 2012-2016

Volunteers at the South River counted 912 herring downstream of the Veterans Memorial Park fish ladder, beginning April 13th, peaking May 27th, and concluding June 2nd; however, consistent with previous years, no herring were seen actually traveling up and over the dam via the fish ladder. The fish ladder is very sensitive to changes in flow and hard to manage but frankly we are not sure why the herring seem adverse to using it. We had this ladder “fixed” by the Massachusetts Division of Marine Fisheries several years ago but clearly there is still something keeping the fish from passing this dam. We will be providing our information to state fish biologists and continue to work with the town of Marshfield to determine the best course of action for this dam.

Stream Gauge Reading

Help contribute important data to our Third Herring Brook and First Herring Brook restoration projects by monitoring flow. If you can read a ruler, you can read a stream gauge! Contact us for training.

We have many opportunities for you to participate in monitoring that supports our restoration projects. If you are interested in any of these, please contact Sara ( at our office or call 781-659-8168. We may have other opportunities coming up this summer, so check back!