Spring on the Mystic means a lot of things--beautiful buds, warblers returning to the parks, and longer, sunnier days--but most of all, the annual river herring migration!
Did you know that every year close to a million herring migrate from the Atlantic Ocean up the Mystic River to spawn? For the last three years, this migration has been one of the top three in the Commonwealth. You can learn all about the amazing return of Mystic Herring here, or check out some Q&A’s we hear from community members below.
Q: What species of river herring migrate up the Mystic River?
A: There are two different species of river herring: Alewife and Blueback. Both species are anadromous: they live mainly in the ocean, but reproduce in freshwater lakes and streams, like Salmon. Unlike Salmon, which typically die in the streams where they spawn, herring return to the ocean and can make several trips upstream throughout their lifetime.
Fun fact: Alewife Brook is named for these fish.
Q: How many river herring make this migration every year?
A: For 2019 it is estimated that 789,000 herring made the journey up the Mystic to spawn. The Mystic River Watershed Association runs multiple programs to help estimate this run size including in-person counting in the spring, plus on underwater “fish cam” and counting platform found here.
Fun fact: river herring have a “natal memory.” This means that they return to their natal (birth) rivers to spawn (breed).
Q: How do I know when the migration starts?
A: The migration starts in the spring. Scientists don’t know exactly what prompts the fish to come start their travels back to spawn. This year the first fish was seen on April 18th--and this is generally when we see the first herring. How you can tell--is look for the birds to migrate back to the Mystic. This includes thousands of Cormorants that can be seen at the Mystic Lakes Dam during the migration (use the graph we did for 2019 press release) or look for the Black Crowned Night Herons found along the banks of the river during the migration. You can also check out our underwater “fish cam” to see when the herring are running.
Q: I’ve heard that river herring used to be plentiful in New England. What happened?
A: Overharvesting in the ocean and the construction of dams--obstructing access to inland spawning habitat--caused a dramatic decline in population. River herring are a US National Marine Fisheries Service “Species of Concern.”
Q: Are there dams on the Mystic, and what impact does this have on the herring?
A: Yes--there are four dams. Amelia Earhardt in Somerville, Mystic Lakes in Medford, Center Falls in Winchester and Scalley Dam in Woburn.
For many years--these dams stopped the fish in their “tracks.” Thanks to the citizen action--including efforts by the Mystic River Watershed Association--there were fish passages installed at the Mystic Lakes Dam (added in 2011) and Center Falls (added in 2017) opening up 200+ acres of spawning habitat. The Amelia Earhardt dam opens for boat passage so a fish ladder is unnecessary at this location. River herring can bypass the dam in Woburn via an adjacent spillway--though improvements will be coming in 2021 (as currently far too many fish can’t make it to Horn Pond).
Q: Are the number of herring migrating on the Mystic growing or shrinking?
A: Since 2012 the number of herring migrating to the Mystic River have tripled. This is thanks to the fish ladders installed since 2011. During the first three years after the Mystic Lakes dam fish ladder was installed we didn’t see much of a difference in population size. During the fourth year the population doubled and has increased since! The key here is that river herring only return after they reach sexual maturity at age 3 or 4. As our Watershed Scientist, Andy Hrycyna, says, “if this experiment of expanding breeding habitat for these fish was successful in increasing the population loyal to the Mystic, you would expect to see the signal in the fourth year, when those first successfully "added" fish returned to be counted. And this is exactly what we saw!”
Q: Can I see the herring?
A: Yes--you can see them--and help us count--using our underwater fishcam! Watch a short video and tell us how many fish you see. Together, we can collect valuable data about these important species. Count Here.
You can also take your family to several spots along the river to look for the fish pooling. This includes the Mystic Lakes Dam, Center Falls Dam and Horn Pond. Finally, during Feb/March of every year we recruit in-person monitors to help us document run size. Sign up for our e-news and we will let you know when we are recruiting.
To find out how river herring made it over the Mystic Lakes dam before the fish ladder and to learn about future improvements to the dams, click here.
