The leaves are changing and the smell of pumpkin spice is in the air. That can only mean one thing – it’s outmigration season!
This spring, NSRWA citizen scientists recorded over 11,000 river herring passing through our monitoring sites, which translates to population estimates in the hundreds of thousands. Many of those adult river herring made it upstream and laid eggs before returning to the ocean a few weeks later. After hatching in the spring, juvenile herring typically begin their journey to the ocean between September and November. They have survived predators from land, air and water, as well as seasonal low flows and contamination from run-off and other discharges, but many will still need to navigate physical barriers on this final leg of their journey.
Few studies focus on juvenile river herring in our waters. We don’t know much about what triggers outmigration, or the impacts of the nutrients anadromous fish (such as river herring) transfer from freshwater to saltwater. We do know that this keystone species needs free-flowing rivers to successfully spawn and promote population growth.
In areas where there are impediments to fish passage, such as dams and fish ladders, it’s essential for operators to manage flows in order to provide enough flow to allow for fish passage downstream. NSRWA and similar organizations work with operators, typically towns or private owners, to set streamflow targets that will allow for successful outmigration. For example, we developed an operational plan with the Town of Scituate to manage flows over the fish ladder at the bottom of Old Oaken Bucket using a series of notched boards and releases from Tack Factory Pond.
Like all “gray” infrastructure, fish ladders are not self-sustaining and these systems need to be manipulated in order to work. This is one of the many reasons NSRWA and our partners at MassBays are working to remove as much gray infrastructure as possible, in order to let nature take the reins and remove human intervention from the equation.