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News Diadromous Fish Update

1/21/2021
  • Division of Marine Fisheries
Fore River Stream Work, Braintree. November 2020.

DMF’s Diadromous Fish Project maintained a nearly routine schedule this year to monitor river herring, shad, eel and smelt populations and work on fishways despite the challenge of the pandemic. 

Spring Recap
Most river herring spawning runs had a down year after the near coast-wide improvements seen in 2019. The impact of the 2016 drought on fish born that year (4-year olds this past spring) is coming into view as a likely factor in the lower numbers in 2020. A few rivers had high herring counts relative to time series data with both the Herring River in Harwich, and the Nemasket River in Middleborough and Lakeville, posting over 800,000 fish. Many others had lower counts in 2020 but maintained the positive trend seen since the harvest ban in 2005. The decent flow conditions experienced in April and May quickly gave way to drought conditions in the summer of 2020, which may not be as severe as 2016, but raise concerns over the potential for poor recruitment again this year.

Fishway Work
The low flow of summer and fall is the right time to work on fishway construction and maintenance. The DMF Fishway Crew focused on five fishway repairs in 2020 that were requested by Towns or identified during routine inspections. Weir notch adjustments and fishway entrance improvements were made at the Bog Pond fishway in Falmouth. While the Broad Street fishway in Weymouth was dewatered for construction, we surveyed the fishway weirs and repaired the weirs and pools with hydraulic cement as needed. 

The fishway at the Elm Street Dam on the Indian Head River received a major tune-up with removal of large debris jams and shrubs growing in the fishway, replacement of 13 Denil baffles, and the installation of new stop log board slots and a trash rack. Our crew returned to the site of a large 2019 job at Herring Brook Park in Pembroke to install an additional concrete fishway weir and make adjustments to the fishway weirs and walls. Finally, while the Wareham Street fishway on the Nemasket River in Middleborough was dewatered from the drought, we refinished several concrete stop log slots that were causing irregular fishway flow. In most cases, the Towns funded materials, and our crew provided the labor. These jobs reflect the efficient model of DMF’s Fishway Crew providing labor to match Town contributions of material costs to repair and rebuild fishways. The material cost range for these five jobs was $200 - $1,100.     

Large Cooperative Jobs
Noteworthy progress was made in 2020 on two long-developing Boston Harbor fish passage improvement projects. The Weymouth Herring Passage and Smelt Habitat Restoration Project in the Back River was completed in October. This project originated from concerns over herring getting trapped behind the gate of a flood control tunnel at the Broad Street Dam over 20 years ago. The project design began over 10 years ago and included a diversion wall to keep fish out of the tunnel, a resting pool for fish, and specific channel designs to improve rainbow smelt spawning habitat. The Town of Weymouth led the project to successful completion this fall. The Fore River Watershed Restoration project includes a fish ladder at the Great Pond Reservoir, two dam removals, and a natural bypass at the rock falls. The project is led by the Town of Braintree, with an excellent team of federal, state, and private partners. The project is now completing the design and permitting stage in hopes of going to construction in 2021.  

Stream Maintenance
Stream maintenance has been practiced in Massachusetts herring runs for centuries. Stream channels with low seasonal outflow can be altered from trash accumulation, erosional sediment, tree falls, leave and stick debris jams, and encroachment of both native and invasive plant growth. These alterations can impede upstream spawning runs and downstream juvenile herring migrations. In worse cases, juvenile herring can be impinged in blockages or diverted out of stream channels. Rivers with higher flows are able to shift and scour these jams, thereby maintaining natural channels. Many streams in coastal Massachusetts do not have surface flows that can prevent these jams. And this problem is exacerbated in municipal water supply watersheds, small watersheds with large groundwater withdrawals, and drought conditions. Combine this modern status with a declining awareness of the importance of stream maintenance since the river herring harvest ban in 2005 and we are seeing conditions that are likely negatively impacting juvenile herring recruitment in some coastal watersheds.  

Traditionally, this work was largely led by municipal crews who were aware of the importance of maintaining the herring runs. Many communities are still doing a great job; however, in other locations, the practice of stream maintenance has faded, and the need for this work has increased as coastal development and water use are negatively impacting stream flow. Since 2016, the DMF Fishway Crew has committed to work on stream maintenance in locations where juvenile river herring emigration is threatened, and to train and educate local crews to restore this essential activity. This work increased this summer and fall as pandemic restrictions limited staff activities and led the crew to focus on smaller fishway jobs and stream maintenance. Also, the regional drought created difficult conditions for downstream passage for juvenile river herring and increased the necessity of stream maintenance at many locations. 

Throughout this past summer and fall, the Fishway Crew worked in 16 coastal river systems with large cooperative efforts in the Jones River (Kingston), Fore River (Braintree), and the Acushnet River (Acushnet)—watersheds where low flow and wetland plant encroachment is physically altering river channels to the point where juvenile emigration will be impacted.  Several jams impassible to adult river herring were removed this spring with local reports in the following days of herring reaching upstream spawning grounds. This fall has been especially challenging with the drought conditions. In many locations, juvenile river herring have been held up by the lack of outflow at pond outlets. When early November rain raised the pond levels, fish spilled out to channels choked with leaves and debris. At two Cape streams, crews saw juvenile herring respond immediately to jam removal and move passively downstream. In the absence of stream maintenance, significant fish mortality could have occurred from fish entrained into the jams.  

Stream maintenance can be controversial because of past occasions when overzealous participants removed too much material from the channel and bank. Secondly, this traditional practice is not well-addressed under the State’s present Wetlands Protection Act, leading to questions on permitting. DMF developed stream maintenance guidelines for diadromous fish runs in 2016 and has been actively working with Town and watershed association partners since to conduct the right amount of work in the field to protect this ancient sea-run migration. The more we work on this task, the more we realize that, if left unchecked, some of these streams will transition to wetland havens for invasive plants. Removing flow restrictions benefits a wide range of aquatic life and in some cases reduces flooding potential in our crowded flood plains. 
 
By Brad Chase, Diadromous Fisheries Project Leader
 

Division of Marine Fisheries 

The Division of Marine Fisheries manages the state’s commercial and recreational saltwater fisheries and oversees other services that support the marine environment and fishing communities.
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