The short version
At the Waquoit Bay Reserve's Cape Coastal Conference in Hyannis on June 18, 2024, two Falmouth officials, Chuck Martinsen (Marine & Environmental Services) and Tom Duncan (Water Quality Management and Shellfish Advisory Committees), described how the town has turned shellfish farming into a nitrogen-removal tool. They covered a decade of work, a three-year pilot with commercial growers in the Eel River (2020 to 2023), and plans to expand. By their figures, the pilot's three growers sold more than 3 million oysters and took in about $141,000, and each acre of oysters removes enough nitrogen to equal roughly 24 households. This is a slide deck from a talk and has not been peer reviewed. This summary is based on the slides.
What the report covers
The slides walk through the town's shellfish program from its first trials to its planned expansion.
- A timeline from small oyster trials in Little Pond (2011 to 2015) through the choice of the Eel River for permitting in 2019.
- A description of the Eel River pilot, in which commercial growers rent town-owned floating gear at town-permitted sites, and the rental fees go into a town shellfish account that buys quahog seed.
- Pilot totals for three growers over 2020 to 2023: oysters sold, weight gained by the oysters (harvest weight minus seed weight, from each grower's weigh-in and weigh-out reports) and revenue.
- A calculation of nitrogen removed per acre and what that equals in households and in the capital cost of other nitrogen fixes.
- A "by the numbers" summary for 2014 to 2024 and a list of next steps and expansion expectations.
What they found
- Oyster sales grew every year. The three growers sold 42,230 oysters in 2020, 636,150 in 2021, 935,353 in 2022 and 1,428,669 in 2023, for a total of 3,042,402 and revenue of $141,390.56 (Martinsen & Duncan, 2024). Their combined weight gain rose from 43,413 kg in 2021 to 57,235 kg in 2023.
- About 106.5 kg of nitrogen per acre. Using the 2021 to 2023 average weight gain of 35,484 kg per acre and an assumption that nitrogen makes up 0.30% of harvest weight, the authors estimate 106.5 kg of nitrogen removed per acre each year. That is 3.32% of the Eel River's 3,210 kg-a-year nitrogen allocation.
- Equal to about 24 households. At 4.5 kg of nitrogen per household per year, one acre is the equivalent of 23.7 households. The slides price that against other fixes: $1,896 for urine-diverting toilets at $80 each, $830,000 for nitrogen-reducing (I/A) septic systems at $35,000 each, and $474,000 to $1.04 million at Falmouth's per-connection sewer costs for Little, Great and Green Ponds. Mashpee's ($93,800) and Barnstable's ($117,000) per-connection costs come to $2.22 million and $2.77 million.
- A planning number and a gap. For planning, the town uses 130 kg of nitrogen per acre for oysters, a target set by the Eel River pilot that the authors say is achievable if the growing plan is followed. They add that no Falmouth-specific checks of nitrogen removal by quahogs or scallops exist.
- Local jobs and volunteers. For 2014 to 2024, the slides list 25 full-time-equivalent jobs, 13,194 volunteer hours on municipal oyster propagation (valued at $268,497.90), and 356,400 town-grown oysters sold to other towns for $69,793.
- A case beyond water quality. The authors argue the program would be worthwhile even if oysters showed no measurable effect on water quality right next to the farms: removal is documented, happens where the water is impaired, brings in revenue instead of costing taxpayers, and shows a shared resource can work.
- Expansion plans. The town sees room for over 35 new farms on 100 to 200 acres, and up to 70 at the very top end, public and private. Next steps listed: a $400,000 Town Meeting request in fall 2024 for permitting, a draft environmental impact report and engineering; $4 million for full implementation, starting with gear in fall 2025; a new public/private manager position; a training program with the Barnstable County Sheriff's office; work with MIT Sloan on business models; and growing the volunteer corps from 300 to 500. Full-scale implementation is shown for 2025 to 2028.
What it means for Waquoit Bay today
The Eel River and Little Pond flow to Falmouth's south-coast estuaries, not into Waquoit Bay. They matter here because the same town is also working on Waquoit Bay's nitrogen problem, and oysters and quahogs are one of the non-sewer tools being weighed. Falmouth's own progress report on its nitrogen plan covers oysters alongside sewers and septic pilots (see Falmouth's plan to cut nitrogen), Mashpee has monitored what its oyster and quahog farms do for the water (see Mashpee's oysters and quahogs), and a three-year Cape Cod study asked whether floating oyster farms help the mud remove nitrogen (see floating oyster farms). For background on why that problem exists, see our post on where Waquoit Bay's nitrogen comes from, and for another Falmouth test of nitrogen removal, groundwater seeps in a restored bog.
Read the slides as the town's own account. The household equivalents rest on an assumed 0.30% nitrogen share of harvest weight and on per-acre weight gains, not on measured water-quality changes at the farms, and the deck says plainly that quahog and scallop removal has not been checked for Falmouth. Shellfish are likely to supplement cutting nitrogen at its source; they won't replace it.
This talk was given at the Waquoit Bay Reserve's 2024 Cape Coastal Conference. Our conference roundup lists all the talks, with slides and videos.
See the presentation
Martinsen, C., & Duncan, T. (2024, June 18). Aquacultural production and nitrogen removal in Falmouth, MA – Current progress & projections [Conference presentation slides]. Cape Coastal Conference, Waquoit Bay National Estuarine Research Reserve, Hyannis, MA. https://waquoitbayreserve.org/wp-content/uploads/Aquaculture-Production-in-Falmouth_Duncan_Martinson_Falmouth.pdf
License: The slides carry no open license, so we link to the Waquoit Bay Reserve's copy and do not host the PDF here. This is a slide deck, not a paper, and the summary covers only what the slides show. A video of the talk is on YouTube. The card image is a title card made from the citation.
Drafted with AI assistance from the linked source.
