Brunswick: A collaborative approach to bolster quahog populations

Contacts

Dan Devereaux – Coastal Resources Manager
ddevereaux@brunswickme.org

SHORT PROJECT SUMMARY (PDF)

BACKGROUND

Prior to 2012, the Town of Brunswick had one of the most robust soft-shell clam populations in the state. Then an increase in green crab predation and a decline in soft-shell clam landings led the town to pivot to propagating hard clams (Mercenaria mercenaria), or quahogs. Quahogs are more predator-resistant than soft-shelled clams, and as ocean temperatures rise, the Maine Coast is becoming increasingly suitable habitat for hard clams.

For the past decade, the Marine Resources Committee has successfully coordinated the planting of juvenile and adult quahogs from high density areas to areas without commercial soft-shell clam or quahog populations. Hard clam landings now exceed soft shell clams landings by weight. Projects such as this, which combine farming techniques with local knowledge, will help bolster quahog populations and ensure the sustainability of the shellfish industry in Brunswick.

Project sites in Maquoit Bay and Middle Bay

TRANSPLANTING QUAHOGS

In 2020, Brunswick received Maine Shellfish Restoration and Resilience funding to purchase and grow hatchery seed with the intention of augmenting the local quahog population. The Town chose study sites in Middle Bay and Maquoit Bay with established shellfish farms where they could site the nursery equipment. The Marine Resources Committee sourced 1-2mm seed quahogs from Muscungus Bay Aquaculture and the Downeast Institute. At the two sites, project staff reared quahog seed in floating nurseries made of mesh spat bags and cages.

The nurseries were tended and flipped to counter biofouling. Weekly water samples were collected at high tide. At the end of the growing season, the seed was split into two groups to overwinter either on-site on the ocean floor, or at the Downeast Institute overwintering facility. The following year, the project staff transplanted the seed into Harpswell Cove.

Results

Brunswick has been successful in the use of overwintering farming techniques, and broadcasting clams into the flats. With the help of shellfishermen and shellfish farmers, over 750,000 quahog seeds, 5-20mm in size, have been planted into Harpswell Cove. The rearing process was also effective; no significant mortality was observed at the nursery site, and the quahog seed grew from an average of size of 2mm to an average of 10mm.

Water quality parameters (turbidity, DO, conductivity, pH, temperature) at both sites fell within acceptable ranges for quahog growth and survival, suggesting that a successful shellfish aquaculture site has the water quality to support the nursery phase of quahog propagation.

Beyond this project, the Marine Resources Committee’s decade-long relaying and reseeding efforts have brought quahogs into fourteen previously unproductive areas, and expanded the local quahog resource.

takeaways

The Marine Resources Committee gleaned several takeaways from this process. First, site selection can be challenging. Brunswick placed their nursery equipment on established aquaculture sites. The process can include extensive permitting and paperwork, and groups should do research to determine feasibility and project cost before starting. The Marine Resources Committee experienced difficulties with staffing and maintenance; this project required more staff time than anticipated and biofouling on gear was significant. Groups should consider a cost-to-benefit ratio before embarking on a similar project and be flexible in planning.

Brunswick will conduct annual shellfish surveys to monitor quahog survival and assess the long-term impact of the project. Finally, diversifying conservation efforts with quahogs could benefit municipal shellfish programs if the decline in soft-shell clams continues.

Project timeline

February 2020

Coordination with Muscungus Bay Aquaculture and Downeast Institute to source 750,000 (1-2mm) seed quahogs
March 2020

Ordered gear and equipment

Town elected to downsize the project to two locations and limit volunteers due to the pandemic
April-May 2020

Obtained permission from farmers to use sites permitted for aquaculture
June 2020

Floated nursery gear and quahog seed in Maquoit Bay and Middle Bay
July-August 2020

Defouling and repacking densities of the quahog seed

Loaded nursery gear with second batch of seed

Began collecting water quality data
October 2020

Prepared seed for overwintering

Repacked densities
November 2020

Split crop for overwintering: half to Downeast Institute, half sunk to the ocean bottom with the help of a diver
May 2021

Quahog seed is retrieved from the ocean floor in the spring
June 2021

Cleaned, sorted, and sized quahog seed

Planted into Harpswell Cove