The soft-shell clam, Mya arenaria, fishery has been an iconic cornerstone of Maine’s coastal economy for >150 years. Since 1975, commercial landings have declined by 80% (Fig. 1), and are correlated directly to climate change and warming of the Gulf of Maine. Fisheries-independent data demonstrate clearly that observed declines are due primarily to predation, especially on 0-year class recruits. Recent interest has piqued among fishermen and managers around adjusting the 2-inch minimum size law, and instituting an upper size limit and/or creating spawner sanctuaries. Decisions about implementing new laws hinge on information related to reproductive output in Mya that is not readily available.
Maine soft-shell clam landings in five-year average (± 95% CI) increments (1950-2023).
Jonesport, Maine, March 2024. Planting clams in wooden boxes and affixing protective tops.
We conducted comparative, manipulative field experiments in three coastal regions along the Maine coast (downeast, midcoast, southwest) over two soft-shell clam spawning seasons (April-August 2023 & 2024; Figs. 2-5). This research program attempted to determine:
1) whether reproductive senility occurs in larger/older individuals
2) what role does spatial and temporal variability play in: a) the relationship between clam size and number of eggs produced per female clam; b) the timing and duration of the spawning season; c) egg viability as a function of clam size.
Bremen, Maine, March 2023. Installing 1-ft x 1-ft x 6-inch deep wooden boxes that were then filled with ambient sediments. Twenty-four soft-shell clams over a range of sizes from 35-100 mm in shell length were added to boxes at three tidal heights, and sampled over 19 weeks beginning in early May and continuing through August.
Jonesport, Maine, March 2023. Installing wooden boxes near the upper intertidal at Flake Point Bar.
The ability of a fishery to be sustainable depends on accurate information about the organism’s reproduction biology. The problem this effort addressed is the lack of published studies examining reproductive output of soft-shell clams, Mya arenaria L., along the Maine coast. This iconic fishery is suffering from multiple stressors associated with climate change as commercial landings have dropped by an average of 35% since 2000, and 80% since 1975. Clammers, local and state managers, and buyers/dealers have all agreed that the proposed work is needed to inform future decisions about how to improve/enhance harvests. Efforts to create an upper size limit and to reduce the lower size limit have met with resistance by the industry due to the lack of information that would be generated by the proposed work. State managers have indicated that the proposed research relates directly to their research objectives to inform soft-shell clam management along the coast.
Brunswick, Maine, March 2023, Barnes Flat in Pennellville.
The specific objectives are to determine spatial (regional; tidal gradient) and temporal (within and between years) variation or trends affecting the:
- relationship between clam size/age and reproductive output (number and size of eggs);
- timing and duration of clam spawning; and,
- viability of eggs as a function of clam size/age, region, tidal height, and time during the spawning season.
Quick Takeaways
- Reproductive senility does not occur in soft-shell clams, meaning that larger/older clams do not produce fewer eggs. The graph below shows the number of eggs released by spawned female clams in 2024 by town.
Examining the ability of males of different sizes to fertilize the eggs of females of different sizes, the size of the female did not matter in these pairings, but sperm from small males (<50mm in length) resulted in 25% less success in fertilization compared to the sperm from larger males.- Less than 2% of soft-shell clams sold by clammers to A.C. Inc in Downeast Maine are greater than75in in size and less than 1% of clams sold by clammers to Cantrell’s Seafood in Southern Maine are greater than 3.5in in size.
ACKNOWLEDGMENTS
This work would not have been possible without the assistance of the Towns of Brunswick, Bremen, and Jonesport, and many community members in each of those locations.
In Brunswick, thank you to the Brunswick Shellfish Committee, Ray Trombley of Casco Bay Seafood, Dan Devereaux, Dan Sylvain, and Chris Green, Lucas Green, Joe Havener, Ken Lund, Blaine Lund, Chad Coffin, Camden Reiss, and David Wilson for their efforts in the field.
In Bremen, thank you to the Bremen Shellfish Conservation Committee, Boe Marsh of Community Shellfish, volunteer Morganne Price, and Dale Witham, James Farrar, Robert Kaler Jr., Travis O’Brien, and Rob Cuddy for their efforts in the field.
In Jonesport, thank you to the Jonesport Shellfish Committee, Sam Stewart and A.C. Inc., and Garrett Libby, Michael Berry Jr., Everett Johnson, and Jason Alley for their efforts in the field.
Thank you to Downeast Institute staff members Brea Salter, Bennett Ellis, Kyle Pepperman, Keane Nunan, Sara Randall, Tessa Houston, Alanna McGovern, Asher Michalski, Ben Capuano, and Madeline Wren for their contributions in fieldwork preparation, work in the field, and lab work assistance.
And, finally, this work would not have been possible without the interns who dissected hundreds of clams for this project. Thank you to Alex Pietras, Taylor King, Shawnee McNally, Willa Dolley, Reilly Hedden, and Matt Nichols.
RESULTS
For information regarding results from Year I (2023), click here: [07_01_2024-third-progress-report-noaa-sk-downeast-institute-1]
For information regarding the Final Report, click here: [final-report-downeast-institute-clam-fecundity-studies ]
Clockwise from bottom right: Dr. Brian Beal demonstrates how the clam boxes will be deployed. Summer 2024 interns Matt Nichols, Willa Dolley, and Reilly Hedden spawning clams. All smiles on our mudflat in Bremen! Summer 2023 intern Taylor King dissects a set of clams. The team that helped plant the 2024 clams in Jonesport on a rainy day (top).
