In May of 2019, DEI scientists deployed studies across the Maine coast that will determine if the brushing method works to increase clam populations. This study marks the first time ever that this popular clam enhancement method has been tested to determine its effectiveness. The results will provide valuable information to clam managers about tools they can use to increase clam harvests and adapt the fishery to the changing marine ecosystem.
The studies are taking place in each of three regions of the Maine coast – Downeast, Midcoast, and Southwest, in the towns of Gouldsboro, Bremen, and Harpswell, respectively. DEI scientists are working directly with the town’s Shellfish Conservation Committees and clammers to deploy the experiments, as well as collect and process the data.
Brushing is the practice of inserting tree boughs into the mudflats. In concept, the brush reduces tidal and wind currents that help to create eddies and provide bottom zones of slow-moving water where recently settled soft-shell clam juveniles may congregate.
The study deployed three sets of brush in each town, and will measure the amount of clams that settle and survive around the brush. In addition, at each location, three nets that protect clams from predators were deployed. The number of clams that settle and survive in brushed areas will be compared to the number of clams that settle and survive in netted plots. This comparison will clarify the utility of the two methods and demonstrate to local shellfish managers the most effective method to increase clam populations.
Results from Baseline Density Clam Surveys, May 2019
During deployment DEI scientists took samples (n=108) of the mud to establish baseline densities of clams in each location. Clams were found in half the samples in Gouldsboro, 26% of the samples in Bremen, and 13% of the samples in Harpswell. The average density of clams in Gouldsboro was 3.4 clams per sq. ft., in Bremen the average density was 1.6 clams per sq. ft., and in Harpswell the average density was 0.6 clams per sq. ft.
The baseline survey results show that the amount of clams in the mud decreases the further south the location. This finding correlates with previous field experiments DEI has done across the coast of Maine. Read more about the baseline survey results here.
Clam harvests in Maine have declined dramatically over the last 30 years. Recent research by DEI has found that increased predation by invasive green crabs and other species are to blame for the decline. The Gulf of Maine’s warming ocean water temperatures drives the increase in predation.
Samples from each of the three sites were collected in November in collaboration with clammers from each community. Read about the sampling effort in Bremen in this Lincoln County News article.
DEI scientists processed the samples, recorded and analyzed the data to find the results. Presentations are being held in each community sharing the findings.
Read about the Gouldsboro results in this Ellsworth American article about the Jan. 7, 2020 presentation to the Gouldsboro Shellfish Committee.
Read about the Bremen results in this Lincoln County News article about the Jan. 8, 2020 presentation to the Bremen Shellfish Committee.
Rad about the Harpswell results in this The Times Record article about the January 28, 2020 meeting to the Harpswell Marine Resources Committee.
The coastwide results will be shared on March 5, 2020 at the Maine Fisherman’s Forum.
Funding for this study came from the Maine Shellfish Restoration and Resilience Project, the Broad Reach Fund, and Maine Sea Grant.