Clam Recruitment Monitoring Network sites in 2022.

Downeast Institute and nine partner communities have established a Clam Recruitment Monitoring Network that spans the coast of Maine. This network measures soft-shell clam and other shellfish recruitment and survival, at two flats in each of twelve municipal shellfish programs from Wells in southern Maine to Sipayik (at Pleasant Point) in eastern Maine.

DEI’s Network partners include the Wells Shellfish Committee, Scarborough Shellfish Conservation Commission, Brunswick Marine Resources Committee, Phippsburg Shellfish Commission, Wiscasset Shellfish Conservation Committee, Bremen Shellfish Conservation Committee, Islesboro Shellfish Conservation Committee, Deer Isle & Stonington Shellfish Committee, Frenchmen’s Bay Regional Shellfish Committee, Beals Shellfish Committee, the Unorganized Township of Edmunds, and the Natural Resources Board of the Passamaquoddy at Sipayik. Clammers, municipal officials, students, and community volunteers work with DEI researchers to collect soft-shell clam recruitment and survival data.

Clam Recruitment is Measured by Using a Simple Tool

Soft-Shell Clams - Shellfish Recruitment at Downeast Institute

Settling clams fall through apertures in the top mesh of the recruitment box. The box protects the clams from most predators, enabling them to survive and grow. At the end of the clam growing season the boxes’ contents, along with core samples of mudflat sediment collected adjacent to the boxes, are analyzed to determine the number of clams that settled onto the mudflats, as well as the number that survived the season. Survivors are important indicators of commercial soft-shell clam populations in subsequent years.

Methods

At each of the eighteen sites, an array of 16 recruitment boxes is deployed in the lower mid intertidal gradient. The boxes are deployed prior to soft-shell clam spawning season and sediment core samples are taken to assess baseline densities of clams. Boxes are retrieved at the end of the clam growing season in November, and sediment core samples from outside the boxes are collected again. These samples from the adjacent unprotected mud, compared to samples from the box, reveal the rate of predator success that season.

Schematic of Soft-Shell Clam Recruitment Monitoring field layout from Downeast Institute

The same field layout for the Soft-Shell Clam Recruitment Monitoring Network was used at all 18 sites.

Results

2021 Clam Recruitment Monitoring Network Final Report

Results from the 2021 Clam Recruitment Monitoring Network can be found in the upcoming Technical Report #3: Clam Recruitment Monitoring Results. The report summarizes and shares data from the fall mudflat survey, information about clam recruitment, temperatures, clam recruit growth, recruitment and growth of other commercially important shellfish species, along with presence and size of green crabs on a town and statewide basis.

Across all sites average clam recruitment density in 2021 was substantially lower than it was in 2020. Last year we found only 19 clams per square ft. in our predator protected boxes vs. 95 clams per square ft. in 2020. The low number of recruits found was likely due to higher numbers of green crabs. In 2021 there were 4.5 green crabs per square ft. across all 21 sites, while in 2020 we found only 2 crabs on average across all 18 sites.

2020 Clam Recruitment Monitoring Network Final Report

Re2020 Clam Recruitment Monitoring Resultssults from the 2020 Clam Recruitment Monitoring Network can be found in the Technical Report #2: Clam Recruitment Monitoring Results. The report summarizes and shares data from the fall mudflat survey, information about clam recruitment, temperatures, clam recruit growth, and presence and size of green crabs on a town and statewide basis.

Across the coast, clam recruitment densities were lower than expected based on data from previous years. Eight of the eighteen sites had average clam densities of less than 10 clams per sq. ft. Only three sites recorded average clam recruit densities of over 100 clams per sq. ft. (Winnock Neck in Scarborough, Dobbins Island in Beals, and Gleason Cove in Sipayik). At Gleason Cove we found a single recruitment box with 4,331 recruits, the second highest number of clams ever recorded in a single box. Gleason Cove received more than 1,000 recruits per sq. ft.

Read a 2-page summary of the overall results here.

May 2020 Baseline Clam Survey Results

In May of 2020, DEI scientists, along with community members, conducted clam surveys in the each of the areas where the clam recruitment monitoring stations were deployed in order to establish baseline densities of clams and their sizes.

The results of the survey, along with information about the Soft-Shell Clam Recruitment Monitoring Network, can be found in Technical Report #1: 2020 Spring Baseline Clam Survey Results. Click on the report to the left to read it.

Green Crab Specific Results (2020 & 2021)

Associate Director Sara Randall presented the green crab specific results during a 2022 Downeast Discussion Climate Change Seminar. 2021 was warmer on the mudflats than 2020, and as a result we found more green crabs at our monitoring stations and less clam recruits. Watch below to learn more.

Funding

From 2020-2021 this project was funded by Maine Sea Grant. Luke’s Lobster Keeper Fund supported the work of documenting recruitment and growth of other commercial shellfish species. In 2022, funding is provided by Maine Economic Improvement Fund Small Campus Initiative and Maine Outdoor Heritage Fund.

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