2017 Freeport Clam Recruitment Study

As part of the Downeast Institute’s applied marine research in Freeport, Dr. Brian Beal continues to work with the Maine Clammers Association to gather information on clam recruitment. After recruitment studies in 2015 and 2016 showed high levels of clam settlement (~1,400 soft-shell clams per square ft) on the east side of the Harraseeket River (the Wolfe Neck side), this year five field sites were set up on the east side. At each of these sites empty recruitment boxes were deployed every two weeks starting at the beginning of May and ending at the end of September.

One of the 220 2017 Recruitment B filled with clams.

Half of the 220 boxes were topped with a 3.2mm mesh and half were topped with a smaller petscreen mesh, while all had petscreen on the bottom. Settling juvenile shellfish fall through the screen and are protected from predators as they grow throughout the season. To determine clam survival outside the predator protected mesh boxes we also took twenty-five 10lb. core samples at each deployment date and every two weeks through October until the ultimate sampling date on Nov. 9. At that time all 220 regular size recruitment boxes (along with 15 larger-scale recruitment boxes of ten 4-ft x 8-ft x 3-in and five 26-in x 8-ft x 3-in boxes) were tagged with identifying information (site number, date deployed, size of mesh, place in site grid) removed from the mud and taken to a processing station. There, the sediment in the box were measured to acquire sedimentation information, and the entire contents of the box were sieved through 1mm mesh. The sediment was washed away with seawater, and the remaining soft-shell clams, razor clams, quahog clams, along with non-commercial clams, green crabs, and milky ribbon worms are placed with their tags into bags inside coolers and taken to DEI’s labratory on Beals Island. There, all animals will be identified, counted, and measured to obtain growth rates. This information will be used to determine the amount of clam recruitment for species such as soft-shell clams and razor clams as well as if there is a peak clam settlement time period. The different size of clams found in the staggered boxes seem to indicate that there may be a secondary and perhaps even tertiary soft-shell clam spawning event during the season. Information from the samples can also be used to obtain more information on clam growth rates in conjunction with the size of  mesh used to protect the clams, and the ability of different size mesh to deter predators.

This year’s recruitment study builds upon key discoveries of previous years, that 1) flats without clams are not “dead mud,” as many areas actually are receiving shellfish recruits, but the clams are not surviving due to high levels of predation; and, 2) clam spawning and settlement is not a single event, but spans throughout the summer and fall.