Field Experiments to Investigate Methods of Attracting Wild Soft- Shell Clam Juveniles to Discrete Areas of the Intertidal Zone in Stockton Harbor (Stockton Springs 2007)

In 2007, DEI received a small grant from the town of Stockton Springs to examine whether the presence or absence of wild soft-shell clam adults and the presence or absence of predator-deterrent netting would enhance the settlement of wild soft-shell clam seed.  In mid-July 2007, Dr. Beal, DEI’s director of research, and students from UMM set up two field tests at a muddy site on the northern side of Stockton Harbor.  The trials continued until October, when bottom samples from each of the plots shown in the panels below were sampled and the number of wild seed counted and measured.  Stockton Spring’s shellfish committee wanted to know if manipulating adult clams and deterring predators — such as crabs and bottom-feeding fish — will enhance areas of the intertidal zone with wild clam juveniles.  (See Final Report)

Top left:  Study site on the north side of Stockton Harbor.  Stockton Springs public landing is in the background.

Middle left:  Commercial soft-shell clams were placed on the surface of 20-ft x 14-ft plots that had received netting or that received no netting.  Controls included similar size netted plots that received no clams, and plots with no clams and no nets. (Experiment I)

Upper right:  A 20-ft x 14-ft plot with netting (1/4-inch aperture).  It is difficult for clams to extend their siphons up through the netting to feed effectively.  Therefore, five Styrofoam floats were affixed to the underside of each net so that during periods of tidal inundation they would bulge up into the water column to reduce their interaction with the clams in the plots.  (Experiment I)

Lower left:  A 20-ft x 14-ft control plot with clams.  One bushel of commercial size clams was broadcast onto the muddy surface.  The majority of clams dug themselves into the mud within 24 hours. (Experiment I)

Lower middle:   One 1-m2 netted plot with Styrofoam toggle.  In Experiment II, commercial size clams were planted in netted plots at densities of 0, 50, 100, and 200.  Control plots (without netting) were also used for two of the four densities (0 and 50).  October sampling will reveal if clam density and/or the presence/absence of netting has an effect on the presence and size of wild soft-shell clam seed.

Lower right:  A series of 1-m2 control plots marked in each corner with a small, wooden lath.

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