Results from the clam ecology study at the Rim River Bridge site in the Machias River Estuary in East Machias were as follows:
High Tide (No Netting): Survival = 11.1% Growth = 7.1 millimeters, which is about 3/10ths of an inch
High Tide (With Netting): Survival = 69.4% Growth = 9.2 millimeters, which is about 3/10ths of an inch
Mid Tide (No Netting): Survival = 5.5% Growth = 3.7 millimeters, which is about 2/10ths of an inch
Mid Tide (With Netting): Survival = 68.1% Growth = 10.3 millimeter, which is about 4/10ths of an inch
Low Tide (No Netting): Survival = 4.2 % Growth = 5.0 millimeters, which is about 2/10ths of an inch
Low Tide (With Netting): Survival = 56.9% Growth = 11.5 millimeters, which is about ½ of an inch.
Clam survival, independent of tidal height, was very low in experimental units (plant pots) that received no netting. The highest survival rate was 11% at the high and 4.2% at the low. The data show that crushed clams, presumably from green crab attack, were more common than live clams, and this indicates how important predation by crabs is at this site. Clams that were protected from predators using deterrent netting had survival rates that ranged from 55% to 70%. This shows that predators can be slowed down, but not completely eliminated from the story. The netting does a good job in keeping predators at bay, but it is not 100% effective.
Clam growth was somewhat surprising. Normally, growth rates would not differ much between protected and unprotected pots, but in each case (High, Mid, and Low intertidal), clams in the protected pots (that is, those covered with the plastic netting – ¼-inch aperture length) grew faster than those in the unprotected pots. The fastest growth observed occurred in protected pots at the low intertidal, where clams increased in shell length by approximately ½-inch.
You can read about the Washington Academy experience in a Bangor Daily News article published on October 15, 2011.