Results from the clam ecology study at Little Machias Bay in Cutler, Maine were as follows:
High Tide (No Netting): Survival = 17.4% Growth = 10.2 millimeters, which is about 4/10ths of an inch
High Tide (With Netting): Survival = 78.5% Growth = 9.9 millimeters, which is about 4/10ths of an inch
Mid Tide (No Netting): Survival = 43.1% Growth = 21.8 millimeters, which is about 9/10ths of an inch
Mid Tide (With Netting): Survival = 72.2% Growth = 20.8 millimeters, which is about 8/10ths of an inch
Low Tide (No Netting): Survival = 31.3 % Growth = 18.9 millimeters, which is about 3/4ths of an inch
Low Tide (With Netting): Survival = 65.3% Growth = 19.1 millimeters, which is about 3/4ths of an inch
These results were a bit surprising, especially showing that survival in unprotected pots was worse at the upper intertidal heights than either of the two lower tidal heights. This may be due in part to the nature of the habitats at the upper vs. mid- and low tide levels. At the upper intertidal at Little Machias Bay, there are many large rocks and some ledges -- all covered with seaweed -- Ascophyllum nodosum. This wrackweed is a great place for green crabs to hide, and many of the clams in the unprotected pots near the upper intertidal mark at this site either were missing or were chipped or crushed, typical of damage caused by green crabs. The not-so-surprising results were that protective netting significantly deters crabs and other predators. The difference between unnetted and netted pots in terms of clam survival at the upper intertidal was night-and-day: 17% vs. 78%. Netting helps keep crabs from preying on juvenile clams. Although a similar result was obtained at the mid- and low tide levels (i.e., netting protects clams), the results were not as dramatic.
The most interesting result of the entire study was the growth rate observed at Little Machias Bay for clams growing near the mid- and low tide mark. Clams increased in shell length by at least 3/4ths of an inch in both protected and unprotected pots. The only surprise was that the clams didn't grow significantly faster at the low tide mark compared to the mid tide mark, but that may be because the times of tidal inundation were not so different between these two levels. In another study, clams should be planted at the extreme low water mark where the tide falls on the new and full moon of each month, followed by growth comparison with clams planted at mid-tide levels. The growth observed at the mid- and lower shore levels was the most of any of the sites in the study. Although we do not know the reason for this relatively fast growth, Cutler clammers and others who have harvested clams from the Little Machias Bay flat will tell you that they knew all along that clams grow very fast there. Our study provides some quantitative data to support those assertions.
We thank the Cutler Shellfish Committee for allowing us to set up and conduct the study from May through September 2011.