Arctic Surf Clam Growth and Valuation
healthyProject Description
Clam harvest epitomizes the problem of collective action in common pool resource settings. Open access to a subtractable resources can lead to overfishing. Municipalities with shellfish ordinances approved by the state can control access to the resource by implementing access rules and can increase the resource through conservation work, including reseeding habitat with cultured (hatchery) seed clams. The largest soft-shell clam harvests in Maine come from towns with this co-management system, where local shellfish committees have instituted some form of collective management. Towns without ordinances experience open access conditions and may be overharvested or have other management challenges. The Cobscook Bay region has struggled with open access.
Clam flat enhancement, be it through seeding, anti-predator netting, or both, is a crucial component of maximizing yield from the Pleasant Point flats in Cobscook Bay. Enhancement with hard shell clam species for developing markets may add value by including higher value species in the catch. The Arctic surf clam holds great potential, but is not found in sufficient density in the intertidal zone to be of commercial value.
Results and Accomplishments
This study was designed to demonstrate the growth potential of soft-shell clams on Easternmost Maine beaches with and without protection from predators. Twelve experimental plots on each of two beaches (24 total) were laid out at Pleasant Point, near Perry, ME (Bioregion 3). The beaches included a fished area known for clam production and an infrequently fished area not known for clam production. Each beach had three blocks consisting of four treatments. Treatments were control (no seed – no net), seed + net, seed – no net, net – no seed. The net treatment consisted of a 4.3m x 6m black nylon net (5mm mesh size) stretched over a 4m x 5.5m area of beach, placed more than half way between the mean low tide line and mid tide line. Each seeded treatment received ~6000 settled juvenile clams, roughly 10 mm – 15mm in shell diameter. The hypothesis was that seeded-netted plots would produce more clams and, potentially, greater growth than clams in non-netted treatments. In addition, netted treatments would produce more clams than non-netted treatments.
Data collection consisted of removing the nets (where necessary) and taking three core samples per treatment per block with a coring device (0.02 m2) to a depth of 20cm. Cores were sieved to collect clams and any predators present. Clams were divided into three categories: alive, dead, and crushed. Crushed was presumed to show active, recent predation by intertidal predators, particularly green crabs. Live clams were measured at the hatchery growth ring (growth ring left from hatchery rearing) and shell edge at capture.
The infrequently clammed beach appeared to be a much less hospitable habitat for softshell clams than the frequently clammed beach; however, few clams were found in either habitat. No live clams were found in the infrequently clammed beach, and clam signs of any sort, crushed or otherwise, occurred twice as often on the frequently clammed beach. The number of cores with no clams was high, producing wide error bars, but on both beaches more signs were found in the seeded-netted treatments. Crushed clams were significantly more numerous in the seeded-netted plots, showing that the predator deterrence was partially effective, but predators eventually managed to get to seed clams under or through the nets. Live calms were found only in the seeded-netted plots on the frequently clammed beach. Although the live clams were of a higher abundance than the dead or crushed categories, statistically there was no difference between the three categories for that treatment on the frequently clammed beach.
Researchers conclude that clams seeded under nets have a considerably higher probability of survival. However, anti-predator equipment must be checked frequently for breeches in the defense and clear predators that might have gotten through.
Summary of Data Being Collected
| Data | Type | Quantity | Location |
| Shell height | mm | Annual measurement | Perry, Maine |
| Chlorophyll-a | ug/L | Monthly measurement | Perry, Maine |
| Temperature | C | Daily measurement | Perry, Maine |
| Clam Density | Bushel per acre | Monthly measurement | Perry, Maine |