| Popis: |
In 2000, the northern quahog (= hard clams) Mercenaria mercenaria population was surveyed in Raritan Bay with the purpose of determining sustainable harvest levels. To complement this population survey, we determined the size-at-age structure and experimentally determined mortality rate and size specific growth of adult clams. Clams of a range of sizes, obtained from the sampling program, were measured, cleaned, and aged by counting growth rings in sectioned shells. Experimental plots were established in the low intertidal zone at two sites in the Raritan/Sandy Hook Bay system. Marked clams of five sizes were planted in three seasons and harvested quarterly. Experimental estimates of mortality and survival were based on collected live and dead individuals and are thus conservative because they do not address the numbers missing. Some of the clams from both sites were removed from the area by predators. Estimated mortality for individuals >25 mm by instantaneous rate yielded a mean of 0.0176. Inte... |
