Transplants of intertidal shellfish for enhancement of depleted populations: Preliminary trials with the New Zealand little neck clam

The New Zealand little neck clam, Austrovenus stutchburyi (Wood 1828), is widely distributed in sheltered intertidal habitats around New Zealand and has long been harvested by recreational and traditional fishers. Clam abundances have declined on many beaches due to excessive harvesting and habitat change, such as sedimentation and pollution. The feasibility of transplanting clams as a method of shellfish enhancement was tested. Manipulative field experiments using tagged clams examined parameters likely to affect growth and survival of transplanted clams, including the size of seed used, density and shore level at which seed is planted out, and the season in which the transplant is undertaken. Juvenile clams (10-18 mm) had a mean recovery rate of 30% after 1 y. Growth was highest for clams transplanted to low on the shore, but mortality was also highest for these clams. Optimal placement of juvenile seed for enhancement would be at mid-shore levels, where more clams were retained and reasonable growth still occurred. A much higher recovery rate (60%-90%) was achieved for adult clams (25-32 mm), and they were more likely to remain in the new area. These pilot trials demonstrate that transplant is feasible and would be particularly successful for adult clams.