Rehabilitation of the northern quahog (hard clam) (Mercenaria mercenaria) habitats by shelling -: 11 years in Barnegat Bay, New Jersey

The use of shell or other coarse material to enhance survival of newly set hard clams (Mercenaria inercenaria) has been suggested as a management strategy to increase clam stocks. Barnegat Bay, New Jersey and surrounding areas supported a large clam fishery throughout the 1950s and 1960s, but this resource has declined in recent years. We established replicate 20 x 70 m plots of high shell density, low shell density, and no shell (control) in a Latin Square design in 1990 and have obtained periodic samples since that time. The shell, obtained from ocean quahog processing plants, had been broken into a variety of sizes. High-density shell received 900 bu per plot, and low-density shell received 300 bu per plot. Plots with high shell density had significantly more clams after 10 years than those with low-density shell or controls. High shell density significantly increased hard clam recruitment, but this exceeded 1 m(-2) in only one year, from the years 1990 to 2000. In plots with low shell or in controls, recruitment never exceeded 0.4 m(-2), and in half or more of the years no recruitment was found. Some individual plots with shell did not enhance recruitment, indicating that factors not investigated must be important as well. In spite of the low recruitment density, there appears to be an increase in survivorship when the shell content is greater than 8000 gm(-2).