Evaluating northern quahog (= hard clam, Mercenaria mercenaria L.) restoration: Are transplanted clams spawning and reconditioning?

Spawner sanctuaries, harvest-free areas planted with high densities of adult clams, are currently being used to restore self-sustaining populations of Mercenaria mercenaria (L.) to Great South Bay, New York. To evaluate and guide this restoration, we monitored the condition and spawning of clams transplanted from two source locations in Long Island Sound since April 2004. Transplanted clams were in relatively high condition and gonad ripeness at time of transplant, spawned the first spring and/or summer after transplant, reconditioned and spawned in subsequent years, but rarely reconditioned to as high of levels as when they were first transplanted. All populations exhibited similar annual patterns of condition and gonad ripeness: both peaked in mid to late spring, dropped steeply through summer with spawning, and they were lowest in fall. In some years condition increased during fall, and the higher the condition attained by the end of fall (mid-December) the greater the peak in condition the following spring. Across years and populations, condition at the end of fall explained ∼89% of the variance in spring peak condition. Consistent differences in condition through time among some populations suggested that location within the bay as well as clam size impact condition. Because of interannual and locational variability, long-term monitoring of this long-lived species is essential for determining factors affecting condition and reproduction, and the ultimate restoration of sustainable hard clam populations.