Geographic origin and culture method influence the overwinter mortality of juvenile hard clams, Mercenaria mercenaria (L.)

Abstract

Abstract Overwinter mortality of juvenile northern quahogs, Mercenaria mercenaria, is a major impediment to the aquaculture industry from the mid-Atlantic US through Atlantic Canada. Mortality occurs during prolonged exposures to low temperatures and/or during the winter–spring transition when water temperatures are rising. Recent efforts to overwinter juveniles of M. mercenaria produced from native Maine (ME, USA) broodstock in eastern ME have found high survival while using a newly adopted methodology (i.e. cages in the water column rather than the standard practice of bottom planting) for overwintering. The current study aimed to determine if the high survivorship was a result of the culture methodology or if the ME genetic stock is better adapted for overwinter survival. Field studies were performed across two consecutive winters in ME, New York (NY) and New Jersey (NJ, USA) to compare survivorship of two size classes of juvenile M. mercenaria using the new methodology to the standard practice of bottom planting, and to compare the survival and physiological condition of the ME stock vs. the NY and NJ stocks across a latitudinal gradient. The ME stock had greater survival than the NY and NJ stock at all sites and in both study years. Both of the ME size classes exhibited lower mortality ( M. mercenaria in eastern Maine cannot be applied effectively to more southern locations. However, the results suggest that selective breeding programs may be able to develop aquaculture stocks that are better adapted to overwintering conditions.