A Possible Relict Population of Mesodesma deauratum (Turton):Bivalvia (Mesodesmatidae) from the Southeast Shoal, Grand Banks of Newfoundland

Abstract

Extremely dense, localized concentrations of Turton's wedge clam Mesodesma deauratum (Turton) were found in quantitative grab samples on poorly sorted, medium to fine, low organic content sands (total organic carbon < 0.05%) at depths of 44–51 m at a single location on eastern Southeast Shoal of the Grand Banks of Newfoundland. Mean densities ranged from 24 to 5890 individuals∙m−2 and wet weight standing crop from 0 to 21.4 kg∙m−2. A peak standing crop of 69.4 kg∙m−2 was observed in one grab. There was a strong bimodal size distribution (17–27 and 34–56 mm shell length) at the site, but the two size groups never occurred together. Based on external growth checks, the smaller individuals were 4–5 yr old and the larger ones 10 to more than 15 yr. This population is suggested to be a relict of shallow littoral populations which probably existed in the area in the late Wisconsinan glacial period.