Assessment of biological parameters for management of mussel seed collection in Amherst Basin (Magdalen Islands, Quebec)

Amherst basin is the only seed collection site used by the mussel growers from Magdalen Islands. Therefore, information is needed in order to assure appropriate management of this site. The reproduction, the larval cycle and the timing and intensity of spat-fall were followed in 1995 and 1996. There were three spawning events in 1995 and only two in 1996. The spawnings of June 10, 1995 and June 8, 1996 supplied the bulk of spat which settled down on collectors. There were only two spatfall peaks in 1995, the first in late June and the second in early August, and only one in 1996 in late June. Collectors provided the same amount of spat (4500 ind /m) both years despite a much greater larval density in 1995. The collectors immersed before July 10, 1995 and June 25, 1996 gave the maximum yield. Spat showed two modes in shell length (8 and 17 mm) in mid-September both years. Only one of the two mussel populations studied contributed clearly to the first spawning event of 1996 despite the proximity (900 m) of the beds. This arises interrogations on the usefulness of a methodology based on the evolution of dry tissue mass of wild adults to identify spawnings responsible for spat collection.