SHELL AND TISSUE-GROWTH OF JUVENILE SEA SCALLOPS (PLACOPECTEN-MAGELLANICUS) IN SUSPENDED AND BOTTOM CULTURE IN LUNENBURG BAY, NOVA-SCOTIA

Hatchery-reared juvenile sea scallops Placopecten magellanicus (mean s hell height = 22.2 +/- 0.1 mm) were grown uncontained on the seabed (5 -9 m depth) and suspended in pearl nets (3 m above the seabed) at thre e sites (Site 1, 2 and 3) in Lunenburg Bay, N. S., Canada, between Mar ch 1992 and March 1993. Shell and tissue growth rates reached their pe ak in mid-summer and decreased to the lowest values in winter, althoug h growth never stopped. Monthly measurements of shell heights of indiv idually tagged scallops in pearl nets (100 per net) and on the seabed, yielded mean (+/- s.e.) annual growth rates of 93 +/- 5.5 and 117 +/- 4.5 mu m/day, respectively, at Site 1, 72 +/- 3.0 and 93 +/- 3.8 mu m /day at Site 2, and 79 +/- 2.8 and 73 +/- 5.6 mu m/day at Site 3. Ther e were significant differences in shell growth rates among the three s ites and between the two culture methods in most of the months. The hi ghest shell growth rates generally occurred at Site 2, regardless of c ulture method. Shell growth rates were significantly higher in bottom than in suspended culture during most measurement periods, Mean final soft tissue condition index of scallops in suspended culture was signi ficantly higher than in bottom culture at Site 2. Mean final adductor muscle condition index and mean final whole dry weights of scallops we re significantly lower in suspended culture than in bottom culture at Site 2. Water temperature at all three sites ranged from similar to -2 to 16 degrees C during the year. There were significant differences i n annual mean particulate organic matter concentration between depths, but not among sites, Annual mean chlorophyll concentration differed a mong sites, but not between depths within sites, Stepwise multiple reg ression analyses, with water temperature, total particulate matter con centration, and chlorophyll concentration as independent variables, we re highly significant for all sites and culture methods. They explaine d between 46% and 66% of the total variance of shell growth rates in s uspended culture and between 36% and 78% in bottom culture, respective ly and 55% and 80% for soft tissue growth rates of scallops in suspend ed and bottom culture, respectively. Growth of scallops in bottom cult ure at these shallow sites is comparable to animals of the same seed p opulations grown in the more expensive and labour-intensive suspended culture at the same sites.