Shell and tissue growth of juvenile sea scallops ( Placopecten magellanicus) in suspended and bottom culture in Lunenburg Bay, Nova Scotia

Abstract

Hatchery-reared juvenile sea scallops Placopecten magellanicus (mean shell 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 three sites (Site 1, 2 and 3) in Lunenburg Bay, N. S., Canada, between March 1992 and March 1993. Shell and tissue growth rates reached their peak in mid-summer and decreased to the lowest values in winter, although growth never stopped. Monthly measurements of shell heights of individually 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 μm/day, respectively, at Site 1, 72 ± 3.0 and 93 ± 3.8 μm/day at Site 2, and 79 ± 2.8 and 73 ± 5.6 μm/day at Site 3. There were significant differences in shell growth rates among the three sites and between the two culture methods in most of the months. The highest shell growth rates generally occurred at Site 2, regardless of culture 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 significantly higher than in bottom culture at Site 2. Mean final adductor muscle condition index and mean final whole dry weights of scallops were significantly lower in suspended culture than in bottom culture at Site 2. Water temperature at all three sites ranged from ~ −2 to 16 °C during the year. There were significant differences in annual mean particulate organic matter concentration between depths, but not among sites. Annual mean chlorophyll concentration differed among sites, but not between depths within sites. Stepwise multiple regression analyses, with water temperature, total particulate matter concentration, and chlorophyll concentration as independent variables, were highly significant for all sites and culture methods. They explained between 46% and 66% of the total variance of shell growth rates in suspended culture and between 36% and 78% in bottom culture, respectively and 55% and 80% for soft tissue growth rates of scallops in suspended and bottom culture, respectively. Growth of scallops in bottom culture at these shallow sites is comparable to animals of the same seed populations grown in the more expensive and labour-intensive suspended culture at the same sites.