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Bibliography of the Maurice Lamontagne Institute

Gaétan DAIGLE

FRÉCHETTE, M., M. GIGUÈRE, G. DAIGLE, 2000. Étude de l'effet du site d'élevage et de la provenance des spécimens sur le potentiel aquicole du pétoncle d'Islande Chlamys islandica (O.F. Müller) en Côte-Nord. Rapp. can. ind. sci. halieut. aquat., 258, 25 p .

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In order to supplement scallop fishery landings in the Mingan region, a number of culture and wild bed management strategies are presently under consideration. One such strategy implies transferring individuals from slow-growth donor sites to fast-growth culture sites. Knowledge about factors responsible for slow growth is necessary to evaluate the chances that relaying operations are successful and profitable. If slow growth were attributable to intrinsic characteristics of individuals (stock effect), such individuals would be of limited value for aquaculture operations. On the other hand, if slow growth were attributable to site effects, knowing whether slow growth results from intrinsically poor general environmental conditions or from overpopulation would be of interest because overpopulation would imply that not all animals would have to be transferred. Growth of individuals remaining on the donor sites would increase after culling. In addition to promoting growth, this would reduce transfer costs. Here we report experiments aimed at testing these possibilities. We made two experiments. The first one was a stock-site experiment. Scallops wer transferred from three donor sites located near île à la Proie (fast growth site), île Sainte-Geneviève and Baie-Johan-Beetz (both slow growth sites) to the site located mear île à la Proie. Controls from each site were grown without being transferred. Such transfers allow to test the relative contribution of stock and stie to variability in growth and survival. Some of grous could not be recovered. The experiment lasted two years. After the first year, individuals from île à la Proie had higher growth than those from the other stocks tested, and individuals from île Sainte-Geneviève grew faster near île à la Proie than near île Sainte-Geneviève. The goal of the secon experiment was to test for overpopulation on a slow-growth site. Scallops were installed in two sites, one populated with scallops, but not the other. On each site, some scallops were installed near the bottom while others were installed far from the bottom. With this set-up, all groups except that one near the bottom in the populated site were free from potential overpopulation effects. Our results are consistent with the hypothesis of no overpopulation in the populated site. On both sites, growth rate was smaller near the bottom, presumably because of higher density or resuspended inorganic particles near the bottom. Computer simulations, however, suggest that depth-related differences in current speed may also provide an explanation to lower growth near the bottom either through direct effects of current speed on scallop clearance rate or through indirect iffects on food replenishment rate within the pearl nets. Our results also suggest that the symmetry of the ears of the shell in the left-right symmetry axis (upper shell-lower shell) was a proxy for survivorship.