Field examination of dispersion patterns of juvenile Iceland scallops (Chlamys islandica) in the northern Gulf of St Lawrence

The movement of juvenile Iceland scallops, Chlamys islandica, was quantifie d in an inshore bed in the Mingan Islands, northern Gulf of St Lawrence, to examine whether the size partitioning over depth in this location, increas ing scallop size with depth, results from a gradual downslope movement as s callops increase in size. Scallops of 30.0-44.9 mm and 45.0-59.9 mm in shel l height were collected using SCUBA, tagged, and released in the centre of two 0.4-km(2) grids at 15 m in depth. After 7 d and 48 d, the net distance moved by the scallops from the release points did not vary between the two size groups but varied significantly between grids. The majority of scallop s (70-94%) moved downslope and the mean movement vectors were not orientate d in the direction of tidal currents, but rather towards increasing depth. The downslope movement of the scallops was possibly explained by more prolo nged swimming bouts when scallops swam downslope. The results suggest that the spatial size partitioning of Iceland scallops at this location is cause d by a gradual downslope movement as the scallops increase in size. This st udy provides the first experimental evidence supporting the controversial h ypothesis of recruitment into adult scallop populations involving swimming of juveniles from nursery areas.