| Summary: | Understanding the connectivity among populations of marine organisms and the spatial scale at which they interact is essential for the identification of fishery stocks and therefore the successful management of commercially exploited species. A range of approaches are available for the study of connectivity and to define the spatial extent of stocks and population structure, these include; tagging studies, elemental fingerprinting, the use of biophysical coupled oceanographic models and the use of genetic tools to determine population structure. The current study used a combination of approaches to understand the connectivity and spatial scales of interaction among populations of Pecten maximus. Twelve new microsatellite markers were developed and together with four previously published markers these were used to genotype fourteen populations of P. maximus across the NE Atlantic. Genetic differentiation analyses identified one large homogenised region around Ireland and the British Isles but with a few isolated populations (Falmouth Bay, Mulroy Bay and to a lesser extent Peel in the Isle of Man). Low but significant structuring was found between the Galicia and the IrishlBritish region. Norway was significantly differentiated from all other populations with similar magnitudes of structure as that found between the Mediterranean populations of Pecten jacobaeus and the populations of P. maximus. A study of spatial variation In reproductive ecology identified small-scale spatial variation « 5km) in the onset of gonad conditioning and the autumn spawning event in the waters off the Isle of Man. The short-term variation in gonad weight among sampling sites appeared to be driven by the rate of change of temperature in the month prior to sampling, whilst long term variation in gonad weight among sites was affected by the average annual chlorophyll a concentrations and scallop density. Whilst there is strong genetic connectivity at a regional spatial scale (Ireland and the British Isles), the presence of some isolated populations, low effective populations sizes and poor synchronisation in reproduction, suggested that it would be unwise to assume high levels of connectivity in all areas of a region for the purpose of fisheries management. Populations with low effective population size or lower levels of immigration could be at risk of over-exploitation with limited potential for recruitment from neighbouring populations.
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