Mytilus species under rope culture in Scotland: implications for management P. J. Dias Æ M. Bland Æ A. M. Shanks Æ A. Beaumont Æ S. B. Piertney Æ I. M. Davies Æ M. Snow Received: 24 March 2008 / Accepted: 26 August 2008 / Published online: 19 September 2008 Ó Springer Science+Business Media B.V. 2008 Abstract Mussel (Mytilus spp.) production is one of the most economically important aspects of global aquaculture and, in Scotland, production has increased from 262 t in 1986 to 4,219 t in 2006. Until recently, mussel production in Scotland was considered to be based exclusively on the blue mussel Mytilus edulis, the native species. In Europe, pro- duction is known to consist of M. edulis and M. galloprovincialis, while a third less profitable species M. trossulus occurs in the Baltic Sea, where it is unexploited. In Scotland, the sympatric occurrence of M. edulis, M. trossulus, M. galloprovincialis and their hybrids in cultivation in Loch Etive has recently been reported, with significant losses in pro- duction attributed to the presence of M. trossulus. Samples of mussels were taken at three depths from 10 rope-farm sites in Loch Etive. The distribution of the Mytilus species and their hybrids in Loch Etive was investigated using the Me 15/16 nuclear DNA locus for species and hybrid identification. All three species and their hybrids were detected and the data were in agreement with the Hardy–Weinberg model suggesting panmixia. Frequencies of M. galloprovincialis and its hybrids were very low. Overall, M. trossulus (37%) was found to be more common than M. edulis (30%) and 23% of the sampled mussels were M. trossulus 9 M. edulis hybrids. Species distribution did not correlate with year of set- tlement nor with salinities taken at the time of sampling. There were significant differences in species distribution due to site location and depth, with M. edulis being more frequent at 8 m depth and M. trossulus more common at shallower depths. These differences might be exploitable in management strategies for continuing production, for example to decrease the prevalence of M. trossulus at shellfish farms in favour of the more desirable M. edulis. P. J. Dias (&) Á M. Bland Á A. M. Shanks Á I. M. Davies Á M. Snow Fisheries Research Services Marine Laboratory, 375 Victoria Road, Aberdeen AB11 9DB, Scotland e-mail: j.dias@marlab.ac.uk P. J. Dias Á S. B. Piertney Institute of Biological and Environmental Sciences, University of Aberdeen, AB24 2TZ Aberdeen, Scotland A. Beaumont School of Ocean Sciences, College of Natural Sciences, Bangor University, Menai Bridge, Gwynedd LL59 5AB, UK 123 Aquacult Int (2009) 17:437–448 DOI 10.1007/s10499-008-9214-6