Population structuring in Norway lobster Nephrops norvegicus (L.) : a molecular genetic approach
The Norway lobster Nephrops norvegicus is a commercial crustacean with a wide distribution across the world. It is heavily fished in UK waters and is one the most valuable landed species (Bailey, Chapman et al. 1993). In 1994 Scottish landings represented 60% of Nephrops landed in the UK and 30% of the worlds landings. In 1995, landings by Scottish vessels were 22,500 tonnes with an approximate value of £48 million (FAO 1996). Approaches to management of Nephrops populations focus on the adult stage of the Nephrops assuming that as the populations are separated due to the fragmented substrate and that Nephrops do not migrate between areas. This is true for the adult animal but not for the planktonic larval phases. This feature of population dispersal has profound demographic consequences, where some populations are maintained by dispersal of juveniles or larval immigrants (Pulliam 1988). Markers that indicate the level of migration between areas would provide important information to management of a marine fishery. Genetic markers represent an approach that, not only gives an indicator of the migration of larvae from parental population, but also measures the successful reproduction of immigrants. During this study two independent but complementary molecular approaches to investigate genetic structuring in Nephrops populations. Markers for this species have not been previously isolated. A polymorphic region of the COI mitochondrial gene was sequenced and six highly variable nuclear microsatellite makers developed. In order to analyse the microsatellite data, which was complicated by large amounts of PCR stutter products, a novel statistical approach was developed. This statistical model extracted information from dinucleotide data that could not be obtained in any other way. This molecular study showed that there are high levels of gene flow between the Scottish Nephrops populations and some low level structuring between these populations and the Irish Sea and Portugal.