The European whitefish Coregonus lavaretus complex represents one of the most diverse radiations within salmonids, with extreme morphological and genetic differentiation across its range. Such variation has led to the assignment of many populations to separate species. In Great Britain, the seven native populations of C. lavaretus (two in Scotland, four in England, one in Wales) were previously classified into three species, and recent taxonomic revision resurrected the previous nomenclature. Here we used a dataset of 15 microsatellites to: (1) investigate the genetic diversity of British populations, (2) assess the level of population structure and the relationships between British populations. Genetic diversity was highest in Welsh (H O = 0.50, A R = 5.29), intermediate in English (H O = 0.41–0.50, A R = 2.83–3.88), and lowest in Scottish populations (H O = 0.28–0.35, A R = 2.56–3.04). Population structure analyses indicated high genetic differentiation (global F ST = 0.388) between all populations but for the two Scottish populations (F ST = 0.063) and two English populations (F ST = 0.038). Principal component analysis and molecular ANOVA revealed separation between Scottish, English, and Welsh populations, with the Scottish populations being the most diverged. We argue that the data presented here are not sufficient to support a separation of the British European whitefish populations into three separate species, but support the delineation of different ESUs for these populations.

This study revealed between-lake genetic structuring between Coregonus lavaretus collected from the only two native populations of this species in Scotland, U.K. (Lochs Eck and Lomond) evidenced by the existence of private alleles (12 in Lomond and four in Eck) and significant genetic differentiation (FST = 0·056) across 10 microsatellite markers. Juvenile C. lavaretus originating from eggs collected from the two lakes and reared in a common-garden experiment showed clear phenotypic differences in trophic morphology (i.e. head and body shape) between these populations indicating that these characteristics were, at least partly, inherited. Microsatellite analysis of adults collected from different geographic regions within Loch Lomond revealed detectable and statistically significant but relatively weak genetic structuring (FST = 0·001-0·024) and evidence of private alleles related to the basin structure of the lake. Within-lake genetic divergence patterns suggest three possibilities for this observed pattern: (1) differential selection pressures causing divergence into separate gene pools, (2) a collapse of two formerly divergent gene pools and (3) a stable state maintained by balancing selection forces resulting from spatial variation in selection and lake heterogeneity. Small estimates of effective population sizes for the populations in both lakes suggest that the capacity of both populations to adapt to future environmental change may be limited.

A key for three putative species apparently found in three geographic areas, i.e. Coregonus clupeoides (in Scotland), Coregonus stigmaticus (in England), and Coregonus pennantii (in Wales) given in a recent review was tested quantitatively using 544 individuals from nine populations. The classification success of the key was very low (27%). It was concluded that there is currently no robust evidence for the recognition of the three putative species. Furthermore, the use of phenotypic characters alone to distinguish putative species in postglacial fish species such as those of the genus Coregonus that show homoplasy in many of these traits is questioned. In the absence of further evidence, it was concluded that a single highly variable species best describes the pattern of phenotypic variation in these U.K. populations. On this basis it is argued that taxonomic subdivision of U.K. European coregonids is inappropriate and that Coregonus lavaretus should prevail as the species name applicable to all populations.

Differences in stable-isotope values, morphology and ecology in whitefish Coregonus lavaretus were investigated between the three basins of Loch Lomond. The results are discussed with reference to a genetic investigation to elucidate any substructuring or spawning site fidelity. Foraging fidelity between basins of Loch Lomond was indicated by δ¹³C and δ¹⁵N values of C. lavaretus muscle tissue. There was, however, no evidence of the existence of sympatric morphs in the C. lavaretus population. A previous report of two C. lavaretus'species' in Loch Lomond probably reflects natural variation between individuals within a single mixed population.

The establishment of refuge populations has become a common management tool for threatened fish species in recent years, yet the effects of translocation are not fully understood in a conservation context. This paper examines the hypothesis that phenotypic changes have occurred during the formation of two refuge populations of the nationally rare powan (a freshwater fish species) which were established in Loch Sloy and Carron Valley Reservoir in Scotland. Significant differences in head morphology, size and growth between the founder and refuge populations and between the two refuge populations were demonstrated. These changes are probably due to a combination of founder effects, intense selection and phenotypic plasticity. These changes can undermine the rationale behind the establishment of refuge populations. The results call into question the usefulness of translocation as a conservation measure; however, there are times when this is the only viable management option available. The future of translocation and the validity of establishing refuge populations for powan conservation are discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Carbon stable‐isotope analysis showed that individual brown troutSalmo truttain Loch Lomond adopted strategies intermediate to that of freshwater residency or anadromy, suggesting either repeated movement between freshwater and marine environments, or estuarine residency. Carbon stable‐isotope (δ13C) values from Loch Lomond brown trout muscle tissue ranged from those indicative of assimilation of purely freshwater‐derived carbon to those reflecting significant utilization of marine‐derived carbon. A single isotope, two‐source mixing model indicated that, on average, marine C made a 33% contribution to the muscle tissue C of Loch Lomond brown trout. Nitrogen stable isotope, δ15N, but not δ13C was correlated with fork length suggesting that larger fish were feeding at a higher trophic level but that marine feeding was not indicated by larger body size. These results are discussed with reference to migration patterns in other species.

Loch Lomond is of national importance. Its range of habitats, diversity of species and rare populations of powan (Coregonus lavaretus) and freshwater feeding river lampreys (Lampetra fluviatilis) warrant high conservation status (Lyle & Maitland, 1994; Maitland et al, 2000). It is also of value for tourism, including sport fisheries for migratory trout (Salmo trutta), salmon (Salmo salar) and pike (Esox lucius), bringing money to the area.