The influence of aquaculture unit proximity on the pattern of Lepeophtheirus salmonis infection of anadromous Salmo trutta populations on the isle of Skye, Scotland.

A total of 230 anadromous Salmo trutta (brown trout) were sampled in five sheltered coastal fjords (or sea lochs) on the Isle of Skye, Scotland, U.K., in 2016 at varying distances from active Atlantic salmon Salmo salar farms. Statistical models were developed to investigate potential correlations between salmon lice Lepeophtheirus salmonis burdens on S. trutta hosts and their proximity to S. salar farm cages. Significant correlations were found between lice burdens and fish fork length and proximity to the nearest S. salar farm. The probability of the presence of L. salmonis on fish hosts increased with fish host size and with distance from the nearest S. salar farm, but total lice burdens were highest in fish sampled near S. salar farms and decreased with distance. The proportion of different life-cycle stages of L. salmonis were also dependent on S. salar farm proximity, with higher juvenile lice numbers recorded at sites near S. salar farm cages. These results highlight the complexity of the relationship between S. trutta and L. salmonis infections on wild fish and emphasize the requirement of further research to quantify these effects to better inform conservation and management strategies, particularly in areas of active S. salar farm facilities.

Comparison of damage to live v. euthanized Atlantic salmon Salmo salar smolts from passage through an Archimedean screw turbine.

This study assessed the usefulness of passing euthanized Atlantic salmon Salmo salar smolts through an Archimedean screw turbine to test for external damage, as compared with live, actively swimming smolts. Scale loss was the only observed effect. Severe scale loss was 5·9 times more prevalent in euthanized turbine-passed fish (45%) than the live fish (7·6%). Additionally, distinctive patterns of scale loss, consistent with grinding between the turbine helices and housing trough, were observed in 35% of euthanized turbine-passed smolts. This distinctive pattern of scale loss was not seen in live turbine-passed smolts, nor in control groups (live and euthanized smolts released downstream of the turbine), which suggests that the altered behaviour of dead fish in turbine flows generates biased injury outcomes.

Inter and intra-population phenotypic and genotypic structuring in the European whitefish Coregonus lavaretus, a rare freshwater fish in Scotland.

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.

Morphological abnormalities in a population of Lampetra planeri, with a short review of petromyzontid teratologies.

Reported here are several deviations (n = 15; 1·96%) from typical morphology in a large sample (n = 767) of European brook lamprey Lampetra planeri from a single population in the Loch Lomond catchment; this includes one specimen bearing a true anal fin. A brief review of petromyzontid teratology is provided.

Evidence of a recent decline in river lamprey Lampetra fluviatilis parasitism of a nationally rare whitefish Coregonus lavaretus: is there a diamond in the ruffe Gymnocephalus cernuus?

Lamprey-induced scarring of the nationally rare Coregonus lavaretus, a known host of a freshwater-resident population of European river lamprey Lampetra fluviatilis, was found to have declined precipitously since the establishment of several non-native fishes in Loch Lomond. Evidence presented in this study points to the possibility that L. fluviatilis in this lake may have altered its trophic ecology in response to the negative impact that non-native species, in particular ruffe Gymnocephalus cernuus, have had on their favoured host.

Sneak male mating tactics between lampreys (Petromyzontiformes) exhibiting alternative life-history strategies.

Interspecific sneak male mating tactics between paired lamprey species are described for the first time. Although alternative mating tactics among petromyzontids have been described previously, including intraspecific sneak males, the presence of sneak male tactics between parasitic and non-parasitic forms suggests that high levels of gene flow between putative lamprey species could remain high, despite large body size discrepancies.

Are phenotypic traits useful for differentiating among a priori Coregonus taxa?

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.

Has habitat heterogeneity promoted phenotypic and ecological sub-structuring among a Coregonus lavaretus population in a large Scottish lake?

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.