Alex A. Lyle

Ecology of Allis Shad Alosa alosa and Twaite Shad Alosa fallax in the Solway Firth, Scotland

The basis of this study were 132 adult Allis Shad and 150 Twaite Shad collected as bycatches from salmon stake nets in Scotland on the north side of the Solway Firth. Most (60%) of the Allis Shad were immature fish 2–3 years of age (mean length 305 mm). Mature males were younger (3–5 years) and smaller (mean length 421 mm) than females (4–6 years and 481 mm mean length). The largest Allis Shad was a female of 515 mm and 2183 g. In contrast, almost all the Twaite Shad were mature, the males younger (3–5 years) and smaller (mean length 341 mm) than the females (4–6 years and 364 mm mean length). The largest Twaite Shad was a female of 400 mm and 1213 g. The food of Allis Shad consisted mainly of small zooplankton with some fish and larger Crustacea. Fine vegetable fragments were common in the stomachs and attributed to filter feeding. The food of Twaite Shad was mainly small fish with some Crustacea. Mature Allis Shad of both sexes with large gonads (maximum female GSI: 20.63) were found throughout the spring and summer but no definite evidence of local spawning was obtained. Mature Twaite Shad of both sexes with large gonads (maximum female GSI: 23.32) were found until early July, thereafter most of the fish were spent. It appears that Twaite Shad spawn locally in June. Some hybrids between the two species were found.

Conservation of the vendace (Coregonus albula), the U.K.'s rarest freshwater fish

Although also formerly present in two lochs in South West Scotland, populations of vendace (Coregonus albula) were until recently believed to persist in only two U.K. lakes, i.e., Bassenthwaite Lake and Derwent Water in North West England. However, although Derwent Water has retained its natural mesotrophic conditions and the status of its vendace population is acceptable, monitoring at Bassenthwaite Lake has failed to record any specimens since 2000 and the species has recently been declared locally extinct. Bassenthwaite Lake has experienced increasing problems from eutrophication, sedimentation and the introduction of fi sh species including roach (Rutilus rutilus) and ruffe (Gymnocephalus cernuus), both of which have more recently also been introduced to Derwent Water and give concern over possible food competition and egg predation. In addition to monitoring, considerable efforts have been made in recent years to conserve vendace through the protection and improvement of their habitats and the establishment of refuge populations. The latter has resulted in the establishment of a population originating from Bassenthwaite Lake in Loch Skeen of South West Scotland, with further attempts still in progress at two other sites. Public awareness of the conservation of this species, which is the U.K.s rarest freshwater fish, has also been actively promoted.

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.

The spawning migration and conservation of smelt Osmerus eperlanus in the River Cree, southwest Scotland

The anadromous smelt Osmerus eperlanus population associated with the River Cree on the Solway Coast, southwest Scotland, is the only one remaining from several which previously occurred in that area. Their spawning migration was studied as a basis for conservation and management proposals. The timing and location of the onset of spawning in February/March was determined by regular inspection of the river bed for smelt eggs. The thermal regime in the lower river during preceding weeks is considered the primary factor in initiating spawning, but prevailing temperature, tide and flow conditions determine exactly where and when. Several local factors must be addressed for future conservation and management, e.g. commercial netting, pollution and the present physico-chemical character of the river. The reintroduction of smelt to other rivers on the Solway Coast should now be seriously considered.

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.