[Show abstract][Hide abstract] ABSTRACT: In 1991, the progeny of female Atlantic salmon, Salmo salar L., were sampled at emergence from sites in 16 rivers in western and northern Scotland. The progeny of farmed females that had escaped from sea-cages were identified by detecting the presence of maternal canthaxanthin in the juveniles’ pigment load. Canthaxanthin was detected among fish sampled from 14 of the 16 rivers examined. Overall, 109 of the 2373 fry sampled carried canthaxanthin with an average frequency over all the rivers examined of 5·1%. This value will underestimate the real frequency of occurrence of the progeny of escaped farmed salmon: some escapees do not contain canthaxanthin and male fish do not contribute to the pigment load of their progeny.
No preview · Article · Apr 2008 · Aquaculture Research
[Show abstract][Hide abstract] ABSTRACT: Large variations in the number of female adult salmon spawning in the Girnock Burn each year (range 28–127) produced smaller variations each year (range 2900–5600) in the number of juvenile migrants. The relative constancy of the parr migrations was achieved by changes in their age composition. There may be no advantage in allowing ova deposition to exceed a level around 200 000 (3.4 m−2) in the Girnock Burn, which would give rise to an average of about 4000 juvenile migrants (0.07 m−2) per season. Large numbers of ova (up to 12.5 m−2) did not decrease the number of juvenile migrants.
No preview · Article · Jan 2006 · Journal of Fish Biology
[Show abstract][Hide abstract] ABSTRACT: Peaks in the emigratory activity of sexually immature, juvenile Atlantic salmon, Salmo salar, occur in autumn and early winter and in spring at the Girnock Burn in Aberdeenshire. Stream temperature is apparently without effect on the release of potentially emigrant fish from the stream. Migrants tend to leave the stream when stream discharge rate is elevated. Whereas downstream movements in autumn and the earlier part of the spring are made almost invariably when the stream's discharge rate is higher than the seasonal norm, later in spring they often occur when discharge rates are lower than the seasonal norm and when no apparent increase in absolute stream discharge rate has occurred. Emigration is depressed in the lunar quarter centred on the full moon. The nature of the relationship between the autumn and spring emigrations is discussed.
No preview · Article · Jan 2006 · Journal of Fish Biology
[Show abstract][Hide abstract] ABSTRACT: Spawning success of Atlantic salmon (Salmo salar L.) was investigated, under near-natural conditions, in the Girnock Burn, an 8-km long tributary of the River Dee in Scotland. Employing minisatellite-based DNA profiling, mating outcomes were resolved over three spawning seasons by assigning parentage to progeny samples removed from spawning nests ('redds'). While individual spawning patterns differed markedly, consistent trends were present over the 3 years studied. Multiple spawning was found to be prevalent. More than 50% of anadromous spawners of both sexes contributed to more than one redd. Up to six redds for a single female and seven for a single male were detected. Both sexes ranged extensively. Distance between redds involving the same parent varied from a few metres to > 5 km. Distances > 1 km were common. Both males and females ranged to a similar extent. Range limit was not correlated to fish size. Pairs were not monogamous, both males and females mating with different partners at different sites. Size assortative mating was apparent among 1991 spawners but was not detected for 1992 or 1995. Redd superimposition was found to be common (17-22% of redds over the 3 years), although it was not correlated to the number of anadromous spawners present. High levels of nonanadromous mature parr mating success (40-50% of total progeny sampled) were recorded, and these likely contribute greatly to the effective population size. The relevance of these findings at the individual and population level is discussed, with particular reference to management implications.
No preview · Article · Apr 2001 · Molecular Ecology
[Show abstract][Hide abstract] ABSTRACT: Stream water temperature data from the Girnock burn, a 30-km2 catchment in Scotland were examined for systematic variation across 30 years of record (1968-1997). The data suggest that there has been no change in mean annual temperature with time, but at a seasonal level there is some indication of an increase in mean daily maximum temperatures during the winter (December to February) and spring (March to May) seasons. For the spring season, there is also evidence that mean temperature has increased. There are no apparent or obvious changes in stream flow to account for this. The strong relationship between air and stream temperatures (r2 = 0.96) implies that changes in the stream are the result of changes in the climate. It is possible that this may occur as a result of the effect of increasing air temperatures which may have also reduced the influence of snow and snowmelt on the catchment during the winter and spring seasons.
No preview · Article · Feb 2001 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: At the Girnock Burn, a tributary of the River Dee in Scotland, a substantial part of the annual production of migrant juvenile salmon (Salmo salar L.) leaves the stream in autumn rather than in spring. Previously, the status of the autumn migrants was uncertain because Carlin tagging indicated that they returned to the stream with a lower frequency than smolts tagged in spring. The difference was not attributable to the smolting of autumn migrants outside of the Girnock Burn and their homing to these new locations since adults tagged as autumn parr were also under-represented in fisheries distant from the home stream. Instead, the differences were probably artifactual and attributable to a seasonal effect of the Carlin tagging procedure itself. When juveniles were tagged instead with wire microtags, recapture rates were similar for autumn and spring migrants. This is consistent with the hypothesis that the autumn migration is an aspect of smolting. Microtagging of all juvenile migrants (paired with adipose fin clipping) indicated that the homing of adult spawners to the Girnock Burn was substantially accurate. Over the period of study 45% of fish of the sea-age classes that were expected to bear adipose fin clips did so.
[Show abstract][Hide abstract] ABSTRACT: Levels of temporal and spatial genetic heterogeneity within and among Atlantic salmon (Salmo salar) populations in Scotland were assessed through starch-gel electrophoretic analysis of variation at 30 protein-coding loci. Over three year-classes the level of temporal variation within populations was generally nonsignificant, although significant heterogeneity among year-classes was found at some loci at some locations. Hierarchical analysis of gene diversity showed that 97.6% of the genetic diversity was found within single sites, with the remaining diversity distributed among sites. While there was no evidence of subpopulation differentiation among a number of samples of Atlantic salmon from the River Tweed system, significant genetic heterogeneity was observed among samples from different river systems within Scotland. Comparison of the levels of among-population heterogeneity in the Atlantic salmon with those found in the closely related brown trout (Salmo trutta) over a similar geographical area shows the Atlantic salmon to be relatively genetically homogeneous.
No preview · Article · Apr 1992 · Canadian Journal of Fisheries and Aquatic Sciences
[Show abstract][Hide abstract] ABSTRACT: As a result of an accident in February 1989, 184 000 growing salmon escaped from a seawater farm located in Loch Eriboll in northern Scotland. Later the same year, the behaviour of wild adults and fish of farmed origin was compared in the nearby River Polla. Wild salmon and farmed escapees were distinguished by their morphology, supported by tissue carotenoid analysis. Radio-tagged salmon of both groups and of both sexes were monitored before and during spawning. Bankside observations were made on tagged and untagged wild and farmed fish over the same period. Carotenoid pigments were determined in ova or alevins sampled later from spawning sites along the river's length. Wild and farmed fish of both sexes spawned throughout the river's length. Overall however, wild fish tended to spawn in the river's higher reaches while farmed escapees tended to spawn lower down. Farmed males were more widely distributed at spawning than farmed females. Farmed fish, particularly females, spawned later than wild females. The extent to which these findings may be generalised to other rivers is discussed in relation to the unique character of the River Polla and particularly the presence of a smolt unit on its lower reaches.