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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.

1992. Genetic protein variation in natural populations of Atlantic salmon (Salmo salar) in Scotland: temporal and spatial variation. Can. J. Fish. Aquat. Sci. 49: 1863-1 872.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.Nous avons mesure I'het6rogkn6it6 gknetique temporelle et spatiale entre populations et a I'interieur de populations de saumons de I'Atlantique (Salmo salar) d'Ecosse grace a une analyse par 6lectrophorese sur gel d'amidon de la variation a 30 loci qui codent les proteines. Sur trois classes annuelles, la variation temporelle a I'interieur des populations n'etait generalement pas significative, mais on a trouv6 une hi.ti.rogi.neit6 significative entre les classes annuelles pour certains loci sur des sites donnes. L'analyse hierarchique de la diversite genktique a montr6 que 97,6 % de cette diversit6 se retrouvait sur des sites pris individuellement, le reste etant distribuk entre les sites. S'il n'y avait aucune indication de differenciation entre des sous-populations parmi un certain nombre d'6chantillons de saumons de I'Atlantique du reseau de la Tweed, on a observe un? hGtkrogenkit6 genetique significative entre des echantillons provenant de differents bassins hydrographiques d'Ecosse. La comparaison de I'het6rogeneit6 parmi les populations de saumons de I'Atlantique avec les resultats obtenus chez I'espece proche que constitue la truite brune (Salmo trutta) dans une zone gkographique similaire montre que le saumon de I'Atlantique presente une relative hetkrogkneite gknktique.T he susceptibility of a fish species to loss of genetic diversity through exploitation or abuse by man depends on the manner in which genetic variation is distributed within and among populations of the species concerned (Ryman 1983). Depletion of genetic variability can have effects at many levels: it may affect the fitness of individuals, reduce the potential of populations for adaptation to changing environments, and ultimately alter the pace of longer term evolutionary processes such 'Author to whom co...

Sea trout (Salmo trutta L.) stocks on the West Coast of Scotland and Ireland have decreased due to reduced survival during the marine phase of their life cycle. Lice‐infested sea trout returning to rivers could indicate that parasite burdens are contributing to the decline. Salmon farms represent a potential source of substantial quantities of sea lice, leading to a conjectured link between parasites on salmon fish farms and infestations on wild sea trout. To investigate the potential infective pressure on sea trout in Loch Shieldaig, offshore and sub‐littoral plankton samples were collected and analysed for sea lice nauplius and copepodid stages. During the plankton survey, numbers of sea lice on a fish farm in the loch reached a maximum in November 2001. Soon after, numbers of sea lice larvae peaked in open‐water samples and then in sub‐littoral samples. Nauplii were found adjacent to the farm and occurred less elsewhere. This study reports a concentration of sea lice larvae at the head of Loch Shieldaig and indicates a possible relationship between sea lice numbers on the fish farm and lice larvae densities in the open‐water of the loch and in the sub‐littoral zone.