Tissue samples from a total of 6 17 Atlantic salmon from seven locations in north-east Ireland were clectrophoretically examined for genetic variation at 28 enzyme loci. Patterns of allelic variation at eight polymorphic loci indicated the existence of genetic differentiation within, as well as among. river systems. This suggests the presence of localized genetically differentiated populations of salmon in N. Ireland. Temporal variation in allelic frequencies was tested among three year classes of wild R. Bush salmon and found to be insignificant compared to the spatial variation. Examination of equivalent year classes of R. Bush hatchery-reared salmon displayed significant temporal variation at five loci, and significant departures from Hardy-Weinberg equilibrium at two loci. Heterozygosity was not reduced in the Bush hatchery population (mean 4.3%) compared to the wild populations sampled (range, 2.9-5.4%; mean, 4.2%). These results are discussed in relation to management of wild populations and maintenance of hatchery stocks .

Five external marks (Panjet, visible implant tag, hot brand, anal finclip and fluorescent pigment) were compared for retention and effect on marine survival in Atlantic salmon, Salmo salar L., ranching experiments aimed at complementing coded wire tagging. Only fluorescent pigment marks and Panjet marks were found to be effective, with retention rates of 76.9% and 90.0% respectively, after one year at sea. The Panjet was the only mark to significantly reduce marine survival (P < 0.001) compared with controls.

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A total of 118 wild Atlantic salmon, Salmo salar L., females were stripped at the River Bush Salmon Station. The total number of eggs (fecundity) and egg diameters were compared for three age groups of adults. Adult length explained the majority of the variation in fecundity whilst freshwater age explained the majority of the variation in egg diameter. Parallel regression analysis for the total number of eggs on fish length relation for 3 years (2000)(2001)(2002) showed significant temporal variation among years. Larger eggs from 2.1+ adults produced longer and heavier swim-up fry than smaller eggs from 1.1+ adults. There was also the suggestion that the survival of eggs from 1.1+ adults was lower than eggs from 2.1+ adults to the swim-up stage. K E Y W O R D S :Atlantic salmon, egg diameter, fecundity, Salmo salar.

The upstream migratory behaviour of wild and ranched Atlantic salmon Salmo salar in a small Irish coastal spate river was investigated using acoustic telemetry. Prespawning migratory behaviour was investigated including movement patterns at a large natural waterfall in the lower reaches of the river. A strong diurnal pattern was observed for upstream migrants at the waterfall indicative of the need for daylight to ascend this complex natural obstacle to migration. Successful passage of the waterfall was also associated with distinct environmental conditions and no difference in migratory ability was detected between wild and ranched origin S. salar. Wild S. salar tended to exhibit a non-erratic, stepwise upstream migration pattern after ascending the waterfall while ranched S. salar had an increased probability of displaying more erratic migratory behaviour. Wild S. salar penetrated further into the river catchment than ranched S. salar, although male ranched S. salar exhibited the greatest cumulative distance moved prior to the spawning period. The management implications of escaped or released ranched S. salar and movement at natural obstacles are discussed.