Artificial deposition of eggs of Atlantic salmon (Salmo salarL.) in a regulated Norwegian river: Hatching, dispersal and growth of the fry

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Abstract
Fertilized eggs of Atlantic salmon (Salmo salar) were artificially deposited in the regulated River Ekso, western Norway. This was done by placing 320–2400 eggs in perforated platic baskets, together with small stones and gravel, buried in the river. To evaluate development of the eggs, some baskets were removed and examined with respect to fertilization and mortality at the eye‐roe stage. After swim‐up of alevins, all baskets were examined for the number of dead eggs. The hatching of eggs was between 55 and 98% in the baskets. There was no correlation between the egg number in the basket and survival. The alevins were restricted to their hatching area for the first month; after the first season they migrated 50 m upstream and 175 m downstream of their birthplace. One year later they occupied the whole area (375 m) between the two weir basins. Mortality was 80% in the first season and 87% in the second (regarded as normal and high, respectively). High mortality was probably due to acid episodes, independent of regulation. Growth was fast and salmon became smolt at age 2+, explained by favourable temperature and low fish density. Competition between salmon and native brown trout (Salmo trutta) seemed to be low as they occupied different habitats.