Abstract:
When wild juvenile (parr) Atlantic salmon (Salmo salar L.) caught by electrofishing, and an equal number of hatchery-reared parr, matched for size the wild ones, were released at three sites in unfamiliar streams containing resident parr, more hatchery-reared than wild parr could be observed by skin-diving in the areas 1 and 2 weeks later. Observed mortalities of wild parr were not sufficiently higher than those of hatchery parr to explain this result. Nor could a higher proportion of wild parr be found hiding compared with hatchery parr when one release site was electrofished a week after the release. Wild parr were found in greater numbers at points farther from one of the release sites than were hatchery-reared parr, and also more wild fish passed through a salmon counting fence approximately 100 m from a fourth release site than did hatchery-reared parr. This greater dispersal of wild parr from the release site compared with hatchery parr has important consequences to estimates of comparative survival between the two stocks.