Does juvenile experience affect migration and spawning of adult Atlantic salmon?

Abstract

This paper documents differences in seasonal time of river ascent and descent, and instream behavior of adult wild and sea-ranched Atlantic salmon (Salmo salar) of the Norwegian River Imsa stock during the period 1981-1989. Wild fish use River Imsa as a nursery, and at an age of 2 years most of them migrate to the sea as smolts. The sea ranched fish are hatchery reared offspring of the River Imsa stock and are released as smolts at the mouth of the river. They are thus deprived of juvenile river life and a downstream smolt migration. Wild and sea ranched salmon feed for 1 or more years in the Norwegian Sea before homing as spawners. Both groups returned simultaneously to coastal Norway, but sea ranched fish ascended the river later and descended sooner after spawning than wild fish. All wild females and almost all wild males (96.2%) spawned in the river, whereas 13.5% and 36.7%, respectively, of the mature sea-ranched females and males left the river unspawned. The annual number, but not the proportion, of unspawned fish increased with increasing density of adult salmon in the river. Unspawned females were medium sized and small (45-70 cm); unspawned males were medium sized and large (50-90 cm). Independent of the density of spawners in the river, sea ranched fish moved up-and downstream the river more often than wild fish. More than 20% of the sea-ranched salmon and less than 1% of the wild salmon passed a trap 100 m above the river outlet more than once in each direction during the same spawning reason. Moreover, sea-ranched salmon were about twice as often seriously injured during spawning as wild fish. Lack of juvenile experience from the river may be the main reason for the behavioral differences between sea-ranched and wild fish.

Factors affecting the within-river spawning migration of Atlantic salmon, with emphasis on human impacts

“…When released in the river mouth or further upstream, hatchery-reared salmon returning to the river as adults tend to have a more erratic movement pattern in the river than wild salmon (Power and McCleave 1980;Jonsson et al 1990;1991a;Potter and Russell 1994;Jokikokko 2002;Croze 2005;Jepsen et al 2005a). As a consequence of this erratic up-and downstream within-river migration, hatchery-reared fish spent a longer time than wild fish in the river before settling down in the spawning area (Jokikokko 2002).…”

“…Most Atlantic salmon in Norway and Canada enter the rivers from May to October (Klemetsen et al 2003), with a general tendency for large multi-sea-winter salmon to enter the rivers earlier in the season than smaller one-seawinter fish (Power 1981;Jonsson et al 1990). In Scotland and other parts of the UK, salmon can enter the rivers in all months of the year, with some individuals entering more than a year prior to spawning (Klemetsen et al 2003).…”

Preference for nearshore and estuarine habitats in anadromous Arctic char (Salvelinus alpinus) from the Canadian high Arctic (Victoria Island, Nunavut) revealed by acoustic telemetry

“…Females preceding males during the upstream migration is not necessarily a widespread phenomenon in other salmonids. For example, there is no difference between sexes in run timing in Atlantic salmon (Fleming 1996; but see Jonsson et al 1990), and males tend to return before females in Alaskan chum salmon (Oncorhynchus keta; Molyneaux and Dubois 1998).…”

Genetic Differentiation among Danish Brown Trout (Salmo trutta) Populations

“…Presumably, the fish are not imprinted to any of the tributaries and, as a consequence, aberrant or ineffective spawning and migratory behavior is expected (HANSEN et al 1987;JONSSON et al 1990). Examples of unsuccessful transplantations of stocks of Salmonid species due to the inadaptive nature of transplanted stocks are given by, La., ALTUKHOV and SALMENKHOVA (1987) and MORAN et al (1991) while studies by TAGGART and FERGUSON (1986) and HAUSER et al (1991) suggest at least some introgression of stocked fish into native gene pools.…”