Homing experiments with parr, smolt and residents of anadromous Arctic char Salvelinus alpinus and brown trout Salmo trutta: transplantation between neighbouring river systems

Abstract

Nordeng H, Bratland P. Homing experiments with parr, smolt and residents of anadromous Arctic char Salvelinus alpinus and brown trout Salmo trutta: transplantation between neighbouring river systems.Abstract -Olfaction is decisive for the homeward migration of anadromous salmonids. Two different olfactory hypotheses for explaining how this mechanism works have been proposed (the imprinting and the pheromone hypothesis), and they differ with regard to the origin of the odours that define home. The pheromone hypothesis assumes that fish respond to strain-specific pheromones and that no imprinting is necessary. The imprinting hypothesis assumes that juvenile fish become imprinted to odours of abiotic or biotic origin in natural rivers; the imprinting may be a single event or may occur sequentially during downstream migration as smolts. The two hypotheses were challenged by reciprocal transplantation of parr, residents and smolt of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) between the Salangen and the Løksebotten rivers. Both rivers empty into the Salangen Fjord, Norway, about 10 km apart. Salangen Arctic char released in the Løksebotten River, and Løksebotten brown trout released in the Salangen River (parr, resident and smolt) initiated spontaneous homeward migration without preceding contact with home stream water. This indicates that site imprinting (single or sequential) could not have been involved. In the sea, the released fish apparently integrated into the migratory system of relatives from their river of origin. Recapture rates did not differ for fish allowed to receive single or sequential imprinting.

Glass‐Eel‐Stage American Eels Respond to Conspecific Odor as a Function of Concentration

“…The glass eel washings also elicited consistent directional movements toward the odor sources based on qualitative observations. These results are consistent with how the conspecific cueing hypothesis is presented in other species, whereby Sea Lampreys, salmonids, and pomacentrids preferred movement toward or settlement in areas containing higher concentrations of conspecific odor (Wagner et al 2009;Ben-Tzvi et al 2010;Nordeng and Bratland 2010;Lecchini and Nakamura 2013). This further substantiates conspecific cueing as a possible mechanism for migration coordination in American Eels.…”

“…Spawning migrations of Sea Lampreys Petromyzon marinus have conformed to predictions consistent with the conspecific cueing hypothesis: adult Sea Lampreys migrating upstream consistently prefer locations with higher concentrations of cues from resident larvae (Wagner et al 2009). Some salmonids have been shown to use conspecific chemical cues during their return migrations to natal rivers (Nordeng and Bratland 2010), and the larvae of multiple pomacentrid species also use such cues when moving into settlement areas on coral reefs (Ben-Tzvi et al 2010;Lecchini and Nakamura 2013). Given that American Eels migrate thousands of kilometers to reach inland waters and that conspecific cueing is present among evolutionarily distant species, American Eels may also use conspecific cues to coordinate their movements.…”

Olfactory imprinting is triggered by MHC peptide ligands

“…In other species, similar olfactory imprinting mechanisms could explain the observed preference for genetically related versus foreign populations1. Chinook salmon ( Oncorhynchus tshawytscha ) and steelhead trout ( Oncorhynchus mykiss ), for example, establish structured groups with greater-than-average genetic relatedness6.…”

“…In an ecological context, olfactory imprinting is known to guide salmon to their natal rivers when they return from the sea to mate and spawn5. The underlying chemical cues may be pheromones of their own population6 and/or environmental cues encountered during the downstream migration towards the ocean78. Olfactory imprinting may also play a major role in the orientation of more marine species which disperse at larval stages but return and settle at natal habitats1.…”

Linking genetic assignment tests with telemetry enhances understanding of spawning migration and homing in sea trout Salmo trutta L.

“…The ability to home is based on juvenile imprinting of the water chemistry in their natal area (Stabell, 1984;Jonsson et al, 1990) or pheromones of their native strain (Nordeng & Bratland, 2006) which they later detect at return migration. This phenomenon also makes it possible for hatchery-reared individuals released as juveniles to return to the release site as adults, even though their homing abilities are less prominent than for wild fish (Jokikokko, 2002;Quinn, 2005).…”