Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss) | Comparing dominance relationships and movement of native marble trout (Salmo marmoratus) and introduced rainbow trout (Oncorhynchus mykiss)

Behaviour observations of the endangered native marble trout (Salmo marmoratus,Cuvier, 1829) and introduced rainbow trout (Oncorhynchus mykiss, Walbaum, 1792)in the laboratory and in a tributary to the Idrijca River in Slovenia were combined tostudy the movements and dominance relationships between individuals of the twospecies in an open field test. Under laboratory conditions, no difference between thespecies was detected for neither time spent actively or distance moved. In speciespaired tests, rainbow trout initiated more aggressive behaviours towards marble troutthanvice versa, and rainbow trout were clearly the dominant individuals. After simul-taneous release in the river, marble trout immediately left the release area and spenttwice as long time as rainbow trout until they settled in an area of the river; there-fore, the release site was immediately occupied exclusively by rainbow trout. Thus,the dominant and aggressive behaviour of rainbow trout seen in the laboratorybefore release might have influenced marble trout's subsequent behaviour in theriver, by marble trout leaving the areas occupied by rainbow trout and moving tolocations further away from the release site. In the field, the marble trout occupiedsites individually, whereas rainbow aggregated at a few locations. Rainbow troutshowed higher movement activity in the morning compared to marble trout. Therewas a positive correlation between swimming speed in the laboratory and movementin the field for marble trout but not for rainbow trout. In conclusion, the results in thisstudy support the need to end stocking of rainbow trout in rivers with native marbletrout. To better understand the interaction between the species, and to develop effi-cient management plans to protect the native marble trout, reference behavioursshould first be understood, and future research in sites where the two species do not co-exist is needed. This is especially important for marble trout for which behaviouralresearch and data are lacking.

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