Agonistic behavior, social dominance, and predator evasion of Oncorhynchus mykiss from lake and stream parents: an evaluation of lacustrine refuges as a conservation strategy for threatened or endangered salmonids

Abstract

The possibility of lakes providing temporary natural refugia for endangered salmonid populations, creating an alternative to hatchery propagation, is the context for this research. To investigate this possibility resident trout (Oncorhynchus mykiss) derived from a population that had been sequestered in a lake for seventy years were compared to fish from their founding anadromous steelhead trout population as well as to hybrid crosses of the two populations. Comparisons were made in the areas of aggression, dominance and predator evasion. In aggression trials the lake-derived population chased more than stream-derived O. mykiss at two life stages, age-0 and age-1. Lake-derived fry and the lake x stream hybrid fry also chased more than the stream x lake hybrid fry. Fin conditions (dorsal and pectoral fin lengths, an index of aggression) did not differ significantly. In dominance acquisition the stream x lake hybrid were least frequently dominant of all the crosstypes, and stream-derived parr were less dominant than lake-derived parr. Avoidance of a Dolly Varden predator by fry showed that the stream x lake hybrids achieved the highest survival rates. Seventy years of sequestration in a lake may be adequate time for divergence in aggressive behavior, social dominance and predator evasion between lake-resident and stream, O. mykiss populations.