Does kin-biased territorial behavior increase kin-biased foraging in juvenile salmonids?

We examined the effects of kin-biased territorial defense behavior on the distribution of foraging attempts and percent weight changes (fitness benefits) in juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in an artificial stream channel. The individual percent weight changes and frequency of aggressive interactions and foraging attempts were quantified in kin (full sibling) and non-kin groups of salmon and trout. We observed kin groups of both species to obtain significantly greater mean and less variable percent weight gains that non-kin groups. In addition, faster-growing (dominant) individuals of both species within kin groups exhibited significantly fewer aggressive interactions than did faster-growing nonkin individuals, while we observed no difference between kin and non-kin slower-growing (subordinate) individuals. Slower-growing kin individuals of both species obtained significantly more foraging opportunities than slower-growing non-kin individuals while there was no difference between faster-growing kin and non-kin individuals. These data suggest that reduced aggression by faster-growing individuals towards slower-growing kin enables slower-growing kin to obtain more foraging opportunities, resulting in higher and less variable percent weight changes. These data also suggest that as a result of kin-biased territorial defense and foraging behavior, juvenile Atlantic salmon and rainbow trout may be able to maximize inclusive fitness potential by defending territories near related conspecifics.