Abstract

Movement allows organisms to respond to heterogeneity in physical and biological conditions both at the individual and population level. Studying the movement of young stream fishes has proven to be problematic because of the difficulty of tagging small fishes using traditional techniques. In this study, recently developed microsatellite markers were used as a method of tagging individual young-of-the-year (YOY) Atlantic salmon ( Salmo salar L.). First, the association between the local-scale distribution patterns of 81 territorial YOY salmon and their degree of relatedness in a natural stream was tested. No significant association between relatedness and distance at the local scale was found. Focal fish were not more related to their nearest-neighbour (mean r x,y = -0.004) than to randomly selected fish (mean r x,y = 0.005), nor were they more related to their four nearest-neighbours (mean r x,y = -0.01) than to non-neighbours (mean r x,y = -0.007). Second, 97 anadromous adults moving into the stream to spawn, four redd locations, as well as 313 of their offspring were sampled in a 1.6 km reach of Catamaran Brook. The initial dispersal of offspring from the four redd locations and resulting long-range dispersion patterns of families were mapped. The average dispersal distance of 69 YOY salmon from the sampled redd locations ranged from 50--955m downstream, and 9--154m upstream. Five maternal and nine paternal half-sibling families were recaptured over an average dispersion distance (linear distance between the most upstream and most downstream sites of capture) of 1340m and 1018m, respectively. Four full-sibling families were identified with an average dispersion distance of 945m. The redd location (for sampled redds) and the most upstream location of a family (linear distance of the most upstream location of capture to the mouth of the brook) were combined and analysed as one variable. Dispersion distance was significantly, and positively correlated with redd or upstream location, with most families dispersing to the mouth of the brook. Third, alternative mating strategies take place in Atlantic salmon males, whereby both anadromous adults and precocious parr compete for fertilization opportunities with anadromous females. The present study suggests that precocious male parr may have fertilized up to 53% of the 313 sampled YOY salmon. This intensive field sampling allowed for the detection of the initial dispersal from redds and the large-scale dispersion of YOY salmon, which would not have been possible using alternative tagging methods. The results of the present study contributes to the understanding of dispersal and dispersion patterns of YOY salmon in freshwater habitats, and are applicable to the conservation and management of salmonid populations.