Westley et al.
Electronic Supplemental Material
Experimental animals
Crosses were made in situ (Middle Rocky and Rennies) or in the laboratory (Waterford)
by fertilizing ova of unique dams with milt of unique sires. Females were lightly anesthetized to
aid in stripping of eggs and fork length measured to the nearest mm (see values in manuscript
text). In contrast, we did not anesthesize the males to reduce handling time and as a consequence
do not have measured lengths. We felt confident not obtaining this information as no non-genetic
paternal effects have been demonstrated in phenotypic traits (e.g. body size or shape) of young
salmonids, in contrast to potentially strong maternal effects [1]. Timing and duration of the
breeding season differs among these populations (personal observations from 2007-2010). To
ensure availability of spawners from the Waterford River (observations suggest this population is
more migratory than the others), we captured individuals during their upstream fall migration
and held them in the laboratory until they matured. Families from Middle Rocky Brook and
Rennies River were spawned in the first week of November, whereas females were not mature in
the Waterford until mid-November and crosses were completed on November 24, 2008.
Experimental streams
Each release site was situated approximately 40 m downstream of complete obstructions
in the form of a perched culvert at Middle Rocky Brook (no brown trout detected above the
culvert, Westley & Fleming personal observations), a 3 m waterfall at Rennies (a barrier even to
full size adult trout; [2]) and an 18 m section of chutes and rapids at the Waterford River where
water velocities exceeded 1.6 ms-1, approximately twice the prolonged swimming capacity of
juvenile brown trout (0.6-0.8 m/s; [3]). Thus the upstream limit of the release locations were
marked by complete obstacles to fish movement and the downstream limits were taken to be
where Middle Rocky and Rennies entered large lakes (Windsor and Quidi Vidi Lakes,
respectively) and where the west branch of the Waterford entered the mainstem of the river.
Typically, brown trout rear in small streams prior to movement into lakes, which presumably
reflects predator avoidance. Similarly, small fish were virtually absent [4] in the large mainstem
Waterford River below our experimental site, which we infer is a reflection of poor habitat for
young of year trout downstream.
Quantifying downstream movement was logistically not possible in the relatively large
Rennies and Waterford locations. These locations are affected by urban development and as a
consequence suffer abrupt changes in water flow and experience frequent flood events during the
fall and early winter (periods of heavy rainfall). Moreover, vandalism to PIT tag antennas or
readers was deemed likely as public access trails paralleled our study sites. In contrast, we
trapped downstream migrants where Middle Rocky Brook drained into Windsor Lake during the
spring of 2010. We did this to ensure that individuals had not left the system alive prior to
electrofishing surveys. The trap was effective (as indicated by the frequent capture of
sticklebacks and trout fry), but only four tagged fish were recovered. Ultimately we feel justified
assuming that downstream movement is consistent with lower relative performance compared to
fish that did not move, but that movement of larger individuals (e.g. wild-born individuals from
Middle Rocky) may in part represent ontogenetic movements as well [5].
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Paez D.J., Morrissey M., Bernatchez L., Dodson J.J. 2010 The genetic basis of early-life
morphological traits and their relation to alternative male reproductive tactics in Atlantic
salmon. Journal of Evolutionary Biology 23(4), 757-768.
Robbins D. 2001 Sea run brown trout (Salmo trutta L.) movement and habitat use in the Quidi
Vidi watershed, St. John's, Newfoundland. St. John's, Memorial University of Newfoundland.
Bull C. 2010 Barriers to fish movements: assessing the impact of individual barriers on the free
passage of fish. Centre for River and Ecosystem Science, University of Stirling.
Westley P.A.H., Conway C.M., Fleming I.A. 2012 Phenotypic divergence of exotic fish populations
is shaped by spatial proximity and habitat differences across an invaded landscape. Evolutionary
Ecology Research 14, 147-167.
Einum S., Finstad A.G., Robertsen G., Nislow K.H., McKelvey S., Armstrong J.D. 2012 Natal
movement in juvenile Atlantic salmon: a body size-dependent strategy? Population Ecology 54,
285-294.
ESM Fig. 1. Posterior density of the effect of fork length (mm), mass (g) or condition factor
(residuals from logged length weight relationship) on survival of transplanted brown trout in
Newfoundland, Canada. Dashed lines represent the 95% credible interval.