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Fishery Bulletin 107(4) 
fry during their early marine life history (Kaeriyama 
and Ueda, 1998; Wertheimer and Thrower, 2007). 
To date, it is unclear how changes in fry abundance 
due to hatchery releases may affect predation risk and 
survival probability for wild chum salmon during their 
early life history. Changes in juvenile salmon abun- 
dance caused by hatchery releases can significantly 
change the dynamics of predator-prey interactions for 
wild fish (Einum and Fleming, 2001; Brannon et al., 
2004). For example, the presence of hatchery fry could 
diminish predation on wild fry in the early marine 
phase by buffering wild fry from predators (Willette et 
al., 2001; Briscoe et al., 2005), could increase preda- 
tion on wild fish by attracting predators and increasing 
predator-prey interactions (Holling, 1959; Beamish et 
al., 1992; Ruggerone and Rogers, 1984), or could lead 
to direct competition for food or space (Levings et al., 
1986; Olla et al., 1998; Ruggerone and Nielsen, 2004). 
Size-selective mortality is not necessarily tied to hatch- 
ery practices or density-dependent interactions, but 
size-selective mortality would inflate our estimates of 
growth and condition. If such a bias did occur, it was 
probably not large enough to eliminate the apparent 
growth rates that we observed. Diminished growth and 
survival of wild fry may occur if the number of preda- 
tors in relation to the number of salmon prey increases 
in response to increased hatchery releases (Ruggerone 
and Rogers, 1984; Beamish et al., 1992; Scheel and 
Hough, 1997), or if such an increase in fry abundance 
results in predators consuming wild chum salmon fry 
at a faster rate than they consume hatchery-produced 
fish (Holling, 1959). 
The estuarine phase of the chum salmon life cycle 
in Taku Inlet provides ample time for interactions to 
occur that may influence survival of chum salmon fry, 
although this phase lasts less than a month. This short 
estuarine phase, however, is a critical period of rapid 
growth (Duffy et al., 2005; Simenstad et al., 1982; 
Wertheimer and Thrower, 2007), when fry must feed 
frequently to gain the energy to smolt, grow, avoid 
predators, migrate, and compete with other members 
of their cohort (Healey, 1982; Fukuwaka and Suzuki, 
2002; Duffy and Beauchamp, 2008). In several studies 
on the daily mortality of chum salmon fry in estuaries, 
it was concluded that a large proportion of each cohort 
dies in the first 21 days at sea (Parker, 1962; Bax, 
1983; Fukuwaka and Suzuki, 2002; Wertheimer and 
Thrower, 2007). Estuarine survivors often more than 
double in weight (Duffy et al., 2005) and larger fry 
are subsequently less susceptible to predation (Parker, 
1971; Hargreaves and LeBrasseur, 1986; Wertheimer 
and Thrower, 2007). Similarly, survival of hatchery- 
reared chum salmon fry is influenced by body size at 
the time of release (Kaeriyama, 1999; Wertheimer and 
Thrower, 2007). Widespread conditions favorable to 
growth can increase survival of chum salmon cohorts 
from many stocks simultaneously (Pyper et al., 2002; 
Mueter et al., 2005; Duffy and Beauchamp, 2008), but 
interannual differences in environmental conditions are 
also reflected in size and survival rates (Wertheimer 
et al., 2004; Seo et al., 2006; Armstrong et al., 2008; 
Sturdevant et al., 2009). 
New recruits to the inner inlet could create a nega- 
tive bias in our estimates of apparent growth of wild 
fry because newly emigrated fry coming from the river 
would likely be smaller. In contrast, new recruits to the 
outer inlet come from the inner inlet and therefore the 
fact that wild fry were larger in the outer inlet than 
the inner inlet supports the conclusion that wild fry 
increased in fork length. Future research should in- 
clude sampling near the mouth of the river itself for the 
benefit of comparing the size and outmigration timing 
of wild fry in the inner inlet with that of wild fry from 
the lower river. This bias did not exist for hatchery fry 
because there were no new recruits of hatchery fry after 
release. Although we do not have data on the length 
of time wild fry reside in the inner inlet, the fact that 
average length did not change substantially through 
the season indicates the catch could have been heavily 
influenced by new recruits. Our data indicated that at 
least some of the increase in length of wild fry in the 
outer inlet was due to actual growth. Fork length of 
early hatchery fry increased throughout the season in 
the outer inlet and wild fry also appeared to increase 
in size as they moved from the inner to the outer inlet. 
Early hatchery fry spent up to a month in the outer 
inlet and our catch data indicated that wild and early 
hatchery fry use habitat similarly. Consistent with other 
research (Healey, 1982; Mortensen et al., 2000; Duffy et 
al., 2005), both groups tended to be smaller in littoral 
than in neritic habitat, indicating that they exhibited 
the behavioral pattern of moving from shallow to deeper 
water with growth. Both size and predation risk can ac- 
celerate hatchery fry dispersal from nearshore habitats 
(Willette, 2001), which could also buffer the smaller 
wild fish from a different predator suite that coincides 
with this transition to offshore zones (Willette, 2001; 
Moss et al., 2005; Sturdevant et al., 2009). 
Food availability for chum salmon fry may directly 
affect their survival, albeit to a lesser degree than 
predation risk (Mortensen et al., 2000; Willette, 2001; 
Willette et al., 2001). Based on a study of the bioener- 
getics of juvenile chum salmon in Icy Strait, Southeast 
Alaska, it was concluded that prey availability does 
not generally limit their growth (Orsi et al., 2004). 
However, compared to our early estuarine research, the 
study of Orsi et al. was conducted in epipelagic habitat 
and focused on larger hatchery and wild fish that had 
been in the marine environment for a minimum of 45 
days; consequently, any competitive interactions may 
have occurred earlier. On the other hand, in studies of 
other estuaries of Southeast Alaska, spring carrying 
capacity far exceeded the estimated abundance of wild 
pink and chum salmon fry (Bailey et al., 1975), and fry 
rapidly outgrew predation vulnerability (Murphy et al., 
1988). If estuarine conditions were equally favorable 
in Taku Inlet, hatchery fish may not directly compete 
with wild fish for food even when their densities are 
relatively high and the fish co-occur; instead, prey could 
be partitioned among size and stock groups of chum 
