434 
Fishery Bulletin 107(4) 
n Catch per boat per day j 
— Chum fry natal year (millions) 
120 O 
100 
20 3 
1984 
1988 1992 
Year 
1996 2000 2004 
0 10 20 30 40 50 60 70 
Chum salmon fry released natal year (millions) 
Figure 1 
Trends in abundance of chum salmon (Oncorhynchus keta) near Taku 
Inlet, Alaska, as (A) annual commercial catch-per-boat-day (CPUE) of 
wild fall-run adults (4-year-old) and Douglas Island Pink and Chum 
(DIPAC) hatchery fry releases (millions of fish), and (B) adult chum 
salmon CPUE versus number of hatchery fry released near the inlet 
(regression of In CPUE : r 2 = 0.77, P <0.01, df=24), 1976-2005. Fry 
data were shifted to four years later to match natal year to adult 
harvest year. 
fry later at a larger size to reduce overlap 
with wild fry, thus decreasing nearshore 
residency of hatchery fish and increasing 
survival of wild fish (Kaeriyama, 1999; 
Wertheimer and Thrower, 2007). 
Douglas Island Pink and Chum 
(DIPAC), an enhancement hatchery near 
Juneau, Alaska, uses two different release 
strategies simultaneously for chum salm- 
on ( Oncorhynchus keta). These strategies 
provide an opportunity to study spatial 
and temporal overlap of wild fry with both 
hatchery fry that are released early at 
a smaller body size and those released 
later and at a larger size. Spatial and 
temporal overlap between these hatchery 
fry and wild fry in the Taku River estu- 
ary is likely because of the proximity of 
the release sites, and thus interactions 
are possible. Hatchery juveniles are re- 
leased near Taku Inlet in the spring when 
wild fry are most abundant. The DIPAC 
hatchery has placed unique thermal 
marks (Orsi et al., 2004) on all groups 
of chum salmon fry released since 1991, 
and has used distinct marks by location 
for smaller earlier groups and for larger 
later groups. DIPAC is thought to have 
more than doubled the annual adult chum 
salmon catch in the region based on re- 
leases of over 100 million fry near Juneau 
each spring; over the past 5 years annual 
catches of returning adult chum salmon 
that were released from DIPAC have aver- 
aged approximately 2 million fish. At the 
same time, independent indices of wild 
chum salmon abundance from the Taku 
River have declined significantly, raising 
questions about stock interactions. Catch 
per unit of effort (CPUE) for wild chum 
salmon caught in the commercial gillnet 
fishery in Taku Inlet is negatively related to the number 
of chum salmon fry released from DIPAC hatchery near 
Juneau during their natal year (Fig. 1; coefficient of 
determination from regression of In adult catch against 
fry releases, r 2 = 0.77, P=0.01). This relationship indi- 
cates that releases of hatchery chum salmon fry may 
contribute to the decline of wild chum salmon. 
Four kinds of potential wild and hatchery interac- 
tions have been proposed, namely 1) marine phase 
ecological interactions, 2) spawning competition and 
interbreeding interactions, 3) induced overharvest- 
ing interactions, and 4) early estuarine phase eco- 
logical interactions. We considered interactions during 
the estuarine life-history phase as the most plausible 
mechanism for the decline in wild Taku River fall 
chum salmon runs because other salmon populations 
in Southeast Alaska have been stable, including Taku 
summer chum salmon runs, and because Pacific salmon 
populations are known to co-vary in response to ocean 
conditions (Pyper et al., 2002; Mueter et al., 2005). 
The estuarine phase is known to be a period of high 
mortality with many variables influencing juvenile 
salmon growth and survival, including density and 
competition (e.g., Simenstad et al., 1982; Willette et 
al., 2001; Wertheimer and Thrower, 2007; Duffy et al., 
2005). Thus, the goal of this study was to investigate 
habitat use and migration timing of wild and hatch- 
ery chum salmon fry in Taku Inlet to evaluate the 
potential for wild and hatchery fish to interact in this 
estuary. Specifically, our objectives were 1) to compare 
the abundance of wild and hatchery chum salmon fry 
raised under early and late rearing strategies in differ- 
ent habitats of Taku Inlet (inner and outer inlet loca- 
tions, littoral and neritic habitats); 2) to compare the 
body size and condition of these groups of fry in differ- 
ent habitats; and 3) to document environmental factors 
that potentially could explain the distribution and size 
of chum salmon fry and the abundance of hatchery fry. 
