Fergusson et al.: Effects of starvation on energy density of Oncorhynchus keta 
223 
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0 . 6-1 
0 . 4 - 
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0.0 
- 0 . 2 - 
- 0 . 4 - 
June 
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Figure 4 
Condition residuals (CR) for individual juvenile chum salmon (Oncorhyn- 
chus keta) starved over time in the laboratory after capture in the marine 
waters of Icy Strait and Upper Chatham Strait in the northern region 
of southeastern Alaska, June and July 2003. The CRs were calculated 
by using the In-transformed experimental fork length and wet weight 
measures for each fish in a regression equation derived from all paired 
ln-weights and ln-lengths of field-caught juvenile chum salmon col- 
lected during the Southeast Coastal Monitoring project, June-August 
(n = 8476) from 1997 to 2008. The 0.0-line represents the expected CR 
of an average fish; therefore, positive values indicate above average 
condition and negative values indicate below average condition. 
( Salvelinus alpinus; Miglavs and Jobling, 
1989), rainbow trout ( O . mykiss; Simp- 
kins et al., 2004), and Atlantic salmon 
(Salmo salar\ Stefansson et al., 2009) for 
starvation periods of 4-6 weeks. Length 
and weight of small (30.1-mm and 0.14-g) 
sockeye salmon decreased significantly 
after 14-49 days of starvation in colder 
water (7.9°C; Bilton and Robins, 1973) 
than that used in our experiment. Like 
the salmonids in the above studies, 
weight of our juvenile chum salmon de- 
creased for the June experimental group, 
but similar conclusions about the July 
fish could not be reported because of the 
shorter experimental period. 
The chum salmon caught in June ini- 
tially had approximately 11% higher 
WBEC and approximately 3% lower %MC 
than fish caught in July — differences that 
could be accounted for by both environ- 
mental and biological variables. In both 
the June and July experimental groups, 
a measurable increase in WBEC and de- 
crease in %MC occurred between days 
zero and one. These changes may have 
been attributed to a physiological stress 
response that caused the fish to lose wa- 
ter and therefore increased the relative 
WBEC and decreased the %MC (Breck, 
2008). Temperature and salinity both af- 
fect fish physiological rates and influence 
ingestion, metabolism, and growth (Brett 
et al., 1969; Mason, 1974; Sheridan et al., 
1983; Jobling, 1994; Weatherley and Gill, 
1995). In our study, field temperature 
was cooler and salinity was higher in 
June (11°C; 26 psu) than in July (13°C; 
23 psu), but fish captured in both months 
were transferred into identical, colder 
(9°C) and more saline (32 psu) environments in the 
laboratory. Monthly differences in temperature and 
salinity were therefore eliminated as variables in the 
experiments. However, the fish captured in June had 
probably smolted more recently (Zaporozhec and Za- 
porozhec, 1993; Hoar, 1998) and spent less time in the 
marine environment, and probably had lower growth 
rates (Orsi et al., 2000) and energy requirements than 
fish captured in July, when it was warmer. 
We accounted for potential size-related effects on 
WBEC and %MC by using length-weight regression 
analysis, which corrected for natural variation in fish 
size; however, the results may still be misleading be- 
cause this regression did not account for differences in 
actual nutritional status or body composition, such as 
protein, lipid, and water content (Miglavs and Jobling, 
1989; Edsall et al., 1999; Kotiaho, 1999; Trudel et al., 
2005; Congleton and Wagner, 2006). Length-weight re- 
gression analysis is useful for initially identifying con- 
dition in relation to a long-term index and to anticipate 
trends in energy density, but to account for changes in 
nutritional status or body composition WBEC, %MC, 
or proximate composition, should be used to verify the 
CR results. 
In our study, stocks of juvenile chum salmon sampled 
from the same habitat did not differ in WBEC or %MC, 
but size did differ significantly. By comparison, for ju- 
venile pink salmon (O. gorbuscha ) captured together 
in marine habitats of Prince William Sound, Alaska, 
differences in length and WBEC between stock groups 
have not been consistent (Paul and Willette, 1997; Boldt 
and Haldorson, 2004; Cross et al., 2008). For fish ~80 
mm in length, the occurrence of length differences be- 
tween juvenile pink salmon stocks depended on the size 
of hatchery fish at time of release (Cross et al., 2008). 
In a concurrent study, juvenile pink salmon length dif- 
fered between stock groups, but WBEC did not (Boldt 
and Haldorson, 2004). Conversely, energy content (so- 
matic) of smaller juvenile pink salmon (~35 mm) did 
differ between stock groups (Paul and Willette, 1997). 
