218 
Effects of starvation on energy density 
of juvenile chum salmon ( Oncorhynchus keta ) 
captured in marine waters 
of Southeastern Alaska 
Emily A. Fergusson (contact author) 
Molly V. Sturdevant 
Joseph A. Orsi 
E-mail address for contact author: emily.fergusson@noaa.gov 
Auke Bay Laboratories 
Alaska Fisheries Science Center 
National Marine Fisheries Service 
17109 Point Lena Loop Road 
Juneau, Alaska 99801 
Abstract — We conducted laboratory 
starvation experiments on juvenile 
chum salmon ( Oncorhynchus keta) 
captured in the neritic marine waters 
of northern Southeast Alaska in June 
and July 2003. Temporal changes in 
fish energy density (whole body energy 
content [WBEC], cal/g dry weight), 
percent moisture content, wet weight 
(g), length (mm), and size-related con- 
dition residuals were measured in the 
laboratory and were then compared 
to long-term field data. Laboratory 
water temperatures and salinities 
averaged 9°C and 32 psu in both 
months. Trends in response variables 
were similar for both experimental 
groups, although sampling intervals 
were limited in July because fewer 
fish were available (n = 54) than in 
June (« = 101). Overall, for June (45- 
d experimental period, 9 intervals), 
WBEC, wet weight, and condition 
residuals decreased and percent 
moisture content increased, whereas 
fork length did not change. For July 
(20-d experimental period, 5 inter- 
vals), WBEC and condition residuals 
decreased, percent moisture content 
and fork length increased, and wet 
weight did not change. WBEC, per- 
cent moisture content, and condition 
residuals fell outside the norm of long- 
term data ranges within 10-15 days 
of starvation, and may be more useful 
than fork length and wet weight for 
detecting fish condition responses to 
suboptimal environments. 
Manuscript submitted 19 May 2009. 
Manuscript accepted 20 January 2010. 
Fish. Bull. 218-225(3020). 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Energy density is an important mea- 
sure of fish nutritional condition and 
is used to assess growth, construct 
energy budgets, and measure energy 
flow in ecosystems (Brett et al., 1969; 
Jobling, 1994; Ban et al., 1996; Edsall 
et al., 1999). Energy density is also 
a critical parameter for bioenergetic 
models (Orsi et al., 2004; Trudel et al., 
2005; Wuenschel et al., 2006; Breck, 
2008). Along with other measures of 
fish condition, such as body composi- 
tion, growth, and length-weight condi- 
tion indices, energy density integrates 
and reflects the history of fish feed- 
ing environments before the time of 
sampling (LeBrasseur, 1969; Edsall et 
al., 1999; Breck, 2008). During good 
feeding periods, fish condition will be 
high, whereas the reverse is expected 
during poor feeding periods as energy 
reserves are depleted to maintain 
standard metabolic needs (Jobling, 
1994) . However, an examination of 
how quickly energy density responds 
during periods of poor feeding that are 
usually associated with low growth 
has been limited to a few studies. In 
general, a balanced energy budget is 
expressed as the equation: ingestion 
= metabolism + growth + excretion, 
which outlines how an energy source 
is used by an organism and what pro- 
portion is allocated to each component 
of the equation (Jobling, 1994; Brett, 
1995) . These allocations depend on the 
initial amount of energy, as well as the 
environmental conditions that affect 
physiological rates, such as tempera- 
ture and salinity (Brett et al., 1969; 
Hoar, 1988; Jobling, 1994). When fish 
are starved, growth typically ceases 
and energy density declines; when 
energy stores are used, the percent- 
ages of fat and protein in the fish 
decrease as the relative water content 
increases (Brett, 1995; Breck, 2008). 
Changes in fish energy density may be 
more detectable on small scales than 
other fish parameters, such as growth, 
during periods of poor feeding condi- 
tions in marginal habitats. 
Juvenile Pacific salmon (Oncorhyn- 
chus spp.) use transitional habitats 
along their seaward migration from 
near shore to the open ocean and 
can experience rapid environmen- 
tal changes that may affect growth 
and energy allocation (Orsi et al., 
2000; Cross et al., 2008). Fish tran- 
sit these demanding environments at 
the same time that they are experi- 
encing increasing energy demands 
while undergoing ontogenetic changes 
in metabolic rate related to salinity 
and smoltification (Hoar, 1998). These 
transitional habitats are presumed to 
be critical feeding areas because prey 
fields also change dramatically, and 
juvenile salmon are often found in 
the presence of planktivorous forage 
fish species that potentially impact 
carrying capacity (Purcell and Stur- 
devant, 2001; Park et al., 2004; Orsi 
et al., 2004). Therefore, understand- 
ing how changes in juvenile salmon 
