Fergusson et al.: Effects of starvation on energy density of Oncorhynchus keta 
219 
energy density reflect habitat quality may give insight 
into factors that affect their growth and survival, par- 
ticularly if food resources may be limited during this 
critical time in their life history (Paul and Willette, 
1997; Boldt and Haldorson, 2004; Cross et ah, 2008). 
We initiated a study to measure changes in condition 
of juvenile chum salmon ( O . keta) captured at sea and 
later denied food resources in the laboratory. In previ- 
ous studies on fish starvation, juvenile chum salmon 
were reared entirely in the laboratory (LeBrasseur, 
1969; Akiyama and Nose, 1980; Murai et al., 1983; 
Ban et al., 1996); however, in our study they experi- 
enced variable environmental conditions at sea before 
being captured and transported back to the labora- 
tory. Thus, these salmon from field collections represent 
natural variation of fish in marine waters better than 
fish reared in controlled laboratory environments. Our 
primary objective was to measure changes in energy 
density, moisture content, weight, length, and a size- 
related condition residual index for field-caught juvenile 
chum salmon in response to starvation in the labora- 
tory over time. We also compared the condition of these 
experimentally starved fish to that determined from a 
long-term data series on field-caught fish 1) to assess 
the range of normally occurring condition values and 2) 
to identify the length of time before experimental values 
fell outside the observed range. 
Methods 
Juvenile chum salmon for the experiments were cap- 
tured in the vicinity of Icy Strait (58°N latitude, 135°W 
longitude) about 50 km west of Juneau, Alaska, in June 
and July 2003. Fish were obtained during the South- 
east Alaska Coastal Monitoring (SECM) Project long- 
term annual survey of juvenile salmon by the Auke Bay 
Laboratories (ABL) aboard the NOAA ship John N. Cobb 
(Orsi et al., 2004). Juvenile chum salmon were collected 
from the neritic waters of Icy Strait and Upper Chatham 
Strait, along the primary seaward migration corridor 
in the northern region of Southeast Alaska (Orsi et al., 
2000, 2004). Preliminary observations along this corridor 
showed that juvenile chum salmon exhibit approximately 
a five-fold increase in body length, 100-fold increase in 
weight, 25% increase in energy density, and more than 
6% decline in body moisture content between May and 
September. We used fish from this locality in June and 
July, the periods of highest abundance and greatest 
interaction with other juvenile salmon species. In June, 
fish were captured with a Kodiak pair-trawl fished at 1 
m/sec for 10 min (Mortensen et al., 2000). In July, fish 
were captured with a Nordic 264 rope trawl fished at 
1.5 m/sec for 20 min (Orsi et al., 2000). All fish caught 
were immediately transferred from the trawl codend to 
static live tanks containing sea water. Juvenile chum 
salmon were then identified and sorted into flow-through 
“live” tanks. The sea water for the tanks was pumped 
from a depth of 3 m and then filtered to prevent feeding 
on zooplankton prey. Before transfer to the laboratory, 
the juvenile chum salmon were held onboard for one 
day in June and four days in July while the surveys 
were completed. To establish a baseline for the start 
of the starvation experiments, on the day of capture a 
subsample of fish were measured (fork length, FL, mm) 
and frozen (-5°C) for later laboratory analysis. Daily 
temperature and salinity measurements were recorded 
and averaged 11.4°C and 26.1 psu in June and 12.7°C 
and 23.2 psu in July. 
In the laboratory, the juvenile chum salmon were 
placed in two living-stream tanks (Frigid Units, Inc., 
Toledo, OH) (200x50x48 cm) with screened baffles sepa- 
rating the inflow and outflow pipes. One unit was allo- 
cated the salmon captured in June; the other unit — the 
salmon captured in July. Ambient sea water from a 
25-m depth in Auke Bay was supplied to the tanks at 
a rate of 3 L/min. Daily temperature and salinity mea- 
surements were recorded in the laboratory tanks and 
averaged 8.6°C and 31.7 psu for June and 8.6°C and 
32.1 psu for July. Sea water was filtered to prevent feed- 
ing on zooplankton prey. The fish were not subjected to 
any strong currents that would increase activity costs. 
To best mimic the photoperiod in the natural environ- 
ment at the time of capture, light conditions in the labo- 
ratory were set at a standard eight hours of darkness, 
one hour of dusk, one hour of dawn, and 14 hours of 
daylight. Subsamples of 10-15 fish were removed from 
the tank at predetermined intervals and sacrificed with 
an overdose of tricaine methanesulfonate (MS-222), 
then frozen (-5°C) individually for later size and calo- 
rimetric analyses. Fish that had died between sacrifice 
intervals were not included in the experiments. 
Frozen juvenile chum salmon were processed for data, 
including energy density in terms of whole body energy 
content (WBEC, cal/g wet weight [WW]), dry weight 
(DW, mg), percent moisture content (%<MC), FL, and wet 
weight (mg). After excising each stomach and removing 
and weighing its contents, we dried the fish to obtain 
DW (full gut minus empty gut, nearest mg) so that un- 
digested prey would not bias the final values. Stomachs 
examined from fish sacrificed after the first time inter- 
val were devoid of prey and therefore stomachs were not 
excised in subsequent time intervals. All viscera were 
replaced in the body cavity before the fish were dried to 
a stable weight (<5 mg change), requiring a minimum 
of 48 hours at 55°C. The DW was recorded and %MC 
of each fish was calculated as ([1 -DW/WW] x 100). 
Each fish was homogenized with a Waring pulverizer, 
then finely ground with a mortar and pestle to yield 
a uniform powder. Susamples of 15 mg were formed 
into pellets with a pellet press and stored in a desic- 
cator to prevent rehydration. A 1425 Parr micro-bomb 
calorimeter was used to obtain cal/g DW for each fish; 
this measure was converted to WBEC by multiplying by 
DW/WW. Estimates of WBEC from replicate subsamples 
were consistent (<2% coefficient of variation). To ac- 
count for potential effects of size variation on WBEC 
and %MC, size-related condition residuals (CR) were 
calculated by using the ln-transformed experimental 
FL and WW measures for each fish. We first derived 
