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Fishery Bulletin 108(4) 
(e.g., Frost, 1988; Bollens et al., 1992a, 1992b; Frost, 
2005 and references therein). Although these stud- 
ies have provided extensive insight into zooplankton 
population dynamics and predator-prey interactions, 
none has specifically reported on the seasonality of zoo- 
plankton community composition from this area. Four 
juvenile salmon species reside in Dabob Bay temporarily 
during outmigration to the Pacific Ocean (Bollens and 
Frost, 1989): Oncorhynchus keta (chum), O. tshawytscha 
(Chinook), O. gorbuscha (pink), and O. kisutch (coho). 
Diets of these four species in the fjord have not been 
described. Feeding habits of juvenile chum salmon in 
neritic waters have been described for a nearby location 
in Hood Canal (Simenstad and Salo, 1980) and feed- 
ing habits of juvenile salmon in other nursery areas of 
Puget Sound have also been described (Simenstad et 
al., 1982; Duffy et al., 2005). 
Much of our understanding of juvenile salmon feed- 
ing ecology in northeast Pacific marine waters has been 
based on detailed analyses of stomach contents, but 
Figure t 
Map of Dabob Bay, Washington. Four species of juvenile 
Pacific salmon — chum ( Oncorhynchus keta), Chinook (O. 
tshawytscha ), coho (O. kisutch ), and pink (O. gorbuscha ) — and 
zooplankton were sampled at two stations between April 
1985 and October 1987 to examine salmon diet, zooplank- 
ton availability, feeding selectivity, and potential competi- 
tion for prey. D=location of the deep (190-m) central bay 
tstation, and S=the location of the shallow (60-m) near- 
shore station. 
has been limited by a lack of corresponding analyses 
of prey fields. Some recent studies have identified the 
importance of prey selectivity as a factor in assess- 
ing the trophic ecology of salmon during early marine 
residence (Landingham et al., 1998; Schabetsberger 
et al., 2003). Furthermore, the highly variable diets 
demonstrated within and between studies indicate that 
temporal (seasonal, interannual, and interdecadal) and 
spatial scales of variability are important, and therefore 
pose a significant challenge for the design of field stud- 
ies. The result has been an incomplete understanding 
of juvenile salmon response to dynamic zooplankton 
prey fields, particularly during one of the most critical 
life-history stages, i.e., the early ocean transition phase 
(Beamish and Mahnken, 2001). 
Our objectives were 1) to investigate the diet compo- 
sition of four salmon species ( Oncorhynchus spp.) col- 
lected from two stations (nearshore-shallow and central- 
basin-deep) in Dabob Bay over three years and several 
seasons; 2) to determine salmon feeding selectivity 
(i.e., their diet in relation to prey availability); 
and 3) to explore potential resource competition 
among these species during their early marine 
residence. 
Materials and methods 
Fish collection and processing 
Between May 1985 and October 1987 we sampled 
two stations in Dabob Bay, WA (47°45'-50'N lat., 
122°50 / W long.): a deep (190 m), central station, 
and a shallow (60 m), nearshore station 9 km apart 
(Fig. 1). Fish were sampled at night (just after 
dusk, i.e., when there was no apparent daylight) 
with two gear types: a midwater trawl with a 
mouth area of 81.0 m 2 (9. 0x9.0 m), and a surface 
tow net with a mouth area of 18.3 m 2 (3. 0x6.1 
m) (see Bollens and Frost, 1989 for details). The 
midwater trawl was towed obliquely from a 50-m 
depth to the surface at a mean speed of 150 cm/s. 
Because of concerns about possible avoidance of 
this net by fish in the upper few meters of the 
water column (e.g., due to ship wake and propeller 
wash), we also deployed the surface tow net in the 
upper three meters of the water column, towed at a 
mean speed of 80 cm/s behind (50 m) and between 
(at a midpoint of 50 m) two different vessels (one 
vessel 5 m and one 15 m in length). Fish were col- 
lected at each station during each of four seasons 
(spring: April-May; early summer: June-July; late 
summer: August; and autumn: October) in each of 
three years (1985-87), except for spring of 1985, 
when no fish were collected (Table 1). 
Fish collected with the midwater or surface 
trawls were sorted and counted, and the catch 
was weighed by species, lengths were measured, 
and then individuals of five predetermined size 
(fork length [FL] ) classes (<49 mm, 50-74 mm, 
