393 
Feeding ecology of juvenile Pacific salmon 
( Oncorhynchus spp.) in a northeast Pacific fjord: 
diet, availability of zooplankton, selectivity for prey, 
and potential competition for prey resources 
Email address for contact author: sbollens@vancouver.wsu.edu 
1 School of Earth and Environmental Sciences 
and School of Biological Sciences 
Washington State University 
14204 NE Salmon Creek Avenue 
Vancouver, Washington 98686 
2 School of Arts & Sciences 
Endicott College 
376 Hale Street 
Beverly, Massachusetts 01915 
3 School of Aquatic and Fishery Sciences 
University of Washington 
1122 Boat Street 
Seattle, Washington 98195 
4 School of Oceanography 
Campus Box 357940, 
University of Washington 
Seattle, Washington 98195 
Abstract — We investigated the feed- 
ing ecology of juvenile salmon during 
the critical early life-history stage 
of transition from shallow to deep 
marine waters by sampling two sta- 
tions (190 m and 60 m deep) in a 
northeast Pacific fjord (Dabob Bay, 
WA) between May 1985 and October 
1987. Four species of Pacific salmon— 
Oncorhynchus keta (chum), O. 
tshawytscha (Chinook), O. gorbusclia 
(pink), and O. kisutch (coho) — were 
examined for stomach contents. Diets 
of these fishes varied temporally, spa- 
tially, and between species, but were 
dominated by insects, euphausiids, 
and decapod larvae. Zooplankton 
assemblages and dry weights differed 
between stations, and less so between 
years. Salmon often demonstrated 
strongly positive or negative selection 
for specific prey types: copepods were 
far more abundant in the zooplank- 
ton than in the diet, whereas Insecta, 
Araneae, Cephalapoda, Teleostei, and 
Ctenophora were more abundant in 
the diet than in the plankton. Overall 
diet overlap was highest for Chinook 
and coho salmon (mean=77.9%) — spe- 
cies that seldom were found together. 
Chum and Chinook salmon were 
found together the most frequently, 
but diet overlap was lower (38.8%) 
and zooplankton biomass was not 
correlated with their gut fullness (% 
body weight). Thus, despite occasional 
occurrences of significant diet overlap 
between salmon species, our results 
indicate that interspecific competition 
among juvenile salmon does not occur 
in Dabob Bay. 
Manuscript submitted 10 September 2009. 
Manuscript accepted 16 June 2010. 
Fish. Bull. 108:393-407 (2010). 
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. 
Stephen M. Bollens (contact author ) 1 
Rian vanden Hooff 1 
Mari Butler 2 
Jeffery R. Cordell 3 
Bruce W. Frost 4 
Juvenile salmon migrating into coastal 
waters face a variety of challenges 
as they adjust to a rapidly changing 
environment, such as outmigration 
timing, physiological acclimation, new 
prey fields, new predators, and com- 
petition for resources (Pearcy, 1992; 
Magnusson and Hilborn, 2003). High 
rates of natural mortality have been 
attributed to the ocean entry transi- 
tion (Parker, 1971; Bax, 1983), yet 
we still have a poor understanding of 
the processes governing this mortal- 
ity. Several mechanisms have been 
hypothesized — disruption of freshwa- 
ter hydrological conditions, degrada- 
tion of estuarine nursery conditions, 
and interannual variability of preda- 
tor abundance and prey resources 
in the marine environment (Levings 
and van Densen, 1990; Willette, 2001; 
Logerwell et ah, 2003). 
Comprehensive management of 
salmon fisheries, including their 
conservation and recovery, requires 
detailed understanding of juvenile 
salmon ecology during this critical 
transition. Increased understanding 
of feeding relationships and poten- 
tial density-dependent effects, such 
as diet overlap among co-occurring 
species and resource limitation could 
allow for a more ecologically based 
approach for rebuilding threatened 
salmon stocks. Specifically, species in- 
teractions and their response to vari- 
ability in prey resources could be im- 
portant factors for predicting marine 
survival and the forecasting of adult 
returns (Logerwell et al., 2003). 
Juvenile salmon have been docu- 
mented feeding in a variety of habi- 
tats, including freshwater (Keeley 
and Grant, 2001; Hampton et ah, 
2006), estuaries (Healey, 1980; Mur- 
phy et ah, 1988; Reese et al., 2009), 
and in the coastal ocean (e.g., Bro- 
deur and Pearcy, 1990; Daly et al., 
2009). Inland marine waters (e.g., 
bays, straits, sounds, fjords, etc.) 
have been characterized less fre- 
quently (Sturdevant et al., 2004; 
Romanuk and Levings, 2005; Saito 
et al., 2009). Like estuaries, these 
inland marine salmon habitats are 
more geographically and ecologically 
diverse than offshore habitats, and 
thus it may be more difficult to gen- 
eralize about juvenile salmon feeding 
ecology in these areas. 
Dabob Bay, a temperate marine 
fjord in Puget Sound, northwestern 
Washington, has been the site of nu- 
merous studies of plankton dynamics 
