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Fishery Bulletin 1 14(2) 
Table 1 
Hypothesized mechanisms and effects (positive [+] and negative [— ]) of selected climate indices on the marine growth of chum 
salmon ( Oncorhynchus keta) in the North Pacific Ocean. Locations are the Gulf of Alaska (GOA), central subarctic North 
Pacific (CNP) and eastern subarctic North Pacific (ENP) oceans, and Washington (WA). Abbreviations include the mixed layer 
depth (MLD), Pacific Decadal Oscillation (PDO), and sea surface temperature (SST). 
Stage Location Index Mechanism Effect 
Fish Creek, southern Southeast Alaska (saltwater entry from February through May) 
Early juvenile 
GOA shelf 
Spring wind 
Plankton bloom 
- 
Midjuvenile 
GOA shelf 
Winter MLD 
Nutrients availability 
+ 
Late juvenile 
GOA shelf 
Fall wind 
Fall bloom 
- 
Immature/maturing 
CNP ENP 
Winter PDO 
Cool, high nutrients+ 
I m m at ur e/m atur i ng 
CNP ENP 
Summer SST 
Warm 
+ 
Quilcene River, Washington (saltwater entry in May) 
Early juvenile 
WA coast 
Upwelling index 
Nutrient upwelling 
+ 
Early juvenile 
WA coast 
Spring transition 
Later upwelling 
- 
Midjuvenile 
GOA shelf 
Winter MLD 
Nutrients availability 
+ 
Late juvenile 
GOA shelf 
Fall wind 
Plankton bloom 
- 
Immature/maturing 
CNP ENP 
Winter PDO 
Cool, high nutrients 
+ 
Immature/maturing 
CNP ENP 
Summer SST 
Warm 
+ 
salmon was negatively correlated with the number of 
fry releases from the hatcheries in coastal waters of 
Japan (Fukuwaka and Suzuki, 2000). Chum salmon 
switched from eating crustacean to gelatinous zooplank- 
ton when pink salmon were more abundant (Tadokoro 
et al., 1996). For chum salmon in the eastern Bering 
Sea, a significant negative relationship was observed 
between catch-per-unit-of- effort of chum salmon and the 
mean growth rate for age 0.2 and age 0.3 chum salmon 
(Azumaya and Ishida, 2000). These observations of prey 
switching, diet overlap, reduced feeding, and survival 
success at higher salmon population levels all provide 
support for the hypothesis that a carrying capacity may 
exist for salmon in the North Pacific Ocean. 
During their marine life, chum salmon from Oregon 
to the Alaska Peninsula are found primarily in the 
Alaska Gyre of the eastern North Pacific Ocean (My- 
ers et al., 2007). In the first year at sea, juvenile chum 
salmon migrate with the counterclockwise Alaska 
Coastal Current along the Alaska coastline above the 
continental shelf (Hartt and Dell, 1986). At a velocity of 
10 cm/s, we estimated that the Alaska Coastal Current 
is able to transport juvenile salmon over 1000 km in 
about 4 months, the approximate distance from Wash- 
ington (WA) to southern Southeast Alaska (Reed and 
Schumacher, 1986); however this estimate was based on 
limited data. During the fall, juvenile pink and chum 
salmon migrate west and southwest along the Alaska 
Peninsula where they enter the swift westward flow- 
ing Alaska Stream (40 cm/s) (Reed and Schumacher, 
1986). During their second through penultimate years 
at sea, immature northeastern Pacific chum salmon 
were primarily distributed to the north and east of the 
western (160°W) and southern (50°N) boundaries of the 
GOA in the eastern North Pacific Ocean (Myers et al., 
2007). During their final year at sea, maturing salmon 
migrate through oceanic and continental shelf habitats 
to return to freshwater to spawn. In some years, imma- 
ture and maturing southern North American stocks of 
chum salmon move into the Bering Sea in late summer 
and fall (Seeb et al., 2004). Because chum salmon oc- 
cupy different regions of the North Pacific Ocean dur- 
ing their ontogenetic migration after first entering the 
marine realm until their return to their natal streams, 
it should be possible to develop habitat-specific growth 
models that could be used to explain variations in 
growth at each life stage. 
Various hypotheses and mechanisms for climate to 
affect habitat-specific marine growth of chum salm- 
on in the North Pacific Ocean are listed in Table 1. 
We expected an increase in growth of chum salmon 
in the eastern North Pacific Ocean to be associated 
with increased ocean productivity due to a stronger 
spring phytoplankton bloom as indexed by reduced 
wind speed (Spies and Weingartner, 2007). Growth was 
also expected to increase with the occurrence of a fall 
bloom, increased coastal upwelling, and an earlier tim- 
ing of spring coastal upwelling (Logerwell et al., 2003). 
During summer, growth was expected to increase with 
a deeper mixing layer in the northern GOA during 
winter that enhances mixing of nutrients and a stron- 
ger spring bloom and enhanced summer feeding for 
juvenile salmon (Sarkar, 2007). Offshore, growth was 
expected to increase with warmer ocean temperatures 
(Martinson et al., 2008, 2009) and increased productiv- 
ity offshore as indexed by the winter Pacific Decadal 
Oscillation (Mantua et al., 1997). 
For this study, we attempt to explore density-depen- 
dent and climate limitations on growth for different 
life stages of chum salmon by examining the effects 
