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Fishery Bulletin 1 14(2) 
and their diets consisted of proportionately more gona- 
tid squid (. Berryteuthis anonychus ) (Aydin et al., 2000). 
In addition, it has also been suggested that differences 
in diet and growth of chum salmon may have been the 
result interannual variations in the summer latitudi- 
nal sea surface temperature minimum (warmer north 
and cooler south of the boundary) in the North Pacif- 
ic Ocean. Salmon in the high seas adapt to climate- 
induced changes in their prey resources by switching 
their diets either within or between trophic levels 
(Kaeriyama et al. 2004). 
After accounting for density-dependent effects, 
growth was positively related to SST. Different possi- 
ble mechanisms exist for immature growth to increase 
with warmer summer SSTs and negative PDO events 
(cooler than average winters) in earlier years. For ex- 
ample, different physical phenomena (e.g., eddies, wind 
patterns, El Nino events) may transport nutrients into 
oceanic water of the North Pacific Ocean. Predomi- 
nant among such phenomena are eddies, which form 
in waters above the continental shelf and slope in the 
eastern North Pacific Ocean (Ladd et al., 2005). In the 
cores of these eddies, iron and nitrate are transported 
from the sea floor to surface waters (Johnson et al., 
2005) and these transported nutrients result in phy- 
toplankton blooms inside the eddies as they move into 
oceanic waters at a rate of a few months to 5 years 
(Ladd, 2007). Zooplankton species are similarly trans- 
ported from the shelf into the GOA (Mackas and Gal- 
braith, 2002a). These eddies form more frequently in 
warmer years and during El Nino events (Crawford 
and Whitney, 1999). In a winter with a negative PDO, 
there is a northerly wind pattern in the eastern North 
Pacific (Mantua et al., 1997) and these winds may push 
these eddies off the shelf and into oceanic waters. Bro- 
deur and Ware (1992) documented positive correlations 
between the intensity of the winter winds and subse- 
quent summer zooplankton biomass in the subarctic 
gyre within the 1956-1962 and 1988-1989 year periods. 
In addition to the effect of eddies and wind on the pro- 
ductivity of oceanic waters, El Nino events can lead to 
a transport of heat and zooplankton from the equator 
that can reach the subarctic waters of the North Pa- 
cific Ocean in 1 year and remain for 2 years (Mackas 
and Galbraith, 2002b). These events of increased ocean 
productivity may initiate and perpetuate a strong year 
class of a given prey taxon with a two-year life span. 
Finally, climate may also have a lag effect on growth 
through the lag effects of climate on mortality, bioen- 
ergetics, predation, competition, prey switching, distri- 
bution, and recruitment that influence growth, abun- 
dance, or the relationship of growth and abundance. 
Uncertainties in regard to the true mechanisms driv- 
ing the annual variation in the growth of chum salmon 
support the use of a model with an error correction 
time series (Noakes et al. 1987). 
No climate-related changes in growth were detected 
during the maturing life stage for the Quilcene stock. 
Our index of growth in length may not capture the 
total effects of climate or population abundance on 
growth. The lack of a significant relationship between 
maturing growth and climate indices in this study may 
be explained by the fact that during this stage, salmon 
growth favors an increase in body weight rather than 
length (Aydin et al., 2000), making it less possible for 
our length-based models to capture changes in growth. 
Alternatively, at larger body sizes, chum salmon switch 
from feeding on zooplankton to feeding on fish and ge- 
latinous zooplankton not used by the other salmon spe- 
cies (Davis et al., 2009). This feeding plasticity may re- 
duce the effects of intra- and interspecific competition 
for the larger, maturing chum salmon. 
Caveats 
Our model with the error correction that incorporated 
the lag structures of the model residuals and climate 
did not adequately predict the values of the reserved 
observations for SW2 of the Fish Creek chum salmon 
and SW3 of the Quilcene River chum salmon. The error 
correction component may have been incorrectly speci- 
fied, the growth and abundance relationships may have 
undergone temporal change, or the time series may 
have been too variable or too short to provide reliable 
coefficient estimates. The error correction did not ac- 
count for the total increase in growth in the late 1990s 
and early 2000s. Helle et al. (2007) suggested that the 
increase in body size of chum salmon in the mid-1990s 
during a period of high population abundance was due 
to an increase in the carrying capacity for salmon in 
the North Pacific Ocean. This question merits further 
investigation. 
Although uncertainty exists regarding whether 
back-calculated abundance indices that are based on 
the numbers of returning salmon, marine mortality, 
and age composition are good indices for abundance 
earlier in life, the assumption that back-calculated 
salmon abundance was a metric of salmon abundance 
earlier in life was supported by a strong correlation 
between the abundances of juvenile pink salmon and 
the returns of adult pink salmon in the following year 
(Orsi et al. 3 ). However, correlation does not imply cau- 
sation. Nonetheless, it would have been preferable to 
base our analysis on a time series of actual abundance 
of juvenile and immature salmon at sea. This was not 
possible, because very few such time series exist and 
those that do exist were too short to be used for this 
study. Alternatively, at-sea estimates of abundance 
would likely be subject to large sampling uncertainty; 
hence the indices based on harvest and assumed mor- 
tality rates may actually be better. 
Implications for management 
During the first year at sea, size was considered a criti- 
cal factor affecting marine mortality rates of salmon 
(Parker, 1971; Holtby et al., 1990). Size attained by the 
first winter at sea was also considered important in de- 
termining year-class strength (Beamish and Mahnken, 
2001). We found that an increase in the abundance of ju- 
