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Influence of ocean and freshwater conditions on C olumbia R iver sockeye salmon Oncorhynchus nerka adult return rates
In recent years, returns of adult sockeye salmon O ncorhynchus nerka to the C olumbia R iver B asin have reached numbers not observed since the 1950s. To understand factors related to these increased returns, we first looked for changes in freshwater production and survival of juvenile migrants. We...
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Published in: | Fisheries oceanography 2014-05, Vol.23 (3), p.210-224 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | In recent years, returns of adult sockeye salmon
O
ncorhynchus nerka
to the
C
olumbia
R
iver
B
asin have reached numbers not observed since the 1950s. To understand factors related to these increased returns, we first looked for changes in freshwater production and survival of juvenile migrants. We then evaluated productivity changes by estimating smolt‐to‐adult return rates (
SAR
) for juvenile migration years 1985–2010. We found
SAR
varied between 0.2 and 23.5%, with the highest values coinciding with recent large adult returns. However, the largest adult return, in 2012, resulted not from increased survival, but from increased smolt production. We evaluated 19 different variables that could influence
SAR
s, representing different facets of freshwater and ocean conditions. We used model selection criteria based on small‐sample corrected
AIC
to evaluate the relative performance of all two‐ and three‐variable models. The model with
A
pril upwelling,
P
acific
N
orthwest
I
ndex (
PNI
) in the migration year, and
PNI
in the year before migration had 10 times the
AIC
c
weight as the second‐best‐supported model, and
R
2
= 0.82. The variables of
A
pril ocean upwelling and
PNI
in the migration year had high weights of 0.996 and 0.927, respectively, indicating they were by far the best of the candidate variables to explain variations in
SAR
. While our analyses were primarily correlative and limited by the type and amount of data currently available, changes in ocean conditions in the northern
C
alifornia Current system, as captured by April upwelling and
PNI
, appeared to play a large role in the variability of
SAR
. |
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ISSN: | 1054-6006 1365-2419 |
DOI: | 10.1111/fog.12056 |