Martinson et al.: Growth and survival of Oncorhynchus nerka 
489 
returned to Karluk River and Lake system on Kodiak 
Island, Alaska, from 1922 to 2000, with the exception 
of seven years for which data were missing. Hereafter, 
we refer to these fish as Karluk sockeye salmon. The 
objectives of this study were 1) to describe how mean 
freshwater and marine growth rates of Karluk sock- 
eye salmon varied over multiyear periods in relation 
to warm and cold C-0 regimes in the North Pacific 
Ocean; 2) to describe how marine growth rates varied 
annually in relation to annual variations in regional 
C-0 indices; and 3) to describe the interrelationships 
among annual growth rates, annual C-0 indices, and 
annual survival. 
Historically, the production of sockeye salmon in 
the Karluk system declined 90% from 1894 to the 
1950s and then increased 30% during the 1990s. Pro- 
posed causes for the decline include the following: 
initial overharvesting of the entire run which led to 
declines in the spawning population (Barnaby 1944); 
overharvesting of the middle part of the salmon run 
(Thompson 2 ); intense predation on juvenile salmon by 
Dolly Varden ( Salvelinus malma) and charr ( Salve - 
linus alpinus) in freshwater (Rounsefell, 1958); loss 
of marine-derived nutrients in the lake (Rounsefell, 
1958); increased population size of threespine stickle- 
back (Gasterosteus aculeatus), a freshwater competitor 
(McIntyre 3 ); asynchrony of the plankton bloom and fry 
emergence (Koenings and Burkett, 1987); and ocean 
climate change (Finney et al., 2000). The analysis 
of salmon-derived nitrogen levels in lake sediment 
cores revealed that from 1752 to 1993, nitrogen lev- 
els oscillated in synchrony with Gulf of Alaska sea 
surface temperatures reconstructed from tree ring 
widths (Finney et al., 2000). In our study, we found 
that Karluk sockeye salmon abundance had undergone 
significant fluctuations in association with C-0 condi- 
tions and regimes. 
Study area 
The Karluk Lake and River system is located on the west 
side of Kodiak Island in the northern Gulf of Alaska 
(Fig. 1). Karluk River is about 36 km long and from 18 to 
165 m wide. Karluk Lake is 19 km long and has an aver- 
age depth of 48 m. Sockeye salmon spawn in the river and 
the lake, and their tributaries. The early-run (June 1- 
July 21) sockeye salmon spawn mostly in tributaries 
of the lake. Scales were collected from adult sockeye 
salmon returning from the ocean and were sampled at 
2 Thompson, W. 1950. Some salmon research problems in 
Alaska. Presented at Alaskan Science conference of the 
National Academy of Science, National Research Council, 
Washington, 9-11 Novemeber, 1950. University of Wash- 
ington, Fisheries Research Institute, Seattle, WA, 39 p. 
3 McIntyre, J. 1980. Further consideration of causes for decline 
of Karluk sockeye salmon. Unpubl. report, 29 p. .S. Fish 
and Wildlife Service, National Fisheries Research Center, 
Seattle, WA. 
the weir located on the river. The weir was located near 
the mouth of the river from 1921 to 1941, 20 km upriver 
from the mouth from 1942 to 1944, and 300 m below 
the lake from 1942 to 2000. The average annual escape- 
ment was 421,146 sockeye salmon, 233,779 Chinook 
salmon ( O . tshawytscha), 630,176 pink salmon, 12,867 
coho salmon, 51 chum salmon, and 1,800 steelhead 
trout (O. mykiss ), for the years 2006-2008 (ADF&G, 
2009). 
Northeastern Pacific salmon distribute and migrate 
primarily in the GOA and central North Pacific Ocean 
(Myers et al., 1996). The GOA continental shelf waters 
encompass an area of 37,000,000 km 2 (Burrell, 1986). 
The GOA is dominated by counterclockwise current 
systems in offshore waters (i.e., Alaska Current) and on 
the continental shelf (i.e., Alaska Coastal Current). Wa- 
ter moves parallel to shore at speeds of 13 to 133 cm/s 
(Reed and Schumacher, 1986). 
Hypotheses and possible mechanisms 
that affect growth and survival 
To explain mechanisms for climate regime conditions 
to affect growth and survival we hypothesized that 1) 
faster growth and higher-than-average brood-year sur- 
vival was expected as a consequence of the warm C-0 
regimes from 1922 to 1946 and from 1977 to 2000, and 
slower growth and lower-than-average brood survival 
was expected as a consequence of the cool C-0 regime 
from 1947 to 1976; 2) annual growth and variation in 
brood survival were expected to correlate positively 
with sea surface temperature, precipitation, and atmo- 
spheric circulation (Atmospheric Forcing Index), and to 
correlate negatively with upwelling and the bifurcation 
of the Pacific Current (Northern Oscillation Index); and 
3) annual growth was expected to correlate positively 
with annual variations in brood survival for Karluk 
sockeye salmon. 
Mechanisms were proposed for the influence of C-0 
indices on increased marine growth and brood survival 
of salmon. Sea surface warming during the spring ini- 
tiates thermal stratification of the water column and 
an algal bloom in the Gulf of Alaska, food for the zoo- 
plankton that salmon feed on. Therefore, warmer sea 
surface temperatures in the spring were expected to 
increase the growth and survival of salmon. Annual 
primary productivity in the GOA is also limited by 
inorganic nitrogen, phosphorus, and silicon (Martin 
and Gordon, 1988). Winter and spring precipitation 
runoff from land to sea brings terrestrial silicon and 
iron into the GOA (Burrell, 1986). Precipitation also ac- 
celerates the Alaska Coastal Current (ACC) and draws 
nutrients in the GOA from the southern waters (Royer, 
1979). Winter and spring downwelling aids in deep- 
mixing of inorganic nutrients into the euphotic zone to 
enhance the bloom of phytoplankton during the spring. 
The Atmospheric Forcing Index (AFI) and the North- 
ern Oscillation Index (NOI) represent two additional 
pathways for nutrient input into the GOA. A positive 
