201 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
@ established in 1881 -< 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—Highly variable recruitment 
and declines in productivity of Chinook 
salmon (Oncorhynchus tshawytscha) 
have created economic and cultural 
hardships throughout Alaska. There- 
fore, it is necessary to understand the 
factors influencing these declines. In 
this study, principal component analy- 
sis and regression were used to deter- 
mine how biological and environmental 
factors have influenced freshwater sur- 
vival, smolt production, and marine sur- 
vival of Chinook salmon in the Chilkat 
River (brood years 1999-2009) and 
marine survival in the Stikine River 
(brood years 1998-2009). Smolt produc- 
tion in the Chilkat River was higher in 
years when parr had shorter average 
mid-eye fork lengths, river discharge 
was low in the fall (P=0.05), and river 
temperatures and discharge were high 
in early spring (P=0.03), indicating 
density-dependent growth in fresh water 
and the importance of river conditions 
to annual growth and abundance of this 
species. Marine survival of fish in the 
Stikine River was positively related 
to smolt length, indicating higher sur- 
vival in years when smolts were larger 
(coefficient of multiple determination 
[R?]=0.26). Greater marine survival of 
salmon in the Chilkat River occurred 
in years when smolt migrations ended 
later in the month of May, smolts were 
larger, and discharge was lower (R7=0.5) 
than in other years. These results 
indicate the importance of the early 
marine period in determining year-class 
strength and highlight the variation in 
mechanisms that influence survival of 
stocks of Chinook salmon. 
Manuscript submitted 2 October 2020. 
Manuscript accepted 2 September 2021. 
Fish. Bull. 119:201—215 (2021). 
Online publication date: 22 October 2021. 
doi: 10.7755/FB.119.4.1 
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. 
Effects of early-life stage and environmental 
factors on the freshwater and marine survival 
of Chinook salmon (Oncorhynchus tshawytscha) 
in rivers of Southeast Alaska 
Stephanie A. Berkman (contact author)! 
Trent M. Sutton‘ 
Franz J. Mueter” 
Brian W. Elliott? 
Email address for contact author: stephberkman@gmail.com 
" Fisheries Department 
College of Fisheries and Ocean Sciences 
University of Alaska Fairbanks 
P.O. Box 757220 
Fairbanks, Alaska 99775 
? Fisheries Department 
College of Fisheries and Ocean Sciences 
University of Alaska Fairbanks 
17101 Point Lena Loop Road 
Juneau, Alaska 99801 
Survival of salmon species (Oncorhyn- 
chus spp.) of the Pacific Ocean varies 
with life stage. As a result, identifying 
critical periods of mortality that deter- 
mine brood strength can lead to more 
specific analyses of biotic and abiotic 
factors that may affect stocks. Although 
life history strategies vary by species 
and stock, most salmon undergo sin- 
gle or multiple freshwater wintering 
periods before migrating to the marine 
environment (McCormick et al., 1998; 
Quinn, 2005). The freshwater overwin- 
ter and early marine entry periods are 
frequently recognized as critical periods 
and bottlenecks for survival in the life 
history of salmon species in the Pacific 
Ocean (Beamish and Mahnken, 2001). 
In fresh water, parr must survive at 
least one winter period of freezing water 
temperatures, low river discharge, sur- 
face ice, and low productivity (Biro et al., 
2004; Huusko et al., 2007). Results of 
previous research indicate that over- 
winter survival of juvenile salmonids is 
3 Division of Sport Fish 
Alaska Department of Fish and Game 
Mile 1 Haines Highway 
Haines, Alaska 99827 
related to body size, with larger individ- 
uals having higher survival rates than 
smaller ones (Zabel and Achord, 2004). 
Larger, faster-growing individuals can 
better escape size-selective mortality 
(such as that resulting from predation), 
have a larger gape size (enabling the 
consumption of a greater diversity of 
prey that are larger and have higher 
energy), have greater lipid reserves, and 
have a lower relative metabolic rate, all 
of which help to sustain them during 
winter months (Houde, 1987; Sogard, 
1997; Biro et al., 2004; Thompson and 
Beauchamp, 2014). Larger body sizes 
may also enable these individuals to 
secure higher quality winter habitats 
(Quinn and Peterson, 1996; Zabel and 
Achord, 2004). 
Environmental conditions before, 
during, and after winter can also influ- 
ence survival (Cunjak, 1988; Lawson 
et al., 2004). Low water temperatures 
(<0°C) reduce metabolic rates, reducing 
feeding efficiency, capability to avoid 
