Berkman et al.: Effects on survival of Oncorhynchus tshawytscha in rivers of Southeast Alaska 203 
of Chinook salmon and long-term data exists for both 
systems. These rivers are 2 of the 11 indicator systems 
selected by the Alaska Department of Fish and Game 
(ADFG) and Fisheries and Oceans Canada to be sam- 
pled and studied as part of in-depth stock assessments 
for Chinook salmon (ADFG CSRT!). This monitoring 
program was initiated because of statewide and regional 
stock declines for this species and the need for increased 
information for run forecasting (ADFG CSRT"’). 
The Chilkat River is a moderately sized, glacially fed river 
that originates at the Chilkat Glacier in British Columbia, 
Canada, and drains into Lynn Canal near Haines, Alaska 
(ADFG CSRT!; Elliott and Peterson”) (Fig. 1). This river 
supports the fifth-largest stock of Chinook salmon in 
SEAK, with an annual spawning run of about 4000 large 
(>660 mm in mid-eye fork length) fish (ADFG CSRT"’). 
Adult Chinook salmon from the Chilkat River typically 
grow in the inside marine waters of northern SEAK (Elliott 
and Peterson’). 
The Stikine River is a transboundary river originating 
in British Columbia and draining near Wrangell, Alaska. 
Chinook salmon in this system are jointly managed by the 
ADFG and Fisheries and Oceans Canada (Jaecks et al.°) 
(Fig. 1). The Stikine River supports the second-largest stock 
of Chinook salmon in SEAK, with an annual spawning run 
of about 22,000 large fish (Pahlke*; ADFG CSRT"). Adult 
Chinook salmon from the Stikine River primarily grow in 
the Gulf of Alaska and the Bering Sea (Pahlke et al.°). 
Chinook salmon in both rivers have a stream-type life 
history, where juveniles reside in fresh water for 1 year 
before migrating downstream as age-2 smolts (Quinn, 
2005; ADFG CSRT"’). The age structure for returning 
adults was similar for Chinook salmon from the Stikine 
and Chilkat Rivers, with most adults returning to 
fresh water after 2—4 years in the marine environment 
(Chapell®). Sampling effort and design of surveys to esti- 
mate smolt abundance and adult return were similar 
for work in both rivers. However, surveys of freshwater 
juvenile Chinook salmon conducted in the fall and spring 
in the Chilkat River allowed assessment of additional 
freshwater processes (overwinter survival and smolt pro- 
duction); as a result, data from each river system were 
analyzed separately. 
? Elliott, B. W., and R. L. Peterson. 2018. Production and harvest 
of Chilkat River Chinook and coho salmon, 2018-2019. Alaska 
Dep. Fish Game, Reg. Oper. Plan SF.1J.2018.10, 47 p.. [Available 
from website.] 
3 Jaecks, T,, P. Richards, S. J. H. Power, P. Etherton, and I. Boyce. 
2015. Estimation of smolt production and harvest of Stikine 
River Chinook salmon, 2015. Alaska Dep. Fish Game, Reg. Oper. 
Plan SF.1J.2015.04, 18 p. [Available from website.] 
* Pahlke, K. A. 2010. Escapements of Chinook salmon in Southeast 
Alaska and transboundary rivers in 2008. Alaska Dep. Fish Game, 
Fish. Data Ser. 10-71, 38 p. [Available from website.] 
» Pahlke, K. A., P. Richards, and P. Etherton. 2010. Production of 
Chinook salmon from the Stikine River, 1999-2002. Alaska Dep. 
é Fish Game, Fish. Data Ser. 10-03, 16 p. [Available from website. ] 
Chapell, R. S. 2013. Production, escapement, and juvenile tag- 
ging of Chilkat River Chinook salmon in 2010. Alaska Dep. Fish 
Game, Fish. Data Ser. 13-25, 48 p. [Available from website. ] 
Chilkat River 
Biological data We estimated values for several biologi- 
cal attributes for Chinook salmon in the Chilkat River by 
using data from 2 efforts conducted by the ADFG: a tagging 
study in which coded-wire tags (CWTs) are attached to 
juveniles in both the fall and spring (we used data for the 
period 2000-2011) and a mark-recapture program that 
targeted adults (we used data for the period 2002-2016) 
(Elliott and Power’; Elliott and Peterson”). The biological 
factors estimated were marine survival, the rate of sur- 
vival from freshwater emigration to return for spawning 
(BYs: 1999-2009); smolt abundance, the number of juve- 
nile salmon in the spring; smolt mean mid-eye fork length 
(in millimeters); parr abundance, the number of juvenile 
salmon in the fall; parr mean mid-eye fork length (in milli- 
meters); and overwinter survival, the survival rate of juve- 
nile salmon from the fall to the spring. 
The mark-recapture survey was executed by using a 
2-event sampling scheme for a closed population. For the 
first sampling event, adult Chinook salmon were captured 
and marked between 10 June and 24 July of each survey 
year in the lower Chilkat River. For the second sampling 
event, adults were captured from August through mid- 
September in each survey year in the 3 principal spawn- 
ing tributaries of the Chilkat River, the Kelsall, Tahini, 
and Klehini Rivers. Chinook salmon captured during 
sampling events were measured to the nearest 5-mm 
interval of mid-eye fork length, their sex was determined, 
scales were sampled, and the fish were inspected for the 
presence or absence of an adipose fin (small fin located 
between the dorsal and caudal fins). Fish that did not have 
an adipose fin were processed and scanned with a CWT 
detector (Elliott and Power’). 
Data from both sampling events were tabulated, and 
Petersen estimators were used to estimate abundance, 
given that all assumptions of the model were met during 
sampling (Seber, 1982). Size, age, and sex selectivity 
in sampling data were evaluated by using Kolomogorov— 
Smirnov tests. If selectivity was present in data from 
either the first or second sampling event, a stratified 
Petersen model was used to eliminate variability in cap- 
ture probability (Elliott and Power’). Adult abundance 
was estimated by using results from both the mark- 
recapture and CWT surveys. Marked adult fish from the 
Chilkat River were primarily recovered in seasonal troll, 
SEAK sport, drift gill-net, or purse seine fisheries during 
annual surveys conducted by the ADFG, which aims to 
sample 20% of the catch of Chinook salmon in SEAK 
(Elliott and Peterson”). Marine survival was calculated 
by using the estimated values for smolt and adult abun- 
dance associated with each BY. 
The CWT survey of juvenile Chinook salmon was initi- 
ated in 2000 to estimate parr and smolt abundance, smolt 
emigration, and marine catch of the stock in the Chilkat 
’ Elliott, B. W., and S. J. H. Power. 2015. Chilkat River Chinook 
salmon escapement studies in 2015. Alaska Dep. Fish Game, 
Reg. Oper. Plan SF.1J.2015.13, 31 p. [Available from website.] 
