Alaska

 

U. S. Department of the Interior 

Bureau of Land Management 

BLM Alaska Open File Report 101 

BLM/AK/ST-05/015+6600+020 

July 2005 

BLM
 

Abundance and Run Timing of Adult Salmon 

in the Tozitna River, Alaska, 2003 

Tim Sundlov, Carl Kretsinger, and Bob Karlen 
The BLM Mission 

The Bureau of Land Management sustains the health, diversity and productivity of the public lands for the 

use and enjoyment of present and future generations. 

Cover Photo 

Tim Sundlov counts salmon as they exit the weir’s live trap, Tozitna River. BLM photo by Craig McCaa. 

Authors 

Carl Kretsinger and Bob Karlen are fisheries biologists with the BLM Northern Field Office in Fairbanks, 

Alaska. Tim Sundlov, formerly with the Northern Field Office, is a fisheries biologist with the BLM Anchorage 

Field Office in Anchorage, Alaska. 

Disclaimer 

The mention of trade names or commercial products in this report does not constitute endorsement or recommendation for use by the federal government. 

Open File Reports 

Open File Reports issued by the Bureau of Land Management-Alaska present the results of inventories or 

other investigations on a variety of scientific and technical subjects that are made available to the public 

outside the formal BLM-Alaska technical publication series. These reports can include preliminary or incomplete data and are not published and distributed in quantity. 

The reports are available while supplies last from BLM External Affairs, 222 West 7th Avenue #13, Anchorage, Alaska 99513 and from the Juneau – John Rishel Minerals Information Center, 100 Savikko Road, 

Mayflower Island, Douglas, AK 99824, (907) 364-1553. Copies are also available for inspection at the Alaska 

Resource Library and Information Service (Anchorage), the USDI Resources Library in Washington, D. C., 

various libraries of the University of Alaska, the BLM National Business Center Library (Denver) and other 

selected locations. 

A complete bibliography of all BLM-Alaska scientific reports can be found on the Internet at: 

http://www.ak.blm.gov/affairs/sci_rpts.html. Related publications are also listed at 

http://juneau.ak.blm.gov. 
Abundance and Run Timing of Adult Salmon 

in the Tozitna River, Alaska, 2003
­

Tim Sundlov, Carl Kretsinger, and Bob Karlen 

BLM Alaska Open File Report 101 

July 2005 

U. S. Department of the Interior
­

Bureau of Land Management
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ABSTRACT 

The Tozitna River project is a multi-agency study to determine escapement, run 

timing, and age–sex–length(ASL)compositionofadultChinookand summerchum 

salmon in a middle Yukon Basin tributary. A resistance board weir was operated 

from 23 June to 8 August 2003. High stream discharge from the periods of 2 to 

6 July and 26 July to 8 August prevented counting and biological sampling; no 

interpolation was made for these periods. Comparison of run timing to 2002 and 

to other tributaries with similar run timing suggests the majority of the Chinook 

salmon run was counted. The escapement for Chinook salmon was 1,819. Females 

composed 18% of the overall escapement. Age groups 1.2 and 1.3 accounted for 

28% and 52% of the escapement, respectively. The majority of the summer chum 

salmon escapement was not counted, and ASL composition was determined with 

partial escapement data. The escapement for summer chum salmon was 8,487, 

and 34% of the total fish sample was female. Age 0.3 comprised 83% of the chum 

escapement. 

ACKNOWLEDGMENTS 

The authors are grateful to the following individuals for providing data collection and assistance under sometimes challenging field conditions: Harris Hyslop, 

Arnold Marks, Roxanne Kennedy, and Daniel Sam, Tanana Tribal Council, Tanana, 

Alaska; Arthur Niven, Matthew Churchman, Seth Beaudreault, and Kelly Hoover, 

Student Conservation Association; Jason Post (relief crew leader), Chad Thompson, Craig McCaa, Tom Edgerton, and Steve Lundeen, Bureau of Land Management, Fairbanks; Kimberly Elkin and Valli Peterson, Tanana Chiefs Conference, 

Fairbanks; Cliff Schleusner and Beth Spangler, U.S. Fish and Wildlife Service, 

Anchorage; Josh Holbrooke, Talkeetna, Alaska. We also appreciate the assistance of the Alaska Department of Fish and Game, Commercial Fisheries Division, 

Anchorage in the scale sampling analysis and Julie Roberts of the Tanana Tribal 

Council for her assistance with the cooperative agreement. A special thanks goes 

to Mr. Jack Blume for the use of his private airstrip on the Tozitna River. Thanks 

also to Fred Anderson, Taylor Brelsford, David Esse, Craig McCaa, Ingrid 

McSweeny, Robin Mills, Dave Parker, Cliff Schleusner, and Dennis Tol for their 

helpful reviews. The U.S. Fish and Wildlife Service, Office of Subsistence 

Management, Anchorage, provided $27,000 in funding through the Fisheries 

Resource Monitoring Program, under FWS agreement number 70181-3-N163. 

Additional funding was provided by the Bureau of Land Management, Northern 

Field Office, Fairbanks. 

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CONTENTS
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Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i
	

Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i
	

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
	

Study Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
	

Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Weir and Trap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Biological Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Abundance Downstream of the Weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Genetic Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Abiotic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
	

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
	

Weir and Trap Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

 Escapement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 

 Chinook Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

 Summer Chum Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
	

Age–Sex–Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

 Chinook Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

 Summer Chum Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
	

Abiotic Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
	

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
	

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
	

Appendix A. Statistical Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
	

FIGURES 

Figure 1. Location of the Tozitna River weir, Alaska, 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
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Figure 2. Daily discharge (m3/s) for the period 21 June – 11 August 2003, Tozitna River, Alaska . . . . . . 4
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Figure 3. Chinook salmon daily counts with quartiles shown (25%, 50%, and 75%) of cumulative 

escapement for the period 26 June – 26 July, 2003, Tozitna River, Alaska. . . . . . . . . . . . . . . . . 6
­

Figure 4. Map showing the locations of four weirs in Alaska monitoring Chinook salmon escapement on Yukon River tributaries: East Fork of the Andreafsky River, Henshaw Creek, 

Gisasa River, and the Tozitna River.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
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TABLES 

Table 1. Daily and cumulative counts for Chinook and summer chum salmon with quartiles shown 

(25%, 50%, and 75%) of cumulative escapement, Tozitna River, Alaska, 2003. . . . . . . . . . . . . . . . 5
­

Table 2. Proportion and estimated number of female Chinook salmon, Tozitna River, Alaska, 2003. . . . . . . 6
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Table 3. Chinook salmon escapement age composition by stratum and sex, Tozitna River, 

Alaska, 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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Table 4. Chinook salmon mid-eye to fork length (mm) by age and sex, Tozitna River, Alaska, 2003 .. . . . . . 8
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Table 5. Proportion and estimated number of female summer chum salmon, Tozitna River, Alaska, 2003. . . 8
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Table 6. Summer chum salmon escapement age composition by stratum and sex, Tozitna River, 

Alaska, 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
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Table 7. Summer chum salmon mid-eye to fork length (mm) by age and sex, Tozitna River, 

Alaska, 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
­

Table 8. Comparison of preliminary Chinook salmon escapement age composition by sex at the 

East Fork (EF) of Andreafsky River, Gisasa River, Henshaw Creek, and the Tozitna River, 

Alaska, 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
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ii
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INTRODUCTION 

Conservation of salmon in the Yukon River drainage 

is complex and challenging for fisheries managers 

because of several biological and social factors: mixedstocks, large geographic spawning distribution, overlapping and compressed run timing, recent declines in 

escapement, multiple user groups, and multi-agency 

management. Several plans and policies have been 

created to manage the Yukon River salmon escapement 

(see Holder and Senecal-Albrecht 1998). Mostly, the 

Yukon River salmon escapement is managed based on 

sustained yield, defined as the average annual yield 

resulting from an escapement level that can be maintained on a continuing basis. 

In 1998, the Yukon River Comprehensive Salmon 

Plan for Alaska (YRCSPA) was developed to improve 

salmon management in the Yukon Area. On October 1, 

1999, the Federal government joined the State of 

Alaska in managing Yukon River fisheries, assuming 

responsibility for subsistence fisheries management in 

inland navigable waters on, and adjacent to, Federal 

conservation lands (Buklis 2002). 

In 2000, the Bureau of Land Management (BLM) 

in Alaska received a Congressional appropriation for 

Yukon River salmon restoration. In response to this 

appropriation, BLM convened interagency coordination meetings to determine the most beneficial use of 

the funding. Emphasis was placed on funding projects 

that would satisfy both BLM and Yukon River fisheries 

management. Yukon River fisheries managers placed a 

priority on addressing escapement and run timing data 

gaps in the middle Yukon River Sub-Basin for Chinook 

(Oncorhynchus tshawytscha) and summer chum (O. 

keta) salmon, as identified in the YRCSPA (Holder and 

Senecal-Albrecht 1998). After interagency coordination meetings, the BLM chose the Tozitna River. BLM 

had in 1986 designated the Tozitna River an Area of 

Critical Environmental Concern for the protection of 

salmon spawning habitat and had identified acquisition 

of baseline resource data as a management objective 

(BLM 1986; Knapman 1989). In addition to addressing 

datagapsidentifiedintheYRCSPA,salmonescapement 

andruntimingdatacollectedontheTozitnaRiverwould 

assist BLM in fulfilling its management objectives. 

Accurate escapement estimates from spawning tributaries are an important fisheries management tool used 

to assist in the determination of production, marine 

survival, harvest, and spawner recruit relationships 

(Neilson and Geen 1981; Labelle 1994). Although 

aerial escapement surveys on the Tozitna River have 

been conducted by the Alaska Department of Fish and 

Game (ADF&G) since 1959, results of aerial surveys 

are inherently variable (Schultz et al. 1993) and should 

only be used to examine trends in relative escapement 

abundance (Barton 1984). Samples taken at weirs are 

considered to be the least biased and most accurate data 

availableforassessingescapementandagecomposition 

of a mixed stock fishery (Halupka et al. 2000). 

ToaccuratelyassessescapementofChinookandsummer chum in the Middle Yukon Sub-Basin, BLM has 

operated a resistance board weir on the Tozitna River 

since 2002. Objectives of the project are to: 

(1) Determine escapement of Chinook and summer 

chum salmon; 

(2) Describe the run timing of Chinook and summer 

chum salmon; 

(3)EstimaterelativeabundanceofChinookandsummer chum salmon downstream of the weir and 

documentspawninglocationsusingaerialsurvey 

techniques; and 

(4) Estimate age–sex–length (ASL) composition 

of Chinook and summer chum salmon such that 

simultaneous 90% confidence intervals have 

maximum width of 0.20. 

Additional project tasks are to: 

(1) Measure water temperature, turbidity, precipitation, stream height, and determine stream 

discharge; 

(2) Collect Chinook and summer chum salmon fin 

tissue samples for the USFWS genetic stock 

analysis; and 

(3) Recover radio telemetry tags for the National 

Marine Fisheries Service and ADF&G Yukon 

Basin Chinook radio telemetry study. 

STUDY AREA 

The Tozitna River is a large, clear-water, northern 

tributary to the middle Yukon River, with a watershed 

area of 4, 212 km2, 90% of which BLM manages (Figure 1). The watershed originates in the southeastern Ray 

Mountains at 1,676 m and flows southwesterly approximately 207 km to its confluence with the Yukon River 

(1,096 river km), 16 km downstream of Tanana. The 

average yearly precipitation is 32 cm with 62% occurring between June and September. Average monthly 

ambient temperature ranges from –28 to 22 °C.1 The 

11949 – 2003 average monthly temperature and precipitation data 

for the Tanana FAA Airport, Alaska, supplied by Western Regional Climate Center, Reno, Nevada. 

1 
 

 

 

Figure 1. Location of the Tozitna River weir, Alaska, 2003. Figure 1. Location of the Tozitna River weir, Alaska, 2003.
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river is usually ice-free in May, and freeze-up commonly occurs by November (J. Blume, Tozitna River 

homesteader,Fairbanks,personalcommunication).Peak 

discharge is correlated with spring snowmelt or highintensity rainstorms during the summer. Water turbidity 

remains low for the period from late June through early 

August, except for periods of high-intensity precipitation. Fish species in the Tozitna River include Chinook 

salmon, summer and fall chum salmon (Barton, 1984), 

coho salmon (O. kisutch), sockeye salmon (O. nerka), 

Dolly Varden (Salvelinus malma), Arctic grayling (Thymallus arcticus), northern pike (Esox lucius), burbot 

(Lotalota),roundwhitefish(Prosopiumcylindraceum), 

slimy sculpin (Cottus cognatus), and longnose sucker 

(Catostomus catostomus). 

The weir site is approximately 80 km upstream from 

the mouth of the Tozitna River. The weir is located between a downstream riffle and upstream deep meander 

pool. At this location the average wetted width at summer flows is 64 m with an average depth of 0.7 m. This 

site is downstream of most Chinook salmon spawning 

(Kretsinger and Sundlov, in preparation). The crosssection is gradually sloping and the substrate consists 

of sand to cobble. 

2 
 

 

 

 

 

 

 

METHODS 

Weir and Trap 

Salmon escapement, run timing, and composition 

were assessed by counting and sampling fish as they 

passed through the resistance board weir fitted with an 

in-stream live trap. Construction and installation of the 

weir were as described by Tobin (1994). 

The trap was preconstructed (Mackey Lake Co., 

Soldotna, AK) and incorporated into the weir on the 

upstream side. The weir was 65 m in width and was 

operational on 19 June. 

The weir panels, base rail, and trap were visually 

inspected daily for possible escapement openings and 

for removal of accumulated debris. 

Biological Data 

All salmon passing through the weir and live trap 

were counted and identified to species. 

Observers wore polarized sunglasses to facilitate in 

fish identification. The counting schedule was 24 h/d, 7 

d/wk and consisted of one observer for each 6 h period. 

Except for sampling, salmon were counted without 

migration interruption as they proceeded through the 

open trap. Hourly counts were summed to achieve a 

daily count (0000–2359 hours). No interpolation was 

made for missed counting periods during high flows, 

which occurred from 2 to 6 July and 26 July to 8 August. 

Run timing was calculated by the proportion of daily to 

cumulative passage to determine quartile (25%, 50%, 

and 75%) dates and peak and median date of passage. 

The live trap was used to capture salmon for biological sampling. The upstream gate of the trap was closed 

for periods to obtain an adequate sample size. During 

sampling, a dip-net was used to capture salmon in the 

live trap. Salmon were then placed in a partially submerged, aluminum cradle for identifying species and 

sex, measuring, and removing scale(s) and a fin clip. 

Lengths were measured to the nearest 5 mm from mideye to fork of the caudal fin. Morphological maturation 

characteristics were used to determine sex. One scale 

for chum and three scales for Chinook salmon were 

removed from the left side, two rows above the lateral 

line and on a diagonal line from the posterior end of 

the dorsal fin to the anterior end of the anal fin (Anas 

1963; Mosher 1968). Scales were then placed on numbered gum cards and sent to the ADF&G, Division of 

Commercial Fisheries in Anchorage for aging. Aging 

was conducted by creating impressions on cellulose 

acetate cards with a heated hydraulic press (Clutter 

and Whitesel 1956) and then examining the scale annuli patterns (Gilbert 1922). European notation (Koo 

1962) was used to record the ages. A holding pen (4 m 

x 2 m) was constructed adjacent to the trap, and after 

sampling, fish were transferred and held for 0.5 h. The 

holdingpenprovidedsampling recoverywithlowwater 

velocity that facilitated upstream migration. 

Abundance Downstream of the Weir 

An aerial survey was to be conducted late in the run 

to estimate relative abundance of Chinook and summer 

chum salmon downstream of the weir and to document 

spawning locations. However, high stream flows and 

turbidities prevented this from occurring. 

Genetic Samples 

Throughouttherun, dorsalfins were clipped from250 

Chinook and 250 summer chum salmon to provide tissue samples for genetic analysis. Fin clips were placed 

in 2 ml sample vials filled with 95% ethanol and sent 

to the U.S. Fish and Wildlife Service Fish Genetics 

Laboratory, Anchorage for processing. 

Abiotic Measurements 

Watertemperature,turbidity,precipitation,andstream 

height data were collected daily from the period 21 

June to 11 August. Water temperature was monitored 

with an Onset® Tidbit temperature logger at the weir, 

recorded every hour, and summarized as daily mean. 

Turbidity was measured using a Hach 2100P Portable 

Turbidimeter. Precipitation was measured daily for 

the previous 24 h with a rain gauge. A staff gauge was 

surveyed to reference marks at the weir to record relative stream height. 

To determine stream discharge, water velocity was 

measured over a range of staff gauge heights using a 

Price AA current meter. Stream height measurements 

wereusedastheindependentvariabletoestimatestream 

discharge for days when discharge was not measured. 

A stream height versus discharge rating was developed 

by combining the direct discharge measurements and 

computer-simulatedpeakflowsusinglog-logregression 

(Rantz et al. 1982). 

Data Analysis 

Temporally stratified random sampling design (Cochran 1977) was used to collect and analyze ASL data, 

with statistical weeks defining strata. Sample size goals 

were established so that simultaneous 90% interval 

estimates of sex and age composition for each week 

havemaximumwidthsof0.20(Bromaghin1993).Strata 

began on Monday and ended the following Sunday 

3 
 

 

 

 

 

 

m3/s)

with a weekly sample size target of 154 chum and 169 

Chinook salmon sampled uniformly throughout the 

week (25 fish/species/day). All target species within the 

trap at the time of sampling were sampled to avoid bias. 

The first and last sampling strata are greater than a week 

because of low escapement for those periods. Details of 

statistical methods are presented in Appendix A. 

RESULTS 

Weir and Trap Operation 

Weather systems in the summer often bring periods of 

rain to the interior of Alaska and occasionally produce 

high stream discharge, which can submerge weir panels 

and allow salmon to migrate over the weir undetected. 

Two strong precipitation events occurred at the weir in 

early and late July (Figure 2). During the period of 2 to 

3 July, 2.1 cm of rain was recorded. This event resulted 

in submerged weir panels from 2 to 6 July, allowing 

salmon to migrate over the weir undetected. Large trees 

werecaughtontheweirpanels,baserail,andtrapduring 

this period. Entire trees were pulled over the weir and 

pushed off the trap and base rail when possible, but on 

occasion debris had to be separated into smaller pieces 

and removed. On 3 July, a large tree and its root mass, 

caughtbythetrapperpendiculartothecurrent,generated 

enough force to cause the trap’s earth anchors to fail; 

subsequently the trap was washed 300 m downstream. 

Several pickets in four panels broke as the trap moved 

downstream over the weir. The trap was then winched 

upstream back into position and the weir panels were Discharge ((m3/s)
	

160

140

120

100

80

60

40

20

0

repaired. The weir was back in operation on 6 July at 

1830 hours. Another strong system in late July brought 

record rainfall to the central interior. The high stream 

dischargesubmergedthepanelsfrom26Julyto7August, 

a result of 5.8 cm of rain. The weir and trap remained 

in place, but several trees had damaged the trap. On 8 

August it was assumed from previous run timing data 

(Kretsinger and Sundlov, in preparation) that the migration period of summer chum and Chinook salmon was 

ending, and removal of the weir and trap was initiated 

duringanavailablewindowofreducedstreamdischarge. 

The removal was completed on 12 August. 

Escapement 

Chinook salmon 

Chinook salmon (N = 1,819) passed through the weir 

from26Juneto26July(Table1).DailyChinookescapement for the last four complete days of counting was 

< 3% of the cumulative escapement. Gisasa River Chinook have similar run timing (Kretsinger and Sundlov, 

in preparation), and 2003 preliminary data indicated 

that the Gisasa River midpoint was 13 July, a day earlier 

than the Tozitna River. More than 95% of the Gisasa 

River Chinook salmon cumulative escapement had occurred by 25 July, suggesting that the majority of the 

Tozitna River Chinook run was counted. The quartile 

days (25%, 50%, and 75%) of cumulative passage for 

Chinook salmon were 9, 14, and 19 July, respectively 

(Table 1 and Figure 3). Interpolation of Chinook salmon 

escapement for the missed counting period of 2 to 6 

July did not affect run timing date determination. The 

6/21 6/26 7/1 7/6 7/11 7/16 7/21 7/26 7/31 8/5 8/10

Date

Figure 2. Daily discharge (m3/s) for the period 21 June – 11 August 2003, Tozitna River, Alaska. 

4 
 

 

Table 1. Daily and cumulative counts for Chinook and summer chum salmon with quartiles shown (25%, 50%, and 75% ) of cumulative escapement, 

Tozitna River, Alaska, 2003. 

Date 

Chinook Summer chum 

Daily 

Count 

Cumulative 

Count 

Cumulative 

Proportion 

Daily 

Count 

Cumulative 

Count 

6/25 0 0 0.00 2 2 

6/26 2 2 0.00 0 2 

6/27 1 3 0.00 2 4 

6/28 0 3 0.00 0 4 

6/29 0 3 0.00 2 6 

6/30 1 4 0.00 1 7 

7/1 0 4 0.00 0 7 

7/2a 4 8 0.00 1 8 

7/3b 0 8 0.00 0 8 

7/4b 0 8 0.00 0 8 

7/5b 0 8 0.00 0 8 

7/6a 25 33 0.02 3 11 

7/7 21 54 0.03 3 14 

7/8 52 106 0.06 13 

92 

146 

106 

138 

72 

155 

184 

72 

65 

238 

472 

27 

119 

265 

371 

509 

581 

736 

920 

992 

1057 

1295 

1767 

7/9 365 471 0.26 

7/10 140 611 0.34 

7/11 50 661 0.36 

7/12 90 751 0.41 

7/13 153 904 0.49 

7/14 62 966 0.53 

7/15 98 1064 0.58 

7/16 61 1125 0.61 

7/17 46 1171 0.64 

7/18 166 1337 0.73 

7/19 123 1460 0.80 

7/20 92 1552 0.85 741 2508 

7/21 117 1669 0.92 864 3372 

7/22 25 1694 0.93 458 3830 

7/23 12 1706 0.94 829 4659 

7/24 54 1760 0.97 1403 6062 

7/25 46 1806 0.99 1689 7751 

7/26a 13 1819 1.00 736 8487 

Boxed areas encompass second quartile, median, and third quartile.
	 a Portion of daily count missed; no interpolation made.

b Entire daily count missed; no interpolation made.
	

5 
date of peak passage was 9 July (n = 365), and the 7 d 

period between 9 and 15 July accounted for 53% of the 

escapement. The midpoint date of passage for Chinook 

salmon in the lower Yukon River was six days earlier 

than the average date for the midpoint (preliminary 

data, ADF&G 2003a). The Tozitna River escapement 

midpoint was six days earlier than 2002. 

Summer chum salmon 

Summer chum salmon (N = 8,487) migrated through 

the weir from 25 June to 26 July (Table 1). Determinations of run timing and escapement for summer chum 

salmon were not possible because a significant portion 

of the run was missed due to high stream discharge. 

Age–Sex–Length 

Chinook salmon 

Overall, Chinook salmon were predominantly age 

1.3 (51.7%) and 1.2 (27.7%) (Table 3). Females were 

generally older (68% age 1.4 and only 31% age 1.3) 

than males (56% age 1.3 and 34% age1.2). The sex composition of Chinook salmon was 18% female, ranging 

from 3% to 55% throughout weekly sampling stratum 

(Table 2). The age structure of the run was reflected in 

size, with females ranging from 725 to 940 mm (97% 

Table 2. Proportion and estimated number of female 

Chinook salmon, Tozitna River, Alaska, 2003. Standard error in parentheses. 

Strata 

6/26–7/7 

Run 

54 

N 

38 

Percent 

Female 

2.6 (2.2) 

Estimate # 

Females 

1 

7/8–7/14 912 208 11.5 (1.1) 105 

7/15–7/21 703 213 20.2 (1.5) 142 

7/22–7/28 150 42 54.8 (4.1) 82 

Total 1819 501 18.2 (0.9) 330 

≥ 750 mm) and the smaller males ranging from 330 to 

975 mm (18% ≥ 750 mm) (Table 4). Mean length of 

females age 1.3 and 1.4 was greater than that of sameage males. 

Summer chum salmon 

Overall, chum salmon were predominantly age 0.3 

(83%) (Table 6). The sex composition of summer chum 

salmon was 34% female, ranging from 0% to 37% 

throughout weekly sampling stratum (Table 5). Female 

chum salmon ranged from 500 to 640 mm and male 

chum salmon ranged from 510 to 675 mm (Table 7). 

Figure 3. Chinook salmon daily counts with quartiles shown (25%, 50%, and 75%) of cumulative escapement 

for the period 26 June – 26 July, 2003, Tozitna River, Alaska. 

0

50

100

150

200

250

300

350

400

6/26 6/29 7/2 7/5 7/8 7/11 7/14 7/17 7/20 7/23 7/26

Date

Count

75%

25%

50%

6 
Table 3. Chinook salmon escapement age composition by stratum and sex, Tozitna River, Alaska, 2003. Standard error 

in parentheses.

Strata Run Sex 

Brood Year and Age

2000 1999 1998 1997 1996 Total 

1.1 1.2 1.3 1.4 1.5 

N % N % N % N % N % N % 

6/26–7/7 54 

Males 0 0.0 9 (7.2) 23.7 22 (8.2) 57.9 6 (6.1) 15.8 0 0.0 37 97 Females 0 0.0 0 0.0 1 a 2.6 0 0.0 0 0.0 1 3 

Subtotal 0 0.0 9 (7) 23.7 23 (8) 60.5 6 (6) 15.8 0 0.0 38 100 

7/8–7/14 912 

Males 1 (.5) 0.5 61 (3.5) 29.3 109 (3.6) 52.4 13 (1.9) 6.3 0 0.0 184 89 Females 0 0.0 0 0.0 12 (10.4) 5.8 12 (10.4) 5.8 0 0.0 24 12 Subtotal 1 (.5) 0.5 61 (3.2) 29.3 121 (3.4) 58.2 25 (2.3) 12.1 0 0.0 208 100 

7/15–7/21 703 

Males 1 (.6) 0.5 61 (3.7) 28.6 92 (3.8) 43.2 15 (2.2) 7.0 1 (0.6) 0.5 170 80 Females 0 0.0 0 0.0 11 (6.7) 5.2 31 (6.9) 14.6 1 (2.3) 0.5 43 20 Subtotal 1 (.5) 0.5 61 (3.1) 28.6 103 (3.4) 48.4 46 (2.8) 21.6 2 (0.7) 1.0 213 100 

7/22–7/28 150 

Males 0 0.0 8 (11.6) 19.0 8 (11.6) 19.0 3 (8.6) 7.1 0 0.0 19 45 Females 0 0.0 0 0.0 4 (8.1) 9.5 19 (8.1) 45.2 0 0.0 23 55 Subtotal 0 0.0 8 (6.1) 19.0 12 (7.1) 28.5 22 (7.8) 52.3 0 0.0 42 100 

Subtotal 

Males 2 (.5) 0.4 139 (4.9) 27.7 231 (5.0) 46.1 37 (3.3) 7.4 1 (0.4) 0.2 410 82 Females 0 0.0 0 0.0 28 (8.8) 5.6 62 (8.9) 12.4 1 (1.4) 0.2 91 18 

Total 1819 2 0.4 139 (3.6) 27.7 259 (4.1) 51.7 99 (3.4) 19.8 2 (0.4) 0.4 501 100 

aStandard error was not calculated because of low sample size. 

7 
 

 

 

 

 

 

 

 

Abiotic Measurements 

Water temperature (°C) at the weir ranged from 6.1 to 

14.0 and averaged 9.6. Turbidity (NTU) ranged from 

0.8 to 56.9 and averaged 3.8. Total precipitation for the 

period was 10.2 cm. Stream height (cm) fluctuated from 

Table 4. Chinook salmon mid-eye to fork length (mm) 

by age and sex, Tozitna River, Alaska, 2003. 

Age 

1.1 

Sex 

Male 

N 

2 

Mean 

378 

SE 

48 

Range 

330–425 

Female 0 – – – 

1.2 Male 139 518 4.3 400–755 

Female 0 – – – 

1.3 Male 231 703 3.5 500–850 

Female 28 778 7.1 725–895 

1.4 Male 37 793 15 440–975 

Female 62 859 5.2 780–940 

1.5 Male 1 805 – 805 

Female 1 865 – 865 

Table 5. Proportion and estimated number of female 

summer chum salmon, Tozitna River, Alaska, 2003. 

Standard error in parentheses. 

Strata 

6/26–7/7 

Run 

14 

N 

10 

Percent 

Female 

0.0 

Estimated # 

Females 

0 

7/8–7/14 722 162 36.4 (1.8) 263 

7/15–7/21 2636 234 36.8 (0.9) 969 

7/22–7/28 5115 149 32.2 (0.7) 1648 

Total 8487 555 33.9a (0.5) 2880a 

aCalculation were determined with partial escapement data 

because of high stream discharge. 

Table 7. Summer chum salmon mid-eye to fork length 

(mm) by age and sex, Tozitna River, Alaska, 2003. 

SE = Standard Error 

Age 

0.2a 

Sex 

Male 

N 

3 

Mean 

560 

SE 

8.7 

Range

545–575 

Female 2 530 15 515–545

 0.3a Male 296 575 1.6 510–655 

Female 165 550 2.1 500–620

 0.4a Male 52 608 4.4 525–675 

Female 22 590 5.4 540–640

 0.5a Male 11 626 9.6 575–675 

Female 4 605 9.6 580–620 

aCalculation were determined with partial escapement data 

because of high stream discharge. 

98 to 207 and averaged 130. Daily discharge (m3/s) 

ranged from 12 to 146 and averaged 37 (Figure 2). 

DISCUSSION 

Assessment of sex and age composition of salmon 

stocks offers insight intotheeffects offisheries managementregulationsandenvironmentalinfluences.In2003, 

there were four weirs in Alaska monitoring Chinook 

salmon escapement on Yukon River tributaries: East 

Fork of the Andreafsky River, Henshaw Creek, Gisasa 

River, and the Tozitna River (Figure 4). These weirs 

provide the most accurate method for assessing sex 

and age composition. This section discusses the low 

proportion of females in escapement data at these four 

weirs, following the conclusion in ADF&G (2002) and 

Wiswar (2000) that the proportion of females should be 

taken into account when assessing escapement. 

TheTozitnaRiver hadthelowestproportionof female 

Chinook salmon of the four Yukon River tributary weirs 

monitoring Chinook salmon in 2002 and 2003 (Table 

8), at 13% and 18%, respectively. Although the 2003 

Tozitna River Chinook escapement was 21% above that 

of 2002, the proportion of females was only 5% higher. 

The low proportion of female Chinook salmon is not 

unique to the Tozitna River and has been documented 

for other Yukon River tributaries. From 1996 to 1998, 

the Gisasa River averaged 20% female, ranging from 

17% to 23%, and the East Fork of the Andreafsky 

River from 1994 to 1998 averaged 35% female, 

ranging from 25% to 42% (Wiswar 2000, Tobin and 

Harper 1999, USFWS 2003). In 2003, preliminary data 

(ADF&G 2003b) indicated that three of the four Yukon 

tributary weirs had sex ratios favoring males (61% to 

82%; Table 8). 

Recently, there has been speculation that the disease-induced mortality caused by the internal parasite 

Icthyophonus hoferi has played a role in the selective 

mortality of female Chinook salmon in the Yukon River. 

Kocan et al. (2003) reported that significantly more 

Yukon River females than males were infected during 

1999 –2002. However, in 2003 the infection in females 

was not significantly different from males, indicating 

this may not be a plausible explanation for the low 

number of female Chinook salmon. 

Low female Chinook sex ratios at weir escapement 

projects are largely the result of the low proportion 

of age 1.4 females, the predominate age class among 

females (Harper and Watry 2001). In 2003, preliminary 

data indicated that age 1.4 female Chinook salmon represented 12% to 29% of escapement at the four Yukon 

tributary weirs monitoring Chinook salmon (Table 8) 

8 
 

 

 

 

 

 

 

 

 

 

Table 6. Summer chum salmon escapement age composition by stratum and sex, Tozitna River, Alaska, 2003. 

Standard error in parentheses. 

Strata Run Sex 

Brood Year and Age 

2000 1999 1998 1997 Total 

0.2 0.3 0.4 0.5 

N % N % N % N % N % 

6/26–7/7 14 

Males 0 0.0 6 (16.3) 60.0 4(16.3) 40.0 0 0.0 10 100 

Females 0 0.0 0 0.0 0 0.0 0 0.0 0 0.0 

Subtotal 0 0.0 6 (16.3) 60.0 4 (16.3) 40.0 0 0.0 10 100 

7/8–7/14 722 

Males 1 (1) 0.6 83 (3.9) 51.2 15 (3.5) 9.3 4 (1.9) 2.5 103 64 

Females 0 0.0 4 9 (4.9) 30.2 7 (4.2) 4.3 3 (2.9) 1.9 59 36 

Subtotal 1 (.6) 0.6 132 (3.1) 81.4 22 (2.7) 13.6 7 (1.6) 4.4 162 100 

7/15–7/21 2636 

Males 1 (.7) 0.4 119 (3.3) 50.9 22 (2.9) 9.4 6 (1.6) 2.6 148 63 

Females 1 (1.2) 0.4 71 (4.1) 30.3 13 (3.9) 5.6 1 (1.2) 0.4 86 37 

Subtotal 2 (.6) 0.8 190 (2.6) 81.2 35 (2.3) 15.0 7 (1.1) 3.0 234 100 

7/22–7/28 5115 

Males 1 (1) 0.7 88 (3.3) 59.0 11 (3.1) 7.4 1 (1) 0.7 101 68 

Females 1 (2.1) 0.7 45 (3.5) 30.2 2 (2.9) 1.3 0 0.0 48 32 

Subtotal 2 (1) 1.4 133 (2.5) 89.2 13 (2.3) 8.7 1(.7) 0.7 149 100 

Subtotal Males 3 (1.1) 0.5 296 (3.4) 53.3 52 (3.2) 9.4 11 (1.3) 2.0 362 66 

Females 2 (1.7) 0.4 165 (3.9) 29.7 22 (3.4) 4.0 4 (1.1) 0.7 193 34 

Total 8487 5 (1) 0.9 461 (2.6) 83.0 74 (2.4) 13.4 15 (1.0) 2.7 555 100 

Table 8. Comparison of preliminary Chinook salmon escapement age composition by sex at the East Fork 

(EF) of Andreafsky River, Gisasa River, Henshaw Creek, and the Tozitna River, Alaska, 2003. 

Location 

EF Andreafsky 

Weir 

Yukon River 

(km) 

167a 

N 

533d 

Sex 

Males 

Brood year and Age 

2000 1999 1998 1997 1996 Total 

1.1 1.2 1.3 1.4 1.5 

% 

0.4 

% 

12.7 

% 

33.2 

% 

6.0 

% 

0.0 

% 

52.3 

Females 0.0 3.2 17.3 26.1 1.1 47.7 

Subtotal 0.4 15.9 50.5 32.1 1.1 100.0 

Gisasa 

Weir 818b 472d 

Males 0.2 5.5 51.3 4.9 0.0 61.9 

Females 0.0 0.0 18.2 18.8 1.1 38.1 

Subtotal 0.2 5.5 69.5 23.7 1.1 100.0 

Henshaw 

Weir 818b 304d 

Males 1.6 19.4 35.5 4.3 0.0 60.9 

Females 0.0 0.0 8.6 28.9 1.6 39.1 

Subtotal 1.6 19.4 44.1 33.2 1.6 100.0 

Tozitna 

Weir 1096c 501d,e 

Males 0.4 27.7 46.1 7.4 0.2 81.8 

Females 0.0 0.0 5.6 12.4 0.2 18.2 

Subtotal 0.4 27.7 51.7 19.8 0.4 100.0 

a Kilometers from the mouth of the Andreafsky River to the mouth of the Yukon River. 

b Kilometers from the mouth of the Koyukuk River to the mouth of the Yukon River. 

c Kilometers from the mouth of the Tozitna River to the mouth of the Yukon River. 

d Preliminary escapement age data from ADF&G, 2003. 

e Preliminary escapement age data from BLM, 2003. 

9 
 

 

 

 

 

 

 

 

 

Figure 4. Map showing the locations of four weirs in Alaska monitoring Chinook salmon 

and 39% in the lower commercial harvest (ADF&G 

2003b). The Tozitna River escapement in 2003 had the 

lowest proportion of age 1.4 female Chinook at 12%. 

ASL composition is not available for the subsistence 

harvest, although in the lower Yukon River it is assumed 

to be similar to the lower commercial harvest, since the 

same gear is used (Menard 1996). 

Chinook salmon harvest in the Yukon River is comprised predominately of commercial and subsistence 

gillnet fisheries. In 2003, the majority of commercial 

harvest (91%; preliminary data, ADF&G 2003) occurred in the lower Yukon River, where gillnet mesh 

size (stretched) was restricted to eight inch or greater. 

Fully 87% of the Chinook salmon subsistence harvest 

in 2002 was taken with gillnets, and 44% of the harvest 

occurred in the lower Yukon River (Brase and Hamner 

2003). There were no gillnet mesh restrictions for the 

subsistence fishery in 2003, although it is thought the 

majority of Yukon River gillnet subsistence fishers use 

eightinchorgreaterbecausethisisarequirementneeded 

to participate in the commercial fishery. 

Yukon Chinook populations are heterogeneous in 

age, size, and sex, and all individuals are not equally 

vulnerable to harvest. For example, Tozitna River 

female Chinook exhibited sexual dimorphism, with 

females longer than males of the same age (Table 4). 

Large-mesh gillnets used during unrestricted meshsize openings select older, larger Chinook salmon, 

which include a much larger proportion of females 

than the salmon caught during small mesh-size periods 

(ADF&G 2002). Salmon encounter gillnets from the 

Yukon River mouth to river km 493 with cumulative 

harvest effects, as the largest and oldest fish are continuously selected as they migrate upstream. The Tozitna 

River escapement project is the furthest upstream of 

the four Yukon River tributary weirs, and in 2002–2003 

(Table8)ithadthelowestfemalesexratioandthelowest 

proportion of age 1.4 female Chinook salmon. 

Another possible explanation of low abundance of 

age 1.4 female Chinook is their possible differential 

exposuretooceanmortality.Theaverageageofmaturity 

for Yukon River Chinook is 6.12 years for females and 

5.64 years for males (McBride et al. 1983). Therefore, 

females’ longer duration of ocean residency may increase exposure to mortality. 

Preliminaryresultsindicatethattheselectiveharvestof 

largersalmoninthecommercialandsubsistencefisheries 

and/ordifferentialmortalitymayhavecontributedtothe 

escapement on Yukon River tributaries: East Fork of the Addreafsky River, Henshaw Creek, 

Gisasa River, and the Tozitna River. Map is adapted from Holder and Senecal-Albrecht (1998).
	

10 
 

 

 

low proportionof femaleChinooksalmonintheTozitna 

River escapement. Reductionand removalof the largest 

and potentially most successful spawners reduces the 

overall fitness of a population and reduces the ability 

to compensate for environmental and anthropogenic 

impacts(Livingston1998). Furthermore,Ricker(1981) 

argues that selective harvest by fisheries changes the 

genetic basis for maturation and can result in a reduction in adult size. Although long-term weir escapement 

data is not available on the Tozitna River and there is no 

conclusive data for selective harvest and/or differential 

mortality, the low proportion of returning females warrants further evaluation and ongoing monitoring. 

11 
 

 

 

LITERATURE CITED
­

ADF&G (Alaska Department of Fish and Game). 

2002. 2002 Yukon Area subsistence, personal use, and 

commercial salmon fisheries outlook and management strategies. Alaska Department of Fish and Game, 

Division of Commercial Fisheries, Regional Information Report Number 3A02-35, Anchorage, Alaska. 

ADF&G. 2003a. Preliminary 2003 Yukon Area Chinook and summer chum salmon fishery summary. 

Alaska Department of Fish and Game, Division of 

Commercial Fisheries, Anchorage, Alaska. 

ADF&G. 2003b. 2003 preliminary age–sex–length 

spreadsheet [unpublished]. Alaska Department of Fish 

and Game, Division of Commercial Fisheries, Anchorage, Alaska. 

Anas, R.E. 1963. Red salmon scale studies. Pages 

114-116 in International North Pacific Fisheries Commission Annual Report, 1961. Vancouver, British 

Columbia. 

Barton, L.H. 1984. A catalog of Yukon River salmon 

spawning escapement surveys. Alaska Deparment of 

Fish and Game, Technical Data Report 121, Juneau, 

Alaska. 

BLM (Bureau of Land Management). 1986. Resource 

management plan and record of decision for the Central 

Yukon planning area. Bureau of Land Management, 

Kobuk District Office, Document Number BLM-AKPT-86-031-1610-026, FF085208, Fairbanks, Alaska. 

Brase, A.L.J., and H.H. Hamner. 2003. Subsistence and 

personal use salmon harvests in the Alaska portion of 

the Yukon River drainage, 2002. Alaska Department 

of Fish and Game, Division of Commercial Fisheries, Regional Information Report Number 3A03-13, 

Anchorage, Alaska. 

Bromaghin, J.F. 1993. Sample size determination for 

interval estimation of multinomial probabilities. The 

American Statistician 47(3):203–206. 

Buklis, L. S. 2002. Subsistence fisheries management 

of federal public lands in Alaska. Fisheries 27(7):10– 

18. 

Clutter, R.I., and L.E. Whitesel. 1956. Collection and 

interpretation of sockeye salmon scales. Bulletin of 

the International Pacific Salmon Fisheries Commission No. 9. New Westminster, British Columbia. 

Cochran, W.G. 1977. Sampling techniques, 3rd edition. John Wiley and Sons, New York. 

Gilbert, C.H. 1922. The salmon of the Yukon River. 

Bureau of Fisheries, Bulletin 38:317–322, Washington. 

Halupka, K.C., M.D. Bryant, M.F. Wilson, and F.H. 

Everest. 2000. Biological characteristics and population status of anadromous salmon in Southeast Alaska. 

General Technical Report: PNW-GTR-468, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Juneau, Alaska. 

Harper, K.C., and C. B. Watry. 2001. Abundance and 

run timing of adult salmon in the Kwethluk River, 

Yukon Delta National Wildlife Refuge, Alaska, 2000. 

U.S. Fish and Wildlife Service, Kenai Fishery Resources Office, Fishery Data Series Number 2001-4, 

Kenai, Alaska. 

Holder, R.R., and D. Senecal-Albrecht (compilers). 

1998. Yukon River comprehensive salmon plan for 

Alaska. Alaska Department of Fish and Game, Juneau, 

Alaska. 

Knapman, L.N. 1989. Watershed activity plan for the 

Tozitna River watershed Area of Critical Environmental Concern. Bureau of Land Management, Kobuk 

District Office, Document Number BLM-AK-PT-89-

013-7200-070, Fairbanks, Alaska. 

Kocan, R., P. Hershberger, and J. Winton. 2003. Effects of Ichthyophonus on survival and reproductive 

success of Yukon River Chinook salmon. Federal Subsistence Fishery Monitoring Program, Final Project 

Report Number FIS 01-200. U.S. Fish and Wildlife 

Service, Office of Subsistence Management, Fishery 

Information Services Division, Anchorage, Alaska. 

Koo, T.S.Y. 1962. Age designation in salmon. Pages 

37–48 in T.S.Y. Koo, editor. Studies of Alaska red 

12 
salmon. University of Washington Publications in 

Fisheries, New Series, Volume I, Seattle, Washington. 

Kretsinger, C. F., and T.J. Sundlov. In preparation. 

Abundance and run timing of adult salmon, with 

observations of streamflow and water quality, in the 

Tozitna River Area of Critical Environmental Concern, 

Alaska 2001. Bureau of Land Management, Northern 

Field Office, Fairbanks, Alaska. 

Labelle, M. 1994. A likelihood method for estimating 

Pacific salmon based on fence counts and mark-recapture data. Canadian Journal of Fisheries and Aquatic 

Sciences 51:552–556. 

Livingston, P.A. (editor). 1998. Draft Bering Sea ecosystem research plan. Alaska Fisheries Science Center, Seattle, Washington. 

McBride, D.N., H.H. Marshall, and L.S. Bulkis. 1983. 

Age, sex and size of Yukon River salmon catch and 

escapement, 1982. Alaska Department of Fish and 

Game, Technical Data Report 90, Juneau, Alaska. 

Menard, J. 1996. Age, sex and length of Yukon River 

salmon catches and escapements, 1994. Alaska Department of Fish and Game, Commercial Fisheries 

Management and Development Division, Regional 

Information Report Number 3A96-16, Anchorage, 

Alaska. 

Mosher, K. 1968. Photographic atlas of sockeye salmon scales. Fishery Bulletin 67:243–280. 

Neilson, J.D., and G.H. Geen. 1981. Enumeration of 

spawning salmon from spawner residence time and 

aerial counts. Transactions of the American Fisheries 

Society 110:554–556. 

Rantz, S.E., et al. 1982. Measurement and computation 

of streamflow, volume 1 and 2 of Water-Supply Paper 

2175. U.S. Geological Survey, Washington, DC. 

Ricker, W.E. 1981. Changes in the average size and 

average age of Pacific salmon. Canadian Journal of 

Fisheries and Aquatic Sciences 38:1636–1656. 

Schultz, K.C., R.R. Holder, L.H. Barton, D.J. Bergstrom, C. Blaney, G.J. Sandone, and D.J. Schneiderhan. 1993. Annual management report for subsistence, 

personal use, and commercial fisheries of the Yukon 

area, 1992. Alaska Department of Fish and Game, Regional Information Report Number 3A93-10, Anchorage, Alaska. 

Tobin, J.H. 1994. Construction and performance of a 

portable resistance board weir for counting migrating 

adult salmon in rivers. U.S. Fish and Wildlife Service, 

Kenai Fishery Resource Office, Alaska Technical Report Number 22, Kenai, Alaska. 

Tobin, J.H. III, and K.C. Harper. 1999. Abundance and 

run timing of adult salmon in the East Fork Andreafsky River, Yukon Delta National Wildlife Refuge, 

Alaska, 1998. US. Fish and Wildlife Service, Kenai 

Fishery Resources Office, Alaska Fishery Data Series 

Number 99-3, Kenai, Alaska. 

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Fork Andreafsky River weir, Chinook salmon percent 

female, 1994–1998 spreadsheet [unpublished]. Kenai 

Fishery Resource Office, Kenai, Alaska. 

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adult salmon in the Gisasa River, Koyukuk National 

Wildlife Refuge, Alaska, 2000. U.S. Fish and Wildlife 

Service, Fairbanks Fishery Resource, Alaska Fisheries 

Data Series Number 2000-1, Fairbanks, Alaska. 

13 
 

 

 

 

 

 

 

 

 

APPENDIX 1. STATISTICAL METHODS 

Within a given stratum m, the proportion of species i passing the weir that are of sex j and age k 

(Pijkm) is estimated as 

Pijkm = nijkm / ni++m 

where nijkm denotes the number of fish of species i, sex j, and age k sampled during stratum m and a 

subscript of “+” represents summation over all possible values of the corresponding variable, e.g., ni++m 

denotes the total number of fish of species i sampled in stratum m. The variance of Pijkm is estimated 

as 

(1 - Pijkm v (P – 1) ijkm ) = (1 - ni++m / Ni++m) (Pijkm ) / ni++m 

where Ni++m denotes the total number of species i fish passing the weir in stratum m. The estimated 

number of fish of species i, sex j, age k passing the weir in stratum m (Nijkm) is 

Nijkm = Ni++m Pijkm 

with estimated variance 

) = N2 v(N ) ijkm i++m v(Pijkm 

Estimates of proportions for the entire period of weir operation are computed as weighted sums of 

the stratum estimates, i.e., 

Pijk = Σ (Ni++m / Ni+++) Pijkm m 

and 

v (Pijk) = Σ (Ni++m / Ni+++)2 v (Pijkm) m 

The total number of fish in a species, sex, and age category passing the weir during the entire period 

of operation was estimated as 

Nijk ijkm = Σ Nm 

with estimated variance 

v(N ) = Σ v (N ) ijk ijkm m 

14