NOAA Technical Memorandum NMFS-AFSC-30

Distribution and Habitat of Adult

Salmon in the Situk River, Alaska:

Potential Impacts of Flooding from

Russell Fiord

by

J. M. Lorenz

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

January 1994
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service’s Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific

and technical publications when complete formal review and editorial

processing are not appropriate or feasible. Documents within this series

reflect sound professional work and may be referenced in the formal

scientific and technical literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC, series established in 1970 by

the Northwest Fisheries Center. The new NMFS-NWFSC series will be used

by the Northwest Fisher/es Science Center.

This document should be cited as follows:.

Lorenz, J. M. 1994. Distribution and habitat of adult salmon in the

Situk River, Alaska: Potential impacts of flooding from Russell Fiord.

U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-30, 27 p.

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
NOAATechnical Memorandum NMFS-AFSC-30

Distribution and Habitat of

Adult Salmon in the Situk River, Alaska:

Potential Impacts of Flooding from

Russell Fiord

by

J. M. Lorenz

Auke Bay Laboratory

Alaska Fisheries Science Center

11305 Glacier Highway

Juneau AK 99801-8626

U.S. DEPARTMENT OF COMMERCE

Ronald H. Brown, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries

January 1994
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iii

ABSTRACT

Distribution and habitat of adult sockeye (Oncorhynchus

nerka), chinook (0. tshawytscha), and pink (0. gorbuscha)

salmon in the Situk River, Alaska, were studied to determine

the effects of predicted flooding from Russell Fiord. Over

4,500 sockeye and 122 chinook salmon were tagged at a weir in

the lower Situk River between 14 June and 21 August 1988.

Surveys were done periodically to estimate the number of adult.

salmon in the survey area and to determine their habitat use

 and migration timing from late June to late September.% All

three species used similar habitat while migrating upstream.

Most tagged sockeye salmon (>90%) emigrated rapidly (median =

11.2 days in transit) and steadily from the flood corridor,,/"

whereas most tagged chinook salmon (>90%) emigrated more 

slowly (median = 51.7 days) from the corridor, often holding

for days in pools or deep glides. Visual estimates of the

number of pink salmon indicated that only about 60% emigrated

from the flood corridor. Salmon used a wide range of habitat

conditions for spawning, --and spawning areas were nearly always

segregated by species. Spawning habitat characteristics of

sockeye salmon differed significantly from those of chinook

salmon. Flooding from Russell Fiord would inundate salmon

migration and spawning areas in the Situk River and probably

cause a short-term decline in salmon production. Long-term

impacts on salmon production are likely to depend on the

quality and availability of habitat after the river channel

has stabilized.

V

CONTENTS

INTRODUCTION . . . . . .

Background . . . . .

METHODS . . . . . . . . . . . . . .

Fish Tagging . . . . . . . . .

Migration Studies . . . . . .

Spawning Studies . . . . . . . .

RESULTS. . . . . . . . .

Sockeye Salmon . . .

Chinook Salmon . . .

Pink Salmon . . . .

DISCUSSION

Habitat Utilization

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Effects of Flooding on Fish and Habitat

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ACKNOWLEDGMENTS . . . . . . . . . . . . . . .

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INTRODUCTION

Pacific salmon (Oncorhynchus spp.) from the Situk River

near Yakutat, Alaska (Fig. l), support valuable commercial,

recreational, and subsistence fisheries that may be in

jeopardy because of an imminent and radical change in river

hydrology: the Hubbard Glacier, about 30 km north of

Yakutat, is predicted to dam Russell Fiord (Fig. 1) within a

decade, causing water from the fiord to flood into the Situk

River (Mayo 1988; Trabant et al. 1991). Clark and Paustian 

(1989) predict that overflow from Russell Fiord into the

Situk River watershed will result in a colder, more turbid

river with discharge 20 times that of the present Situk River

(Mayo 1988).

To determine how the predicted flooding may affect adult

salmon and their habitat in the Situk River, a baseline

evaluation of their present distribution and habitat use was

needed. This study describes migratory timing, spawning

distribution, and habitat characteristics of adult sockeye

(0. nerka), chinook (0. tshawytscha), and pink salmon

(0. gorbuscha) in the Situk River in 1988; it also speculates

on how predicted flooding may affect adult salmon distribution and abundance in the Situk River.

Background

Over the last 7,000 years, Russell Fiord has repeatedly

been dammed by glaciers and has overflowed into the Situk

River watershed (Mayo 1988; Trabant et al. 1991). The most

recent overflow from the fiord was a result of damming by the

Nunatak Glacier (Fig. 1) that ended 100-120 years ago

(de Laguna et al. 1964; Clark and Paustian 1989). In 1986,

water was impounded for 132 days(29 May-8 October) in

Russell Fiord by an ice dam from Hubbard Glacier (Seitz

et al. 1986); Water in the newly formed lake rose over 25 m

above sea level (Seitz et al. 1986) and came within 14

vertical meters of overflowing into the Situk River watershed

(Paul 1988). The ice dam eventually collapsed, but Hubbard

Glacier continues to advance and is expected to form a

larger, more stable dam that may persist for several hundred

years (Trabant et al. 1991). Such a dam would cause glacial

water to flow into the Situk River watershed (Mayo 1988;

Trabant et al. 19.91).

Overflow from Russell Fiord into the Situk River watershed would create a river very different from the present

one; now the Situk River channel is less than 30 m wide and

has a discharge rate that averages 10-15 m3

/s, and has not

exceeded 92 m3/s since gaging began in 1988 (Lamke et al.

1991). The new river channel is expected to stay within the

current Situk River watershed except near the mouth where it

probably will spill over into watersheds now occupied by the
Figure 1. --Location map of the Situk River, Russell Fiord and

several glaciers near Yakutat, Alaska.
3

Lost River and Kunayosh Creek (Fig. 2; Paul 1988). The new

channel-probably will range from about 100 m wide near the

Russell Fiord outflow to over 2,500 m wide near the river

mouth (Paul 1988). Discharge from the newly formed lake is

expected to average about 220 m3/s, with peak discharge near

1,000 m3/s (Mayo 1988). The river would also be colder and

more turbid because of the predominately glacial origin of

the discharge.

METHODS

Fish Tagging

Sockeye and chinook salmon were tagged at a weir in the

lower Situk River between 14 June and 21 August 1988. Sockeye salmon were tagged with spaghetti tags and chinook salmon

with Peterson disc tags (Table 1). Tags were deployed in

three lots, each a different color designating a different

period of the run (early, 7 June-7 July; middle, 8-25 July;

and late, 26 July-22 August). Because few chinook salmon

were available for tagging, Lotek1

 30 MHz radio transmitters

were orally inserted into the stomachs of 32 disc-tagged

chinook (Table 2) to improve tracking and observation of that

species.

Migration Studies

Twice every other week between 14 June and 8 August,

channels in the predicted flood corridor between the Situk

River bridge and the boat landing at the end of Lost River

Road (Fig. 2) were surveyed by boat to observe fish and

determine habitat use. Tagged fish were counted and pink

salmon numbers were visually estimated during each survey

(Tables 2-4).

Signals from radio-tagged chinook salmon were located

during surveys by scanning the transmitter frequencies with

Advanced Telemetry Systems receivers; maximum range with a

directional loop antenna was about 0.5 km. By using the

directional antenna while attenuating the receiver's gain,

the receiver also functioned as a directional indicator until

it was within a few meters of a transmitter. The locations

of most radio-tagged fish were established visually by

approaching the signal until the fish were observed. Some

radio-tagged fish in cover or deep water, however, could not

be seen, and their positions were estimated by triangulation.

1

Reference to trade namesdoes not imply endorsement by the National Marine

Fisheries Service, NOAA.
Figure 2. --Estimated course of 1,000 m3

/s of water flow from

Russell Fiord through the Situk River watershed

(adapted from Paul 1988).
Table 1. --Numbers of sockeye and chinook salmon tagged, and

escapement through the Situk River weir in three

periods between 14 June and 21 August 1988.

Species Period Number tagged Escapement % Tagged

Table 2.--Date, cumulative number of radio-tagged chinook,

and number of radio-tagged chinook located in

adult salmon migration surveys of the main-stem

Situk River, 1988. Numbers of radio-tagged fish

that were subtracted (pre-spawn mortality or tag

loss) from the cumulative counts are in

parentheses.

Date

Fish tagged Tags located

Early Middle Late 'Early Middle Late
6

Table 3. --Survey dates, cumulative numbers of tagged sockeye

salmon (Xi), numbers of tagged sockeye observed

(ni), and sockeye observation efficiencies 

during adult salmon migration surveys of the mainstem Situk River, 1988. Data used to determine

observation efficiencies are in italics. Numbers

of radio-tagged chinook salmon in each category are

in parentheses.

Fish tagged (Xi) Tags observed (ni)

Date, Early Middle Late Early Middle Late
7

Table 4. --Date and estimated number of pink

salmon observed during surveys of

the main-stem Situk River, 1988.

Date Fish

observed

Where chinook salmon were observed or located by telemetry, or where groups of sockeye (>lO -fish) or pink salmon

(>20 fish) were observed, these environmental data were

recorded: habitat type (pool,. riffle, or glide), average'

depth (mean of three or more measurements), and amount

(absent, common, or abundant) of cover (i.e., overhanging or

submerged riparian vegetation and large woody debris [LWD]).

Not all tagged fish in the survey area were observed

during each survey (Tables 2-3); therefore, the number of

tagged fish in the survey area was estimated as the number of

tagged fish observed times observation efficiency (a; Tables

2-3): Observation efficiency was calculated from one survey

in each tagging period by the equation

(1)

where is observation efficiency, n is the number. of tagged

fish observed during the survey that had been tagged since

the tagging period began, and x is the cumulative number of

fish tagged since the tagging period began. I assumed that

1) all fish tagged since the start of a tagging period

remained in the survey area until the data for observation

efficiencies in that period were compiled, 2) observation

efficiency was constant during a tagging period, and
8

3) (observation efficiency of radio-tagged. fish was 1. The

number of fish, in the survey area was estimated for each tag

group by the equation

(2)

where is the estimated number of tagged fish in the survey

area at survey i, and ni is the number of tagged fish.

observed during survey i.

The proportion of tagged fish from each group remaining

in the 'survey area was calculated with the equation

(3)

where is the proportion of tagged fish remaining in the

survey area at survey i, and xi is the cumulative number of

fish tagged up to survey i.

Regression of on survey date provided an empirical

model of emigration from-the boat survey area for each group

of tagged fish. Logarithmic transformation, (Sokal and Rohlf

'1969) of sockeye emigration data provided the best regression

fit, probably due to both the proportional data and the fact

that fish bound for 'spawning areas in Old Situk River

(Fig. 3) stayed in the survey area for long periods, thus positively skewing the P distribution. Angular transformation (Sokal and Rohlf 1969) of chinook emigration data

provided the best regression fit,

is proportional.

probably because the data

The nonnormal distributions of also

indicate that medians are the best measures of central

tendency for this data: An F test was used to compare the

slopes of the regression lines, thereby determining whether

emigration rates varied significantly between tagged groups..

When significant differences were found, Scheffe's test

(Snedecor and Cochran 1967) was applied to determine which.

emigration rates were unlike the others. Regressions of data

for disc-tagged and radio-tagged chinook salmon did not

differ significantly (P > 0.5; t test) within any tagging

period, and the data for the two tag groups were pooled by

tagging period.

Equations were derived from the regressions to 1) es&-

mate P within a tag group for any date (d, where d was 1 on

1 January and 366 on 31 December) after tagging of that group

began; and 2) estimate the number of days of residency (D)in

the main-stem flood corridor for any proportion (p) of a tag

group. The equations for chinook are
Figure 3. --Distribution of stream-spawning sockeye salmon and

sites sampled for spawning habitat characteristics

in the Situk River watershed, 1988.
The equations for sockeye are

where S is the slope of the regression line, C is a constant,

and e is the base of the natural logarithm. Factors used in

equations 4-7 and indices of variability are summarized in

Table 5. Relationships between emigration rate and date were

illustrated by plotting P values (expressed as percentages)

versus survey dates,.

Table 5. --Data to estimate and (equations 4-7) for groups of

tagged fish in the main-stem flood corridor of the

Situk River, 1988. R

2

 values and standard errors of

the regression slopes and estimates also are provided.

First Standard error

day of

Period Slope Constant tagging. R2

, 'Slope Estimate

Spawning Studies.

Several areas of the watershed (Situk River, West Fork

Situk, Old Situk River, and Mountain Stream; Fig. 2) were

surveyed by boat, foot, and fixed-wing aircraft to locate

spawning salmon. Surveys took place 27 July-30 September:

ground surveys were discontinued on 15 September, but an

aircraft survey was done on 30 September.
11

During surveys, tagged fish were counted and approximate

numbers and locations of untagged salmon were recorded on

1:42,240 scale maps. Observed salmon spawning range also was

recorded on maps during all surveys. Spawning-habitat characteristics of sockeye and chinook salmon were measured

during ground surveys. Spawning by sockeye and chinook

salmon was observed in 19 reaches (i.e. isolated groups of

spawning sites), and spawning-habitat characteristics were

measured at 63 spawning sites (31 and 32 sites, respectively;

Figs. 3 and 4) in those reaches.' Water depth was measured to

the nearest centimeter at the surface of the undisturbed

substrate adjacent to each spawning site. At the site of

each depth measurement,. water velocity (cm/s) was averaged

from measurements with an electronic current meter at 0.2 and

0.8 of the depth, and surface and intragravel (15 cm into the

substrate) temperatures were measured with an electronic

thermometer. Where individual redds could be discerned

(26 sockeye and 19 chinook salmon redds), maximum length and

width were measured and substrate composition in the area

disturbed by redd construction was visually estimated. Redd

length and width were measured to the nearest centimeter and

substrate composition was recorded in percentages of three

size classes: fine (<2 mm), gravel (2-100 mm), and coarse

(>lO cm).

RESULTS

About 10% of all sockeye and chinook salmon-were tagged,

but the number of tagsdeployed and the percentage of the

escapement tagged varied by period (Table, 1).

Upstream migrant salmon of all three species usually

shared habitat. Migrating fish in the flood corridor were

most frequently observed in pools or -in deep (>l m) glides

along banks with cover from overhanging or submerged riparian

vegetation.

'Estimated numbers of tagged fish between the weir and

the bridge on the Situk River declined significantly

(P < 0.001; F test) over time for all tag groups, as fish

emigrated from the flood corridor. Migration rates, however,

differed significantly (P < 0.05; F test) among groups of

tagged fish both within and between species, Most (95% of

sockeye and 97% of chinook) tagged fish left the flood corridor, but tagged sockeye salmon emigrated from the survey area

(median = 11.2 days) significantly faster (P < 0.01; F test)

than tagged chinook salmon (median = 51.7 days).

About 43,000 salmon were seen in spawning areas (11,500

sockeye, 438 chinook, and 31,000 pink). Each species usually
12

Figure 4. --Distribution of spawning chinook salmon and sites

sampled for spawning habitat characteristics in

the Situk River watershed, 1988.
13

spawned in a separate area, although pink salmon occasionally

spawned where chinook or sockeye salmon were spawning. Few

(<5% of the escapement; Table 1) sockeye and chinook salmon

were observed spawning in the flood corridor (Figs. 3 and 4),.

whereas about 40% of observed pink salmon spawning was in the

flood corridor (Fig. 5). Spawning salmon were observed. in

all habitat types (pools, riffles, and glides) and used

diverse hydraulic and substrate conditions (Table 6).

Sockeye Salmon

Most sockeye salmon emigrated steadily from the migration survey area in the flood corridor (Table 3). Models of

emigration by groups of tagged sockeye salmon (Fig. 6) fit

the observed data (R = 0.96, 0.95, and 0.87 for early,

middle, and -late tagging periods, respectively). Sockeye

salmon tagged late in the run left the migrationsurvey area

at a significantly (P < 0.05; Scheffe's test) faster rate

than sockeye salmon tagged in the early or middle periods.

Most (95%) sockeye salmon tagged early in the run had

migrated out of the survey area by 10 August, whereas most

(95%) sockeye salmon tagged in the middle and late parts of

the run left the survey area by 17 August (Table 3). Migrating sockeye salmon frequently concentrated where deep (>l m)

glides intersected quiet pools (often formed behind large

woody debris) or in glides along channel margins with overhanging or submerged riparian vegetation.

Sockeye salmon were observed to spawn over a 2-month

period. Spawning sockeye salmon were first seen about 5 km

upstream of the Situk River bridge on 27 July, during the

first ground survey in that area; they were most abundant the

second or third weeks of August, and rare on 30 September.

About 90% of the sockeye salmon in the survey area spawned

near lakes (Fig. 3); spawning density was greatest within

3 km downstream of Situk Lake. Large groups of sockeye

salmon also spawned in other areas: directly upstream of

Situk Lake in Mountain Stream, in the area immediately

upstream of the road crossing of the Old Situk River, and

downstream of Mountain Lake (Mountain Stream). Spawning of

sockeye salmon also was observed elsewhere (Fig. 3) in the

Situk River, Old Situk River, and near Redfield Lakes (West

Fork of the Situk River).

Most (65%) sockeye salmon that were observed during

spawning surveys spawned in glides, but some (30%) spawned in

pools and a few (5%) in riffles. Sockeye salmon used an

average of 3.7 m of stream bed to construct a redd.

Spawning sites averaged 49.6-cm water depth and 26.5-cm/s

water velocity. Substrate composition at redd sites averaged

23% fine sediment, 72% gravel, and 5% coarse sediment.
Figure 5. --Distribution of stream spawning pink salmon in the

Situk River watershed, 1988.
15

Table 6. --Characteristics of sockeye and chinook salmon

spawning habitat in the Situk River, 1988. Mean

values are presented with standard errors in

brackets.

Sockeye Chinook
16

Figure 6.--Curves illustrating estimated percentages of three

respective groups of tagged sockeye and chinook

salmon between the weir and the bridge on the

Situk River, Alaska, from June through September

1988. Shaded areas encompasS tagging dates.
17

Differences between surface water and intragravel temperature

(averaging 9.1°C and 6.2°C, respectively) indicate that

upwelling groundwater often was present in sockeye salmon

spawning areas. All measured characteristics of habitat

(Table 5) used by stream-spawning sockeye salmon differed

significantly (P < 0.05; t test) from those used by chinook

salmon; sockeye salmon spawning areas had shallower and

slower water, smaller substrate, and more evidence of

groundwater influence than chinook salmon spawning areas.

Chinook Salmon

Tagged chinook salmon emigrated more slowly (P < 0.01;

F test) from the migration survey area in the flood corridor

than did sockeye salmon, but most (99%) left the flood corridor by 1 September (Table 3).

of tagged chinook salmon (Fig.

Models of emigration by groups

6) fit the observed data (R =

0.76, 0.90, and 0.79 for early, middle, and late tagging

periods, respectively). Emigration rates differed significantly (P < 0.001; F test) among groups, of tagged-chinook

salmon; chinook salmon tagged in the late period emigrated

from the survey area significantly more quickly (P < 0.05;

Scheffe's test) than those tagged in the early or middle

periods. Migrating chinook salmon were found primarily in

deep (>2 m), open pools or deep (>l m) glides along banks

with overhanging or submerged riparian vegetation. Radiotagged chinook salmon often held in the same pool for nearly

the entire time they were monitored in the flood corridor,

and then moved quickly (within 1 or 2 days) to spawning

areas. Radio-tagged chinook salmon using deep glides usually

moved upstream more steadily than chinook salmon using deep

pools.

Chinook salmon spawning was observed between 30 July and

14 September. Spawning chinook salmon were first observed

about 1.5 km upstream of the Situk River bridge on 30 July;

they were most abundant about the first, week of September,

and spawning ceased before 30 September; no spawning chinook

salmon were observed during the aerial survey on 30 September,

and radio telemetry indicated that most (>90%) radio-tagged

fish were well downstream of, their spawning sites and

presumably were dead.

All chinook salmon spawned in either riffles or glides.

Chinook salmon used an average of 19.0 m2 of stream bed to

construct a redd. Spawning sites had a mean water depth of

79.6 cm and mean water velocity of 73.0 cm/s. Substrate

composition at redd sites averaged 5.3% fine sediment, 76.0%

gravel, and 18.7% coarse sediment. Mean water temperature in

chinook salmon spawning areas was 12.2°C and mean intragravel

temperature was 11.9°C (Table 6).
18

Radio-tagged chinook salmon were closely tracked

throughout the survey and provided detailed data on migration

patterns and habitat use. Of 30 radio-tagged chinook salmon,

26 were tracked to spawning areas. Only four radio-tagged

fish were not tracked to spawning areas: one migrated well

upstream but died of unknown causes before spawning, one was

caught at an undisclosed location by a sport fisherman, and

two regurgitated their radio tags 'near the Situk River weir

soon after tagging. Twenty-four (92%) of the remaining

radio-tagged chinook salmon spawned between the Situk River

bridge and Situk Lake (Fig. 4), the area with the highest

density of chinook salmon spawning. One radio-tagged chinook

salmon spawned within 1 km downstream of the Situk River

bridge,, and one also spawned in the lower 1 km of the West

Fork. A few chinook salmon (about 10-15) without tags also

were observed spawning in other areas (Fig. 4): within 3 km

downstream of the Situk River- bridge and in Mountain Stream

upstream of Situk Lake.

Pink Salmon

Migrating pink salmonwere observed primarily in glides

with overhanging vegetation or in transitional areas between

pools and riffles. Spawning pink salmon were first observed

on 10 August about 10 km upstream of the Situk River landing,

and 'were last observed on 8 September near the boat landing.

Many pink salmon spawned in one of three-areas: from 7 km

upstream of the landing to 4 km downstream of Situk Lake, in

the Old Situk River from its mouth to 1 km downstream of

Forest Highway 10, and sporadically in the West Fork from its

mouth to Redfield Lakes (Fig. 5).

shallow (<40 cm),

Pink salmon spawned in

open glides or in transitional areas

between pools and riffles.

DISCUSSION

Habitat Utilization

Migratory behavior and habitat use by sockeye, chinook,

and pink salmon in the Situk River in 1988 were similar to

those reported for the species in other rivers. Adult

sockeye salmon in the Situk and other river systems migrate

rapidly from salt water to lacustrine areas (Bevan 1962;

Ricker 1966) and remain there until they spawn either in

lakes or in streams connected to lakes (Foerster 1968).

Sockeye salmon that spawned in the Situk River used habitat

similar to that used by sockeye salmon in other streams

(Foerster 1968; Leman 1989): relatively shallow,

low-velocity water and variable substrate that was often

infused with upwelling groundwater.
1 9

Adult chinook salmon in the Situk River often held in

large pools or deep runs until mature, as they do 'in other

river systems (Hamilton and Buell 1976; Burger et al. 1985).

Chinook salmon in the Situk River spawned in relatively deep,

fast water and used large substrate, as they do in other

parts of their range (Smith 1973; Reiser and Bjornn 1979).

Pink salmon in the Situk River apparently migrated

directly to spawning areas, consistent with their migratory

behavior in other coastal streams (Ishida 1966; Heard 1978).

Spawning pink salmon in the Situk River used habitat with

characteristics similar to spawning habitat used by other

pink salmon populations (Neave 1966; Reiser and Bjornn 1979).

Effects of Flooding on Fish and Habitat

Flooding from Russell Fiord would impact habitat in the

Situk River used by migrating and spawning salmon. Discharge

from the fiord is predicted to be more than 20 times the

volume of the present Situk River (Paul 1988), which would

inundate or erode all existing channels downstream of the

Situk River bridge (Seitz et al. 1986; Paul 1988). Overflow

from Russell Fiord could persist for decades, possibly

centuries (Mayo 1988; Trabant et al. 1991), providing both a

larger body of water to serve as fish habitat than the

present Situk River and access to new fish habitat in the

Russell Fiord watershed.

Duration and timing of the potential flooding will

determine the magnitude of effects on fish habitat; in any

case, several years will probably pass before inundated areas

become stable. A persistent ice dam that would cause a

relatively constant flow from Russell Fiord is predicted;

however, a number of ice dams may initially form and fail,

causing intermittent flooding, of, the Situk River watershed

(Trabant et al. 1991). Fish habitat within the new

floodplain, however, would begin to stabilize only when a

relatively constant flow regime is established. A stable

channel and, thus, stable fish habitat should be established

after 3-5 years of relatively constant flow (Clark and

Paustian 1989).

Migration corridors of all anadromous fish would be

affected by flooding from Russell Fiord, although fish may

still use the same corridors and maintain the same run

timing. The new river would be large and turbid, and would

offer good cover for holding and migrating fish; however,

fish in the flood corridor when. flooding begins may be

injured and displaced or cut off from spawning areas, as coho

salmon and steelhead were in the Toutle and Cowlitz Rivers

(Washington) after the 1980 eruption of Mount St. Helen's

(Stober et al. 1981). Some fish also may attempt to avoid
2 0

the turbid water. Pink salmon in the Bella Coola River,

British Columbia, for example, delay spawning migrations and

select alternate spawning areas to avoid glacial turbidity

(Wickett 1958). The glacial runoff from Russell Fiord would

certalinly decrease water temperature in the flood corridor

and may cause fish to migrate more sluggishly. Changes in

river temperature should not affect maturation rates because

salmon gonad maturation is not greatly affected by changing

water temperature (Billard 1985) within the range likely in

the Situk River.

Location of the main spawning areas is a factor in

determining the initial impacts of flooding on Situk River

salmon populations; most sockeye and chinook salmon now spawn

outside the predicted flood corridor, whereas many pink

salmon spawn inside the flood corridor. Spawning areas

outside the flood corridor would not be directly impacted by

flooding; however, spawning areas in the flood corridor would

be affected by channel morphology changes, increased fine

sediment, and lowered temperature. Spawning areas in the

flood corridor may be eroded or buried as a new channel

develops under the influence of the new flow regime. Fine

sediment mobilized by erosion and sediment from glacial

turbidity also could clog or cement spawning gravel (Cooper

1965), and thus impede the intragravel water flow necessary

for egg incubation (Wickett 1958; Reiser and Bjornn 1979).

Cooler water temperature would slow egg and alevin development (Leitritz and Lewis 1980), thereby delaying hatching,

emergrence, and seaward migration.

Timing and duration of the flood event, or events, also

could: contribute to the initial impacts of flooding on Situk

River salmon populations; closure of Russell Fiord is most

likely to occur during spring, with overflow occurring

7-14 months later (Trabant et al. 1991). Thus, a flood would

probably begin between December and August, thereby affecting,

either eggs and alevins in the gravel or migrating salmon. A

flood beginning in winter would probably destroy a large

proportion of the pink salmon year class. My observations

indiciate that 40% of the adults spawned within the flood

corridor in 1988. In 1990 an estimated 84% of downstream

migrant pink salmon fry came from within the flood corridor2

. A flood beginning in spring or summer could affect

migrations of juvenile or adult salmon; juvenile salmon may

be washed out to sea before they are ready and adult fish may

avoid flooded areas, thereby escalating competition in other

spawning areas. In any case, flooding could decrease salmon

production initially.

2J. Thedinga, Fishery Biologist,, Auke Bay ,Laboratory, 11305 Glacier Hwy.,

Juneau, AK 99801-8626. Pers. commin., March 1990.
21

A series of ephemeral dams that cause intermittent

flooding could also cause cumulative effects, including those

outlined above and additional effects caused by dewatering of

river channels; river flow would decrease by more than 90%

following the collapse of a Russell Fiord ice dam and many

channels would dry up, stranding and killing fish and possibly dewatering redds. Thus, a single overflow event of long

durationy-although potentially destructive--would probably be

less detrimental to salmon populations than intermittent

flooding.

A persistent ice dam could eventually form in Russell

Fiord, and river channels and salmon habitat could stabilize.

Side channels and some parts of main channels probably would

provide rearing and spawning areas, as they do in other large'

glacial rivers (Lake 1984; Lorenz and Eiler 1989; Murphy

et al. 1989). Impoundment of Russell Fiord would increase

the hydraulic gradient between the Situk River watershed and

Russell Fiord, potentially creating new groundwater outflows

that could provide salmon spawning and rearing habitat (Clark

and Paustian 1989). Groundwater outflow channels are important to spawning populations of sockeye, chum (0. keta), and,

coho salmon (0. kisutcb) in other watersheds, such as the

Kamchatka River basin, U.S.S.R. (Leman 1989). Fish also. 

could have access to new habitat in Russell Lake and its

watershed. All streams flowing into Russell Fiord are steep,

high-energy streams that probably have little potential as

spawning habitat; however,. the lake is a potential rearing

area for juvenile sockeye and coho salmon.

After the river channels stabilize, species composition

and size of salmon populations in the Situk River may

continue to change as fish populations adapt to available

habitat. Some species, or population cohorts within a

species (stocks), may adapt more readily to the new

conditions than others. Many chum and sockeye salmon, for

example, spawn in some glacial rivers (Bishop 1981; Lorenz

and Eiler 1989), whereas most other salmon do not. Sockeye

and chinook salmon also rear at moderate densities in some

glacial river habitats (Wood et al. 1987; Murphy et al.

1989).

Some Situk River salmon seem to exhibit spawning and

rearing strategies that could enable them to adapt to the

predicted habitat conditions after flooding begins,. The last

overflow from the fiord was relatively recent (<120 years),

and these fish may be remnants of populations adapted to

previous episodes of- overflow from Russell Fiord. Some

aspects of the habitat-utilization patterns and life history

 of sockeye salmon that spawn in Old Situk River; for example,

indicate that they may be a remnant population. Many sockeye
22

salmon in Old Situk River (and also the main channel of the'

Situk River) use riverine spawning areas permeated by groundwater, a habitat component that should become more available

in the Situk River watershed should Russell Fiord become

impounded (Clark and Paustian 1989). Most (>90%3

) sockeye

salmon that spawn in Old Situk River use areas with little

access to lake rearing habitat for their offspring and,

therefore, go to sea before overwintering; most sockeye salmon in Alaska spawn in areas with access to lakes (Foerster

1968) because their offspring rear in lakes for at least a

year before going to sea; however, sockeye salmon that go to

sea before overwintering are common in glacial rivers and

groundwater-fed streams in Alaska (McPherson 1987). Chinook

salmon in the Situk River also may be a remnant population

from previous overflow events because populations of chinook

salmon in Alaska usually are found in large river systems

rather than small coastal streams like the Situk River,

(Kissner 1986).

The short duration of this study prohibited collection

of data on some species, such as coho salmon and steelhead

(0. mykiss); that contribute significantly to Situk River

fisheries. This study, therefore, probably did not reveal

all the potential impacts of flooding. The study may

underestimate the area and range of conditions used by

also.,

sockeye, chinook, and pink salmon, because their escapements

to the Situk -River in 1988 were below average (Table 7).

In conclusion, this study confirms that habitat used by

adult salmon exists in the corridor where flooding from

Russell Fiord into the Situk River is predicted. If flooding

of the predicted magnitude occurs, some salmon habitat would

be altered or destroyed and salmon migration and distribution

patterns may change. Flooding would directly affect migration habitat of all salmon species and large areas of pink 

salmon spawning habitat. Flooding also, may affect other

spawning areas by displacing, large numbers of spawning fish

(primarily pink salmon) into those areas. Timing of the

initial flood event or events could determine the immediate

effects of flooding on Situk River fish populations.

less of initial population changes, however, long-term

Regardproduction of salmon from the Situk River could be limited by'

the innate abilities of endemic fish stocks to use post-flood 

habitat.

3

Alaska Department of Fish and Game, Commercial Fisheries Division Scale

Laboratory, 802 Third Street, Douglas, AK 99824, unpublished data, 1990.
Table 7. --Escapement of sockeye, chinook, and pink salmon to

the Situk River in 1988 compared to the mean and

range of escapements between 1979 and 1988.

Escapement in 1988 as a percentage of the 10-year 

average is in parenthesis.

Escapement

years Sockeyea

Chinookb Pinka

a

Unpublished data provided by Gordon F. Woods, Alaska Dep. Fish and Game,

Commercial Fisheries Div.; P.O. Box 68, Yakutat, AK 99689, August 1990.

b

Compiled from Hubartt and Kissner (1987) and Bethers and Ingledue (1989).

c

Mean and range for even year pink salmon escapements between 1980 and 1988

ACKNOWLEDGMENTS

I thank S. Feldhausen, F. Ryman, -A. Yanotti,

B. Kirkpatrick, and J. Turley for their assistance in fish

tagging and data collection for this project. I also thank

the Commercial Fisheries Division of the Alaska Department of

Fish and Game, Yakutat, for making this project possible

through use of the tagging facility at the Situk River weir.
24

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