FWS/OBS-82/1 0.60

JANUARY 1984

L f

7

HABITAT SUITABILITY INFORMATION:

RAINBOW TROUT

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SK

361

.U54

no. 82-

10.60

and Wildlife Service

i

S. Department of the Interior
FWS/OBS-82/10.60

January 1984

HABITAT SUITABILITY INFORMATION: RAINBOW TROUT

by

Robert F. Raleigh

P.O. Box 625

Council, 10 83612

Terry Hickman

Endangered Species Office

U.S. Fish and Wildlife Service

1311 Federal Building

125 S. State Street

Salt Lake City, UT 84138

R. Charles Solomon

Habitat Evaluation ProceG~res Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

Drake Creekside Building One

2627 Redwing Road

Fort Collins, CO 80526-2899

and

Patrick C. Nelson

Instream Flow and Aquatic Systems Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

Drake Creekside Building One

2627 Redwing Road

Fort Collins, CO 80526-2899

Western Energy and Land Use Team

Division of Biological Services

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

Raleigh, R. F., T. Hickman, R. C. Solomon, and P. C. Nelson. 1984. Habitat

suitability information: Rainbow trout. U.S. Fish Wildl. Servo

FWS/OBS-82/10.60. 64 pp.
PREFACE

The Habitat Suitability Index (HSI) models presented in this publication

aid in identifying important habitat variables. Facts, ideas, and concepts

obtained from the research literature and expert reviews are synthesized and

presented in a format that can be used for impact assessment. The models are

hypotheses of species-habitat relationships, and model users should recognize

that the degree of veracity of the HSI model, SI graphs, and assumptions will

vary according to geographical area and the extent of the data base for

individual variables. After clear study objectives have been set, the HSI

model building techniques presented in U.S: Fish and Wildlife Service (1981)1

and the general guidelines for modifying HSI models and estimating model

variables presented in Ter-rel l et al. (1982)2 may be useful for simplifying

and applying the models to specific impact assessment problems. Simplified

models should be tested with independent data sets if possible.

A brief discussion of the appropriateness of using selected Suitability

Index (SI) curves from HSI models as a component of the Instream Flow

Incremental Methodology (IFIM) is provided. Additional SI curves, developed

specifically for analysis of rainbow trout habitat with IFIM, also are

presented.

The U. S. Fi sh and Wi 1dl i fe Servi ce encourages mode 1 users to

comments, suggestions, and test results that may help us increase the

and effectiveness of this habitat-based approach to impact assessment.

send comments to:

Habitat Evaluation Procedures Group or

Instream Flow and Aquatic Systems Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2627 Redwing Road

Ft. Collins, CO 80526-2899

provide

utility

Please

1U.S. Fish and Wildlife Service.

habitat suitability index models.

Ecol. Servo n.p.

1981. Standards for the development of

103 ESM. U.S. Fish Wildl. Serv., Div.

2Terrell, J. W., T. E. McMahon, P. D. Inskip, R. F. Raleigh,

Williamson. 1982. Habitat suitability index models: Appendix A.

for riverine and lacustrine applications of fish HSI models with

Evaluation Procedures. U.S. Fish Wildl. Servo FWS/OBS-82/10.A. 54

iii

and K. L.

Guidelines

the Habitat

pp.
;v
CONTENTS

Page

PREFACE iii

FIGURES vi

TABLES vi i

ACKNOWLEDGMENTS vi i i

HABITAT USE INFORMATION 1

Genera1 1

Age, Growth, and Food 1

Reproduct ion 2

Anadromy 3

Specific Habitat Requirements.......... 4

HABITAT SUITABILITY INDEX (HSI) MODELS..... 9

Model Applicability............................................... 11

Mode 1 Descri pt ion 11

Suitability Index (SI) Graphs for Model Variables 13

Riverine Model 23

Lacustrine Models................................................. 32

Interpreting Model Outputs........................................ 33

ADDITIONAL HABITAT MODELS 33

Mode 1 1 33

Model 2 36

Model 3 36

Model 4 36

INSTREAM FLOW INCREMENTAL METHODOLOGY (IFIM) .. 37

Suitability Index Graphs as Used in IFIM 37

Availability of Graphs for Use in IFIM 39

REFERENCES 54

v
Number

1

2

3

4

5

FIGURES

Diagram illustrating the relationship among model

variables, components, and HS1 ..

SI curves for rainbow trout spawning velocity, depth,

substrate, and temperature .

SI curves for rainbow trout fry velocity, depth, substrate,

and temperature .

SI curves for rainbow trout juvenile velocity, depth,

substrate, and temperature .

$1 curves for rainbow trout adult velocity, depth,

substrate, and temperature .

vi

10

41

45

49

52
Number

1

2

3

4

5

6

TABLES

Matrix table for displaying suitability indices (S1l s) for

rainbow trout habitat variables .

Literature sources and assumptions for rainbow trout suitability indices .

Sample data sets using the nonanadromous riverine rainbow

trout HS1 model .

Average va 1. ue method .

Average value, probability method .

Ava il abil ity of curves for I FIM ana lysis of rainbow trout

habi tat .

vii

22

24

34

35

35

40
ACKNOWLEDGMENTS

Robert Behnke, Colorado State University; Leo Lentsch, U.S. Fish and

Wildlife Service; and Tom Weshe, University of Wyoming, provided comprehensive

reviews and many helpful comments and suggestions for improving the manuscript

and the model. The Oregon Cooperative Fishery Research Unit conducted the

literature review for the report. Cathy Short and Tric1a Rosenthal conducted

editorial reviews, and word processing was provided by Carolyn Gulzow and Dora

Ibarra. The cover illustration was prepared.by Jennifer Shoemaker.

viii
RAINBOW TROUT (Salmo gai rdneri)

HABITAT USE INFORMATION

Genera 1

Because of variations in their life history pattern and the habitat in

which they spend the majority of their adult lives, rainbow trout (Salmo

gairdneri) can be subdivided into three basic ecological forms: (1) anadromous

steel head trout; (2) resident stream rainbow trout; and (3) lake or reservoir

dwelling rainbow trout. It is important to recognize that there is a genetic

or hereditary basis for each ecological form. For example, a "Lake or

reservoi r" rainbow may react very di fferent ly to envi ronmenta 1 stimul i

associated with survival, feeding, and growth if it belongs to a population

that has been evolving and adapting to the particular lake for hundreds or

thousands of years, when compared to hatchery rainbow trout that have just

been released in the lake.

Nonanadromous rainbow trout are native to the Pacific Coast drainages

inland as far,as the Rockies and from the Rio del Presidio River in Mexico to

the Kuskokwim River in Southwestern Alaska (Behnke 1979). They are also

native to the Peace River drainage of British Columbia and the headwaters of

the Athabaska River (of the McKenzie River basin) in A"lberta (MacCrimmon

1971). Their present range extends from the Arctic Circle to 550 S latitude.

They are perhaps the most widely introduced fish species; the only continent

lacking rainbow trout is Antarctica (McAfee 1966; MacCrimmon 1971). Rainbow

trout occur from 0 to 4,500 mabove sea level (MacCrimmon 1971).

Anadromous steel head trout are di stri buted along the Pacifi c coast from

the Santa Ynez Mountains, California, to the Alaska Peninsula (Jordan and

Evermann 1902; Withler 1966). Large rainbow trout on and north of the Alaska

Peninsula appear to be nonanadromous.

Age, Growth, and Food

Female rainbow trout typically become sexually mature during their third

year; males become sexually mature during their second or third year (Holton

1953; Lag1er 1956; McAfee 1966). Life expectancy averages 3 to 5 years in

most southern lake populations, but life expectancy of steel head and northern

lake populations appears to be 4 to 8 years. Maximum size also varies with

population, area, and habitat. Steelhead may grow to 122 cm long and weigh

16 kg. The average angl er I s catch is 3.6 to 4 kg. Great Lakes rainbow grow

to 244 cm, but seldom exceed 9 kg (Scott and Crossman 1973). Size in wild

1
rainbow trout appears to be a function of longevity, delayed age at maturity,

and length of ocean residence for steel head.

Adult and juvenile rainbow trout are basically opportunistic feeders and

consume a wide variety of foods. Availability of different foods depends on

many factors, including water type, season, and size of the trout (McAfee

1966). The diet of rainbow trout consists mainly of aquatic insects (Allen

1969; Carlander 1969; Baxter and Simon 1970; Scott and Crossman 1973), although

foods, such as zooplankton (McAfee 1966), terrestrial insects, and fish

(Carlander 1969), are locally or seasonally important. The relative importance

of aquatic and terrestrial insects to resident stream rainbow trout varies

greatly among di fferent envi ronments, seasonally and di elly, and wi th the age

of the trout (Bisson 1978). Forty to fifty percent or more of the summer food

of trout in headwater streams may be composed of terrestrial insects (Hunt

1971). Adult stream rainbow trout occasionally consume significant quantities

of vegetation, mostly algae (McAfee 1966). Stream trout have no mechanism to

break down cell walls in vegetation and cannot obtain nutrients from it,

therefore, vegetation is thought to be consumed because of the invertebrates

attached to it (Behnke pers. comm.). Bottom fauna may comprise 83 to 94% of

the winter diet of adult and juvenile lake rainbow trout (Crossman and Larkin

1959). Lake trout usually reach 30 cm in 1ength before they actively prey on

other fish species (Crossman 1959; Crossman and Larkin 1959; Johannes and

Larki n 1961).

Reproduction

Rainbow trout spawn almost exclusively in streams. Some rainbow and

rainbow-cutthroat trout hybrids have successfully reproduced in lakes without

tributary streams (Behnke, pers. comm.). Spawning in certain river systems

may occur in intermittent tributary streams (Everest 1973; Price and Geary

1979). In one case, up to 47% of the stream rainbow trout population spawned

in intermittent tributaries that dried up in midsummer and fall (Erman and

Leidy 1975; Erman and Hawthorne 1976). Spawning normally occurs from January

to July, depending on location. Hatchery selection has resulted in fall

spawning strains, and spawning of hatchery fish may occur in almost any month

of the year, depending on the strain (Behnke 1979). A few populations outside

of the native range have modified their spawning times to avoid adverse

environmental conditions (Van Vel son 1974; Kaya 1977). Viable eggs have

resul ted from December and January spawning at water temperatures of 0.3 to

2.00 C in a tributary of Lake Huron (Dodge and MacCrimmon 1970). However,

eggs exposed to long periods of 0 to 40 C temperatures suffered high mortality

and abnormalities.

The female generally selects a redd site in gravel substrate at the head

of a riffle or downstream edge of a pool (Greeley 1932; Orcutt et al. 1968).

The redd pit, constructed primarily by the female, is typically longer than

the female and deeper than her greatest body depth (Greeley 1932). Average

depth of egg deposition is 15 cm (Hooper 1973).

Rainbow trout residing in lakes and reservoirs have a similar life history

pattern to the steelhead trout, but generally lack a physiological smolt

2
stage. Juveniles migrate from natal streams to a freshwater lake rearing

ar-ea , instead of to the ocean. Lake rainbow trout most commonly spend two

summers in a stream and two summers in a lake before maturing (Greeley 1933).

Spawning takes place during the growing season in an inlet or an outlet stream,

with more than 90% of the trout returning to the stream of natal origin

(Greeley 1933; Lindsey et al. 1959). Lakes with no inlet or outlet streams

generally do not possess a reproducing population of rainbow trout. Whether

spawning adults enter through an inlet or an outlet, they and their progeny

wi 11 return to the 1ake (Lindsey et a 1. 1959). These movements from natal

sites to lake rearing areas appear to be directed by genetic/environmental

interactions (Raleigh 1971).

Spawning usually begins one month earlier in the outlet than in the inlet

(Lindsey et al. 1959; Hartman et al. 1962); the difference in time is

apparently related to temperature differences (Lindsey et al. 1959). In

Bothwell Creek, a tributary of Lake Huron, 65% of the spawning run were repeat

spawners (Dodge and MacCrimmon 1970). The typical survival rate of repeat

spawners is 10-30%, with extremes from 1% to more than 65%.

Average fecundity of rainbow trout is related to length, but is highly

variable, ranging from 500 to 3,161 eggs per stream resident female (Carlander

1969). Fecundity of lake resident females ranges from 935 to 4,578 eggs per

female, with an average of 2,028 eggs per female (Mann 1969).

Anadromy

Anadromous stee1head spawn in freshwater streams. Stee1head smolt and

migrate in late spring (Wagner 1968; Chrisp and Bjornn 1978). Photoperiod

appears to be the dominant triggering mechanism for parr-smolt transformation,

with temperature affecting the rate of transformation (Wagner 1974). Smolts

that have not migrated by approximately the summer solstice revert to parr and

attempt to migrate the following season (Zaugg and Wagner 1973). Juveni les

reside in freshwater for 1 to 4 years before migrating to the sea as smolts.

They mature after 1 to 4 years of ocean residence and return to freshwater

rivers to spawn (Chapman 1958; Withler 1966). A large number of the steel head

adults die after spawning, but some (3 to 53%) return to the ocean and spawn

again (Bjornn 1960; Withler 1966; Fulton 1970). Steel head spawners tend to be

larger and older in the northern portion of their range (Withler 1966).

There are both winter and summer-run steel head. Summer-run adults enter

freshwater rivers in the spring and early summer. Winter-run steel head enter

freshwater rivers in the fall and winter. As many as 98.8% of the trout

return to their natal stream (McAfee 1966). Both groups typically spawn in

the spring and early summer months, March through early July (Withler 1966;

Orcutt et al. 1968), although spawning at other times of the year has been

reported. Summer-run and winter-run steel head are distinguished by differences

in behavior prior to spawning and, to a limited extent, by appearance (Withler

1966).

3
When fish migrate from freshwater to saltwater, they are moving from a

hypotonic medium to a hypertonic medium. Gill Na-K ATPase activity appears to

be related to saltwater tolerance and smolting (Conte and Wagner 1965; Zaugg

and Wagner 1973; Adams et al. 1975). Water temperature affects Na-K-related

ATPase activity. Juvenile steelhead kept in water warmer than 13° C from

March to June experienced reduced levels of smoltification and very low levels

of ATPase activity (Zaugg and McLain 1972; Zaugg and Wagner 1973; Wagner

1974). Water temperatures of 10.5 to 13° C resul ted ina moderate ATPase

response, and temperatures of 6.5 to 10° C resulted in the highest activity

levels for the longest period of time (Adams et al. 1975). The effect of

temperature on ATPase activity is reversible within a season (Zaugg and McLain

1972) .

Coefficient of condition is another indicator of. parr-smolt transformation. Juvenile steelhead not undergoing a smolt transformation do not lose

wei ght; whereas, steel head undergoi ng transformati on lose enough wei ght to

resul tin a greatly reduced coeffi ci ent· of condi t i on (Adams et a 1. 1973;

Wagner 1974).

A fork length (i .e., anterior most extremity to the notch in the tail fin

of fork-tailed fish or to the center of the tail fin when the tail is not

forked) of 160 mm is the average length juvenile parr must reach before they

undergo the physiological and morphological changes of smolting (Fessler and

Wagner 1969; Chri sp and Bjornn 1978). Hatchery-reared stee 1head typi ca lly

reach critical size in one growing season, but native stream steelhead usually

require two or more growing seasons (Chrisp and Bjornn 1978). Migrating

smolts at the lower end of the minimum length requirement stay in the ocean

longer than smolts that are larger in size when they migrate (Chapman 1958).

The freshwater habitat requirements of adult and juvenile steel head are

assumed to be essentially the same as those for other rainbow trout. Exceptions for steelhead are: (1) low temperature « 13° C) requirements during

the spring months for smoltification of juveniles; and (2) the presence of

moderate temperatures (preferably s 20° C) and freshets (periodic high flows)

during the upstream migration of adults.

Specific Habitat Requirements

Optimal rainbow trout riverine habitat is characterized by clear, cold

water; a silt-free rocky substrate in riffle-run areas; an approximately 1:1

pool-to-riffle ratio, with areas of slow, deep water; well-vegetated stream

banks; abundant instream cover; and relatively stable water flow, temperature

regimes, and stream banks (Raleigh and Duff 1980).

Optimal lacustrine habitat is characterized by clear, cold, deep lakes

that are typically oligotrophic, but may vary in size and chemical quality,

particularly in reservoir habitats. Rainbow trout are primarily stream

spawners and generally requi re tri butary streams with gravel substrate in

riffle areas for reproduction to occur.

4
Trout production is typically greatest in streams with a pool-to-riffle

ratio of approximately 1: 1 (Fortune and Thompson 1969; Thompson and Fortune

1970). Pools are inhabited throughout the year by adult and juvenile stream

rainbow trout. Pools are important to trout as a refuge from adverse conditions during the winter. Because pools differ in their ability to provide

resting areas and cover, this model subdivides pools into three classes.

Lewis (1969) found that streams with deep, low velocity pools containing

extensive cover had the most stable trout populations.

Available trout literature does not often clearly distinguish between

feedi ng stations, escape cover, and wi nter cover requi rements. Prime

requisites for optimal feeding stations appear to be low water velocity and

access to a p1entiful food supply; i. e., energy accretion at a low energy

cost. Water depth is not clearly defined as a selection factor, and overhead

cover is preferred but not essential. Escape cover, however, must be nearby.

The feeding stations of dominant adult trout include overhead cover when

available. The feeding stations of subdominant adults and juveniles, however,

do not always include overhead cover. Antagonistic behavior occurs at feeding

stations and hierarchies are established, but escape cover is often shared.

Cover is recognized as one of the essential components of trout streams.

Boussu (1954) was able to increase the number and weight of trout in stream

sections by adding artificial brush cover and to decrease numbers and weight

of trout by removing brush cover and undercut banks. Lewi s (1969) reported

that the amount of cover was important in determining the number of trout in

sections of a Montana stream. Stewart (1970) found that mean depth and underwater, overhanging bank cover were the most important variables in determining

the density of brook and ra t nbow trout longer than 18 cm in a northcentral

Colorado stream. Cover for adult trout consists of areas of obscured stream

bottom in water 15 cm deep with a velocity of s 15 cm/sec (Wesche 1980).

Wesche (1980) reported that, in larger streams, the abundance of trout 15 cm

in length increased with water depth; most trout were at depths of at least

15 em. Cover is provided by overhanging vegetation; submerged vegetation;

undercut banks; instream objects, such as debris piles, logs, and large rocks;

pool depth; and surface turbulence (Giger 1973). A cover area of 25% of the

total stream area provides adequate cover for adult trout; a cover area of

15% is adequate for juveniles. The main uses of summer cover are probably

predator avoidance and resting.

In some streams, the major factor limiting salmonid densities may be the

amount of adequate overwi nteri ng habi tat, rather than the amount of summer

rearing habitat (Bustard and Narver 1975a). Winter hiding behavior in

salmonids is triggered by low temperatures (Chapman and Bjornn 1969; Everest

1969; Bustard and Narver 1975a,b). Cutthroat trout were found under boulders,

log jams, upturned roots, and debris when temperatures neared 4 to 8° C,

depending on the water velocity (Bustard and Narver 1975a). Everest (1969)

found juvenile rainbow trout 15 to 30 cm deep in the substrate, which was

often covered by 5 to 10 cm of anchor ice. Lewis (1969) reported that, during

wi nter, adult ra i nbow trout tended to move into deeper water (fi rst cl ass

pools). Bjornn (1971) indicated that downstream movement during or preceding

winter did not occur if sufficient winter cover was available locally. Trout

5
move to winter cover to avoid physical damage from ice scouring (Hartman 1965;

Chapman and Bjornn 1969) and to conserve energy (Chapman and Bjornn 1969;

Everest 1969).

Headwater trout streams are relatively unproductive. Most energy inputs

to the stream are in the form of allochthonous materials, such as terrestrial

vegetation and terrestrial insects (Idyll 1942; Chapman 1966; Hunt 1971).

Aquatic invertebrates are most abundant and diverse in riffle areas with

rubble substrate and on submerged aquatic vegetation (Hynes 1970). However,

optimal substrate for maintenance of a diverse invertebrate population consists

of a mosaic of mud, gravel, rubble, and boulders, with rubble dominant. A

pool-to-riffle ratio of about 1:1 (approximately a 40 to 60% pool area) appears

to provide an optimal mix of food producing and rearing areas for trout

(Needham 1940). In riffl e areas, the presence of fi nes (> 10%) reduces the

production of invertebrate fauna (based on Cordone and Kelly 1961; Crouse et

al. 1981).

Canopy cover is important in maintaining shade for stream temperature

control and in providing allochthonous materials to the stream. Too much

shade, however, can restrict primary productivity in a stream. Stream temperatures can be increased or decreased by controlling the amount of shade.

About 50 to 75% midday shade appears optimal for most small trout streams

(adapted from Oregon/Washington Interagency Wildlife Conference 1979). Shading

becomes less important as stream gradient and size increase. In addition, a

well vegetated riparian area helps control watershed erosion. In most cases,

a buffer strip about 30 m wide, 80% of which is either well vegetated or has

stab1e rocky stream banks, provi des adequate erosi on control and ma i nta ins

undercut stream banks characteristic of good trout habitat. The presence of

fines in riffle-run areas can adversely affect embryo survival, food production, and cover for juveniles.

There is a definite relationship between the annual flow regime and the

quality of trout habitat. The most critical period is typically during base

flow (lowest flows of late summer to winter). A base flow 50% of the average

annual daily flow is considered excellent for maintaining quality trout

habitat, a base flow of 25 to 50% is considered fair, and a base flow of < 25%

is considered poor (adapted from Binns and Eiserman 1979; Wesche 1980).

Adult. Dissolved oxygen requirements vary with species, age, prior

acclimation temperature, water velocity, activity level, and concentration of

substances in the water (McKee and Wolf 1963). As temperature increases, the

dissolved oxygen saturation level in the water decreases, while the dissolved

oxygen requi rement for the fi sh increases. As a resul t, an increase in

temperature resulting in a decrease in dissolved oxygen can be detrimental to

the fish. Optimal oxygen levels for rainbow trout are not well documented,

but appear to be 7 mg/l at temperatures 150 C and 9 mg/l at temperatures

> 150 C. Doudoroff and Shumway (1970) demonstrated that swimming speed and

growth rates for salmonids declined with decreasing dissolved oxygen levels.

In the summer (~ 100 C), cutthroat trout generally avoid water with dissolved

oxygen levels of less than 5 mg/l (Trojnar 1972; Sekulich 1974).

6
The incipient lethal level of dissolved oxygen for adult and juvenile

rainbow trout is approximately 3 mg/l or less, depending on environmental

conditions, especially temperature (Gutsell 1929; Burdick et al. 1954;

Alabaster et al. 1957; Downing and Merken 1957; Doudoroff and Warren 1962).

Although fish can survive at concentrations just above this level, they must

make various physiological adaptations to low levels of dissolved oxygen that

may jeopardize their health (Randall and Smith 1967; Kutty 1968; Hughes and

Saunders 1970; Cameron 1971; Holeton 1971). For example, low levels of

dissolved oxygen can result in reduced fecundity and even prevent spawning.

Large fluctuations in dissolved oxygen may cause a reduction in food consumption and impaired growth (Doudoroff and Shumway 1970).

The upper and lower i nci pi ent 1etha 1 temperatures for adult ra i nbow are

25° and 0° C, respectively (Black 1953; Lagler 1956; McAfee 1966; Bidgood and

Berst 1969; Hokanson et a1. 1977). Zero growth rate occurred at 23° C for

rainbow trout in the laboratory (Hokanson et al. 1977). Changes in the natural

growth rate of rainbow trout are detrimental to their development and survival.

Therefore, 25° C should 'be considered the upper limit suitable for rainbow

trout and then only for short periods of time. Adult lake rainbow trout

select waters with temperatures between 7 to 18° C (Fast 1973; May 1973) and

avoid permanent residence where temperatures are above 18° C (May 1973).

Adult stream rainbow trout select temperatures between 12.0 and 19.3° C

(Garside and Tait 1958; Bell 1973; Cherry et al. 1977; McCauley et al. 1977).

Dickson and Kramer (1971) reported that the greatest scope of rainbow trout

activity occurred at 15 and 20° C when tested at 5° C temperature intervals.

Stream rainbow trout select temperatures between 12 and 19° C; lake resident

trout avoid temperatures> 18° C. Therefore, the optimal temperature range

for rainbow trout is assumed to be 12 to 18° C.

The depth distribution of adult lake rainbow trout is usually a function

of dissolved oxygen, temperature, and food. Adult lake rainbow trout remain

at depths s the 18° C isotherm and at di sso 1ved oxygen 1eve 1s > 3 mg/l (May

1973; Hess 1974).

Focal point velocities for adult cutthroat trout at territorial stations

in Idaho streams were primarily between 10 and 14 em/sec, with a maximum of

22 em/sec (Griffith 1972). The focal point velocities for adult rainbow trout

are assumed to be similar.

Precise pH tolerance and optimal ranges are not well documented for

rainbow trout. Most trout populations can probably tolerate a pH range of 5.5

to 9.0, with an optimal range of 6.5 to 8.0 (Hartman and Gill 1968; Behnke and

Zarn 1976).

Withler (1966) suggested that the correlation between the winter steel head

run and increased water volume indicates that a freshet condition is required

to initiate upstream movement of spawners. Everest (1973) stated that speed

of migration of summer-run steel head in the Rogue River was inversely related

to temperature and di rectly related to streamfl ows. Hanel (1971) observed

that steelhead migration into the Iron Gate fish hatchery ceased when the

water temperature dropped to 4° C and did not resume for several weeks until

7
the temperature increased. This suggests that water temperatures should be

> 4° C but s 18° C, and streamflow conditions should be above normal seasonal

flows during upstream migrations of steel head adults.

Embryo. Incubation time varies inversely with temperature. Eggs usually

hatch within 28 to 40 days (Cope 1957), but may take as long as 49 days (Scott

and Crossman 1973). The optimal temperature for embryo incubation is about 7

to 12° C. Calhoun (1966) reported increased mortalities of rainbow embryos at

temperatures < 7° C and normal development at temperatures z 7 but s 12° C.

The optimal water velocity above rainbow trout redds is between 30 and

70 cm/sec. Velocities less than 10 cm/sec or greater than 90 cm/sec are

unsuitable (Delisle and Eliason 1961; Thompson 1972; Hooper 1973).

The combined effects of temperature, dissolved oxyqen , water velocity,

and gravel permeability are important for successful incubation (Coble 1961).

In a 30% sand and 70% gravel mixture, only 28% of implanted steel head embryos

hatched; of the 28% that hatched, only 74% emerged (Bjornn 1969; Phillips et

al. 1975). Optimal spawning gravel conditions are assumed to include s 5%

fines; z 30% fines are assumed to result in low survival of embryos and

emerging yolk-sac fry. Suitable incubation substrate is gravel that is 0.3 to

10.0 cm in diameter (Delisle and Eliason 1961; Orcutt et al. 1968; Hooper

1973; Duff 1980). Optimal substrate size depends on the size of the spawners,

but is assumed to average 1.5 to 6.0 cm in diameter for rainbows < 50 cm long

and 1.5 to 10.0 em in diameter for spawners 50 cm long (Orcutt et al. 1968).

Doudoroff and Shumway (1970) reported that sa lmon i ds that incubated at low

dissolved oxygen levels were weak and small with slower development and more

abnormalities. Dissolved oxygen requirements for rainbow trout embryos are

not well documented, but are assumed to be similar to the requirements for

adults.

Fry. Rainbow trout remain in the gravel for about 2 weeks after hatching

(Scott and Crossman 1973) and emerge 45 to 75 days after egg fertilization,

dependi ng on water temperature (Calhoun 1944; Lea 1968). When movi ng from

natal gravels to rearing areas, rainbow trout fry exhibit what appears to be

three di sti nct geneti ca lly controlled movement patterns: (1) movement downstream to a larger river, lake, or to the ocean; (2) movement upstream from an

outlet river to a lake; or (3) local dispersion within a common spawning and

rearing area to areas of low velocity and cover (Raleigh and Chapman 1971).

Fry of 1ake resident fi sh may either move into the 1ake from natal streams

during the first growing season or overwinter in the spawning stream and move

into the lake during subsequent growing seasons.

Fry residing in streams prefer shallower water and slower velocities than

do other 1ife stages of stream trout (Mi 11 er 1957; Horner and Bjornn 1976).

Fry utilize velocities less than 30 cm/sec, but velocities less than 8 cm/sec

are preferred (Griffith 1972; Horner and Bjornn 1976). Fry survival decreases

with increased velocity after the optimal velocity has been reached (Bulkley

and Benson 1962; Drummond and McKinney 1965). A pool area of 40% to 60% of

the total stream area is assumed to provide optimal fry habitat. Cover in the

form of aquatic vegetation, debris piles, and the interstices between rocks is

critical. Griffith (1972) states that younger trout live in shallower water

and stay closer to escape cover than do older trout. Few fry are found

8
more than 1 m from cover. As the young trout grow, they move to deeper,

faster water. Everest (1969) suggested that one reason for this movement was

the need for cover, which is provided by increased water depth, surface turbulence, and substrate that consists of large material.

Stream resident trout fry usually overwinter in shallow areas of low

velocity near the stream margin, with rubble being the principal cover (Bustard

and Narver 1975a). Optimal size of substrate used as winter cover by rainbow

fry and small juveniles ranges -from 10 to 40 cm in diameter (Hartman 1965;

Everest 1969). An area of substrate of this size class that is 10% of the

total habitat probably provides adequate cover for rainbow fry and small

juveniles. The use of small diameter rocks (gravel) for winter cover may

result in increased mortality due to greater shifting of the substrate (Bustard

and Narver 1975a). The presence of fi nes (~10%) in the riffl e-run areas

reduces the value of the area as cover for fry and small juveniles. Mantelman

(1958) reported a preferred temperature range of 13 to 19° C for fry. Because

fry occupy habitats contiguous with adults, thei r temperature and oxygen

requirements are assumed to be similar to those of adults.

Juvenile. Griffith (1972) reported focal point velocities for juvenile

cutthroat in Idaho of between 10 and 12 cm/sec, with a maximum velocity of

22 cm/sec. Metabolic rates are highest between 11 and 21° C, with an apparent

optimal temperature of between 15 and 20° C (Dickson and Kramer 1971). In

steel head streams, temperatures should be < 13 but> 4° C (optimal 7 to 10° C)

from March until June for normal smoltification to occur (Wagner 1974; Adams

et al. 1975).

Common types of cover for juvenile trout are upturned roots, logs, debris

piles, overhanging banks, riffles, and small boulders (Bustard and Narver

1975a). Young salmonids occupy different habitats in winter than in summer,

with log jams and rubble important as winter cover. Wesche (1980) observed

that larger cutthroat trout (> 15 cm lDng) and juveniles (~ 15 cm) tended to

use instream substrate cover more often than they used streamside cover

(undercut banks and overhanging vegetation). However, juvenile brown trout

preferred streamside cover. An area of cover 15% of the total habitat area

appears to provide adequate cover for juvenile trout.

Because juvenile rainbow trout occupy habitats contiguous with adults,

their temperature and oxygen requirements are assumed to be similar.

HABITAT SUITABILITY INDEX (HSI) MODELS

Figure 1 illustrates the assumed relationships among model variables,

components, and the HSI for the rainbow trout model.

9
Habitat variables Model components

Ave. thalweg d~ePth (V.)

% instream cover (V6A)---------=:3~ Adult

~6 pools (VIC)

Pool class rating (V, S)

% instream cover (V6J)

% pools (VlO)----~---------===-JUVenile

Pool class rating (V, S)

% substrate size Class~(v.)

% pools (V,,) Fry

% riffle fines (V, 6B) HSI

Ave. max. temp. (V2 )

Ave. min. D.O. (V3 )

Ave. water velocity

Ave. gravel size in

spawning areas (V,)

% riffle fines (V, 6A)

------===:::::::~~ Embryo

Max. temperature (V,)

Ave. min. D.O. (V3 )

---======~~ Other a

Ave. base flow (V,.)

pH (V, 3) -----------__

Predominant substrate

% streamside vegetation

%midday shade (V,,)b----------------J

%Ave. daily flow (V,.)c--------------J

% riffle fines (V,6B)---------~

% streamside vegetation

aVariables that affect all life stages.

bOptional variables.

CSteelhead variable.

Figure 1. Diagram illustrating the relationship among model variables,

components, and HSI.

10
Model Applicability

Geographic area. The following models are applicable over the entire

North American range of the rainbow trout.

Season. The model rates the year-round freshwater habitat of rainbow

trout.

Cover types. The model is applicable to freshwater riverine or lacustrine

habitats.

Minimum habitat area. Minimum habitat area is the minimum area of continuous habi tat that is requi red for a speci es to 1i ve and reproduce. Because

trout can move considerable distances to spawn or locate suitable summer or

winter rearing habitat, no attempt has been made to define a minimum amount of

habitat for the species.

Verification level. An acceptable level of performance for this rainbow

trout model is for it to produce an index between 0 and 1 that the authors and

other biologists familiar with rainbow trout ecology believe is positively

correlated with long term carrying capacity of the habitat. Model verification

consisted of testing the model outputs from sample data sets developed by the

authors to simulate rainbow trout habitat of high, medium, and low quality and

model review by rainbow trout experts.

Model Description

The HSI model consists of five components: Adult (CA); Juvenile (CJ);

Fry (CF); Embryo (CE); and Other (CO), Each life stage component contains

variables specifically related to that component. The component Co contains

variables related to water quality and food supply that affect all life stages

of rainbow trout.

The model utilizes a modified limiting factor procedure. This procedure

assumes that model variables and components with suitability indices in the

average to good range, > 0.4 but < 1.0, can be compensated for by hi gher

suitability indices of other related model variables and components. However,

variables and components with suitabilities s 0.4 cannot be compensated for

and, thus, become limiting factors for the habitat suitability.

Adult component. Variable V6 , percent instream cover, is included because

standing crops of adult trout are assumed to be related to the amount of cover

available based on studies of brook and cutthroat trout. Percent pools (V i O)

is included because pools provide cover and resting areas for adult trout.

Variable V lO also quantifies the amount of pool habitat that is needed.

Variable ViS' pool class rating, is included because pools differ in the

amount and quality of escape cover, winter cover, and resting areas that they

11
provide. Average thalweg depth (V 4 ) is included because average water depth

affects the amount and quality of pools and instream cover available to adult

trout and the migratory access to spawning and rearing areas.

Juvenile component. Variables Vs , percent instream cover; VlD , percent

pools; and ViS' pool class rating are included in the juvenile component for

the same reasons listed above for the adult component. Juvenile rainbow trout

use these essential stream features for escape cover, winter cover, and resting

areas.

Fry component. Variable Va, percent substrate size class, is included

because trout fry utilize substrate as escape cover and winter cover. Variable

Vi O, percent pools, is included because fry use the shallow, slow water areas

of pools and backwaters as resting and feeding stations. Variable V1 6 , percent

riffle fines, is included'because the percent fines affects the ability of the

fry to utilize the rubble substrate for cover.

Embryo component. It is assumed that habitat suitability for trout

embryos depends primari lyon average maximum water temperature, V2 ; average

minimum dissolved oxygen, V3 ; average water velocity, Vs ; gravel size in

spawning areas, V7 ; and percent riffle fines, ViS' Water velocity (Vs ),

gravel size (V 7 ) , and percent fines (ViS) are interrelated factors that effect

the transport of dissolved oxygen to the embryo and the removal of metabolic

waste products from the embryo. In addition, the presence of too many fines

in the redds blocks movement of the fry from the i ncubati ng gravels to the

stream.

Other component. This component contains model variables for two subcomponents, water qual i ty and food supply, that affect all 1i fe stages. The

subcomponent water quality contains four variables: maximum temperature (Vi);

average minimum dissolved oxygen (V 3 ) ; pH (V 1 3 ) ; and average base flow (V 1 4 ) .

The waterflow of all streams fluctuates on a seasonal cycle, and a correlation

exists between the average annual daily streamflow and the annual low base

flow period. Average base flow (V 14 ) is included to quantify the relationship

between annual water flow fluctuations and trout habitat suitabil ity. These

four variables affect the growth and survival of all life stages except

embryos, whose water quality requirements are included with the embryo

component. The subcomponent food supply conta ins three vari ab1es: domi nant

substrate type (V 9 ) ; percent streamside vegetation (V ll ) ; and percent riffle

fines (ViS)' Predominant substrate type (V 9 ) is included because the abundance

of aquatic insects, an important food item for rainbow trout, is correlated

with substrate type. Variable V16 , percent fines in riffle-run and spawning

areas, is included because the presence of excessive fines in riffle-run areas

12
reduces the production of aquatic insects.

allochthonous materials are an important

productive trout streams.

Variable Vll is included because

source of nutrients in cold, unVariables V1 2 , VI?' and V18 are optional variables to be used only when

needed and appropriate. Streamside vegetation, V1 2 , is an important means of

controlling soil erosion, a major source of fines in streams, and for input of

terrestrial insects. Variable VI?' percent midday shade, is included because

the amount of shade can affect water temperature and photosynthesis in streams.

Average daily flows, V18 , are associated with rapid upstream migration of

steel head adults. Variables V1 2 and VI? are used primarily for streams 50 m

wide where temperature, photosynthesis, or erosion problems occur or when

changes in the riparian vegetation are part of a potential project plan.

Variable V18 is used only for habitat evaluation for spawning migration of

steel head trout.

Suitability Index (SI) Graphs for Model Variables

This section contains suitability index graphs for the 18 model variables.

Equations and instructions for combining groups of variable SI scores into

component scores and component scores into rainbow trout HSI scores are

included.

The graphs were constructed by quantifying information on the effect of

each habitat variable on the growth, survival, or biomass of rainbow trout.

The curves were built on the assumption that increments of growth, survival,

or biomass plotted on the y-axis of the graph could be directly converted into

an index of suitability from 0.0 to 1.0 for the species, with 0.0 indicating

unsuitable conditions and 1.0 indicating optimal conditions. Graph trend

1ines represent the authors' best estimate of suitabi 1ity for the various

levels of each variable. The graphs have been reviewed by biologists familiar

with the ecology of the species, but some degree of SI variability exists.

The user is encouraged to modify the shape of the graphs when existing regional

information indicates that the variable suitability relationship is different

from that illustrated.

The habitat measurements and the SI graph construction are based on the

premise that extreme, rather than average, values of a variable most often

1imit the carrying capacity of a habitat. Thus, extreme conditions, such as

maximum temperatures and minimum dissolved oxygen levels, are often used in

the graphs to derive the SI values for the model. The letters Rand L in the

habitat column identify variables used to evaluate riverine (R) or lacustrine

(L) habitats.

13
14
R,L

V3 Average mlnlmum 1.0

dissolved oxygen

(mg/1) during the 0.8 late growing season ><

low water period and QJ

"'0

during embryo develop- s::

...... 0.6

ment (adult, juvenile, >,

fry, and embryo), +J

'r-

.-- 0.4 'rFor lacustrine habitats, ..Cl

ttl

use the dissolved oxygen

+J

'r- 0.2

readings in temperature ::I

(/)

zones nearest to optimal 0.0 where dissolved oxygen

3

6

9 is > 3 mg/1. mg/1 A = 15° C B = > 15° C

R V,. Average thalweg depth 1.0

(em) during the late

growing season low >< 0.8 water period (adult). QJ

"'0

s::

A= 5 m stream width ...... 0.6

B=> 5 m stream width 'r-

:;:::: 0.4

..Cl

ttl

+J

'r- 0.2 ::I

(/)

0.0

a 15 30 45 60

em

R

Vs Average velocity 1.0

(em/sec) over spawning

areas during embryo >< 0.8 development. QJ

"'0

s::

...... 0.6

>,

+J

'r-

:;:::: 0.4

..Cl

ttl

+J

'; 0.2 (/)

0.0

a 25 50 75 100

em/sec

15
R Percent instream

cover during the

late growing season

low water period

at depths 15 cm

and velocities < 15 cm/sec. J = juveniles A = adults

x 0.8 OJ

"'C

oS 0.6

;= 0.4 .r-

..0

to

.~ 0.2 :J

VJ

o 10 20%

30 40

R Average size of substrate (cm) in spawning areas, preferably

during the spawning

period. A = average size of

spawner

< 50 cm

B= average size of

spawner 50 cm

To derive an average

value for use with graph V7 , include areas containing the best spawning

substrate sampled until

all potential spawning

sites are included or

until the sample contains

an area equal to 5% of the

total rainbow habitat

being evaluated.

16

1.0

x 0.8 OJ

"'CC

......

>, 0.6

+J

.r-

:;: 0.4

..0

to

+J

.r-

:J 0.2 VJ

0.0

0

5

em

10
R Percent substrate size

class (10 to 40 cm)

used for winter and

escape cover by fry

and small juveniles.

x 0.8

(]J

-0C

0.6

>,

+J

:;:::: 0.4

.0

co

0.2 :::J

V'l

o.a ~""""'P'"T'".......--,,........--..,...-~ a 5 10%

15 20

I-

- lIR Vg Preaominant (~ 50%) 1.0

substrate type in

riffle-run areas for 0.8 food production. -0c

A) Rubble or small ...... 0.6

boulders (or >,

+J

aquatic vegeta- :;:::: 0.4 tion in spring .0

areas) predom- co

+J

inant; limited .; 0.2

amounts of V'l

gravel,1arge 0.0

boulders, or

bedrock.

S) Rubble, gravel,

boulders, and fines

occur in approximately equal amounts,

or gravel is predominant. Aquatic

vegetation mayor

may not be present.

C) Fines, bedrock, or

large boulders are

predominant. Rubble

and gravel are

insignificant

(~ 25%).

17

AB

Substra te type

C
R VlO Percent pools during 1.0 the late growing

season low water

x 0.8 period. OJ

"'C

C

0.6

e-,

.....

.....

r- 0.4 ..c

n::l

0.2 :::J

V)

0.0

0 25 50 75 100

%

R Vll Average percent vege- 1.0

tational ground cover

and canopy closure

x 0.8 (trees, shrubs,and OJ

"'C grasses-forbs) along c

the streambank during ~0.6

>, the summer for

allochthonous input. .....

:;::0.4 Vegetation Index = ..c

2(% shrubs) + 1.5(% n::l

grasses) + (% trees). ..... 0.2 :::J

V)

(For streams 50 m wide) 0.0

0 100 200 300

Vegetation index

R V12 Average percent rooted 1.0

(Optional) vegetation and stable

rocky ground cover

along stream bank. x O.8

OJ

"'C

.s 0.6

;::0.4 .....

..c

n::l

..... 0.2 :::J

V)

0.0

0 25 50 75 100

%

18
R,L V13 Annual maximal or 1.0 minimal pH. Use the

measurement with the

lowest 51 value. 0.8

-c

c

For lacustrine habitats, ......

>, O. 6

measure pH in the zone +J

with the best combination ......

of dissolved oxygen and 0.4

temperature. to

+J

.; 0.2

V'l

0.0

5 6 7 8 9 10

pH

R V14 Average annual base 1.0

flow regime during the

late summer or winter

x 0.8 low flow period as a Q)

percentage of the -c

c

average annual daily ...... 0.6

flow. >,

+J

......

:;:::: 0.4 .c

to

+J

.; 0.2

V'l

0.0

a 25 50 75 100

%

19
Pool class rating

.

.

-

R V15 Pool class rating during 1.0

the late growing season

low flow period. The 0.8 rating is based on the "0 % of the area that con- e

tains pools of the three ...... a 6

>,'

classes described below: .j.J

....

;':0.4

A) 30% of the area ..0

to is comprised of .j.J

1st-class pools. .; 0.2 VI

B) 10% but < 30%

of the area is 0.0

1st-class pools

or 50% is 2ndclass pools.

C) < 10% of the area

is 1st-class pools

and < 50% is 2ndclass pools.

A B C

(See pool class descriptions below)

• First-class pool: Large and deep. Pool depth and size are sufficient to provide a low velocity resting area for several adult

trout. More than 30% of the pool bottom is obscured due to depth,

surface turbul ence, or the presence of structures, such as logs,

debris piles, boulders, or overhanging banks and vegetation. Or,

the greatest pool depth is 1.5 m in streams s 5 m wide or 2 m

deep in streams> 5 mwide.

• Second-class pool: Moderate size and depth. Pool depth and size

are sufficient to provide a low velocity resting area for a few

adult trout. From 5 to 30% of the bottom is obscured due to surface

turbulence, depth, or the presence of structures. Typical secondclass pools are large eddies behind boulders and low velocity,

moderately deep areas beneath overhanging banks and vegetation.

• Third-class pool: Small or shallow or both. Pool depth and size

are sufficient to provide a low velocity resting area for one to a

very few adult trout. Cover, if present, is in the form of shade,

surface turbulence, or very limited structures. Typical third-class

pools are wide, shallow pool areas of streams or small eddies behind

boulders. The entire bottom area of the pool is visible.

20
R V16 Percent fines « 3 mm) 1.0 in riffle-run and

spawning areas during

average summer flows. 0.8

"'0

s::

A = spawning ......

>, 0.6 B = riffle-run .j.J

......

:;:::: 0.4 ..0

to

.j.J

.; 0.2 Vl

0.0

a 15 30 45 60

%

R V17 PerGent of stream area 1.0

(Optional) shaded between 1000 and

1400 hrs (for streams

50 m wide). Do not 0.8

"'0

use for cold « 18° C s::

...... max. temp. ), unproduc- >, 0.6

tive streams. .j.J

......

r-

:0 0.4 to

.j.J

.; 0.2 Vl

0.0

a 25 50 75 100

%

R V18 Percent average daily 1.0

(Optional) flow during the season

of upstream migration of x 0.8 adult st.eel head . Q)

"'0

s::

...... 0.6

>,

.j.J

......

:;:::: 0.4 ..0

to

.j.J

...... 0.2 Vl

0.0

25 50 75 100 125

%

21
An HS1 based on the concept of a limiting factor can be obtained for a

particular life stage of rainbow trout, or all life stages combined, by

selecting the lowest suitability index (S1) for the appropriate listed habitat

variables as is done in Table 1.

Alternate models and mathematical methods of aggregating S1 1s into life

stage and species HS1 1s are presented in the following pages.

Table 1. Matrix table for displaying suitability indices (S1 Is) for

rainbow trout habitat variables.

S1 1 s

Variables Adult Embryo Fry Juvenile Other

V1 Maximum temper~ture X

V2 Maximum temperature (embryo) X

V3 Minimum dissolved 02 X X

V2 Average thalweg depth X

Vs Average velocity (spawning) X

V, % cover X X

V7 Substrate size (spawning) X

V. % substrate class X

Vg Substrate type (food) X

VlO % pools X X X

Vll % riparian vegetation X

V12 % ground cover (erosion)a

V13 Maximum-minimum pH X

V14 Average annual base flow X

VlS Pool class X X

V16 % fines X X X

V17 % shadea

VlI % average daily flowa

aOptional variables.

22
Data sources and the assumptions used to construct the suitability index

graphs for rainbow trout HSI models are presented in Table 2.

Riverine Model

Thi s mode 1 uses a 1ife stage approach with fi ve components: adult;

juvenile; fry; embryo; and other.

Case 2:

Case 3: Steel head (CAS)

If V4 or (V i O x Vi s)I/2 is S 0.4 in either equation, then C

A = the lowest

factor score.

Juven il e (CJ)' CJ variables: V6; VIC; VIS; and V2A

Case 1:

V6 + VlQ + VlS

C = J 3

Or, if any variable is S 0.4, CJ = the lowest variable score.

23
Table 2. Literature sources and assumptions for rainbow trout

suitability indices.

Variable and a

source Assumptions

Black 1953

Garside and Tait 1958

Dickson and Kramer 1971

Hanel 1971

May 1973

Cherry et al. 1977

Snyder and Tanner 1960

Calhoun 1966

Zaugg and McLain 1972

Zaugg and Wagner 1973

Wagner 1974

Randall and Smith 1967

Doudoroff and Shumway 1970

Trojnar 1972

Sekulich 1974

Delisle and Eliason 1961

Estimated by authors.

Delisle and Eliason 1961

Thompson 1972

Hooper 1973

Silver et al. 1963

Average maximal daily water temperatures have a greater effect on trout

growth and survival than minimal

temperatures. The temperature that

supports the greatest scope of

activity is optimal. In addition,

the temperature range associated with

rapid migration rates for adult steelhead is optimal.

The average maximal daily water temperature during the embryo and smoltification development periods that is related

to the highest survival of embryos and

normal development of smolts is optimal.

Temperatures that reduce survival or

development of smolts are suboptimal.

The average minimal daily dissolved

oxygen level during embryo development

and the late growing season that is

related to the greatest growth and

survival of rainbow trout and trout

embryos is optimal. Dissolved oxygen

concentrations that reduce survival

and growth are suboptimal.

Average thalweg depths that provide

the best combination of pools,

instream cover, and instream movement

of adult trout are optimal.

The average velocities over spawning

areas affect habitat suitability

because dissolved oxygen is carried

to, and waste products are carried

away from, the developing embryos.

Average velocities that result in

the highest survival of embryos are

optimal. Velocities that result in

reduced survival are suboptimal.

24
Table 2. (continued)

a Variable and source Assumptions

Boussu 1954

Elser 1968

Lewis 1969

Wesche 1980

Orcutt et al. 1968

Bjornn 1969

Phillips et al. 1975

Duff 1980

Trout standing crops are correlated

with the amount of usable cover.

Usable cover is associated with

water 15 em deep and velocities

15 em/sec. These conditions are

associated more with pool than with

riffle conditions. The best ratio

of habitat conditions is approximately

50% pool area to 50% riffle area. Not

all of the area of a pool provides

usable cover. Thus, it is assumed

that optimal conditions exist when

usable cover comprises < 50% of the

total stream area.

The average size of spawning gravel

that is correlated with the best water

exchange rates, proper redd construction, and highest fry survival is assumed

to be optimal. The percent total spawning area needed to support a good nonanadromous trout population

was calculated from the following

assumptions:

1. Excellent riverine trout habitat

supports about 500 kg/ha.

2. Spawners comprise about 80% of

the weight of the population.

500 kg x 80% = 400 kg of

spawners.

3. Rainbow adults average about

0.2 kg each.

400 kg

0.2 kg

= 2,000 adult spawners

per hectare

4. There are two adults per redd.

2,000 = 1 000 pairs 2 '

25
Table 2. (continued)

a Variable and source Assumptions

5. Each redd covers 0.5 m2 •

1,000 x 0.5 500 m2/ha

6. There are 10,000 m2 per hectare.

105~~0 = 5% of total area ,

Hartman 1965

Everest 1969

Bustard and Narver 1975a

Pennak and Van Gerpen 1947

Hynes 1970

Binns and Eiserman 1979

Elser 1968

Fortune and Thompson 1969

Hunt 1971

Idyll 1942

Delisle and Eliason 1961

Chapman 1966

Hunt 1971

Oregon/Washington Interagency

Wildlife Conference 1979

Raleigh and Duff 1980

Hartman and Gill 1968

Behnke and Zarn 1976

The substrate size range selected

for escape and winter cover by trout

fry and small juveniles is assumed to

be optimal.

The predominant substrate type containing the greatest numbers of aquatic

insects is assumed to be optimal for

insect production.

The percent pools during late summer

low flows that is associated with the

greatest trout abundance is optimal.

The average percent vegetation along

the streambank is related to the

amount of allochthonous materials

deposited annually in the stream.

Shrubs are the best source of

allochthonous materials, followed by

grasses and forbs, and then trees.

The vegetational index is a reasonable

approximation of optimal and suboptimal

conditions for most trout stream

habitats.

The average percent rooted vegetation

and rocky ground cover that provides

adequate erosion control to the stream

is optimal.

The average annual maximal or minimal

pH levels related to high survival of

trout are optimal.

26
Table 2. (concluded)

a Variable and source Assumptions

V1 4 Duff and Cooper 1976

Binns 1979

V1 S Lewis 1969

V1 6 Cordone and Kelly 1961

Bjornn 1969

Phillips et al. 1975

Crouse et al. 1981

V1 7 Sabean 1976, 1977

Anonymous 1979

V1 B Withler 1966

Everest 1973

Flow variations affect the amount and

quality of pools, instream cover, and

water quality. Average annual base

flows associated with the highest

standing crops are optimal.

Pool classes associated with the

highest standing crops of trout are

optimal.

The percent fines associated with the

highest standing crops of food organisms,

embryos, and fry in each designated area

are optimal.

The percent of shaded stream area

during midday that is associated with

optimal water temperatures and photosynthesis rates is optimal. b

The above average daily flows (freshets)

associated with rapid upstream migration~

of steel head adults are optimal. Low

flows associated with migration delays

are suboptimal.

aThe above references include data from studies on related salmonid species.

This information has been selectively used to supplement~ verify, or fill

data gaps on the habitat requirements of rainbow trout.

bShading is highly variable from site to site. Low elevations with warmer

climates require abundant shading to maintain cool waters. At higher

elevations with cooler climates, the absence of shading is beneficial because

it results in higher photosynthetic rates and warming of water to a more

optimal temperature.

27
Case 2: Steel head (CJ S)

Or, if VI O or (Va X V1 6 ) 1/ 2 is 0.4, CF

= the lowest factor score.

V .

Sl

habitat area 10.05 (output cannot exceed 1.0)

Steps in calculating CE:

A. A potential spawning site is a ? 0.5 m2 area of gravel, with an

average diameter of 0.3 to 8.0 cm, covered by flowing water? 15 cm

deep. For steelhead, increase the spawning site area from 0.5 to

2.0 m and the gravel size to 0.3 to 10.0 cm. At each spawning site

sampled, record:

1. The average water velocity over the site;

2. The average size of all gravel 0.3 to 8.0 cm;

3. The percentage of fines < 0.3 cm in the gravel; and

4. The total area.

B. Derive a spawning site suitability index (V s) for each site by combining

Vs, V7 , and V1 6 values for each site as follows.

C. Derive a weighted average (Vs) for all sites included in the sample.

Select the best V

s

scores until all sites are included or until

a total spawning area equal to, but not exceeding, 5% of the total

trout habitat has been included, whichever comes first.

n

r A.

. 1 1 1=

total

28
where Ai = the area of each spawning site in m2 , but L Ai cannot

exceed 5% of the total habitat

= the individual 5I Is from the best spawning areas

until all spawning sites have been included or until

the 5I Is from an area equal to 5% of the total habitat

being evaluated have been included, whichever occurs

first.

Disregard area restrictions for steel head. Because advanced juvenile

and adult steelhead mature in the ocean, they can theoretically

utilize a much greater spawning area than nonanadromous rainbows.

D. Derive CE

CE = the lowest score of V2 , V3 , or V

s

(V 9 x V1 G)1/2 + V1 1

2

1/2

where N = the number of variables within the brackets. Note that

variables'V 1 2 and V1 7 are optional and, therefore, can

be omitted (see page 13).

HSI determination. HSI scores can be derived for a single life stage, a

combination of two or more life stages, or all life stages combined. In all

cases, except for the embryo component (C E), an HSI is obtained by combining

one or more life stage component scores with the Co component score.

1. Equal Component Value Method. The equal component value method assumes

that each component exerts equal influence in determining the HSI. This

method should be used to determine the HSI unless information exists that

sUggests that individual components should be weighted differently.

Components: CA; CJ ; CF; CE; and Co

29
where N = the number of components in the equation

Or, if any component is 5 0.4, the HSI = the lowest component value.

Solve the equation for the number of components included in the

evaluation. There will be a minimum of two; one or more life stage

components and the component (CO), unless only the embryo life stage

(CE) is being evaluated, in which case, the HSI = CEo

2. Unequal Component Value Method. This method also uses a life stage

approach with five components: adult (CA) ; juvenile (CJ ) ; fry (CF);

embryo (CE); and other (CO). However, the Co component is divided into

two subcomponents, food (COF) and water quality (COQ). It is assumed that

the COF subcomponent can either increase or decrease the suitability of

the habitat by its effect on growth at each life stage, except embryo.

The COQ subcomponent is assumed to exert an influence equal to the combined

influence of all other model components in determining habitat suitability.

This method also assumes that water quality is excellent; i.e., COQ = 1.

When COQ is < I, the HSI is decreased. In addition, when a basis for

weighting the individual components exists, model component and subcomponent weights can be increased by multiplying each index value by multiples

> 1. Model weighting procedures must be documented.

Components and subcomponents: C

A; CJ ; CF; CE; C

OF; and COQ

Steps:

A. Calculate the subcomponents COF and COQ of Co

(V g x V1 6 ) 1/ 2 + Vii

COF = 2

Or, if any variable is 5 0.4, COQ = the value of the lowest variable.

30
B. Calculate the HSI by either the noncompensatory or the compensatory

option.

Noncompensatory option. This option assumes that degraded water

quality conditions cannot be compensated for by good physical

habitat conditions. This assumption is most likely to be true

for small streams (~ 5 m wide) and for persistently degraded water

quality conditions.

Or, if any component is 0.4, the HSI =the lowest component value.

where N = the number of components and subcomponents inside the

parentheses or, if the model components or subcomponents

are weighted, N = the summation of weights selected

For steel head, substitute CAS and CJ S for C

A and CJ.

If only the embryo component is being evaluated, then HSI = CE x COQ'

Compensatory option. This method assumes that moderately degraded

water quality conditions can be partially compensated for by good

physical habitat conditions. This assumption is most useful for

large rivers (~ 50 m wide) and for temporary poor water quality

conditions.

1)

Or, if any component is 0.4, the HSI ' = the lowest component value.

where N = the number of components and subcomponents in the

equation or, if the model components or subcomponents

are weighted, N = the summation of the weights

selected

For steel head, substitute CAS and CJ S for C

A and CJ.

2) If C

OQ is < HSI ' , then HSI = HSI ' x [1 - (HSI ' - COQ)];

if C

OQ is HSI, then HSI = HSI '.

31
3) If only the embryo component is being evaluated, substitute

CE for HSI ' and follow the procedure in Step 2.

Lacustrine Models

The following models are designed to evaluate rainbow trout lacustrine

habitat. The lacustrine model contains two components, water quality (CWO)

and reproduction (CR) .

Water Ouality (CWO).

Or, if the SI scores for V1 or V3 are S 0.4, CWO = the lowest SI

score for V1 or V3 •

Note: Lacustrine rainbows require a tributary stream for spawning and

embryo development. If the embryo life stage habitat is included in

the evaluation, use the embryo component steps and equations in the

riverine model above, except that the area of spawning gravel needed

is only about 1% of the total surface area of the lacustrine habitat.

n

r A. Vsi i =1 1

Vs= total habitat area /0.01 (output cannot be > 1.0)

HSI

If only the lacustrine habitat is evaluated, the HSI = CWO.

32
Interpreting Model Outputs

Model HSI scores for individual life stages, composite life stages, or for

the species as a whole are a relative indicator of habitat suitability. The

HSI models, in their present form, are not intended to predict standing crops

of fishes throughout the United States. Standing crop limiting factors, such

as interspecific competition, predation, disease, water nutrient levels, and

length of growing season, are not included in the aquatic HSI models. The

models contain physical habitat variables important in maintaining viable

populations of rainbow trout. If the model is correctly structured, a high

HSI score for a habitat would indicate near optimal regional conditions for

rainbow trout for those factors included in the model, intermediate HSI scores

would indicate average habitat conditions, and low HSI scores would indicate

poor habitat conditions. An HSI of 0 does not necessarily mean that the

species is not present; it does mean that the habitat is very poor and that

the species is likely to be scarce or absent.

Rainbow trout tend to occupy riverine habitats where few other fish

species are present. Thus~ factors such as disease, interspecific competition,

and predation may have 1itt1e affect on the model. When the rainbow trout

model is applied to rainbow trout streams conta t ni nq few other species and

similar water quality and length of growing season conditions, it should be

possible to calibrate the model output to reflect the size of standing crops

within some reasonable confidence limits. This possibility, however, has not

been tested with the present model.

Sample data sets selected by the authors to represent high, intermediate,

and low habitat suitabilities are in Table 3, along with the Sl l s and HSI's

generated by the rainbow trout nonanadromous riverine model. The model outputs

calculated from the sample data sets (Tables 4 and 5) reflect what the authors

believe carrying capacity trends would be in riverine habitats with the listed

characteristics; thus, the model meets the specified acceptance level.

ADDITIONAL HABITAT MODELS

Modell

Optimal riverine rainbow trout habitat is characterized by:

1. Clear, cold water with an average maximum summer temperature of < 22° C;

2. Approximately a 1:1 pool-to-riffle ratio;

3. Well vegetated, stable stream banks;

4. Cover 25% of the stream area;

5. Relatively stable water flow regime with < 50% of the annual

fluctuation from the average annual daily flow;

33
Table 3. Sample data sets using the nonanadromous riverine rainbow trout

HS1 model.

Data set 1 Data set 2 Data set 3

Variable Data S1 Data S1 Data S1

Max. temperature

(0C) VI 14 1.0 15 1.0 16 1.0

Max. temperature

(0C) V2 12 1.0 15 0.66 17 0.4

Min. dissolved O2

(mg/l) VJ 9 1.0 7 0.73 6 0.42

Ave. depth (cm) V4 25 0.9 18 0.6 18 0.6

Ave. velocity

(cm/s) Vs 30 1.0 25 0.7 20 0.57

% cover V, 20 A 0.95 10 A 0.65 10 A 0.65

J 1.0 J 0.92 J 0.92

Ave. gravel size

(cm) V7 4 1.0 3 1.0 2.5 1.0

Predom. substrate

size (cm) V. 15 1.0 7 0.7 7 0.7

Predom. substrate

type Vg Class A 1.0 Class 8 0.6 Class 8 0.6

% pools VlO 55 1.0 15 0.65 10 0.46

% streamside

vegetation Vll 225 1.0 175 1.0 200 1.0

% bank vegetation V12 95 1.0 40 0.6 35 0.5

Max. pH VlJ 7.1 1.0 7.2 1.0 7.2 1.0

% average base

flow V14 37 0.8 30 0.6 25 0.5

Pool class rating Vl5 Class A 1.0 Class 8 0.6 Class C 0.3

% fines (A) VlG 5 1.0 20 0.5 20 0.5

% fines (8) VlG 20 0.9 30 0.6 30 0.6

% midday shade V17 60 1.0 60 1.0 60 1.0

34
Table 4. Average value method.

Suitability index

Variable

Component

Data set 1 Data set 2 Data set 3

C

A

CJ

CF

CE

Co

Species HSI

0.95 0.62 0.37

1. 00 0.72 0.30

1.00 0.65 0.55

1. 00 0.66 0.40

0.96 0.79 0.73

0.98 0.68 0.30

Table 5. Average value, probability method.

Suitability index

Variable Data set 1 Data set 2 Data set 3

Component

C

A 0.95 0.62 0.37

CJ 1. 00 0.72 0.30

CF 1. 00 0.65 0.55

CE 1. 00 0.66 0.40

COF 0.97 0.80 0.80

COQ 0.95 0.81 0.68

Species HSI

Noncompensatory 0.94 0.56 0.30

Compensatory 0.95 0.70 0.30

35
6. Relatively stable summer temperature regime, averaging about

13° C ± 4° C; and

7. A relatively silt free rocky substrate in riffle-run areas.

HSI = number of attributes prese~t

7

Model 2

A riverine trout habitat model has been developed by Binns and Eiserman

(1979) and Binns (1979). Transpose the model output of pounds per acre to an

index as follows:

HSI = mod:l output.of pounds per acre

reglonal maXlmum pounds per acre

Model 3

Optimal lacustrine rainbow trout habitat is characterized by:

1. Clear, cold water with an average summer midepilimnion temperature

of < 22° C;

2. Dissolved oxygen content of epilimnion of 8 mg/l;

3. Access to riverine spawning tributaries;

4. A midepilimnion pH of 6.5-8.0; and

5. Abundance of aquatic invertebrates.

HSI = number of attributes present

5

However, a high elevation lake with optimal habitat will have only a

fraction of the trout production of a more eutrophic lake at a lower elevation,

if no other fish species are present in either lake.

Model 4

A low effort system for predicting habitat suitability of planned cool

water and cold water reservoirs as habitat for individual fish species is also

available (McConnell et al. 1982).

36
INSTREAM FLOW INCREMENTAL METHODOLOGY (IFIM)

The U.S. Fish and Wildlife Service1s Instream Flow Incremental Methodology

(IFIM), as outlined by Bovee 1982, is a set of ideas used to assess instream

flow problems. The Physical Habitat Simulation System (PHABSIM), described by

Milhous et al. 1981, is one component of IFIM that can be used by investigators

interested in determining the amount of available instream habitat for a fish

species as a function of streamflow. The output generated by PHABSIM can be

used for several IFIM habitat display and interpretation techniques, including:

1. Optimization. Determination of monthly flows that minimize habitat

reductions for species and life stages of interest;

2. Habitat Time Series. Determination of the .impact of a project on

habi tat by impos i ng project operation curves over hi stori ca1 fl ow

records and integrating the difference between the curves; and

3. Effective Habitat Time Series. Calculation of the habitat requirements of each life stage of a fish species at a given time by using

habitat ratios (relative spatial requirements of various life

stages).

Suitability Index Graphs as Used in IFIM

PHABSIM utilizes Suitability Index graphs (SI curves) that describe the

instream suitability of the habitat variables most closely related to stream

hydraulics and channel structure (velocity, depth, substrate, temperature, and

cover) for each major life stage of a given fish species (spawning, egg incubation, fry, juvenile, and adult). The specific curves required for a PHABSIM

analysis represent the hydraulic-related parameters for which a species or

life stage demonstrates a strong preference (i .e., a pelagic species that only

shows preferences for velocity and temperature will have very broad curves for

depth, substrate, and cover). Instream Flow Information Papers 11 (Milhous

et al. 1981) and 12 (Bovee 1982) should be reviewed carefully before using any

curves for a PHABSIM analysis. SI curves used with the IFIM are quite similar

to the SI curves developed in many HSI models. These two types of SI curves

may be interchangeable after conversion to the same units of measurement

(English, metric, or codes). SI curve validity is dependent on the quality

and quantity of information used to generate the curve. The curves used need

to accurately reflect the conditions and assumptions inherent to the model(s)

used to aggregate the curve-generated SI values into a measure of habitat

suitability. If the necessary curves are unavailable or if available curves

are inadequate (i.e., built on different assumptions), a new set of curves

should be generated.

37
There are several ways to develop 51 curves. The method selected depends

on the habitat model that will be used and the available database for the

species. The transferabil ity of the curve is not obvious and, therefore, the

method by which the curve is generated and the extent of the database are very

important. Care also must be taken to choose the habitat model most appropriate for the specific study or evaluation; the choice of models will determine the type of 51 curves that will be used.

A system with standard terminology has been developed for classifying 51

curve sets and describing the database used to construct the curves in IFIM

applications. There are four categories in the classification. A category

one curve has a generalized description or summary of habitat preferences as

its database. This type of curve is based on information concerning the upper

and lower limits of a variable for a species (e.g., juveniles are usually

found at water depths of 0.3 to 1.0 m). Expert opi ni on can also be used to

define the optimal or preferred condition within the limits of tolerance

(e.g., juveniles are found at water depths of 0.3 to 1.0 m, but are most

common at depths from 0.4 to 0.6 m).

Utilization curves (category two) are based on frequency analyses of fish

observations in the stream environment with the habitat variables measured at

each sighting [see Instream Flow Information Paper 3 (Bovee and Cochnauer

1977) and Instream Flow Information Paper 12 (Bovee 1982:173-196)]. These

curves are designated as utilization curves because they depict the habitat

conditions a fish has been observed to use within a specific range of available

conditions. If the data are correctly collected for utilization curves, the

resul t i ng function represents the probabi 1ity of occurrence of aparti cul ar

environmental condition, given the presence of a fish of a particular species,

P(EIF). However, due to sampling problems, a utilization curve cannot be

assumed to reflect fish preference or optimal conditions. Also, utilization

curves may not be transferable to streams that differ substantially in size or

complexity from the streams where the data were obtained.

A preference curve (category three) is a utilization curve that has been

corrected for environmental bias. For example, if 50% of the fish are found

in pools over 1.0 m deep, but only 10% of the stream has such pools, the fish

are actively selecting that type of habitat. Preference curves approximate

the function of the probabi 1i ty of occurrence of a fi sh ina gi ven set of

environmental conditions:

P(FIE) - P(EIF) - P( E)

38
Only a limited number of experimental data sets have been compiled into

IFIM preference curves. The development of these curves should be the goal of

all new curve development efforts for use in IFIM.

An additional set of curves is still largely conceptual. One type of

curve under consideration is a cover-conditioned, or season-conditioned,

preference curve set. Such a curve set woul d con s i st of di fferent depthvelocity preference curves as a function or condition of the type of cover

present or the time of year. No fourth category curves have been developed at

this time.

The advantage of these last two sets of curves is the significant improvement in precision and confidence in the curves when applied to streams similar

to the streams where the original data were obtained. The degree of increased

accuracy and transferability obtainable when applying these curves to dissimilar streams is unknown. In theory, the curves should be widely transferable to any stream in which the range of environmental conditions is within

the range of conditions found in the streams from which the curves were developed.

Availability of Graphs for Use in IFIM

Numerous curves are available for the IFIM analysis of rainbow trout

habitat (Table 6). Investigators are asked to review the curves (Figs. 2-5)

and modify them, if necessary, before using them.

Spawning. For IFIM analyses of rainbow trout spawning habitat, use

curves for the time period during which spawning occurs (which is dependent on

locale). Spawning curves are broad and, if more accuracy is desired, investigators are encouraged to develop their own curves which will specifically

reflect habitat utilization at the selected site.

Spawning velocity. Hartman and Galbraith (1970) measured water velocities

0.66 feet above 550 redds during April through June, 1966 and 1967, in the

Lardeau River, British Columbia, and found few redds constructed in areas

where vel oci ties were 1ess than 1.0 feet per second (fps); most redds were

associated with velocities ranging 1.6 to 3.0 fps (velocities from zero to

greater than 4.0 fps were available). Smith (1973) determined that 95% of the

redds (n = 51) observed in the Deschutes River, Oregon, were in velocities

ranging from 1.6 to 3.0 fps; Hooper (1973) measured velocities over redds

(n = 10) which ranged from 1.4 to 2.7 fps in the South Fork of the Feather

River, Cal ifornia; and Orcutt et al. (1968) found that average velocities

0.4 feet above redds (n = 54 to 68) ranged from 2.3 to 2.5 fps in Idaho

streams. The SI curve for spawning velocity (Fig. 2) assumes that velocities

less than 1.0 or greater than 3.0 fps are unsuitable for rainbow trout

spawning.

39
+'>0

o

Table 6. Availability of curves for IFIM analysis of rainbow trout habitat.

Velocitl a SUbstratea,b Temperaturea Covera Depth

Spawning Use SI curve, Use SI curve, Use SI curve, Use SI curve, No curve

Fig. 2. Fig. 2. Fig. 2. Fig. 2. necessary.

Egg incubation Use SI curve, Use SI curve, Use SI curve Use SI curve No curve

Fig. 2. Fig. 2. for V7B. for V2B. necessary.

Fry Use SI curve, Use SI curve, Use SI curve, Use SI curve, No curve

Fig. 3. Fig. 3. Fig. 3. Fig. 3. available.

Juvenile Use SI curve, Use SI curve, Use SI curve, Use SI curve, Use SI curve

Fig. 4. Fig. 4. Fig. 4. Fig. 4. for V6.

Adult Use SI curve, Use SI curve, Use SI curve, Use SI curve, Use SI curve

Fig. 5. Fig. 5. Fig. 5. Fig. 5. for V6.

aWhen use of SI curves is prescribed, refer to the appropriate curve in the HS1 or 1F1M section.

bThe following categories must be used for 1F1M analyses (see Bovee 1982):

1 = plant detritus/organic material

2 = mud/soft clay

3 = silt (particle size < 0.062 mm)

4 = sand (particle size 0.062-2.000 mm)

5 = gravel (particle size 2.0-64.0 mm)

6 = cobble/rubble (particle size 64.0-250.0 mm)

7 = boulder (particle size 250.0-4000.0 mm)

8 = bedrock (solid rock)
I

0.0 I .- o 2 3 4 5

Velocity (ft/sec)

Coordinates 1.0

x -L

0.0 0.0 >< 0.8

0.9 0.0 QJ

"'0

1.6 1.0 t:

....... 0.6 3.0 1.0 >,

3.1 0.0 +J

100.0 0.0 ...... 0.4 ..D.

ttl

+J 0.2 U1

1.0

x -L

0.0 0.0 x 0.8 - 0.6 0.0 QJ

"'0

0.7 1.0 t:

.......

8.2 1.0 0.6

>,

8.3 0.0 +J

...... 100.0 0.0 0.4 - ..D.

ttl

+J

...... 0.2- U1

0.0

0 2 4 6 8 10

Depth (ft)

1.0

x -L

0.0000 0.0 0.8 0.0005 0.0 x

QJ

0.0010 1.0 "'0

t:

4.0000 1.0 ....... 0.6

4.1000 0.0 >,

+J

100.0000 0.0 ......

r- 0.4 ......

..D.

ttl

+J

...... 0.2 U1

o.0 -I-__--r-_..J-__--.-_~

o 1 2 3 456 7 8

Substrate particle diameter (inches)

Figure 2. SI curves for rainbow trout spawning velocity,

depth, substrate, and temperature.

41
Coordinates 1.0

x -.L

0.0 0.0 >< 0.8

35.0 0.0 Q)

"'0

36.0 1.0 s::

.- 0.6 60.0 1.0 >,

61.0 0.0 'r100.0 0.0 ..-

.r- 0.4 ..c

co

'r- 0.2 :J

(/)

0.0

•

-

-

-

.

. • o 20 40 60 80 100

Temperature (OF)

Figure 2. (concluded)

42
Spawning Dept~. Smith (1973) found 95% of rainbow trout redds in depths

greater than 0.6 feet; Hooper (1973) found depths of redds ranged from 0.7 to

1.1 feet; Orcutt et al. found redds in depths from 0.7 to greater than

5.0 feet; Hartman and Galbraith (1970) found the majority of redds (n = 550)

in depths ranging from 1.6 to 8.2 feet, and the most intensive nest digging

occurred in depths of 5.7 to 6.6 feet (maximum depths available ranged from 13

to 16 feet). Therefore, depths less than 0.6 and greater than 8.2 feet are

assumed to be unsuitable for spawning (although 8.2 feet may not be the upper

limit; Fig. 2).

Spawning substrate. Hartman and Galbraith (1970) found that gravel

composed of particle sizes ranging from 0.04 to 4.0 inches in diameter were

utilized for spawning, two-thirds of which were from 0.5 to 3.0 inches in

diameter (particle sizes to 18 inches in diameter were available). Hooper

(1973) found that preferred spawning substrate consisted of particles from 0.5

to 1.5 inches in diameter, although particles from 0.25 to 3.0 inches were

utilized; Orcutt et al. (1968) found that steelhead favored gravels from 0.5

to 4.0 inches in diameter; Coble (1961) stated that salmonids dug redds in

substrates ranging from silt to 3-inch diameter cobble (particles up to

4 inches in diameter were available) in Lincoln County, Oregon. Therefore,

substrates consisting of particle sizes ranging from silt « 0.002 inches) to

cobble (4.0 inches) are considered suitable for spawning (t.houqh not necessarily suitable for egg incubation; Fig. 2). The particle size range of

spawning substrate selected may be dependent on the size of the spawner.

Spawning cover. No information was found in the literature concerning

cover requirements for rainbow trout spawning. The author assumes that cover

is not important, and it may be omitted from the FISHFIL (Milhous et al.

1981).

Spawning temperature. Scott and Crossman (1973) stated that rainbow

trout usually spawn at 50 to 60° F; Carlander (1969) stated that peak spawning

near Finger Lakes, New York, occurred at 42 to 55° F; Hooper (1973) stated

that temperatures ranging from 37 to 55° F are desirable for spawning; and

Orcutt et al. (1981) found that spawning occurred at 36 to 47° F in Idaho

streams. The author assumes that temperatures rangi ng from 36 to 60° Fare

suitable for spawning (Fig. 2), depending on locale.

Egg incubation. For IFIM analyses of rainbow trout egg incubation

habitat, curves should be used for the time period from the beginning of

spawning to 30 to 100 days beyond the end of spawning, depending on locale and

water temperatures (Carlander 1969). The recommended analysis of incubation

with IFIM is the effective spawning program, which computes suitability of

each stream cell based on both spawning and incubation criteria over a range

of flows. This program is explained in a working paper available from IFG

(Mil hous 1982).

Egg incubation velocity. Evidence suggests that water velocity may not

be important for embryo hatchi ng success if di sso 1ved oxygen concentrations

around embryos are greater than 2.6 ppm (Coble 1961; Silver et al. 1963;

Reiser and White 1981, 1983). At low concentrations of dissolved oxygen,

43
however, apparent velocities must be sufficient to deliver oxygen to embryos,

remove metabolic waste products, and keep the substrate free from silt.

Silver et al. (1963) found that rates of development and lengths of fry upon

hatching were greater at higher velocities and dissolved oxygen concentrations.

Therefore, given suitable spawning velocities (Fig. 2),it may be assumed that

egg incubation velocities above redds which range from 1.0 to 3.0 fps (at

adequate levels of dissolved oxygen and suitable substrate) will yield suitable

apparent velocities among embryos. Another type of incubation velocity

criteria is based on the shear velocities needed to prevent sediment of various

sizes from sett1i ng out on the redds. Thi s approach is documented in the

effective spawning working paper mentioned above.

Egg incubation depth. Depth may not be an important variable for egg

incubation in many cases (Reiser and White 1981, 1983) as long as eggs are

kept moist during incubation and redds are submerged when fry begin to hatch

and emerge. Therefore, the author assumes that the S1 curve for spawning

depth (Fig. 2) may also be used for egg incubation depth.

Egg incubation substrate. Although rainbow trout utilize a wide range of

substrate types for spawning (Coble 1961), the author assumes that particles

must be at least 0.5 inches in diameter to permit adequate percolation for

successful embryonic development, and the S1 curve for V78 (page 16) may be

used.

Egg incubation cover. The author assumes that cover is not important,

and cover may, therefore, be omitted from F1SHF1L. The egg incubation

substrate curve should satisfy embryo cover requirements.

Egg incubation temperature. Kwain (1975) found the highest survival rate

for ra i nbow trout embryos at temperatues of 45 and 50° F; low survi va1 (15 to

40%) at 59° F; and moderate survival at 37 and 41° F. According to Hooper

(1973), the desirable temperature range for egg incubation of trout is 42 to

54° F, and the extremes are 35 and 61° F. Therefore, the S1 curve for V2B

(page 14) may be used.

Fry. Rainbow trout fry lose their yolk sacs at lengths of 1.4 to

1.6 inches, approximately 3-4 months after hatching (Carlander 1969). The

author assumes that fry habitat is required from the end of the spawning

period to 4 months beyond the end of the egg incubation period (from the time

that fry emerge from the spawning gravel to when they become juveniles).

Fry velocity. Moyle et al. (1983) observed fry (~ 2 inches in length) in

Cherry and Eleanor Creeks (n=404), Putah Creek .(n=134), and Deer Creek (n=81),

California. Maximum velocities available were 2 fps in Putah Creek and > 3.44 fps in Cherry, Eleanor, and Deer Creeks. Weighted mean frequencies

were calculated for each velocity and then normalized, with the highest

frequency being set to S1 = 1.0 (Fig. 3).

44
Coordinates

...... 0.4

0.6

0.8

"'C

c

.......

......

-1.-

1.00

0.78

0.19

0.04

0.01

0.01

0.00

0.00

x

0.00

0.49

0.98

1.48

1. 97

2.46

2.95

100.00

o.0 4--------"'T"""'----~=opooI--+

o 2

Mean water column velocity (ft/sec)

n == 619

-

8 10

I I

,

4 6

Depth (ft )

n == 642

I

2

I

,

o

0.0 +---,1'"""'"""'.......,.:=.....-'1'---+

0.6

x 0.8 Q)

"'C

C

.......

...... 0.4 - ......

.0

n::l

+J

...... 0.2- :::l

(/)

-1.-

0.00

0.11

1.00

1.00

0.29

0.13

0.04

0.02

0.01

0.01

0.00

0.00

x

0.00

0.10

0.82

1.64

2.46

3.28

4.10

4.92

5.74

7.38

8.20

100.00

0.6

c-,

+J

x 0.8 Q)

"'C

C

.......

...... 0.4 .0

n::l

+J

.; 0.2 (/)

.x.:

0.00

0.00

0.02

0.01

O. 17

0.13

1.00

1.00

0.18

0.00

0.00

x

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

8. 1

100.0

o 1 234 5 6 7 8

Substrate type (see code key, page 39)

n == 597

Figure 3. SI curves for rainbow trout fry velocity, depth,

substrate, and temperature.

45
Coordinates 1.0

x 1-

0.0 0.00

>< 0.8 32.0 0.00 Q)

37.4 0.08 "'0

c

50.0 0.80 ....... 0.6

56.8 1.00 -fJ

66.2 1.00 .....

r- 0.4 69.8 0.80 .....

.0

77.0 0.00 rtl

-fJ

100.0 0.00 ..... 0.2 (./)

0.0

0 20 40 60 80 100

Temperature (OF)

Figure 3. (concluded)

46
Fry depth. The SI curve for fry depth was developed in the same manner

as the velocity curve, using data from Deer Creek (n=103), Cherry and Eleanor

Creeks (n=404), and Putah Creek (n=135) (Moyle et al. 1983). Depths to 1.7 ft

were available 'in Putah Creek; to 6.6 ft in Deer Creek; and to greater than

9.0 ft in Cherry and Eleanor Creeks. The fi na1 curve (Fi g. 3) was modifi ed

based on the assumption that SI = 1.0 at depths ranging from 0.82 ft (as in

Putah and Deer Creeks) to 1.64 ft (as in Cherry and Eleanor Creeks); and that

SI = 0.0 at a depth of 0.0 ft and SI = 0.11 at a depth of 0.1 ft. For depths

greater than 1.7 ft, Putah Creek was excl uded, and for depths greater than

6.6 ft, Deer Creek was excluded from the analysis.

Fry substrate. The SI curve for fry substrate was generated in the same

way as the curves for depth and velocity. Substrate available in Putah Creek

(n=123) ranged from mud to bedrock; and in Deer Creek (n=70), Cherry Creek,

and Eleanor Creek (n=404) it ranged from silt to bedrock. The curve (Fig. 3)

was modified based on the assumption that SI = 1.0 for cobbles (as in Deer and

Putah Creeks) and for boulders (as in Cherry and Eleanor Creeks). Bustard and

Narver (1975) also found that age 0 steelhead associated with substrate

consisting primarily of particles from 4 to 10 inches in diameter (cobble) in

Carnation Creek, British Columbia, during the winter.

Fry cover. Cover requirements of rainbow trout fry are unknown by IFASG

at this time. The author assumes that substrate is used for cover, and thus

cover may be omitted from FISHFIL; or a cover curve may be developed by the

investigator.

Fry temperature. Peterson et al. (1979), in lab experiments, found that

temperatures preferred by rainbow trout fry (between 1.1 and 1.8 inches in

length) ranged from 56.8 to 58.6° F (n=30). Kwain and McCauley (1978) found

that age was a factor in temperatures preferred (selected) by rainbow trout,

and fry at 1 month selected 66.2° F; at 2 months, 65.3° F; at 3 months,

64.4° F; and at 5 months, 59.7 to 63.7° F. Kwain (1975) found that the growth

rate of fry at 50 F was ten times greater than at 37.4° F. Based on the

i nformat ion avail ab1e for fry up to 1. 8 inches in 1ength and up to 4 months

after hatching, the SI curve for temperature (Fig. 3) is assumed to be reasonably accurate. It will be modified as new information becomes available.

Juvenile. Juvenile rainbow trout range in length from approximately 1.8

to 7.9 inches, or from 4 months of age to sexual maturity (usually age II or

III; Carlander 1969). Juveniles are probably the most difficult life stage

for which to develop criteria, because of the variability in size.

Juvenil e velocity. Factors whi ch may affect velocity preferences of

rainbow trout include water temperature, size and activity of the individual

trout, stream flow, season, habitat availability, species interactions, and

stream location (Logan 1963; Chapman and Bjornn 1969; Bjornn 1971; Everest and

Chapman 1972; Bustard and Narver 1975; Moyle et al. 1983). Moyle et al.

(1983) observed juvenile rainbow trout (from 2.0 to 4.7 "inches in length) in

Putah Creek (n=35), Deer Creek (n=108), Martis Creek (n=58), Cherry Creek, and

Eleanor Creek (n=300), and in the Tuolumne River (n=45). The maximum velocity

available in Putah Creek was 2.0 fps; in the Tuolumne River it was 2.5 fps; in

Martis Creek it was 4.2 fps; and in Deer, Cherry, and Eleanor Creeks it was

47
greater than 3.4 fps. Data from all streams were used to generate the velocity

curve (Fig. 4). Weighted means were calculated for each velocity and then

normalized, with the highest 51 being set to 1.0. The final curve is very

similar to the results of Bustard and Narver (1975) who collected Age 0 (n~78)

and Age 1+ (n~122) juvenile steelhead trout in Carnation Creek, British

Columbia, during the winter. They found that juveniles preferred velocities

less than 0.5 fps, and almost no individuals were found in velocities greater

than 1 fps at 45° F. Gosse (1982), however, found that vel ociti es preferred

by juvenile rainbow trout « 9 inches in length) were partially dependent upon

activity (random or stationary swimming), season, and flow. Gosse found that

the average mean column velocities occupied by juveniles in low to high flows

during random swimming ranged from 0.40 to 0.56 fps in the winter and from

0.43 to 0.75 fps in the summer. During stationary swimming, velocities ranged

from 0.66 to 1.18 fps in the winter and from 1.05 to 2.00 fps in the summer.

Differences may be due in part to differences in the sizes of the juveniles

observed (Chapman and Bjornn 1969).

Juvenile depth. Factors which may affect depth preferences of juvenile

rainbow trout are the same as those which affect velocity preferences. Observations of Moyle et al. (1983) in Putah Creek (n=36, maximum depths of 1.7 ft),

Martis Creek (n=58, depths to 4 ft), Deer Creek (n=126, depths to 6.6 ft),

Tuloumne River (n=44, depths to greater than 9 ft), and Cherry and Eleanor

Creeks (n=301, depths to greater than 9 ft), of juveniles (2.0 to 4.7 inches

in length) indicated substantial variability in depth preferences from stream

to stream, with most fish located in depths of 1 to 4 ft. Bustard and Narver

(1975), however, found that Age 0 steel head in Carnation Creek, British

Columbia, preferred depths to 1.5 ft, while Age 1+ steelhead preferred depths

greater than 3 ft. Also, Gosse (1982) found that the average water depths

occupied by juvenile rainbow trout « 9 to 10 inches in length) in the Green

River below Flaming Gorge Dam, Colorado, ranged between 10 and 14 ft in the

summer and between 18 and 20 ft in the winter (n=lll to 291). Therefore, it

is easy to see that juvenile rainbow trout may occupy a wide variety of depths,

and it is recommended that investigators develop their own depth curves, or

assume that 51 = 1.0 for all depths 2.0 feet (Fig. 4).

Juvenile substrate. Moyle et al. (1983) found most juvenile rainbow

trout (2.0 to 4.7 inches in length) over gravel and cobble in Martis Creek

(n=53), over cobble and boulders in Deer Creek (n=103), and over boulders in

Cherry and El eanor Creeks (n=301). The composite we i ghted substrate curve

(Fig. 4) shows a preference for boulder substrate. In the Green River, Gosse

(1982) found most juveniles « 9 to 10 inches in length) over cobble and

boulders during st.at tonary swimming, but over silt and sand during random

swimming. Bjornn (1971) found a correlation between the movement (out

migration) of juvenile trout and the lack of large cobble substrate in Idaho

streams. Therefore, it may be assumed that cobble and boulders are suitable

juvenile substrate, or curves may be developed that are specific to the area

of interest.

Juvenile cover. Cover requirements or preferences of juveniles are

unknown. It may be assumed that substrate curve reflects cover requirements;

cover curves may be developed by the investigator; cover may be omitted from

FI5HFIL; or, the curve for V

6 may be used to represent juvenile rainbow trout

cover requirements (page 16).

48
Coordinates

0.6

x

0.00

0.49

0.98

1.48

1.97

2.46

3.44

3.50

100.00

.x.:

1.00

0.99

0.59

0.24

0.08

0.02

0.02

0.00

0.00

1. 0 -r-_-...I---.........------fx 0.8

Q)

-0

c

.....

-,.... 0.4 .,....

.0

re:s

+.>

.,.... 0.2 :::s

l/)

2

o.0 -I-.............--.,.......--.............:::=:;::::i.

o

Mean water column velocity (ft/sec)

n = 546

.,....

.,.... 0.4

0.6

x 0.8

Q)

-0

c

.....

.0

re:s

+.>

.; 0.2 l/)

-L

0.0

1.0

1.0

x

0.0

2.0

100.0

0.0 ..................---.--................---....+

o 2 4 6 8 10

Depth (ft)

n = 565

x

0.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

8. 1

100.0

.x.:

0.00

0.00

0.02

0.11

0.21

0.77

1.00

0.47

0.00

0.00

0.8

-0

c

.....

e-, 0.6 +.>

.,....

0.4 re:s

+.>

.; 0.2 l/)

0.0 -r-__IIIIIIIl:i-....--......--.--_ __+_

o 1 234 5 6 7 8

Substrate type (see code key, page 39)

n = 457

Figure 4. SI curves for rainbow trout juvenile velocity, depth,

substrate, and temperature.

49
Coordinates

x

0.0

32.0

50.0

72.0

84.0

100.0

1-

0.0

0.0

1.0

1.0

0.0

0.0

x 0.8 Q)

"'0

C

.......

>, 0.6

.....

..... 0.4

..0

ro

.....

:::J 0.2 U1

o. 0 4-_......""'- .....

o 20 40 60 80 100

Temperature (oF)

Figure 4. (concluded)

50
Juvenile temperature. There has been a great deal of variability among

results of studies undertaken to determine temperature preferences of juvenile

rainbow trout. Cherry et al , (1975) found that temperatures selected and

avoided were a function of acclimation temperature; that rainbow juveniles

selected temperatures ranging from 53 to 72° F when acclimated to 43 to 58° F;

and that the lowest avoidance temperature was 41° F and the highest avoidance

temperature was 77° F at the given accl imation temperatures. Coutant (1977)

listed preferred temperatures of 64 to 66° F and 72° F, and avoidance temperatures of 57 and 72° F. Lee and Rinne (1980) found the critical thermal maxima

for juveniles to be 84° F. McCauley et al. (1977) stated that acclimation

temperatures had no significant effect upon preferred temperatures of

juveniles, which ranged from 50 to 55° F. Kwain and McCauley (1978) found

that temperature preferences were a function of age, and that juvenile rainbow

trout 12 months after hatching preferred a temperature of 55° F. No studies

were found which addressed maximum growth rate/low mortality temperatures. A

final curve was drawn based on the limited information available and professional judgment (Fig. 4).

Adult. For the purposes of this model, rainbow trout are considered to

be adult when they are greater than 7.9 inches in length at age II or III, and

sexually mature (Carlander 1969).

Adult velocity. Moyle et al. (1983) collected rainbow trout adults

(which they defi ned to be > 4.7 inches in 1ength) from Deer Creek (n=104;

maximum velocity> 3.4 fps), Cherry and Eleanor Creeks (n=360; maximum velocity

> 3.4 fps), and the Tuolumne River (n=93; maximum velocity = 2.4 fps). The

resulting weighted normalized curve suggests that preferred mean column velocities are near 0.5 fps. Lewis (1969), however, found a positive correlation

between rainbow trout density and water velocity of 1.65 fps. Gosse (1982)

found that rainbow trout generally tended to reposition themselves in the

water column as streamflow changed, and that fish nose velocity varied less

than mean column velocity with changes in streamflow. Average fish nose

velocities for stationary swimming during the winter ranged from 0.7 to 1.0 fps

(n=640); during the summer they ranged from 0.9 to 1.1 fps (n=224); for random

swimming during the winter they ranged from 0.5 to 0.7 fps (n=308); and during

the summer they ranged from 0.4 to 0.6 fps. Average mean column velocities

for stationary swimming during the winter ranged from 1.1 to 1.7 fps (n=606);

during the summer they ranged from 1.5 to 2.0 fps (n=219); for random swimming

during the winter they ranged from 0.6 to 0.8 fps (n=308); and during the

summer they ranged from 0.6 to 0.7 fps (n=l71). Therefore, the fi na1 curve

(Fig. 5) reflects the range of mean water column velocities preferred by adult

(> 5 to 9 inch lengths) rainbow trout, although preferred fish nose velocities

ranged from 0.5 to 1.1 fps. An investigator may choose to develop new curves

specific to the area of interest.

51
Coordinates 1.0

x .x.:

0.00 0.81 ><

Q) 0.8 0.50 1.00 "'0

t:: 2.00 1.00

2.46 0.02 >, 0.6

2.95 0.02 ,.... 3.44 0.01 ......

..0 0.4

3.50 0.00 to

+.l

100.00 0.00 ......

::::l

V') 0.2

0.0

a 2

Mean water column velocity (ft/sec)

1.0 . x .s: I 0.0 0.0

1.5 1.0 Q)

>< 0.8- - 10.0 1.0 "'0

t::

100.0 1.0

>, 0.6-

.jJ

......

J ,.... 0.4 ......

..0

to

+.l

......

::::l 0.2-

V')

0.0 I T T

a 2 4 6 8 10

Depth (ft)

1.0 x .s.:

0.0 0.00

1.0 0.01 >< 0.8

2.0 0.01 Q)

"'0

3.0 0.75 t::

0.6 5.0 0.75 >,

6.0 1.00 +.l

......

7.0 1.00 ,....

...... 0.4

8.0 0.20 ..0

to

8. 1 0.00 +.l

...... 0.2 100.0 0.00 ::::l

V')

0.0

a 2 3 4 5 6 7 8

Substrate type (see code key, page 39)

Figure 5. S1 curves for rainbow trout adult velocity, depth,

substrate, and temperature.

52
Coordinates

x

0.0

32.0

55.4

70.0

84.2

100.0

-.L

0.0

0.0

1.0

1.0

0.0

0.0

>< 0.8

OJ

"0

C

-- 0.6

t'

;:: 0.4 .r-

.0

ta

.;J

'r- 0 2 :::::l •

(/')

o 20 40 60 80 100

Temperature (OF)

Figure 5. (concluded)

53
Adult depth. Depths most utilized (n=361) in Cherry and Eleanor Creeks

ranged between 1.5 and 2.5 ft, whereas depths most uti 1i zed in the Tuolumne

River ranged between 2.5 and 4.1 ft (Moyle et al. 1983). Adults in the Green

River, however, primarily utilized depths ranging from 12 to 17 ft (Gosse

1982). Therefore, it may be assumed that the SI = 1.0 for all depths greater

than 1.5 ft (Fig. 5), or curves may be developed that are specific to the area

of investigation.

Adult substrate. Adults (> 4.7 inches) in Deer Creek (n=96) primarily

utilized cobble; in Cherry Creek and Eleanor Creek, and the Tuolumne River

(n=448) they primarily utilized boulders (Moyle et al. 1983). In the Green

River, adults (> 9 to 10 inches in length) utilized Gobble and boulders during

stationary swimming; and silt, sand, and boulders during random swimming

(Gosse 1982). The final curve (Fig. 5) is based on professional estimation.

Adult cover. Sufficient information was not located for the development

of a curve for adult trout cover requiremen~s. Lewis (1969) found a positive

correlation between the amount of cover and adult density. Butler and

Hawthorne (1968) found that rainbow trout had less affinity for cover than

brook or brown trout. The investigator has several options when considering

cover. Cover may be omitted as a model variable; cover curves may be developed

independently; it may be assumed that cover is adequately addressed by

substrate and depth; or the curve for V6 (page 16) may be used to represent

adult cover requirements.

Adult temperature. Preferred temperatures of rainbow trout adults have

been found to be 55.4, 59.0, 61.7, 64.4, and 66.0 to 70.0° F (Coutant 1977;

Spigarelli and Thommes 1979). Temperature selection may be a function of

acclimation temperature, size of fish, and time of year. Lee and Rinne (1980)

determined the critical thermal maxima at 84.2° F. The final curve (Fig. 5)

is based on this information.

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55
Bovee, K. D. 1982. A guide to stream habitat analysis using the Instream

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57
Di ck son , 1. W., and R. H. Kramer. 1971. Factors i nfl uenci ng scope for acti vity and active standard metabolism of rainbow trout (Salmo gairdneri).

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Elser, A. A. 1968.

habi tat zones

97(4):389-397.

Fish populations of a trout stream in relation to major

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Erman, D. C., and V. M. Hawthorne. 1976. The quantitative importance of an

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Everest, F. H. 1969. Habitat selection and spatial interaction of juvenile

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1973. Ecology and management of summer steelhead in the Rogue

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58
Everest, F. H., and D. W. Chapman. 1972. Habitat selection and spatial

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59
Hartman, G. F., and C. A. Gill. 1968. Distributions of juvenile steelhead

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constant temperatures and diel temperature fluctuations on specific

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Toronto.

1970. The ecology of running waters.

555 pp.

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shiners (Richardsonius balteatus) and rainbow trout (Salmo gairdneri) in

two British Columbia Lakes. J. Fish. Res. Board Can. 18(2):203-220.

60
Jordan, D. S., and B. W. Evermann. 1902. American food and game fishes.

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species in the Southwestern United States. Trans. Amer. Fish. Soc.

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a trout stream.

Physical factors influencing fish populations in pools of

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trout to inlet and outlet spawning streams at Loon Lake, British Columbia.

J. Fish. Res. Board Can. 16:695-719.

Logan, S. M. 1963. Winter observations on bottom organisms and trout in

Bridger Creek, Montana. Trans. Amer. Fish. Soc. 92(2):140-145.

MacCrimmon, H. R. 1971. World distribution of rainbow trout (Salmo

gairdneri). J. Fish. Res. Board Can. 28:663-704.

Mann, J. T. 1969. Occurrence and spawning of rainbow trout (Salmo gairdneri

Richardson) in selected Dale Hollow tributaries. M.S. Thesis, Tennessee

Tech. Univ., Cookeville.

Mantel man,!.!. 1958. Temperature criteri a for freshwater fi sh:

and procedures. U.S. Environ. Protection Agency, Duluth, MN.

Cited by Brungs, W. A., and B. R. Jones 1977.

61

protocol

130 pp.
1977. Influence of accliin rainbow trout, Salmo

May, B. E. 1973. Seasonal depth distribution of rainbow trout (Salmo

ga i rdneri) in Lake Powe 11 . Proc. Utah Acad. Sci., Arts, and Letters

50:64-72.

McAfee, W. B. 1966. Rainbow trout. Pages 192-215 in A. Calhoun, ed. Inland

fisheries management. Calif. Dept. Fish Game. 546 pp.

McCauley, R. W., J. R. Elliot, and L. A. A. Read.

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suitability index models: a low effort system for planned coolwater and

coldwater reservoirs. U.S. Fish Wildl. Serv., FWS/OBS-82/10.3. 47 pp.

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Quality Control Board Publ. 3A. Sacramento, CA. 548 pp.

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incubation-spawning analysis. U.S. Fish Wildl. Serv., unpubl ished.

21 pp.

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U.S. Fish Wildl. Servo FWS/OBS-81/43. 273 pp.

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cutthroat trout. J. Fish. Res. Board Can. 14(5):687-691.

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1953. The mortal ity of trout. Sci. Am. 188:81-85.

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Subcommittee. 1979. Managing riparian ecosystems (zones) for fish and

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Habitat Subcommittee of the Oregon/Washington Interagency Wildl. Conf.

44 pp.

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physical nature of the substrate in a northern Colorado trout stream.

Ecology 28:42-48.

62
Peterson, R. H., A. M. Sutterlin, and J. L. Metcalfe. 1979. Temperature

preference of several species of Salmo and Salvelinus and some of their

hybrids. J. Fish. Res. Bd. Can. 36:1137-1140.

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effects of gravel mi xtures on emergence of coho sa 1mon and stee 1head

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from natal gravels to rearing areas. Ecology 52(2):291-297.

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1977. The effects of shale removal on stream temperature in Nova

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63
Smith, A. K. 1973.

depth criteria

102(2):312-316.

Deve1opment and app 1i cati on of spawni ng vel oci ty and

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stream. Ph.D. Thesis, Colorado State Univ., Ft. Collins. 78 pp.

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cutthroat trout. M.S. Thesis, Colorado State Univ., Ft. Collins. 59 pp.

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population in McConaughy Reservoir, Nebraska. Trans. Am. Fish. Soc.

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in Oregon. Trans. Am. Fish. Soc. 97:374-379.

1974. Seawater adaptation independent of photoperiod in

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trout (Sa1mo gairdneri) along the Pacific Coast of North America. J.

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Zaugg, W. S., and H. H. Wagner. 1973. Gill ATPase activity related to parrsmo1t transformation and migration in stee1head trout (Sa1mo g~irdneri):

i nf1 uence of photoperi od and temperature. Comp. Biochem. Phys i 01.

45B:955-965.

64
5027'% ·ft'll

REPORT DOCUMENTATION I._REPORT 1'10.

PAGE FWS/OBS-82/10.60 4. TUI. Illd Subtltl.

Habitat Suitability Information: Rainbow trout

2.

1

5. "_It O.t.

, January 1984

7. Autllor(,) R.F. Raleigh, T. Hickman, R.C. Solomon, and P.C. Nelson

9. ~rfo""inc Orpniz.tion 1'1.,". Ind "'del",S' Habi ta t Eva 1ua ti on Procedures Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2627 Redwing Road

Fort Collins, CO 80526-2899

12. Sgon'onncOrpniatl_N.m••ndAdd.... western t:.nergy and Land use leam

Division of Biological Services

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

15. SlIlllliemem.ry l'Iot.. Washi ngton, D. C. 20240

·IL "'1lafnC! (Wmit: 200 _rClSl

L ~""nninc OrpnlUtion R.Dt. 1'10.

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11. CAntr8CtlC'l ar GrameG) No.

(C'l

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113. TYIM of "eoolt &. Penod e-nd

A review and synthesis of existing information was used to develop riverine and

lacustrine habitat models for rainbow trout (Salmo gairdneri) a freshwater species.

The models are scaled to produce indices of habitat suitability between 0 (unsuitable

habitat) and 1 (optimally suitable habitat) for freshwater areas of the continental

United States. Other habitat suitability models found in the literature are also

included. Habitat suitability indices (HSI's) are designed for use with Habitat

Evaluation Procedures previously developed by the U.S. Fish and Wildlife Service.

Also included are discussions of Suitability Index (SI) curves as used in the

Instream Flow Incremental Methodology (IFIM) and SI curves available for an IFIM

analysis of rainbow trout habitat.

17. Oocument An.t~is •• Oncnoto"

Mathematical models

Fishes

Aquatic biology

Habitability

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Salmo gairdneri

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REGION I

Regional Dire ctor

US. Fish and WildlifeService

L1uyd Five Hundred Building, Suite 1692

'i00 N.!:. Multnumah Street

POri land. Oregon 97232

REGION 4

Regional Dire ct or

lS Fish and Wildlife Service

Richard B. Rus ell Building

r Spring St reet , S.w.

Atlanta , Georgia 30303

REGION 2

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 1306

Albuquerque , ew Mexico X7103

REGION 5

Regional Director

U.S. FISh and Wildlife Service

One Gate ay Center

Newton Corner, MassachU' e t502158

EGlON 7

Regional Dir ctor

U.S. Fish and Wildlife Service

1011 E. Tudor Road

Anchorage, Alaska 99'i03

REGION 3

Regional Director

U.S. Fish and Wildlife Service

Federal Building, Fort Snelling

Twin Cities. Minnesota S5 I I I

REGION 6

Regional Director

U.S. Fish lind Wildlife Service

P.O. Box 25486

Denver Federal Center

Denver. Color do 80225
DEPARTMENT OF THE I

u.s. FISH AND WILDLIFE SERVICE

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As the Nation's principal conservation aleney, the Department of the Interior has responsibility for most of our .nationally owned public lands and natural resources. This includes

fosterinK the wisest use of our land and water resources, protectinK our fish and wildlife,

preservinl th.environmental and cultural values of our national parks and historical places,

and providing for the enjoyment of life throuah outdoor recreation, The Department a.,

sesses our energy and mineral resources and works to assure that their development is in

the best interests of all our people. The Department also has a major responsibility for

American Indian reservation communities and for people who live in Island territories under

U.S. administration.