FWS/OBS-82/1 0.49

SEPTEMBER 1983

HABITAT SUITABILITY INDEX MODELS:

COHO SALMON

SK

361

.U54

no. 82-

10.49

h and Wildlife Service

s. Department of the Interior
Thi s model is designed to be used by the Division of Ecological Services

i n conjunction with the Habitat Evaluation Procedures.
FWS/OBS-82/10.49

September 1983

HABITAT SUITABILITY INDEX MODELS: COHO SALMON

by

Thomas E. McMahon

Habitat Evaluation Procedures Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2627 Redwing Road

Ft. Collins, CO 80526

Western Energy and Land Use Team

Division of Biological Service

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This report should be cited as:

McMahon, T. E. 1983. Habitat suitability index models: Coho salmon. U.S.

Dept. Int., Fish Wildl. Servo FWS/OBS-82/10.49. 29 pp.
PREFACE

The habitat use information and Habitat Suitability Index (HSI) models

presented in this document are intended for use in impact assessment and habitat management activities. Literature concerning a species, habitat requirements and preferences is revi ewed and then synthesized into subjective HSI

models, which are scaled to produce an index between 0 (unsuitable habitat)

and 1 (optimal habitat). Assumptions used to transform habitat use information into these mathematical models are noted and guidelines for model application are described. Any models found in the literature which may also be used

to calculate an HSI are cited. A section presenting Instream Flow Incremental

Methodology (IFIM) will be included in this series in the near future. The

IFIM section will include a discussion of Suitability Index (SI) curves, as

are used in IFIM and a discussion of SI curves available for the IFIM analysis

of coho salmon habitat.

Use of habitat information presented in this publication for impact

assessment requires the setting of clear study objectives. Methods for modifying HSI models and recommended measurement techniques for model variables are

presentert in Terrell et al. (1982).1 A discussion of HSI model building

techniques is presented in U.S. Fish and Wildlife Service (1981).2

The HSI model presented herein is the combination of hypotheses of

species-habitat relationships, not statements of proven cause and effect

relationships. Results of model performance tests, when available, are

referenced; however, models that have demonstrated reliability in specific

situations may prove unreliable in others. For this reason, the U.S. Fish and

Wildlife Service encourages model users to send comments and suggestions to

help increase the utility and effectiveness of this habitat-based approach to

incorporate the coho salmon in fish and wildlife planning. Please send

comments to:

Habitat Evaluation Procedures Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2627 Redwing Road

Fort Collins, CO 80526

lTerrell, J. W., T. E. McMahon, P. D. Insk ip , R. F. Raleigh, and K. L.

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

for riverine and lacustrine applications of fish HSI models with the Habitat

Evaluation Procedures. U.S. Dept. Int., Fish Wildl. Servo FWS/OBS-82/10.A.

54 pp.

2U.S. Fish and Wildlif~ Service.

habitat suitability index models.

Serv., DiY. Ecol. Servo n.p.

1981. Standards for the development of

103 ESM. U.S. Dept. Int., Fish Wildl.

iii
iv

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CONTENTS

Page

PREFACE iii

ACKNOWLEDGMENTS vi

HABITAT USE INFORMATION................................................ 1

Genera 1 1

Age, Growth, and Food 1

Reproduction...................................................... 2

Freshwater Res; dence 2

Smoltification 2

Specifi c Habitat Requi rements 3

HABITAT SUITABILITY INDEX (HSI) MODELS 8

Model Applicability 8

Model Description................................................. 9

Suitability Index (SI) Graphs for Model Variables " 12

Interpreti ng Mode 1 Outputs 22

ADDITIONAL HABITAT MODELS 22

REFERENCES '................................ 22

v
ACKNOWLEDGMENTS

T. Nickelson, Oregon Department of Fish and Game, Corvallis, B. Nelson,

B. Persons, and especially G. Wedemeyer, U.S. National Fisheries Research

Laboratory, Seattle, and R. C. Solomon, U.S. Fish and Wildlife Service, Fort

Collins, reviewed drafts of this document and offered many constructive suggestions. However, the reader should not construe this as an endorsement of the

model contents. The present document is an independent synthesis and interpretation of the literature. A preliminary set of habitat evaluation criteria,

developed by R. Stuber, U.S. Forest Service (formerly with the HEP Group), and

H. Li and C. Schreck of the Oregon Cooperative Fishery Research Unit, was

utilized in development of this document. C. Short provided editorial

assistance. Word processing was by C. J. Gulzow and D. E. Ibarra. J. R.

Shoemaker drew the cover illustration. K. Twomey greatly assisted in final

preparation of the manuscript.

vi
COHO SALMON (Oncorhynchus kisutch)

HABITAT USE INFORMATION

General

The coho salmon (Oncorhynchus kisutch) is native to the northern Pacific

Ocean, spawning and rearing in streams from Monterey Bay, California, to Point

Hope, Alaska, and southward along the Asiatic coast to Japan. Its center of

abundance in North America is from Oregon to Alaska (Briggs 1953; Godfrey

1965; Hart 1973; Scott and Crossman 1973). Coho salmon have been successfully

introduced into the Great Lakes and reservoirs and lakes throughout the United

States to provide put-and-grow sport fishing (Scott and Crossman 1973;

Wigglesworth and Rawson 1974). No subspecies of coho salmon have been

described (Godfrey 1965).

Age, Growth, and Food

Coho salmon typically return to spawn in freshwater at ages III or IV at

lengths and weights ranging from 45 to 60 cm and 3.5 to 5.5 kg, respectively

(Shapovalov and Taft 1954; Godfrey 1965; Scott and Crossman 1973). Coho from

Alaska tend to be older and larger at spawning than those further south due to

a longer period of freshwater residence (Drucker 1972; Crone and Bond 1976).

A significant percentage of spawning runs, particularly in the southern portion

of the coho's range, may consist of precocious males (jacks) that mature and

return to spawn after only 6 to 9 months in the ocean (Shapovalov and Taft

1954).

Growth rate of coho during freshwater rearing is variable both between

and within streams (Drucker 1972; Crone and Bond 1976) and is probably determined, to a large extent, by food availability and temperature. Size, as a

function of growth, may play an important role in escapement and survival rate

in coho populations; larger seaward migrant coho (smolts) have a higher probability of returning as adults and are larger and more fecund than smaller

individuals of a cohort (Crone and Bond 1976; Bilton 1978).

Young coho feed mainly on drifting aquatic and terrestrial insects (Demory

1961; Mundi e 1969; Scott and Crossman 1973). As they grow, coho become

increasingly piscivorous, preying primarily on salmonid fry (Scott and Crossman

1973). In the ocean or in lakes and reservoirs, coho feed on fish and

crustaceans (Grinols and Gill 1968; Hart 1973; Scott and Crossman 1973; Healey

1978). Coho do not feed during spawning migrations.

1
Reproduction

Coho salmon return to natal streams to spawn from midsummer to winter,

depending on latitude. In the southern part of the range, spawning occurs in

December and January (Briggs 1953; Shapovalov and Taft 1954). In Alaska,

spawning occurs in October (Drucker 1972; Crone and Bond 1976) and, in the

Great Lakes, in early September - October (Scott and Crossman 1973). Coho in

North America migrate upstream during a single fall run, unlike other salmon,

which may migrate upstream in multiple runs throughout the year (Scott and

Crossman 1973). Entry into freshwater often coincides with ri ses in streamflow, particularly in streams with low summer flows (Shapovalov and Taft

1954).

Spawning behavior of coho has been summarized by Morrow (1980). Spawning

occurs primarily in moderate-sized coastal streams and tributaries of larger

ri vers. Coho do not utili ze main channels of 1arge ri vers for spawni ng as

heavily as do chinook (0. tshawytscha) or intertidal reaches as heavily as do

chum (Q. keta) and pink (Q. gorbuscha) salmon (Scott and Crossman 1973).

Supplementation of declining runs of wild spawning stocks with hatchery fish

is increasing in the Northwest (Fulton 1970; Korn 1977).

Incubation period varies inversely with temperature and usually lasts 35

to 50 days (Shapovalov and Taft 1954). Fry emerge 20 to 25 days after hatching

(Mason 1976a).

Freshwater Residence

Coho fry emerge from the gravel from early March to mid-May. Newly

emerged fry aggregate along stream margins, in shallow pools, and in backwaters

and eddies (Lister and Genoe 1970; Stein et al. 1972). Fry gradually move

into deeper pools, where they become aggressive and territorial. Fry unable

to hold a territory emigrate downstream into the ocean (Hartman et al. 1982)

or elsewhere in the stream system (Shapovalov and Taft 1954) because of intraspecific competition for food and space (Chapman 1966a). Coho that emigrate

in their first spring or summer of life as age 0 fish [usually < 40 mm fork

length (FL)] often constitute a major portion of the seaward migrants, but

thei r probabi 1ity of returni ng as adul ts is extremely low (Crone and Bond

1976; Hartman et .a l . 1982). Otto (1971) demonstrated that age 0 coho are

poorly equipped physiologically to survive and grow in the high salinities

encountered in the ocean.

Scales from returning adults indicate that the vast majority of coho

reside in freshwater for at least 1 year prior to seaward migration. In the

southern part of the range, coho commonly remain in freshwater for 1 to 2

years (Shapovalov and Taft 1954; Godfrey 1965). In Alaska, freshwater

residence lasts from 2 to 4 years (Drucker 1972; Crone and Bond 1976).

Smo 1t ifi ca t ion

Myriad processes and factors initiate, control, and affect parr-smolt

transformation (smoltification) in coho and other anadromous salmonids. An

important requirement of hatchery or naturally produced coho juveniles is that

2
the resulting smolts be fully able, behaviorally and physiologically, to

migrate to the sea, grow, develop normally, and return to their native stream

and successfully spawn. Among the environmental factors that influence

smoltification, photoperiod, temperature, and flow are especially critical

(Parry 1960; Hoar 1965; Clarke et al. 1978; Clarke and Shelbourn 1980;

Wedemeyer et al. 1980).

Smoltification and seaward migration in coho occurs in the spring

(Shapovalov and Taft 1954; Drucker 1972; Crone and Bond 1976), with some

exceptions (Chapman 1962). Migration often follows periods of rapid temperature warming (Shapovalov and Taft 1954). Coho smolts in California are

reported to migrate to sea in April - May (Shapovalov and Taft 1954); in

southeast Alaska, migration peaked in mid-June (Crone and Bond 1976).

Parr-smolt transformation is primarily a function of size, rather than of

age. Minimum size for successful smoltification in coho is near 100 mm FL

(Shapovalov and Taft 1954; Drucker 1972; Crone and Bond 1976). This size

corresponds closely to the 90 mm threshold size of coho for maximum salinity

tolerance (Conte et al. 1966). Smaller coho may show signs of transformation

to smolts (e.g., silvery color, increased buoyancy, and salinity tolerance),

but other critical aspects of the process are usually lacking (e.g., migratory

behavior), and they do not develop fully until the threshold size is attained

(Wedemeyer et al. 1980).

Due to the reduction in spawning habitat and spawning runs, natural

reproduction of coho salmon is increasingly supplemented by release of

hatchery-reared smolts. However, a perennial problem in the use of hatcheryproduced juvenile salmonids is that ocean survival is often below estimated

survival of naturally produced smolts. The failure to produce good quality

smolts centers on the release of fish at a size, age, and time unsuitable for

their ocean survival and on their exposure to environmental conditions that

adversely affect growth and survival. Wedemeyer et al. (1980) have reviewed

this problem in depth and propose guidelines for rearing and release of

hatchery smolts to maximize the number returning as adults.

Specific Habitat Requirements

Coho salmon utilize a variety of freshwater habitats and tolerances and

requirements change with season and age. Although most developmental changes

and movements to different habitats are gradual, it is useful to delineate the

freshwater life cycle into four distinct life stages and to specify factors

assumed to affect habitat quality for each life stage. These life stages are

defined as follows:

1. Adult. Sexually mature coho migrating from the ocean to natal

stream to spawn.

2. Spawning/embryo/alevin. From period of egg deposition to hatching

and emergence of fry from redds (Alevins =yolk-sac fry).

3
3. Parr. Fry (age 0) and juvenile (age 1+) coho residing in rearing

streams.

4. Smolt. Seaward migrant juveniles undergoing parr-smolt transformation.

Adult. Accessibility of the spawning stream and water quality appear to

be the major factors affecting coho during upstream migration. Dams may

completely block upstream passage, and other physical features may become

impossible to cross at low (e.g., debris jams or waterfalls) or high (e.g.,

excessive velocities) flows (Reiser and Bjornn 1979). Thompson (1972)

recommended a minimum depth of 0.18 m and a maximum velocity of 244 cm/sec as

criteria for successful upstream migration of adult coho.

Water quality can affect upstream migration of coho through direct

mortality, increasing the susceptibility of the coho to diseases, or adversely

altering the timing of the migration and rate of maturation (Holt et al.

1975). Temperatures 25.5° are lethal to migrating adults (Bell 1973).

Sublethal temperatures may result in major prespawning mortalities through

activation of latent infections (Wedemeyer 1970). Disease infection rates in

coho increase markedly at temperatures above 12.7° C (Fryer and Pilcher 1974;

Holt et al. 1975; Groberg et al. 1978). Temperatures s 13° C have been

recommended to minimize prespawning mortality of coho during upstream migration

(Wedemeyer, pers. comm.).

Dissolved oxygen (D.O.) levels> 6.3 mg/l are recommended for successful

upstream migration of anadromous salmonids (Davis 1975). Lower D.O. concentrations adversely affect upstream migration by reducing the swimming ability of

migrants and by el iciting avoidance responses. Maximum sustained swimming

speed of coho is sharply reduced at D.O. levels < 6.5 rug/l at all temperatures

(Davis et al. 1963). It is assumed that adult coho respond to low D.O. levels

in a fashion similar to juveniles and avoid waters with D.O. concentrations

< 4.5 mg/l (Whitmore et a1. 1960).

Spawning/embryo/alevin. Coho salmon construct redds in swift, shallow

area s at the head of ri ffl es (Burner 1951; Bri gg s 1953; Shapova1ov and Ta ft

1954). Preferred redd construction sites in riffle areas have velocities of

21 to 70 cm/sec and minimum depths 15 cm (Smith 1973). Gravel and small

rubble substrate with low amounts of fine sediments is optimum for survival,

growth, and development of embryos and alevins and for later emergence of fry

(Platts et al. 1979). Percent composition of various size classes of substrate

resulting in high survival of embryos and alevins has not been established.

Reiser and Bjornn (1979) estimated that redds with 1.3 to 10.2 cm diameter

substrate sizes and a low percentage of fines result in high survival of

embryos. An inverse relationship between percent fines < 3.3 mm and emergence

of fry has been well established in field (Koski 1966; Hall and Lantz 1969;

Cloern 1976) and laboratory (Phillips et al. 1975) experiments. In all

studies, emergence of coho fry was high at < 5% fines but dropped sharply at

15% fines.

4
Survi va 1 and emergence of embryos and a1evi ns is greatly i nfl uenced by

D.O. supply within the redd (Mason 1976a). D.O. concentrations 8 mg/l are

required for high survival and emergence of fry. Embryo survival drops significantly at levels S 6.5 mg/l; concentrations < 3 mg/l are lethal (Coble 1961;

Shumway et al. 1964; Davis 1975). D.O. supply available to coho in redds is

determined primarily by the interrelationship of gravel permeability. water

velocity. and D.O. concentration. When any of these factors, acting alone or

in combination, reduces the intragravel O2 supply below saturation. hypoxial

stress occurs, resulting in delayed hatching and emergence, smaller size of

emerging fry. and increased incidence of developmental abnormalities (Alderice

et al. 1958; Coble 1961; Silver et al. 1963; Shumway et al. 1964; Mason 1976a).

D.O. concentrations at or near saturation, with temporary reductions no lower

than 5 mg/l, are recommended as criteria necessary for successful reproduction

of anadromous salmonids (Reiser and Bjornn 1979).

Burner (1951) observed coho spawning in Oregon at temperatures of 2.5 to

12.00 C. Temperatures of 4.4 to 9.40 C are considered suitable for spawning

(Bell 1973). Temperatures in the 4.4 to 13.30 C range are considered optimum

for embryo incubation; survival decreases if these thresholds are exceeded

(Bell 1973; Reiser and Bjornn 1979).

Parr. Coho parr require an abundance of food and cover to sustain fast

growth rates, avoid predation, and avoid premature displacement downstream to

the ocean in order to successfully rear in freshwater and migrate to the sea

as smolts (Mundie 1969). Mason and Chapman (1965) found that the number of

coho parr remaining in stream channels is dependent on the amount of food and

cover available; if food or cover is decreased, emigration from the area

subsequently is increased. Mason (1976b) substantially increased summer

carrying capacity of a coho stream by supplemental feeding; however, these

gains were largely lost because numbers exceeded winter carrying capacity.

Dill et al. (1981) found that territory size in coho is inversely related to

the amount of available food. Low levels of food result in larger and fewer

territories per unit area, increased emigration of resident fry, and slower

growth rate of remaining fish. Small, slow growing parr may remain in freshwater for longer periods (with an attendant high mortality rate) until

threshold size for smolting is reached or may migrate to the sea at a time

when chances for survival are slim (Chapman 1966a).

Substrate composition, riffles, and riparian vegetation appear to be the

most important factors influencing production of aquatic and terrestrial

insects as food for coho (Mundie 1969; Giger 1973; Reiser and Bjornn 1979).

Hi ghest production of aquati c invertebrates is found in stream substrates

comprised of gravel and rubble (Giger 1973; Reiser and Bjornn 1979). Pennak

and Van Gerpen (1947) reported that the production of benthic invertebrates is

greater in rubble> bedrock> gravel > sand. Because substrate size is a

function of water velocity, larger substrate sizes are associated with faster

currents. Thus, food production is also high in riffles (Ruggles 1966; Waters

1969). Pearson et al. (1970) found that coho production per unit area in

Oregon streams is higher in pools with larger riffles upstream. However,

increased fines in riffles can reduce production of benthic food organisms

(Phillips 1971). Crouse et al. (1981) reported that coho production is lowest

in laboratory stream channels when embeddedness of the rubble substrate is

5
high (80 to 100%) and the percent (by volume) of fines (~ 2.0 mm) exceeds 26%.

Lastly, riparian vegetation along coho streams acts as habitat for terrestrial

insects, as well as a source of leaf litter utilized by stream invertebrates

as food (Chapman 1966b; Mundie 1969).

Coho parr are most abundant in large, deep [generally> 0.30 m(Nickelson,

pers. comm.)] pools, where they congregate near instream and bank (overhead)

cover of logs, roots, debris, undercut banks, and overhanging vegetation

(Ruggles 1966; Lister and Genoe 1970; Mason 1976b). Nickelson and

Reisenbichler (1977) and Nickelson et al. (1979) found positive correlations

between standi ng crop of age 0+ coho and pool volume. Studi es in Oregon by

Nickelson (pers. comm.) suggest that pools of 10 to 80 m3 or 50 to 250 m2 in

size with sufficient riparian canopy for shading are optimum for coho production. A pool to riffle ratio of 1:1 provides optimum food and cover conditions

for coho parr. Ruggles (1966) found that the greatest number of coho fry

remained in stream channels consisting of 50% pools and 50% riffles; numbers

of fry remaining in channels of either 100% pools or 100% riffles could be 39%

and 20% lower, respectively.

As water temperatures decrease below 90 C, coho fry become 1ess active

and seek deep (~ 45 cm), slow « 15 cm/sec) water in or very near « 1 m)

dense cover of roots, logs, and flooded brush (Hartman 1965; Bustard and

Narver 1975a). Beaver ponds and quiet backwater areas, often some distance

from the main stream channel and dry during summer low flow periods, are also

utilized as winter habitat (Narver 1978). Several studies indicate that the

amount of suitable winter habitat may be a major factor limiting coho production (Chapman 1966a; Mason 1976b; Chapman and Knudsen 1980). Swimming ability

of coho is decreased as the water temperature drops; therefore, winter cover

is critical for protection from predation, freezing, and, especially, displacement by winter freshets (Bustard and Narver 1975b; Mason 1976b; Hartman et al.

1982). Chapman and Knudsen (1980) found a very low winter biomass of coho in

channelized and grazed sections of streams in Washington, which they attributed

to the reduced pool volumes and amount of instream and bank cover present in

those areas.

Several studies have shown a positive relationship between stream carrying

capacity for coho and streamflow (McKernan et ~l. 1950; Mathews and 01 son

1980; Scarnecchia 1981). Strong positive correlations have also been found

between total stream area and measures of coho biomass (Pearson et al. 1970;

Burns 1971). Lowest returns of adult coho coincide with low summer flows

coup1ed wi th hi gh wi nter floods (McKernan et a1. 1950). Burns (1971) found

that highest mortality of coho and other salmonids in the summer occurred

during periods of lowest flows. Higher streamflows during rearing appear to

provide more suitable habitat for growth and survival through increased production of stream invertebrates and availability of cover (Chapman 1966a; Giger

1973; Scarnecchia 1981). Stabilization of winter flows and increases in

summer flows have led to increased production of coho (Lister and Walker 1966;

Mundie 1969). Narver (1978) suggested that stream enhancement techniques

aimed at reducing displacement downstream during winter floods and at providing

deep pools during summer low flows could substantially increase stream rearing

capacity for coho.

6
Growth rate and food conversion efficiency of coho fry is optimum at D.O.

concentrations above 5 mg/l. Below 4.5 mg/l, growth and food conversion

rapidly decreases to the point where growth ceases or is negative (below

3 mg/l) (Herrmann et al. 1962; Brett and Blackburn 1981). Swimming speed

decreases below the saturation level, especially below 6 mg/l (Dahlberg et al.

1968). D.O. concentrations < 4.5 mg/l are avoided (Whitmore et al. 1960).

Upper incipient lethal temperatures for coho fry range from 22.9 to 25.0° C

(acclimation temperatures of 5 to 23° C) (Brett 1952). Significant decreases

in swimming speed occur at temperatures> 20° C (Griffiths and Alderice 1972),

and growth ceases at temperatures above 20.3° C (Bell 1973). Stein et al.

(1972) found that the growth rate of coho fry was hi gh in the 9 to 13° C

temperature range, but slowed considerably at temperatures near 18° C. Brungs

and Jones (1977) reported that growth of coho occurred from 5 to 17° C.

Streamside vegetation plays an important role in regulating the temperature in reari ng streams. Cooler wi nter water temperatures may occur if the

stream canopy is absent or reduced, adversely affecting egg incubation (Chapman

1962). Where streamsi de vegetation is intact but the surroundi ng watershed

has been logged, warmer wi nter water temperatures may resul t, shifting the

period of emergence of fry and downstream movement of smolts to earlier, and

less favorable, periods (Hartman et al. 1982). In areas where the stream

canopy has been reduced, the resultant warmer summer temperatures may make the

habitat unsuitable if the temperature exceeds 20° C (Stein et al. 1972) or may

increase the mortality of fry from disease (Hall and Lantz 1969). However,

too much stream canopy can also reduce habitat suitability for coho fry. For

example, Chapman and Knudsen (1980) found reduced coho biomass in stream

sections where the canopy was very dense. Pearson et al. (1970) reported that

coho fry appear to avoid areas of dense shade; they suggested that stream

canopy enclosing> 90% of the sky may exceed the optimum level.

In summary, optimum rearing habitat for coho parr consists of a mixture

of pools and riffles, abundant instream and bank cover, water temperatures

that average between 10 to 15° C in the summer, D.O. near the saturation

level, and riffles with low amounts of fine sediment (Reiser and Bjornn 1979).

Streamside vegetation is an important component of coho habitat because it

provides food, cover, temperature control, and bank stabilization (Narver

1978).

Smolt. The radical physiological and behavioral changes that occur

during smoltification make this stage particularly sensitive to environmental

stress factors. Blockage and delay of migration by dams, unfavorable stream

flows and temperatures, fluctuations in food supplies, predation, gas supersaturation below dams, activation of latent infections due to environmental

stress, interference wi th saltwater adaptation in estuari es because of gill

infestations, and handling stress and descaling during transportation around

dams are major sources of mortal i ty and reduced ocean survi vabi 1i ty of coho

smolts (Wedemeyer et al. 1980).

El evated water temperatures can accelerate the onset of smoItifi cation

and shorten the smolting period and may result in seaward migration of smolts

at a time when conditions are unfavorable (Wedemeyer et al. 1980). Zaugg and

McLain (1976) reported that the period of high gill ATPase activity (indicative

7
of high salinity tolerance and other adaptations necessary for parr-smolt

transformation) in coho smolts held at 20° C occurred from mid-March to early

April; at 15° C, it occurred from mid-March to early May; and, at 10° C, a

normal pattern resulted with a peak in ATPase activity from mid-March to early

July. By shortening the duration of smolting and accelerating desmoltification, sublethal temperatures can lead to parr-reversion of coho smolts in

estuaries where exposure to predation and risk of infection is high, thereby

diminishing the number of coho smolts entering the ocean (Wedemeyer et al.

1980). Wedemeyer et al. (1980) recommend that temperatures follow a natural

seasonal cycle as closely as possible to those present in the coho's native

range to ensure optimum conditions for smoltification and timing of seaward

migration. Specifically, temperatures should not exceed 10° C in late winter

to prevent accelerated smolting; temperatures should not exceed 12° C during

smolting and seaward migration in the spring to prevent shortened duration of

smolting and premature onset of desmoltification and to reduce the risk of

infection from pathogens (see Adult section).

Exposure to pollutants can have a major deleterious impact on smoltification and early marine survival of anadromous salmonids (see review by Wedemeyer

et al. 1980). For example, Lorz and McPherson (1976) found that, at very low

levels of copper (20 to 30 ~g/l), migratory behavior and gill ATPase activity

in coho smolts was greatly suppressed and high mortalities resulted from

exposure to saltwater. Low concentrations of herbicides have also been found

to inhibit smolt function and migratory behavior (Lorz et al. 1978).

The lethal threshold for gas supersaturation in coho smolts is 114.5%.

No deaths were reported at 110% supersaturation, but the majority of fish

exhibited symptoms of gas-bubble disease (Rucker and Kangas 1974; Nebeker and

Brett 1976).

Specific D.O. requirements for coho smolts are unknown, but are probably

similar to those for parr.

HABITAT SUITABILITY INDEX (HSI) MODEL

Model Applicability

Geographic area. The model was developed from information gathered on

habitat requirements of coho salmon throughout its native and introduced

range. This general model is designed to be applicable to all the above areas

but is limited to the freshwater stage of the life cycle: upstream migrant;

embryo; parr; and smolt.

Season. The model is structured to account for changes in seasonal as

well as life stage requirements of coho salmon during those parts of the life

cycle when they inhabit freshwater. Because rearing streams are utilized

year-round, the model is developed to measure the suitability of a given

habitat to support parr for the entire year and to support embryos during the

spawning and incubation period.

8
Cover types. The model is oriented primarily to small coastal streams

and tributaries of larger rivers, which are the major spawning and rearing

areas of coho salmon. Habi tat requi rements of coho in 1arge ri vers, where

some spawning and rearing occurs and which serve as "highways to the sea" for

upstream and downstream migrant wild and hatchery-reared coho, are less wellknown and are not adequately addressed in this model. Water quality variables

are the only variables in this model that may be applicable when coho inhabit

large rivers. Variables that measure habitat suitability for adult coho in

lakes, reservoirs, estuaries, or the ocean are not included in this model.

Water quality. The model has limited utility in areas where water quality

variables (e.g., toxic substances and gas supersaturation) are major factors

limiting coho populations. If toxic substances are being discharged into a

river, Wedemeyer et al. (1980) should be consulted for information on the

types of substances that can adversely affect survival of smolts.

Verification level. The model represents the author's interpretation of

how specific environmental factors combine to determine overall habitat suitability for coho salmon. The model has not been field tested.

Model Description

The HSI model that follows is an attempt to condense information on

habi tat requi rements for coho into a set of habitat eva 1uat ion cri teri a,

structured to produce an index of overall habitat quality. A positive relationship between HSI and carrying capacity of the habitat is assumed (U.S.

Fish and Wildlife Service 1981), but this relationship has not been tested.

As a con sequence of thei r homing to natal streams to spawn, coho and

other anadromous salmonids commonly form local races and stocks, exhibiting

adaptations to the particular set of environmental conditions present in the

spawning streams (larkin 1981; Maclean and Evans 1981). The generalized HSI

model presented does not take into account the different stocks or subpopulations. The model was developed, and should be applied, with the following

statement by Banks (1969: 131) in mind: ". .. the consequences of man-made

changes (on anadromous salmonids) ... can be predicted in general terms from

the existing literature, but (due to the formation of local stocks) each

situation is unique ... and requires studies of the special needs of each

river system as well as the flexible application of general principles".

The model consists of those habitat variables that affect the growth,

survival, abundance, distribution, behavior, or other measure of well-being of

coho, and therefore can be expected to have an impact on the carrying capacity

of a habitat. Coho salmon habitat quality, in this model, is based on parameters assumed to affect habitat suitability for each of four life stages of

coho salmon during residence in freshwater (Fig. 1). Variables affecting

habitat suitability for parr are further delineated into the life requisite

components of: water quality; food; and cover. It was assumed that the most

limiting factor (i.e., lowest SI score) defines the carrying capacity for coho

salmon; thus,

HSI = minimum value for suitability indices Vl to VlS.

9
Habitat variables

Suitability

indices Life sta~

Vg

Food

Vs

VlQ

Vll

Cover

V12

V13

V7 -----~Water Qual ity --~ Parr ------; HSI

v,'=====-=-==- Smolt

V15

Vegetation composition of

riparian zone

D.O. during seaward migration

Proportion of pools

Percent cover

Percent pools

Percent pools

D.O. during upstream

migration

Winter cover

Percent canopy

D.O. during rearing

Temperature during parrsmolt transformation

and seaward migration

D.O.-incubation

Temperature during upstream migration

Substrate composition

Substrate composition

Temperature-incubation

Temperature during rearing

Figure 1. Diagram showing habitat variables included in the HSI model for

coho salmon and the aggregation of the corresponding suitability indices

(SII S ) into an HSI. HSI = the lowest of the fifteen suitability index

ratings.

10
Adul t component. V1 was i ncl uded in thi s component because temperature

can result in direct mortality, can increase coho susceptibility to infectious

diseases, or can alter the timing of migration and rate of maturation of coho

salmon during migration from the ocean to the spawning stream. Because D.O.

levels below saturation can elicit avoidance behavior and reduce the swimming

ability in coho, D.O. (V2 ) also was included as a variable that affects habitat

suitability for upstream migrants.

No specific variables were included in this component as measures of the

accessibility of the spawning stream. Nevertheless, physical features encountered by coho while migrating upstream should be considered when evaluating

habitat suitability. Features that impede or delay migrants from moving

upstream (see Adult section) would make suitable habitat, as defined by the

model, less useable.

Spawning/embryo/alevin component. V3 was included in this component

because embryo survi va1 decreases when temperatures duri ng i ncubat i on exceed

the optimum temperature boundary of 13.3° C. V4 was included because D.O.

levels below the saturation level induce hypoxial stress in embryos and alevins

and lead to decreased quantity and quality of emerging fry. Vs was included

because percent emergence of fry is related to substrate composition of

spawning redds.

Parr component. Water quality: V6 was included because temperature

affects swimming speed, growth, and survival of coho parr. V7 was included

because D.O. concentration affects growth, food conversion, swimming speed,

and avoidance behavior of parr. VB was included because coho numbers (or

biomass) are related to the quantity of stream canopy cover.

Food: Vg was included because it was assumed that the direct (terrestrial

insects) and indirect (leaf litter as food for aquatic insects) production of

food utilized by coho parr varies with the amount and type of riparian vegetation present. V1 0 was included because the production of aquatic insects, as

well as coho parr, has been related to the amount of riffle areas present in a

stream. Vs was included because the production potential of aquatic insects

is related to the substrate composition.

Cover: V10 and V11 were i ncl uded because the abundance of coho parr

varies with the amount (V1 0 ) and type (V 1 1 ) of pools present in a stream. V1 2

was included because coho parr are commonly associated with instream and bank

cover. V1 3 was included because the amount of suitable winter cover may be a

major factor affecting coho production.

11
Smolt component. V1 4 was included because temperature greatly affects

the timing and duration of parr-smolt transformation, can alter the timing of

seaward migration, and can affect the susceptibility of smolts to infection.

Although specific data are lacking, ViS was included because D.O. concentration

could potentially impact smolt migration through its effects on swimming

ability, by eliciting avoidance behavior, or by resulting in the direct

mortality of smolts.

Suitability Index (SI) Graphs for Model Variables

All variables pertain to riverine (R) habitat. Table 1 lists the information sources and assumptions used in constructing each SI graph.

Habitat

R

Variable

Maximum temperature

during upstream

migration.

R V2 Minimum dissolved 1.0

oxygen concentration

during upstream

migration. 0.8

-0

l::

...... 0.6

>,

+J

.,...

;;::0.4

..c

10

+>

.; 0.2 VI

0.0

4 5 6 7 8

mg/l

12
R V3 Maximum temperature 1.0

from spawning to emergence of fry. 0.8

x

Q)

"'0

s:: 0.6 ........

>,

+J

0.4

..a

co

+J 0.2 ::l

Vl

0.0

a 10 20

°C

R Minimum dissolved oxygen

concentration from spawning to emergence of fry.

1. a ;-- a.-'--"~_ _+

x 0.8

Q)

"'0

s::

........ 0.6

>,

+J

;:: 0.4

..a

co

.;:0.2

::l

Vl

o. a -t--....-o#---r---o..--._--+

13

a 50

mg/l

100
1.0

0.8 x

QJ

-g 0.6 .......

>-

0.4

..a.B 0.2 ......

=' Vl

0.0

0 50 100

% gravel & rubble

0 % embeddedness 100

1.0

0.8 x

QJ

"0

oS 0.6

c-,

+-'

0.4 ......

..a

0.2

=' Vl

0.0

0 25 50

% fines

A. Percent of gravel

(10 to 60 mm) and

rubble (61 to 250 mm)

present.

B. Percent fi nes « 6

mm) or percent

embeddedness of

substrate.

Substrate composition

in riffle/run areas.

or % embeddedness, whichever is

lower.

SI -- A + B h B ov -2-- were = /0 fines

R

R Maximum temperature

during rearing (parr).

1. 0 +--...I.p.-"""""'~~--....I----+-

x 0.8

QJ

"0

oS 0.6

c-,

+-'

;'::0.4 ......

..a

.~ 0.2

=' Vl

8 12 16 20 24

o. 0 +-....-.,...--r-""'.....-,-~-~

4

14
R V7 Minimum dissolved oxygen 1.0

concentration during

rearing (parr). 0.8 x

Q)

"'C

c

...... 0.6

>,

.,....

r- 0.4 .,....

..0

ttl

.,.... 0.2

Vl

0.0

0 2 4 6 8 10

mg/l

1.0 R Va Percent vegetative

canopy over rearing

stream. 0.8

x

Q)

"'C

c 0.6 ......

>,

0.4 .,....

r-

.,....

..0

ttl 0.2 .,....

Vl

0.0

0 50 100

% canopy

R Vg Vegetation index of 1.0 riparian zone during

summer. 0.8

x

Vegetation Index = 2 (% canopy Q)

"'C

cover of deciduous trees and c

...... 0.6

shrubs) + (% canopy cover of

grasses and forbs) + (% .,.... 0.4

canopy cover of conifers). r-

.,....

For measurement techniques, see ..0

ttl Terrell et al. (1982), p. A.19 .,.... 0.2

and A.37. Vl

0.0

0 50 100 150 200 250

Vegetation Index

15
R VlO Percent pools during 1.0

summer low flow period.

0.8

x

QJ

-0

c: 0.6 ......

>,

-+-)

;:: 0.4 .,....

.,....

::s

V)

O.

0 50 100

% pools

R VII Proportion of pools 1.

during summer low flow

period that are 10 to x 0.8 80 m3 or 50 to 250 m2 QJ

in size and have suffi- -0

cient riparian canopy 0.6

to provide shade.

;:: 0.4 .,....

::s

V)

o.

0 50 100

% pools with canopy

1. R V12 Percent instream and

bank cover present

during summer low flow x O.

period. QJ

-0

c:

...... 0.6

;:: o. .,....

O.U+---r---r---r-~--+

o 10 20 30 40 50

%cover

16
R Percent of total area

consisting of qUiet

backwaters and deep (~ 45 cm) pools with

dense cover of roots,

logs, debris jams,

flooded brush, or deeplyundercut banks during

winter.

x 0.8

<U

"0

..... 0.6

:'::0.4 .....

0.0+--.,..--......----.---..--+

o 10 20 30 40 50

%quiet area

R V110 Maximum temperature 1.0

during (A) winter

(Nov.-March) in

x 0.8 rearing streams and <U

(B) spring-early summer "0

(Apri 1-July) in streams .5 0.6

where seaward migration +oJ

of smolt occurs. ;:: 0.4 ..... A. - - - - .a

to

B. 0.2 ::::s

II)

0.0

4 8 12 16 20 24

°C

R VlS Minimum dissolved oxygen 1.0 concentration during

April-July in streams

where seaward migration x 0.8

occurs. <U

"0

..... 0.6

.....

.....

..... 0.4

.a

to

+oJ

..... 0.2 ::::s

II)

0.0

0 2 4 6 8 10

mg/1

17
Table 1. Sources of information and assumptions used in construction

of the suitability index graphs are listed below. "Excellent" habitat

for coho salmon was assumed to correspond to an S1 of 0.8 to 1.0, "good"

habitat to an S1 of 0.5 to 0.7, IIfair" habitat to an S1 of 0.2 to 0.4,

and "poor" habitat to an 51 of 0.0 to 0.1.

Variable Assumptions and sources

Temperatures that are lethal or that correspond to high mortality

rates in infected coho are poor (Bell 1973; Fryer and Pilcher 1974;

Holt et al. 1975). Temperatures where mortality of infected coho

is moderate or where activation of latent infections begins to

increase are fair (Fryer and Pilcher 1974; Groberg et al. 1978).

Temperatures that correspond to low disease mortality (Fryer and

Pilcher 1974; Holt et al. 1975) and that are recommended for

minimizing prespawning mortality are excellent (Wedemeyer pers.

comm.).

D.O. levels that correspond to undiminished swimming ability

(Davis et al. 1963) and that are recommended for successful

upstream migration (Davis 1975) are excellent. Levels where

swimming speed is greatly reduced (Davis et al. 1963) and

avoidance is high (Whitmore et al. 1960) are poor.

Temperature ranges corresponding to those recommended as optimum

for spawning and for incubation of embryos (Bell 1973) are

excellent. Temperatures outside of this range are less suitable.

D.O. levels at or near the saturation level corresponded to the

highest survival and emergence of fry and, therefore, are

excellent. Levels that correspond to reduced emergence, delays

in hatching or emergence, smaller size of fry, or increased

incidences of developmental abnormalities (Alderice et al. 1958;

Cobel 1961; Silver et al. 1963; Shumway et al. 1964; Mason 1976a)

are fair. D.O. levels below 5 mg/J (Reiser and Bjornn 1979) or

that approach lethal conditions (3 mg/l) (Coble 1961; Shumway

et al. 1964; Davis 1975) are poor.

18
Table 1. (continued).

Variable Assumptions and sources

(Embryo) Substrate composition that corresponds to high embryo

survival and high emergence of fry is excellent. Compositions

that contribute to reduced emergence (high percentage of fines,

high embeddedness) are good-poor depending on the severity of

the impact on survival and emergence (Koski 1966; Hall and Lantz

1969; Phillips et al. 1975; Cloern 1976; Platts et al. 1979;

Reiser and Bjornn 1979).

(Parr-Food) Gravel-rubble substrate composition corresponds to a

high production of aquatic invertebrates (Giger 1973; Reiser and

Bjornn 1979) and, therefore, is excellent in providing food for

coho. Other substrates produce decreasing amounts of invertebrates in this order: rubble> bedrock> gravel> sand (Pennak

and Van Gerpen 1947). It is assumed that the higher the percentage fines or percent embeddedness, the lower the production of

aquatic invertebrates (Phillips 1971; Crouse et al. 1981).

Temperatures that correspond to high growth (9 to 13° C) (Stein

et al. 1972) are excellent. Temperatures that correspond to

reduced growth (Stein et al. 1972) are fair. Temperatures that

are lethal or where growth of parr ceases are poor.

D.O. levels that correspond to the highest growth and food

conversion rates (Herrmann et al. 1962; Brett and Blackburn

1981) are excellent. Levels that correspond to greatly reduced

swimming speed (Dahlberg et al. 1968), avoidance behavior

(Whitmore et al. 1960), and cessation of growth are poor.

It is assumed that 50 to 75% canopy enclosure is excellent.

Other percentages are less suitable because cooler winter and

warmer summer temperatures, associated with low canopy cover,

result in decreased survival of embryos and fry (Chapman 1962;

Hall and Lantz 1969; Stein et al. 1972). Lower biomass of coho

corresponds to a high percent (> 90%) of canopy closure (Pearson

et al. 1970; Chapman and Knudson 1980), so percentages 90% are

fair.

Based on the work of Chapman (1966b), deciduous trees and shrubs

are excellent as habitat for terrestrial insects and in providing

high amounts of leaf litter used as food for aquatic invertebrates.

Grasses/forbs and conifers are less suitable. The equation was

formulated so that no riparian vegetation rates poor and so that

75% deciduous trees and shrubs rates excellent. It was based on

the assumption that deciduous trees and shrubs provide twice the

amount of terrestrial insects and leaf litter per unit area as do

grasses/forbs and conifers.

19
Table 1. (continued)

Variable Assumptions and sources

(Food-Cover) A pool to riffle ratio of 1:1 in streams is excellent in providing both food and cover for coho parr because:

(1) food production is highest in riffles (Ruggles 1966; Waters

1969); (2) coho fry are most abundant in pools (Ruggles 1966;

Lister and Genoe 1970; Mason 1976b); and (3) the highest number

of coho fry remained in stream channels with a 1:1 ratio (Ruggles

1966). Higher or lower percentages of pools are less suitable

because fewer coho fry remain in the stream channels (Ruggles

1966). This variable should be measured during summer low flow

because this is the critical summer period for parr (Burns 1971).

The graph is based on studies on Oregon streams by Nickelson and

colleagues where: (1) positive correlations were found between

standing crop of age 0+ coho and pool volume (Nickelson and

Reisenbichler 1977; Nickelson et al. 1979); and (2) coho fry

biomass was highest in pools 10 to 80 m3 or 50 to 250 m2 in size

(Nickelson pers. comm.). It is assumed that a positive relationship exists between proportion of pools 10 to 80 m3 or 50 to

250 m2 in size and habitat suitability (= carrying capacity) for

coho fry. If such pools are absent from the reach, it is assumed

that some other pool habitat would exist but would be poor,

capable of supporting parr in relatively small numbers (therefore, 51 =0.2 at 0%).

Because there is a positive relationship between number of coho

parr remaining in an area and amount of instream cover (Mason and

Chapman 1965) and, because parr are most abundant near instream

and bank cover (Ruggles 1966; Lister and Genoe 1970; Mason

1976b), it is assumed that habitat suitability is proportional to

the amount of instream or bank cover present in a reach. Zero

percent cover is assigned an 51 of 0.2 because the stream may

still be able to support coho parr, although at a greatly reduced

level.

It is assumed that quiet backwaters and deep pools with dense

cover are excellent winter habitat for coho parr because parr are

most abundant in these areas during the winter (Hartman 1965;

Bustard and Narver 1975a). Because several studies infer that the

amount of suitable winter habitat may be a major factor limiting

rearing capacity and smolt production (Chapman 1966a; Mason 1976b;

Chapman and Knudsen 1980), it is assumed that habitat suitability

;s proportional to the amount of suitable winter habitat available.

Zero percent winter cover has an 51 rating of 0.2 because it is

assumed that other potential sites can still support some overwintering parr. Thirty percent and above has an 51 of 1.0,

because it is assumed that optimum values of this variable are

obtainable in conjunction with optimum riffle-pool ratios (V 1 0 ) '

20
Table 1. (concluded).

Variable Assumptions and sources

Temperatures that correspond to a long and normal pattern of gill

ATPase activity during smoltification (Zaugg and McLain 1976) are

excellent, as are temperatures recommended for optimum smoltification and timing of seaward migration; i .e., 10° C during winter

and 12° C during spring (Wedemeyer et al. 1980; Wedemeyer pers.

comm.). It is assumed that the shorter the duration of gill ATPase

activity, the less suitable the temperature. Also, temperatures

> 12° C are considered fair-poor because the risk of infections

from pathogens is assumed to be higher than at lower temperatures

(Fryer and Pilcher 1974; Holt et al. 1975).

It is assumed that D.O. requirements for smolts are similar to

those of parr, thus the same assumptions and sources used in

developing the D.O. graph for parr (V7 ) were used in constructing

the 51 graph for V1 S .

21
~~!preting Model Outputs

The model described above is a generalized description of habitat requirements for coho salmon and, as such, the output is not expected to discriminate

among different habitats with a high resolution at this stage of development

(see discussion in Terrell et al. 1982). Each model variable is considered to

have some effect on habitat quality for coho, and the suitability index graphs

depict what the measurable response is assumed to be. However, the graphs are

derived from a series of untested assumptions, and it is unknown how accurately

they depict habitat suitability for coho salmon. The model assumes that each

model variable alone can limit coho production, but this has not been tested.

A major potential weakness in the model is that, while the model variables may

be necessary in determining suitability of habitat for coho, they may not be

sufficient. Species interactions and other factors not included in this model

may determine carrying capacity to a greater degree than the variables included

in this model. Data describing measurable responses for additional factors

are, however, scarce or nonexistent and, therefore, the variables do not meet

the standards for consideration as variables in HSI model development (U.S.

Fish and Wildlife Service 1981).

I recommend interpreting model outputs as indicators (or predictors) of

excellent (0.8 to 1.0), good (0.5 to 0.7), fair (0.2 to 0.4), or poor (0.0 to

0.1) habitat for coho salmon. The output of the generalized model provided

should be most useful as a tool in comparing different habitats. If two study

areas have different HSI's, the one with the higher HSI is expected to have

the potential to support more coho salmon. The model also should be useful as

a basic framework for formulating revised models that incorporate site specific

factors affecting habitat SUitability for coho salmon and more detailed

variable measurement techniques on a site-by-site basis.

ADDITIONAL HABITAT MODELS

No other habitat models that could be utilized in habitat evaluation for

coho salmon were located in the literature. The user is referred to Terrell

et al. (1982) and U.S. Fish and Wildlife Service (1981) for techniques to

modify this model to meet project needs.

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22
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23
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24
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25
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the

IV.

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26
Mathews, S. B., and F. W. Olson. 1980. Factors affecting Puget Sound coho

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27
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28
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29
29

\g. Secunty C:ass (Th,s ".oortl 21. ,'lo. at POtes

Unclassified

:0. SecUrtty Class (This .~oC.1

Coho salmon

Oncorhychus kitsutch

Habitat suitability index

50272 '101

REPORT DOCUMENTATION ,1._ REPORT NO. I 2. 13. R....Di.nt's AccaMl_ No.

PAGE FWS/OBS-82/10.49 I

4. Titl. and SubCltl. Is.. A_It Oec.

Index Models: Coho Salmon ' September 1983 Habitat Suitabil i ty I.

7. Aumons) L Perlarminc O....niutlon Reot. No.

T. E. McMahon

9. Perlorminc O....nizerlon N.m. and Add,.... Habitat Evaluation Procedures Group 10. '""'i8Ct/Tull/Wortc Unit Ifo.

U.S. Fish and Wildlife Service

Western Energy and Land Use Team 11. ContrRt(Q or ~,.nc(G) No.

Creekside One Building \,<:1 2627 Redwing Road

80526-?HQQ IGl Fort Collins CO

12. SlXInso"nc O....niutlon N.m. alOd Add,.... Western Energy and Land Use Team 113. TYlIe of A.OOIt " PerIod Cowred

Division of Biological Services

Research and Development I Fish and Wildlife Service 1

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15. Suellll.m.ncery Not.. Washington. DC 20240

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A review and synthesis of existing information were used to develop a riverine

habi tat model for Coho Salmon (Oncorhychus kitsutch) an anadromous species. The model is scaled to produce an index of habitat suitability between 0 (unsuitable habitat) and 1 (optimally suitable habitat) for riverine areas of the continental

United States. Habitat suitability indices (HSI's) are desi9ned for use with

Habitat Evaluation Procedures previously developed by the U.S. Fish and Wildlife Servi ce. .

\7. Oocum.nt "'nelYSls •. 0_lltors

Ma thema ti ca1 models

Fishes

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REGION 1

ilegjomtl Director

U.S. Fish and Wildlife Service

lloyd FiveHundred Bullding, Suite 1692

500 N.E. Multnomah Street

P-ortland, Oregon 97232

REGION 4

Regional Director

U.S. Fish and Wildlife Service

~kh.rd B. Russell Building

7S Spring Street, S.W.

Atlanta, Georgia 30303

REGION 2

Reponal Director

u.s. Fish and WildlJfe Service

P.O. 8.91 1306

Albuquerqut!,NewMexico81103

REGION 3

Regional Director

U.S. Fish and Wildlife Service

federal Burldiug . FOil Snelhng

TWin Cures, Minnesota 'is I II
DEPARTMENT OF THE INTERIOR

u.s. FISH AND WILDLIFE SERVICE

l '.S. ...SHaWIlIK .....: ,.;t:NVN't:

" ' :\. ••#

..•• .. 1 ... rOO · , "

As the Nation's principal conservation Biency, the Department of the Interior has respenslbility for most of our .nationally owned public lands and natural resources. This includes

fosterini the wisest use of our land and water resources, protectinl our fish and wildlife,

preservini th.environmental and cultural values of our national parka and historical places,

and providing for the enjoyment of life throulh outdoor recreation. The Department ...

sesses our enefIY 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.