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BIOLOGICAL REPORT 82(10.119)

NOVEMBER 1986

HABITAT UITABILITY INDEX MODELS

AND INSTREAM FLOW SUITABILITY

CURVE : REDBREAST SUNFISH

Fish and Wildlife Service

SK ). Department of the Interior

361

. U54

no . 82-

10 .119
MODEL EVALUATION FORM

Habitat models are designed for a wide variety of planning applications where habitat information is an important consideration in the

decision process. However, it is impossible to develop a model that

performs equally well in all situations. Assistance from users and

researchers is an important part of the model improvement process. Each

model is published individually to facilitate updating and reprinting as

new i nformat i on becomes ava i 1ab 1e. User feedback on model performance

will assist in improving habitat models for future applications. Please

complete this form following application. or review of the model. Feel

free to include additional information that may be of use to either a

model developer or model user. We also would appreciate information on

model testing, modification, and application, as well as copies of modified

models or test results. Please return this form to:

Habitat Evaluation Procedures Group

or

Instream Flow Group

U.S. Fish and Wildlife Service

2627 Redwing Road, Creekside One

Fort Collins, CO 80526-2899

Thank you for your assi stance.

Speci es

Habitat or Cover Type(s)

Geographic

Location

Type of Application: Impact Analysis Management Action Analysis

Baseline Other -------------------------

Variables Measured or Evaluated

Was the species information useful and accurate? Yes No

If not, what corrections or improvements are needed?-----------
Were the variables and curves clearly defined and useful? Yes No

If not, how were or could they be improved? -------------

Were the techniques suggested for collection of field data:

Appropriate? Yes No

Clearly defined? Yes No

Easily applied? Yes No

If not, what other data collection techniques are needed?

Were the model equations logical? Yes No

Appropriate? Yes No

How were or could they be improved?

Other suggestions for modification or improvement (attach curves,

equations, graphs, or other appropriate information)

Additional references or information that should be included in the model:

Model Evaluator or Reviewer Date ------------ -------

Agency _

Address

Telephone Number Comm:----------- FTS _
Biological Report 82(10.119)

November 1986

HABITAT SUITABILITY INDEX MODELS AND INSTREAM FLOW

SUITABILITY CURVES: REDBREAST SUNFISH

by

John M. Aho

Charles S. Anderson

Savannah River Ecology Laboratory

University of Georgia

Drawer E

Aiken, South Carolina 29801

and

James W. Terrell

Habitat Evaluations Procedures 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

Performed for

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:

Aho, J. M., C. S. Anderson, and J. W. Terrell. 1986. Habitat suitability index models and instream flow suitability

curves: redbreast sunfish. U.S. Fish Wildl. Servo BioI. Rep. 82(10.119). 23 pp.

ii
PREFACE

The Habitat Suitability Index (HSI) models and Suitability Index (SI)curves presented in this publication are intended

to be an aid in identifying variables that determine the quality of redbreast sunfish habitat. Facts, concepts, field

data, and opinions obtained from both published and unpublished reports are documented and presented in a format that can be used for habitat assessment and development of management alternatives.

This report contains two major parts: (1) a Habitat Use Information section, which provides a general summary

of the habitats used throughout the life cycle of the redbreast sunfish, and (2) a Habitat Suitability Index Models

section, which presents hypothesized relationships between various environmental variables and the concept of

habitat quality for redbreast sunfish.

Proper use of the models or individual SI curves with the Habitat Evaluation Procedures (HEP) requires project

scoping and the setting of clear study objectives. If HEP is to be used, HSI model building techniques presented

by the U.S. Fish and Wildlife Service (1981) and the general guidelines for modifying HSI models presented by Terrell et al. (1982) may be useful for applying the HSI models and any additional habitat requirement data to specific

habitat assessment problems. Hamilton and Bergersen (1984) summarize variable measurement techniques that

should be useful when attempting site specific habitat evaluations.

The HSI models and SI curves are hypotheses of species-habitat relationships, and users should recognize that

the degree of veracity of the models, curves, and assumptions will likely vary according to geographical area and

to the extent of the data base for each of the individual variables. The models and curves have not been tested

against field data. Therefore, the U.S. Fish and Wildlife Service encourages users of the models or curves to send

comments, suggestions, and field results that may help increase the utility and effectiveness of this habitat-based

approach to impact assessment. Please send comments to:

Habitat Evaluation Procedures Group or

lnstream Flow and Aquatic Systems Group

Western Energy and Land Use Team

U.S. Fish and Wildlife Service

2627 Redwing Road

Fort Collins, CO 80526-2899

ill
IV
CONTENTS

PREFACE , , iii

ACKNOWLEDGMENTS vi

HABITAT USE INFORMATION 1

General 1

Age, Growth, and Food 1

Reproduction 1

Specific Habitat Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2

HABITAT SUITABILITY INDEX (HSI) MODELS 4

Model Applicability 4

Model Description-General 5

Model Description-Riverine 7

Model Description-Lacustrine 8

Model Description-Palustrine 9

HSI Determination 9

Suitability Index (SI) Graphs for Model Variables 10

Interpreting Model Outputs 17

ADDITIONAL HABITAT MODELS 17

INSTREAM FLOW INCREMENTAL METHODOLOGY 18

REFERENCES 18

v
ACKNOWLEDGMENTS

James P. Clugston, u.s. Fish and Wildlife Service, National Fishery Research Laboratory, Gainesville, Florida; Prescott Brownell, U.S. Fish and Wildlife Service, Ecological Services, Charleston, South Carolina; and two anonymous

reviewers provided useful comments and criticisms on a draft version of the text. William D. McCort, Lyndon C.

Lee, and J. Whitfield Gibbons, all with the Savannah River Ecology Laboratory, also provided assistance in the

development of model concepts. Ronnie Gilbert, University of Georgia, Athens, provided access to unpublished

data on redbreast standing crops. Many reviewer comments were incorporated. However, the reader must not construe reviewer assistance as an endorsement of the model approach taken, the SUitability Index curves, or the

. habitat models, which are an independent synthesis and interpretation of the literature. Jim Zuboy provided editorial

assistance. Word processing was by Elizabeth Barstow, Patricia Gillis, and Dora Ibarra. The cover figure was drawn

by D. Raver, U.S. Fish and Wildlife Service. The Savannah River Ecology Laboratory is operated by the University

of Georgia for the Department of Energy under contract DE-AC09-76SROO-819.

vi
REDBREAST SUNFISH (Lepomis auritus)

HABITAT USE INFORMATION

General

The redbreast sunfish (Lepomis auritus) is a widely distributed centrarchid in the eastern United States (Atlantic slope) (Scott and Dahlberg 1971;Scott and Crossman

1973;Carlander 1977).Its native range extends from New

Brunswick, Canada, south to Florida, and east of the

Appalachian Mountains. Populations in Texas and Oklahoma are thought to originate from introductions. The

redbreast sunfish is considered by many investigators

to be predominantly a stream-dwelling species, but it can

successfully establish populations in lacustrine and

palustrine (river-swamp) environments. Redbreast sunfish exploit a variety of ecological conditions and

habitats from sea level to at least 1,345 meters elevation

including headwater streams, coastal plain rivers, and

lakes of various sizes (Shannon 1966). Among congeneric

species of centrarchids, redbreast sunfish hybridize with

warmouth (Lepomis gu/osus), bluegill (L. macrochirus),

green sunfish (L. cyanellus), and pumpkinseed

(L. gibbosus) (Scott and Crossman 1973).

Despite the popularity and value of the redbreast sunfish as a game fish, particularly in southeastern waters,

relatively little information is available on its life history

and habitat preferences. Recently, reductions in the

abundance of redbreast sunfish have been reported from

several different watersheds in the Southeast. The reasons for these observed declines are unknown, but pesticide contamination of the water, loss of suitable habitat, and overexploitation are suspected (Davis 1972;

Michaels et al. 1981; Sandow et al. 1974).

Age, Growth, and Food

Growth rates of redbreast sunfish are variable both within

and between populations (Carlander 1977), but all exhibit

patterns of indeterminant growth. There is a general tendency for growth rates to be greatest in the more

southerly populations; however, some northern populations have comparable growth rates. In these northern

locations, the increased growth rates are presumably due

to changes in the density of redbreast sunfish and/or in

prey availability. Despite the variability in size at a given

age for different populations, sexually mature individuals

have been first observed at age II; most individuals older

than age III are reproductively active (Davis 1972; Bass

and Hitt 1974; Sandow et al. 1974; Carlander 1977). Maximum age for the species is reported as 8 years, but the

average life span appears to be between 4 to 5 years.

Redbreast sunfish adults and juveniles are considered

to be generalist invertivores; they use both benthic and

drift-oriented foraging modes to feed on the nymphal

stages of aquatic insects, particularly dipterans,

ephemeropterans, and trichopterans, as well as terrestrial insects (Bass and Hitt 1974; Sandow et al. 1974;

Coomer et al. 1977;Benke et al. 1979; Henry 1979). Cooner

and Bayne (1982)reported a higher percentage of terrestrial insects in the stomachs of redbreast sunfish 101

mm total length than in the stomachs of individuals :5100

mm. Redbreast sunfish also ingest significant amounts

of decapod crustaceans and fish. As opportunistic

feeders, diet varies according to prey availability and size.

Their foraging behavior is, therefore, similar to that of

several other species of sunfish as described by Keast

and Webb (1966), Werner (1974), and Werner and Hall

(1974). Plant material is occasionally observed in stomach contents, but is probably associated with prey capture and not selectively consumed. The diet of the larval

and fry stages has not been intensively studied, but they

feed primarily upon zooplankton, exhibiting size selectivity due to gape limitations (Lemly and Dimmick 1982).

It is not known if larvae are opportunistic or speciesselective in their prey preference.

Reproduction

Redbreast sunfish have an annual reproductive cycle

(Hellier 1967; Davis 1972; Bass and Hitt 1974;Sandow et

al. 1974; Siler 1975). Although females bearing ripe ova

have been observed from April to October throughout the

southeastern United States, peak spawning occurs
2

between May and August, with a north-south cline in the

timing of reproduction. In contrast to other species of

centrarchids where individuals are known to be multiple

spawners (e.g., warmouth-Toole 1946(cited in Larimore

1957); bluegill-Wrenn and Grannemann 1980), redbreast

sunfish appear to spawn only once during the summer

(J. Germann, Georgia Department of Natural Resources,

Dearing; pel's. comm.). Temperatures of 20-25 DC are

associated with maximum spawning activity (Davis 1972;

Bass and Hitt 1974; Sandow et al. 1974).

Eggs are deposited in nests built and guarded by males

(Scott and Crossman 1973). Nest location is typically

associated with natural physical obstructions in lotlc systems (e.g., logs, stumps, boulders) (Davis 1972), but redds

have been observed in the quiet backwaters of streams

or congregated in open areas of lakes, ponds, and reservoirs. Davis (1972)reported an average nest diameter of

0.9 m and the depth of the nest depression to be 12-20

em with all nests being located in water depths of

35-38 em. Other studies have indicated considerably

more variation in the depth placement of the nest

(25-150 em) but all have shown a preference for shallow

water (Raney 1965; Bass and Hitt 1974; Sandow et al.

1974). Most redbreast sunfish nests are found on firm

substrates. Sand and gravel (particle size 0.1~0.5 em) are

preferentially selected over other substrate types, Particularly silt or detrital materials, for nest construction

(Davis 1972; Bass and Hitt 1974;Sandow et al. 1974). The

redbreast sunfish appears to be a colonial spawner with

internest distances ranging from 30-60 em (Raney 1965).

Specific Habitat Requirements

Cover, current velocity, and variables correlated with

velocity (e.g., gradient, riffle/pool ratios) appear to be

major determinants of the distribution and abundance

of redbreast sunfish in lotic systems. Both juvenile and

adult redbreast sunfish are usually found in shallow

water areas situated near cover, although they can be

found in deep water, particularly during summer when

surface water temperatures are high or during winter

when large aggregations form in low velocity, pool

habitats (BredeI' and Nigrelli 1935). Cover types used by

the redbreast sunfish include hard structure, such as

fallen trees, stumps, or root masses, and in situ vegetation (Davis 1972; Bass and Hitt 1974; Sandow et al. 1974;

Benke et al. 1979). Either type of cover provides a source

of shelter, but the availability of hard structure is a major

factor influencing spawning (i.e., nest site selection),

foraging behavior, and invertebrate prey production.

Where detailed observations have been made on nest

placement, all nests have been located adjacent to hard

structural objects (Davis 1972; Bass and Hitt 1974; Sandow et al. 1974). Invertebrate production on these same

types of hard structure has been shown to account for

more than 60% of the food of Lepomis spp. (including

the redbreast sunfish) in the Satilla River, Georgia (Benke

et al. 1979; Henry 1979; Benke et al. 1985). It has been

proposed, therefore, that invertebrate production is substrate limited (Benke et al. 1979; Henry 1979; Benke 1984;

Benke et al. 1985) and its magnitude may strongly

influence fish production. Using morphological characteristics of the fish to infer patterns of habitat utilization,

Gatz (1981)identified redbreast sunfish as being maneuverable and visually-oriented predators that prefer areas

of low water velocity. Thus, they are adapted for existence in structured environments.

Stream pools, protected margins, backwaters, and adjacent marshes are used by all life history stages of the

redbreast sunfish. Redbreast sunfish are capable of

establishing populations over a wide range of lotic conditions (Shannon 1966);however, they, and centrarchids

in general, are more abundant in low «2 m/km) rather

than moderate to high gradient streams (Finnell et al.

1956; Funk 1957a; Moyle and Nichols 1973; Trautman

1981). Redbreast sunfish also prefer moderate-size

streams (4-40 m average width) over small headwater

streams. Fluctuations in river discharge can have a major

effect on recruitment, growth, and survival. In the Satilla

River, Georgia, for example, periods of low, stable flow

have increased rates of recruitment to existing stocks

(Michaels et al. 1981). If maintained for an extended

period of time, however, low flows can decrease growth

rates and survival of the older age classes due to a loss

of habitat area and substrate for invertebrate production

(Michaels et al. 1981). Variable discharge patterns

between years, whether natural or due to periodic

releases from impoundments, can cause significant fluctuatlons in year class strength (Horwitz 1978).

Redbreast sunfish are commonly found in lacustrine and

palustrine environments, but the populations are not as

well studied as in riverine habitats. Fertile lakes, ponds,

and reservoirs with an extensive littoral zone generally

support large standing crops of several centrarchid species in southeastern waters (Lewis and English 1967;

Clugston 1973; Jenkins 1976; Winter 1977; Ploskey and

Jenkins 1982). While the redbreast sunfish was not a

major component of the centrarchid assemblage in any

of these studies, similar trends in abundance and

biomass across lacustrine productivity gradients are

anticipated in lakes and reservoirs containing significant

numbers of this sunfish. The development of a large littoral zone, however, is not a requisite for the establishment and persistence of the redbreast sunfish, as some

small populations have been found in lentic systems having virtually no aquatic macrophyte development or hard

structure cover (Clugston 1973; Aho and Anderson,
Savannah River Ecology Laboratory (SREL), pers. obs.),

For example, in Pond C, a 67 ha reservoir receiving heated

effluents from a nuclear production reactor on the Savannah River Plant in South Carolina, macrophyte establishment is limited to less than 5% of the shoreline, yet redbreast sunfish have persisted for> 20 years consistently

constituting :5 5% of the fish assemblage. The presence

of deep water is important for overwintering and as a

retreat from high surface water temperatures during the

summer (Breder and Nigrelli 1935).

Water quality requirements for redbreast sunfish are not

completely known. Redbreast sunfish are commonly

found in both clear and tannin-stained water (Scott and

Dahlberg 1971; Scott and Crossman 1973; Bass and Hitt

1974; Sandow et al. 1974). Moderate turbidity levels

(25-100 Jackson Turbidity Unit's [JTU's]) are positively

related to abundance of other centrarchids (Cross 1967;

Moyle and Nichols 1973; Trautman 1981) and may have

a similar relationship to the population size for redbreast

sunfish. Values within this range should not impair foraging success, but when turbidity level exceeds 100 JTU's,

the visual acuity and reactive distance of the fish is

progressively reduced (O'Brien 1979). As demonstrated

for largemouth bass (Micropterus salmoides) (Buck 1956;

Bulkley 1975; Muncy et al. 1979),high turbidity levels also

can affect reproductive success through an increase in

larval mortality or by altering the relationship of body size

to fecundity through a reduction in growth rate. Redbreast sunfish are tolerant of low pH, having been found

in several locations where pH levels are near 4.0 (Shannon 1966; Scott and Crossman 1973; Sandow et al. 1974;

Carlander 1977).Assuming redbreast sunfish respond to

pH similar to bluegill, increased mortality would be

expected at long-term exposure to pH values less than

4.0 and greater than 10.0 (Trama 1954; Calabrese 1969;

Ultsch 1978). However, they are anticipated to exhibit an

avoidance behavioral response tr these extreme water

quality conditions, similar to tha' .eported for bluegill by

Prete et al. (1981), if conditions are more favorable at

other locations. In environments where low pH has been

considered an important determinant of centrarchid species abundance and distribution patterns (e.g., Lepomis

spp. and Enneacanthus spp. in the New Jersey coastal

plain), no significant reductions in growth and survival

could be demonstrated for species thought to be intolerant of these conditions (Graham and Hasting 1984).

Instead, pH determines the trophic qualities of the system that control food availability (type and quantity) and

thus, strongly influences population dynamics (Graham

and Hastings 1984). The interaction of pH on lentic or

lotic trophic status may, therefore, be influential in the

observed patchy distribution and abundance of redbreast

sunfish throughout the southeastern U.S. and the

remainder of its range.

3

Adult. Temperature is an important characteristic of a

fish's habitat, an axis of its multidimensional niche

(Magnuson et al. 1979).Temperature preference and crltical thermal maxima of the redbreast sunfish are not well

known for any life history stage. Mathur et al. (1981) used

regression methods to describe the relationship of acute

temperature preference (temperature selected by fish

within a few hours after they are placed in a thermal gra·

dient) to acclimation temperature. They concluded that

the redbreast sunfish and four other centrarchids (includ·

ing largemouth bass and bluegill) have similar acute

preferenda. Redbreast sunfish have been observed at

temperatures as high as 33-35 °C, based on collections

made in thermally impacted reservoirs on the Savannah

River Plant, South Carolina (Aho and Anderson, Savannah River Ecology Lab (SREL),pers. obs.: Clugston 1973;

Siler 1975). The seasonal distribution patterns of the redbreast sunfish, however, parallel those of the largemouth

bass in thermally impacted cooling reservoirs (Clugston

1973; Siler 1975; Aho and Anderson, pers. obs.), Therefore, the actual mean thermal preferenda of the redbreast

sunfish probably more closely approximates the values

determined for the largemouth bass (27-29 0c) (Coutant

1975a,b; Reynolds et al. 1976; Reynolds and Casterlin

1976; Block et al. 1984)or green sunfish (28°C) (Beitinger

et al. 1975)than for bluegill (29-31 0c) (Cherry et al. 1975;

Beitinger 1976; Beitinger and Magnuson 1976; Peterson

and Schutsky 1976; Reynolds and Casterlin 1976;

Beitinger 1977; Block et al. 1984). The critical thermal

maxima is also anticipated to be closer to the approxlmate value of 36°C reported for largemouth bass (Brett

1956; Holland et al. 1974; Smith and Scott 1975; Cvancara et al. 1976; Reynolds and Casterlin 1979) for the

aforementioned reasons. Exact temperature selection

also may be modified by intra- or interspecific interactions as has been observed for largemouth bass and

bluegill in these thermal environments (Block et al. 1984).

Mean thermal preferenda and optimal growth temperatures are closely correlated (Beitinger and Fitzpatrick

1979; McCauley and Casselman 1981; Kellogg and Gift

1983); therefore, temperatures of 25-30 °C should result

in maximum growth, survival, and reproduction. Reduced

growth and survival are expected to occur at temperatures less than 15°C or greater than 33 °C.

Dissolved oxygen (DO) concentration requirements also

are incompletely known, but presumably are similar to

those of the bluegill. No adverse effects on growth, survival, or distribution patterns of bluegill have been

detected when values have exceeded 5.0 mgll (Stewart

et al. 1967; Petit 1973). Prolonged exposure to levels

below 1.0 mgll is considered lethal (Moore 1942).

Spawning and embryo. Nests are constructed in shallow water « 1.5 m) (Davis 1972; Bass and Hitt 1974; San-
4

dow et al. 1974); thus, rapid reductions in water level of

more than 1 m during the spawning period may adversely

affect embryo development and survival. Nest site water

velocities range from 3.4 to 56.1 cm/s with a mean of 17.9

em/sec (Davis 1972). The larvae, upon hatching, will utilize both hard structural cover and vegetated areas for

shelter and feeding sites. Temperatures corresponding

to a high le~el of spawning activity in the redbreast sunfish (21.0-25.0 0c) (Davis 1972), and that are optimum for

incubation of largemouth bass embryos (21-27 0c) (Kelly

1968;Coutant 1975a,1977), are assumed to provide excellent conditions for embryo growth and survival. Fluctuations in water temperature have been reported to significantly reduce spawning activity, embryo survival, and

growth for many species of centrarchids (Larimore 1957;

Wrenn and Grannemann 1980).

The dissolved oxygen requirements of redbreast sunfish

embryos are not well documented. For largemouth and

smallmouth bass (Micropterus aotomieuti, no adverse

effects on embryonic growth, development, and survival

were observed when DO concentrations exceeded 5 mgll.

DO levels less than 2.0 mgll are lethal to bass embryos

(Siefert et al. 1974; Eipper 1975).

Fry. Fry are found in shallow water and are usually

associated with either hard structure or vegetation cover

types. A reduction in the amount of available structural

space for the fry will probably limit growth and survival,

because cover provides both shelter and a source of

food. However, the relationship between the percent of

a water body with suitable fry cover types and adult

recruitment is unknown. We assumed that areas of low

current velocity (less than 10 cm/s) are required in order

for fry to maintain their stream position for feeding (Kallemyn and Novotny 1977).Temperature and DO concentrations corresponding to maximal rates of growth and survival are assumed to approximate those for the adult and

embryo stages.

Juvenile. The habitat requirements of juvenile redbreast

sunfish are not known. We assumed that they are similar to adult requirements or other juvenile lepomids,

except juveniles seem to prefer slightly faster current

velocities and are more abundant in smaller size « 4 m

average width) streams (Aho and Anderson, pers. obs.),

HABITAT SUITABILITY INDEX (HSI) MODELS

Model Applicability

Geographic area. The models were developed to quantify changes in wetland habitats on the Savannah River

Plant (SRP) located near Aiken, South Carolina, concornmitant with the restart of 0118 of five on-site nuclear

production reactors (L-Reactor). Alterations in redbreast

sunfish habitat are anticipated as a result of changes

in channel morphology due to greatly increased water

discharge rates and the elevation of water temperatures

with the downstream release of thermal effluents. The

standard of comparison for each of the individual suitability indices is the optimal value of individual or population responses (e.g., growth, survival) reported for the

species. Model variables should be applicable throughout the native and introduced ranges of redbreast sunfish in North America. However, a suitability index of 1.0

(optimum) may never occur in water bodies in the North

for temperature related variables that do not reach the

optimal values found in the southern portion of the species range. The model is designed for use primarily in

the southeastern coastal plain, where streams are low

gradient « 2 rn/krn) with few riffle/pool sequences. The

relationship of abundance to either gradient or the

amount of pool habitat is not considered. Gradient and

amount of pool habitat may be more important in other

areas where redbreast sunfish are found. For most centrarchids, reductions in population size occur as gradient

increases. Greater quantities of pool habitat result in

increased populations (Larimore 1957; Minckley 1963;

Trautman 1981).

Season. The model provides an index of the ability of

an area to support a self-perpetuating population of redbreast sunfish throughout the year. Conditions believed

to preclude reproduction or cause all individuals to leave

an area result in an HSI of O.

Cover types. The models are applicable to riverine,

lacustrine, and palustrine habitats as classified by

Cowardin et al. (1979). For the SRP and all other thermally

impacted aquatic environments, it is assumed that some

cool-water refuge areas will be present if portions of the

water body have water temperatures exceeding lethal

levels. These refuges are necessary to ensure the survival

of the animal populations in a water body and provide

a source pool for future recolonization and recovery once

the environmental stress (e.g., thermal effluent) is either

reduced or eliminated.

Minimum habitat area. Minimum habitat area is defined

as the minimum area of contiguous suitable habitat that

is required for a species to live and reproduce. Although

information is available determining mobility and home

range size of several species of centrarchids (e.g., largemouth bass-Lewis and Flickinger 1967; Warden and

Lorio 1975;Quinn et at, 1978;Winter 1977;Fish and Savitz

1983;bluegill-Gunning and Shoop 1963;Fish and Savitz

1983; longear sunfish-Gunning and Shoop 1963; Berra

and Gunning 1972),only limited information is available
on the redbreast sunfish. While no studies have deter·

mined home range size, the redbreast sunfish has been

found to be a semimobile species (sensu Funk 1956) with

< 50% of the individuals remaining within 0.16 km of the

original point of capture and some individuals moving

in excess of 8 km (Hudson and Hester 1975). Other

studies have found centrarchids to be more restrictive

in their movement patterns (see above citations). Thus,

the relationship of home range size to minimum habitat

area is currently unknown, so no attempt has been made

to specify the minimum habitat area for the redbreast

sunfish.

Verification level. The suitability indices and HSI

models are conceptual models that are open to modification. As preliminary attempts to quantify habitat

requirements, they should be interpreted with caution.

The models were synthesized from information available in the literature, personal observations, and relationships for other congeneric species. They have not been

tested against habitats of known quality to determine

their validity. However, as a first step in the model verification and validation process (Farmer et al. 1982), fish

biologists and ecologists familiar with this species, or

other centrarchids, were consulted. Many reviewer comments and criticisms regarding our description of the

habitat requirements of the redbreast sunfish were incorporated into the final model documentation. However,

we were not able to follow reviewer suggestions that the

relationship of model-generated HSI's to observed population levels be field tested before the model is used to

justify decisions. Reviewers did not necessarily agree

that the SI curves or modeling approach were valid.

Future refinements through field testing and modifications of structure (c.f. Layher and Maughan 1985) should

lead to greater model applicability. The useability (but

not the accuracy) of the model was evaluated in the field

by one of the reviewers (Brownell).

Model Description-General

The use of the Habitat Suitability Index (HSI) for displaying habitat quality in the Habitat Evaluation Procedures

(HEP) (U.S. Fish and Wildlife Service 1981) is based on

the precept that the HSI is a linear index of the concept

of "carrying capacity." We have tried to adhere to that

precept, but have not tested the model as an index of

carrying capacity, and therefore do not have evidence of

our success or failure in following the precept. In developing the individual suitability index (Sl) graphs (which are

used together to provide a single HSI that represents the

concept of carrying capacity for an entire year), relationships of physical, chemical, and biological parameters

to population performance measures should be formulated. The first step in the development of these graphs

5

is to define the independent variables (e.g., amount of

cover, depth of water overlying the sediments, current

velocity, dissolved oxygen concentration) believed to

influence the carrying capacity of the habitat. Each

model variable must be capable of being measured in

the field and should account for spatial and temporal variation of the habitat variable, to be useful for the generation of a meaningful Habitat Suitability Index. The

model variable definitions are subjective. Many of the

habitat variables from which the model variables are

defined vary both temporally and spatially, and specific

levels will be either selected for, or avoided by, the fish.

The model variable definitions are interpretive rules for

transforming habitat variable data into model variable

values. Alternative rules are certainly possible, and users

are encouraged to modify model variable definitions to

reflect their knowledge of how the species reacts to temporal and spatial variation in habitat variables.

Many of the variables selected for use in the development

of suitability index graphs are likely to interact; however,

we did not have enough data to examine variable interrelationships. Instead, we used the concept of maximum

performance (Li et al. 1984) to define an individual suitability index. Under this concept, an individual or population response (e.g., standing crop) is used as the measure of performance (dependent variable) and the

suitability index represents the highest proportion of the

maximum known performance that has been measured

in conjunction with each independent variable value. For

example, using standing crop as the measure of performance, the highest standing crop possible with an Sl of

0.8 should be 0.8 times the highest known standing crop.

Variable values with an Sl equal to 1.0 are assumed to

be necessary for the occurrence of maximal species performance. Variable values having an Sl < 1.0 are

assumed to be sufficient to preclude the occurrence of

a performance level higher than that obtained as the

product of the SI and the maximum performance level

known to occur. Standing crops (or other measures of

performance) associated with, for example, an Sl equal

to 0.8 could be below 0.8 times the maximal value of performance, because interactive factors other than the variable for which the Sl was calculated determine actual

standing crop.

Estimates of the standing crop of redbreast sunfish from

a variety of habitat types are not readily available in the

literature. Where measurements have been made,

biomass varies substantially both within and between

years. For example, in the Satilla River, Georgia, standing crop values have been found to range from 1.9 to 27.5

kg/ha in October rotenone samples for the years 1970,

1972-74, and 1977-79, and from 0.9 to 9.2 kg/ha within

a month (September-October 1973) from either the same
6

or closely associated sites (R. Gilbert, University of Georgla, Athens; letter dated August 16, 1985). Other sites in

the State of Georgia have redbreast sunfish standing

crop estimates of 0.4-30.3kg/ha. This wide range of variability, together with a lack of associated habitat data,

precluded the development of empirically derived SI

graphs or the derivation of statistical models based on

fish standing crop as a measure of population performance. Instead, we used information detailing the distribution, abundance, growth rate, survivorship, and

reproductive capabilities of the redbreast sunfish and its

congeners, as described in the literature, to formulate

judgements (l.e., the SI curves) on how different levels

of the model variables we defined might limit standing

crop. The accuracy of the SI curves in depicting these

limiting relationships is uncertain. However, Layher

(1983) found good agreement between some SI curves

developed in a similar manner for other centrarchids, and

SI curves he developed empirically from plots of average

population sizes associated with different variable

values.

How suboptimum variable values might actually limit

populations is not addressed in the SI curves or HSI

models. We have identified potential pathways through

food, water quality, reproduction, and cover components

(Figures 1, 2, and 3). However, the proper classification

of a variable into a specific component is not critical for

model usage because the model gives equal weight to

all variables.

Habitat variables Life requisites

Percent hard structural cover (V1)

Food/cover (CF/d

Percent vegetative cover (V2)

Percent hard structural cover (V1)

Temperature during spawning season (V4)

Reproduction (CR)

Current velocity (V5)

Substrate composition (V6) HSI

pH (V?)

Dissolved oxygen (V8)

Water quality (Cwo)

Turbidity (V9)

Temperature during growing season (V10)

Stream width (V13) Other (CO>

Figure 1. Habitat variables and life requisites in the riverine HSI model for the redbreast sunfish. HSI is equal to

the lowest suitability index rating for a habitat variable.
Habitat variables

Total dissolved solids during growing season (V11)

Percent ~"rrj structural cover (V1)

Percent vegetative cover (V2)

Percent area as littoral zone (V12)

Percent hard structural cover (V1)

Temperature during spawning season (V4) --------

Substrate composition (V6) -----------------i

Percent area as Iittoral zone (V12)

pH (V7)

Dissolved oxygen (V8)

Turbidity (V9)

Temperature during growing season (V10)

Life requisites

Cover (Cd

Reproduction (CR)

Water quality (Cwo)

7

HSI

Figure 2. Habitat variables and life requisites in the lacustrine HSI model for the redbreast sunfish. HSI is equal

to the lowest suitability index rating for a habitat variable.

Model Description-Riverine

Food and cover component. Percent of the habitat area

composed of hard structural cover (V1) and vegetative

cover (V2)were included because: (1)the distribution and

abundance of the redbreast sunfish and other related

species of centrarchids is closely associated with structural cover, and (2) vegetative cover provides an additional substrate to increase production of invertebrates

that can be used as a food resource (Bass and Hitt 1974;

Benke et al. 1979; Henry 1979; Benke et al, 1985).

Although both cover types are used by redbreast sunfish,

distinction is made because each provides different substrate for prey (vertebrate or invertebrate) utilization and

secondary production (Benke et al. 1979; Henry 1979; Mlnshall 1984;Benke et al. 1985). Of the two cover types, hard

structure appears to be more important to the redbreast

sunfish as a food/cover source than does in situ

vegetation.

Reproduction component. The percent of hard structural cover (V1) available in the habitat and benthic substrate composition characteristics (V6) were chosen as

indicators of reproductive requirements of the redbreast

sunfish because spawning generally occurs in areas

adjacent to natural physical obstructions and redbreast

sunfish select sand/gravel substrates for nest construction. Water temperature during spawning and embryonic

development (V4) and current velocity (V5) were also

included in this component due to their influence on nest

site selection, nest integrity, the overall success of

spawning, and their direct impact on the growth and survival of the embryos and larvae.
8

Habitat variables

Percent hard structural cover (V1)

Percent vegetative cover (V2)

Percent vegetated wetland exceeding critical water

depth (V3) -----------------

Percent hard structural cover (V1)

Temperature during spawning season (V4)

Current velocity (V5)

Substrate composition (V6)

pH (V7)

Dissolved oxygen (VB)

Turbidity (V9)

Temperature during growing season (V10)

Life requisites

Reproduction (CA)

Water quality (Cwo)

HSI

Figure 3. Habitat variables and life requisites in the palustrine HSI model for the redbreast sunfish. HSI is equal

to the lowest suitability index rating for a habitat variable.

Water quality component. Dissolved oxygen (VB), pH

(V7), and water temperature during the growing season

(V10) were selected because these variables affect the

growth, survival, and abundance of redbreast sunfish and

related species. Turbidity (V9) is used in this model

because of its influence on growth and abundance as

indicated by studies on related species of centrarchids.

Increased turbidity also reduces the growth of aquatic

vegetation used by redbreast sunfish for shelter,

reproduction, or as a substrate for food resource production. The influence of toxic substances on fish performances is not addressed by the model.

Other component. Stream width (V13) is important

because the distribution and abundance of the redbreast

sunfish differs between small headwater streams and

large rivers.

Model Description- Lacustrine

Food component. Mean total dissolved solids (TDS)

concentration during the growing season (V11) is used

as an indicator of lacustrine productivity. Positive correlations between sunfish standing crop and TDS have

been reported in several reservoir systems, presumably

due to greater quantities and availability of food organisms being produced at higher TDS concentrations. Itis

assumed that TDS levels will be below those that can

cause ion regulatory or osmoregulatory stress.

Cover component. The percent of hard structural cover

(V1) and vegetative (V2) cover within a habitat are

included in this component for the same reasons

provided in the riverine model description. The percent

of the lake classified as littoral zone (V12) is included
9

100

•

E • ~~ • • .- c: ••• ~8. •

EfB •••

•

0'" 50 • •

Q)"g • • • ~5 • •• c~ • • • • ••• ~~ • • • • •

Q) • • • • • • •

D- • • •• •

• •

0 • •

0.0 0.5 1.0

Habitat Suitability Index

If the above assumption is true and limiting environmental conditions during the time period the standing crop

was produced are accurately represented by model input

data, then the relationship of HSlto actual observed

standing crops will be as shown in Figure 4.

Figure 4. Assumed relationship of HSI to percent of

maximum standing crop, or other response assumed to

Same as described for the represent carrying capacity. Reproduction component.

riverine model.

Food and cover component. Food and cover variables

are identica.l to those described in the riverine model. An

additional variable, percent vegetated wetland exceeding a minimum critical water depth (V3), is also included

because redbreast sunfish require a minimum depth

within the macrophyte beds if they are to be utilized for

shelter, feeding, or reproduction. This variable also provides a measure of wetland permanency for all life history stages of the redbreast sunfish.

Model Description-Palustrine

because the redbreast sunfish generally occurs in nearshore habitats among natural physical obstructions and

macrophytes.

Water quality component. Same as described for the

riverine model.

Reproduction component. The percent of hard structural cover (V1), benthic substrate composition characteristics (V6), and temperature during the spawning season (V4) are included for the same reasons provided in

the riverine HSI model. The percentage of littoral zone

(V12)is included as a measure of the quantity of the total

lake habitat available to the redbreast sunfish for

spawning.

Water quality component. Same as described for the

riverine model.

HSI Determination

We believe that environmental conditions represented by

suitability indices (SI's) below 1.0 are sufficient to prevent maximum standing crops from occurring regardless

of the value of the other habitat variables. We assume,

therefore, that the most limiting factor (i.e., the variable

with the lowest SI) defines the upper limit, in terms of

proportion of maximum standing crop, for redbreast sunfish populations in the aquatic system being evaluated.

Thus, determination of the HSI for each model type

equals:

HSI (Riverine) = Minimum SI of [V1, V2, V4, V5, V6, V7,

VB, V9, V10, V13j

HSI (Lacustrine) = Minimum SI of [V1, V2, V4, V6, V7, VB,

V9, V10, V11, V12j

HSI (Palustrine) = Minimum SI of [V1, V2, V3, V4, V5, V6,

V7, VB, V9, V10j

For aquatic environments receiving cooling system water

from nuclear power plants, nuclear reactors, or conventional coal power generating facilities, the SI values for

V4 and V10 should be calculated from annual temperature profiles, instead of seasonal periods in the life history of the species. Water temperatures in portions of

some aquatic environments may exceed critical lethal

levels even during winter, so application on a year-round

basis is necessary. For these special cases, we assume

carrying capacity is dependent on the proportion of the

aquatic system that is within certain temperature limits

and thus useable by the species. Thus, the overall Sl for

V4 and V10 in these disturbed habitats is the weighted

arithmetic mean of the products obtained when

individual habitat areas are multiplied by both the SI for

the area and a weighting factor for the temporal duration of those environmental conditions. For example, if

an entire lake was being evaluated as potential habitat,

and 40% of the lake had completely unsuitable (i.e.,

SI = 0) temperatures during the growing season (e.g., a

240-day period each year), while the other 60% had an

SI of 0.1 for 170 days and an SI of 0.2 for 70 days, then

the SI for V10 for the entire lake would be computed as

follows:
10

SI (240 days x 0.0 x 40%) + (170 days x 0.1 x 60%) + (70 days x 0.2 x 60%)

.:240 days x 40%) + (170 days x 60%) + (70 days x 60%)

SI = 0.08

While formulated for thermally disturbed systems,

weighting by time and area also can be applied to natural aquatic habitats. The above example used an agricultural growing season (average number of days between

last spring frost and first fall frost) representative of the

southeastern U.S. as the basis for the calculations,

because agricultural growing season is anticipated to be

related to suitable water temperatures for fish growth in

unimpacted systems. When heated effluents are released

on a year-round basis, the weighting factor for time could

be 365 days.

Suitability Index (SI) Graphs for Model Variables

Suitability index graphs are based on the responses of

redbreast sunfish and other centrarchids to habitat

parameters presented in the habitat use section. The

responses (e.g., growth, survival) are not the same for all

variables. The suitability index ranges from 0.0 (unsuitable) to 1.0 (optimal) and was derived using the rationale

presented in Table 1 for the 13 model variables.

Model variables emphasize the extreme, rather than the

average, conditions for most habitat parameters,

because we assume that extreme conditions will most

often limit the carrying capacity of the habitat. Some flexibility is provided in model variable definitions because

fish can avold, or withstand, Short-term, localized,

unsuitable conditions. Gilbert (1984) found that HSI

models based on SI's that had flexible definitions of habitat variables were generally better predictors of fish

standing crops than similar HSI models with stringent,

inflexible definitions.

Table 1. Sources of information and rationale used in the construction of the suitability index graphs for the redbreast sunfish. Habitat classified as "excellent" has a suitability index of 0.8 to 1.0, "good" 0.5 to 0.7, "fair" 0.2

to 0.4, and "poor" 0.0 to 0.1.

Variable

V1

V2

V3

Sources of information and rationale

A large amount of physical obstruction In the habitat is assumed to be suboptimal because it: (1)interferes with

visual predatory behavior; (2) provides excessive refugia, through structural complexity, which limits accessibility to potential invertebrate preyspecies,and,consequently;reducespopulation growth parametersdue to increased

foraging costs (Crowder and Cooper 1979, 1982); and (3) can reduce the amount of suitable spawning habitat to

a level that may negatively affect adult-larvae recruitment dynamics. Based on available information for other

centrarchids, 25-70% hard structural cover (e.g., logs, stumps, root masses, rocks) is estimated to be the most

productive habitat for this species. Extreme conditions (less than 5% and greater than 90% hard structure cover)

may still provide valuable habitat, but growth, survival, and reproduction are probably limited under these physical habitat conditions to the extent that standing crop would be reduced.

The amount of vegetative cover is important for the same reasons provided in the hard structural cover section.

A different functional relationship is expected, however, because utilization of this cover type is assumed to be

secondary to the use of hard structural cover. It probably has greater importance as an additional substrate to

increase invertebrate secondary productivity that can be used as a food resource than as shelter (Bass and Hilt

1974; Sandow et al. 1974; Benke et al. 1979; Henry 1979; Benke 1984; Benke et al. 1985). Excessive amounts of

vegetative cover may reduce redbreast sunfish populations.

In river-swamp systems (palustrine), extensive macrophyte growth can develop along shallow channel margins,

to the extent of choking the waterway and acting as a sediment trap. To be utilized as a source of cover by, and

provide food resources for, redbreast sunfish, there must be a critical minimum depth of water overlying the sediments. Water depths < 10 cm contain few juvenile and adult fish (Aho and Anderson, pers. obs.) and are rated

poor. Although these shallow areas may be used as nursery areas for larvae upon hatching, when all life history

stages are collectively examined, water depths < 10 cm are rated as poor habitat for fish utilization. The occurrenceand abundanceof redbreastsunfish increaseswith depth, andoptimal conditions arepresumed wherespecies

usage and abundance are highest. Additionally, if nesting takes place among, or adjacent to, these vegetated
11

Table 1. (Continued)

Variable

V4

V5

V6

V7

V8

Sources of information and rationale

areas, some minimal depth is necessary based on observations of nest site selection. Most redbreast sunfish

nests have been found in waters exceeding 25 cm in depth, thus, 20 cm is a conservative estimate of the depth

level required to provide adequate spawning habitat for the redbreast sunfish. The depth of water also provides

a measure of the degree of wetland permanency, which is critical to fish utilization and secondary production.

Specific information correlating water temperatures with maximal embryonic development and survival are lacking for the redbreast sunfish. It is assumed, however, that temperature requirements for growth and survival are

more similar to those reported by Kelly (1968)and Coutant (1977) for largemouth bass than the requirements given

by Clugston (1966)and Banner and Van Arman (1973) for bluegill. This assumption is based on observations made

in thermally impacted reservoirs on the Savannah River Plant, where bluegills construct nests in areas of higher

temperatures along a thermal gradient than do either largemouth bass or redbreast sunfish (Clugston 1973; Siler

1975; Aho and Anderson, pers. obs.), Therefore, temperatures corresponding to periods of maximum spawning

activity (20-25 DC) (Davis 1972; Bass and Hill 1974; Sandow et al. 1974) and optimal temperatures for incubation

of largemouth bass eggs (21-27 0c) are regarded as being optimum. Temperatures outside of this range are considered less suitable and values < 15°C and >32 DC, which result in greatly reduced embryonic development

and survival, are rated poor.

Nest establishment and integrity and egg, embryo, and larval survival are several of the major determinants of

the distribution and abundance of the redbreast sunfish. Current velocities corresponding to the mean value for

nest site construction (Davis 1972) are rated as optimum. Adults and juveniles have greater ability to maintain

position in the stream than the larval stages; thus, they are more tolerant of variations in flow regime. Velocities

up to 35 cm/s are considered to be good for adults and juveniles because of highest abundance of fish in this

range. Current velocities up to 20 crn/s are considered optimal for the fry and embryo stages. Reduction in species abundance occurs in streams having average velocities >35 ern's (Bass and Hilt 1974; Sandow et al. 1974)

and represent habitats rated as fair to poor.

The availability of suitable nesting substrate is recognized as being a major factor affecting reproductive success of centrarchid fishes (Breder 1935; Kramer and Smith 1962; Muncy et al. 1979). Redbreast sunfish appear

to require a mixture of sand and gravel to spawn successfully (Davis 1972; Bass and Hill 1974; Sandow et al. 1974).

Similar to bluegills (Stevenson et al. 1969). nests located on sand or gravel substrates produced the greatest number of larvae. Silt or substrates with high organic composition (probably having a high oxygen demand and lillie

interstitial water flow) are regarded as being poor habitats for reproduction, based on the effects of low dissolved

oxygen concentrations on egg and embryo survival and development of related species as reported by Siefert

et al. (1974), Eipper (1975), and Muncy et al. (1979). Reductions in survival of the embryonic stages can also be

affected by the composition of the sand/gravel mixtures used in nest construction (Bain and Helfrich 1983). Our

best estimate of optimal benthic substrate is that more than 40% of the substrate (at preferred spawning depths)

should consist of a mixture of predominately coarse sand and gravel (substrate classes as defined by Cummins

1962).The fish should be able to sweep away fine layers of silt to utilize underlying sand and gravel, but we could

not find any description of how deep a layer could be swept away.

No data are available on specific negative impacts of pH on growth, survival, and reproduction of the redbreast

sunfish. They have been collected in streams with a pH range of 4.8 to 8.4 in North Carolina, indicating this range

is suitable for the occurrence of natural populations. Optimal pH range is assumed to be the range in which growth

and abundance have been reported to be good in southeastern coastal plain habitats (6.5-8.5) (Bass and Hill 1974;

Sandow et al. 1974; Michaels et al. 1981).This range falls within values cited for many different species of freshwater fish (Stroud 1967).Regarding long-term exposure, pH values < 4.0 or > 10.0 are likely to reduce the probability of long-term survival of the population and are rated poor.

Dissolved oxygen (DO)concentrations (>5.0 mg/l) corresponding to highest growth (Stewart et al. 1967;Dourdoroff

and Shumway 1970)are deemed excellent. DO concentrations between 2.0 and 5.0 mg/l are associated with avoidance behavior and moderate reductions in growth rates and survival for other centrarchids [e.g., 3.0 mg/l at 20 DC

for warmouth (Larimore 1957); <5 mg/l for largemouth bass (Katz 1959; Whitmore et al. 1960; Petit 1973)]and are

classified as good to fair habitats. Extended exposure to DO levels below 2.0 mg/l greatly reduces the survival

of smallmouth and largemouth bass embryos (Siefert et al. 1974; Eipper 1975) and are considered poor.
12

Table 1. (Concluded)

Variable

V9

V10

V11

V12

V13

Sources of information and rationale

Low to moderate turbidity levels are rated excellent because many species of sunfish, including the redbreast

sunfish, attain their highest growth rates in clear water (Jenkins et al. 1955; Bass and Hitt 1974). They are also

abundant in tannin-stained waters and marshes (Sandow et al. 1974;Germann et al. 1975;Benke et al. 1979;Michaels

et al. 1981), sluggish streams, backwaters, and lakes (Moyle 1976;Smith 1979;Trautman 1981). Turbidities exceeding

100 JTU's begin to negatively impact growth and abundance of other centrarchids (l.e., warmouth. green sunfish,

bluegill, and largemouth bass) (Jenkins et al. 1955; Buck 1956; Cross 1967; Moyle and Nichols 1973; Pflieger 1975;

Smith 1979) and are rated only good to fair.

Water temperatures corresponding to optimal growth and survival of adult, juvenile, and fry life history stages

of the redbreast sunfish are not known. Optimal water temperatures are assumed to be similar to those of other

centrarchids. For example, growth and survival are regarded as being good in the range of 18-32 °C, but maximal

values for both of these responses have been observed at temperatures of 25-30 °C for largemouth bass, bluegill,

and green sunfish (Hart 1952; Strawn 1961; Banner and Van Arman 1973; Beitinger et al. 1975; Coutant 1975a,b,

1977; Coutant and Cox 1976; Brungs and Jones 1977; Lemke 1977; Venables et al. 1978; Magnuson and Beltinger

1979; Wrenn and Grannemann 1980; Coutant and DeAngelis 1984).Temperatures < 15°C and >35 °C are rated

poor because population performance measures of many species of centrarchids are either greatly reduced or

mortality increases at these temperatures.

For most lacustrine systems, low concentrations of total dissolved solids (TDS)indicate low productivity, whereas

extremely high levels may induce osmoregulatory stress or ion regulation problems for many organisms. For reservoir

sport fishes, including several species of sunfishes but not redbreast sunfish, a positivecurvilinear relationship

between standing crop and TDS has been demonstrated (Jenkins 1976).TDS levels correlated to maximum sportfish standing crops for midwestern reservoirs range from 100 to 400 ppm and are rated as optimum habitat. However, comparable TDS values are rare in southeastern lentic habitats unless turbidity is high. The proposed relationship is likely to be a conservative estimate of maximum performance within the natural range of the redbreast

sunfish. Further work is necessary to verify if a TDS-standing crop relationship exists.

In ponds and lakes, redbreast sunfish frequent shallow water and are usually associated with areas of vegetation

or hard structural cover. Based on relationships observed for other centrarchids (e.g., green sunfish, Moyle and

Nichols 1973; Stuber et al. 1982),35% of the benthic substrate should have either hard structure or vegetation

as cover types. The optimal percentage of littoral zone is then represented by the value that results when 35%

of the total pond or lake's bottom is covered and 80% cover exists within any given area of the water body. Depending

on geographic location (north vs. south) or the presence of environmental stress (e.g., thermal effluent additions),

too extensive a littoral zone may, however, lower habitat quality, since this species, and other centrarchids, uses

deep water in the summer to escape high water temperatures and in the winter to form large aggregations (Breder

and Nigrelli 1935; Emig 1966).Too much vegetation associated with the littoral zone may also affect the foraging

success and, hence, growth rates and body-size fecundity relationships.

The distribution and abundance of redbreast sunfish varies according to stream width. Abundance is highest in

streams of intermediate size and therefore they are rated as optimum habitat. Declines in abundance have been

recorded in larger rivers (Chable 1947; Bass and Hitt 1974; Sandow et al. 1974).Suboptimum, but still "good" habltat conditions, are assumed to exist when stream width surpasses some threshold value (e.g., 30 meters).
V1

V2

V3

Variable

Percent hard structure cover during average

spring-summer water levels.

Percent vegetative cover during average springsummer water levels.

Percent of vegetated wetland with a depth

2:20 cm (palustrine habitats).

13

1.0

x 0.8

Q)

"0

c 0.6 >.

-.0 0.4 ro

-::J

en 0.2

0.0

a 25 50 75 100

%

1.0

x 0.8

Q)

"0

c 0.6 >.

-.0 0.4

ro

-::J

en 0.2

0.0

a 25 50 75 100

%

1.0

x 0.8

Q)

"0

c 0.6 >.

-.0 0.4

ro

-::J

en 0.2

0.0

a 25 50 75 100

%
. .

· -- ·

· I--

I I

14

V4 Maximum water temperature at preferred spawning depth (0.2-1.5 m) sustained for at least one

week during the spawning season (embryo).

1.0

X 0.8

Q)

"0

c 0.6

>-

+-'

.0 0.4 +-'

:::J

en 0.2

0.0

15 20 25 30 35

V5

V6

Percent of stream area during spawning season

that has a current velocity :5 20 crn/s and is at

least zo cm in depth.

Percent bottom area (during spawning season)

at preferred spawning depth (0.2-1.5 m) composed primarily of coarse sand or fine gravel

(0.1-0.5 cm diameter particle size).

1.0

x 0.8

Q)

"0

c 0.6

>-

+-'

:0 0.4 +-'

:::J

en 0.2

0.0

0 25 50 75 100

%

1.0

x 0.8

Q)

"0

c 0.6

>-

+-'

.0 0.4 +-'

:::J

en 0.2

0.0

0 25 50 75 100

%
V7 Least suitable pH during spawning and growing

season.

15

1.0

x 0.8

Q)

"'C

c: 0.6 >.

-

.0 0.4 cu

-:::J

(f) 0.2

0.0

0 3 6 9 11

pH

. -

va Minimum dissolved oxygen range during spawning and growing season.

A..Seldom below 5.0 mgll

B. Usually between 3.0 and 5.0 mg/l

C. Usually between 1.5 and 3.0 mgll

D. Often below 1.5 mg/l

1.0

x 0.8

Q)

"'C

c:

0.6 >.

-.0 0.4 cu

-:::J

(f) 0.2

0.0

A B

Class

C D

V9 Maximum monthly average turbidity during

spawning and growing season.

1.0

x 0.8

Q)

"'C

c: 0.6 >.

-.0 0.4 cu

-:::J

(f) 0.2

0.0

0 50 100 150 200

JTU
-

- -

-

16

V10 Maximum weekly water temperature (1-2 m

deep) sustained during growing season (adult,

juvenile, larvae).

1.0

X 0.8

Q)

"0

c 0.6

>- +-'

.0 0.4 +-'

::J

en 0.2

0.0

15 20 25 30 35

V11 Mean total dissolved solids concentration of surface waters (1-2 m deep) during growing season.

1.0

x 0.8

Q)

"0

C

>-

0.6 +-'

:0 0.4 +-'

::J

en 0.2

0.0

0 200 400 600 800

ppm

,

,

B ,,

V12 Percent littoral zone area at average summer

water level.

A. Southern areas

B. Northern areas

1.0

x 0.8

Q)

"0

c 0.6

>- +-'

.0 0.4 +-'

::J

en 0.2

0.0

0 25 50

%

75 100
V13 Mean stream width at average summer flow.

Interpreting Model Outputs

The model has not been rigorously tested in the field to

compare model outputs to species or population

responses such as growth, survival, standing crop, or

production. Rigorous testing should be conducted before

the model is used to justify decisions. The variables

selected are based on commonly measured aquatic habitat characteristics. Preliminary use of the model (Prescott Brownell, letter dated 14 Jan 86) has indicated that

most variables can easily be estimated in field situations,

but there are some problems estimating substraterelated variables when the water is turbid or site access

is difficult. Depending on local conditions, the variable

definitions may be refined to reflect constraints on sampling water quality or substrate or to incorporate additional knowledge of the species' habitat requirements.

The HSI's generated by using all (or some) of the model

variables should be interpreted as ratings of the potential of an area of habitat to support a resident, selfsustaining population of redbreast sunfish. We do not

expect that selection of the lowest Sl value for a sample

site will, in fact, result in a model that will accurately predict actual standing crop or secondary production,

because habitat variables alone do not determine population levels. We recognize the importance of potential

biotic interactions (e.g.,predation, intra- and interspecific

competition within and between the sunfishes and other

members of the fish assemblage) in influencing potential patterns of distribution and abundance. However, as

the physical habitat forms the template to which the animal must also respond, habitat factors known to affect

performance of populations or individuals are being used

in a model assumed to predict habitat-induced population limits. The accuracy of the model-generated HSI as

17

1.0

x 0.8

(1)

"0

c 0.6

>-

....

:c 0.4 ns

=:

::J

en 0.2

0.0

0 10 20 30 40

m

a predictor of habitat-induced population limits is currently unknown and may vary between different

geographical areas. Our extensive use of data for other

centrarchid species probably will reduce model accuracy.

The model, however, can be evaluated with field measurements from environments that include the range of

variables found in the proposed area of application to

determine which, if any, model variables are important

in limiting population levels. For example, Nelson and

Miller (1984)used principal component analysis to identify HSI model variables that explained variation in standing crops of three species of centrarchids. These variables were then used as the basis of a simplified model

with improved resolution properties for predicting standing crop. Layher and Maughan (1985) used standing stock

estimates to develop individual SI graphs. Given the

appropriate information on population dynamics and

habitat featues, a multivariate approach should be a useful means to examine these complex macrohabitat

properties, possibly through path analysis (c.t, Shively

and Jackson 1985).

ADDITIONAL HABITAT MODELS

If predictions of actual, rather than maximum expected

population levels, are required for HSI determination, the

selection of additional statistical models, weighting of

specific variables, or the choice of additional variable

measurements may be important. For example, Li et al.

(1984) used stepwise discriminant analysis to predict

three levels of fish standing crop. Layher (1985) formulated SI graphs from standing crop data for channel catfish (/ctalurus punctatus) to predict effects of changes

in flow on standing crop. Rabern (1984) predicted stand-
18

ing crops of southeastern stream fish directly from habitat data, bypassing altogether the development of suitability indices.

Foltz (1982) presented regression equations for predicting fish species diversity and catch per unit effort (CPUE)

of all fish species combined, using a data set gathered

from tst, 2nd, and 3rd order steams in the Piedmont area

of the Savannah River drainage. Redbreast sunfish were

only a minor (:51.0% by number) component of the fish

captured in these streams. However, positive correlations

of stream width and percent rubble to CPUE existed for

the more common species, including several species of

centrarchids. We expect a similar pattern (to a point) of

a positive effect on redbreast sunfish populations with

increasing stream width and the occurrence of greater

substrate heterogeneity. Consideration of these trends

has been used in the development of SI curves for V6 and

V13.

INSTREAM FLOW INCREMENTAL METHODOLOGY

At the time of the development of this report (June 1986),

no SI curves for use with the Instream Flow Incremental

Methodology (IFIM) were available; however, a Delphi

exercise for constructing curves has been Initated. GuIdance and examples of techniques for developing SI

curves for use with IFIM are provided by Bovee and Cochnauer (1977),Stalnaker (1979), Baldridge and Ames (1982),

Orth and Maughan (1982), Orth et al. (1982), Hamilton and

Nelson (1984), Moyle and Baltz (1985), and Bovee (in

preparation). The above references should be useful in

designing a field study to develop curves and as an aid

in interpreting habitat ratings derived from the SI curves.

However, IFIM should not be used by individuals who

have not received formal training in the use of the meth·

odology. Use of the curves and IFIM to quantify habitat

changes is critiqued by Patten (1979), Mathur et al. (1985),

and Moyle and Baltz (1985).

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23

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CONF-781101. Nat. Tech. Info. Serv., Springfield, VA.
50272-101

REPORT DOCUMENTATION 11. REPORT NO.

PAGE Bioloaical n 82 rin.ug) 12.

3. Reclplent'. Acc....on No.

.. Title .nd SUbtitle

Habitat Suitability Index Models and Instream Flow

Suitability Curves: Redbreast Sunfish

7. Author(.)

J. M. Aho, C. S. Anderson, and J. W. Terrell

9. Performln. Oraenlz.tlon N.me .nd Add..... National Ecology Center

Division of Wildlife &Contaminant

Research

U.S. Fish and Wildlife Service

2627 Redwing Rd.

Fnrt rnllinc:: rn Anl;?h-?AQQ

12. Sponsorln. O,..nlutlon N.me .nd Addr... Na ti ona1 Ecology Center

Division of Wildlife &Contaminant

Resea rch

Fish and Wildlife Service

II c:: ... n~ +ho Tn+oV'; nV'

5. Report O.te

November 1986

L

L Performln. O,..nlz.tlon Rept. No.

10. ProjKtIT••k/Work Unit No.

11. ContrKt(C) or Gr.nt(G) No.

(C)

(G)

13. Type of Report & Period Covered

14.

15. Supplement.ry Not..

lL Abstract (limit: 200 _rds)

Washington, DC 20240

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

Suitability Index (HSI) model and instream flow suitability curves for the redbreast

sunfish (Lepomis auritus). The model consolidates habitat use information into a

framework appropriate for field application. and is scaled to produce an index between

0.0 (unsuitable habitat) and 1.0 (optimum habitat). HSI models are designed to be used

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

Servi ce.

17. Document An.lysl. •• Descriptors

Fishes

Ha bita bi1ity

Mathematical models

b. Identlfiers/Open·Ended Term.

Redbreast sunfish

Lepomis auritus

Habitat suitability

c. COSATt FIeld/Group

*U.S. GOVERNMENT PRINTING OFFICE: 1916--773-0603 I 6501.0

lL Av.lI.blllty Stetement

Release unlimited

(5.. ANSI-Z39.18)

19. security CI••• (Thl. Report)

Unclassified

20. security CI••• (Thl. P••e)

Unclassified

See 'netruct'on. on Rever.e

21. No. of P....

23

22. Price

OPTIONAL FORM 272 (4-77>

(Formerly NTI5-35)

Dep.rtment of Commerce
.. ....,-. .. ..

""

*Headquarters, 0lvI5 10n Of Biolog ical

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)( Eastern Energy and Land Use Team

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• Locat ions of RegIonal Ollices

UGION 1

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Uoyd Five Hundred Building, Suite 1692

500N.E. Multnomah Street

Portland, Oregon 97232

REGION 4

Regional Director

U.S. Fish and Wildlife Service

Richard B. Russell Building

75 Spring Street, S.W.

Atlanta, Georgia 30303

,

,

I __r----

6!

,----- L, J_

1

, : ,--- I ,

I

REGION 2

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 1306

Albuquerque, New Mexico 87103

REGION S

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

Newton Comer, Massachusetts 02158

REGION 7

Regional Director

U.S. Fish and Wildlife Service

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,."

REGION 3

Regional Director

U.S. Fish and Wildlife Service

Federal Building, Fort Snelling

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REGION 6

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 25486

Denver Federal Center

Denver, Colorado 80225
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