United States EPA 910-R-01 -007
Environmental Protection August, 2001
Agency
Technical Synthesis
Scientific Issues Relating
to Temperature Criteria for
Salmon, Trout, and Char
Native to the Pacific
Northwest
A summary report submitted to the Policy
Workgroup of the EPA Region 10 Water
Temperature Criteria Guidance Project
Geoffrey Poole, US Environmental Protection Agency
Jason Dunham, US Forest Service
Mark Hicks, Washington Department of Ecology
Dru Keenan, US Environmental Protection Agency
Jeffrey Lockwood, National Marine Fisheries Service
Elizabeth Materna, US Fish and Wildlife Service
Dale McCullough, Columbia River Inter-Tribal Fish Commission
Chris Mebane, Idaho Department of Environmental Quality
John Risley, US Geological Survey
Sally Sauter, US Geological Survey - BRD
Shelley Spalding, US Fish and Wildlife Service
Debra Sturdevant, Oregon Department of Environmental Quality
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Preface
This document is a product of a Technical Workgroup established by the U.S. Environmental Protection
Agency (EPA) to assist them in developing temperature criteria guidance for EPA Region 10. The purpose
of the EPA guidance is to help Pacific Northwest states and tribes adopt water temperature standards that:
• Meet the biological requirements of native salmonids (Pacific salmon, trout, and char) species for
survival and recovery pursuant to the Endangered Species Act (ESA).
• Provide for the protection and propagation of salmonids under the Clean Water Act (CWA).
• Meet the salmonid rebuilding needs of federal trust responsibilities with treaty tribes.
The project focuses on salmonids because the ESA, CWA, and tribal treaties all address the protection
and/or restoration of salmonids. Additionally, this approach is scientifically sound since salmonids can also
be viewed as "umbrella species" that are indicators of the biological integrity of aquatic ecosystems in the
Pacific Northwest. Where salmonid populations are healthy, habitat conditions are apt to be suitable for other
native aquatic species as well.
To provide a scientific foundation for the project, the Technical Workgroup developed five technical
summaries on the major physical and biological considerations for developing water temperature standards:
1. thermal effects on salmonid physiology,
2. thermal effects on salmonid behavior,
3. interactions between multiple stressors - thermal and other - affecting salmonids,
4. thermal influences on salmonid distribution, and
5. spatial and temporal variation in patterns of stream temperature.
Each of these summary papers is available on the internet under the "Water" link at the EPA's Region 10
website (http://www.epa.gov/regionlO/) or by contacting EPA Regional Office in Seattle, WA.
This document has two purposes. First, it attempts to concisely synthesize the findings of the technical
summaries. Second, it outlines several conclusions drawn by the Technical Workgroup based on the literature
review included in the technical summaries. Therefore, this document takes the first step beyond the technical
summaries and begins to discuss the implications of the technical findings for water quality criteria for
temperature. The conclusions outlined toward the end of this document represent the collective interpretation
of the scientific literature by the Technical Workgroup rather than "facts" established by experimentation.
Further, a panel of experts on salmonid biology and stream temperature provided external, independent peer
review of the technical summaries, this synthesis, and its conclusions. Thus, this synthesis and its conclusions
are important in that they represent broad consensus of the members of the Technical Workgroup and
concurrence of the majority of the scientific review panel.
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Contents:
Preface ii
Introduction 1
Project Background 1
Clean Water Act 1
Endangered Species Act 2
Treaty Rights and the Trust Responsibility 2
Project Structure 3
How cold must water temperatures be to support salmonids? 3
How much cold water is necessary to support salmonids? When and where must it exist? 6
Biological diversity 7
Natural temperature dynamics 8
Incorporating thermal regimes 9
How do human activities affect stream temperatures? 11
How can we contend with scientific uncertainty when establishing temperature criteria? 13
Implications for Water Temperature Standards 15
References 18
Appendix A: Technical Interpretation of the Project Goals 19
11
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Scientific Issues Related to Temperature Criteria for Salmon,
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Introduction
Water temperature affects the distribution, health,
and survival of native salmonids (salmon, trout, and
char) and other aquatic organisms by influencing
their physiology and behavior. Since salmonids are
ectothermic (cold-blooded), temporally and spatially
heterogeneous thermal conditions are a resource that
fish utilize through behavioral means to control body
temperature within narrow limits (see Behavioral
technical summary). Water temperatures, along with
adequate flow, food, oxygen, shelter, and other
resources, determine habitat suitability for each
species. While community composition is shaped by
numerous habitat components, each of which can
provide optimal or suboptimal conditions,
temperature is an important aspect of habitat quality.
Further, temperature acts synergistically with other
environmental stressors, thereby affecting the ability
of individual fish to survive and reproduce, and
affecting salmonid population viability.
Water that is too warm can cause direct mortality
of salmonids. In addition, temperature influences
the abundance and well-being of organisms by
controlling their metabolic processes. While lethal
temperatures occur in nature and can be locally
problematic, temperatures in the range where
sublethal effects occur are widespread and may have
the greatest effect on the overall well-being and
patterns of occurrence of our native fish populations.
As stream temperatures and patterns of heating and
cooling (the "thermal regime") change due to land
management or other impacts, salmonid fishes may
be exposed to temperatures outside their physiologic
optimum, and fish communities may be altered
accordingly (see Distribution technical summary).
Salmonids have physiological (see Physiology
technical summary) and behavioral (see Behavior
technical summary) adaptations to temperature
dynamics that once allowed them to thrive in the
ecologically-diverse rivers and streams of the Pacific
Northwest, even though stream temperatures have
never been optimal in all places and at all times (see
Spatio-temporal technical summary). However,
where human-caused changes to stream thermal
regimes have occurred, they have contributed to
degradation of habitat conditions that prevent
salmonids from continuing to flourish. While many
factors contribute to the decline in native salmonid
populations, alteration of temperature regimes has
played an important role where it has occurred, both
directly and through synergistic interaction with
other factors such as habitat loss and disease.
Project Background
Many laws and regulations govern the use of
water in the United States. In the Pacific Northwest,
two federal statutes play key roles: the Clean Water
Act (CWA) and the Endangered Species Act (ESA).
The CWA provides the statutory basis for water
quality standards programs and defines broad water
quality goals. The ESA provides a means whereby
the ecosystems upon which threatened and
endangered species depend may be conserved, and
to provide a program for the conservation of such
species. Under the ESA, all federal departments are
required to conserve threatened and endangered
species. Further, under federal treaties with the
Columbia River tribes, the federal trust
responsibility imposes an obligation on all federal
agencies to protect and restore fish and their habitats
as necessary to fulfill the intent of the treaties.
The ESA is an important statute in the regulation
of water quality, because threatened and endangered
salmonids depend on cold, clean water, and because
federal agencies are required to cooperate with state
and local agencies to resolve water resource issues
in concert with conservation of endangered species.
The issues of clean water (CWA) and species
recovery (ESA) are widespread. Many major
watersheds in the region contain streams listed as
"water quality limited" due to temperature, and most
are important to the recovery of at least one listed
salmonid species. Both the CWA and ESA should
therefore play complementary roles in the recovery
of salmonids in the Pacific Northwest.
Clean Water Act
A water quality standard defines the water quality
goals for a water body by designating the use or uses
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Scientific Issues Related to Temperature Criteria for Salmon,
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to be made of the water, by setting "criteria"
necessary to protect the uses, and by preventing or
limiting degradation of water quality through
antidegradation provisions. Under section 304(a) of
the CWA, EPA publishes water quality criteria that
reflect available scientific information on the levels
of specific chemicals or parameters for the
protection of aquatic life or human health. These
criteria are intended to provide protection for all
surface waters on a national basis, and may be used
by states as a basis for developing enforceable water
quality criteria as part of their standards. The criteria
are provided as guidance, to assist states and tribes
in setting water quality standards.
The foundation for EPA's national criteria for
temperature was established by the National
Academies of Sciences and Engineering in a review
for EPA, Water Quality Criteria 1972: Report to
the U.S. Environmental Protection Agency. The
report focuses on preferred methods and procedures
for judging thermal requirements rather than on
providing specific numerical values for various
species of concern. The report suggested that species
and life stages be protected from several levels of
negative effects of increased temperature: lethal
effects, sublethal effects, habitat exclusion, and
reproductive continuity. The report also focused on
the importance of establishing upper limits for a
maximum weekly average temperature, and on
establishing a time-dependent maximum
temperature for short exposures. The work was
based on the physiological requirements of species
and did not take into account the physical aspects of
stream or lake systems. EPA later augmented this
work and established numeric temperature criteria
for certain species including coho and sockeye
salmon (EPA 1976).
EPA's 1986 Quality Criteria for Water report, as
updated in National Recommended Water Quality
Criteria (EPA 1999), contains summaries of all
contaminants and conditions for which EPA has
developed criteria recommendations. The criteria
serve as guidance to assist states and tribes in
adopting water quality standards, as required by
section 303(c) of the CWA. Once adopted, states
and tribes are to submit the standards to EPA for
review and approval or disapproval. EPA reviews
the standards to determine compliance with the
CWA and implementing regulations and to ensure
the criteria associated with the standard are
protective of the designated beneficial uses.
Endangered Species Act
When a state proposes a water quality standard
that may affect species listed as threatened or
endangered populations under the ESA, EPA must
consult with the U.S. Fish and Wildlife Service
(USFWS) and/or the National Marine Fisheries
Service (NMFS) prior to approving the standard, in
order to ensure that the proposed standard will not
jeopardize the continued existence of a listed
species. In order to streamline the process of review
and consultation for future water temperature
standards in the Pacific Northwest, EPA Region 10
developed a program that allows Oregon,
Washington, Idaho, Native American tribal
governments, EPA, NMFS, and USFWS to develop
guidance jointly for the development of water
temperature criteria. All of the participating
agencies and tribes hope to use the final product to
harmonize the ESA and CWA with respect to water
temperature standards, and to help remove water
temperature as an impediment to the recovery of
imperiled native salmonids.
Treaty Rights and the Trust Responsibility
Through their treaties, tribes reserved the right to
fish at all usual and accustomed fishing places and
to take a "fair share" of the fish destined to pass to
such areas. The Supreme Court has determined that
the tribes' fair share is 50 percent of the harvestable
fish, unless a moderate living standard can be met
with less. Guaranteed by treaty, these tribal fishing
rights may only be abrogated by specific
congressional legislation - no one may use any
method to otherwise deprive treaty fishermen of
their right to a fair share of the anadromous fish
(those that migrate from streams to the ocean and
back).
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Scientific Issues Related to Temperature Criteria for Salmon,
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As trustee of the tribes, the federal government
also has the affirmative obligation to safeguard the
subject matter of the treaty fishing right - the fish.
Thus, federal agencies must use their authorities in
a manner that will protect and prevent degradation
of the habitat needed to support anadromous fish
species. At a minimum, agencies have the duty to
refrain from activities that will interfere with the
fulfillment of treaty fishing rights. Anything less
would amount to a de facto abrogation of Native
American treaty rights. Thus, unless federal agencies
can demonstrate that treaty fishing rights are
presently being fulfilled, they cannot justify
approving activities that will cause further
degradation of anadromous fish habitat. Similarly,
they cannot "balance" their treaty obligations against
competing impacts to non-Native Americans or
"delay" such obligations in order to minimize those
impacts.
The federal trust obligation also mandates that
Federal agencies enhance salmonid habitat where
necessary to safeguard the fish that underlie the
treaty fishing right. Arguably, this Federal trust
obligation does not cease once a fish run becomes
viable, but must continue to allow for harvestable
populations offish and meaningful fulfillment of the
treaty right to take fish.
Project Structure
EPA initiated development of guidance for
regional temperature criteria through a multi-agency
effort intended to develop guidance for regional
temperature criteria that would be protective of
native salmonids, would recognize the natural
temperature potential and limitations of streams,
could be effectively incorporated by states and tribes
in water quality standards programs, and would be
endorsed by EPA, USFWS, NMFS, states, and tribes
in the Pacific Northwest. Additionally, it is intend
that EPA use the new criteria guidance to evaluate
revisions to state and tribal temperature standards,
and that states and tribes will use the new criteria
guidance to revise their temperature standards. The
Technical Workgroup developed a technical
interpretation of the project goals (see Appendix A)
that articulates the goals in terms of viable salmonid
populations, distribution of coldwater habitat to
support viable populations, and coldwater habitat
support of all life history stages of salmonids.
The individuals involved in the project are
employees of tribes and state and federal agencies,
and are divided into a technical and a policy
workgroup. The Policy Workgroup is comprised of
agency/tribal managers and has the ultimate
decision-making authority regarding the final form
of the guidance. The Technical Workgroup,
comprised of agency and tribal scientists, is
responsible for developing draft guidance and
providing technical review of the Policy
Workgroup's final decision.
Water temperature improvement alone can not
restore native fish populations; however,
temperature improvements are necessary to restore
requisite freshwater habitat for both resident
salmonids (those that fulfill their entire life cycle in
streams, rivers, and/or lakes) and anadromous
salmonids. Relatively high freshwater survival is
necessary to produce sufficient numbers of spawning
adults. For example, since mortality is high during
the egg to smolt periods in the freshwater and
estuarine phases of anadromous salmonid
development, reducing mortality during these stages
offers significant opportunities for restoration of
anadromous fish (Federal Caucus 2000). For
anadromous fish, freshwater survival is particularly
important during periods of poor ocean productivity.
How cold must water temperatures be
to support salmonids?
Viable populations of native salmonids in the
Pacific Northwest need abundant cold water that is
well-distributed over space and time to meet their
freshwater habitat needs (see Physiology, Behavior,
Multiple stressors, and Distribution technical
summaries). The importance of cold water habitat
to salmonids is documented by scientific research
(summarized in the Physiology, Behavior, and
Multiple stressors technical summaries). The
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
thermal tolerances expressed by salmonids are lower
than those expressed by other groups of fishes, such
as centrarchids (e.g., smallmouth bass, perch) and
cyprinids (e.g., carp, northern pikeminnow).
Salmonid feeding, growth, resistance to disease,
competitive ability, and predator avoidance are
impaired by unsuitable temperatures (see
Physiology, Behavior, and Multiple stressors
technical summaries). For instance, adult fish
holding in warm water experience bioenergetic
stress and consume their stored energy more rapidly,
which may result in reduced spawning success.
Prolonged holding in sub-optimal temperatures can
result multiple stresses, such as concurrent thermal
stress, disease, and energy depletion. Additionally,
thermal stress experienced while fish are holding can
decrease gamete viability. Warm temperatures can
alter growth and development rates for juveniles and
salmonids that feed in fresh water. In addition,
warm water can present thermal barriers to adult and
juvenile migrations. If enough fish are affected,
salmonid population viability may be reduced.
Temperature-dependent life stages for salmonids
include spawning, egg incubation, emergence,
rearing, smoltification, migration, and pre-spawn
holding. Any of these salmonid life stages can be
present (depending on species and location) during
summer months when streams in Pacific Northwest
are warmest. Scientific evidence suggests that small
increases in temperatures (e.g., 2-3°C) above
biologically optimal ranges can begin to reduce
salmonid fitness in some of these life stages.
While individual salmonids may be observed in
streams where temperatures exceed laboratory-
determined thermal tolerances, these observations
alone are not grounds for concluding that warmer
streams and rivers can support healthy salmonid
populations. Individual fish may stray or be trapped
in waters where temperatures are stressful or
ultimately lethal. Further, if coldwater pockets
(micro-refugia) are available in warm streams, small
number of salmonids may be able to survive by
exploiting these cold areas for short periods to avoid
heat stress (see Behavioral technical summary), even
though the majority of habitat in the stream is too
warm to support salmonids
Thermal conditions supporting and/or impairing
various life stages and biological functions of some
salmonids have been identified, primarily in
laboratory settings (Table 1). These numbers are
based on documenting the response of individual
fish to various water temperatures. Therefore, there
is some uncertainty regarding whether many of the
temperatures listed are appropriate targets for
supporting viable salmonid populations in rivers and
streams. This uncertainty is compounded because
most laboratory studies address single stressors
while providing optimal conditions for other
environmental factors, even though temperature
does not act independently from other factors (Table
2, see also Multiple stressors technical summary).
For example, when salmonids are fed to satiation,
temperatures associated with maximum growth-rates
are higher than under conditions of more natural
(limited) food supply. Similarly, allowing
salmonids to slowly acclimate to warm temperatures
in the laboratory will extend their thermal tolerance,
yet migrating salmonids pass rapidly through
thermally diverse environments and may not have
time to acclimate in the field. It is difficult to mimic
field conditions in the laboratory, or to disentangle
the effects of the multiple, interacting factors in
complex natural systems. Because field conditions
are more ecologically complex than laboratory
settings, the uppermost laboratory-derived thermal
limits are not likely to prevent adverse effects in a
natural setting. Thus, where studies have attemped
to derive the uppermost thermal limits for
salmonids, they have measured responses of
individual fish to water temperature in a laboratory
setting. Stream temperatures may have to somewhat
cooler than measured uppermost thermal tolerances
in order to support viable salmonid populations in
natural settings.
Because various salmonid species and life stages
show high fitness in a range of laboratory-derived
optimal water temperatures, these temperatures (e.g.,
optimal temperatures shown on Table 1) can provide
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Scientific Issues Related to Temperature Criteria for Salmon,
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Table 1. Estimates of thermal conditions known to support various life stages and biological functions of
bull trout (a species extremely intolerant of warm water) and anadromous (ocean-reared) salmon. These
numbers dp not represent rigid thresholds, but rather represent temperatures above which adverse effects
are more likely to occur. In the interest of simplicity, important differences between various species of
anadromous salmon are not reflected in this table and requirements for other salmonids are not listed.
Likewise, important differences in how temperatures are expressed are not included (e.g., instantaneous
maximums, daily averages, etc.). These numbers are taken from the Physiology technical summary; that
summary should be consulted for more detailed discussions and for references to scientific literature that
support these numbers.
Consideration
Anadromous Salmon
Bull Trout
Temperature of common summer habitat use
Lethal temperatures (one week exposure)
Adult migration
Swimming speed
Gamete viability during holding
Disease rates
Spawning
Egg incubation
Optimal growth
Smoltification
10-17°C
Adults: >21-22°C
Juveniles: >23-24°C
Blocked: >21-22°C
Reduced: >20°C
Optimal: 15-19°C
Reduced: >13-16°C
Severe: >18-20°C
Elevated: 14-17°C
Minimized: <12-13°C
Initiated: 7-14°C
Optimal: 6-10°C
Unlimited food: 13-19°C
Limited food: 10-16°C
Suppressed: >11-15°C
6-12°C
Juveniles: >22-23°C
Cued: 10-13°C
Initiated: <9°C
Optimal: 2-6°C
Unlimited food: 12-16°C
Limited food: 8-12°C
conservative guidance for identifying instream
temperatures most likely to protect salmonids. We
do not intend to imply, therefore, that all streams
must provide these optimal conditions at all times or
in all places. We simply intend to focus our
attention on identifying temperatures that are very
likely to support viable salmonid populations.
The scientific research reviewed in the
Physiology, Behavior and Multiple-stressor
technical summaries shows that salmonids require a
diversity of cold water temperatures in streams
(Table 1) and that these temperatures must exist at
appropriate locations and at appropriate times of the
year. While laboratory evidence suggests adult
salmon can generally survive a week or more at
constant temperatures of 21°C and can often tolerate
temperatures as warm as 18°C for prolonged periods
under controlled experimental settings, constant
temperatures above 16°C have been shown to be
intolerable for species such as bull trout. Not only
do different species have unique temperature
requirements, but individual species have unique
temperature requirements for different life stages
(spawning, incubation, juvenile growth, seawater
adaptation, and adult migration) (see Physiology
technical summary). The times at which those life
stages occur are highly variable among streams of
our region. In consideration of the available
scientific information, we conclude that viable
salmonid populations will require a variety of cold
water temperatures (Table 1) that are well-
distributed over space and time.
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Scientific Issues Related to Temperature Criteria for Salmon,
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Table 2. Examples of considerations for interpreting laboratory observations of thermal tolerances and
preferences for salmonids.
Consideration Effect
Implication
Acclimation
Feeding
Social
interactions
Physiochemical
conditions
Handling
Fish size/stage
Exposure
When salmonids are
acclimated to warmer
temperatures in the lab,
incipient lethal and other
threshold temperatures
rise to a limited extent
Feeding to satiation
increases optimal growth
temperatures relative to
when food is limited.
Food quality and cost of
foraging may also be
important
Can mitigate or
exacerbate various
thermal stresses
Can alter stress response
in a number of ways
Causes additional stress
Response may be size,
age, or stage-dependent
Exposure in lab and
field settings may differ
Results from laboratory studies are not directly comparable unless
acclimation conditions are the same. Further, direct comparisons between
lab and field conditions may be precluded because temperatures may vary
considerably in the field. To make comparisons between lab and field
studies, some researchers assume that fish are acclimated to a temperature
between the mean and the maximum daily temperature.
In the field, food availability is usually limited. Thus, lab tests where
feeding levels are at satiation can overestimate suitable temperatures for
growth and certain other performances. Also, food quality in the
laboratory may differ from foods available in the field, and fish in the field
must expend more energy to locate, and capture prey. Foraging costs
(energy expenditure) may be reduced considerably under laboratory
conditions than under field conditions, thereby reducing stress.
Social conditions in the field, especially territoriality, are key components
of salmonid population regulation and behavior. Experimental studies
seldom consider the role of social factors, which could mitigate or
exacerbate responses to stressful temperatures. Unnatural social
circumstances in the laboratory include, but are not limited to: possible
high fish densities, wild vs. hatchery fish behavior, and altered community
age structure. In the field, high fish density or low food availability can
result in fish being forced to inhabit marginal thermal habitat. Mixtures of
species and age classes can intensify social interactions in the field,
whereas lab studies typically use single species and age classes per test.
Artificial lighting, photoperiod, thermal regulation, water chemistry,
habitat structure (lab apparatus), cover, etc., may not reflect field
conditions and are tied to physiological and behavioral responses to stress.
Response may be partially determined by physical features of the
experimental apparatus (e.g., horizontal vs. vertical thermal gradient in
preference tests).
Repeated handling of fish, invasive procedures, and interaction with
apparatus (e.g., tank maintenance), can alter both physiological and
behavioral responses to stress.
Most laboratory studies focus on early life stages (e.g., eggs, fry,
juveniles). This may not reflect the total life cycle in the wild. For
example, adults and emergent fry can be more sensitive to elevated
temperature then juveniles.
Natural streams have a diurnal range of temperatures and may have cooler
areas in pools, tributaries, or where ground water upwells where fish can
take refuge from warm temperatures. Fish in a laboratory aquarium cannot
escape their test conditions, which may be constant.
How much cold water is necessary to
support salmon ids? When and where
must it exist?
Temperature criteria to protect salmonids have
traditionally attempted to identify the warmest water
temperatures that can support salmonids. However,
identifying water temperature thresholds is not
sufficient to ensure support for viable salmonid
populations.1 It is also important to determine how
much cold water is needed, and here and when it be
available.
Native Pacific salmon, trout, and char have
complex life histories (Figure 1) that evolved in the
spatially and temporally dynamic landscapes of the
Viable populations are defined in Appendix A
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Scientific Issues Related to Temperature Criteria for Salmon,
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Pacific Northwest (see Distribution technical
summary). Accordingly, providing enough cold
water at the right places and times to support the
recovery of native salmonids will require restoration
and protection of natural ecosystem processes and
patterns, including thermal regimes and spatial
patterns of thermal habitat (see Spatial-temporal
technical summary). Thus, our understanding of the
biological and physical diversity of natural processes
should provide guidance for developing temperature
criteria. Maintaining biological diversity and natural
system dynamics are important goals when
considering how much cold water is necessary, when
it is necessary, and where it is necessary.
Biological diversity
The spatial and temporal dynamics of natural
thermal regimes lead to variations in life history
characteristics (e.g., growth, timing of migration,
age at reproduction). These characteristics interact
in complex ways to determine individual fitness, and
patterns of life history variability, viability, and
productivity among populations and species. Within
a species, individuals and populations with different
life cycles and life histories may fare differently
under changing environmental conditions.
Variability in life history strategies may therefore
confer stability and increased productivity to
salmonid populations in naturally variable
environments. Alteration of natural thermal regimes
may cause populations to decline or important life
history variability to be lost (see Spatio-temporal
technical summary).
Criteria for temperature standards sometimes use
specific characteristics of individuals and/or
populations (e.g., density offish, growth, fecundity,
or survival) to simplify the task of managing or
tracking population response. However, there is risk
associated with using a small set of population
indices (e.g., Sullivan 2000) or attempting system-
wide maximization of any of these measures because
of interaction or feedback among multiple factors.
For instance, Holtby (1988) found that logging
increased winter water temperature and subsequently
the growth of juvenile coho salmon. While this
Streams, Rivers
and/or Lakes Estuary
Ocean
Adult
Figure 1. A simplified general sequence of
events in the life cycle of salmonid fishes. All
salmonids deposit eggs in freshwater (stream or
lake) habitats. Depending on temperature and
other factors, eggs hatch into alevins (sac fry).
Alevins typically remain in or near spawning
substrates until the yolk sac is absorbed.
Following absorption of the yolk sac, the young
are referred to as "fry." This stage signifies the
initiation of active feeding and development into
fully formed juveniles. Juveniles may remain in
their natal tributary or lake and mature as adults.
This is referred to as a "resident" life history.
Known migratory life histories include
migrations to non-natal lakes and streams
(potadromy) and marine habitats (anadromy).
The transition to the marine environment
involves complex physiological changes, referred
to as "smoltification" in juvenile salmonids.
Adults of some species may make repeated
transitions between freshwater and marine
habitats, however. Migratory behavior varies
substantially among species, and within and
among local populations, in many cases.
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Scientific Issues Related to Temperature Criteria for Salmon,
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might be expected to be beneficial, the increased
growth accompanied earlier migration, reduced
marine survival, and an overall reduction in the
number of returning fish. This illustrates how
attempting to maximize a single metric (in this case,
growth) might have unintended negative
consequences for the population as a whole. This is
not to say that growth should be ignored as an
important factor for monitoring salmonid
populations. It simply underscores that single
measures are not effective indicators of population
status and that attempts to maximize such measures
are associated with biological risks. In fact, these
simplified approaches may reduce rather than
preserve natural biological diversity and viability of
salmonid populations by focusing attention on
specific performance measures at the expense of
other important aspects of biological diversity
(Lichatowich 1997).
Natural temperature dynamics
Natural landscapes represent a complex mosaic
of physical and biological diversity. Ecosystem
processes that shape these physical and biological
patterns can operate on a number of scales in time or
space. A natural thermal regime can be considered
in terms of magnitude, frequency, duration, and
timing of events (e.g., summer maximum
temperatures) and rates of change (i.e., how fast
temperatures heat or cool) at different temporal and
spatial scales.
Temporal scale. Temporal variation of a thermal
regime can be considered in terms of variability
A.
00:00 10:00 20:0(
B.
Habitat unit
Network
Stream reach
"Patch"
or "Stream'
Figure 2. Examples of temporal
and spatial variation in thermal
regimes. (A) Annual, seasonal,
and daily thermal regimes. (B)
Different spatial scales where
habitat variability is often
considered, (see Frissell et al.
1986, Hawkins et al. 1991,
Montgomery and Buffmgton 1998,
Dunham et al. 2001).
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
among years, within a year (among seasons), within
seasons (among days or weeks), and within a single
day (among hours) (Figure 2). Thermal regimes
affect salmonids at all of these scales (see Spatio-
temporal technical summary). Decadal-scale
variation in climate and temperature (e.g., El Nino
events, Pacific decadal oscillations) may affect long-
term patterns of productivity in salmon populations.
Within years, the timing and locations of various
parts of the salmonid life cycle are linked to seasonal
patterns of stream temperature and habitat
availability. Smaller-scale weekly or daily
variability in temperature also may be important as
they affect chronic or acute thermal stress (see
Physiology technical summary) and individual
behaviors, such as migration, habitat selection,
predator avoidance, competition, and behavioral
thermoregulation (see Behavior technical summary).
Spatial scale. Spatial pattern is an important part
of a thermal regime. Spatial variation can occur
within a few meters, such as with pools and riffles,
within a larger habitat scale including stream
reaches, individual streams, and stream networks
(Figure 2). Two important aspects of the spatial
distribution of thermal habitat are the size and
locations of thermal refuges. For coldwater fish,
thermal refuges can be defined as patches of cold
water that allow individuals or populations to persist
in a thermal regime that ranges (in time or space)
outside of the zone of tolerance or preference for a
given species. Thermal refuges may range in size
from fine scale (e.g., pockets of cold water provided
by thermal stratification and localized ground water
upwelling to cold side channels and backwaters in
alluvial systems) to coarse scale (e.g., thermal
variation between headwater creeks to larger main-
stem rivers; see Spatio-temporal technical
summary).
Landscape context. Protection offish at specific
sites is not sufficient to guarantee the health of a
local population. Emerging evidence (see
Distribution technical summary) suggests the health
of local populations may depend on the landscape
context - specifically, the size, number,
connectivity, location, and quality of occupied and
unoccupied habitats within which the population
lives. The landscape context refers to the spatial as
well as temporal dynamics of habitat change and
occupation. Where habitat is degraded, fish
populations that decline will not recover until the
habitat has recovered. In some cases, however,
habitat is not just degraded, but a disturbance
renders the habitat temporarily unsuitable (e.g. local
temperature increases in a portion of a stream
network) for salmonid survival. In these cases,
although that habitat may ultimately recover, the loss
of certain species from the disturbed area can be
either temporary or permanent. Species loss is likely
to be temporary if other suitable habitats (refuges
from disturbance) are: 1) large enough to maintain
viable populations of affected fish, and 2) inter-
connected to allow emigration from the refuge(s) to
the disturbed site when (or if) it recovers from the
disturbance. This underscores the fact that not all
suitable habitat is necessarily occupied at all times in
a dynamic natural landscape. Therefore, protection
of some amount of currently occupied and
unoccupied habitat may be needed to provide a
sufficiently large network of well-connected habitat
distributed across the landscape (Figure 3). Specific
answers to the questions of precisely "how large?"
or "how connected?" are only beginning to be
addressed as principles of conservation biology are
integrated into salmonid ecology (see Distribution
technical summary), but those efforts suggest that
habitat must be widespread and well-connected in
order to meet a goal of maintaining viable salmonid
populations.
Incorporating thermal regimes
While we do not fully understand how natural
ecosystems function, natural conditions serve as
models of stream temperature dynamics known to
have supported viable salmonid populations. It is
difficult to prescribe "appropriate" thermal regimes
from inferences about biological conditions or
physical conditions alone. Our biological
understanding of salmonids has provided important
insights into the effects of temperature, but it does
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
Figure 3. Example of temporal variation in patterns of habitat
occupancy by salmonids in a dynamic landscape. Circles
represent potential "patches" (Dunham et al., in press) of
suitable habitat in a stream network (lines). Filled circles
represent occupied habitats, and unfilled circles indicate
unoccupied habitats. Temporal variation in stream habitats can
change habitat suitability over time, and affect patterns of
habitat occupancy. Even if stream conditions remain static,
external factors (e.g., ocean productivity cycles) may cause
variation in fish populations and habitat occupancy over time.
Either will produce patches of potentially suitable, but
unoccupied, habitat and a dynamic of local extinction and
recolonization by different species (Reeves et al. 1995, Rieman
and Dunham 2000).
not directly address the causes of thermal
degradation. If one accepts that salmonids are
adapted to survive in the historic conditions of the
Pacific Northwest, it follows that temperature
standards that encourage attempts to restore an
ecosystem's thermal dynamics (e.g., address the
causes of thermal degradation) will provide a very
high likelihood of supporting viable salmonid
populations.
In an ideal world, we might eliminate thermal
degradation by restoring stream temperatures to pre-
settlement thermal regimes that historically
supported viable salmonid populations. However,
restoration of historical conditions can be an
unreasonable goal given that restoration
opportunities may be limited to varying degrees by
certain "irreversible" human-caused or natural
landscape changes, such as development of major
urban centers and volcanic eruptions. Yet, the
continuing collapse of salmonid populations
suggests that the existing amount and distribution of
suitable habitat in the Pacific Northwest is
inadequate to maintain viable salmonid populations.
Therefore, based on the scientific review contained
in the technical summaries, the Technical
Workgroup concludes water temperature criteria
should ideally address thermal regimes, and that four
actions relevant to thermal regimes may be
necessary and should be strongly considered in order
to ensure adequate amounts and distributions of cold
water to support salmonid populations.
1) Immediate protection of remaining suitable
habitat from thermal degradation.
2) Restoration of some amount of thermally
degraded habitat. Given that thermal
degradation in many streams may not be
reversible due to policy considerations or social
and economic realities, it is likely that much or
even all habitat that can be restored will need to
10
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
be restored in order to support viable
populations.
3) Implementation of restoration across a broad
spectrum of habitats from headwaters to ocean
because the life histories of salmonids span
entire watersheds.
4) Protection and restoration targets based on
consideration of a wide array of evidence with
an emphasis on natural temperature dynamics.
Engineering artificial thermal regimes may entail
greater uncertainty and risk than attempting to
mimic natural processes and patterns (see Poff et
al. 1997 for a discussion of the importance of
maintaining or restoring natural regimes).
How do human activities affect
stream temperatures?
Water temperature is determined by interactions
between the amount of water flowing in the stream,
the structural configuration of the stream and
riparian zone, and various factors external to the
stream/riparian zone (see Spatio-temporal technical
summary). In many river basins of the Pacific
Northwest, land management activities have (1)
reduced connectivity (i.e., the flow of energy,
organisms, and materials) between streams, riparian
areas, floodplains, ground water, and uplands; (2)
altered floodplain function, wetlands, water tables,
and base flows; (3) elevated fine sediment yields,
making streams wider and shallower, with fewer
Riparian
Management
i
n Riparian 1
tJ vegetation |
1
bpl-',nil, 1
IB stability |
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\
3
a
Upland Water
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*
1
Channel 1 1 Dam
Engineering | | Operation
1
Upland VV LWD mW Stream flow
vegetation f^ dynamics &J regime
j 1
Upland •• Sediment
lydro ogy PB mobility
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b> Downstream *
pU sedimentation
i ' i
1
'
PP Streambed
pBl conductivity
bv Channel
pi width
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Q Shade
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i '
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^9 inlilLrt
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wm Groundwater
•I temperature
•J Heat exchange with
•1 atmosphere
pe
-
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•• Return flow
Pi temperature
i
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^p Instream
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- ^
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i
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Sediment pp Peak stream
transport pB flows
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•• Channel stability,
PB efficiency, and simplicity
PP Channel and water
MM table e evation
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PP Floodplain
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^J Channel Water Temperature |
Figure 4. Some pathways of human-caused warming of stream channels (From Poole and Berman 2001.).
The symbol "+" indicates an expected (but not certain) increase, "-" an expected (but not certain)
decrease, and "A" either an expected increase or decrease depending on the specific circumstance or
measurement used. This graphic is designed to illustrate the complexity associated with stream
temperature dynamics. It is not intended to be a comprehensive summary. Additional arrows and boxes
are possible under various conditions.
11
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
pools; (4) reduced instream and riparian large woody
debris that traps sediment, stabilizes stream banks,
and helps form pools; (5) reduced or eliminated
riparian vegetation; and (6) altered peak flow
volumes and timing (FEMAT 1993, Henjum et al.
1994, Rhodes et al. 1994, Wissmar et al. 1994,
National Research Council 1996, Spence et al. 1996,
Oregon Coastal Salmon Restoration Initiative 1997,
Quigley and Arbelbide 1997, Mclntosh et al. 2000).
Thus, human activities can alter stream temperature
through a variety of complex and interactive
pathways (Figure 4). In developing guidance for
water quality criteria, we believe it is important to
consider a wide array of pathways by which human
actions alter temperature and the ways in which
different approaches to temperature standards might
be effective or ineffective at addressing the influence
of each pathways.
Human-caused changes to stream temperature are
often hard to quantify, often because of difficulty
determining what the "natural" water temperature
would have been in the absence of human-caused
degradation. However, scientific research has shown
that human activities have the potential to alter
thermal regimes (see Spatio-temporal technical
summary). Along with changes in mean
temperature, more subtle changes in stream
temperature may be manifested as changes in
temperature extremes, in temperature variation, or in
the timing of temperature extremes (see Spatio-
temporal technical summary). Although some
human impacts (e.g., dams) can reduce diurnal
temperature variation, human-caused degradation
often simplifies stream structure, which eliminates
the coldest water habitats and reduces spatial
temperature variation within stream reaches. At the
same time, human-caused degradation often
increases the daily and seasonal temperature
variation in stream reaches by interrupting natural
processes that buffer stream temperature such as
riparian shade, in-stream flow, and ground water
influx, (see Spatio-temporal technical summary).
While these effects might seem to offset one
another, they instead have a synergistic negative
effect on salmonid populations. Increases in daily
and seasonal variation expose fish to higher
summertime maximum temperatures. At the same
time, loss of coldwater habitat that reduces spatial
variation within stream reaches precludes
salmonids' ability to escape high temperatures or
avoid other detrimental physiological and ecological
conditions (see Behavior technical summary).
Human influences on stream temperature are
inherently cumulative; as the amount and intensity
of land-use and river flow regulation increase in a
basin, so too does the magnitude of in-stream
temperature changes (see Spatio-temporal technical
summary). Thus, problematic water temperatures
are most apt to occur in basins where urbanization
and intensive land-use activities (such as logging
and agriculture) are widespread and/or where dams
or water withdrawals have substantially altered
natural flow regimes. In these basins, stream
warming will occur if human actions cause more
heat to be added to stream, and some of that heat
will remain in the stream as water moves
downstream. Any accumulated additional heat will
remain in the stream until downstream conditions
(e.g., riparian vegetation, geomorphology, etc.)
create the opportunity for heat to dissipate back out
of the stream channel (see Spatio-temporal technical
summary). Some streams dissipate added heat
effectively and may eventually return to pre-
disturbance conditions, while others will retain at
least some of the added heat for long distances. The
distance over which the additional heat can persist in
a stream may range from a few meters to many
kilometers. Thus, in some circumstances, heat
added to cold headwater streams might not create
thermally unsuitable salmonid habitat in the
headwaters themselves, but may instead contribute
to unacceptably warm temperatures at some distance
downstream.
In areas where human activities have warmed
streams, those same activities often eliminate
naturally-occurring thermal refugia (from pockets of
cold water in warmer streams to entire watersheds
that contain thermally optimal temperature regimes)
or isolate such refugia from other suitable thermal
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
habitat. Loss of these important landscape features
reduces the ability of salmonids to avoid thermal
stress and therefore is apt to decrease survivorship
through periods of temperature extremes (see
Spatio-temporal and Distribution technical
summaries).
How can we contend with scientific
uncertainty when establishing
temperature criteria?
Developing temperature criteria to protect
salmonids is challenging in part because scientific
understanding of stream temperature dynamics,
salmonid biology/ecology, and their interactions is
imperfect. To maximize the potential for success,
the process of developing criteria must be founded
on scientific information yet be flexible to
accommodate scientific uncertainty. Clearly, there
are limits to our knowledge. For instance, our
knowledge regarding historical distributions of
salmonids is extensive, but the details regarding
population sizes and habitat utilization within each
individual basin is often limited. Data describing
historical thermal regimes is scarce and our
knowledge of natural distributions of coldwater
habitat is imperfect. In addition, we lack the ability
to precisely measure or predict the interactions
between thermal stress and other biophysical
stressors in the freshwater environment. Although
salmonid distributions can be correlated with
Table 3. Examples of uncertainties and certainties associated with determining criteria for water temperature
standards based on protecting viable populations of salmonids in the Pacific Northwest.
Uncertainty
Certainty
How Cold
How Much,
When and
Where?
Human
Influence
Relationships between lab-derived temperature
thresholds and requisite temperatures in the field
Maximum allowable temperatures that will
support viable populations
Precise thresholds of harmful temperatures (e.g.,
see Table 2)
Effects of multiple stressors
Mechanisms and dynamics of cumulative effects
on stream temperature dynamics
Patterns of environmental variability required to
support populations
Historical thermal regimes in streams
Measures of historical fish distribution and trends
in fish populations
Data on the alteration of thermal regimes
Exactly what management actions are necessary to
protect salmonids
Maximum levels of degradation that will allow
salmon to persist
Salmonids can experience physiological stresses where
water temperatures are not optimal
General ranges of water temperatures necessary for
survival and reproduction.
Both lethal and sub-lethal effects affect salmonid
survival
Thermal tolerance in salmonids is affected by other
stresses and vice versa.
Cumulative effects occur and can result in synergistic
temperature changes within in streams subject to
multiple disturbances.
Complex physical habitat structure creates spatially and
temporally diverse coldwater habitats that salmonids
have evolved to exploit
Salmonid survival requires a variety of cold water
temperatures that are well-distributed over space and
time.
Salmonid populations have declined precipitously and
their distributions have been reduced throughout the
region
Thermal regimes have been altered substantially over
time; where altered, streams are generally warmer in
the summer and more spatially homogeneous
The types of activities affecting stream temperature
Salmonid populations require a safety buffer in the face
of a variable environment
13
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
thermal regimes (see Distribution and Behavioral
technical summaries), the population responses to
changes in thermal regime cannot be precisely
specified because a multitude of factors influences
salmonid population dynamics. Further, we are
uncertain about the precise number and distribution
of specific coldwater habitat features (e.g., thermal
refugia) needed to restore thermal regimes and
support viable populations.
Yet, in spite of these shortcomings, our scientific
knowledge is extensive and can provide substantial
guidance to the development of temperature criteria.
We know salmonids need cold water. We know that
much larger salmonid populations occupied a much
greater network of northwest streams and rivers only
150 years ago. We know that salmonids evolved to
exploit and rely upon the natural thermal regimes of
Northwest rivers. We have extensive research
showing how the physical structure of streams and
rivers influences thermal regimes. We know that
many human activities have altered (e.g., typically
warmed) natural thermal regimes. Some major
sources of uncertainty and certainty are contrasted in
TableS.
While uncertainty constrains our ability to
precisely qualify and quantify the risks associated
with different management actions, scientific
knowledge has defined many causal relations that
exist between the thermal environment, biotic
community, and human activities. This certainty
affords confidence in the desired outcome of
management actions (Tickner et al. 2000). Given
uncertainty, we are challenged to make decisions
based on what we know, while taking adequate
precautions to avoid irretrievable or irreversible
mistakes. Thus, in moving forward scientists have
recommended a cautious and conservative approach,
especially when actions may affect threatened or
endangered species. For instance, when managing
natural resources in the face of uncertainty, Ludwig
et al. (1993) offered some guiding principles:
consider a range of alternatives and favor actions
that accommodate uncertainties; favor actions that
are informative; probe and experiment; monitor
results; update assessments and modify policies
accordingly; and favor actions that are reversible.
Others have recommended that sources of certainty,
uncertainty, and related assumptions that underlie
temperature criteria development be clearly and
completely documented (see Tickner et al. 2000, for
examples).
Participants in this project are charged with
developing new temperature criteria guidance that
will provide sufficient cold water to restore and
sustain viable salmonid populations, yet there is no
way to determine with certainty exactly how cold
streams must be, how much coldwater habitat is
needed, and what spatial and temporal
configurations will be requisite. However, from the
certainties listed in Table 3, we can infer several
tenets from which criteria robust to uncertainty can
be designed.
1) Human actions have caused thermal degradation
of aquatic habitats. Although it is only one of
many factors, it is an important factor that has
contributed to declines in salmonid populations.
2) Existing amounts and/or spatial and temporal
distributions of essential habitat, including
thermal dynamics thereof, may not be sufficient
to support viable salmonid populations.
3) Restoration and protection of thermal regimes
will need to address the amount and distribution
of thermally suitable water and its spatial and
temporal association with other characteristics of
salmonid habitat.
While restoration of stream temperature will not
be the only action necessary to restore salmonid
populations, we conclude that widespread
restoration of temperature regimes will favor
recovery of salmonids. We further conclude that
restoration will require modification of human
actions shown to cause thermal degradation and that
temperature criteria will need to define "coldwater
habitat" and provide guidance for determining the
amount and distribution thereof. Thus, to meet the
goals of this project (Appendix A), we conclude that
the available science suggests that salmonid
14
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
recovery will require more cold water than is
currently available, and that the cold water must be
well distributed and connected.
As the results of efforts and progress to provide
cold, well-connected, and well-distributed aquatic
habitat are compiled, and as salmonid populations
change in response to those efforts, criteria may be
revisited and refined. Yet, in light of scientific
uncertainties, the threatened and endangered status
of salmonids in the Pacific Northwest and the extent
of human alterations to their habitat, and conclusions
of other scientists (e.g., Ludwig et al. 1993, Tickner
et al. 2000) we believe it is important to avoid
initially underestimating the thermal requirements of
salmonids.
Implications for Water Temperature
Standards
In concept, a conventional approach to
developing water quality standards (such as often
A) Toxic Pollutants
High
Low
Pollutant Concentration
B) Maximum Summertime Water Temperature
High
•s
:: I
Low
32 38 42 48 54 60 66 72 78
Summertime Maximum Temperature (F)
n
84
Figure 5. Illustrations of hypothetical relationships between expected frequency of in-stream conditions
(in the absence of human-caused degradation) and associated biological risk. In these illustrations,
"biological risk" is determined as the risk of negative impacts on individual fish. Top: For some water
quality constituents (such as some toxics), conditions with high biological risk are rare in the absence of
human-caused degradation. Thus, a single threshold-based water quality standard can be set such that
pristine streams are unlikely to violate the standard and biological risk is avoided (for instance, line "z").
Bottom: For stream temperature, no such single threshold exists. If a standard is set to avoid substantive
risk (for instance, line "x"), temperatures in some streams will not comply with the standard even when
human-caused temperature changes have not occurred. If a threshold is set so that virtually all "non-
degraded" streams will comply with the standard (for instance, line "y"), fish may be exposed to
substantial risk. NOTE: These graphs are for illustrative purposes only. No temperature data were used
to construct temperature frequency curves, nor were laboratory data used to develop risk curves.
15
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
used for toxic pollutants) attempts to identify a
threshold value that is low enough to minimize risks
to aquatic biota. For many parameters, the threshold
level is above the range of naturally-occurring
conditions in streams. Where this occurs (Figure 5,
top), a conventional threshold standard is effective,
scientifically defensible, and relatively easy to
determine. For water temperature, however, there
are several reasons why a single threshold approach
to determining water quality criteria can be
problematic.
Stream temperatures associated with increased
biological risk might occur relatively frequently in
some stream reaches under natural conditions
(Figure 5, bottom). Natural stream conditions would
violate temperature thresholds that were predicated
on eliminating biological risk to individual fish.
Natural stream temperatures vary across space and
time, particularly in large, dynamic landscapes such
as the Pacific Northwest. Applying a conventional
standard may result in two undesirable consequences
illustrated by Figure 6. First, human-caused
warming of the best thermal habitat may be allowed
where local stream temperatures are naturally below
the water quality criterion. Second, streams
naturally warmer than the criterion will be identified
as candidates for remediation. Salmonids require a
variety of cold water temperatures, but a single
threshold standard does not recognize the diversity
of water temperatures needed by various species and
over space and time.
Temperature standards are developed primarily to
protect aquatic biota as the beneficial use most
sensitive to water temperature. Yet, water
temperature is the expression of a set of heat transfer
processes that are in turn influenced by the
physiographic, climatic, and hydrologic variables
acting on a particular stream segment. Some of
these variables can be altered by human activity and
some cannot. Therefore, in setting water
temperature standards to protect aquatic biota both
the biological and physical processes must be
considered. A good standard will protect high-
quality habitat and guide restoration of degraded
habitat, while recognizing that some naturally warm
reaches are also part of the aquatic landscape. It will
limit the extent to which the standard may be under-
protective in some locations and overly stringent in
others.
Warmer
I
0)
9J
H
Colder
'Naturally" warm waters violate the
standard
Thermal degradation would not be prevented
Natural Stream Temperature Profile
Headwaters
Mouth
Figure 6. Two difficulties of implementing a single threshold as a temperature standard. First, a single
numeric standard may fail to prevent degradation of the highest quality (coldest) habitat. Second, natural
temperatures may violate the standard thus requiring an attempt to determine whether the violation is
natural or the result of human-caused temperature changes.
16
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
The next task of the Technical Workgroup is to
develop conceptual models or frameworks for a
temperature standard. In order to avoid the
limitations and achieve the objectives described
above, the workgroup is analyzing the characteristics
of conventionally derived standards and thinking
about alternate ways to structure a standard.
Described below are possible alternative factors to
new standards that the workgroup will consider and
evaluate.
Standard development. By convention, water
quality standards are designed to remove
unacceptable stresses on individual fish.
Alternatively, a standard could attempt to describe
conditions that would be necessary to maintain
viable populations.
Comparison used. The type of comparison used
to determine compliance may range from single
temperature thresholds to multiple thresholds or
even thermal regimes. Single thresholds are
individual numbers that are compared to measures
of water temperature. Multiple thresholds are
groups of thresholds that can be compared across
space and/or time to measures of water
temperatures. Regimes are compared using metrics
that describe the spatial or temporal distribution of
temperatures such as mean, range, variance, and
timing.
Scientific foundation of numeric values. Numeric
values for standards can be determined based on
salmonid biology (e.g., lethal or optimal
temperatures for salmonids), temperature dynamics
of streams (e.g., patterns of heating and cooling), or
a combination of both.
Spatial scale of a management unit. For water
quality standards, a management unit is the type of
geographic unit that is deemed either in or out of
compliance with the standard. By convention,
individual water bodies, stream reaches, or point
locations are used as management units.
Alternatively, a management unit could be defined
as a basin or sub-basin. As long as enough well-
distributed and connected cold water is present,
these larger geographic units could be in compliance
in spite of naturally warm water at some sites.
Number of measurements. Compliance can be
determined based on different measurement
conventions: individual samples, multiple samples,
or a census of stream temperatures. Each of these
conventions is applicable over both space and time.
For instance, a temperature census over time is
accomplished using a continuous recording data
logger. A census over space might be accomplished
using a remote sensing technique to map the
distribution of water temperatures along the entire
river.
Each of the approaches will have a unique set of
opportunities and challenges. The flexibility
associated with these different approaches may
result in criteria that protect the thermal
requirements of salmonids while accommodating
naturally warm waters. Yet this flexibility could
incrementally weaken protection and increase
extinction risks. Thus, these alternatives must be
considered with caution. The task before the
Technical Workgroup is to identify criteria with
characteristics that will best ensure the thermal
conditions necessary to support viable salmonid
population while reducing the instances where
naturally warm water is deemed out of compliance.
17
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Scientific Issues Related to Temperature Criteria for Salmon,
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Columbia River basin. Ecological Applications 10(5): 1478-
1496.
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Protection Agency. 594 pp.
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Washington, DC. 452 pp.
Oregon Coastal Salmon Restoration Initiative. 1997. State of
Oregon, Salem.
Poole, G. C., and C. H. Berman. 2001. An ecological
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and mechanisms of human-caused thermal degradation.
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Quigley, T.M. and S.J. Arbelbide (Tech. Eds). 1997. An
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Portland, OR.
Reeves, G.H., L.E. Benda, K.M. Burnett, P.A. Bisson, and J.R.
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
Appendix A: Technical Interpretation of the Project Goals
The following project goals were identified by the Policy Workgroup to guide the Technical
Workgroup in development of temperature criteria.
Project Goal Statements (from the Policy Workgroup)
To Develop EPA Regional Temperature Criteria Guidance that:
• Meets the biological requirements of native salmonid species for survival and recovery pursuant
to ESA, provides for the restoration and maintenance of surface water temperature to support and
protect native salmonids pursuant to the CWA, and meets the salmon rebuilding needs of federal
trust responsibilities with treaty tribes
• Recognizes the natural temperature potential and limitations of water bodies
• Can be effectively incorporated by states and tribes in water quality standards programs
The new criteria guidance will be jointly developed by EPA, USFWS, NMFS, States, and Tribes in
the Pacific Northwest:
• States and tribes will use the new criteria guidance to revise their temperature standards, if
necessary
• EPA and the Services will use the new criteria guidance to evaluate state and tribal standard
revisions
Recovery Target (from the Policy Workgroup)
The temperature criteria guidance that would support "sustainable and harvestable levels of
salmonids."
To facilitate communication and understanding between the Policy and Technical Workgroup, the
Technical Workgroup developed the following interpretation of the project goals based on the
literature reviewed in the five technical summaries described in the Preface to this document.
To meet the project goal, the Technical Workgroup believes it is necessary to develop EPA regional
temperature criteria guidance that:
• if attained, would provide thermal habitat capable of supporting viable populations1 (including
a surplus for human harvest) of all native salmonids
• protects high quality thermal habitat while minimizing circumstances where compliance would
require remediation beyond a system's thermal potential can be implemented and enforced
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Scientific Issues Related to Temperature Criteria for Salmon,
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Thus, temperature criteria should describe thermal regimes that promote the following characteristics
of salmonid populations:
Population size is large enough to:
• Maintain genetic and phenotypic diversity2 over the long term
• Survive environmental variation3 and catastrophic disturbance
• Provide ecological functions;4
• Allow a population surplus that can be harvested by humans
Population growth rate is positive.5
Population distributions:
• Are extensive within and across sub-basins;6
• Allow full utilization of habitat potential7 (temporally and spatially) of sub-basins, which
allows natural expression of multiple life history strategies8.
• Are comprised of well-connected9 sub-populations.
Additionally Temperature criteria should describe thermal regimes that promote the following
features of salmonid habitats
• Natural thermal regimes are established across the maximum extent of the landscape.
• Habitats are well-connected.
• Habitat supports all life history stages and strategies.
1 The Technical Workgroup defines a "viable population" as a population where the population growth rate, size,
and distribution are as described later in this appendix. See also McElhany et al. (2000) for a more comprehensive
discussion of viable salmon populations.
2 Small population sizes can result in loss of genetic information from the population gene pool such as run timing,
age structure, size, fecundity, morphology behavior, and molecular genetic characteristics.
3 "Environmental variation" includes the natural annual variations that can be summarized statistically. This also
includes foreseeable cyclic patterns of climatic change.
4 Salmon are a keystone species in ecosystems of the PNW. For example, nutrients from carcasses are vital in
providing nutrients to riparian vegetation and for the feeding and growth of freshwater biological communities including
juvenile salmonids.
5 Most salmon populations that are currently listed under the ESA have population growth rates (e.g., spawner-
spawner ratios) that are extremely depressed and static or are low and declining. Populations can recover only if these
population growth rates have ratios of >1.0. A population is only fishable and sustainable if there are more adults
returning to the spawning grounds to spawn than are needed to replace the numbers of the parent generation. Also, an
excess is needed to compensate for natural fluctuations in environmental conditions throughout the geographic range of
the salmon life cycle (including ocean conditions) that lead to periodic fluctuations in survival.
This allows source sub-populations to be maintained so that they contribute to the stability of the overall population by
providing centers of high productivity and contributing a source of strays to colonize other habitats within the sub-basin.
Habitat potential is an inherent characteristic of a watershed that has a high level of ecosystem integrity. Elements of the
watershed that define its potential include its potential natural vegetation, climate, lithology, geomorphology, biota, hydrology, and
soils. These elements interactively set up instream habitat conditions (channel geomorphology, hydrologic regime, water temperature
regime, riparian vegetation community types and dynamics, channel substrate characteristics). Given various levels of anthropogenic
disturbance to the watershed, alterations to the watershed and/or stream channels and riparian areas can shift the processes that
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Scientific Issues Related to Temperature Criteria for Salmon,
Trout, and Char Native to the Pacific Northwest
produce in-stream habitats so that they disfavor salmonids. This can come about through alterations in the regimes for large wood
input, water temperature, water routing, nutrient input, and sediment. Water temperature regime can be altered by the combined
effects of shifts in the woody debris input, riparian vegetation condition (current state of the vegetation, given all possible states that
are defined by its potential), sediment delivery to the channel (affecting intergravel flow, channel morphology, and pool depth and
frequency).
A life history strategy is one of the means by which a life cycle can be structured so that life functions are realized. Functions
include growth, survival, development, mating, reproduction, incubation, emergence, rearing. When a watershed exhibits a state of
high integrity, the ability of the watershed to develop high quality aquatic habitats is great and multiple life history strategies become
available for salmonids to complete these functions. Watershed and habitat degradation tend to eliminate many life history strategies
(e.g., those strategies that depend upon mainstem rivers, low elevation habitats, floodplain or off-channel habitats).
When sub-populations are well connected, they are capable of interbreeding. This allows better maintenance of genetic integrity
in the gene pool because the genes are maintained by a larger, more integrated population. Small, isolated populations with few or
poorly connected sub-populations tend to be unstable over time and gradually disappear. They are not resistant to extreme
environmental conditions because the entire population can be affected by a single event or disturbance. Populations comprised of
well-distributed and connected sub-populations have greater resistance to perturbation because there is lesser likelihood that major
portions of the population will be affected by a single event. Likewise, if some life history strategies involve spawning at a different
time or in a different location, greater population stability results from this "hedging" against extinction.
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