Authors
Dale A. McCullough, Ph.D.
Report Citation
McCullough, D.A. 1999. A Review and Synthesis of Effects of Alterations to the Water
Temperature Regime on Freshwater Life Stages of Salmonids, with Special Reference
to Chinook Salmon. Seattle, Wash, U.S. Environmental Protection Agency, Region 10.
Publication Date
22 February 1999
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A Review and Synthesis of Effects of Alterations to the Water Temperature Regime
on Freshwater Life Stages of Salmonids, with Special Reference to Chinook Salmon
Abstract
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Despite the great significance of the Columbia River Thermal Effects Study (a joint
publication of the USEPA, NMFS, and AEC) and a compilation of temperature criteria
and methods by the National Academy of Sciences in the 1970s that has been key EPA
guidance on water temperature, too little attention has been placed on the key role
of thermal pollution of river systems in reducing fish survival and production.
The current review and synthesis of effects of water temperature on salmonids is
an attempt to update important aspects of these earlier works in light of current
ecological understanding. This revision is in terms of numeric criteria by species
and life stage but, more importantly, is an explanation of the concepts that must
be considered to fully protect salmonids from thermal effects under the Endangered
Species Act. Regulation of water temperature in salmon-bearing streams of the Pacific
Northwest involves selection of appropriate biologically-based temperature standards
and then creation of implementation procedures that insure that the biological intent
is effected on necessary spatial and temporal scales. Selection of standards involves
a thorough review of the effects of temperature on key life stages of species, variation
in response among species and stocks, and an ability to estimate immediate and delayed
biological responses from temperature statistics. Implementation involves consideration
of problems such as where, when, and how to monitor water temperature in a watershed
and developing a process for responding to violations of standards. This report
deals primarily with a review of biological aspects of temperature in the environment,
but the best understanding of the influence of temperature will not be effective
unless implementation procedures are also meaningful. The tight interconnection
between these two elements necessitated a broader review that incorporated a wide
variety of spatial and temporal issues in fish ecology. In this context, full protection
was viewed in terms of entire life cycle effects, single and multiple species, variation
among stocks of a species, multiple environmental gradients, watershed to reach
scales, and multiple biological responses (survival, growth, preference, fitness,
reproduction, migration, swimming, feeding, etc.). In consideration of the entire
life cycle of spring chinook, it would be most preferable for adults to enter the
Columbia River with water temperatures of 3.3-13.3°C. Temperatures of 21.0°C
must be avoided because they represent thermal blockages and also are near adult
upper incipient lethal temperatures. Temperatures >15.5°C greatly enhance incidence
of disease and mortality rate. Adults must be able to proceed rapidly upstream to
holding areas without encountering migration blockages, excessive delays, and without
excessive metabolic expenditures negotiating falls or ladders. Holding areas must
have adequate cover and low temperatures to reduce metabolic losses and pre-spawning
mortality. Holding temperatures <16.0°C (maximum) at the time of egg maturation
in holding females are essential for maximum egg viability and initiation of spawning
activities. Temperatures <12.8°C and declining provide best spawning conditions
and highest survival upon egg deposition. High egg mortality can be expected if
temperatures are <1.7°C at egg deposition, although this is uncommon. Proper
incubation temperature requires accumulation of necessary thermal units so that
development rate results in best emergence timing. Prolonged autumn high temperatures
or early spring warming can result in early emergence if they prematurely fulfill
thermal unit cumulation. Temperature at emergence must be limited to 14.0°C
(max.) for initiation of feeding. Optimum juvenile growth occurs between 10 and
15.6°C. Growth rate declines to zero at approximately 21°C, but considering
mortality rate when juveniles are fed at higher temperatures, zero net growth of
the population occurs at a lower temperature (19.1°C). The upper incipient lethal
level for juveniles is 25.1°C. In the field the distributional limit is approximately
22-24°C. Smoltification and outmigration proceed best at temperatures <12.2°C. It
is vital for smolts to begin their downstream migration early enough to avoid higher
temperatures that discourage migration. In the mainstem, temperatures >18.3°C
can result in desmoltification and residualism. Temperature regulation and monitoring
must be done at a watershed scale in order to fully protect the species found along
the river continuum. Survey data are very useful in establishing the downstream
limits of distribution. Most salmonids are restricted to stream zones having maximum
temperatures <22-24°C. Bull trout and redband trout represent the lower and upper
extremes in thermal tolerance. The general uniformity in thermal response among
stocks of a species tends to obviate the need for geographically different biological
standards to protect endangered species. Densities of various salmonid species have
been shown to decline from a maximum under near optimum conditions to zero at the
downstream distribution limit. Distribution is a function of temperature, but species
are also distributed along multiple environmental gradients. Optimum habitat for
a species involves temperature regime, but also is strongly influenced by channel
gradient, substrate composition, pool frequency, large woody debris and other cover
elements, oxygen concentration, and competitors or predators. In the context of
management of an entire stream system, constituting the fish production unit of
an endangered population, the most difficult challenge in application of any single
quantitative standard to a stream is to not have the standard applied immediately
to headwater areas. The effect of such management is to elevate temperature in the
headwaters where temperature may then become 'optimal' but numerous other environmental
factors may not be optimal, thereby losing the productive capacity of habitats in
the normal center of distribution further downstream. Survival and fitness of a
fish population should be evaluated on multiple time scales. A conventional scale
is a weekly temperature regime during periods of extreme temperatures. It is assumed
that regulating the maxima will result in appropriate regimes in other seasons.
A bioenergetic analysis involves evaluation of the effect of temperature regime
during the entire life cycle (or freshwater phase) on the energy balance (i.e.,
energy storage, diversion to growth and reproduction versus energy costs attributed
to thermal stress). Within shorter time frames the capacity to cope with environmental
stress is a function of power budgeting. An organism with a high thermal load has
a reduced scope for activity when confronted with instantaneous power demands (e.g.,
peak swimming, predator avoidance). Under a reduced scope, the organism is at higher
risk of exhaustion, predation, or disease.
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