Independent Scientific Advisory Board

for the Northwest Power and Conservation Council,

Columbia River Basin Indian Tribes, 

and NOAA Fisheries

 851 SW 6th Avenue, Suite 1100

Portland, Oregon 97204

ISAB@nwcouncil.org

Viability of ESUs Containing 

Multiple Types of Populations 

Robert E. Bilby 

Peter A. Bisson 

Charles C. Coutant 

Daniel Goodman 

Susan Hanna 

Nancy Huntly 

Eric J. Loudenslager 

Lyman McDonald 

David P. Philipp 

Brian Riddell 

Ad Hoc Members 

Jeffrey Olsen 

Richard Williams

April 8, 2005 

ISAB 2005-2
i 

Viability of ESUs Containing Multiple Types of Populations 

Contents 

Executive Summary ........................................................................................ii 

Introduction..................................................................................................... 1 

Background ..................................................................................................... 1 

Definitions....................................................................................................... 3 

Answers to Questions...................................................................................... 8 

Part I. Hatchery Questions........................................................................... 8 

Part II. Anadromous/Resident Questions .................................................. 23 

References..................................................................................................... 33 
ISAB 2005-2 ESU Viability: Executive Summary 

ii 

Viability of ESUs Containing Multiple Types of Populations 

Executive Summary 

The ISAB has been asked by NOAA Fisheries to answer a series of questions about the viability 

of ESUs that contain a mixture of hatchery and wild fish and/or resident and anadromous fish. 

We felt that in order to respond to these questions, the ESU concept required some expansion to 

include considerations of the elements required for viability. We have termed this expanded 

definition a “Viable ESU”. To be viable an ESU needs more than simple persistence over time; 

it needs to be in an ecologically and evolutionarily functional state. Evaluation of ESU viability 

should not only rest on the numbers of component populations or on the abundance and 

productivity of those individual populations, but also should be based on the integration of 

population dynamics within the ecosystem as a whole. This concept of ESU viability does not 

accommodate the loss of populations or the anadromous or resident life history form from any 

given ESU, because that loss would represent a loss in diversity for the ESU that would put its 

long-term viability at risk. This argument is based on evidence that an ESU needs to contain 

viable populations inhabiting a variety of different habitats, interconnected as a metapopulation, 

if that ESU is to fulfill the entire complement of ecological and evolutionary interactions and 

functions. 

We consider a Viable ESU to consist of a group of populations existing together as a 

metapopulation that as an entity is self-sustaining for the foreseeable future. Each population of 

a viable ESU needs to exhibit the abundance, productivity, diversity, and spatial distribution of 

natural spawners sufficient to accomplish the following: avoid the loss of genetic and/or life 

history diversity during short-term losses in abundance that are expected parts of environmental 

cycles; fulfill key ecological functions that are attributable to the species, such as nutrient cycling 

and food web roles; and provide for long-term evolutionary adaptability to changing 

environmental conditions. However, given the high uncertainty in prediction of future 

environmental conditions, as well as the uncertainty in interpretation of how genetic or other 

diversity metrics will be expressed in future environments, prudent management would hedge 

bets by avoiding loss of currently small, peripheral, or in any way seemingly less valuable ESU 

components. 

Establishing the policy boundaries for ESU viability assessment is likely to be as important to 

the eventual outcome as the method used in the assessment. The natural populations associated 

with integrated hatchery programs are generally not themselves viable and the habitats upon 

which they depend are usually inadequate. If the policy decision is made that self-sustaining 

natural populations are not required for an ESU to be viable, it is likely that the number of extant 

natural populations will continue to decrease and the impetus behind current efforts to improve 

habitat conditions will be greatly reduced. We believe that the current science indicates that 

ESUs dependent upon hatchery production cannot be viable ESUs according to the definition of 

this term we are using in this report. Therefore, a policy that recognizes such ESUs as viable 

would need to use a definition of viability much different from the one we are using. The 

biological validity of such a definition would be questionable. 
ISAB 2005-2 ESU Viability: Executive Summary 

iii 

Summary of ISAB Responses to NOAA Questions 

Part I: Hatchery Questions

Question #1A Are there scientifically sound methods for evaluating the contribution of “in 

ESU” hatchery stocks to the viability of an ESU? 

At least three different modeling approaches are being used to assess viability of biological 

entities (i.e., populations, ESUs, DPSs, species), population viability analyses (Beissinger and 

McCullough 2002), quantitative rule-based systems (Mace and Stuart 1994, Musick 1999), and 

expert opinion systems (Maquire and Cochrane 2001, Marcot et al. 2001). The population 

viability analysis entails building a detailed and specific model of the population and its future 

environment and is the most scientifically rigorous approach. The validity of rule-based systems 

and expert opinion depends on how closely the rules or opinion are based on accepted scientific 

theory and empirical facts (e.g., Brown et al. 2004). Regardless of which method is employed, 

the objectives of the assessment, the questions being addressed, and the policy parameters 

associated with the objectives need to be stated clearly. Policy parameters that need to be 

clarified include the time horizons for viability and the likelihood (probability) of viability. 

Question #1B If such methods exist, are they reliable for predicting viability over long-term 

(centuries or longer), medium-term (decades), and/or short-term (a decade or less) timeframes? 

While methods exist to assess viability, their reliability for application to salmonids is not well 

understood at present. In general, the accuracy of point predictions is expected to decrease as the 

time horizon increases. And in general, it is expected that the uncertainty about medium to long 

term point predictions will be large. For this reason, viability assessments should quantify the 

uncertainty as well as a point prediction. In this sense, the “reliability” of a viability assessment 

method is better gauged by the credibility of its quantification of uncertainty than by whether the 

point predictions (e.g., “best estimate”) are uncertain. It is clear that the reliability of viability 

assessment methods for salmonids could be improved significantly by continued directed 

research and monitoring. 

Question #1C Are the currently available data for any of the Columbia River salmon ESUs 

sufficient to enable the application of these methods? 

Some supplementation programs reviewed by the ISAB (2003) are collecting appropriate data 

for assessment of viability. The Hood River and Yakima supplementation projects have detailed 

monitoring plans in place and two additional projects, the Northeast Oregon Hatchery (NEOH) 

and the Johnson Creek Artificial Propagation Enhancement Project, have been proposed. The 

only ongoing study of which we are aware that could provide some information on the 

performance of naturally spawning populations after the termination of supplementation is the 

Idaho Supplementation Study (ISS). However, lack of completeness of the data being collected 

in the ISS could compromise the application of the results of the study to this question. More 

subjective assessment methods also have been used. The SHIEER (Salmonid Hatchery Inventory 

and Effects Evaluation Report) assessment of integrated programs by NOAA Fisheries (NOAA 

2004b) is a case-by-case professional judgment review of the effects of hatchery programs on the 
ISAB 2005-2 ESU Viability: Executive Summary 

iv 

viability of the natural populations. Professional judgment was used in this effort because data 

that were needed for a more rigorous assessment were often not available. Even where some of 

these data were available, the relationship between the reported facts and the conclusions about 

the effect on viability was not particularly transparent. 

Question #2A In an integrated hatchery-natural system that is operated according to currently 

accepted best conservation practices (e.g., as described by the Hatchery Scientific Review 

Group), what does the available scientific information indicate about the probability that the 

natural component of the population would lose the ability to sustain itself without further 

augmentation? 

 

Goodman (2004 and 2005) summarized the demographic and fitness consequences of an 

integrated natural/hatchery salmon population, and extended this modeling effort by 

incorporating harvest. Goodman (2004) also drew the following additional conclusions 

regarding the performance of an integrated system relative to an unsupplemented population, 

and the ISAB concurs with them: 

1. Integration will almost certainly increase the potential for harvest that is sustainable as 

long as the integration continues, but this increase will cease immediately upon 

termination of supplementation and may be replaced by a decline. 

2. Integration will probably increase the number of fish participating in natural spawning for 

as long as integration continues, but this increase will cease immediately upon 

termination of integration and may be replaced by a decline. 

3. Integration certainly will not increase the natural spawning fitness of the supplemented 

stock. 

4. Integration may depress the natural spawning fitness of the stock, and this depression in 

replacement rate will be manifest for as long as integration continues and will continue to 

express itself for some number of generations after integration is terminated. 

5. The probability and magnitude of the depression in natural spawning fitness of the 

integrated population will increase with the magnitude of the sustainable harvest that is 

extracted. 

6. The probability and magnitude of the depression in natural spawning fitness of the 

integrated population will increase with the magnitude of the broodstock mining rate. 

7. There is a possibility of runaway domestication selection in an integrated breeding 

program that departs from strict supplementation by drawing some of its broodstock from 

returning hatchery progeny. 

8. The feasibility of adhering to a strict protocol of drawing broodstock only from natural 

origin fish will depend on the natural spawning and hatchery spawning productivities of 

the stock, and on limitations of harvest below levels that would otherwise be sustainable. 

9. The feasibility of compliance with a cap on the broodstock mining rate and a floor on the 

fraction of natural origin fish among those spawning naturally will depend on the natural 

spawning and hatchery spawning productivities of the stock, and on limitation of harvest 

below levels that would otherwise be sustainable. 
ISAB 2005-2 ESU Viability: Executive Summary 

v 

Question #2B What does the available science indicate about how rapidly this might occur? 

Available evidence suggests that fitness declines rapidly with hatchery culture; substantial 

declines occur after only a few hatchery generations. The current status of integrated 

hatchery/wild populations also has some bearing on this question. Washington State hatcheries 

are undergoing a review by the Hatchery Scientific Review Group (HSRG) and Columbia Basin 

hatcheries are under going a review by the Northwest Power and Conservation Council’s 

Artificial Production Review Evaluation (APRE). The programs range from 2 to 115 years old. 

Only 2 of 97 natural populations appear to be self-sustaining at this time. In most cases, poor 

habitat conditions are limiting the recovery of the natural population. Nonetheless, there is little 

evidence of self-sustaining natural populations in integrated hatchery/natural systems. 

Question #2C If a naturally spawning population becomes unsustainable without hatchery 

augmentation, what does the current scientific information say about the likelihood that the 

population would be able to re-establish self-sustainability, and if so, under what conditions and 

over what time frame? 

Lynch and O’Healy (2001) and Goodman (2004 and 2005) conclude that a natural population 

has the potential to readapt to the natural environment once the integration with a hatchery 

program is terminated. The principal caveat is that if the deleterious effects of integration 

produce a population that is unable to replace itself, the rate of readaptation must be rapid 

enough to offset the poor productivity before the population is extirpated. Empirical evidence 

related to this question can be drawn from efforts to reintroduce coho, spring- and fall-run 

Chinook, and chum salmon in the Columbia Basin. Results from these programs to date suggest 

that reestablishing self-sustaining populations is likely to be the exception, rather than the rule 

unless ecological/habitat/overharvest problems are solved, and augmentation programs have 

been implemented in a manner that minimizes genetic/adaptive impacts on the natural 

population. 

PART II: Anadromous/Resident Questions 

Question #1 What is known about how resident fish contribute to the long-term viability of 

ESUs that contain both anadromous and resident fish? 

 

Although the genetic similarity of sympatric resident and anadromous life histories of rainbow 

trout does suggest that interbreeding occurs at some level, evidence is not universally conclusive 

that resident populations play a key role in supporting the productivity or abundance of any 

steelhead population (or the reverse). The resident life histories may positively influence 

viability of an ESU that contains sympatric resident and anadromous forms by contributing to the 

overall abundance and diversity (because residency is an important life history strategy in many 

circumstances). The role of the resident life history in maintaining population connectivity and 

spatial structure is unclear, but it undoubtedly differs in timing and extent from the anadromous 

life history. As a result, the presence of both resident and anadromous life-history forms is 

critical for conserving the diversity of steelhead/rainbow trout populations and, therefore, the 

overall viability of ESUs. 
ISAB 2005-2 ESU Viability: Executive Summary 

vi 

Question #2A Does the loss of anadromy from a population have a sufficient effect on ESU 

diversity to reduce the likelihood of long-term persistence of the ESU? 

 

Loss of anadromy will undoubtedly change the structure and connectedness of metapopulations 

within the ESU. The two life history forms (anadromous and resident) likely play different roles 

in the maintenance of population structure and the loss of one form may change the population 

structure by altering patterns of gene flow. When either anadromy or residency is lost, 

populations will likely become more isolated and vulnerable to loss of genetic diversity. 

Ultimately, this loss of diversity will reduce the probability of long-term persistence. 

Question #2B What is the evidence that once the anadromous life history form is lost from an 

ESU, a self-sustaining anadromous population can be re-established (either naturally or as part 

of reintroduction effort) from the resident component of the ESU at some time in the future? 

 

Based on the available information, it seems unlikely that a population of resident trout can 

consistently reestablish a steelhead population. There is evidence that the capacity to express 

anadromy is retained in a population of resident trout for many generations after extirpation of 

the anadromous life history form (Thrower et al. 2005). However, it is uncertain whether the 

smolting and survival rates exhibited by smolts from resident fish would be sufficient to enable 

reestablishment of a viable steelhead life history type. One of the few cases of a resident 

population giving rise to an anadromous component is an example from Argentina (Pascual et al. 

2001). In this case, however, the anadromous population that arose from the introduced resident 

fish did not reestablish an extirpated population but expanded into an unoccupied niche. We 

conclude that once anadromy is lost from an ESU, resident populations are not likely to 

regenerate self-sustaining anadromous populations in the short or intermediate term, and that the 

ESU viability would be largely compromised. 

Question #3 What does current scientific information tell us about the abundance, productivity 

and diversity of salmon or steelhead ESUs that have lost one or more life-history trajectories? 

The available evidence indicates that the loss of one or more life-history types from an ESU can 

impact abundance and productivity. The effect on ESU diversity and spatial distribution is less 

speculative; loss of a life-history type from an ESU clearly impacts these attributes. The ISAB 

concludes that the maintenance (or restoration, where possible) of all of the naturally occurring 

life history types of an ESU should be one of the goals of salmon recovery. 
ISAB 2005-2 ESU Viability 

1 

Viability of ESUs Containing Multiple Types of Populations

Introduction 

At the request of NOAA Fisheries, the ISAB is responding to a series of questions that have 

arisen in response to recent court cases (e.g., Alsea Valley Alliance v. Evans U.S. District Court 

Ruling September 12, 2001 -- Alsea Decision) and other developments that have emphasized the 

complexity of evaluating the viability of Evolutionarily Significant Units (ESUs). These 

questions specifically address the assessment of the viability of ESUs that contain both hatchery 

and natural populations or steelhead (Oncorhynchus mykiss) ESUs that contain both anadromous 

and resident life-history forms. 

Five questions were posed. To help the ISAB answer these questions, a series of presentations 

were made to the ISAB, and we attended a NOAA Fisheries sponsored workshop held in late 

March: ESU Symposium/Workshop: Considering Life History, Behavioral, and Ecological 

Complexity in Defining Conservation Units and Assessing Viability in Pacific Salmon.

The presentations made to the ISAB relevant to these questions included: 

• Implementation of the NOAA policy regarding inclusion of hatchery fish in ESUs – Rob 

Jones

• Contribution of resident O. mykiss to ESU viability – Jeff Hard 

• O. mykiss status review update – Robin Waples 

Background 

The Alsea Decision (Alsea Valley Alliance vs. Evans), which in some ways prompted the 

management questions that are the subject of this scientific review, was a legal ruling on a 

procedural issue, not on a scientific one. The Court ruled that because under the ESA an ESU is 

a legally defined population unit, decisions on whether or not to list an ESU as Endangered or 

Threatened must be made considering an ESU in its entirety. In contrast to this legal context, 

conservation biologists consider an ESU in a biological context. That is, an ESU is a 

demographically and genetically distinct component of a species that because of its past 

evolutionary history has differentiated from other such components in the process of becoming 

adapted to its local environment. As such, an ESU represents a component of the species that, if 

extirpated, is not fully replaceable. Although it is possible that its habitat may at some point in 

time be recolonized from other ESUs within the species, all or some of the original ESU’s life 

history characteristics may not become reconstituted. The ISAB has responded to the questions 

from NOAA using this scientific interpretation of ESUs; comparison to the legal interpretation 

may not be one to one. 
ISAB 2005-2 ESU Viability 

2 

Prior to the Alsea Decision, NOAA Fisheries focused nearly exclusively on naturally spawning 

populations, both for identifying ESUs and for evaluating their viability. Hatchery stocks were 

generally included in an ESU if they belonged to the same evolutionary lineage and had not 

diverged substantially from the natural-origin fish in the ESU. Hatchery-origin components of 

an ESU whose natural-origin components were listed under the ESA, were themselves listed 

only if they were considered essential for recovery (see FR 58:17573). In response to the Alsea 

Decision, NOAA Fisheries has proposed to continue to include hatchery stocks in ESUs in cases 

where they are genetically similar to natural populations in an ESU. In addition, when making 

listing decisions, NOAA Fisheries has proposed to consider the contribution that these hatchery 

stocks make to the viability of the ESU as a whole (Proposed Policy on the Consideration of 

Hatchery-Origin Fish in Endangered Species Act Listing Determinations for Pacific Salmon and 

Steelhead -- FR 69: 31354). 

Resident O. mykiss have been considered part of steelhead ESUs because most available data 

indicate that in areas accessible to anadromous fish, the resident fish are genetically similar to the 

anadromous fish. Although resident fish generally have not been listed under the ESA, listing 

the anadromous component of a steelhead ESU, but not the resident component, results in the 

legal problem identified in the Alsea Decision, i.e., listing only a part of an ESU. In recent status 

review updates the Biological Review Team (BRT) concluded that the anadromous life-history 

component of a steelhead ESU was such an important component of the ESU’s diversity that it 

was biologically reasonable to equate the extinction risk of the ESU with the extinction risk of 

only the anadromous part of the ESU. Legally, a component of an ESU may be designated as 

essential for recovery (i.e., necessary, but not sufficient). 

It is within this context that the ISAB has been asked to answer the five specific questions about 

the viability of ESUs that contain a mixture of hatchery and wild fish and/or resident and 

anadromous fish. Because both of these circumstances require determining ESU viability in a 

specific context, the ISAB begins with a list of our definitions for “hatchery fish”, “natural fish”, 

“resident fish”, and “anadromous fish”. The ISAB follows these definitions with an explanation 

of our scientific understanding of an ESU, and from that foundation defines a Viable ESU and 

develops a framework for assessing ESU viability. 

There are certain fundamental differences between a “Viable Salmonid Population” (VSP) as 

defined by NOAA in McElheny et al. (2000), and a viable ESU as we use the term here. To be 

viable an ESU needs more than simple persistence over time; it needs to be in an ecologically 

and evolutionarily functional state. Evaluation of ESU viability should not only rest on the 

numbers of component populations or on the abundance and productivity of those individual 

populations, but also should be based on the population dynamics within the ecosystem as a 

whole. For example, populations are needed throughout the landscape to promote the 

evolutionary diversity needed for adaptation to systematic environmental change (e.g., global 

warming). This concept of ESU viability does not accommodate the loss of either the 

anadromous or resident life history form from any given ESU, because that loss would represent 

a loss in diversity for the ESU that would put its long-term viability at risk. In addition, although 

this concept of ESU viability may not preclude the presence of hatchery-origin individuals 

within an ESU, it does preclude the dependence of ESU viability on hatchery-origin individuals 

and it precludes the replacement of the original wild population with a hatchery derived one. 
ISAB 2005-2 ESU Viability 

3 

This argument is based on evidence that an ESU needs to contain viable populations inhabiting a 

variety of different habitats interconnected as a metapopulation, if that ESU is to fulfill the entire 

complement of ecological and evolutionary interactions and functions. As a result, there needs 

to be sufficient connectivity among the spawning habitats of the component populations to allow 

the migration of individuals to recolonize vacant habitats in the event of local extirpation. 

Definitions 

Hatchery Fish. Individuals produced from eggs/fry that were incubated/reared in a fish 

hatchery before release to complete their life-cycle under natural conditions, regardless of the 

culture history of the parents. 

Natural Fish. Individuals produced from eggs that were fertilized by natural spawning and 

incubated instream in gravel and subsequently from fry reared in natural habitats before 

migration to the ocean, regardless of the culture history of the parents. 

Resident Fish. Individuals that remain in freshwater and do not inhabit marine waters for a 

portion of their life-cycle. The parents could have been either resident or anadromous. 

Anadromous Fish. Individuals produced from eggs that are incubated in freshwater and that 

subsequently undergo a downstream migration and enter marine waters, before returning as 

adults from a marine migration to reproduce in freshwater. The parents could have been either 

resident or anadromous. 

Evolutionarily Significant Unit (ESU). We adopt the NOAA Fisheries definition (Waples 

1991, 1995) for an ESU: An ESU consists of a group of populations that meets two distinct 

criteria: 

1. an ESU must be substantially reproductively isolated from other conspecific units, and 

2. it must represent an important component of the evolutionary legacy of that species. 

Expanding beyond these two criteria, the ISAB expects the various component populations 

within each ESU to be differentiated from one another as a result of adaptation to their local 

environments, yet linked through occasional gene flow in what is now termed a metapopulation 

(see Hallerman 2003). A key feature of the metapopulation concept is that natural recolonization 

from other populations of the same ESA can replace or replenish local populations within the 

ESU that are extirpated, significantly increasing the likelihood of long-term persistence of the 

ESU. It is likely that only some of these component populations could at any one time serve as 

source populations for such recolonization, but it is not possible to predict which component 

population that will be. Furthermore, the populations serving as sources for recolonization are 

expected to change over time in response to habitat alterations, harvest pressure, climate change, 

etc. Finally, it is the genetic and life history diversity within and among these component 

populations that provides the genetic material (heritable variation) that allows the ESU to adapt 

to the changing environmental conditions of the future (Noss 1990). 
ISAB 2005-2 ESU Viability 

4 

The essential dynamic characteristic of a metapopulation (ESU) is spatially and temporally 

varying highly abundant and productive source populations providing recruits to less abundant 

and productive habitats. In the absence of this property, if there are insufficient productive 

source populations for recruitment to less productive habitats, the less productive sites will 

become vacant and recolonization would be unlikely in a reasonable timeframe. The failure to 

maintain sufficient connectivity and source populations within an ESU could have long-range, 

negative consequences for the entire metapopulation. Because of the interrelationship among the 

populations within an ESU, the overall viability of the entire ESU is more than the simple sum of 

the viability of each of its component populations. We emphasize that maintaining the viability 

of ESUs will also require maintaining the availability of diverse environments that support the 

full suite of life histories that might be expressed by the component populations. To ensure that 

this critical linkage between ecological and evolutionary potentials and habitat protection is 

maintained, it is essential that both ESU and Critical Habitat Policies be consistent. 

Viable ESU (VESU). Using our expanded definition of an ESU, we consider a Viable ESU 

(VESU) to be a group of populations existing together as a metapopulation that as an entity is 

self-sustaining for the foreseeable future because it has the abundance, productivity, diversity, 

and spatial distribution of natural spawners sufficient to allow the ESU to: 

1. rebound from periods of low abundance that are expected, natural phases of population 

cycles; 

2. avoid the loss of genetic and/or life history diversity during these short-term periods of low 

abundance; 

3. provide colonists, in the form of straying adults, that are capable of establishing new 

populations in suitable but otherwise vacated habitats; 

4. fulfill key ecological and societal functions that are attributable to the species; these can 

include societal functions such as human harvest; 

5. provide for long-term evolutionary adaptability to changing environmental conditions. 

Rationale for the Viable ESU Definition

The Viable ESU definition above is intended to expand the concept of viability beyond a narrow 

focus on measures of near-term persistence (i.e., the probability of extinction in the near-term) to 

recognize the function that a salmon ESU serves in Pacific Northwest ecosystems. This concept 

of ESU viability requires both genetic competency of individuals and genetic variation within 

and between locations, as well as enough suitable habitats to realize the genetic potential of these 

individuals. Fundamental population principles state that the status of a population, ESU, or 

species is a function of the genetic constitution of the individuals, the abiotic environment in 

which those individuals live, and the interaction of those individuals with the rest of the 

biological community. 

Evaluation of ESU viability should rest not only on the numbers of component populations 

and/or their individual abundances, but also on the population dynamics within integrated 

metapopulations. There needs to be sufficient connectivity between spawning habitats for 

migrating individuals to recolonize vacant habitats in the event of extirpation caused by 

environmental catastrophes (e.g., the eruption of Mount St. Helens or more local disturbances 

such as fire, sever floods or drought, destructive land use and land development). Component 
ISAB 2005-2 ESU Viability 

5 

populations of an ESU that are located throughout the landscape promote the diversity in form 

and function that can provide the genetic resources for adaptation to systematic environmental 

change (e.g., global warming or climate cycles on various time scales). 

Relationship of the ISAB Definition of a Viable ESU to NOAA Fisheries’ Definition of a 

Viable Salmonid Population (VSP, McElhany et al 2000) 

NOAA Fisheries adopted a Viable Salmonid Population concept (McElhany et al 2000) to guide 

their Technical Recovery Teams developing recovery plans for ESA listed Pacific salmon. A 

VSP is an independent population of any Pacific salmonid (genus Oncorhynchus) that has a 

negligible risk of extinction due to threats from demographic variation (random or directional), 

local environmental variation, and genetic diversity changes (random or directional) over a 100-

year timeframe. 

Four parameters are used for evaluating the viability of any given VSP: 

1. Abundance (Spawning ground escapements are calculated separately for natural-origin 

and hatchery-origin returning adults.) 

2. Productivity (Spawner-to-spawner ratios or adult replacement rates are calculated 

separately for natural-origin and hatchery-origin returning adults, and the impacts of 

hatchery-origin smolts on natural-origin smolts are assessed.) 

3. Diversity (Variation in the genetic composition, phenotypic attributes, and life histories 

are determined separately for natural-origin and hatchery-origin components.) 

4. Spatial Distribution (Physical location within the watershed of natural-origin and 

hatchery-origin returning adults and smolts.) 

In determining the condition (risk status) of a single population, each of the four VSP parameters 

is assessed individually, with the overall result being a synthesis of those assessments, not a 

simple summation. It might seem logical to define the criteria for assessing the viability of an 

ESU in a manner directly parallel to that already used to identify a “Viable Salmonid 

Population” (VSP). In fact, such an approach has been proposed by NMFS (Federal Register – 

June 15, 2004). The ISAB, however, concludes that such an approach fails to consider 

adequately a number of attributes needed for long term, self-sustaining persistence of an ESU. 

Simply ramping up the current VSP approach to Columbia River Basin ESUs might suggest that 

some ESU components could be considered expendable if other components had sufficiently 

high abundance or productivity. The ISAB believes, however, that any effective approach to 

defining a Viable ESU must explicitly accommodate the high degree of uncertainty about the 

future states of the environment and about the expression of genotypic or other indirect measures 

of diversity as phenotypic diversity in those future actual conditions in time and space. Given 

the high uncertainty in exact prediction of future environmental conditions, as well as the 

uncertainty in interpretation of how genetic or other diversity metrics will be expressed in future 

environments (and so how the diversity of phenotypes may interact with and influence one 

another), prudent management would hedge bets by avoiding loss of currently small, peripheral, 

or in any way seemingly less valuable ESU components. 
ISAB 2005-2 ESU Viability 

6 

Because of the differences between Viable ESUs and VSPs, as explained above, we believe that 

reliance on the VSP criteria alone is an overly simplistic approach that fails to account for the 

complex nature of the interactions among the components of ESUs. Because an ESU may 

incorporate a large amount of ecologically important geographic and genetic structure, any 

assessment of ESU viability must rest on the integration of the entire group of individual 

population viability assessments into a logical whole. As a result, the four parameters used to 

assess population viability, although still relevant for consideration, would need to be considered 

in a more sophisticated manner, expanded as follows: 

1. Abundance - Assessment of abundance cannot simply be determined by the total 

number of returning spawners across the ESU, but must rely on the integration of 

component abundances. That is, extraordinary abundances of a single component, 

either of natural or hatchery-origin, cannot overcome the risks incurred as a result of 

low abundances among other components within the ESU. 

2. Productivity - Similarly, assessment of productivity cannot simply be determined by 

calculating the adult replacement rate across the ESU, but must rely on the integration 

of component productivities. That is, one highly productive component cannot 

overcome the risks associated with a number of the other components having low 

productivities. 

3. Diversity - This assessment needs to consider how the variation in both genetic and 

ecological (e.g., life history) characters inherent in the ESU as a whole is distributed 

among its components. 

4. Spatial Distribution - This assessment needs to include not only a determination of 

how the distribution of component populations throughout the ESU would impact risk 

of catastrophic events, but also how demographic and genetic connectivity is affected. 

So, to reiterate our basic ecological/evolutionary premise, a Viable ESU needs to have for each 

of its component populations the abundance, productivity, diversity, spatial distribution of 

natural spawners and mutual connectivity among components sufficient to accomplish the 

following: avoid the loss of genetic and/or life history diversity during short-term losses in 

abundance that are expected parts of environmental cycles; fulfill key ecological functions that 

are attributable to the species, such as nutrient cycling and food web roles; and provide for longterm evolutionary adaptability to changing environmental conditions. 

Scientists and managers in the Columbia River Basin are facing difficulty devising measures for 

diversity that can be directly translated into ecological or evolutionary currency, such as absolute 

and relative demographic performance. There are ways to begin to build understanding of such 

metrics in nature. For instance, theory of coexistence (of species or populations or phenotypes or 

components of ESUs) indicates that the independence of demographic response (productivity in 

the terms of the VSP and new VESU attributes) of components of an ESU over space, time, or 

both is a significant and useful measure of expressed diversity. Combined with other basic 

demographic information, such a measure (e.g., complement of covariation of the ESU 

components productivities) could be used to quantify demographic diversity within the ESU and 

to analyze how such diversity contributed to persistence in time, space, or both of the entire ESU 

(Chesson and Huntly 1988, 1989, 1994, 1997; Chesson and Rosenzweig 1991, Chesson 2000). 

This same body of theory argues that another key metric for understanding persistence of ESU 
ISAB 2005-2 ESU Viability 

7 

components (stated as populations in the theory, but arguably extended quite naturally to the 

ESU scenario) and the diversity of ESUs (stated as diversity – species richness in the theory -- 

but again arguably extended naturally to the ESU scenario) is the tendency for components to 

rebound when rare. When this is the case, the ESU is expected to persist, i.e., it is viable. 

Similarly, the same logic and analysis can be applied a step up to look at ESUs within a species 

or at ESU or populations within a community of interacting species. Beginning to measure 

comparative productivity over the range of environmental conditions that occur over space and 

time and to analyze similarity of the productivities of components of ESUs (or ESUs of a 

regional population, or ESUs of one species with those of other species in the same region) could 

allow us to better quantify ecologically meaningful diversity. Similarly, we could examine the 

correlations of genetic diversity or life history diversity with the integrated measure of diversity 

that is provided by comparative productivity of ESU components in different locations at the 

same time or over the time-series of conditions in the same place or places. 

Active research is needed on the above-described and other approaches to relating measures of 

diversity to integrated demographic metrics that directly relate to persistence of one or many 

populations in order to better solve the problems the ISAB is asked to address in this review. 

Finally, establishing the policy boundaries for any ESU viability assessment is likely to be as 

important to the eventual outcome as the method used in the assessment. Deciding on these 

legal/policy choices will likely determine the trajectory of the natural populations of salmon and 

steelhead as well as the habitat quality of rivers and streams in the Pacific Northwest. The 

natural populations associated with integrated hatchery programs are generally not themselves 

viable and the habitats upon which they depend are usually inadequate (see below). If the policy 

decision is made that self-sustaining natural populations are not required for an ESU to be viable, 

it is likely that the number of extant natural populations will continue to decrease and the 

impetus behind current efforts to improve habitat conditions will be greatly reduced. 

In the Artificial Propagation Evaluation Report (NOAA 2004a) Section 3.2 page 27 Clarification 

of Proposed Hatchery Listing Policy, by contrast, those authors argued that the presence of 

natural populations was not required for an ESU to be viable. The Hatchery Listing Policy says 

that it is important to conserve natural populations, but it does not require that natural 

populations be recovered under all circumstances. This policy conclusion is not consistent with 

the current understanding of the relevant science, which indicates that a salmon or steelhead ESU 

should not be considered viable if the natural component of the population is unlikely to persist 

in the absence of the continued release of hatchery-produced fish. 
ISAB 2005-2 ESU Viability 

8 

Answers to Questions 

Part I. Hatchery Questions 

Question #1A Are there scientifically sound methods for evaluating the contribution of “in 

ESU” hatchery stocks to the viability of an ESU?

Background: 

The methods necessary to evaluate effects of “supplementation” on long-term fitness of naturally 

spawning salmon and steelhead are identical to those needed for an evaluation of the contribution 

of “in ESU” hatchery stocks to the viability of the naturally spawning proportion of an ESU. As 

defined by the Regional Assessment of Supplementation Project (RASP), the primary objective 

of supplementation is the conservation of the target population, i.e., to maintain or increase 

natural production, while maintaining the long-term fitness of the target population and keeping 

the ecological and genetic impacts on non-target populations within specified biological limits. 

A review of salmon and steelhead supplementation was recently completed by the ISAB (2003). 

Findings 2, 3, and 4 from the ISAB Supplementation report (2003) are applicable to the present 

questions and are restated here as appropriate: 

Finding 2: Contemporary genetic/evolutionary theory, and the literature that supports it, indicate 

clearly that the natural spawning of progeny of an “in ESU” hatchery stock can present 

substantial risks to natural populations of salmon and steelhead. 

Finding 3: The immediate net demographic benefit or harm to population abundance from 

natural spawning of progeny of an “in ESU” hatchery stock depends on three things, intrinsic 

biological parameters of the stock in its environment, policy constraints, and management 

control variables. The integration of these factors, much less their measurement, has not been 

adequately considered in ESU viability evaluations to date. 

Finding 4: Current monitoring and evaluation efforts are inadequate to estimate either benefit or 

harm from allowing the natural spawning of ESU hatchery stock progeny. The correct 

parameters are not being measured consistently. 

Finding: 

At least three different modeling approaches are being used to assess viability of biological 

entities (i.e., populations, ESUs, DPSs, species), population viability analyses (Beissinger and 

McCullough 2002), quantitative rule-based systems (Mace and Stuart 1994, Musick 1999), and 

expert opinion systems (Maquire and Cochrane 2001, Marcot et al. 2001). In addition, analysis 

of empirical data from “supplementation studies” are of value for evaluation of the contribution 

of “in ESU” hatchery stocks to the viability of the naturally spawning proportion of an ESU. 

Each method has strengths and weaknesses. The population viability analysis approach is the 

most fundamental. It entails building a detailed and specific model of the population and its 

future environment. Although this effort is a demanding undertaking, it is the most scientifically 

rigorous. The validity of rule-based systems rests on verification (calibration) against detailed 

models for a broad enough spectrum of specific cases to establish the generality of the accuracy 
ISAB 2005-2 ESU Viability 

9 

of the rules. In the absence of such calibration, the validity of the rules may be open to question. 

The validity of expert opinion depends on how closely the opinion is founded on accepted 

scientific theory and empirical facts (e.g., Brown et al. 2004). 

A fully detailed population viability analysis for salmonids that accounts for metapopulation 

phenomena, life history variations, environmental variation, and the influences of hatcheries will 

require some considerable investment in modeling and in obtaining adequate empirical 

determinations of the key parameters. Some of the component models are available as 

mathematical formalisms. For example, Goodman (2004 and 2005) has developed a model that 

could be used to evaluate whether or not an integrated hatchery and natural population of salmon 

or steelhead was self-sustaining. That model, however, highlights critically important 

parameters for which, in fact, empirical estimates are not currently available. 

Regardless of which method would be employed, the objectives of the assessment, the questions 

being addressed, and the policy parameters associated with the objectives need to be stated 

clearly. For example, addressing the contributions of hatchery individuals to the viability of an 

ESU could be perceived as the prospects for persistence of natural spawning while the hatchery 

program continues to operate, the prospects for persistence of the population after termination of 

the hatchery program, or the prospects for persistence of a particular life history component. 

These are very different viability assessments. Policy parameters that need to be clarified 

include the time horizons for evaluating viability and the required likelihood (probability) of 

viability. In the case of an assessment of the viability of an ESU that includes hatchery 

programs, the essential policy parameter that needs to be stated clearly is whether or not an ESU 

can be considered viable if it is maintained only through artificial production. That is, if there 

are no self-sustaining natural populations, can the ESU be considered viable? If there are selfsustaining natural populations, but the ESU as a whole is judged to not be viable, can it be 

elevated to “viable” status by including hatchery programs? We believe that the current science 

indicates that ESUs dependent upon hatchery production cannot be viable ESUs according to the 

definition of this term we are using in this report. Therefore, a policy that recognizes such ESUs 

as viable would need to use a definition of viability much different from the one we are using. 

The biological validity of such a definition would be questionable. 

Question #1B If such methods exist, are they reliable for predicting viability over long-term 

(centuries or longer), medium term (decades), and/or short term (a decade or less) timeframes?

Finding: 

While methods exist to assess viability, their reliability for application to salmonids is not well 

understood at present. In general, the accuracy of point predictions is expected to decrease as the 

time horizon increases. And in general, it is expected that the uncertainty about medium to long 

term point predictions will be large. For this reason, mature methods for viability assessment 

quantify the uncertainty as well as delivering a point prediction. In this sense, the “reliability” of 

a viability assessment method is better gauged by the credibility of its quantification of 

uncertainty than by whether the point predictions (e.g., “best estimate”) are uncertain. Prudent 

decision systems take uncertainty into account, so credible quantification of uncertainty leads to 

better decisions. It is clear that the reliability of viability assessment methods for salmonids 
ISAB 2005-2 ESU Viability 

10 

could be improved significantly by continued directed research and monitoring. The reliability 

of a fully detailed population viability analysis can be evaluated one case at a time by 

considering the comprehensiveness and realism of the model and the empirical basis for the 

parameter values used. The reliability of alternative methods could be evaluated by comparison 

to a portfolio of validated population viability analyses or by retrospective application to a set of 

empirical case studies with known outcomes. This evaluation has not been attempted 

systematically for situations with the complexity of the salmonid ESUs under consideration here. 

Sufficient time has not elapsed since scientists began predicting the likelihood that a salmonid 

population (or ESU) would lose viability to develop confidence in alternative methods. Elapsed 

time must be coupled with appropriate monitoring to establish whether or not the viability 

changed as predicted by the assessments. 

Question #1C Are the currently available data for any of the Columbia River salmon ESUs 

sufficient to enable the application of these methods?

Background: 

The ISAB has previously recommended monitoring that could evaluate the effects of 

supplementation (ISAB 2003). These same recommended parameters should be monitored to 

answer the questions concerning the contribution of “in ESU” hatchery stocks to the viability of 

an ESU. We strongly support the funding of adequate monitoring for these supplementation 

projects. 

In addition to our review of supplementation (ISAB 2003), an inspection of both the HSRG and 

APRE reports reveals that the vital statistics needed to assess the sustainability of an integrated 

hatchery (natural population, the abundance of hatchery and natural adults, hatchery and natural 

replacement rates, broodstock mining rate, proportion of hatchery fish on the natural spawning 

grounds, harvest rates, and harvest selectivity) are lacking for many programs. Assessing the 

contribution of integrated (and segregated) hatchery programs to ESU viability using expert 

systems may be possible in the absence of rigorous data, but the results are highly uncertain. 

Finding: 

Some supplementation programs reviewed by the ISAB (2003) are collecting appropriate data 

for assessment of viability. For example, the Hood River and Yakima supplementation projects 

have detailed monitoring plans in place. Since our 2003 review, two additional projects, the 

Northeast Oregon Hatchery (NEOH) and the Johnson Creek Artificial Propagation Enhancement 

Project, have proposed monitoring that would help evaluate the benefit of ESU hatcheries for 

maintaining the viability of naturally spawning populations in the ESU. The proposed increases 

in monitoring, however, are not currently being funded. 

The only ongoing study of which we are aware that could provide some information on the 

performance of naturally spawning populations after the termination of supplementation (i.e., 

ESU hatchery affect) is the Idaho Supplementation Study (ISS). Supposedly, supplementation 

was stopped in 2004 on treated streams in the ISS and the study is entering Phase III where data 

collections (and analysis) are intended to address critical uncertainties about the efficacy of 

supplementation. If useful data are collected, some answers could be available within two to 
ISAB 2005-2 ESU Viability 

11 

three generations of spring/summer Chinook salmon. Unfortunately, the ISS may not have the 

level of specificity needed to fully evaluate many hypotheses about the effects of 

supplementation on naturally spawning populations. Based on the recent ISRP review of the ISS 

(ISRP 2003), only one basic parameter, redds per mile, was analyzed to relate various levels of 

supplementation to production. Critical questions about the relationship of ESU hatchery stocks 

to the naturally spawning segment of the ESU cannot be answered if only redds per mile are 

evaluated in Phase III of the ISS, or if proposed genetic and environmental monitoring is not 

included in the NEOH and Johnson Creek studies 

In addition, the SHIEER (Salmonid Hatchery Inventory and Effects Evaluation Report) 

assessment of integrated programs by NOAA Fisheries (NOAA 2004b) appears to have been a 

case-by-case professional judgment review of the effects that a given hatchery program has on 

the viability of the natural population. The application of professional judgment was used 

because data that were needed for a more rigorous assessment for most of the programs were not 

available. Even where some of these data were available, the relationship between the reported 

facts and the conclusions about the effect on viability was not particularly transparent. 

Question #2A In an integrated hatchery-natural system that is operated according to currently 

accepted best conservation practices (e.g., as described by the Hatchery Scientific Review Group 

-- http://www.longlivethekings.org/HRP_Publications.html), what does the available scientific 

information indicate about the probability that the natural component of the population would 

lose the ability to sustain itself without further augmentation? 

Background: 

The following definition of Integrated Conservation Hatchery Programs is incorporated from 

HSRG documents to provide a context for our response. 

An integrated conservation (emphasis added) hatchery program is associated with a 

specified natural population from which gene flow occurs. The goal of an integrated 

program is to demographically increase the abundance of fish representing a natural 

population (two environments, one gene pool) with the natural environment driving the 

adaptation and fitness of a composite population of fish that spawns both in a hatchery 

and in the wild. 

Some of the HSRG Management Guidelines for Integrated Programs are: 

1. Use natural-origin adults in the hatchery broodstock. The percentage of natural-origin adults 

in the broodstock should be a minimum of 10% to avoid divergence of the hatchery population 

from the natural component. 

2. The proportion of natural-origin fish in the broodstock must exceed the proportion of the 

hatchery-origin fish spawning in the wild for the natural environment to drive adaptation. 

3. A general rule of thumb is that the total number of adults (hatchery- and natural-origin) used 

for broodstock cannot exceed the total number of natural-origin escapement. 
ISAB 2005-2 ESU Viability 

12 

These broodstock management guidelines impose limitations on the size of the program. These 

limitations depend on the ability to control the mix of hatchery- and natural-origin fish both on 

the spawning grounds and in the hatchery. They also depend on the number of natural spawners 

available for hatchery broodstock – i.e., the productivity of the natural environment and the 

harvest rate of natural fish. 

The primary scientific foundation for the integrated program’s management guidelines is drawn 

not only from the well developed theory and practice in population genetics and animal breeding 

concerning natural selection and optimum phenotypes when a population is exposed to two or 

more environments (either spatially or temporally), but also from the theory of the effect of gene 

flow on fitness of populations exposed to different environments (Hedrick 1985, Lande 1980, 

Lande and Arnold 1983). In general, when two population components experience different 

natural selective forces, if the rate that genes move from one population component to another 

exceeds the difference in natural selection, the phenotype of that population component will 

predominate in both environments. That is, gene flow overwhelms the difference in natural 

selection, and the individuals occupying both environments resemble the individuals from the 

dominating environment. 

This general theory has been explored for the specific case of integrated (supplemented, 

supported) hatchery and natural salmon populations (Lynch and O’Healy 2001, Ford 2002, 

Goodman 2004 and 2005). Allele frequencies can change in the hatchery component of the 

integrated population due to relaxed selection as a result of the increased egg to smolt survival 

(Lynch and O’Healy 2001), domestication selection in the hatchery (Ford 2002), and strong 

selection in the wild on the hatchery products after release (Reisenbichler et al. 2004). When 

natural selection is relaxed, alleles that are deleterious in the wild, and consequently kept at low 

frequencies, can predominate or even become fixed in the hatchery component of the population. 

This condition becomes progressively more deleterious for the naturally spawning component 

when the hatchery population receives only few natural-origin fish as broodstock, and makes a 

large contribution to natural spawning. Lynch and O’Healy (2001) conclude that under a broad 

range of gene exchanges between the hatchery and natural components, an equilibrium reduction 

in fitness of 50% is reached in 10-20 generations. When the hatchery population is nearly 

closed, with very relaxed selection, fitness is lost much more rapidly. 

Natural selection that occurs in the captive population component is termed domestication 

selection (Campton 1995). Selection that occurs in captivity can be deleterious to the natural 

component because alleles that are advantageous in captivity may not be advantageous in the 

wild (Ford 2002). Interbreeding between hatchery-origin and natural-origin individuals can alter 

the phenotype of the natural population and produce reduced relative reproductive performance 

(aka reduced fitness). The rate of decline in the fitness of the natural population component is a 

function of the strength of the selection difference in the two environments, the proportion of 

natural-origin fish in the hatchery broodstock, and the proportion of hatchery-origin fish 

spawning in the wild. When selection is strong, there can be a 50% reduction in naturalspawning fitness in less than 20 generations under a broad range of broodstock management 

conditions (Ford 2002). Ford (2002) also coupled a model of fitness reduction in a natural 

population owing to domestication selection in the hatchery environment with a model of the 
ISAB 2005-2 ESU Viability 

13 

carrying capacity of the natural environment and the reproductive rate of the natural population. 

Fitness reduction in the natural population was larger when the carrying capacity of the natural 

population and the natural spawning replacement rate was less. Ford (2002) concluded that 

naturally spawning individuals of natural-origin were essential to reduce the change in the 

phenotype of the natural population component, and that improving habitat to increase the 

carrying capacity of the natural environment and the replacement rate of the natural spawning 

population component may be the most effective way to minimize phenotype change in a natural 

population, even when those improvements are insufficient to permit the population to sustain 

itself. Strong selection on the hatchery component, different from the selection operating on the 

natural population, can occur after release in the natural environment, because the hatchery 

products enter the natural environment at a different size, age, and physiological state, and 

possibly at a different season, than their natural counterparts. This can lead to the evolution of a 

different post-release life history, one that is adaptive for hatchery-reared fish, but maladaptive 

for natural spawning (Reisenbichler et al. 2004, Goodman 2004 and 2005). 

Finding:

Goodman (2004 and 2005) summarized the demographic and fitness consequences of an 

integrated natural/hatchery salmon population, and extended this modeling effort by 

incorporating harvest. Goodman (2004) also drew the following additional conclusions 

regarding the performance of an integrated system relative to an unsupplemented population, 

and the ISAB concurs with them: 

1. Integration will almost certainly increase the potential for harvest that is sustainable as long as 

the integration continues, but this increase will cease immediately upon termination of 

supplementation and may be replaced by a decline. 

2. Integration will probably increase the number of fish participating in natural spawning for as 

long as integration continues, but this increase will cease immediately upon termination of 

integration and may be replaced by a decline. 

3. Integration certainly will not increase the natural spawning fitness of the supplemented stock. 

4. Integration may depress the natural spawning fitness of the stock, and this depression in 

replacement rate will be manifest for as long as integration continues and will continue to 

express itself for some number of generations after integration is terminated. 

5. The probability and magnitude of the depression in natural spawning fitness of the integrated 

population will increase with the magnitude of the sustainable harvest that is extracted. 

6. The probability and magnitude of the depression in natural spawning fitness of the integrated 

population will increase with the magnitude of the broodstock mining rate. 

7. There is a possibility of runaway domestication selection in an integrated breeding program 

that departs from strict supplementation by drawing some of its broodstock from returning 

hatchery progeny. 
ISAB 2005-2 ESU Viability 

14 

8. The feasibility of adhering to a strict protocol of drawing broodstock only from natural origin 

fish will depend on the natural spawning and hatchery spawning productivities of the stock, and 

on limitations of harvest below levels that would otherwise be sustainable. 

9. The feasibility of compliance with a cap on the broodstock mining rate and a floor on the 

fraction of natural origin fish among those spawning naturally will depend on the natural 

spawning and hatchery spawning productivities of the stock, and on limitation of harvest below 

levels that would otherwise be sustainable. 

Question #2B What does the available science indicate about how rapidly this might occur? 

Finding: 

Loss of Fitness in Hatchery-Origin Salmon and Steelhead 

The RSRP reviewed and analyzed empirical evidence of whether or not, and how fast, hatchery 

fish lose fitness for natural spawning (RSRP 2004). The major evidence they identify is adopted 

for this report. 

The RSRP compiled studies of salmonids for which the relative fitness of hatchery fish in the 

wild can be compared to that of wild fish and for which there is information on the number of 

generations the fish have been in hatcheries. They chose only those studies in which hatchery 

fish came from rivers that were the same as or nearby to the origin of the wild fish and those in 

which hatchery fish came from other regions of the species’ range. They also excluded studies 

in which most, if not all, of the “wild” fish were derived from prior hatchery escapes. 

Six studies met their criteria. A study with Danish brown trout had the longest period in culture, 

about 12.5 generations (50 years) (Hansen 2002). Columbia River basin winter- and summerrun steelhead studies provided contrasts from populations that had been in culture from 7 to 9 

generations (Hulett et al. 1996, Leider et al. 1990). Commercially farmed Atlantic salmon 

provided populations that had spent 2-5 generations in the hatchery environment (Fleming et al. 

2000). Estimates of relative reproductive success for each gender in three brood years (1995-

1996, 1996-1997, and 1997-1998) of Hood River winter-steelhead provide evaluations of 

populations in culture for a single generation. 

The RSRP concluded: “despite the limitations of each study, there is a relationship between the 

relative fitness of hatchery fish and the number of generations in hatchery culture (Figure 1). 

Relative fitness of hatchery fish declines regularly with the number of generations in culture. An 

exponential curve fit to the data indicates that fitness is lost in excess of 20% per generation. 

Even if the actual loss rate is overestimated by these data (recall that Blouin’s results indicated 

approximately a 10% loss in one generation), they suggest that fitness is lost rapidly in 

hatcheries.” 
ISAB 2005-2 ESU Viability 

15 

Figure 1. Relative fitness of hatchery to wild salmonids (From RSRP 2004). 

The analysis in the RSRP report includes only iteroparous salmonid species. While unlikely, 

semelparous species – those that die after spawning – might exhibit a different rate of change in 

reproductive fitness associated with the number of generations under hatchery culture. Also, the 

RSRP did not use a few studies that showed equal or greater fitness for hatchery fish, arguing 

that “wild” populations in these cases were really just feral hatchery populations. The ISAB 

concurs with this approach and analysis. 

Status of Natural Populations Integrated with Pacific Northwest Hatchery Programs

Directed by the United States Congress, Washington State hatcheries are undergoing a review by 

the Hatchery Scientific Review Group (HSRG) and Columbia Basin hatcheries are under going a 

review by the Northwest Power and Conservation Council’s Artificial Production Review 

Evaluation (APRE). Both of these reviews categorized each hatchery program as either 

integrated or segregated. NOAA Fisheries identified which of these integrated programs were 

associated with natural populations for each of the listed ESUs (NOAA Fisheries 2004a: 

SHIEER Report). In their review the HSRG reported the status of the viability of the natural 

population integrated with a hatchery population and the status of the habitat used by the natural 

population. In the review by the APRE, the status of the natural population and habitat was also 

reported, but in this case the status was the combined natural and artificial components. The 

NOAA Fisheries SHIEER Report compiled a list of programs and evaluated whether they 

believed hatchery fish were contributing to the natural population. This evaluation did not report 

on the status of the natural population or the habitat. 

Using the HSRG, APRE, NOAA Fisheries SHIEER, and the NOAA-Fisheries Biological 

Review Team status report (NOAA Fisheries 2004b), the ISAB assigned one of three status 

categories to each natural population: critical (generally referring to populations in low 

abundance with productivities less than 0.90), at risk (populations in low abundance with 

productivities 0.90 - 1.0), or healthy. The ISAB also assigned one of three categories to the 

habitat: inadequate, limiting, or healthy. 
I

16 

This assessment is compiled into Table 1, for steelhead, chinook, coho, and chum salmon. 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

Steelhead 

Lower Columbia Steelhead ESU 

Cowlitz Cispus River Cowlitz Winter Run 1996 Cowlitz Tilton River Cowlitz Winter Run 2002 Cowlitz Upper Cowlitz Cowlitz Winter Run 1996 Cowlitz Lower Cowlitz Cowlitz Winter Run 1967 

Kalama Kalama Kalama Winter Run 1998 Kalama Kalama Kalama Summer Run 1999 

Clackamas Clackamas Clackamas Winter Run 1991 

Sandy Sandy River Sandy River Late Winter Run 2000 

Hood River Hood River Hood River Winter Run 1991 Hood River Hood River Hood River Summer Run 1998 

Middle Columbia Steelhead ESU 

Umatilla Umatilla Umatilla Summer Steelhead 1992 

Walla Walla Touchet River Touchet Summer Steelhead 2000 

Deschutes Deschutes Deschutes Summer Steelhead 1974 

Yakima Yakima Yakima Summer Steelhead 2000 
I

17 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

Upper Columbia Steelhead ESU 

Wenatchee Wenatchee WDF Wenatchee Program 1996 

Methow Methow Wells Hatchery 1982 Methow Methow Winthrop Hatchery 1982 

Okanogan Omak Creek Methow/Sp-Methow 2003 

Snake River Steelhead ESU 

Clearwater Clearwater Dworshak B-run Steelhead 1969 

Imnaha Imnaha Summer Steelhead 1982 

Tucannon Tucannon Summer Steelhead 2002 

Chinook 

Puget Sound Chinook ESU 

 Nooksack Kendall Creek/Spring 1979  Skagit Marblemount/Spring 1978  Skagit Marblemount/Summer 1995  Skagit Marblemount/Fall 1999  Tulalip Bay Tulalip/Summer 1999  Stillagamish N.F.Stillagamish/Su 1980  Snohomish Wallace/Summer 1973  Green Soos Ck/F 1901  Green Keta Ck/F 1987  Puyallup Voights Ck/F 1917 
I

18 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

Puget Sound Chinook ESU (cont.) Puyallup Diru Ck/F 1979 

 Puyallup White R/Su 1989  Nisqually Clear/Kalama/F 1979  Dungeness Dungeness/Sp 1992  Elwha Elwha/F 1953 

Lower Columbia ESU 

Columbia Estuary Chinook River Sea Resources/Fall 1982 Columbia Estuary Big Creek Fall Chinook/Tule 1941 

Cowlitz Cowlitz Cowlitz/Fall 1963 Cowlitz Cowlitz/Sp Cowlitz/Spring 1968/1999 Cowlitz Toutle/Sp Toutle/Sp 1950/1985 

Kalama Kalama Kalama/Spring* 1959 Kalama Kalama Kalama/Fall 1895 

Elochman Elochman Elochman/Fall 1956 

Lewis Lewis Lewis/Spring 1960 

Washougal Washougal Washougal/Fall 1955 

White Salmon White Salmon Spring Creek NFH/Fall 1901 

Sandy Sandy River Sandy River/Spring 2002 

Upper Willamette ESU 

Willamette N.F. Santiam River N.F. Santiam/Spring 1950 

 M.F. Willamette Willamette/Spring 1957 
I

19 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

 McKenzie McKenzie/Spring 1930  S.F. Santiam S.F. Santiam/Spring 1968  Clackamas Clackamas/Spring 1979 

Upper Columbia ESU Wenatchee Chiwawa/Sp 1989 

 Wenatchee White R/Sp 1999  Methow Twisp/Sp 1992  Methow Chewuch/Sp 1992  Methow Methow/Sp-Methow 2001  Methow Methow/Sp-Winthrop 2001 

Snake River Fall ESU Snake River Lyons Ferry/Fall 1984 

Snake River Sp/Su ESU Salmon McCall S.F./ Su 1974 

 Salmon McCall Johnson Ck/Su 1998  Salmon Sawtooth/Sp 1985  Salmon Pahsimeroi/Su 1980  Grande Ronde Catherine Ck/Su 1995  Grande Ronde Up Grande Ronde/Su 1995  Grande Ronde Lostine R/Su 1995  Imnaha Imnaha/Sp-Su 1982  Imnaha Big Sheep Creek/Sp-Su 1997  Tucannon/Sp Tucannon/Sp 1985 
I

20 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

Coho 

Lower Columbia Coho ESU 

Grays Grays River Type - S Coho Program 1961 Grays Grays River Sea Resources Type - S 1996 Grays Grays River Deep River Type - S Coho 1993 

 Big Creek Big Creek Hatchery Coho 1941 

Elochoman Elochoman River Type - S Coho Program 1954 Elochoman Elochoman River Type - N Coho Program 1954 

Cowlitz Uper Cowlitz Type - N Coho Program Cowlitz Lower Cowlitz Type - N Coho Program 1967 Cowlitz Toutle River Type - S Coho Program 1951 

Lewis N.F. Lewis R. Type - S Coho Program 1991 Lewis N.F. Lewis R. Type - N Coho Program Lewis Cedar Creek Fish First Wild Coho Lewis N.F. Lewis R. Fish First Type - N Coho 

Clackamas Clackamas River Eagle Creek NFH Coho 1957 

Sandy Sandy River Sandy River Coho Program 

Washougal Washougal River Type - N - Coho 1985 

Columbia Gorge Lower Gorge Tribs Bonneville/Cascade/Oxbow Coho 
I

21 

Species/ESU/Subbasin River Basin Program/Stock 

Date of 

Culture 

Chum 

Lower Columbia Chum ESU 

Columbia Estuary Chinook River Sea Resources/ Fall 1996 

Grays Grays River Grays River/ Fall 1997 

Washougal Washougal River Washougal-Duncan Creek/ Fall 2002 

Hood Canal Summer Chum ESU 

Bio Quilcene River Big Quilcene Quilcene NFH/ Summer 1992 

Western Hood Canal Hamma Hamma Hamma Hamma H/ Summer 1998 

Southwestern Hood Canal Lilliwaup Creek Lilliwaup Creek/ Summer 1992 

Union River Union River 2000 

North Hood Canal Big Beef Creek Big Beef Creek Hatchery/ Su 1996 

Discovery Bay Salmon Creek Salmon Creek Hatchery/ Su 1992 

Port Townsend Bay Chimacum Creek Chimacum Creek Hatchery/ Su 1996 

Sequim Bay Jimmycomelately C Jimmycomelately C H/ Su 1999 
ISAB 2005-2 ESU Viability 

22 

Based on this compilation from the Columbia River Basin and Puget Sound domains, there are 

approximately 97 integrated hatchery programs for steelhead (21), Chinook (48), coho (17), and 

chum (11) salmon. For steelhead, 14 populations are categorized as at risk and seven as critical; 

all have limiting or inadequate habitat. For Chinook salmon, 17 populations were categorized as 

at risk, 19 as critical, and two as healthy (Clackamas in the Upper Willamette Chinook ESU and 

Marblemount Summer - Skagit R in the Puget Sound Chinook ESU). Only two locations, the 

Lewis River and the Washougal River, in the lower Columbia River Basin had healthy habitat. 

The remaining 46 Chinook programs had inadequate or limiting habitat. For coho salmon, two 

populations (Clackamas and Sandy Rivers) were at risk and the remaining 15 critical. Habitat 

was rated as limiting in streams of the two at risk populations and inadequate in the remaining 

15. For chum salmon, three Lower Columbia Chum ESU populations were rated as at risk with 

inadequate habitat and eight Hood Canal Summer Chum ESU populations were rated as at risk 

with inadequate habitat. 

From a brief scanning of the narratives of these programs, most appear to fall short of achieving 

the HSRG criteria for having 10% or more of the broodstock be of natural-origin and having less 

than 5% of the natural spawning adults be of hatchery-origin. The programs range from 2 to 115 

years old. The question of how long these programs can operate before the natural-origin 

population is no longer self-sustaining appears to be moot. Only 2 of 97 natural populations 

appear to be self-sustaining at this time, primarily because of limited habitat. To move toward 

the recommendations of the HSRG and the theoretical work of both Ford (2002) and Goodman 

(2004 and 2005), the first step toward improving these programs is to improve the carrying 

capacity of the environment and the productivity of the natural-origin salmon and steelhead. 

Nonetheless, there is little evidence of self-sustaining natural populations in integrated 

hatchery/natural systems. 

Question #2C If a naturally spawning population becomes unsustainable without hatchery 

augmentation, what does the current scientific information say about the likelihood that the 

population would be able to re-establish self-sustainability, and if so, under what conditions and 

over what time frame?

Background: 

If a naturally spawning population becomes unsustainable for ecological reasons, such as 

degraded habitat or imposed mortality, the only prospects for re-establishing self-sustainability 

are to correct the ecological problems. Hatchery augmentation may be used to “buy time” for a 

short duration while ecological problems are being addressed, but during this period the 

cumulating (probably compounding) genetic/adaptive problems caused by the hatchery phase 

reduces the ability of eventual reestablishment. Theoretical consideration of the genetic/adaptive 

aspects of this question is addressed by Lynch and O’Healy (2001) and Goodman (2004 and 

2005). Empirical evidence to address this question can be drawn from efforts to reintroduce 

coho, spring- and fall-run Chinook, and chum salmon. 

Lynch and O’Healy (2001) and Goodman (2004 and 2005) conclude that a natural population 

has some potential to readapt to the natural environment once the integration with a hatchery 

program is terminated. The principal caveat is that if the deleterious effects of integration 
ISAB 2005-2 ESU Viability 

23 

produce a population that is unable to replace itself, readaptation will also have to offset the 

consequences of demographic failure. If the rate of readaptation cannot offset the poor 

productivity, the population could become extirpated before it readapts. Under these conditions, 

when the natural population component receives substantial gene flow from the hatchery 

component, it may require several dozens of generations to recover lost fitness (Lynch and 

O’Healy). The rate of recovery will depend on the average selection coefficient against the 

deleterious alleles that had accumulated under conditions of relaxed selection. If a proportion of 

the deleterious alleles became fixed in the natural population during integration, the time to 

recovery may be substantially greater. This would require new, or back, mutations and/or the 

migration of wild-type alleles from other population sources. 

In the Columbia River basin, coho salmon have been reintroduced into the Wenatchee, Yakima, 

Umatilla, and Clearwater subbasins. Spring Chinook have been reintroduced into the Umatilla 

and Hood River subbasins, and fall Chinook into the Umatilla River subbasin. In the Hood 

Canal, summer-run chum have been reintroduced into two streams. The success of these 

programs has been variable, but none has reestablished self-sustaining runs. These 

reintroduction programs have taken eggs from one location, reared them at a hatchery, and then 

released them into a foreign environment. These programs are challenged both by the number of 

generations that the hatchery fish have been under culture and by the environmental differences 

between the donor and recipient environments. A few of the programs (Umatilla spring-run 

Chinook and Yakima coho) have been sufficiently successful in returning first generation 

hatchery-origin adults that eggs to continue the programs are taken in-situ, rather than from the 

origin donor stock location. Other programs (Hood River spring-run Chinook) have not 

achieved that level of success and rely on continued importation of fish or eggs. The recent 

Umatilla subbasin plan did not anticipate that either the fall-run Chinook or coho reintroduction 

programs would become self-sustaining in the foreseeable future. 

Finding: 

Based on these observations, reestablishing self-sustaining populations is likely to be the 

exception, rather than the rule unless ecological/habitat/overharvest problems are solved and 

augmentation programs have been implemented in a manner that minimizes genetic/adaptive 

impacts on the natural population. 

Part II. Anadromous/Resident Questions 

Question #1 What is known about how resident fish contribute to the long-term viability of 

ESUs that contain both anadromous and resident fish? 

Background: 

The long-term viability of an ESU depends to a substantial degree on the conservation of the 

diversity of the various life histories inherent within it. As a result, when considering the 

question of how fish with one life history strategy (e.g., residency) contribute to the viability of 

an ESU containing at least two life history strategies (residency and anadromy), we need to 

consider how resident fish influence the four viability parameters (abundance, productivity, 

diversity, spatial distribution) of both life histories. Such an assessment needs to consider gene 
ISAB 2005-2 ESU Viability 

24 

flow between forms, its resulting impact on fitness, and the role of each form in metapopulation 

processes. This assessment must recognize that the two forms may or may not be reproductively 

isolated. Empirical evidence supports anadromy and residency in the same gene pool (partial 

anadromy, Jonsson and Jonsson 1993, Docker and Heath 2003), reproductive isolation of 

sympatric populations exhibiting the alternative migratory forms (Zimmerman and Reeves 

2000), and genetic differentiation between the migratory forms on a small spatial scale (e.g., 

Narum et al. 2004). 

Abundance: 

The assessment of abundance as a viability parameter must integrate individual population 

abundances of both forms. Nevertheless, the presence of viable, natural spawning, populations 

of resident O. mykiss will positively influence ESU viability simply by increasing the overall 

abundance (resident + anadromous). Evolutionary theory suggests the abundance of anadromous 

and resident rainbow trout in an ESU (here we consider only resident fish below migration 

barriers) will depend largely on the habitat characteristics that influence the relative fitness of 

each strategy (Hendry et al. 2004, Jonsson and Jonsson 1993). Therefore, as the habitat 

characteristics change (as a result of natural or anthropogenic factors), we expect the relative 

abundance of the two migratory forms to change (Jonsson and Jonsson 1993). For example, 

habitat alterations (e.g., dams) have caused a decline in anadromous populations in some ESUs 

(e.g., Upper Columbia River, NOAA Fisheries 2003). Consequently, the resident form is the 

major source of abundance. The viability of these ESUs is positively influenced by the 

abundance of resident rainbow trout. In general, however, viability is likely diminished because 

of the levels of lost productivity, diversity, and spatial distribution that accompany loss of the 

anadromous form (see below). 

Productivity:

It has been clear since the 1940’s that resident rainbow trout are the major (if not exclusive) 

source of production of resident fish, and that steelhead are the major (if not exclusive) source of 

production of anadromous fish. Neave (1944) collected eggs from resident x resident and 

steelhead x steelhead crosses from the Cowichan River in British Columbia in 1938 and 1939. 

The resulting parr were marked and released back into the river and adults from the crosses were 

recaptured through 1944. He found that all recaptured adult fish of steelhead parents were 

anadromous and all recaptured offspring of resident trout crosses remained in freshwater, 

suggesting a strong genetic component to life history. In fact, Neave (1944) suggested that these 

results indicated that resident rainbow trout and steelhead should be considered separate species. 

More recent work on this topic has used the Sr/Ca ratios in the primordia of otoliths to indicate 

whether the maternal parent of that fish was reared in salt or fresh water. Phelps et al. (1997) 

applied this technique to 16 returning steelhead from the Kalama River and found that all of 

these fish were the offspring of anadromous females. Unfortunately, no resident rainbow trout 

were analyzed in this study. This technique, however, was later applied to assess the parentage 

of resident and anadromous rainbow trout in both the Deschutes River, Oregon and the Babine 

River, British Columbia (Zimmerman and Reeves 2000). Otoliths from 20 steelhead and 38 

resident rainbow trout were collected from the Deschutes River. All steelhead examined had 

anadromous maternal parents and all resident trout were produced by resident mothers. The 

maternal parentage of the Babine River fish was not as consistent. Of the 24 steelhead examined 
ISAB 2005-2 ESU Viability 

25 

from this system, one had a resident maternal parent. Of the nine resident trout examined, two 

had otolith chemistry indicating that the maternal parent was anadromous. The authors attributed 

the high degree of segregation of the resident and anadromous rainbow trout populations in the 

Deschutes River to a difference in spawning time and spawning habitat characteristics; steelhead 

spawn about 9-10 weeks earlier than resident fish and select spawning habitat in deeper water 

with larger substrate size. 

There is some additional evidence in California river systems that resident rainbow trout can 

produce anadromous offspring. Otolith chemistry of steelhead smolts from the central California 

coast indicated these fish were the offspring of both resident and anadromous mothers 

(Zimmerman, unpublished data as cited in Zimmerman and Reeves 2000). Similarly, a small 

number of smolts emigrating from Sespe Creek, a tributary of the Santa Clara River, have been 

traced to resident rainbow trout stocked in this stream (Entrix Inc., 1996). There is no evidence, 

however, that any of the smolts produced by the resident trout in these streams have contributed 

to the very few adult steelhead that currently return to these California systems. Although it is 

clear that the each of the two life history forms can produce offspring that apparently initiate the 

alternative form, the degree at which this occurs, much less its impact, is most likely population, 

or even location, specific. 

Diversity and Spatial Distribution: 

Even though the breeding and otolith studies cited above found limited evidence to suggest cross 

contributions of the two life history forms, molecular genetic studies have found evidence for a 

reasonable amount of historical geneflow. For example, genetic characterization of resident and 

anadromous forms of rainbow trout in the Deschutes and Walla Walla Rivers found few 

distinctions between the two life history forms. Chilcote (1976) used protein electrophoresis to 

examine 13 polymorphic loci of resident and anadromous fish from five sites in the Deschutes 

and found that only a single resident population, one that was isolated above two impassable 

waterfalls, exhibited significant deviation in allele frequencies from the other populations. In a 

subsequent study of O. mykiss in the Deschutes River, differences in protein and meristic 

characters were found between resident populations isolated above waterfalls and downstream 

fish, but no differences were found in sympatric populations of resident and anadromous rainbow 

trout (Currens et al. 1990). Narum et al. (2004) found evidence of weak but significant genetic 

differentiation between sympatric resident and anadromous rainbow trout in the mainstem Walla 

Walla River, but not the Touchet River. Narum et al. (2004) suggest the two life history forms 

may mate assortatively by size or spawning time in the Walla Walla River. Alternatively, 

evidence of reproductive isolation could reflect the stocking of out-of-basin steelhead of Snake 

River origin in the mainstem Walla Walla River. Collectively, these results suggest that 

significant genetic exchange occurs at least sporadically between resident and anadromous forms 

of rainbow trout in the Deschutes and Walla Walla systems (Chilcote 1976). The more recent 

otolith work appears to indicate, however, that this level of geneflow may not be consistent. 

Both “anadromous” and “resident” forms may be highly migratory, and the two migratory forms 

may play geographically distinct roles in colonization and the maintenance of genetic diversity 

and population structure. Resident rainbow trout in large freshwater systems can be highly 

migratory (Meka et al. 2003) and may contribute more to gene flow on a fine spatial scale than 

do steelhead. Steelhead may contribute more to gene flow on a broad spatial scale (between 
ISAB 2005-2 ESU Viability 

26 

distant watersheds and across saltwater), thereby providing a mechanism for genetic connection 

among isolated populations of resident rainbow trout. There is some support for such an 

anadromous/nonanadromous dichotomy in gene-flow pattern if one compares across species. 

Castric and Bernatchez (2004) found that nonanadromous brook charr exhibit a higher rate of 

fine-scale dispersal than co-occurring anadromous Atlantic salmon (Salmo salar), consistent 

with the different migratory behaviors of the two species. As a result, resident and anadromous 

fish may both play key roles in recolonization efforts within an ESU, with the relative 

importance of each form varying with environmental circumstances. 

There are few if any examples of the diversity and spatial structure of resident and anadromous 

populations of O. mykiss in pristine rivers in the western US, largely because most river basins 

have been extensively altered by human development. There is evidence, however, that broad 

life history diversity exists in some rivers of the Kamchatka Peninsula of eastern Asia where 

environmental impacts have been far fewer. The following figure illustrates the variation in life 

histories of O. mykiss inhabiting adjacent river basins in relatively pristine ecosystems. 

Figure 2. Variation in the proportion of different life history strategies in O. mykiss [Parasalmo 

mykiss, according to Russian authors] in eight rivers on the west coast of the Kamchatka 

Peninsula. Six life history strategies were recognized from scale analysis: two different 
ISAB 2005-2 ESU Viability 

27 

patterns of anadromy, estuarine residency, riverine-estuarine migrants, “half-pounders” 

(<1 year at sea), and strict freshwater residency. Each strategy is represented by a 

different shading pattern (from Pavlov et al. (2001). 

This figure illustrates two important points. First, considerable life history diversity, including 

multiple variations of anadromy and residency, tends to be expressed in this species where the 

freshwater environment contains the full range of habitats to which the species has adapted over 

time. Second, the relative importance of different life histories can vary markedly in adjacent 

rivers and in different parts of the drainage system, suggesting that local conditions strongly 

influence which life history will predominate. Life history variation may also occur within a 

river system over both short- and long-term temporal scales. Pavlov et al. (2001) found that the 

relative contribution of different life histories to the population varied in a continuum along a 

river from headwaters to mouth, rather than being expressed as discrete resident and anadromous 

populations. Such variation may be essential for long-term population persistence in changing 

environments. 

Finding: 

Although the genetic similarity of sympatric resident and anadromous life histories of rainbow 

trout does suggest that interbreeding occurs at some level, there is little information for specific 

populations on the extent to which resident rainbow trout contribute to the abundance of the 

anadromous life history component. That is, evidence is not universally conclusive that resident 

populations play a key role in supporting the productivity or abundance of any steelhead 

population (or the reverse). On the other hand, the resident life histories may positively 

influence viability of an ESU that contains sympatric resident and anadromous forms by 

contributing to the overall abundance and diversity (because residency is an important life 

history strategy in some circumstances). The role of the resident life history in maintaining 

population connectivity and spatial structure is unclear, but it undoubtedly differs in timing and 

extent from the anadromous life history. As a result, the presence of both resident and 

anadromous life-history forms is critical for conserving the diversity of steelhead/rainbow trout 

populations and, therefore, the overall viability of ESUs. 

Question #2A Does the loss of anadromy from a population have a sufficient effect on ESU 

diversity to reduce the likelihood of long-term persistence of the ESU? 

Background: 

Loss of anadromy will undoubtedly change the structure and connectedness of metapopulations 

within the ESU. The two life history forms (anadromous and resident) likely play different roles 

in the maintenance of population structure (as suggested above), and the loss of one form may 

change the population structure by altering patterns of gene flow. In particular, long distance 

migrations between major watersheds and through saltwater can only be accomplished by 

anadromous O. mykiss. When either anadromy or residency is lost, populations will likely 

become more isolated and vulnerable to loss of genetic diversity. 
ISAB 2005-2 ESU Viability 

28 

Finding: 

Based on the evidence presented below, the ISAB concludes that the likelihood of long-term 

persistence would be substantially compromised by the loss of anadromy in O. mykiss ESUs. 

Question #2B What is the evidence that once the anadromous life history form is lost from an 

ESU, a self-sustaining anadromous population can be re-established (either naturally or as part 

of reintroduction effort) from the resident component of the ESU at some time in the future? 

Background:

Once anadromy has been lost from a population or ESU, it is unclear whether or not this life 

history could be reestablished within a population of entirely resident fish; evidence on this is 

equivocal. The potential for reestablishment of anadromy by resident fish most likely depends 

greatly upon which resident fish population is being considered. Unfortunately, there is no 

reliable method to predict where and when resident populations are capable of this process at all, 

much less within a timeframe important to recovery.

One way to assess this question is to weigh the evidence that anadromous and nonanadromous 

forms can be derived from one another. There are some reports in the literature of resident 

rainbow trout populations establishing anadromy. Rainbow trout from several sources, including 

some fish from California that were derived at least partly from steelhead, were introduced into 

numerous rivers in Argentina starting in the early 20th century. Populations of resident rainbow 

trout were established in many of these systems. Anadromy, however, was not reported from 

this region until 2001, when it was determined that a population in the Santa Cruz River had 

developed an anadromous form (Pascual et al. 2001). Microsatellite evaluation indicated that the 

now sympatric resident and anadromous forms from this river were genetically indistinguishable 

and appeared to be most closely related to the fish from California. The newly established 

Argentine anadromous population may, however, exhibit some differences from steelhead 

populations in California. 

The capacity for a resident rainbow trout population to reestablish an anadromous form also may 

be influenced by the environment. In both the Yakima and the Willamette Rivers, there are 

resident O. mykiss populations in headwater tributaries and cool upper reaches of the mainstem 

rivers. Steelhead spawning in these rivers are spatially segregated from resident trout spawning. 

Cramer et al. (2003) propose that O. mykiss juveniles migrate from spawning and rearing 

tributaries when flows are reduced in the late summer/fall. If these migrating individuals arrive 

at mainstem habitats that have sufficient flow and low temperature, they halt their migration and 

become residents. If flows in the mainstem are low and temperatures high, they continue a 

downstream migration until they reach the ocean. Even in river systems like the Deschutes, 

where both life history types occur in sympatry, anadromous and resident life history types use 

different tributaries and river habitats (Zimmerman and Reeves 2000). 

A striking example of the potential for a resident population to reestablish anadromy was 

reported from Alaska (Thrower et al. 2004). Juvenile trout were captured in 1926 from a stream 

that contained steelhead and transported to a lake that was isolated from the ocean by several 

barrier waterfalls. These stocked fish established a resident population in this lake. In 1996, a 
ISAB 2005-2 ESU Viability 

29 

study (Thrower et al. 2004) was undertaken to determine the propensity for fish from the lake 

population to produce smolts after 70 years of selection against this life history trait. The 

proportion of juvenile fish smolting was compared with the smolting rate of offspring from 

steelhead captured in the lower river. Not surprisingly, the smolting rate of the lake fish was 

lower than that of the steelhead. Even after 70 years of selection against anadromy, however, 

nearly half the fish produced from a cross of a resident male with a resident female smolted. 

These smolts were subsequently released from the hatchery where the crosses were produced, 

and marine survival was evaluated. Offspring from the lake fish survived at a lower rate than 

smolts from anadromous parents (0.7% versus 2.8%). This is one of the only experiments where 

the production of smolts and subsequent marine survival of a resident population of rainbow 

trout has been quantified. 

There is also evidence that resident rainbow trout populations are unlikely to reestablish an 

anadromous form. Steelhead in California historically occurred south to nearly the Mexican 

border (BRT 2003). Anadromy has been lost in many of these watersheds despite the presence 

of resident rainbow trout populations. It is not clear whether or not the failure to reestablish 

anadromy is due to an inability of the extant resident populations to express this life history trait 

or the loss of habitats critical to support of steelhead. 

We conclude from these various observations that there are likely both genetic and environment 

determinants for the expression of anadromous and resident O. mykiss life-history variation. 

Whether the underlying genetic mechanisms generate life-history plasticity (the production of 

different life-history types by a single genotype under different environmental conditions) or 

polymorphism (the production of different life-history types by different genotypes), or a 

combination of both, is not known. Regardless of the genetic mechanism, however, maintaining 

the anadromous population component is likely very important. Empirically this is demonstrated 

by the experiments with resident O. mykiss in Alaska (Thrower et al. 2004), where the resident 

fish have reduced performance after isolation from the anadromous component of the population. 

Theoretically, both plasticity (Kingsolver et al. 2002) and polymorphism (Meyers and Bull 2002) 

are maintained by evolution in spatially or temporally variable environments with gene exchange 

between individuals in the different environments. 

We feel that in addressing this question, it is also important to consider the reciprocal situation, 

i.e., whether or not a self-sustaining resident population can be re-established (either naturally or 

as part of a reintroduction effort) from the anadromous component of the ESU at some time in 

the future. Although the effect of the diversity introduced into a rainbow trout ESU by 

anadromy on the long-term viability of that ESU is difficult to assess directly, there are examples 

where the existence of an anadromous life history form has clearly aided in the recovery of 

depressed populations. Large catastrophic disturbances are relatively common in many of the 

areas occupied by these fish in western North America. Large wildfires, volcanic eruptions, and 

earthquakes all have the potential to reduce or extirpate trout populations in freshwater. Because 

a substantial proportion of a steelhead population is in the ocean at any given point in time, that 

portion is immune from such large disturbances. These fish can later serve to recolonize areas 

impacted by the disturbance. Perhaps the most striking example of this situation occurred 

following the eruption of Mt. St Helens in 1980. Steelhead that were at sea during the 1980 

eruption rapidly reoccupied areas of the South Fork Toutle River and Green River (a tributary of 
ISAB 2005-2 ESU Viability 

30 

the North Fork Toutle River) where adequate habitat remained after the eruption. As a result of 

the availability of these colonizing fish, steelhead populations in the affected area rebounded 

rapidly with populations achieving fishable levels by the mid 1980s (Lucas 1985). Whether 

resident populations were re-established by steelhead is less certain, however. Some rainbow 

trout were present above migration barriers in upper Toutle River tributaries before the eruption, 

but these fish may have originated from resident trout stocked in headwater lakes. Hatchery 

steelheads were widely stocked in Toutle River tributaries to accelerate the recovery of naturally 

spawning fish after the eruption. In one stream, a resident rainbow trout population was 

established as a result of steelhead supplementation; over a 20-year period the rainbow trout 

population completely displaced the native coastal cutthroat trout population that lived there 

(Bisson et al. 2005, in press). 

Finding:

Based on the available information, it seems unlikely that a population of resident trout can 

consistently reestablish a steelhead population. The only clear evidence of a resident population 

giving rise to an anadromous component is the example from Argentina (Pascual et al. 2001). In 

this case, however, the anadromous population that arose from the resident fish did not 

reestablish an extirpated population but expanded into an unoccupied niche. If shifts in life 

history are common in steelhead generated by resident parents, reestablishment of a selfsustaining anadromous component of a population or ESU could be very difficult. The work of 

Thrower et al. (2005) suggests that the capacity to express anadromy is retained in a population 

of resident trout for many generations. In this study, the smolting rate and marine survival of the 

smolts produced by the resident fish were lower than that of the offspring of steelhead. In 

addition, it remains uncertain whether or not the smolting and survival rates exhibited by the 

resident fish would be sufficient to enable reestablishment of a viable steelhead life history type. 

Based on the various empirical observations of O. mykiss life-history variations and on principles 

from theory, we conclude that once anadromy is lost from an ESU, resident populations are not 

likely to regenerate self-sustaining anadromous populations in the short or intermediate term, and 

that the ESU viability would be largely compromised.

Question #3 What does current scientific information tell us about the abundance, productivity 

and diversity of salmon or steelhead ESUs that have lost one or more life-history trajectories?

Background: 

For this discussion, we consider the term “lost” to mean loss of a significant number of 

populations and not necessarily complete elimination. We consider the phrase “life-history 

trajectory” to include traits other than anadromy/nonanadromy. Life-history trajectory also 

refers to the variation (within a species or ESU) in the season and amount of time that different 

runs of fish occupy the freshwater, estuarine, and ocean environments. Life-history variation can 

be dramatic, as in the difference between resident kokanee and anadromous sockeye salmon 

(both O. nerka) and as in the difference between odd and even year pink salmon (O. gorbuscha). 

It can also be subtle, as in the variation in adult run timing in lower Columbia River Chinook 

salmon that return in the spring, early fall (tules), and late fall (lower river brights) to different 

tributary spawning streams. Sometimes these life-history trajectories are placed in the same ESU 

(e.g., the Lower Columbia River Chinook ESU), and at other times they are placed in their own 
ISAB 2005-2 ESU Viability 

31 

ESU (e.g., Sacramento River Chinook salmon are placed in separate fall, winter, and spring-run 

ESUs). 

The loss of a life-history trajectory will likely result in a decline in population abundance and 

productivity, as well as lost diversity. As a result, a decline in ESU viability is expected. This 

conclusion is based on a large body of literature showing that life history trajectories are the 

outcome of generations of selection, allowing for local adaptation and maximum use of 

heterogeneous habitat (Taylor 1991). Pacific salmon have evolved a large array of unique life 

history types that allow them to persist in dynamic and volatile environments. Many examples 

have been reported that reveal the importance of life history variation to the resilience and longterm persistence of Pacific salmon. Hilborn et al. (2003) described the importance of multiple 

life history strategies to the resilience and sustainability of sockeye salmon in Bristol Bay, 

Alaska. Here, as in other areas (e.g. Fraser River basin, Wood 1995), the sockeye have evolved 

beach and tributary spawning subpopulations that exhibit distinct morphological and behavioral 

differences specific to the two environments (Quinn et al. 2001). These sockeye also exhibit a 

bi-modal timing in adult returns (mid- and late-summer) that appears to be linked to the thermal 

regime of the incubation habitat (Quinn et al. 2001). Hilborn et al. (2003) show that these and 

other life history traits allow the Bristol Bay sockeye complex to persist despite major changes in 

climatic conditions affecting the freshwater and marine environments. They show that life 

history strategies that dominate during one climatic regime are minor producers during others. 

Another example of how life history strategies are linked to local adaptation and increased use of 

the environment was presented by Brannon (1967). Brannon demonstrated that sockeye salmon 

spawning in lake outlets have evolved a juvenile migratory strategy that differs from populations 

that spawn in lake tributaries. Specifically, the juveniles emerging from gravel at the outlet must 

swim upstream to reach lake rearing environment, whereas the juveniles emerging from gravel in 

the tributaries must swim downstream (Brannon 1967). 

Adult run timing is also an important life history strategy linked to the environment and local 

adaptation. Chinook salmon exhibit perhaps the greatest diversity of adult run schedules (Healy 

1991). For example, the Lower Columbia River ESU consists of spring run chinook, fall (tule) 

chinook, and late fall (bright) chinook. The different runs have likely evolved to utilize unique 

habitat, increasing the resilience of the chinook in this area. The importance of maintaining all 

run times was recognized by the BRT in assessing viability (NOAA 2003). They concluded the 

decline and loss of some spring-run populations contributed to the finding that this ESU was 

likely to become endangered in the foreseeable future. 

Loss of one or more life histories from an ESU certainly has an effect on ESU diversity and often 

on spatial distribution. As noted above, steelhead provide a mechanism of genetic connection 

among populations of resident rainbow trout. This genetic interchange may have a significant 

impact on the evolutionary pathway of the resident populations. Thus, the presence of both 

resident and anadromous life history forms likely plays a key role in determining the diversity of 

rainbow trout populations and ESUs. 
ISAB 2005-2 ESU Viability 

32 

There is less empirical evidence regarding the effect of a reduction in life history diversity on 

productivity or abundance. As noted above, however, there is the theoretical basis to expect that 

a decrease in life-history diversity could impact abundance and productivity. For example, the 

existence of an anadromous form in a population or ESU does provide a mechanism for the 

recolonization of habitats where populations were extirpated by a catastrophic disturbance event 

or human actions. Typically, these types of extirpations do not affect an entire ESU. 

Nonetheless, if steelhead were not available to recolonize areas of habitat that were depopulated 

by such disturbances, recovery of abundance and productivity could take much longer. 

The significance of multiple life history types in the support of ESU viability also has been 

recognized by the BRTs in the recent status reviews (NOAA 2003). For example, the Lower 

Columbia Chinook ESU consists of a combination of fall run (tules), late fall run (brights), and 

spring run life history trajectories inhabiting coastal, western Cascade, and Columbia gorge 

ecological zones (Myers et al. 2003). The loss of many of the spring Chinook populations from 

the Lower Columbia River ESU was one of the factors supporting their decision to list these 

ESUs as threatened (NOAA 2003). The same situation applies to the Puget Sound Chinook 

ESU, where early-returning (spring) fish have been greatly reduced from historical levels. In 

both cases, the differential impact on the spring life history form is due, in part, to dams blocking 

access to the high-elevation habitat that historically supported these fish. The Chinook salmon 

populations in these ESUs have low abundance and productivity, in part due to the loss of the 

spring life history type and the habitats that supported these fish. 

This loss of spring-run biodiversity has ramifications beyond increasing the probability that the 

entire ESU will become extinct. Salmon are keystone species in the watersheds that they 

historically have inhabited. Their presence contributes to the diversity of life by cycling nutrients 

and modifying habitats. Their extinction would increase the risk of extirpation for other species. 

Keystone species support the ecosystem (entire community of life) of which they are a part. The 

ISAB emphasized in our definition of a Viable ESU that viability included having sufficient 

abundance and diversity to continue to provide the ecosystem functions typically attributed to 

salmon. Loss of life-history trajectories will undoubtedly reduce the resilience of not only the 

ESU, but also the community to which these fish belonged. 

Finding: 

The available evidence indicates that the loss of one or more life-history types from an ESU can 

impact abundance and productivity. The effect on ESU diversity and spatial distribution is less 

speculative; loss of a life-history type from an ESU clearly impacts these attributes. The ISAB 

concludes that the maintenance (or restoration, where possible) of all of the naturally occurring 

life history types of an ESU should be one of the goals of salmon recovery. 
ISAB 2005-2 ESU Viability 

33 

References 

Beissinger, S. R., and D. R. McCollough. 2002. Population Viability Analysis. University of 

Chicago Press, Chicago, Il. 593 pp. 

Bisson, P. A., C. M. Crisafulli, B. R. Fransen, R. E. Lucas, and C. P. Hawkins. (2005, in press). 

Responses of fish to the 1980 eruptions of Mount St. Helens. In V. H. Dale, F. R. 

Swanson, and C. M. Crisafulli, editors. Mount St. Helens: 20 years of research in a 

volcanically disturbed landscape. Springer-Verlag, New York, USA. 

Brannon, E.L. 1967. Genetic control of migrating behavior of newly emerged sockeye salmon 

fry. Int. Pac. Salmon Fish. Comm. Prog. Rep. 16:31p 

Brown, G., Smith, C., Alessa, L., Kliskey, A. 2004. A comparison of perceptions of biological 

values with scientific assessment of biological importance. Applied Geography, 24, 161-

180 

BRT. 2003. Preliminary conclusions regarding the updated status of listed ESUs on west coast 

salmon and steelhead. B. steelhead. February 2003 Co-manager review draft. NOAA 

Fisheries, Northwest Fisheries Science Center, Seattle, WA. 

 

Campton, D. E. 1995. Genetic effects of hatchery fish on wild populations of Pacific salmon and 

steelhead: what do we really know? American Fisheries Society Symposium 15:337-

353. 

Castric V. and L. Bernatchez. 2004. Individual assignment test reveals differential restriction to 

dispersal between two salmonids despite no increase of genetic differences with distance. 

Mol. Ecol., 1299-1312. 

Chesson, P.L. and N. Huntly. 1988. Community consequences of life-history traits in a variable 

environment. Acta Zoologica Fennici 25:5-16. 

Chesson, P. and N. Huntly. 1989. How do short-term instabilities affect long-term community 

dynamics? Trends in Ecology and Evolution 4:293-298. 

Chesson, P. and M. Rosenzweig. 1991. Behavior, heterogeneity, and the dynamics of interacting 

species. Ecology 72:1187–1195. 

Chesson, P. and N. Huntly. 1994. Temporal hierarchies of variation and the maintenance of 

diversity. Plant Species Biology 8:195-206. 

Chesson, P. and N. Huntly. 1997. The roles of harsh and fluctuating conditions in the dynamics 

of ecological communities. American Naturalist 150:519-553. 
ISAB 2005-2 ESU Viability 

34 

Chesson, P. 2000. General theory of competitive coexistence in spatially varying environments. 

Theoretical Population Biology 58: 211 - 237 

Chilcote, M. W. 1976. Genetic comparisons of Deschutes River steelhead and rainbow trout at 

selected enzyme loci. M.S. thesis, Oregon State University, Corvallis, OR. 

Cramer, S. P., D. B. Lister, P. A. Monk, and K. L. Witty. 2003. A review of abundance, trends, 

hatchery and wild fish interactions, and habitat features for the Middle Columbia 

Steelhead ESU. 96 Pages. S.P. Cramer and Associates, Inc. 39330 Proctor Blvd, Sandy, 

OR 97055 

Currens, K. P., C. B. Schreck, and H. W. Li. 1990. Allozyme and morphological divergence of 

rainbow trout (Oncorhynchus mykiss) above and below waterfalls in the Deschutes River, 

Oregon. Copeia 1990:730-746. 

Docker MF, and D.D. Heath. 2003. Genetic comparison between sympatric anadromous 

steelhead and freshwater resident rainbow trout in British Columbia, Canada. Conserv. 

Genet., 4, 227-231. 

Entrix, Inc. 1996. Results of fish passage monitoring at the Vern Freeman Diversion Facility, 

Santa Clara River. prepared for United Water Conservation District, Santa Paula, 

California. 

Fleming, I. A., K. Hindar, I. B. Mjolnerod, B. Jonsson, T. Balstad, and A. Lamberg. 2000. 

Lifetime success and interactions of farm salmon invading a native population. Proc. 

Roy. Soc. Lond. B 267:1517-1523. 

Ford, M. J. 2002. Selection in captivity during supportive breeding may reduce fitness in the 

wild. Conservation Biology 16: 815-825. 

Goodman, D. 2005. Selection equilibrium for hatchery and wild spawning fitness in integrated 

breeding programs. Canadian Journal of Fisheries and Aquatic Sciences. 62(2): 374-

389.

Goodman, D. 2004. Salmon supplementation: demography, evolution, and risk assessment. 

Pages 217-232 in M. J. Nickum, P. M. Mazik, J. G. Nickum, and D. D. MacKinlay, 

editors. Propagated fish in resource management. American Fisheries Society, 

Symposium 44, American Fisheries Society, Bethesda, Maryland. 

Hallerman, E.M. editor. 2003a. Population genetics: Principles and applications for fisheries 

scientists. American Fisheries Society, Bethesda, MD. 

Hansen, M.M. 2002. Estimating the long-term effects of stocking domesticated trout into 

wildbrown trout (Salmo trutta) populations: an approach using microsatellite DNA 

analysis of historical and contemporary samples. Mol. Ecol. 11:1003-101. 
ISAB 2005-2 ESU Viability 

35 

Healy M.C. 1991. The life history of chinook salmon (Oncorhynchus tshawytscha). In C. Groot 

and L. Margolis (eds), Life history of Pacific salmon, p. 313-393. University of British 

Columbia Press, Vancouver, B.C. 

Hedrick, P. W. 1985. Genetics of populations. 629 pp. Jones and Barlett, Boston. 

Hilborn, R., T.P. Quinn, D.E. Schindler and D.E. Rogers. 2003. Biocomplexity and fisheries 

sustainability. Proc. Natl. Acad. Sci. USA, 100: 6564-6568. 

Hulett, P.L., C.W. Wagemann, and S.A. Leider. 1996. Studies of hatchery and wild steelhead in 

the lower Columbia region. Progress report for fiscal year 1995, report no. RAD 96-01. 

(Available from Washington Department of Fish and Wildlife, 600 Capitol Way North, 

Olympia, Washington 98501-1091). 

ISAB (Independent Scientific Advisory Board). 2003. Review of salmon and steelhead 

supplementation. Northwest Power Planning Council. ISAB, 2003-3. Portland, Oregon. 

255 p. 

ISRP (Independent Scientific Review Panel). 2003. Review of Idaho supplementation studies. 

Northwest Power Planning Council. 2003-8. Portland, OR. 

Jonsson B. and N. Jonsson. 1993. Partial migration: niche shift versus sexual maturation in 

fishes. Rev. Fish Biol. Fisheries 3: 348-365. 

Kingsolver, J. G., D. W. Pfennig, and M. R. Servedio. 2002. Migration, local adaptation and the 

evolution of plasticity. Trends in Ecology and Evolution 17:540-541. 

Lande, R. 1980. Genetic variation and phenotypic evolution during allopatric speciation. 

American Naturalist 116: 463-479. 

Lande, R. and S.J. Arnold. 1983. The measurement of selection on correlated characters. 

Evolution 37: 1210-1226. 

Lieder, S.A., P.L. Hulett, J.J. Loch, and M.W. Chilcote. 1990. Electrophoretic comparison of the 

reproductive success of naturally spawning transplanted and wild steelhead trout through 

the returning adult stage. Aquaculture 88: 239-252. 

Lucas, R. E. 1985. Recovery of game fish populations impacted by the May 18, 1980 eruption 

of Mount St. Helens. Part I. Recovery of winter-run steelhead in the Toutle River 

watershed. Washington Department of Game, Fishery Management Report 85-9A, 

Olympia, Washington. 

Lynch, M. and M. O'Healy. 2001. Captive breeding and the genetic fitness of natural 

populations. Conservation Genetics 2: 363-378. 
ISAB 2005-2 ESU Viability 

36 

Mace, G. M. and S. N. Stuart. 1994. Draft IUCN red list categories, version 2.2. Species 21-

22:13-24. 

Maquire, L., and J. F. Cochrane. 2001. Expert opinion. Pages 100 – 118. in Andelman, S. J., S. 

Beissinger, J. F. Cochrane, L. Gerber, P. Gomex-Priego, C. Groves, J. Haufler, R. 

Holthausen, D. Lee, L. Maguire, B. Noon, K. Ralls, and H. Regan. Scientific standards 

for conducting viability assessments under the National Forest Management Act: report 

and recommendations of the NCEAS working group. National Center for Ecological 

Analysis and Synthesis, Santa Barbara, CA. 160pp. http://www.nceas.ucsb.edu/nceasweb/3960/NCEASviabilityfinalreport1201.pdf. 

Marcot, B. G., R. S. Holthausen, M. G. Raphael, M. Rowland, and M. Wisdom. 2001. Using 

Bayesian belief networks to evaluate fish and wildlife population viability under land 

management alternatives from an environmental impact statement. Forest Ecology and 

Management 153:29-42. 

McElheny, P., M.H. Ruckelshaus, M.J. Ford, T.C. Wainwright, and E.P. Bjorkstedt. 2000. 

Viable salmonid populations and the recovery of evolutionarily significant units. U.S. 

Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-42, 156 p. 

Meka, J.M., E.E. Knudsen, D.C. Douglas, and R.B.Benter. 2003. Variable migratory patterns of 

different adult rainbow trout life history types in a southwest Alaska watershed. Trans. 

Am. Fish. Soc., 132: 717-732. 

Musick, J. A. 1999. Criteria to define extinction risk in marine fishes. Fisheries 24:6-12. 

Myers, J., C. Busack, D. Rawding, and A. Marshall. 2003. Historical population structure of 

Willamette and Lower Columbia River Basin Pacific salmonids. WLC-TRT Report. 

NOAA Fisheries Northwest Fisheries Science Center. Seattle WA. 

Meyers, L. A., and J. J. Bull. 2002. Fighting change with change: adaptive variation in an 

uncertain world. Trends in Ecology and Evolution 17:551-557. 

Narum, S.R., C. Contor, A. Talbot, and M.S. Powell. 2004. Genetic divergence of sympatric 

resident and anadromous forms of Oncorhynchus mykiss in the Walla Walla River, 

U.S.A. J. Fish Biol., 65: 471-488. 

Neave, F. 1944. Racial characteristics and migratory habits in Salmo gairdneri. Journal of the 

Fisheries Research Board of Canada 6: 245-251. 

NOAA Fisheries. 2003. Updated status of Federally listed ESUs of West Coast salmon and 

steelhead. West Coast Salmon Biological Review Team. NOAA Fisheries Northwest and 

Southwest Fisheries Science Centers. July 31, 2003. 
ISAB 2005-2 ESU Viability 

37 

NOAA Fisheries. 2004a. Artificial Propagation Evaluation Workshop Report. NOAA Fisheries, 

Northwest Region, Protected Resources Division. May 18, 2004. Available on the 

internet at: www.nwr.noaa.gov/1srd/Prop_Determins/

NOAA Fisheries. 2004b. Salmonid Hatchery Inventory and Effects Evaluation Report. NOAA 

Fisheries Northwest Region Salmon Recovery Division. May 18, 2004. Available on the 

internet at: www.nwr.noaa.gov/1srd/Prop_Determins/. 

Noss, F.R. 1990. Indications for monitoring biodiversity: a hierarchical approach. Conservation 

Biology 4: 355-364. 

Pascual, M., P. Bentzen, C. Riva Rossi, G. Mackey, M. T. Kinnison and R. Walker. 2001. First 

documented case of anadromy in a population of introduced rainbow trout in Patagonia, 

Argentina. Transactions of the American Fisheries Society 130: 53-67. 

Pavlov, D. S., K. A. Savvaitova, K. V. Kuzischin, M. A. Gruzdeva, S. D. Pavlov, B. M. 

Mednikov, and S. V. Maksimov. 2001. The Pacific noble salmon and trouts of Asia. 

Scientific World, Moscow. ISBN 5-89176-115-7. 200 p. 

Phelps, S. R. et al. 1997. Genetic analysis of Washington steelhead: preliminary results 

incorporating 36 new collections from 1995 and 1996. Olympia, Washington 

Department of fish and Wildlife, Fish Management Program, Progress Report. 

Quinn, T. P, L. Wetzel, S. Bishop, K. Overberg, and D. E. Rogers. 2001. Influence of breeding 

habitat on bear predation and age at maturity and sexual dimorphism of sockeye salmon 

populations. Canadian Journal of Zoology 79: 1782-1793. 

Reisenbichler, R. R., S. P. Rubin, L. Wetzel, and S. R. Phelps. 2004. Natural selection after 

release from a hatchery leads to domestication in steelhead, Oncorhynchus mykiss.. 

Pages 371-383. in K. M. Leber, H. L. Blankenship, and S. Kitada, editors. Stock 

enhancement and sea ranching: developments, opportunities and pitfalls. Blackwell 

Scientific Publication Ltd., Oxford, UK. 

RSRP 2004. Report from meeting of August 30 – September 2, 2004. 

http://www.nwfsc.noaa.gov/trt/rsrp.htm 

Taylor, E.B. 1991. A review of local adaptation in salmonidae with particular reference to 

Pacific and Atlantic salmon. Aquaculture, 98: 185-207 

Thrower F.P., J.J. Hard and J.E. Joyce. 2004. Genetic architecture of growth and early lifehistory transitions in anadromous and derived freshwater populations of steelhead. J. Fish 

Biol. 65: 286-307. 

Waples, R.S. 1991. Pacific salmon, Oncorhynchus spp., and the definition of “species” under the 

Endangered Species Act. Mar. Fish Rev. 53:11-21. 
ISAB 2005-2 ESU Viability 

38 

Waples, R.S. 1995. Evolutionarily significant units and the conservation of biological diversity 

under the Endangered Species Act. In J.L. Nielsen (ed), Evolution and the Aquatic 

Ecosystem: Defining unique units in population conservation. Am. Fish. Soc. Symp. 

17:8-27. 

Wood, C. C. 1995. Life history variation and population structure in sockeye salmon. Pages 195 

– 216 in J. L. Nielsen, editor. Evolution and the aquatic ecosystem: defining unique units 

in population conservation. American Fisheries Society Symposium 17, Bethesda, 

Maryland. 

Zimmerman, C. E. and G. H. Reeves. 2000. Population structure of sympatric anadromous and 

nonanadromous Oncorhynchus mykiss: evidence from spawning surveys and otolith 

microchemistry. Canadian Journal of Fisheries and Aquatic Sciences 57: 2152-2162. 

________________________________________ 

w:\em\ww\isab projects and reports\1 isab final reports\isab 2005-2 esu viability.doc