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This document is available to the public through:

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161
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EXECUTIVE SUMMARY

The Endangered Species Act (ESA) allows listing of “distinct population segments” of

vertebrates as well as named species and subspecies. The policy of the National Marine Fisheries

Service (NMFS) on this issue for anadromous Pacific salmonids is that a population will be

considered “distinct” for purposes of the ESA if it represents an evolutionarily significant unit

(ESU) of the species as a whole. To be considered an ESU, a population or group of populations

must 1) be substantially reproductively isolated from other populations, and 2) contribute

substantially to ecological/genetic diversity of the biological species. Once an ESU is identified,

a variety of factors related to population abundance are considered in determining whether a

listing is warranted.

In March 1994, in response to a petition seeking protection under the ESA for two

populations of pink salmon in Washington State, NMFS initiated a status review of pink salmon

in Washington, Oregon, and California, and formed a Biological Review Team (BRT) to conduct

the review. This report summarizes biological and environmental information gathered in that

process.

Proposed Pink Salmon ESUs

Pink salmon (Oncorhynchus gorbuscha) spawn around the Pacific Rim from 44oN to

65oN in Asia and from 48oN to 64oN in North America. Washington appears to be the southern

limit of the spawning distribution of pink salmon in North America; no persistent populations of

pink salmon have been documented in Oregon or California, and pink salmon do not occur in

Idaho. The BRT examined genetic, life history, biogeographic, physiographic, and environmental

information to identify where ESU boundaries for pink salmon should be located. Patterns of

genetic differentiation and life history in pink salmon were found to be the most informative for

this process. Based on this examination, the BRT identified two pink salmon ESUs in

Washington and southern British Columbia. These ESUs, which largely reflect the distinction

between even- and odd-year broodlines that are characteristic of pink salmon throughout their

natural range, are described as follows:

1) Even-year pink salmon. The only persistent population of even-year pink salmon in

Washington occurs in the Snohomish River. Although several attempts were made in this century

to transplant even-year pink salmon from Alaska and British Columbia to the Puget Sound

region, there is no indication that these attempts were successful. Furthermore, life history and

genetic information for Snohomish River even-year pink salmon is consistent with the hypothesis

that this population resulted from a natural colonization event. The nearest even-year pink

salmon populations occur in British Columbia, at least 130-150 km away. On the basis of

available information, the BRT could not resolve with any degree of certainty the extent of the

ESU that contains the Snohomish River even-year pink salmon population. After considering all
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available information, about half of the BRT members concluded that the Snohomish River

even-year population is in an ESU by itself, whereas half judged that the ESU also included

populations from British Columbia. In any case, the BRT unanimously agreed that any

conclusion about the extent of the even7year pink salmon ESU should be regarded as provisional

and subject to revision should substantial new information become available.

2) Odd-year pink salmon. The BRT considered several possible ESU scenarios for

odd-year pink salmon. The majority of BRT members concluded that all odd-year pink salmon

populations in Washington are part of a single ESU. This ESU includes populations in

Washington as far west as the Dungeness River (or the Elwha River, if that population is not

already extinct) and in southern British Columbia (including the Fraser River and eastern

Vancouver Island) as far north as Johnstone Strait. A minority of BRT members concluded that

populations from Washington rivers draining into the Strait of Juan de Fuca are members of a

separate ESU. All members agreed that, collectively, odd-year pink salmon in Washington

contain a considerable amount of genetic and life history diversity, with populations from the

Dungeness, Nooksack, and Nisqually Rivers being the most distinctive in this regard. Several

small odd-year populations occur on southwestern Vancouver Island, but little information is

available to ascertain the relationship of these populations to the proposed odd-year ESU.

Additional information on these populations is needed to resolve the question of whether

odd-year pink salmon in Washington and southern British Columbia are in one or more ESUs.

Assessment of Extinction Risk

The ESA (section 3) defines the term “endangered species” as “any species which is in

danger of extinction throughout all or a significant portion of its range.” The term “threatened

species” is defined as “any species which is likely to become an endangered species within the

foreseeable future throughout all or a significant portion of its range.” According to the ESA, the

determination whether a species is threatened or endangered should be made on the basis of the

best scientific information available regarding its current status, after taking into consideration

conservation measures that are proposed or are in place. In this review, the BRT did not evaluate

likely or possible effects of conservation measures and, therefore, did not make

recommendations as to whether identified ESUs should be listed as threatened or endangered

species; rather, the BRT drew scientific conclusions about the risk of extinction faced by

identified ESUs under the assumption that present conditions will continue. The resulting

conclusions for each ESU follow.

1) Even-year pink salmon. The BRT was unanimous in concluding that this ESU is not

presently at risk of extinction. Nevertheless, nearly all BRT members expressed concerns about

the status of this ESU. Although available escapement data suggest that the even-year pink

salmon population in the Snohomish River has been increasing since 1980, the low abundance

and isolation of this population--when coupled with the lack of variable age structure in pink

salmon--suggest that the population is at some risk due to demographic or environmental
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fluctuations. All BRT members agreed that this population should be closely monitored, even if it

is determined to be part of a larger ESU.

2) Odd-year pink salmon. The BRT was unanimous in concluding that this ESU as a

whole is not presently at risk of extinction. Most populations appear to be healthy, and overall

abundance appears to be close to historical levels. The two most distinctive Puget Sound

populations (from the Nooksack and Nisqually Rivers) both show nonsignificant trends in recent

abundance, and no other factors were found that would suggest that either of these populations is

at immediate risk. However, most BRT members expressed concerns about the status of certain

populations within this ESU. For odd-year pink salmon, two of the three U.S. populations along

the Strait of Juan de Fuca are in steep decline, and the third may already be extinct. The

population nearest to these three occurs in northern Hood Canal and, is also declining. However,

the remaining odd-year populations in the United States, as well as most of those in southern

British Columbia, show no evidence of sustained declines, and many are increasing in

abundance. In addition, the other U.S. populations that are the most distinctive based on genetic

and life history characteristics appear to be healthy. The majority of BRT members therefore

concluded that the odd-year pink salmon ESU is not presently at risk of extinction or

endangerment. However, BRT members unanimously expressed concern about the status of the

marginal populations along the Strait of Juan de Fuca, and concern that further erosion of these

populations might eventually pose risk to a significant portion of the ESU as a whole. In

addition, evidence exists for a recent decline in body length of odd-year Washington pink

salmon, which increases risk to these populations by limiting their ability to respond to

perturbation. A similar decline has also been observed in pink salmon from southeastern Alaska.
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ACKNOWLEDGMENTS

The status review for west coast pink salmon was conducted by a team of researchers

from the National Marine Fisheries Service (NMFS). This biological review team relied on

information in the Endangered Species Act Administrative Record for West Coast Pink Salmon,

which was developed pursuant to this review and includes comments, data, and reports submitted

by the public and by state, tribal, and federal agencies. The authors acknowledge the efforts of all

who contributed to this record, especially the Washington Department of Fish and Wildlife,

Oregon Department of Fish and Wildlife, California Department of Fish and Game, U.S. Fish

and Wildlife Service, and Northwest Indian Fisheries Commission.

In addition, the authors are grateful to several fishery scientists and managers for

assembling and providing information that aided the development of this report and for providing

critical reviews of our analyses of this information. Much of the information provided was

previously unpublished and represents the most comprehensive body of biological information

available on pink salmon in North America south of Alaska and northern British Columbia.

Several of these scientists and managers provided their . recommendations on the reliability and

utility of this information. In particular, the authors thank Jim Ames, Don Hendrick, Dr. James

Shaklee, Jim Uehara, and Sewall Young of the Washington Department of Fish and Wildlife;

Gary Graves and Keith Lutz of the Northwest Indian Fisheries Commission; Dr. Anthony

GharTett and Dr. William Smoker of the University of Alaska; Dr. Terry Beacham, LeRoy Hop

Wo, and Wilf Luedke of the Canadian Department of Fisheries and Oceans; and Frank Thrower

of the NMFS Alaska Fisheries Science Center.

The biological review team for this status review included: Dr. Stewart Grant, Dr. Jeffrey

Hard, Dr. Robert Iwamoto, Dr. Orlay Johnson, Dr. Robert Kope, Dr. Conrad Mahnken, Dr.

Michael Schiewe, William Waknitz, Dr. Robin Waples, and Dr. John Williams, all from the

NMFS Northwest Fisheries Science Center (NWFSC), Dr. Peter Dygert from the NMFS

Northwest Region, and William Heard from the Auke Bay Laboratory of NMFS’s Alaska

Fisheries Science Center.

Several NWFSC staff made substantial contributions to the preparation of this status

review. JoAnne Butzerin, Sharon Damkaer, and Dr. Robert Iwamoto edited earlier versions of

this report and made numerous suggestions to improve its presentation. Peggy Busby and Laurie

Weitkamp provided much of the environmental information presented in this review, information

that they collected during their preparation of status reviews. for west coast steelhead and coho

salmon, respectively. Kathleen Neely drafted the maps and assisted in editing the other figures.
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INTRODUCTION

Scope and Intent of the Present Document

Pink salmon (Oncorhynchus gorbuscha) is a widespread species of Pacific salmon,

occurring regularly in most major river basins around the Pacific Rim from Washington State

to North Korea, and occasionally in rivers as far south as northern California and the Japanese

island of Hokkaido (Heard 1991). Recently published investigations have reported that

several local populations of pink salmon in Washington and California have become extinct

or are at high risk of extinction, and that the abundance of others is depressed (e.g., Nehlsen

et al. 1991, Moyle et al. 1995). These declines led to a petition to the National Marine

Fisheries Service (NMFS) to list populations of pink salmon as threatened or endangered

“species” under the U.S. Endangered Species Act (ESA; technical terms and abbreviations

such as “ESA” are defined in the glossary in the Appendix). Under the ESA, the term

“species” is defined rather broadly to include subspecies and “distinct population segments”

of vertebrates (such as salmon) as well as taxonomic species.

The National Marine Fisheries Service was petitioned in March 1994 by the

Professional Resources Organization-Salmon (PRO-Salmon) to list Elwha River and fall-run

Dungeness River pink salmon as threatened or endangered species under the ESA (PROSalmon 1994). At about the same time, NMFS also received petitions for several additional

populations of Pacific salmon in the Puget Sound area. In response to these petitions and the

more general concerns for the status of Pacific salmon throughout the region, NMFS (1994)

announced that it would initiate ESA status reviews for all species of anadromous Pacific

salmonids. These comprehensive reviews will consider all populations in the states of

Washington, Oregon, California, and Idaho and are scheduled for completion in 1996. This

proactive approach should facilitate more timely, consistent, and comprehensive evaluation of

the ESA status of Pacific salmonids than would be possible through a long series of reviews

of individual populations.

This document considers environmental and biological information for pink salmon

populations in Washington, Oregon, California, and southern British Columbia (Fig. 1).

These populations will be collectively referred to in this document as west coast pink salmon.

The scope of this review thus encompasses, but is not restricted to, the two populations

identified in the PRO-Salmon (1994) petition.

Because the ESA stipulates that listing determinations should be made on the basis of

the best scientific information available, NMFS formed a team of scientists with diverse

backgrounds in salmon biology to conduct this review. This Biological Review Team (BRT)

discussed and evaluated scientific information presented at two public meetings held in

Seattle in December 1994 and February 1995 as well as information gathered independently

by the authors of this report. The BRT also reviewed additional information submitted to the

ESA administrative record for pink salmon. This document represents the findings and

conclusions of the BRT on the status of west coast pink salmon under the ESA.
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Figure 1. Range of pink salmon populations considered in this status review. Marine

abundance patterns modified from Bonar et al. (1989).
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Key Questions in ESA Evaluations

In determining whether a listing under the ESA is warranted, two key questions must

be addressed:

1) Is the entity in question a “species” as defined by the ESA?

2) If so, is the “species” threatened or endangered?

These two questions are addressed in separate sections of this report. If it is determined that a

listing(s) is warranted, then NMFS is required by law (1973 ESA Sec. 4(a)(1)) to identify one

or more of the following factors responsible for the species’ threatened or endangered status:

1) destruction or modification of habitat; 2) overutilization by humans; 3) disease or

predation; 4) inadequacy of existing regulatory mechanisms; or 5) other natural or human

factors. This status review does not formally address factors for decline, except insofar as

they provide information about the degree of risk faced by the species in the future.

The “Species” Question

As amended in 1978, the ESA allows listing of “distinct population segments”, of

vertebrates as well as named species and subspecies. However, the ESA provides. No

specific guidance for determining what constitutes a distinct population, and the resulting

ambiguity has led to the use of a variety of approaches for considering vertebrate populations.

To clarify the issue for Pacific salmon, NMFS published a policy describing how the agency

will apply the definition of “species” in the ESA to anadromous salmonid species, including

sea-run cutthroat trout and steelhead (NMFS 1991). A more detailed discussion of this topic

appeared in the NMFS “Definition of Species” paper (Waples 1991a). The NMFS policy

stipulates that a salmon population (or group of populations) will be considered “distinct” for

purposes of the ESA if it represents an evolutionarily significant unit (ESU) of the biological

species. An ESU is defined as a population that 1) is substantially reproductively isolated

from conspecific populations and 2) represents an important component of the evolutionary

legacy of the species.

The term “evolutionary legacy” is used in the sense of “inheritance”--that is,

something received from the past and carried forward -into the- future. Specifically, the

evolutionary legacy of a species is the genetic variability that is a product of past evolutionary

events and that represents the reservoir upon which future evolutionary potential depends.

Conservation of these genetic resources should help to ensure that the dynamic process of

evolution will not be unduly constrained in the future.

The NMFS policy identifies a number of types of evidence that should be considered

in the species determination. For each of the two criteria (reproductive isolation and

evolutionary legacy), the NMFS policy advocates a holistic approach that considers all types

of available information as well as their strengths and limitations. Isolation does not have to

be absolute, but it must be strong enough to permit evolutionarily important differences to
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accrue in different population units. Important types of information to consider include

natural rates of straying and recolonization, evaluations of the efficacy of natural barriers, and

measurements of genetic differences between populations. Data from protein electrophoresis

or DNA analyses can be particularly useful for this criterion because they reflect levels of

gene flow that have occurred over evolutionary time scales.

The key question with respect to the second criterion is, If the population became

extinct, would this represent a significant loss to the ecological/genetic diversity of the

species? Again, a variety of types of information should be considered. Phenotypic and life

history traits such as size, fecundity, migration patterns, and age and time of spawning may

reflect local adaptations of evolutionary importance, but interpretation of these traits is

complicated by their sensitivity to environmental conditions. Data from protein

electrophoresis or DNA analyses provide valuable insight into the process of genetic

differentiation among populations but little direct information regarding the extent of adaptive

genetic differences. Habitat differences suggest the possibility for local adaptations but do not

prove that such adaptations exist.

The “Extinction Risk” Question

The ESA (section 3) defines the term “endangered species” as “any species which is

in danger of extinction throughout all or a significant portion of its range.” The term

“threatened species” is defined as “any species which is likely to become an endangered

species within the foreseeable future throughout all or a significant portion of its range.”

NMFS considers a variety of information in evaluating the level of risk faced by an ESU.

Important considerations include 1) absolute numbers of fish and their spatial and temporal

distribution; 2) current abundance in relation to historical abundance and carrying capacity of

the habitat; 3) trends in abundance, based on indices such as dam or redd counts or on

estimates of recruit-to-spawner ratios; 4) natural and human-influenced factors that cause

variability in survival and abundance; 5) possible threats to genetic integrity (e.g., selective

fisheries and interactions between hatchery and natural fish); and 6) recent events (e.g., a

drought or a change in management) that have predictable short-term consequences for

abundance of the ESU. Additional risk factors, such as disease prevalence or changes in life

history traits, may also be considered in evaluating risk to populations.

According to the ESA, the determination of whether a species is threatened or

endangered should be made on the basis of the best scientific information available regarding

its current status, after taking into consideration conservation measures that are proposed or

are in place. In this review, we do not evaluate likely or possible effects of conservation

measures. Therefore, we do not make recommendations as to whether identified ESUs should

be listed as threatened or endangered species, because that determination requires evaluation

of factors not considered by us. Rather, we have drawn scientific conclusions about the risk of

extinction faced by identified ESUs under the assumption that present conditions will

continue (recognizing, of course, that natural demographic and environmental variability is an

inherent feature of “present conditions”).
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Artificial Propagation

NMFS policy (Hard et al. 1992, NMFS 1993) stipulates that in determining 1)

whether a population is distinct for purposes of the ESA, and 2) whether an ESA species is

threatened or endangered, attention should focus on “natural” fish, which are defined as the

progeny of naturally spawning fish (Waples 1991a). This approach directs attention to fish

that spend their entire life cycle in natural habitat and is consistent with the mandate of the

ESA to conserve threatened and endangered species in their native ecosystems. Implicit in

this approach is the recognition that fish hatcheries are not a substitute for natural ecosystems.

Nevertheless, artificial propagation is important to consider in ESA evaluations of

anadromous Pacific salmonids for several reasons.

First, although natural fish are the focus of ESU determinations, possible effects of

artificial propagation on natural populations must also be evaluated. For example, stock

transfers might change the genetic or life history characteristics, of a natural population in

such a way that the population might seem either less or more distinctive than it was

historically. Artificial propagation can also alter life history characteristics such as smolt age

and migration and spawn timing.

Second, artificial propagation poses a number of risks to natural populations that may

affect their risk of extinction or endangerment. These risks are discussed below in the

Assessment of Extinction Risk section. In contrast to most other types of risk for salmon

populations, those arising from artificial propagation are often not reflected in traditional

indices of population abundance. For example, to the extent that habitat degradation,

overharvest, or hydropower development have contributed to a population’s decline, these

factors will already be reflected in population abundance data and accounted for in the risk

analysis. The same is not true of artificial propagation. Hatchery production may mask

declines in natural populations that will be missed if only raw population abundance data are

considered. Therefore, a true assessment of the viability of natural populations cannot be

attained without information about the contribution of naturally spawning hatchery fish.

Furthermore, even if such data are available, they will not in themselves provide direct

information about possibly deleterious effects of fish culture. Such an evaluation requires

consideration of the genetic and demographic risks of artificial propagation for natural

populations. The sections on artificial propagation in this report are intended to address these

concerns.

Finally, if any natural populations are listed under the ESA, then it will be necessary to

determine the ESA status of all associated hatchery populations. This latter determination

would be made following a proposed listing and is not considered further in this document.
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Summary of Information Presented by the Petitioner

This section briefly summarizes information presented by the petitioner (PRO-Salmon

1994) to support its arguments that two populations of pink salmon on Washington’s Olympic

Peninsula qualify as a threatened or endangered species under the ESA. We discuss this

information and related issues in the following sections, and we evaluate the status of west

coast pink salmon in the conclusions of the Assessment of Extinction Risk section.

Distinct Population Segments

A petition to list two pink salmon populations as protected species under the ESA was

received by NUFS from PRO-Salmon on 14 March 1994. The status of these two

populations, in the lower Dungeness River and the Elwha River, was characterized as

“critical” by WDF et al. (1993). In the planned revision of the Washington State Salmon and

Steelhead Stock Inventory (SASSI), the Washington Department of Fish and Wildlife

(WDFW) is likely to recommend that Elwha River pink salmon be reclassified as extinct (J.

Ames1

). Both petitioned populations are odd-year populations that spawn or have spawned in

systems draining into the Strait of Juan de Fuca from the northern side of the Olympic

Peninsula. No other rivers along the Strait of Juan de Fuca appear to support persistent pink

salmon populations (Williams et al. 1975, WDF et al. 1993).

With respect to the two criteria established by NMFS to define a “species” of Pacific

salmon, the petitioner argued that the lower Dungeness and Elwha River populations of pink

salmon were both reproductively isolated from other pink salmon populations. Reproductive

isolation was inferred primarily on the basis of distance to nearest neighboring population; for

lower Dungeness River pink salmon, this distance is approximately 10 km (to the upper

Dungeness River population), and for Elwha River pink salmon, this distance is about 25 km

(to the lower Dungeness River population). According to the petitioner, genetic data, in the

form of allozyme variation, support a hypothesis for at least partial reproductive isolation of

the lower Dungeness River population (Shaklee et al. 1991), but no genetic data exist for the

Elwha River population (VIDF et al. 1993, J. Shaklee2

).

In its petition, PRO-Salmon provided little information that addresses the

“evolutionary significance” criterion. The petitioner argued that spatial and temporal isolation

of the lower Dungeness River population from the upper Dungeness River population, due to

differences in run timing and spawning location, contribute to the distinctiveness of the lower

1

J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., January 1995.

2

J. Shaklee, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., November 1994.
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river population. No quantitative data are available to support a hypothesis for the

distinctiveness of the Elwha River population.

Population Abundance

The petitioner noted that the run size for lower Dungeness River pink salmon declined

from about 11,000 spawners per year between 1969 and 1979 to 6,600 fish in 1981, following

severe flooding in January 1980. (The recorded historical high was 210,000 fish in 1963).

Recent abundance has ranged from less than 150 to more than 750 spawners, about 5% of

pre-flood levels and 0.1% of the historic high (WDF et al. 1993, PRO-Salmon 1994). The run

size for Elwha River pink salmon crashed from about 4,800 spawners per year (1969-79) to

an estimated 200 fish or less since 1981, following severe flooding in January 1980. (The

recorded historical high was 40,000 fish in 1963.) Since 1981, less than 35 pink salmon have

been observed in the Elwha River over all of the odd-numbered years combined, and only 4

have been observed since 1989 (PRO-Salmon 1994, J. Uehara3).

Causes of Decline for Pink Salmon

The petition identified several threats to the viability of lower Dungeness River pink

salmon: water withdrawals from the lower river during the holding and spawning periods in

late summer and fall, habitat degradation due to increased urbanization along the river, diking

for flood control, and possible sewage contamination. Any or all of these factors may be

inhibiting natural recovery of pink salmon. In addition, timber harvest near the river and

artificial propagation of coho salmon at Dungeness Hatchery may impede recovery (PROSalmon 1994; Hiss 1994, 1995).

Finally, harvest in mixed-stock fisheries, especially in fisheries that target Fraser River

pink salmon in the Strait of Juan de Fuca, may limit the ability of this population to recover

naturally (estimated total exploitation rate on the lower Dungeness River population = 47%,

PRO-Salmon 1994). The petitioner suggested that similar factors threaten the viability of

Elwha River pink salmon, although urbanization and timber harvest are apparently less

significant factors in this drainage, and hatchery production on the river includes chinook

salmon and steelhead as well as coho salmon. Unlike the Dungeness River, the Elwha River

is obstructed by two dams, the Elwha and Glines Canyon Dams. These structures prevented

access by pink salmon to 35 km of the river early in this century, and pink salmon spawning

is currently limited to the lowest 5 km of the river. However, the petitioner noted that the

Elwha River population did not decline to extremely low levels until the late 1970s (PROSalmon 1994). Nevertheless, based on the petitioner’s information, the abundance of this

population apparently has been depressed since at least the late 1960s.

3

J. Uehara, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., February 1996.
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INFORMATION RELATING TO THE SPECIES QUESTION

Environmental Features

The spawning populations of west coast pink salmon that are the focus of this review

are presently distributed over a small region of the contiguous 48 United States, in

northwestern Washington from its border with British Columbia (49°N) south to the

Nisqually River (48°N) in southern Puget Sound. Although climatic features do not vary

markedly in this region, diverse patterns of vegetation, weather, soils, and water quality exist

there. This section summarizes environmental and biological information relevant to

determining the nature and extent of ESUs for pink salmon in this region (see also Weitkamp

et al. 1995).

Physiography and Geology

Pink salmon inhabit areas in northwestern Washington and southern British Columbia

that are represented by several physiographic regions: the Coast Range Province, which

extends in the United States from the Strait of Juan de Fuca southward to the Klamath

Mountains and from the Pacific Ocean eastward to the lowlands west of the Cascade

Mountains, and in Washington includes the Olympic Mountains and Willapa Hills; the PugetWillamette Lowland, which covers Puget Sound and the Willamette River Valley in the

United States; the Coast Mountains of British Columbia, which include in Washington the

Cascades North and Cascades South areas; the Coastal Trough, which covers the area

surrounding the Strait of Georgia and Johnstone Strait; and the Outer Mountains of

Vancouver Island (McKee 1972, Lasmanis 1991). These regions are geologically diverse.

Most of the encompassed area, with the exception of the Olympic Mountains and higher

elevations in the Cascade Mountains, was glaciated during the Pleistocene Epoch (Booth

1987).

As a result of Pleistocene glaciation, the Puget Sound lowlands contain a thick layer

of moraine. The North Cascades along northern Puget Sound and southwestern British

Columbia are composed of a wide spectrum of metamorphic rock types. Like the Olympic

Peninsula, the coastal mountains of British Columbia are com. posed of basalt and

sedimentary rock as well as volcanic and nonvolcanic rock (McKee 1972). The most unique

aspect of the Olympic Peninsula is its massive foundation of marine basaltic flow (McKee

1972). The northern coastal area where pink salmon presently spawn has been heavily

influenced by marine sedimentation, as have other lowland areas in the region. In present-day

Washington and southern British Columbia, the lowlands surrounding Puget Sound probably

have the most complex hydrologic history because of their repeated exposures to alternating

glaciation and deposition of marine sediment.
9

Temperature, Precipitation, and Hydrology

Climate varies primarily with latitude along the west coast of North America, and this

region exhibits south-to-north gradients of increasing average precipitation and declining

average temperature. The coastal region has a mild climate with warm, relatively dry

summers and cool, wet winters.

Pink salmon typically enter fresh water and spawn at a time of year when streamflow

is low and water temperature is relatively high. Streamflows are lowest in August and

September, and there is some tendency for streamflows to reach their lowest points later in

rivers on the Strait of Juan de Fuca and in Hood Canal than in systems on Puget Sound. Water

temperatures in northwestern Washington are generally highest in July and August

(Hydrosphere Data Products, Inc. 1993). Because run timing and spawn timing are sensitive

to these factors, streamflow patterns determine the temporal availability and suitability of

spawning and incubation habitat for pink salmon.

The Olympic Peninsula is much wetter (160-380 cm precipitation/yr) than the rest of

Washington, with considerable snowfall (over 150 cm/yr) at higher elevations. The abundant

precipitation results at least partially from the relatively high elevation of the Olympic

Mountains (1,000-2,000 m). Persistent spawning populations of pink salmon are found only

in watersheds draining the northern and eastern sides of the Peninsula. Maximum and

minimum air and water temperatures are cooler in the Olympic Peninsula than farther south,

reflecting effects of both latitude and elevation. Annual maximum and minimum water

temperatures are 10°C to 14°C and 2°C to 4°C, respectively, whereas annual maximum and

minimum air temperatures are approximately 21°C and 2°C, respectively.

The wet climate of the Olympic Peninsula continues north along the west coast of

Vancouver Island and along the British Columbia mainland north of Vancouver Island.

Limited hydrographic data (Farley 1979) indicate that water-flow patterns in this area are

similar to those on the Olympic Peninsula, with relatively high flows throughout the year.

Summer air temperatures generally decrease with increasing latitude--the Olympic coast is a

few degrees warmer than the southwestern coast of Vancouver Island, which is a few degrees

warmer than the northwestern coast and the mainland north of Vancouver Island.

A smaller gradient of decreasing average precipitation exists from west to east in

northwestern Washington. East of the Olympic Peninsula, precipitation rapidly decreases

because of the rainshadow caused by the Olympic and Vancouver Island Mountains to the

north, and the Willapa Hills to the south. The rainshadow, which becomes apparent along the

northern coastline of the Peninsula west of the Elwha River, continues through lowland Puget

Sound, up the lowlands bordering the Strait of Georgia, to the south end of Queen Charlotte

Strait. Most Washington streams that support pink salmon are found in Puget Sound. Most of

this area receives less than 120 cm rain per year, with some areas receiving as little as 50 cm

per year (U.S. Dep. Commerce 1968).
10

A slight summer temperature cline appears to exist within the northern rainshadow

region; average maximum air temperatures in Puget Sound and Hood Canal (20°C-24°C) are

slightly higher than those in the Strait of Georgia (16°C-20°C), which in turn are higher than

those in areas inside Vancouver Island farther north (14°C-16°C). In contrast, winter air

temperatures are more uniform and average 0°C-5°C throughout the area. Stream

temperatures in the area are generally cool, with a maximum of 12°C-20°C in summer and

0°C-4°C in winter (Hydrosphere Data Products, Inc. 1993).

Marine Upwelling

No major variations in upwelling patterns occur along the coasts of British Columbia

and Washington (Smith 1983, Landry et al. 1989). Upwelling in this region is primarily wind

driven (Bakun 1973, 1975; Thompson 1981). One exception to this pattern has been observed

off the southwestern comer of Vancouver Island where consistent and strong upwelling

appears to occur throughout the year (Denman et al. 1981). Upwelling in this area is thought

to be caused by current-driven as well as wind-driven events, a condition that leads to relative

temporal and spatial stability.

Vegetation

Vegetation patterns in Washington and southern British Columbia are affected by

precipitation gradients. Coastal regions in Washington and British Columbia are forested with

a Sitka spruce (Picea sitchensis)-dominated floral community, which also includes western

hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), red alder (Alnus rubra), and

Douglas fir (Pseudotsuga menziesii) as major species. This vegetation type is restricted to

coastal regions and river valleys extending a few kilometers inland over coastal plains, and to

elevations above 150 m in areas immediately adjacent to the ocean (Franklin and Dyrness

1973).

Sitka spruce forests are replaced by western hemlock-dominated forests along the

Strait of Juan de Fuca to the north and east. This vegetation type also includes western

hemlock, Douglas fir, red alder, and western red cedar. The transition between Sitka spruce

and western hemlock along the Strait of Juan de Fuca occurs at about the Elwha River on the

Olympic Peninsula and Sooke Inlet on Vancouver Island. Be-cause of Puget Sound’s lower

precipitation and glacial soils, drought-tolerant western white (Pinus monticola), lodgepole

(Pinus contorta), and occasionally ponderosa (Pinus ponderosa) pines, occur more frequently

here than elsewhere in the western hemlock zone.

Zoogeography

Along the east coast of the North Pacific Ocean within the range considered in this

status review, a distinct faunal boundary for marine fishes occurs off the northern tip of

Vancouver Island (approximately 50°N) (Allen and Smith 1988). Within the range of pink

salmon in the Pacific Northwest, only one major freshwater ichthyogeographic region has
11

been described: the Columbia (McPhail and Lindsey 1986, Minckley et al. 1986). Thus, no

pattern of variation in marine fishes associated with pink salmon is evident in Washington

and southern British Columbia.

Estuarine fish assemblages show regional differences based on presence or absence of

species, but only a single group exists in northwestern Washington (Monaco et al. 1992). This

group, the Fjord Group, occurs within inland estuaries of Puget Sound and Hood Canal. Other

estuary groupings are less evident and seem to depend more on characteristics of individual

estuaries than on geographic location.

The distribution of marine invertebrates shows transitions between major faunal

communities similar to those of marine fishes (Hall 1964, Valentine 1966, Hayden and Dolan

1976, Brusca and Wallerstein 1979). The primary cause of this zonation has been attributed to

geographic variation in temperature (Hayden and Dolan 1976), but other abiotic (Valentine

1966) and biotic (Brusca and Wallerstein 1979) factors may also influence invertebrate

distribution patterns.

The distributions of many amphibians appear to begin and end at several common

geographical areas within the range of pink salmon in Washington; the Strait of Georgia and

Vancouver Island are the northern extent of many amphibian distributions (tailed, Ascaphus

truei, and red-legged, Rana aurora, frogs; Pacific giant, Dicamptodon ensatus, western

longtoed, Ambystoma m. macrodactylum, western red-backed, Plethodon vehiculum, Oregon

slender, Batrachoseps wrighti, and brown, Ambystoma g. gracile, salamanders) (Cook 1984).

In addition, several amphibians are restricted to the Olympic Peninsula (Olympic torrent,

Rhyacotriton olympicus, and Van Dyke’s, Plethodon vandykei, salamanders), whereas other

species occur in most areas in western Washington and Oregon except in the Olympic

Peninsula (Pacific giant and Dunn’s, Plethodon dunni, salamanders) (Leonard et al. 1993).

Ecoregions

The U.S. Environmental Protection Agency has developed a system of ecoregion

classification based on perceived patterns of factors such as climate, topography, potential

natural vegetation, and soils (Omernik and Gallant 1986, Omernik 1987). Under this system,

the range of pink salmon in Washington covers two ecoregions that border on salt water: the

“coast range” ecoregion, which extends from the Strait of Juan de Fuca to Monterey Bay,

from the ocean to about the crest of the coastal mountains; and the “Puget lowland”

ecoregion, which begins in Washington at about the Dungeness River near the eastern end of

the Strait of Juan de Fuca and extends through Puget Sound to the British Columbia border.

Summary

The above information indicates that the Olympic Peninsula is environmentally

distinct from the rest of northwestern Washington. However, the gradients in temperature and

precipitation within the range of pink salmon in Washington and southern British Columbia
12

Pink Salmon Life History

Distribution and Life Cycle

Pink salmon occur around the Pacific Rim of Asia and North America north of about

40°N to greater than 70°N (Neave et al. 1967, Takagi et al. 1981). However, the spawning

distribution of pink salmon is much more restricted, ranging from 48°N (Puget Sound,

Washington) to 64ON (Norton Sound, Alaska) in North America and from 44°N (North

Korea) to 65°N (Anadyr Gulf, Russia) in Asia (Heard 1991, Mathisen 1994; Fig. 2). In North

America, pink salmon populations regularly occur in marine waters as far south as

Washington State and spawn in this area as far south as Puget Sound and the Olympic

Peninsula (Williams et al. 1975, WDF et al. 1993; Fig. 1). Between 70 and 80% of the

Washington pink salmon spawning escapement occurs in northern Puget Sound (WDF et al.

1993, Big Eagle & Assoc. and LGL Ltd. 1995).

Pink salmon spawn during the late summer and fall in both large and small rivers;

they prefer clean, coarse gravel in shallow (10-100 cm) pools and riffles exposed to

moderately fast (30-150 cm/s) currents. These fish generally avoid spawning in deep, slowmoving water or on muddy, sandy, or heavily silted substrate (Heard 1991). Water

temperatures during peak spawning activity range from about 5°C to 15°C and are generally

higher in southern populations. This species tends to spawn closer to tidewater than other

species of Pacific salmon, generally within 50 kin of a river mouth (Heard 1991, WDF et al.

1993). However, populations returning to large systems such as the Fraser River and Skeena

River watersheds in British Columbia migrate up to 500 kin upstream to spawn, and a

substantial fraction of other populations may spawn intertidally (Hunter 1959, Noerenberg

1963, Jones 1978). Pink salmon mature at the smallest average size of any species of Pacific

salmon (1.0-2.5 kg) and show marked sexual dimorphism (Davidson 1935, Pritchard 1937,

Beacham and Murray 1985). Spawning populations throughout much of, the range of pink

salmon may be extremely large, often exceeding hundreds of thousands of adult fish (Heard

1991, WDF et al. 1993).

Mortality of juvenile pink salmon in fresh water is high, ranging from about 75% to

over 99%, and most of this mortality occurs before emergence from the gravel (Hunter 1959,

McNeil 1966). Upon emerging from the gravel, pink salmon alevins migrate rapidly

downstream, generally in schools and usually in darkness (Heard 1991). Juveniles grow most

rapidly during their residence in the nearshore marine environment (up to approximately I

mm. per day and 5-6% body weight per day). Preferred prey are small crustaceans, especially

euphausiids, amphipods, and cladocerans (McDonald 1960, Bailey et al. 1975). After a few

weeks to a few months in estuaries and nearshore habitat, pink salmon move offshore, where

are not sharp ones, and, on the basis of the physical and biological factors examined here, the

precise geographic boundary separating these two areas is not well defined.
13
14

they migrate at sea for 12-16 months (Heard 1991). Tagging studies suggest that southern

populations from Washington and British Columbia have a more restricted oceanic migration

than Alaskan populations (Takagi et al. 1981, Ogura 1994; Fig. 3).

Pink salmon do not presently occur in Idaho (Heard 1991); it is unknown whether the

species occurred there historically. Along the coasts of Washington, Oregon, and California,

persistent populations of pink salmon have been documented only in Washington (Ayers

1955, Herrmann 1959, Heard 1991, Mathisen 1994, H. Weeks4

), although pink salmon have

been observed spawning in rivers in central and northern California in the past (Scofield

1916, Evermann and Clark 1931, Snyder 1931, Taft 1938, Smedley 1952, Hallock and Fry

1967). Nehlsen et al. (1991) described pink salmon from the Klamath and Sacramento Rivers

in California as extinct and pink salmon from California’s Russian River as at high risk of

extinction.

Recent observations of pink salmon in California have been rare. No pink salmon

have been observed spawning in the Russian River in recent years, but a few adult fish are

observed occasionally in the Klamath River system (Moyle et al. 1995, P. Moyle5). In the last

20 years, only one fish was observed in the Garcia River, and only one or two fish have been

caught annually for several years in the Klamath River. Over this same period, three male

pink salmon were collected from the American River, and an additional fish was observed

there (Moyle et al. 1995). The capture of seven juvenile pink salmon on the Sacramento-San

Joaquin River system in March 1990 is evidence that some pink salmon spawned successfully

there (Moyle et al. 1995).

Adult pink salmon are rarely observed in Oregon coastal rivers, and none have been

recorded in the last several years (H. Weeks6). Nevertheless, successful spawning of pink

salmon in Oregon has been documented in the past through the collection of juvenile pink

salmon from Yaquina Bay near Newport in the late 1950s (C. Bond7).

Along the north coast of the Olympic Peninsula and on the outer Washington coast,

adult pink salmon are also relatively rare. Small escapements (10-100 adults) have been

4

H. Weeks. Oregon Department of Fish and Wildlife, P.O. Box 59, Portland, OR

97207. Pers. commun., September 1994.

5

P. Moyle, Department of Wildlife and Fisheries Biology, University of California,

Davis, CA 95616. Pers. commun., September 1994.

6

H. Weeks. Oregon Department of Fish and Wildlife, P.O. Box 59, Portland, OR

97207. Pers. commun., September 1994.

7

C. Bond, Department of Fish and Wildlife, Nash Hall, Oregon State University,

Corvallis, OR 97331. Pers. commun., September 1994.
15

Figure 3. Graphical summary of presumed marine migrations of pink salmon originating

from streams in Washington, British Columbia, and southern southeastern Alaska.

Figure modified from Takagi et al. (1981) and data in Hartt and Dell (1986) and

Ogura (1994).
16

observed occasionally in the Sekiu, Hoko, and Lyre Rivers. As late as the early 1970s, adult

pink salmon were caught in Native American setnets on the Quillayute and Hoh Rivers in

both even and odd years, and some spawning (less than 500 adults) was observed a few

decades ago in the Quillayute River below the confluence of the Bogachiel and Soleduck

Rivers (Williams et al. 1975). At about this same time, relatively large numbers (< 1,500) of

adults were observed spawning annually on riffles on both the Queets, and Quinault Rivers

(the length of this period is unclear). Small numbers have also been observed in several

streams in the Chehalis River Basin (Williams et al. 1975).

Pink salmon are rare in the Columbia River Basin, especially upstream of Bonneville

Dam. However, adult pink salmon have been observed migrating up the Columbia River past

Bonneville and The Dalles Dams in small numbers (Table 1). According to the Army Corps

of Engineers’ Fish Passage Reports for the Columbia River Basin, no adult pink salmon have

been counted at darns upstream of The Dalles; Dam (U.S. Army Corps of Engineers 1994).

However, Basham and Gilbreath (1978) stated that several adult pink salmon were observed

in 1975 at John Day Dam (45) on the Columbia River and at Little Goose Dam (12) and

Lower Granite Dam (1) on the Snake River. In the same year, Basham and Gilbreath (1978)

recovered five pink salmon carcasses (4 female, I male) from the lower Tucannon River

between October 18 and November 1. The females appeared to have spawned due to the few

remaining eggs in their body cavities and the erosion of the lower lobes of their caudal fins.

In 1991, a record 550 adult pink salmon were observed migrating past Bonneville

Dam, and minimum pink salmon abundance for the lower Columbia River that year was

estimated at nearly 1,700 adults (H. Fiscus). In that year, approximately 225 pink salmon

redds were observed by Washington Department of Fisheries (WDF, now the Washington

Department of Fish and Wildlife (WDFW)) biologists in the Cowlitz River, a lower Columbia

River tributary. Also in 1991, 32 pink salmon were observed at Cascade Hatchery on the

lower Columbia River, and one was observed in the Clackamas River.

Pink salmon have been recovered occasionally in ocean fisheries off the coasts of

Oregon and southern Washington (Hubbs 1946, Bonar et al. 1989). At least some of these fish

are apparently stray fish from Puget Sound streams (e.g., Van Hyning 1959). A recent review

of Pacific salmon populations in Washington (WDF et al. 1993) concluded that pink salmon

populations do not exist outside Puget Sound and the northern Olympic Peninsula.

This information suggests that spawning populations of pink salmon no longer occur

regularly south of northwestern Washington. The remainder of this report therefore focuses on

the status of pink salmon in Washington and southern British Columbia.

8

H. Fiscus, Washington Department of Fish and Wildlife, P.O. Box 999, Battleground,

WA 98604. Pers. commun., January 1995.
17

Table 1. Counts of pink salmon over Bonneville and The Dalles Dams, Columbia River,

1938-94. Data from U.S. Army Corps of Engineers (1994).
18

Broodlines

In addition to their small size, extreme sexual dimorphism, and lack of extended

residence in fresh water as juveniles, pink salmon differ from other species of Pacific salmon

in another important respect. Because essentially all pink salmon mature at 2 years of age

(Gilbert 1914, Anas 1959, Bilton and Ricker 1965, Turner and Bilton 1968), this species

lacks variable age structure. Two broodlines result from generations spawning in alternate

years. Throughout much of the range of this species, many rivers that support pink salmon

populations produce both even- and odd-year broodlines which may have arisen

independently and have presumably been genetically isolated for hundreds or thousands of

generations (Aspinwall 1974, Gharrett and Smoker 1991, Heard 1991). Although 1- and

3-year-old adults have been recorded (Anas 1959, Foster et al. 1981, Alexandersdottir and

Mathisen 1983), almost all pink salmon are 2 years of age at maturity (Gilbert 1914, Bilton

and Ricker 1965, Turner and Bilton 1968). Fish in the broodline that matures in

even-numbered years are referred to as even-year pink salmon; fish in the other broodline,

which matures in alternate, odd-numbered years, are referred to as odd-year pink salmon

(Aspinwall 1974, Johnson 1979, McGregor 1982, Beacham et al. 1985). Even distinct

broodlines in the same river differ for a variety of life history as well as genetic characteristics

(Heard 1991).

The geographical distributions of these two broodlines are not random. At the

southern extent of the pink salmon range in North America, odd-year pink salmon are most

abundant (Atkinson et al. 1967, WDF et al. 1993). Pink salmon in southern British Columbia,

including the Fraser River, are dominated by odd-year fish (Aro and Shepard 1967). British

Columbia populations north of the Fraser River support both odd- and even-year populations,

as do those in southeastern Alaska (Heard 199J). Even-year pink salmon dominate runs in the

Queen Charlotte Islands and become more abundant than odd-year pink salmon in western

Alaska (Neave 1952, Aro and Shepard 1967, Ricker and Manzer 1974). In Asia, even-year

pink salmon generally become more abundant than odd-year pink salmon as latitude increases

(Heard 1991). The reasons for this variation in broodline dominance remain a major unsolved

problem in pink salmon biology (Ricker 1962, Heard 1991).

The relative abundance of these broodlines can fluctuate dramatically over time, even

within the same system (Neave 1952, Ricker 1962). In recent decades, pink salmon south of

central British Columbia have been dominated by odd-year fish (Aro and Shepard 1967,

Beacham et al. 1985), and even-year fish are almost completely absent from Washington

(Atkinson et al. 1967, WDF et al. 1993). Even-year pink salmon in Washington are known

only from the Snohomish River on Puget Sound, where spawning escapements have ranged

from a few hundred to over 2,000 fish over the last decade (WDF et al. 1993).

With the exception of those in the Fraser River, the sizes of even- and odd-year pink

salmon populations in British Columbia generally increase with latitude. In odd-numbered

years, large populations (100,000 spawners or more) also occur in some rivers on the east side

of Strait of Georgia and Johnstone Strait (Stefanson et al. 1993); in even-numbered years,

however, the largest populations occur primarily along Johnstone Strait and farther north (Aro
19

and Shepard 1967; Gould et al. 1988; Stefanson et al. 1989, 1991). Several small populations

(less than a few hundred to a few thousand spawners) of pink salmon occur in southern

British Columbia, including southern Vancouver Island. On the east coast of Vancouver

Island south of the Puntledge and Tsolum Rivers, populations spawning in odd-numbered

years are relatively small and probably only rarely exceed a few thousand fish. On the west

coast of the island, populations spawning in odd-numbered years probably rarely exceed this

size south of Nootka Sound. However, escapement estimates for these populations are

probably not very reliable (L. Hop Wo9

, W. Luedke10).

Several small populations of pink salmon in southern British Columbia are not well

characterized. The even-year pink salmon populations nearest to the Snohomish River appear

to spawn in Vancouver Island rivers at least 130-150 km away (and perhaps considerably

further), possibly in the lower Fraser River (T. Beacham11), along Stuart Channel in the

western Strait of Georgia, or between Sooke Inlet and Port San Juan on southwestern

Vancouver Island (Aro and Shepard 1967). These areas also support the odd-year populations

that appear to be nearest to Washington pink salmon populations (Aro and Shepard 1967).

Run Types

Pink salmon populations vary in timing of adult migration and spawning but often

lack the distinct seasonal “runs” observed in several other species of Pacific salmon. The

return of maturing pink salmon to fresh water occurs from June to September and tends to

advance with increasing latitude (Neave et al. 1967). In North America, pink salmon spawn

primarily from August to October, with spawning becoming progressively later at lower

latitudes (Heard 1991). Pink salmon runs in some areas can be divided into early and late

components, and sometimes these components exhibit spatial separation as well (e.g.,

southeastern Alaska: Royce 1962, Sheridan 1962, Smoker et al. in press; Fraser River, British

Columbia: Ward 1959; Asia: Ivankov 1968).

Davidson et al. (1943) characterized two general strategies of upstream migration and

maturation in pink salmon: 1) immediate entry into the stream, where final maturation occurs,

and a consequent delay until spawning, and 2) final maturation in the estuary, subsequent

entry into the stream (often contingent on flow variation), and immediate spawning. These

9

L. Hop Wo, Canadian Department of Fisheries and Oceans, Fisheries Branch, South

Coast Division, 3225 Stephenson Point Road, Nanaimo, B.C. V9T 1K3. Pers. commun.,

May 1995.

10W. Luedke, Canadian Department of Fisheries and Oceans, Fisheries Branch, South

Coast Division, 3225 Stephenson Point Road, Nanaimo, B.C. V9T 1K3. Pers. commun.,

March 1995.

11T. Beacham, Canadian Department of Fisheries and Oceans, Biological Sciences

Branch, Pacific Biological Station, Nanaimo, B.C. V9R 5K6. Pers. commun., December

1994.
20

strategies of maturation show some evidence of being genetically based (Davidson et al.

1943; see also Smoker et al. in press). Because spawn timing may influence outmigration

timing in pink salmon, and because some evidence indicates that outmigration timing affects

marine survival (Taylor 1980, Mortensen et al. 1991), spawn timing is likely to be an

important component of local adaptation in pink salmon as well as in other species of Pacific

salmon.

In Washington and southern British Columbia, river entry occurs from July to

October, and spawning is generally observed from August to October (Neave 1963, Heard

1991, WDF et al. 1993). In Washington, timing of river entry and spawning are generally

earliest in northern Puget Sound and in the upper Dungeness River on the Olympic Peninsula

(WDF et al. 1993).

Pink Salmon Populations in Washington

Thirteen spawning populations of pink salmon have been identified in Washington

(WDF et al. 1993). For 12 of these populations, spawning occurs only in odd years; the sole

even-year population exists in the Snohomish River in Puget Sound (Fig. 4).12 Four odd-year

populations occur in the Nooksack, Skagit, Stillaguamish, and Snohomish Rivers in northern

Puget Sound, where most pink salmon are produced in Washington. Two odd-year

populations occur in southern Puget Sound in the Puyallup and Nisqually Rivers. Three

oddyear populations occur in Hood Canal in the Hamma Hamma, Duckabush, and

Dosewallips Rivers. In addition, three odd-year populations have been identified by VVDF et

al. (1993) on the Strait of Juan de Fuca: upper Dungeness (“summer” population), lower

Dungeness (“fall” population), and Elwha Rivers (Fig. 4).

Pink salmon have been observed periodically in other Washington rivers, including

the Skokomish River on Hood Canal and the Bogachiel River on the western Olympic

Peninsula (Williams et al. 1975). Elwha River pink salmon now appear to be extinct, as no

adult fish have been observed there since 1989 despite extensive annual surveys for chinook

salmon. Because of the temporal overlap in spawning distributions of chinook and pink

salmon in the Elwha River, pink salmon should have been observed there if they had been

present. Pink salmon apparently occurred historically in the Green/Duwamish River system in

12Neave (1965, p. 2) reported that Washington state biologists historically observed a

persistent, but small (up to a few hundred adults) even-year run of pinks in Day Creek, a

Skagit River tributary, and he noted that only one transplant was made into the Skagit River

prior to the known presence of these fish, in 1914. He argued that the Day Creek run should

be considered endemic because of the poor success of even-year pink salmon transplants to

Puget Sound. This run no longer appears to exist (D. Hendrick, Washington Department of

Fish and Wildlife, 333 E. Blackburn Rd., Mount Vernon, WA 98273, pers. commun., January

1995).
21

Figure 4. Principal pink salmon spawning streams in northwestern Washington. Stream

names are in boldface. Figure modified from IPSFC (1958).
22

Puget Sound; the Washington Department of Fisheries (WDF) (1916-64) reported these fish

as “very scarce” in the Green River, and absent from Burns, Newaukum, Spaight, and Soos

Creeks. The highest annual number of adult pink salmon observed in the Green River over

the last several decades is 13. Up to 16 adults have been observed in the Cedar River in the

Lake Washington watershed, but these are believed to be strays (J. Ames13).

Several aspects of the life history and ecology of pink salmon in Washington and

southern British Columbia are poorly understood in detail. Topics for which data were

insufficient to assist the BRT in evaluating possible ESUs for pink salmon include variation

in fecundity, development rate, growth and mortality, length of fry residence and migration in

the nearshore marine environment, behavior, and physiology, and several aspects of spawning

habitat. The remainder of this section concentrates on topics that were important in

determining proposed ESUs for pink salmon in Washington and southern British Columbia.

Spawning Habitat

In northwestern Washington rivers, pink salmon generally spawn in relatively fastflowing shallow water in small, clear water drainages and in both clear water and turbid large

drainages (Bonar et al. 1989, WDF et al. 1993). Some intertidal spawning may also occur, but

it is probably not extensive in this region. Several populations spawn a considerable distance

upstream or under unusual river conditions. For example, “summer” Dungeness River (Strait

of Juan de Fuca) pink salmon return earlier than “fall” Dungeness River pink salmon and

spawn above RKm 16, about 11 km upstream from the fall fish spawning in the lower river

(Johnson 1973, WDF et al. 1993). Some Dosewallips River pink salmon (Hood Canal)

migrate more than 15 kin upstream to spawn. In southern Puget Sound, pink salmon spawn in

the Puyallup River primarily above RKm 20, in South Prairie Creek and in other tributaries as

well as the main stem. Spawning by pink salmon in the Nisqually River occurs primarily in

the main stem between RKm 35 and RKm 65.

In northern Puget Sound, pink salmon spawning occurs in the following locations: Nooksack

River (all three forks), up to RKm 40 in both main stem and tributaries; Skagit River,

between RKm 37-149 (especially above RKm 124) and also in the Sauk River up to RKm 64;

Stillaguamish River, between RKm 9-54 in the South Fork (primarily RKm 30-48) and

throughout the North Fork; and Snohomish River, between RKm 21-34 for both odd-year and

even-year populations, especially above RKm 29 (both populations also spawn in the

Skykomish River, but use of the river for spawning is more extensive for odd-year fish; only

the odd-year fish are known to spawn in the Snoqualmie River) (WDF et al. 1993).

Spawning can occur in water carrying substantial amounts of glacial silt in the

Nisqually and Nooksack Rivers. Although the Puyallup River also contains substantial glacial

13J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., February 1996.
23

runoff, nearly all known pink salmon spawning occurs in two clear water tributaries, South

Prairie and Kapowsin Creeks (WDF et al. 1993).

Migration, Spawning, and Emergence Timing

Migration--Little detailed information is available on the migration routes and timing

of different pink salmon populations from Washington and southern British Columbia. Neave

et al. (1967) reported that the return migration of maturing fish in the eastern North Pacific

occurs mostly between June and September. The marine migration of pink salmon in this

region has been infer-red from tagging data to be less extensive than that of fish from more

northern populations (Takagi et al. 1981, Ogura 1994). Pink salmon migrating from

Washington and British Columbia are believed to remain east of about 150°W longitude and

south of about 59°N latitude in the Gulf of Alaska. Thus, they probably overlap at sea with

pink salmon originating from southeastern and central Alaska (Takagi et al. 1981). Ogura

(1994) summarized recoveries of pink salmon tagged in Washington and southward and

found that these recoveries were restricted to the east of 137W longitude and between 48° and

55°N latitude.

Several early tagging studies were conducted to determine the final migratory

pathways of pink salmon returning to British Columbia and Washington (Pritchard and

DeLacy 1944, DeLacy and Neave 1948, IPSFC 1958, WDF 1959). A graphical summary of

the information gathered in these studies is given in Figure 5. Most pink salmon returning to

Washington are believed to travel east through the Strait of Juan de Fuca, but some fish

probably also use the Johnstone Strait/Strait of Georgia corridor during their return migration

(IPSFC 1958). In addition, returning Fraser River and other southern British Columbia pink

salmon may migrate through either corridor.

Although available information is insufficient to discriminate fish from different

populations as they migrate into nearshore marine waters in Washington and southern British

Columbia to reach spawning grounds, WDF et al. (1993) have outlined some prominent

patterns. Generally, differences in migration timing of maturing pink salmon in this region are

small; differences among populations within areas can be larger than differences among

populations from different areas. Even-year pink salmon returning to the Snohomish River in

Puget Sound begin appearing in catches in early June and drop off sharply after mid- to late

September. Peak abundance off the river mouth generally occurs in late August (WDF et al.

1993).

For odd-year pink salmon returning to Washington rivers, timing of arrival to terminal

areas (i.e., near estuaries and river mouths) shows no clear geographic pattern. Maturing fish

returning to streams in northern Puget Sound generally arrive at these areas between mid

August and late September. The earliest run appears to occur to the Nooksack River, the latest

to the Skagit River. In southern Puget Sound, fish arrive at terminal areas primarily between

mid-July and mid-August. In Hood Canal, fish arrive between mid-July and early September

(WDF et al. 1993). Pink salmon appear off the Dungeness River in the Strait of Juan de Fuca
24

Figure 5. Principal migration routes for adult pink salmon returning to southern British

Columbia and Washington. Figure modified from WDF (1959).
25

earlier than pink salmon returning to other Washington rivers. Fish that migrate to the

Dungeness River begin arriving at the river’s mouth as early as mid-June and continue to

show up until early August, with abundance off the river mouth declining after river entry

between late July and early September. These fish constitute the two distinct runs that return

to the upper and lower river, respectively, and show considerable temporal differentiation in

average spawn timing (WDF et al. 1993).

Spawn timing--Pink salmon populations can vary considerably in their arrival timing

at spawning grounds (Sheridan 1962, WDF et al. 1993), and some evidence exists for

substantial differences in spawn timing within a single river system. For example, Taylor

(1980) and Gharrett and Smoker (1993a) identified early and late spawning populations in

Auke Creek, Alaska that were also differentiated by their patterns of fly outmigration timing.

These populations have not yet been distinguished by allozymic variation (Lane et al. 1990).

Because this sort of life history variability can have consequences for fitness (Taylor 1980,

Mortensen et al. 1991), it may be instrumental in maintaining adaptive diversity within and

among populations. The fact that such life history variation may not be detected with routine

allozyme surveys indicates the importance of considering this variation when attempting to

identify distinct population units (Gharrett and Smoker 1993b, Hard 1995a). However, the

interpretation of life history variation is complicated because this variation may also be quite

sensitive to environmental variation (Waples 1991a, Hard 1995b).

In Washington and southern British Columbia, river entry occurs from July to

October, and spawning is generally observed from August to October (Neave 1963, WDF et

al. 1993). In their SASSI document, WDF et al. (1993) reported that average timing of river

entry and spawning are generally earlier in northern Puget Sound and in the upper Dungeness

River on the Olympic Peninsula than elsewhere in northwestern Washington. As noted in an

earlier section, the Dungeness River has two populations of pink salmon: “summer” run fish

enter the river in ocean-bright condition in July and August, hold in the river for up to a few

weeks before final maturation, and spawn above RKm 16 in August and September; “fall”

run fish enter the river already exhibiting much of their spawning morphology and coloration

in August and September, spawning soon afterward in the lower river. These dark fall-run fish

spawn below RKm 5 an average of 2 weeks later than summer-run fish (WDF et al. 1993, J.

Uehara14).

The Washington Department of Fish and Wildlife has surveyed pink salmon

escapement (counts of live and dead adults) in many northwestern Washington rivers since

the late 1950s. The Department uses an “area under the. curve” method (Ames 1984) to

estimate escapement from many of these surveys and from an estimate of spawner life in the

stream (generally, 10 or 15 days). Escapement curves generated with this method can also be

used to derive median spawn timing for different rivers in various years. One means of

14J. Uehara, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., January 1995.
26

deriving an estimate of median spawn timing for a given reach or drainage in a particular year

is to determine the date at which half the area under the curve is reached. Since these curves

are actually a series of connected trapezoids, it is a straightforward matter to calculate this

date. This method may be preferable to using peak counts because the median spawn date

should be less sensitive than peak count to variation in the shape of the spawning distribution.

Data from WDF spawning surveys conducted between 1983 and 1993 were used to

calculate median run timings and examine their patterns. Table 2 summarizes these data and

compares them to the range of spawning dates observed in these systems and summarized by

VVDF et al. (1993). It should be noted that 1) no data were available from Snohomish River

even-year pink salmon for this analysis, 2). the Elwha River statistics were based on a single

survey in 1985, and 3) few surveys have been made in the Nisqually River. It should also be

noted that spawning curves for some river reaches that may contain significant spawning

populations are not yet available. In some cases, several surveys within a river and year were

combined to determine the median date for that river. For these reasons, data generated from

the spawning curves should be examined with caution.

Nevertheless, a complex pattern for odd-year pink salmon run timing is evident from

this limited analysis. In general, the run timing estimates derived from spawning curves

correspond well to the midranges of spawning reported by WDF et al. (190); the exceptions

are estimated median run timings for Puyallup River and Elwha River pink salmon, which are

both earlier than the midranges interpolated from the VVDF et al. (1993) report. However, it

should be noted that the Puyallup River median timing is within the range reported by WDF

et al. (1993), and the Elwha River median timing is based on only a single year.

In general, it appears that pink salmon spawn earliest in the upper Dungeness River

(average of the median calendar dates ± SE = 245 ± 0.8, where day 245 = 2 September),

followed by the Nooksack River (North Fork, 254 ± 0.8), lower Dungeness River (265 ± 2.7),

Hood Canal (major rivers only, 269 ± 6.5), Puyallup River (270 ± 4. 1), Skagit River (275 ±

0.8), Stillaguamish River (279 ± 1.3), Snohomish River (280 ± 0.7), and Nisqually River (283

± 1.3). The general pattern appears to be that Peak spawning is earliest for Strait of Juan de

Fuca populations and the Nooksack River, with peak spawning in Hood Canal occurring 2-3

weeks later on average, and peak spawning in Puget Sound (excluding the Nooksack and

Nisqually Rivers) occurring another week after that.

Run timing for Nisqually River pink salmon is the latest for all Washington

populations examined, based on 2 years of surveys. Timing of peak spawning of even-year

pink salmon in the Snohomish River is about 3-4 weeks earlier than that of odd-year fish,

even though these two groups of fish use some of the same habitat (D. Hendrick15) .

15D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., January 1995.
27

Table 2. Comparison of estimates of median run timing for Washington pink salmon

(generated from 1983-93 spawning curves; WDFW, unpubl. data) to spawn timing

ranges and approximate midranges (WDF et al. 1993). Estimates are in calendar

days, where 1 September = day 244 and 15 October = day 288. N refers to the

number of spawner surveys in the sample.
28

Table 2. Continued.
29

Resident Fish

Like pink salmon in many populations from more northern regions, pink salmon in

British Columbia and Washington often spend an extended period in the nearshore marine

Even-year Snohomish River fish spawn during about the same time that even-year fish spawn

farther north in central British Columbia (Aro and Shepard 1967; Gould et al. 1988;

Stefanson et al. 1989, 1991).

Emergence timing--WDFW biologists have also collected unpublished observations

on development of pink salmon embryos during redd surveys in many of the Washington

rivers that support these fish. However, the collection of this information has become

infrequent in recent years. Examination of the available information indicates that hatching

generally occurs between late January and early March, but the patterns are highly variable

both among river systems and within these systems among years. No clear interdrainage

patterns are evident from these data. Emergence timing is not directly assessed with these

data but would appear to occur primarily in March and April. Because of large gaps in the

data and the sensitivity of embryonic development to environmental conditions in the river,

the BRT concluded that this information is not likely to be useful in aiding ESU

determinations for Washington pink salmon.

Outmigration and Estuarine Use

Juvenile pink salmon generally begin migrating downstream. immediately upon

emerging from the gravel. Based on work in the Fraser River by Vernon (1966) and in

Hooknose Creek, British Columbia by Hunter (1959), pink salmon fry migrate downstream

primarily in March and April in this region, although migration can extend into May. Pink

salmon outmigrating from rivers draining into Puget Sound and Hood Canal appear to use

nearshore areas in these embayments extensively for early rearing (Jewell 1966). The degree

of habitat overlap between odd-year populations is unknown.

Little is known about the migratory and feeding habits of juvenile pink salmon

outmigrating into the Strait of Juan de Fuca. Hiss (1994) found that juvenile pink salmon

began migrating into Dungeness Bay in 1994 by April, peaked in their migration in late April,

and had largely left the estuary by the third week in May. Fry ranged in length from 35 to 75

mm over the sampling period; some fry captured in early April were more than 45 mm long,

suggesting that they had entered the estuary in March.

In addition, preemergent fry samples collected in the Dungeness River in late

February and early March showed that 80-90% of fry were near yolk-sac absorption,

suggesting an early outmigration (WDFW, unpubl. data). It was unclear from Hiss’ (1994)

study whether there was any spatial or temporal separation between juvenile pink salmon

from the lower and upper Dungeness River. The study did not address where these pink

salmon go after they leave Dungeness Bay; it is unclear whether these fish migrate west

through the Strait of Juan de Fuca or (possibly) east and north through the Strait of Georgia.
30

environment feeding and growing rapidly before they move offshore (Manzer and Shepard

1962, Phillips and Barraclough 1978, Healey 1980). This period may be as long as 2 to 3

months (reviewed by Heard 1991). However, most pink salmon migrate to the open ocean by

late summer or early fall.

An exception to this pattern appears in some pink salmon from Puget Sound (and

possibly Hood Canal) that spend their entire marine phase in the nearshore environment. This

behavior has been inferred from tagging studies described by Jensen (1956) and Hartt and

Dell (1986). Jensen (1956) tagged 873 small (1-1.5 kg) pink salmon in the Tacoma Narrows

in June 1955 and sampled these fish in various parts of Puget Sound for the next 4 months to

ascertain their origin. These fish were presumed to be resident to Puget Sound on the basis of

their small size. Tagged fish remained in the general area for about I month, then moved

generally north along the eastern shore of Puget Sound. Most of the tags were recovered by

sport fishers. The results were largely inconclusive, but three of the four recoveries were

made on spawning grounds in the Stillaguamish River, and Jensen suggested the

Stillaguamish River population as a possible source of resident pink salmon. Small pink

salmon have been repeatedly observed spawning in Pilchuck Creek, a Stillaguamish River

tributary, as long as 20 years ago (W. Waknitz16).

The Suquamish Tribe sampled immature pink salmon in central Puget Sound in

October and November 1976, catching hundreds of them to both the north and south of

Bainbridge Island (Hartt and Dell 1986). These fish were about 23 cm long at capture, a size

described as “larger than most pinks that had migrated hundreds of miles in the open sea by

September” (Hartt and Dell 1986). The captured fish would probably not migrate offshore

that late in the year. It is unlikely that this reticence to move to the open ocean is related to

their size; Jensen (1956) believed these fish adopted residence in Puget Sound for the marine

phase of the life cycle. So far as is known, this unusual practice of forgoing migration on the

high seas is not documented for any populations of pink salmon outside Washington (W.

Heard17). “Resident” chinook and coho salmon also occur in Puget Sound (Haw et al. 1967).

Presumably resident pink salmon (based on their small size of 35-45 cm) supported a

sport fishery in Puget Sound in odd-years from the late 1940s until the early 1960s (Haw et al.

1967). These fish were harvested primarily in southern Puget Sound, especially in the Tacoma

Narrows and Commencement Bay areas, with gear that incorporated an attractant device

composed of a large spinner blade preceded by a rudder to control line twist (known as

“shovel and rudder” gear; F. Haw18).

16W. Waknitz, NMFS Northwest Fisheries Science Center. Unpubl. observations.

17W. Heard, NMFS Alaska Fisheries Science Center Auke Bay Laboratory, 11305

Glacier Hwy., Juneau, AK 99801. Pers. commun., January 1995.

18F. Haw, Northwest Marine Technology, Inc., Shaw Island, WA 98286. Pers.

commun., January 1995.
31

Body Morphometry, Fecundity, and Egg Size

Body morphometry--Beacham (1985) and Beacham et al. (1988) observed

significant variation in body size and shape both within and among broodlines of British

Columbia pink salmon. Variation in morphometric characters (particularly head size, caudal

peduncle thickness, and fin size) tended to show greater variation among fish in different

broodlines returning to the same river drainage than among fish of different populations

within broodlines. Because larger fish with larger heads, thicker caudal peduncles, and larger

fins were usually associated with large rivers, the authors interpreted these results as evidence

for morphometric adaptation to natal river conditions.

To assist in stock separation analyses, WDFW and its predecessor WDF have been

collecting tissue samples from adult pink salmon for protein electrophoresis in several

Washington rivers since 1985. Staff biologists have also measured the body lengths of

sampled adults (WDFW, unpubl. data). Although these samples may not be representative of

the entire spawning populations, sampling in each river was generally conducted in more than

1 year and often in several different locations (S. Young19). Early measurements were of

snout-to-fork (SF) length (a measure commonly used by U.S. fishery biologists) to the nearest

centimeter, but in more recent sampling the measurements have been of postorbital-tohypural plate (POH) length (a measure more commonly used by Canadian fishery biologists).

The POH measurement has the advantage that it is unaffected by snout and tail erosion in

spawning adults.

All even-year fish sampled from the Snohomish River were collected in 1990, and all

fish measurements were POH lengths. For odd-year populations, fish measurements were

either SF or POH lengths, depending on the year of sampling. Separate linear regression

equations were necessary to convert SF to POH for both males and females. Regression

equations were not available to convert SF to POH; instead, regression equations to convert

SF to mideye-to-hypural plate (MEH) length were generated from relationships between SF

and mideye-to-fork (MEF) length and between MEF and MEH given for Alaskan pink

salmon by Nickerson (1979). Although MEH is smaller than POH, the use of MEH can be

justified because 1) MEH and POH are highly correlated, 2) the difference between them is

small (< 1 cm), and 3) all measurements analyzed here are rounded to the nearest centimeter.

Thus, the practice of using both MEH and POH in this analysis should have little potential to

bias the results. The equations (including their correlation coefficients and sample sizes)

relating MEH and SF for odd-year pink salmon are

males: MEH = 2.4301 + 0.8179 x SF; r2

= 0.974 (n = 27);

females: MEH = 0.6777 + 0.8652 x SF; r2 = 0.972 (n = 38).

19S. Young, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., February 1995.
32

The results of these manipulations of WDFW’s unpublished size data are summarized

in Table 3. Analysis of variance of the data indicated highly significant (P < 0.0001) effects of

sex and sampling year. The sex effect reflects the strong sexual dimorphism that is

characteristic of pink salmon. Multiple comparisons (Newman-Keuls test, Sokal and Rohlf

1981) among sampling years, after data among drainages were pooled, indicated a substantial

general decline in MEH for odd-year pink salmon over time (1993 < 1991 < 1989 < 1987 <

1985; P < 0.0001). The data in Table 3 indicate that the size decline over time is common to

all the populations sampled in more than one year. Data are available for Snohomish River

even-year pink salmon from only I year, but these were the smallest fish observed in all

Washington samples (Table 3).

Significant variation among drainages was also observed in odd-year pink salmon

when sampling years and sexes were pooled. The relationship among drainages, in order of

increasing adult MEH length, was

Nooksack < lower Dungeness < Nisqually < upper Dungeness < [Skagit, Snohomish,

Stillaguamish, Dosewallips] < [Puyallup, Duckabush] < Hamma Hamma.

where group differences were significant (P < 0.05). Hood Canal Hatchery fish were. similar

in length to Skagit, Snohomish, Stillaguamish, and Dosewallips River fish. In general, the

smallest fish appear to exist in cold, turbid rivers in Puget Sound (Nooksack and Nisqually

Rivers) and along the Strait of Juan de Fuca (lower and upper Dungeness River), and the

largest fish tend to exist in Hood Canal. Although the Puyallup River is also heavily glacially

influenced, all fish were sampled from a clear water tributary, South Prairie Creek, where the

majority of spawning in that river is observed (WDF et al. 1993, J. Uehara20). No size data are

available for Elwha River pink salmon.

Beacham and Murray (1985) and Beacham et al. (1988) calculated POH length data

for several even- and odd-year pink salmon populations in British Columbia, and these data

provide some basis for comparison with the Washington data. Beacham and Murray (1985)

found that even-year fish were shorter (P < 0.01) than odd-year fish among the central and

southern British Columbia populations they examined, a general result previously reported for

body weight by Godfrey (1959). Snohomish River even-year-adult pink salmon sampled by

WDF in 1990 are similar in size to pink salmon in the even-year populations from the central

mainland and northern Vancouver Island described by Beacham and Murray, although the

Snohomish River fish tend to be smaller than the even-year British Columbia average. The

length estimates for odd-year populations in Washington taken in recent years (Table 3), with

the exception of the Snohomish and Skagit River populations, tend to be smaller than the

average for odd-year British Columbia populations reported by Beacham and Murray (1985).

20J. Uehara, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., January 1995.
33

Table 3. Means and standard errors (SE) of mideye-to-hypural plate lengths (odd-year fish)

and postorbital-to-hypural plate lengths (even-year fish) for adult pink salmon

sampled in Washington (WDFW, unpubl. data). For each drainage, multiple samples

collected in the same year have been pooled to increase sample sizes; mean sample

size was 105.5 fish (range, 18-274). Measurements are in centimeters.
34

However, many of the lengths taken in 1985 and 1987 in Washington are larger than the

British Columbia average, which is based on 1981 and 1983 collections.

Snohomish River even-year pink salmon, based on the 1990 sample, are most similar

in length to even-year males sampled from large rivers on the central British Columbia coast

and to even-year females sampled from small rivers on Vancouver Island (Beacham et al.

1988). For odd-year males, the greatest length similarities between Washington and British

Columbia pink salmon samples are Nooksack River and small Fraser River tributaries; all

other Puget Sound rivers and large Fraser River tributaries, except for Nisqually River, which

is most similar to large south coast and Vancouver Island rivers; all Hood Canal rivers and

large Fraser River tributaries; upper Dungeness River and large Fraser River tributaries; and

lower Dungeness River and small Fraser River tributaries.

For odd-year females, the greatest similarities exist between the following: Nisqually

River and both large and small north coast rivers as well as small Fraser River tributaries;

lower Dungeness River and large Skeena. River and Vancouver Island tributaries; and all

other Puget Sound rivers and large Fraser River tributaries. These odd-year comparisons are

based on Washington collections made in 1985 (the last year sampling was conducted by

Beacham et al. 1988), except for the Nooksack (1987), Nisqually (1991), upper Dungeness

(1987), and lower Dungeness Rivers (1989). In Washington, there is no apparent relationship

between the length of adult pink salmon and river size, as reported for the more

comprehensive survey of British Columbia populations by Beacham et al. (1988). No data are

available for other morphometric characters in Washington pink salmon.

Two caveats are important to emphasize in interpreting these comparisons. First, the

possibility that sampling was not random within drainages cannot be excluded and could bias

these results. Second, because much of the Washington and British Columbia length sampling

was done in different years, these comparisons should be regarded with caution, as adult pink

salmon size can vary significantly between years (Ricker et al. 1978).

Fecundity and egg size--Beacham and Murray (1993) summarized geographic

patterns of fecundity and egg size in pink salmon. When fecundity was standardized to a body

length of 435 mm, fecundity in both even- and odd-year fish tended to increase with latitude

over the range of about 49°N to 61°N in North America. However, available information was

meager for Alaskan populations, and considerable variability existed among the British

Columbia populations sampled. For odd-year pink salmon in British Columbia, Beacham and

Murray (1993) found that fecundity was generally lower in Vancouver Island and upper Fraser

River populations than in other British Columbia populations. For even-year British

Columbia pink salmon, fish from the Queen Charlotte Islands had the highest fecundities.

Pink salmon egg size (weight and diameter) showed considerable geographic variation

within both broodlines but showed no clear relationship with latitude for either broodline.

Egg size (when standardized by body length) tended to be larger in even- than in odd-year

pink salmon in British Columbia (Beacham et al. 1988, Beacham and Murray 1993). In

British Columbia, egg weight and diameter tended to be largest in Skeena River populations
35

for odd-year fish and in the Queen Charlotte Islands for even-year fish. Southern British

Columbia populations showed a considerable degree of scatter in egg size (Beacham and

Murray 1993). Among several odd-year populations of British Columbia pink salmon

sampled for egg size, populations with larger eggs produced heavier alevins with greater

amounts of yolk, but the relationship between egg and alevin size depended on temperature

under controlled incubation conditions (Beacham and Murray 1986). No clear relationship

between egg or alevin size and embryonic survival was observed by these workers.

Homing and Straying

Homing and straying are prominent features of Pacific salmon biology that can have,

significant effects on population structure. Consequently, these related behaviors are relevant

to ESU determinations for these species. Pink salmon have a widespread reputation for

straying at higher rates than other species of Pacific salmon (e.g., Horrall 1981). If true, then

if straying pink salmon also reproduce successfully, the elevated rate of gene flow would be

expected to result in a less conspicuous population structure and, potentially, reduced

opportunity for local adaptations to be maintained in this species. (The analysis of genetic

variation provided in the next section sheds some light on the level of population structure in

pink salmon.)

Few well-designed studies have been carried out to estimate straying rates in Pacific

salmon, and the empirical evidence supporting the hypothesis that pink salmon stray at

relatively higher rates than other species of Oncorhynchus is mixed (Quinn 1993, Altukhov

and Salmenkova 1994). Early work by Davidson (1934) in Washington (Hood Canal) and

southeastern Alaska and by Pritchard (1939) in British Columbia produced estimates of

straying of about 10%, based on recovery of tagged adults, but Ricker (1962) concluded that

this rate was probably rarely exceeded by natural pink salmon.

Helle (1966) moved adult pink salmon from Olsen Creek in Prince William Sound,

Alaska to a location 5 km away and recovered 91% of them in Olsen Creek. Gharrett (1985)

detected no straying of genetically marked odd-year pink salmon from Auke Creek, Alaska to

two other pink salmon streams within 10 km of Auke Creek; however, he did provide some

evidence for higher straying of even-year fish to both another- run within Auke Creek and

another drainage. Altukhov and Salmenkova (1994) reviewed pink salmon straying data from

marked fry released from North American and Asian hatcheries and found that estimates

ranged from 0.1 to 11.5%. Although most estimates of straying are based on recoveries of

adults from streams in the vicinity of the natal stream, Heard (1991) discussed some data that

indicate pink salmon can travel several hundred kilometers from the natal stream during their

adult migration. Quinn (1993) summarized these studies in this way: “the conclusion that

[pink salmon) stray more commonly than other salmon species seems premature.”

Nevertheless, the rapid colonization of systems newly available to pink salmon

indicates that this species has an unusual ability to expand into suitable habitat when
36

conditions are favorable. The rapid expansion of pink salmon into the Great Lakes after their

accidental introduction (Kwain and Laurie 1981); the recolonization of Sashin Creek,

southeastern Alaska, by even-year pink salmon after nearly complete experimental removal of

the even-year run (Merrell 1962, Heard 1991); and the immediate recolonization of the upper

Fraser River after almost 35 years of blocked access (Vernon 1962) are testaments to this

ability. In addition, the reports of pink salmon periodically spawning south of northwestern

Washington, in the absence of any evidence for permanent spawning populations in these

southern areas, suggest that pink salmon homing behavior is highly plastic. Finally, maturing

pink salmon show a strong propensity to move around between neighboring streams, at least

in certain areas, prior to spawning (Jones and Thomason 1983).

Straying in pink salmon may depend strongly 9n spawning location and on conditions

at time of spawning. In a recent study in Prince William Sound, Sharp et al. (1994) estimated

straying rates between 9 and 53% in coded-wire tagged odd-year wild and hatchery pink

salmon. Several factors May contribute to the relatively high straying observed: 1) Prince

William Sound is a highly dynamic geological zone, having experienced two major

earthquakes in the last century that destroyed many streams and created others; 2) a large

fraction of Prince William Sound pink salmon spawn intertidally--approximately 72-77% in

even years and 35-57% in odd years prior to the 1964 Good Friday earthquake (Noerenberg

1963); and 3) the southwestern part of Prince William Sound was heavily affected by the 11

million gallon Exxon Valdez oil spill in 1989 (S. Rice21). In addition, because coded-wire

tagging of juvenile pink salmon must occur at the emergent fry stage, some question has been

raised as to whether the tagging itself may impair the homing of these fish (Morrison and

Zajac 1987; J. Seeb, Alaska Department of Fish and Game, pers. commun., cited in Mathisen

1994).

Levels of natural straying in pink salmon are therefore unclear and may vary widely

among populations and within populations under different conditions. More importantly, the

genetic consequences of straying in pink salmon are not well understood.

Artificial Propagation of Pink Salmon

Because artificial propagation of Pacific salmonids has been widespread for many

years, the influence of hatchery fish needs to be considered in most ESA status reviews.

NMFS policy (NMFS 1993) stipulates that in determining whether a population is distinct for

purposes of the ESA, attention should focus on natural fish (Waples 1991a). The decision to

focus on natural fish is based entirely on ecosystem considerations; the question of the

relative merits of hatchery versus natural fish is a separate issue. Fish are not excluded from

ESA consideration simply because some of their direct ancestors may have spent time in a

21S. Rice, NMFS Alaska Fisheries Science Center, Auke Bay Laboratory, Juneau, AK

99801. Pers. commun., March 1995.
37

fish hatchery, nor does identifying a group of fish as “natural” as defined here automatically

mean that they are part of a listed ESU. For a discussion of artificial propagation of Pacific

salmonunder the ESA, see Hard et al. (1992).

Transplants into Washington

It is commonly believed that even-year pink salmon historically either were absent

from Washington or were at an abundance too low to sustain harvest (Rounsefell 1938,

Atkinson 1956, Ellis and Noble 1959). Consequently, WDF made several attempts earlier in

this century to establish even-year pink salmon runs in northwestern Washington (WDF

1916-1964, Neave 1965, Roppel 1982). These efforts are summarized in Table 4.

More than 82 million eyed pink salmon eggs were transported from Alaska to various

locations in Washington in even-numbered years between 1910 and 1932. In addition, more

than one million odd-year Alaskan eggs were brought into Washington from southeastern

Alaska in 1929 (Table 5). An estimated 85 million juveniles resulting from these transplanted

eggs (see explanation in Table 4) were released between 1911 and 1933; these releases

produced no recorded returns of even-year adults to Washington rivers, including the

Snohomish River (Ellis and Noble 1959, Neave 1965).

However, Neave (1965) stated that “it appears that streams were not examined for

actual escapements,” and “in 1924 the traps along the west coast of Vancouver Island, which

had never caught pink salmon in the even-numbered, or off years for this variety, reported

total catches of more than 20,000 small pinks, resembling the Alaska variety which had been

transplanted” (note that in 1923, over 14 million fry from Prince William Sound eggs were

released into Washington waters, including nearly a million fry planted in the Skykomish

River; Table 4).

Attempts to establish even-year pink salmon in the state were renewed between 1944

and 1956 with the transport of, nearly 4 million eyed eggs from the Skeena River drainage in

British Columbia (and possibly 200,000 eggs from Alaska in 1948; Table 4). Of the 1.3

million fry released, at least several hundred apparently survived to return as adults, but there

is no evidence that returns were sustained beyond one or two generations (Ellis and Noble

1959, Neave 1965). The most substantial return appeared to result from a 1949 release of

299,000 fry (Lakelse River) into the Samish River, where an estimated 300-500 adults

returned in 1950 (Neave 1965).
38

Table 4. Documented transplants of even-year pink salmon into Washington. Data are from

WDF (1916-64). Neave (1965), and Roppel (1982). The number of eggs transported

to Washington hatcheries is generally that provided by USBF shipping records

(Neave 1965, Roppel 1982); the number of fry released into Washington watersheds

is generally that provided by WDF planting records (WDF 1916-64, Neave 1965).

Note that in some cases the estimated number of juveniles released exceeds the

estimated number of eggs transplanted. In addition, it was not always possible to

identify the number of fry released from specific broodstocks.
39

Table 4. Continued.
40

Table 4. Continued.
41

Table 5. Major releases of juvenile pink salmon (fed and unfed fry) in Washington and

Oregon. Data from WDF (1916-64), WDF et al. (1993), and NRC (1995).
42

Table 5. Continued.
43

Table 5. Continued.
44

Table 5. Continued.
45

Table 5. Continued.
46

Table 5. Continued.
47

Artificial Propagation in Washington

A selected review of artificial propagation activity involving pink salmon in

Washington is provided in Table 5. This review focuses heavily on historical stock transfers

within the state. For about 25 years beginning in the 1950s, pink salmon were produced in

Washington hatcheries around Puget Sound in relatively large numbers. Movements of fish

among hatcheries and drainages in Puget Sound, Hood Canal, and the Dungeness River on

the Olympic Peninsula were common during this period, but very few pink salmon were

transplanted to areas outside Puget Sound. Three hatcheries have dominated pink salmon

production in the state: Hood Canal Hatchery on Finch Creek in Hood Canal, Puyallup

Hatchery on Voight Creek in southern Puget Sound, and Dungeness Hatchery on the

Dungeness River on the Olympic Peninsula. In recent years, only Hood Canal Hatchery has,

maintained an active pink salmon production program. A population of odd-year pink salmon

was established in 1953 at Hood Canal Hatchery from the gametes of adults returning to the

upper Dungeness River (approximately 90%) and Dosewallips River (approximately 10%).

Since then, production of odd-year fish has ranged from a low of less than 15,000 fry (in

1955) to a high of over 4 million fry (in 1988).

Summary

Although major efforts were made several decades ago to increase the abundance of

even-year pink salmon in Washington, it. is not clear that any of these attempts were

successful. Even-year pink salmon are known in Washington only from the Snohomish River

(WDF et al. 1993). The origin of this population is uncertain; these fish could be endemic or

could have resulted from one or more transplants of even-year fish into the state. Regardless

of its origin, however, this population appears to have been naturally self-sustaining for at

least the last eight generations (its status prior to 1980 is unclear; WDF et al. 1993).

Most hatchery production of pink salmon in Washington is composed of odd-year fish

released from Hood Canal Hatchery in southern Hood Canal. These fish are generally

released into Finch Creek, the location of the hatchery, and the hatchery typically uses local

broodstock (Table 5). As noted above, however, this broodstock was originally derived from

adults returning to the Dungeness and Dosewallips Rivers in 1953. Hood Canal Hatchery

production over the last decade has averaged about a million fry released locally every other

year into Finch Creek (Table 5). Other recent releases, such as those into the Nooksack River,

Voight Creek, Minter Creek, and Chambers Creek, have been relatively small and appear to

have used local broodstock. Thus, although artificial propagation of pink salmon in the past—

particularly stock transfers from Dungeness and Hood Canal Hatcheries around northwestern

Washington--may have affected the population structure of odd-year pink salmon in Puget

Sound, recent hatchery production has probably had little effect on this structure.

Stock transfers of pink salmon in British Columbia are summarized elsewhere in Aro

(1979) and NRC (1995).
48

Genetic Information

Differences Between Even- and Odd-year Pink Salmon

Because pink salmon mature and spawn on a strict 2-year cycle, genetic isolation

between odd- and even-year spawners is nearly complete, and several genetic and biological

variables differ between them. The electrophoretic analysis of enzymatic proteins has been

used extensively to measure the genetic differences between odd- and even-year fish and to

resolve genetic structure among populations within these groups. One approach for detecting

reproductive isolation is to compare frequencies of protein variants (allozymes) among

samples. The finding of significant frequency differences between groups can be taken as

evidence of reproductive isolation. Another approach to identifying reproductively isolated

groups is. to estimate genetic distances between samples and to analyze these distances with a

clustering algorithm, such as the unweighted pair group method with averages (UPGMA;

Sneath and Sokal 1973) or with an ordination technique such as multidimensional scaling

analysis (Lessa 1990). When the geographic distribution of genetic variability is continuous

and not hierarchical or disjunct, such as in a clinal or reticular pattern, multidimensional

scaling is more appropriate than agglomerative clustering (Lessa 1990). Multidimensional

scaling is a nonmetric ordination technique that depicts genetic relationships among

populations in two or three dimensions and can reduce the distortion that may exist in

phenograms because populations are represented in fewer dimensions. When genetic

relationships among populations reflect nonhierarchical or semihierarchical geographic

variation, multidimensional scaling diagrams are often a more effective means of showing

these relationships (Lessa 1990).

Geneticists have used several genetic distance measures (e.g., Cavalli-Sforza and

Edwards 1967, Rogers 1972, Nei 1978) to study the population structure of pink salmon as

well as other salmonids. A considerable literature has developed on the pros and cons of these

measures. For example, an attractive feature of the Rogers’ and Cavalli-Sforza and Edwards’

distances is that they satisfy the triangle inequality--that is, given three populations (A, B, Q,

the sum of the distances from A to B and from A to C will always be greater than the distance

from A to C. On the other hand, neither of these distance measures employs a correction for

sample size, so the distances are biased upwards, especially for small sample sizes. In

contrast, Nei’s distance is unbiased, but does not always satisfy the triangle inequality.

Another important consideration is that both Nei’s and Rogers’ distance measures can be

affected by different levels of heterozygosity between populations, whereas Cavalli-Sforza

and Edwards’ measure is not. Discussions of these and other features of genetic distances

appear in Nei (1987), Hillis and Moritz (1990), and Rogers (1991). Unfortunately, most of

this discussion has focused on the merits of the various measures for phylogenetic

reconstruction among species and higher taxa. No one has rigorously or quantitatively

evaluated the performances of these distances in assessing the genetic population structures of

species like salmon, which typically are separated by relatively small genetic distances.
49

Since it is unclear which distance measure is “best” in any given application, we

analyzed each set of data with more than one method to identify results that may not be

robust. Nei’s unbiased genetic distance has been used in several studies of pink salmon, but

we computed all three distance measures for most data sets. In most cases, the different

genetic distance measures yielded results that were highly correlated. For simplicity we report

only results for Rogers’ and Cavalli-Sforza and Edwards’ distance measures. Both distance

measures range from 0.0 (identity) to 1.0 (complete dissimilarity). Cases in which the results

differed substantially among measures are identified in the text.

For many polymorphic enzyme-encoding loci, strong allozyme frequency differences

have been reported between even- and odd-year broodlines spawning at the same localities in

Alaska (Aspinwall 1974, Johnson 1979, McGregor 1982), Canada (Beacham et al. 1985), and

Russia (Salmenkova et al. 1981, Altukhov et al. 1983, Kartavtsev 1991). Shaklee and

Varnavskaya (1994) reported a large genetic difference between even- and odd-year pink

salmon from the Snohomish River, the only North American locality south of British

Columbia that supports a spawning population of even-year pink salmon. The average Nei’s

genetic distance (Nei 1978) between even- and odd-year pink salmon in British Columbia

was 0.018 (Beacham et al. 1988). However, since this estimate was based only on

polymorphic loci, it is likely to overestimate the true genetic distance between the two

broodlines. . The actual distance, which includes monomorphic loci in its estimate, is

probably not more than half this value (or about 0.009). This distance is typical of conspecific

populations of other animals (Thorpe 1982), and represents an “upper bound” to the largest

distance expected to exist between populations within broodlines.

In addition to allozyme frequency differences, other genetic differences have been

reported between even- and odd-year spawners. Gorshkova (1983) found that Kamchatka

oddyear pink salmon show a chromosomal polymorphism of presumably acrocentric fusions,

in which the diploid number is 53 or 54 chromosomes, whereas even-year spawners

consistently had only 52 chromosomes.

At Auke Creek in southeastern Alaska, Gharrett and Smoker (1991) made crosses

between even- and odd-year spawners to search for possible outbreeding depression in their

offspring. Cyropreserved sperm from even-year males was used to fertilize eggs from oddyear

females the following year. In the first generation, the number of returning first-generation

hybrids and their average date of return were not significantly different from the respective

numbers and return times of control fish of the same age, but variability among the hybrids in

morphological characters was greater than that among control fish. Second-generation

hybrids showed a reduced return rate and greater bilateral asymmetry in meristic characters,

which were interpreted as possible genetic effects of outbreeding depression in hybrids

between the two broodlines.
50

Even-year Pink Salmon: Genetic Variability Among Regions

Even-year adult pink salmon spawn throughout much of the species’ range but tend to

increase in abundance with latitude (Heard 1991). In southern British Columbia and

Washington, even-year spawners are less abundant than odd-year spawners, but they are as

abundant or more abundant than odd-year spawners in parts of northern British Columbia and

western Alaska. Even-year spawners are also abundant in Asia and tend to outnumber

odd-year spawners in northern areas. Most genetic studies of even-year spawners have been

made in Alaska and British Columbia; the information available for Asian even-year pink

salmon is more limited. Several studies indicate that the degree of genetic differentiation

among populations of even-year pink salmon is consistently lower than the degree of genetic

differentiation between even- and odd-year spawners (McGregor 1983, Beacham et al. 1988,

Gharrett et al. 1988, Shaklee and Varnavskaya 1994, Zhivotovsky et al. 1994).

No single study has included samples collected over the entire range of even-year

spawners. Zhivotovsky et al. (1994) analyzed allelic frequencies for 20 loci (sAAT-3*,

ADA-2*, mAH-3, mAH-4*, CK-A1*, CK-A2*, G3PDH-1*, GPI-B1*, GPI-B2*, GPI-A*,

LDH-A1* , LDH-A2*, LDH-B2*, LDH-C*, sMDH-A1,2*, sMDH-B1*, sMDH-B2*,

mMEP-1*, MPI*, PEPD-1*, PEPD-2*, and sSOD-1*) in samples from southeastern Alaska

(McGregor 1982, Lane et al. 1990), northwestern Alaska (Gharrett et al. 1988), and Hokkaido

in Japan (Noll et al. 1994). These samples encompassed about three quarters of the

geographic range of even-year pink salmon. Zhivotovsky et al. (1994) conducted a gene

diversity analysis, which partitions the total genetic diversity observed in a set of samples into

its regional components, at five hierarchical levels. The results indicated that 2.7% of the

diversity was due to genetic differences between odd- and even-year spawners, and 2.3% was

due to differences between Asian and North American samples. About 1.8% of the total

diversity was due to regional differences between southeastern Alaska and western Alaska

(including the Aleutian Islands). About 2% of the diversity was due to within-region

variability, including geographic and run-timing differences in the same river system.

In samples from the Aleutian Islands, northwestern Alaska and Kodiak Island,

Gharrett et al. (1988) examined 29 enzymatic loci (21 of which were polymorphic) and found

the greatest regional genetic differentiation between the group of Aleutian

Island-northwestern Alaska samples and a single sample from southcentral Alaska. Gharrett

et al. (1988) then combined allelic frequencies for sMDH-B1*,sMDH-B2*; PGM-2*, ME-1*,

G3PDH-1*, and PGDH* for Alaskan samples with those for samples from Sakhalin Island in

Russia (Salmenkova and Omel’chenko 1982, Altukhov et al. 1983). A maximum-likelihood

tree based on these frequencies indicated that the Russian samples were most closely related

to Alaskan samples from Norton Sound and the Aleutian Islands and more distantly. related to

samples from Bristol Bay. The sample from southcentral Alaska was most distantly related to

the Russian samples. Although these results are consistent with those obtained by

Zhivotovsky et al. (1994), it is not clear whether the major genetic discontinuity between

eastern and western even-year spawners occurs between Asia and North America across the

Bering Sea or across the Alaska Peninsula.
51

Several allozyme studies have been made of North American even-year spawning

populations of pink salmon, but no study has included samples from the entire range of

even-year spawners. Populations from northwestern Alaska appear to be most closely allied

with Aleutian Island populations (Gharrett et al. 1988), but these authors did not address the

relationship between these populations and those farther south. In British Columbia, Beacham

et al. (1988) detected three regional groups: 1) populations on the Queen Charlotte Islands

(these populations are distinct from all other British Columbia populations), 2) populations in

the Skeena, River and farther north, and 3) populations in central and southern British

Columbia, including Vancouver Island.

An important question in evaluating the status of the Snohomish River even-year

population is resolution of its origin. It may be a natural population or it may have originated

from eggs translocated from Alaska or British Columbia (Table 4). To address this issue, we

analyzed a set of allelic frequencies consisting of a single Snohomish River sample (J.

Shaklee22) and 34 samples from British Columbia (Beacham et al. 1988). This group of

samples had 15 polymorphic loci in common, 9 of which showed common allelic frequencies

of 0.95 or less in at least 1 sample. Frequencies for some loci were missing for Cluxewe,

Glendale, Kemano, and Puntledge Rivers, so we substituted the average of frequencies in the

two nearest populations for these loci. Other loci in these samples did not show strong allelic

frequency differences between nearby populations. For odd-year spawning pink salmon,

Shaklee et al. (1991) found a consistent difference in the scoring of two loci, sAAT-3* and

PGDH*, between his laboratory and the laboratory that produced the data presented by

Beacham et al. (1988) (see White and Shaklee 1991 for a discussion of this issue). Beacham

et al. (1988) reported a 0.105 higher average frequency for the common allele of sAAT-3* and

a 0.060 higher average frequency for the common allele of PGDH* in his samples than was

found by J. Shaklee in samples taken from the same localities in different years. We therefore

adjusted allelic frequencies for these two loci in the 34 samples from British Columbia. The

adjustment was based on a comparison of allelic frequencies in 13 populations of odd-year

pink salmon reported in Beacham et al. (1988) and later studied by Shaklee et al. (1991).

This basic set of data was then combined for analysis with data from Nickerson

(1979) for Prince William Sound, and McGregor (1983), Gharrett et al. (1988), and

unpublished data provided to us by A. J. Gharrett23 for western, central, and southeastern

Alaska, and the Aleutian Islands (Table 6). We also examined allelic frequencies for Kodiak

Island (Johnson 1979), but as only four polymorphic loci were in common with data from

British Columbia and Washington, we did not use these results to draw conclusions. We

22J. Shaklee, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Unpubl. data.

23A.J. Gharrett, Juneau Center, School of Fisheries and Ocean Sciences, University of

Alaska Fairbanks, 11120 Glacier highway, Juneau, AK 99801.
52

Table 6. Samples used in analyses of even-year pink salmon allozyme variability. Locality

numbers appear in Figures 6-13.
53

Table 6. Continued.
54

Table 6. Continued.
55

hypothesized that if the Snohomish River even-year spawners descended from eggs

transplanted from Alaska or British Columbia earlier in this century, they may show genetic

affinities to present-day Alaska or British Columbia even-year populations.

In the first analysis, allelic frequencies for populations in Prince William Sound

(Nickerson 1979) were included with frequencies for populations in Washington and British

Columbia and used to estimate Rogers’ (1972) genetic distances based on 10 polymorphic

loci (sAAT-3*, GPI-A* , GPI-B1*, G3PDH-1*, LDH-B2*, sMDH-A1*, sMDH-B1*,

mMEP-1*, PGDH*, and PGM-2*). The UPGMA phenogram (Fig. 6) showed two distinct,

nonoverlapping clusters: one including Prince William Sound samples (localities 43-64), and

the other including British Columbia samples (localities 2-34). The Snohomish River sample

(locality 1) fell within the cluster of British Columbia samples. Multidimensional scaling

analysis (NTSYS-pc; Rohlf 1993) of these distances (Fig. 7) showed a similar geographical

arrangement of the Prince William Sound and British Columbia samples, with the Snohomish

River sample appearing at the edge of the British Columbia cluster on the opposite side of the

cluster space from the Prince William Sound samples.

The second analysis included Snohomish River (locality 1), British Columbia

(localities 2-34), and several localities in southeastern (localities 35-42) and southcentral

Alaska, (localities 65-67; McGregor 1983, A. J. Gharrett24), the Aleutian Islands (localities

68-76; Gharrett et al. 1988), and western Alaska (localities 77-80; McGregor 1983). A

UPGMA phenogram (Fig. 8) of Rogers’ genetic distances based on 10 polymorphic loci in

common among the studies (sAAT-3*, ADA-2*, CK-A1*, GPI-B1*, G3PDH-1*, sMDH-A1*,

sMDH-B1*, mMEP-1*, PGDH*, and PGM-2*) showed 2 major clusters. One cluster

included samples from the Aleutian Islands, Kodiak Island and western Alaska, and the other

included samples from southeastern Alaska and British Columbia. The sample from the

Snohomish River was located within the cluster of British Columbia samples.

Multidimensional scaling of Rogers’ genetic distances showed close agreement between the

geographic locations of the samples and their general positions in the clusters apparent in the

multidimensional scaling (Fig. 9). Samples from western Alaska and the Aleutian Islands

were located at one end of the multidimensional space; those from southeastern Alaska were

placed in an intermediate position, and those from British Columbia were at the other end of

the multidimensional space. The Snohomish River sample occupied a position at the extreme

end of the multidimensional space, opposite the samples from Alaska.

The results of these analyses demonstrate that the even-year Snohomish River sample

is genetically more closely related to even-year populations from British Columbia than to

those from Alaska. If this sample is representative of Snohomish River even-year pink

salmon, these analyses lend strong support to an argument that this population did not arise

from an Alaskan transplant.

24A.J. Gharrett, Juneau Center, School of Fisheries and Ocean Sciences, University of

Alaska Fairbanks, 11120 Glacier Highway, Juneau, AK 99801. Unpubl. data.
56

Figure 6. UPGMA phenogram of Rogers’ (1972) genetic distances, based on 10 polymorphic

loci (see text), between samples of even-year pink salmon collected in Washington

(J. Shaklee, Washington Department of Fish and Wildlife, P.O. Box 43151,

Olympia, WA 98501, unpubl. data), British Columbia (Beacham et al. 1988), and

Prince William Sound, Alaska (Nickerson 1979). Locality numbers are given in

Table 6.
57
58

Figure 8. UPGMA phenogram of Rogers’ genetic distances, based on 10 polymorphic loci

(see text), between samples of even-year pink salmon from central and western

Alaska (McGregor 1983), the Aleutian Islands (Gharrett et al. 1988), central and

southeastern Alaska (McGregor 1983; A.J. Gharrett, Juneau Center, School of

Fisheries and Ocean Scineces, University of Alaska Fairbanks, 11120 Glacier

Highway, Juneau, AK 99801, unpubl. data), British Columbia (Beacham et al.

1988), and the Snohomish River, Washington (J. Shaklee, Washington Department

of Fish and Wildlife, P.O. Box 43151, Olympia, WA 98501, unpubl. data).

Locality numbers are given in Table 6.
59
60

We then analyzed a set of data that combined the Washington sample and the samples

from British Columbia to estimate the relationship of the Snohomish River sample to its

nearest geographic neighbors to the north. However, genetic data for even-year spawners on

southern Vancouver Island and in the Fraser River were not available; as noted in an earlier

section, such fish are rare in these areas. Excluding the Alaska samples allowed us to include

more loci in our analysis. We were aware that in British Columbia, Beacham et al. (1988)

found highly significant allelic frequency differences for most polymorphic loci among

evenyear populations within three areas: 1) the south (localities 2-13 in Table 6) and central

(localities 14-22) coasts of British Columbia, 2) the north (localities 23-27) coast. of British

Columbia, and 3) the Queen Charlotte Islands (localities 28-34). The amount of heterogeneity

among areas was substantially greater than that among localities within areas.

In our analysis of unadjusted allelic frequencies, the UPGMA clustering of Rogers’

genetic distances (based on 15 loci: sAAT-3*, ADA-2*, CK-A1*, GPI-B1*, G3PDH-1*,

mIDHP-1*, LDH-B1*, LDH-C*, sMDH-A1*, sMDH-B1*, mMEP-1*, PEPB-1*, PEPD-2*,

PGDH*, and PGM-2*) placed the Snohomish River sample outside the cluster of British

Columbia samples (Fig. 10). The Snohomish River sample also appeared as an outlier in the

multidimensional scaling of these genetic distances (Fig. 11). In the analysis of adjusted

allelic frequencies, the Snohomish River sample was embedded among samples from

southern and central British Columbia in the UPGMA phenogram (Fig. 12). The Snohomish

River sample showed a closer genetic affinity to samples from eastern Vancouver Island and

central British Columbia when the multidimensional scaling was based on adjusted allelic

frequencies (Fig. 13) than when the frequencies were unadjusted (Fig. 11). The analysis of

Beacham et al. (1988), which used Nei’s genetic distance, showed three distinct groups of

even-year spawning pink salmon in British Columbia: 1) Queen Charlotte Islands, 2) north

and central coasts, and 3) south coast and Vancouver Island. In our analysis using Rogers’

distance, groups 2 and 3 were less distinct.

If the Snohomish River population had experienced a strong reduction in population

size at or since the time of its founding, a reduction in the amount of genetic variability might

be apparent. Average heterozygosities with frequencies adjusted for sAAT-3* and PGDH*

ranged from 0.134 to 0.171 among the British Columbia even-year pink salmon samples and

was 0.134 in the Snohomish River sample. The Snohomish River population is at the lower

end of this range of heterozygosities but does not appear to have lost a substantial amount of

genetic variability relative to other populations. Therefore, if the Snohomish River even-year

population experienced a reduction in population size or a founder effect, it apparently was

not severe or protracted.

A hierarchical gene diversity analysis of 15 polymorphic loci (including adjusted

frequencies for sAAT-3* and PGDH*) indicated that 98.5% of the total genetic diversity in

British Columbia and Washington samples of even-year pink salmon was contained on

average within populations, 0.9% was due to allelic frequency variability among populations

within the areas, and 0.6% was due to differences among the 5 areas. This analysis suggests
61

Figure 10. UPGMA phenogram of Rogers’ genetic distances, based on 15 polymorphic loci

(see text) and unadjusted allelic frequencies for sAAT-3* and PGDH* (see text),

between samples of even-year pink salmon from British Columbia (Beacham et al.

1988) and the Snohomish River, Washington (J. Shaklee, Washington Department

of Fish and Wildlife, P.O. Box 43151, Olympia, WA 98501, unpubl. data).

Locality numbers are given in Table 6.
62
63

Figure 12. UPGMA phenogram of Rogers’ genetic distances based on 15 polymorphic loci

(see text) and adjusted allelic frequencies for sAAT-3* and PGDH* (see text),

between samples of even-year pink salmon from British Columbia and the

Snohomish River, Washington. Locality numbers and sources of data as in Figure

10.
64
65

that the loss of a single population would not lead to substantial loss of overall genetic

diversity as detected by allozymes in even-year pink salmon. The partitioning of genetic

variability at other parts of the genome is less well understood, not as easily quantified, and

may be different.

Odd-year Pink Salmon: Genetic Variability Among Regions

Odd-year spawners occur throughout the range of pink salmon, but they are more

abundant in the southern parts of this range in both Asia and North America. Several

researchers have examined the genetic structure of odd-year populations in various regions,

and some of these studies have included samples from other geographic regions; thus, a

preliminary comparison of within- and among-region variability is possible. Shaklee and

Vamavskaya (1994) examined 8 samples of Russian odd-year spawners and compared them

with 15 samples of odd-year and 1 sample of even-year pink salmon collected from localities

extending from southeastern Alaska, through British Columbia to Washington. Their cluster

analyses of genetic distances based on 33 variable loci revealed groups of populations from

three geographic areas: 1) Russia, 2) northern North America, including southeastern Alaska

and northern British Columbia, and 3) southern British Columbia and Washington. The

Russian and northern North American groups were genetically more closely related to one

another than either was to the southern North American group. These analyses indicated the

existence of a genetic discontinuity between northern and southern odd-year British Columbia

populations that is larger than the discontinuity between Alaskan and Russian populations.

Similar results were found by Varnavskaya and Beacham (1992), who combined their

allelic frequency data with those of Johnson (1979), McGregor (1983), and Beacham et al.

(1988) to calculate genetic distances between samples based on five loci in common to these

studies. Varnavskaya and Beacham’s cluster analysis of genetic distances indicated that the

odd-year spawners of Kodiak Island, southeastern Alaska and northern British Columbia were

more closely related to odd-year spawners of the Kamchatka Peninsula than they were to odd

year spawners in southern British Columbia. However, these authors found that genetic

distances between these groups were small relative to the distances between odd- and even

year spawners.

Odd-year Pink Salmon: Genetic Variability Within Regions

Asia--Glubokovskii and Zhivotovskii (1986) proposed a fluctuating stock model for

the population structure of Russian pink salmon in an attempt to explain variability in genetic

differentiation among these populations. They advanced this model as an explanation for

periodic changes in population structure that “are due to fluctuations of intensity of [genetic]

exchange ... between populations which is caused by the appearance of new and the

disappearance of old migrational barriers (both natural and anthropogenic).” The model

predicts that genetic differences (as measured with allozymes) among these populations are

unstable because of shifts in impediments to gene flow. These authors suggested that

population structure in pink salmon follows this model for two reasons: 1) the abundances of

fish in the same broodline changed markedly over time in an area, especially in the Kurile and
66

Sakhalin Islands and on the Kamchatka Peninsula (Ivankov 1986); and 2) early genetic

studies (Altukhov et al. 1983, Utter et al. 1980) indicated low levels of genetic differentiation

among populations. Early genetic studies of Asian pink salmon (Kartavtsev et al. 1981,

Salmenkova et al. 1981) failed to find the degree of genetic subdivision among populations

that was present in other species of salmon. However, more recent studies of Asian

populations (see below), have revealed a degree of genetic subdivision among populations

that is similar to that observed among populations in North America. The agreement of the

earlier results with the expectations of the fluctuating stock model may be largely due to

analyses involving few loci, because the more comprehensive recent analyses are at odds with

these expectations.

Four recent studies examined Asian populations in more detail. First, Kartavtsev

(1991) studied allozymic variability at 5 loci in samples from 22 Asian rivers over 3 to 5

generations and found little allelic frequency heterogeneity among samples within 4 areas: 1)

western Sakhalin Island, 2) eastern Sakhalin Island, 3) the Sea of Okhotsk, and 4) the

Kamchatka Peninsula. Kartavtsev found significant differences between some of these areas

in some years but not others, and concluded that extensive gene flow between localities was

responsible for the genetic homogeneity among populations.

Second, Kartavtsev et al. (1992) extended the analysis of these data and found no

significant deviations from expected Hardy-Weinberg genotypic proportions in samples

pooled over geographic areas. Although the fit to Hardy-Weinberg proportions in the pooled

sample was consistent with a lack of geographic. differentiation among populations, this

approach for detecting genetic differences among samples is weak.

Third, Vamavskaya and Beacham (1992) studied allozyme variability at 12 loci in

pink salmon from 8 rivers on the east coast of the Kamchatka Peninsula. These samples were

collected at river mouths, however, and therefore may not represent spawning-ground

populations. G-tests detected significant (P < 0.05) overall allelic frequency heterogeneity

among samples at five loci, and randomization tests detected significant heterogeneity at three

loci. Cluster analysis of genetic distances showed that the samples from the Hailula and Uka

Rivers were distinct from the other samples, but the genetic distances between these and the

remaining samples were small.

Finally, in a larger study, Shaklee and Vamavskaya (1094) examined the products of

44 protein-encoding loci and found variability at 24 loci in 8 samples of odd-year spawners

collected in 1991 from 8 localities in the Sea of Okhotsk, the Kamchatka Peninsula, and the

western Bering Sea. None of these localities had been represented in the work of Varnavskaya

and Beacham (1992). A geographically nested contingency-table analysis of allelic

frequencies at 23 loci demonstrated significant total heterogeneity among the 8 samples for 3

loci, but the sum of the G-test statistics over variable loci was not significant. Shaklee and

Varnavskaya (1994) detected little heterogeneity within, the three regions and found only a

single locus that showed significant differences among the three regions. Multidimensional

scaling of Cavalli-Sforza and Edwards’ (1967) chord genetic distances between samples

failed to show any geographically meaningful relationships among samples.
67

British Columbia--Beacham et al. (1985) collected spawning-ground samples from 4

rivers in British Columbia in 1982 (even-year spawners) and from 21 rivers in British

Columbia and Washington in 1983 (odd-year spawners). Samples of odd-year spawners were

divided into three geographic areas for analysis: 1) Johnstone Strait and Strait of Georgia

(nine localities), 2) Fraser River (seven localities), and 3) Puget Sound (four localities).

Significant allelic frequency heterogeneity was detected within each area, but the sums of Gtest statistics over loci indicated that the greatest amount of heterogeneity was due to

differences among localities in Johnstone Strait and the Strait of Georgia. Cluster analysis of

genetic distances based on 14 polymorphic loci detected 3 groups corresponding to the groups

used in the contingency-table tests, except that the sample from the south coast Indian River,

just north of the Fraser River, was included with the Fraser River samples and not with the

Johnstone Strait samples. The Fraser River and Puget Sound samples were more closely

related to one another than either was to the samples from northern British Columbia.

Beacham et al. (1988) examined a much larger number of samples at 33 even-year and

47 odd-year spawning sites in British Columbia and 4 odd-year sites in Puget Sound. To test

for allelic frequency differences, they divided odd-year spawners into 5 areas and found a

significant degree of allelic frequency heterogeneity among localities for most of the 15

polymorphic loci examined. As was the case for even-year pink salmon (see above), on a

larger geographic scale they found substantially greater heterogeneity in odd-year pink

salmon populations among areas than among localities within areas. Cluster analysis of

genetic distances between the British Columbia samples (not all of the loci were examined in

Puget Sound samples) showed two somewhat distinct Canadian groups: a cluster including

most of the northern island and mainland localities, and a cluster including Fraser River,

Vancouver Island, and south coast localities. However, the cluster of northern samples was

heterogeneous as it also contained five samples from southern British Columbia.

Washington-Shaklee et al. (1991) examined allelic frequency variability for 21

variable loci in 26 odd-year spawning localities in British Columbia and Washington in 1985,

1987, and 1989. A total of 52 collections were grouped into 26 samples by pooling multiple

year data at several localities, since little temporal variability was present among samples

taken from different generations at the same locality. Samples from minor tributaries were

also pooled in Hood Canal, the Snohomish River, the Stillaguamish River, the Skagit River,

and the Nooksack River, since little variability was present among tributaries within these

river systems. An analysis of chord genetic distances between samples revealed three

geographic clusters: 1) north coast British Columbia and northern populations from south

coast British Columbia; 2) southern populations from south coast British Columbia and

Fraser River and Puget Sound (except Nooksack River); and 3) Hood Canal and Washington

Strait of Juan de Fuca and Nooksack River (Fig. 1 in Shaklee et al. 1991).

The genetic definitions of groups 1 and 2 by Shaklee et al. (1991) were consistent

with those of Beacham et al. (1985, 1988) to the extent that localities in the two studies

overlapped. The second group consisted of three geographic subgroups: a) south coast of

British Columbia on the Strait of Georgia, b) Fraser River and its tributaries, and c) Puget
68

Sound. The samples from Hood Canal/Strait of Juan de Fuca (Olympic Peninsula) had not

been examined by Beacham et al. (1985, 1988), but in the analysis by Shaklee et al. (1991)

they appeared to represent a distinguishable cluster lying outside the Puget Sound, Fraser

River and southern British Columbia clusters. The sample from the Nooksack River (northern

Puget Sound) clustered with those from Hood Canal. Shaklee et al. (1991) hypothesized that

the genetic similarity between the Nooksack River and Hood Canal populations reflected a

supplementation of the natural Nooksack River population with eggs from the Hood Canal

Hatchery in 1977. However, a subsequent analysis suggested that the Nooksack River

population may be naturally distinct from other odd-year populations in Washington and

southern British Columbia (J. Shaklee, Shaklee et al. 1995).

Shaklee et al. (1995) also reported the results of analyses of samples from the upper

and lower Dungeness and Nisqually Rivers, so that allelic frequencies are now available for

19 naturally spawning populations in Washington. No genetic data were available for pink

salmon from the Elwha River, where they may be extinct, or from the South Fork of the

Nooksack River, where odd-year, spawners are known to occur. We conducted our own

analyses of Washington samples by combining them with British Columbia samples

processed in the same laboratory (Shaklee et al. 1991). Allelic identities among these samples

are, therefore consistent. Since some river systems were represented by a single sample,

samples of Washington fish were not pooled by river system; this configuration ensured that

the full range of interpopulation variability would appear in the analyses.

Considering the 19 Washington sampling localities alone, we calculated 4 different

genetic distances based on 23 polymorphic loci (sAAT-3*, sAAT-4*, ADA-2*, mAH-4*, sAH*,

ALAT*, CK-A1*, CK-C1*, GPI-B2*, GPI-A*, G3PDH-1*, FDHG*, GDA*, sIDHP-2*,

LDH-A1*, LDH-B1*, sMDH-A1,2*, sMDH-B1,2*, MPI*, PEPD-2*, PEP-LT*, PGDH*, and

PGM-2*), and used UPGMA cluster analysis and multidimensional scaling analysis to

examine relationships among samples. The results distinguished three Washington groups: 1)

Dungeness River, 2) Hood Canal, and 3) Puget Sound (Fig. 14, UPGMA). In the UPGMA

tree of chord genetic distances, the two samples from the Nooksack River clustered with

Hood Canal samples, as found by Shaklee et al. (1991), and the sample from the Nisqually

River was positioned outside the Hood Canal and Puget Sound clusters. Multidimensional

scaling of chord genetic distances (Fig. 15) showed three groups, but multidimensional

scaling of other genetic distances was less successful in distinguishing Hood Canal and Puget

Sound samples as separate clusters.

The minimum-spanning tree, in which branches connect nearest genetic neighbors,

indicated that samples from both the Nooksack and Nisqually Rivers are probably outliers

from the Puget Sound group. None of the populations showed greatly reduced levels of

genetic variability relative to the other populations that would indicate strong recent

25J. Shaklee, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Unpubl. data.
69

Figure 14. UPGMA phenogram of Cavalli-Sforza and Edwards’ (1967) chord genetic

distances, based on 23 polymorphic loci (see text), between samples of odd-year

pink salmon from Washington (Shaklee et al. 1991; J. Shaklee, Washington

Department of Fish and Wildlife, P.O. Box 43151, Olympia, WA 98501, unpubl.

data). Localities (abbreviation): Lower Dungness (LD), Uper Dungeness (UD),

Grey Wolf (GW), Doeswallips (Do), Duckabush (Du), Hamma Hamma (Ha),

Middle Fork Nooksakc (MN), North Fork Nooksack (NN), Nisqually (Ni),

Puyallup (Pu), Sauk (Sa: Skagit), Skykomish (Sy: Snohomish), Bacon (Bc:

Skagit), Snohomish (Sh), South Fork Stillaguamish (SSt), Skagit (Sk: main stem),

Finney (Fi: Skagit), North Fork Stillaguamish (NSt), and Snoqualmie (Sq:

Snohomish).
70

Figure 15. Multidimensioanl scaling and minimum spanning tree of chord genetic distances,

based on 23 polymorphic loci (see text), between samples of odd year pink

salmon from Washington. Localities and sources of data as in Figure 14.
71

reductions in population size. A hierarchical gene diversity analysis of allelic frequencies for

the 19 Washington populations indicated that geographic subdivisions accounted for a very

small proportion of the total diversity: 98.7% of the total allelic frequency variability was

contained on average within populations; 0.3% was due to differences among tributaries

within rivers; 0.5% was due to differences among rivers within regions; and 0.5% was due to

differences among regions.

To put genetic variability among Washington odd-year spawners into a broader

geographic perspective, we conducted additional analyses, adding 17 samples from British

Columbia (Shaklee et al. 1991). This combined set of allelic frequencies for 20 polymorphic

loci (sAAT-3*, sAAT-4*, ADA-2*, mAH-4*, sAH*, ALAT*, CK-A1*, CK-C1*, GDA*, GPDH1*, FDHG*, sIDHP-2*, LDH-A1*, sMDH-B1,2*, mMEP-1*, MPI*, PEPD-2*, PEP-LT*,

PGDH*, and PGM-2*) included 36 populations extending from northern British Columbia to

Puget Sound. A UPGMA cluster analysis of chord genetic distances between populations

(Fig. 16) again indicated a major subdivision between north coast British Columbia samples

and all other southern samples--the same result reported by Beacham et al. (1988) and

Shaklee et al. (1991). Four clusters appeared among the southern samples: 1) Olympic

Peninsula, 2) south coast British Columbia, 3) Fraser River, and 4) Puget Sound. One

difference between this tree and the preceding one was in the positions of the Hood Canal and

Nooksack River samples, both of which clustered more closely with the Dungeness River

samples in the larger set of data (Fig. 16). Multidimensional scaling of the chord genetic

distances (Fig. 17) revealed the major discontinuity between southern and northern British

Columbia populations, but southern populations were distributed more or. less continuously

with small discontinuities between 1) Dungeness River, 2) Hood Canal, 3) Puget Sound, 4)

Fraser River, and 5) south and central coasts of British Columbia. In this analysis, the

Nooksack River sample was manifest as an outlier from the Hood Canal cluster rather than

from the Puget Sound cluster, as it was in the preceding analysis of Washington samples

alone. This change in configuration resulted from the use of overlapping but different samples

of loci in the two analyses, and indicates that the genetic relationship of the Nooksack River

population to other Washington and British Columbia populations is not well resolved.

The results of the gene diversity analysis did not change substantially with the

addition of the Canadian samples in the analysis. Most (97.9%) of the variability was

contained, on average, within populations; 0.2% was due to variability among localities

within rivers; 0.8% was due to differences among rivers within regions; 0.7% was due to

differences among regions; and 0.3% was due to differences between north coast British

Columbia samples and the other southern samples.

The island model of migration can be used to estimate the number of migrants

between each population in this analysis by assuming that allelic frequencies at all loci reflect

an equilibrium between the differentiating effect of random genetic drift and the

homogenizing effect of gene flow (Wright 1951). The FST value (a measure of genetic

differentiation among populations), averaged over all loci, was 0.021 and yielded an estimate
72

Figure 16. UPGMA phenogram of chord genetic distances, based on 20 polymorphic loci

(see text), between samples of odd-year pink salmon in Washington and British

Columbia. Localities and sources of data as in Figure 14, with the following

additional localities from British Columbia (abbreviation): Fraser River (FR: main

stem), Vedder (Ve), Harrison (Hr), Coquihalla (Co), Thompson (Th), Seton (Se),

Bridge (Br), Indian (In), Skwawka (Sw), Quinsam (Qu), Kakweiken (Ka), Phillips

(Ph), Wakeman (Wa), Adam (Ad), Keogh (Ke), Babine (Ba), and Andesite (An).
73
74

of 11-12 migrants into each population per generation. This measure provides a rough

estimate of the level of intermixing between populations. However, if the populations are not

at equilibrium (i.e., if insufficient time has elapsed since population expansion during the

current interglacial period), then this statistic overestimates gene flow between populations.

On the other hand, this approach may underestimate the number of migrants into salmon

populations because salmon straying does not strictly follow the island model of migration.

Conclusions

Genetic data do not show a close affinity between the single population of even-year

pink salmon in the Snohomish River in Washington and any known source of eggs

translocated to Washington from northern British Columbia and Alaska. The analysis of

available data indicates that the Snohomish River even-year pink salmon population is

genetically most closely related to central and south coast British Columbia populations and

is a peripheral population at the southern extreme of the geographic distribution of even-year

spawners. However, genetic data are not available for even-year spawners from southern

Vancouver Island and the Fraser River, and the Snohomish River population may be closely

related to these populations.

Odd-year pink salmon populations located around the Pacific Rim can be divided into

three major genetic groups: 1) Asia, 2) Alaska and northern British Columbia, and 3)

southern British Columbia and Washington. Populations in the first two groups are more

closely related to one another than they are to populations in the third group. These major

divisions may have resulted from the formation of glacial barriers during the last ice age

(Beacham et al. 1988). The populations within each region are also genetically subdivided to

some degree, and the degrees of subdivision among populations within each of the three

regions are about the same.

Four subgroups of odd-year spawners are distinguishable within southern British

Columbia and Washington: 1) Olympic Peninsula, 2) south coast of British Columbia, 3)

Puget Sound, and 4) Fraser River. Groups 3 and 4 are most closely related to each other, and

groups 2 and I are progressively more distantly related to groups 3 and 4. Within Washington,

the populations of the Nooksack and Nisqually Rivers are genetic outliers and do not fall

within expected geographic clusters in the analyses. The relationship of the Nooksack River

population to other populations depended on the sample of loci and populations used in the

analyses: in analyses limited to samples from Washington, it was genetically closest to Puget

Sound populations, but when analyses included British Columbia samples and a different set

of loci, it tended to show greater affinity to Hood Canal populations. Consequently, the

relationship of this population to other populations in the region is unclear.

It should be recognized that the conclusions drawn from these analyses must be

tempered by the fact that the analyses were generated with data from several studies with

different sets of loci and different means of generating and interpreting electrophoretic data.

Some of the analyses involved an implicit assumption that the different sets of data are
75

compatible, an assumption that has been shown to be invalid for some pink salmon studies

(White and Shaklee 1991).

Discussion and Conclusions on ESU Determinations

Based on the genetic, life history, and ecological information presented above, the

Biological Review Team identified two ESUs for North American pink salmon in

Washington and southern British Columbia. In the following discussion we describe these

ESUs and outline the issues that were valuable to the BRT in making each ESU

determination.

Even-year Pink Salmon

A single population of even-year pink salmon occurs in the United States south of

Alaska, in the Snohomish River. This population is genetically much more similar to even

year pink salmon from British Columbia and Alaska than it is to odd-year pink salmon from

Washington. This pattern of similarity is also found in life history traits such as body size and

run timing. This result is consistent with numerous other studies that have found large genetic

differences between even- and odd-year pink salmon from the same area, with the magnitude

of the differences roughly comparable to that found between coastal and inland steelhead,

Oncorhynchus mykiss (Okazaki 1984, Reisenbichler et al. 1992). The BRT concluded,

therefore, that Snohomish River even-year pink salmon are in a different ESU than odd-year

pink salmon from Washington.

The origin of the Snohomish River even-year population and its relationship to other

even-year populations in British Columbia and Alaska is less certain. Although several

concerted efforts were made between 1910 and 1956 to introduce even-year pink salmon

from Alaska and British Columbia into Puget Sound, no direct evidence indicates that any

were successful in producing sustained returns. The allozyme studies described here also

failed to show a similarity of the Snohomish River sample to any of the putative sources of

stock transfers for which data are available.

Although available data do not provide evidence to support the hypothesis that the

Snohomish River population has resulted from a human-mediated stock transfer in this

century, this possibility cannot be excluded entirely. Not all sources of even-year stock

transfers are known, and some of those that are known have not been characterized

genetically. The genetic distinctiveness of the cur-rent Snohomish River population might

have resulted from genetic change (founder effect or subsequent genetic drift or both)

associated with a natural colonization event, but it might also have occurred relatively

recently as a result of similar processes in an introduced population. In addition, available

genetic information for the Snohomish River sample is based on a single year’s collection.

Nevertheless, the BRT concluded that even-year pink salmon in the Snohomish River

should be presumed to be a native population in the absence of more convincing evidence
76

that it is not. This decision was reached because 1) observed genetic and life history traits” of

this population are consistent with what might be expected from a natural colonization, and

2) this population has apparently been naturally self-sustaining in the Snohomish River for at

least 8 generations (and possibly for 25 or more).

At present, the Snohomish River population is relatively small (up to a few thousand

adults per generation), and this raises the issue of the importance of historical population size

in considering and defining ESUs. Because ESUs are intended to represent units that are

largely independent from other such units over evolutionarily important time frames, Waples

(1991a, p. 19) argued in the NMFS “Definition of Species” paper that

A Pacific salmon population should not be considered an ESU if the historic size (or

historic carrying capacity) is too small for it to be plausible to assume the population

has remained isolated over an evolutionarily important time period. In making this

evaluation, the possibility should be considered that small populations observed at

present are still in existence precisely because they have evolved mechanisms for

persisting at low abundance.

The small size of the current Snohomish River even-year population suggests that it

may be part of a larger geographic unit on evolutionary time scales (hundreds or thousands of

years). However, the Snohomish River odd-year population, which has the same spawning

habitat available, is 1-2 orders of magnitude larger, so it is possible that the even-year

population was also larger in the past. If so, long-term persistence of the even-year population

in isolation from other even-year populations would be easier to explain.

The Snohomish River even-year pink salmon population is geographically isolated by

several hundred kilometers from other even-year populations of appreciable size. However,

life history features of the Snohomish River even-year population are similar to those in other

even-year populations from central British Columbia. For example, peak spawning time of

Snohomish River even-year pink salmon is comparable to that of some British Columbia

even-year pink salmon, yet it is about 2 weeks earlier than that of Snohomish River odd-year

pink salmon. This timing differs despite spatial overlap in habitat use by even- and odd-year

adults in that system. Results of genetic analyses depend heavily on whether an adjustment is

made for possible differences between laboratories in methods for recording the data. A

comparison of published data suggests that the Snohomish River even-y . ear population is

genetically the most distinctive of any sample from the United States or southern British

Columbia. However, the Snohomish River population is much less distinctive in analyses of

adjusted allelic frequencies.

The BRT could not resolve with any degree of certainty the extent of the ESU that

contains the Snohomish River even-year pink salmon population. This issue was particularly

difficult because it is not clear which analyses--those with or without the adjustment for

possible bias--should be preferred. After considering all available information, about half the

BRT members concluded that the Snohomish River even-year population belongs in an ESU
77

by itself, and half concluded that it belongs in an ESU with populations from British

Columbia. Most of those favoring the latter scenario felt that the ESU probably includes all

even-year pink salmon from streams entering the Strait of Georgia and Johnstone Strait.

In any case, the BRT was unanimous in agreeing that any conclusion about the extent

of the even-year pink salmon ESU should be regarded as provisional and subject to revision

should substantial new information become available on 1) the Snohomish River population,

2) the history and success of transplanting even-year pink salmon into northwestern

Washington, or 3) small populations of even-year pink salmon in southern British Columbia

that are at present poorly understood.

Odd-year Pink Salmon

Genetic, life history, and environmental data were the most important factors in

consideration of ESUs for odd-year pink salmon. Environmental and ecological

characteristics generally show a strong north-south trend, but no substantial differences were

identified that consistently differentiated Washington and British Columbia populations. An

east-west gradient, separating populations along the Strait of Juan de Fuca from those to the

east, was considered more important for evaluating pink salmon populations. In addition,

three, U.S. rivers supporting odd-year pink salmon populations (the Nisqually, Nooksack, and

Puyallup Rivers) are dominated by glacial runoff, which may promote special adaptations in

spawning populations. However, glacial rivers are also common in most other areas of pink

salmon distribution throughout the Pacific Rim.

Although odd-year pink salmon show considerable variation in body size among

populations in Washington, the range of this variation does not exceed that found in British

Columbia. Among U.S. populations, Nooksack River fish average the smallest and Hood

Canal fish the largest in body size. Time of peak spawning varies over about a 4- to 5-week

period in northwestern Washington; spawning occurs earliest in the Nooksack and Upper

Dungeness Rivers, followed by Hood Canal and then Puget Sound (excluding the Nooksack

and Nisqually Rivers), with the latest spawning occurring in the Nisqually River.

Some pink salmon appear to reside in Puget Sound during their marine phase rather

than migrating to the open ocean (Jensen 1956, Hartt and Dell 1986). This behavior has not

been documented for pink salmon in other areas, but this may simply reflect a lack of

appropriate studies. Furthermore, resident Puget Sound fish have not yet been associated with

any particular freshwater population(s), so the importance of this trait in helping to define

odd-year pink salmon ESUs is not clear.

Comprehensive genetic analyses show that odd-year pink salmon from southern

British Columbia and Washington are clearly in a different evolutionary lineage than nearby

even-year populations and more northerly odd-year populations. Within the southern British

Columbia Washington group, there is also evidence of geographic population genetic

structure, with some differences among populations from the Dungeness River, Hood Canal,
78

Puget Sound, the Fraser River, and southern and central British Columbia. In some analyses,

samples from the Nisqually and Nooksack Rivers were both genetic outliers but were not

similar to each other. However, none of the genetic differences found within the southern

British Columbia-Washington group are very large in absolute magnitude. For example, the

FST Value (averaged over all loci) for all odd-year samples of pink salmon from Puget Sound

to central British Columbia was only 0.021, considerably smaller than the value found among

populations within the. ESU for Snake River spring/summer chinook salmon (O.

tshawytscha) (FST = 0.034; Waples et al. 1993) or among populations of steelhead (O.

mykiss) within the Klamath Mountains Province ESU (FST = 0.033; NMFS, unpubl. data26).

Although genetic differences (as determined by protein electrophoresis) among

odd-year pink salmon populations in the Puget Sound/British Columbia area are relatively

modest, the. general geographic coherence of the structure that does exist indicates that there

has been some reproductive isolation among pink salmon populations within this larger area.

The BRT next considered whether any of these individual groups of populations (Dungeness

River, Hood Canal, Puget Sound, Fraser River, southern and central British Columbia) might

represent a substantial contribution to ecological/genetic diversity of the species as a whole.

As noted above, the BRT did not find strong environmental or ecological differences among

these areas. Two of the U.S. rivers dominated by glacial runoff (Nooksack and Nisqually) also

have pink salmon populations that are genetically somewhat distinctive.. However, the two

populations are not similar to each other, either on the basis of genetic or life history

characteristics, so it seems unlikely that they are evolving together as a unit independent from

other odd-year pink salmon populations. A minority of the BRT believed that these two

populations were distinctive enough to each be separate ESUs, but most members thought

that they simply represented part of the natural variability within a larger ESU.

There was somewhat stronger concurrence among BRT members that odd-year pink

salmon populations from the Strait of Juan de Fuca (i.e., those in the Dungeness and Elwha

Rivers) were in a separate ESU from other Puget Sound and British Columbia odd-year

populations. Evidence to support this view is based on genetic differences detected by protein

electrophoresis, geography and habitat differences, and the fact that recent declines (including

the possible extinction of the Elwha River population) are shared by Strait of Juan de Fuca

populations but not Puget Sound populations. Notably, the upper Dungeness River population

shows an extraordinarily early run timing for the region and an apparently unique maturation

strategy. However, no life history data are available for the Elwha River population, and the

lower Dungeness River population has life history features similar to those of other Puget

Sound populations. Furthermore, although there are some habitat and ecological differences

between the Dungeness and Elwha Rivers and others in the Puget Sound area, a stronger

environmental transition is found west of the Elwha River, where much wetter areas typical

of the Olympic Peninsula are encountered (Weitkamp et al. 1995). The majority of the BRT

26Modified from the value reported by Busby et al. (1993) by omitting samples from

outside the ESU.
79

therefore concluded that the populations of the Dungeness and Elwha Rivers (if the latter still

exists) are part of the larger Puget Sound/British Columbia ESU for odd-year pink salmon.

Based on currently available information, the BRT concluded that the northern

boundary of the Puget Sound/southern British Columbia ESU corresponds to the geographic

location where a strong genetic discontinuity was observed in the Johnstone Strait region of

British Columbia. The ESU does not include northern British Columbia, Alaskan, or Asian

populations. In Washington, the westernmost populations in this ESU are both found in the

Dungeness River, but the ESU presumably would also include the Elwha River population, if

a remnant still exists. The BRT felt there was insufficient information to determine whether

other populations on the Olympic Peninsula or farther south,(if any such populations exist)

would be included in this ESU. Also uncertain is the relationship of odd-year populations

from southwestern Vancouver Island to this ESU.

It is clear that pink salmon populations within the Puget Sound/southern British

Columbia ESU contain a substantial amount of genetic and life history diversity. Much of this

diversity is contained within the “marginal” populations in Washington, which represent the

southernmost regularly spawning populations of North American pink salmon and are likely

to be important for colonizing available habitat in this region when conditions are favorable

to do so (Scudder 1989, Lesica and Allendorf 1995). The ESU has representatives that are

distinctive on the basis of run timing and maturation strategy, and may include an unknown

population or populations that lack an oceanic migration, using instead a protected

embayment for the marine phase of development and growth. In addition, the ESU has

populations that spawn far from tidewater, in stream reaches heavily influenced by glacial

runoff.

ASSESSMENT OF EXTINCTION RISK

Background

As outlined in the Introduction above, NMFS considers a variety of information in

evaluating the level of risk facing an ESU. Aspects of several of these risk considerations are

common to all pink salmon ESUs. These are discussed in general below; more specific

discussion of factors for each of the ESUs under consideration here can be found in the

following sections. Because we have not taken future effects of conservation measures into

account (see Introduction), we have drawn scientific conclusions about the risk of extinction

faced by identified ESUs under the assumption that present conditions will continue. Future

effects of conservation measures will be taken into account by the NMFS Northwest and

Southwest Regional Offices in making listing recommendations.

Absolute Numbers

The absolute number of individuals in a population is important in assessing two

aspects of extinction risk. For small populations that are stable or increasing, population size
80

can be an indicator of whether the population can sustain itself into the future in the face of

environmental fluctuations and small-population stochasticity; this aspect is related to the

concept of minimum viable populations (MVP) (Gilpin and Soul6 1986, Thompson 1991).

For a declining population, present abundance is an indicator of the expected time until the

population reaches critically low numbers; this aspect is related to the concept of “driven

extinction” (Caughley 1994).

In addition to total numbers, the spatial and temporal distribution of adults is

important in assessing risk to an ESU. Spatial distribution is important both at the scale of

river basins within an ESU and at the scale of spawning areas within basins

(“metapopulation” structure). Temporal distribution is important both among years, as an

indicator of the relative health of different brood-year lineages, and within seasons, as an

indicator of the relative abundance of different life history types or runs.

Traditionally, assessment of salmon populations has focused on the number of

harvestable or reproductive adults, and these measures comprise most of the data available for

Pacific salmon. In assessing the future status of a population, the number of reproductive

adults is the most important measure of abundance, and we focus here on measures of the

number of adults escaping to spawn in natural habitat. However, total run size (spawning

escapement + harvest) is also of interest because it indicates potential spawning in the

absence of harvest. Data on other life history stages (e.g., freshwater smolt production) can be

used as a supplemental indicator of abundance.

Because the ESA (and NMFS policy) mandates a biological review that focuses on

viability of natural populations, we attempted to distinguish natural fish from hatchery

produced fish. All statistics are based on data that indicate total numbers or density of adults

that spawn in natural habitat (“naturally spawning fish”). The total of all naturally spawning

fish (“total escapement”) is divided into two components: “Hatchery produced” fish are

reared as juveniles in a hatchery but return as adults to spawn naturally; “natural” fish are

progeny of naturally spawning fish.

Historical Abundance and Carrying Capacity

The relationship of current abundance and habitat capacity to that which existed

historically is an important consideration in evaluating risk for several reasons. Knowledge of

historical population conditions provides a perspective of the conditions under which present

stocks evolved. Historical abundance also provides the basis for establishing long-term

population trends. Comparison of present and past habitat capacity can also indicate

long-term population trends and problems of population fragmentation.

Although the relationship of present abundance to present carrying capacity is

important for understanding the health of populations, the fact that a population is near its

current capacity does not in itself mean that it is healthy. If a population is near capacity, there

will be limits to the effectiveness of short-term management actions to increase its
81

abundance, and competition and other interactions between hatchery and natural fish may be

important considerations because hatchery supplementation will further increase population

density in a limited habitat.

Quantitative assessments of habitat are quite rare, although rough estimates of

carrying capacity are frequently made for setting management goals. From the evidence

available, overall natural production of pink salmon does not appear to be below historical

levels for the odd-year ESU considered here, and production in the even-year ESU has been

generally increasing over the last 15 years. In the odd-year ESU, however, abundance in some

individual populations appears to be severely depressed, and some of these declines could be

due in part to habitat degradation in individual drainages (e.g., Dungeness River pink salmon;

Lichatowich 1993).

Trends in Abundance

Short- and long-term trends in abundance are a primary indicator of risk in salmonid

populations. Trends may be calculated from a variety of quantitative data, including dam or

weir counts, stream surveys, and catch data. These data sources and methods are discussed in

more detail below, under Approach. When data series are lacking, general trends may be

inferred by comparing historical and recent abundance estimates, or by considering trends in

habitat quantity or condition.

The role of artificial propagation (in the form of hatcheries) for Pacific salmon

requires careful consideration in ESA evaluations. Artificial propagation has implications

both for evaluating production trends and in evaluating genetic integrity of populations.

Waples (1991a,b) and Hard et al. (1992) discussed the role of artificial propagation in ESU

determination and emphasized the need to focus on natural production in the threatened or

endangered status determination. Because of the ESA’s emphasis on ecosystem conservation,

this analysis focuses on naturally reproducing salmon. A fundamental question in ESA risk

assessments is whether natural production is sufficient to maintain the population without the

constant infusion of artificially produced fish. A full answer to this question is difficult

without extensive studies of relative production and interactions between hatchery and natural

fish.

When such information is lacking, the presence of hatchery fish in natural populations

leads to substantial uncertainty in evaluating the status of the natural population. For

Washington pink salmon, hatchery production is small relative to natural production and is

localized in southern Hood Canal. Therefore, the presence of hatchery fish among naturally

spawning pink salmon is not likely to have a substantial effect on our attempts to evaluate the

sustainability of natural production for individual populations in this review.
82

Factors Causing Variability

Variations in the freshwater and marine environments are thought to be a primary

factor driving fluctuations in salmonid run size and escapement (Pearcy 1992, Beamish and

Bouillon 1993, Lawson 1993). Recent changes in ocean condition are discussed below.

Habitat degradation and harvest have probably made stocks less resilient to poor climate

conditions, but these effects are not easily quantifiable.

Threats to Genetic Integrity

In addition to being a factor in evaluating natural replacement rates, artificial

propagation can substantially affect the genetic integrity of natural salmon populations in

several ways. First, stock transfers that result in interbreeding of hatchery and natural fish can

lead to loss of fitness in local populations and loss of diversity among populations. The latter

is important to maintaining long-term viability of an ESU because genetic diversity among

salmon populations -helps to buffer overall productivity against periodic or unpredictable

changes in the environment (Fagen and Smoker 1989, Riggs 1990). Ricker (1972) and Taylor

(1991) summarized some of the evidence for local adaptations in Pacific salmon that may be

at risk from stock transfers.

Second, because a successful salmon hatchery dramatically changes the mortality

profile of a population, some level of genetic change relative to the wild population is

inevitable, even in hatcheries that use local broodstock (Waples 1991b). These changes are

unlikely to be beneficial to naturally reproducing fish.

Third, even if naturally spawning hatchery fish leave few or no surviving offspring,

they still can have ecological and indirect genetic effects on natural populations. On the

spawning grounds, hatchery fish may interfere with natural production by competing with

natural fish for territory or mates. If they successfully spawn with natural fish, they may divert

production from more productive natural-by-natural crosses. The presence of large numbers

of hatchery juveniles or adults may also alter the selective regime faced by natural fish.

For smaller stocks (either natural or hatchery), small-population effects (inbreeding,

genetic drift) can also be important concerns for genetic integrity. Inbreeding and genetic drift

are well understood at the theoretical level, and researchers have found inbreeding depression

in various fish species (reviewed by Gall 1987 and Allendorf and Ryman 1987). Other studies

(e.g., Simon et al. 1986, Withler 1988, Waples and Teel 1990; see also Campton 1995) have

shown that hatchery practices commonly used with anadromous Pacific salmonids have the

potential to affect genetic integrity. However, we are not aware of empirical evidence for

inbreeding depression or loss of genetic variability in any natural or hatchery populations of

Pacific salmon or steelhead.
83

For Washington pink salmon, genetic concerns, particularly those related to stock

transfers and small-population effects, are relevant primarily to Snohomish River even-year

pink salmon and Hood Canal odd-year pink salmon.

Recent Events

A variety of factors, both natural and human-induced, affect the degree of risk facing

salmon populations. Because of time-lags in these effects and variability in populations,

recent changes in any of these factors may affect current risk without any apparent change in

available population statistics. Thus, consideration of these effects must go beyond

examination of recent abundance and trends. Unfortunately, forecasting future effects is rarely

straightforward and usually involves qualitative evaluations based on informed professional

judgment, A key question regarding the role of recent events is: Given our uncertainty

regarding the future, how do we evaluate the risk that a population may not persist?

For example, climate conditions are known to have changed recently in the Pacific

Northwest, and Pacific salmon stocks south of British Columbia have been affected by

changes in ocean production that occurred during the 1970s (Pearcy 1992, Lawson 1993).

Much of the Pacific coast has also been experiencing drought conditions in recent years,

which may depress freshwater salmon production. However, at this time we do not know

whether these climate conditions represent a long-term change that will continue to affect

stocks in the future or whether these changes are short-term environmental fluctuations that

can be expected to be reversed in the near future. Possible future effects of recent or proposed

conservation measures have not been taken into account in this analysis.

Other Risk Factors

Other risk factors typically considered for salmonid populations include disease

prevalence, predation, and changes in life history characteristics such as spawning age or size.

We have not found evidence that any of these factors are widespread throughout any pink

salmon ESU, except for the apparent decline in body size of adult pink salmon previously

discussed under Pink Salmon Populations in Washington. Factors that may be important for

individual populations are noted in the ESU summaries below.

Approach

Previous Assessments

In considering the status of ESUs, we evaluated both quantitative and qualitative data.

Among the qualitative data considered were previous reviews of the status of pink salmon

(Nehlsen et al. 1991, WI)F et al. 1993). These reviews used different definitions of population

and different criteria to assess the status of the populations. Nehlsen et al. (1991) classified

populations as at high risk of extinction, moderate risk of extinction, or of special concern.

They considered populations at high risk of extinction to have likely reached the threshold for
84

classification as endangered under the ESA. Populations were placed in this category if they

had declined from historical levels, were continuing to decline, or had spawning escapements

less than 200. Populations were classified as at moderate risk of extinction if they had

declined from historical levels but presently appear to be stable at a level above 200

spawners. Nehlsen et al. (1991) felt that populations in this category had reached the

threshold for threatened status under the ESA. Populations were classified as of special

concern if a relatively minor disturbance could threaten them, if insufficient data were

available for them, if they were influenced by large releases of hatchery fish, or if they

possessed some unique character. Nehlsen et al. (1991) also listed some populations that they

considered as possibly extinct, but did not discuss populations not considered to be at some

risk. They classified pink salmon in the Skokomish (southern Hood Canal) and Elwha Rivers

as at high risk of extinction, and pink salmon in the Dungeness River as at moderate risk of

extinction (Table,7). They listed California runs in the Klamath and Sacramento Rivers as

extinct, and the run in the Russian River as possibly extinct.

WDF et al. (1993) classified populations as to origin (“native,” “non-native,”

“Mixed,” or “unknown”), production (“wild,” “composite,” or “unknown”), and status

(“healthy,” “depressed,” “critical,” or “unknown”). Status categories were defined as healthy,

“experiencing production levels consistent with its available habitat and within the natural

variations in survival for the stock”; depressed, “production is below expected levels ... but

above the level where permanent damage to the stock is likely”; and critical, “experiencing

production levels that are so low that permanent damage to the stock is likely or has already

occurred.”

Of the 15 populations of pink salmon identified by WDF et al. (1993; see Table 7), 9

were classified as healthy, 2 as critical, 2 as depressed, and 2 as unknown. They classified all

runs as wild production and all except those in the North and Middle Forks of the Nooksack

River as native origin. Pink salmon spawning in these two forks of the Nooksack River are

likely to be designated as native runs in the 1995 revision of SASSI, based on new sample

collections and interpretation of genetic data (J. Ames27, J. Shaklee28). Nine of the Puget,

Sound and Hood Canal populations were classified as healthy and two in the Nooksack River

were of unknown status. Populations in the Dosewallips and upper Dungeness Rivers were

classified as depressed, and populations in the lower Dungeness and Elwha Rivers were

classified as critical (Table 7).

Various problems arise in applying results of these studies to ESA evaluations. One

major problem is that the definition of “stock” or “population” varied considerably in scale

27J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., April 1995.

28J. Shaklee, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., April 1995.
85

Table 7. Status of pink salmon populations assessed in previous reviews.
86

among studies, and sometimes among regions within a study. Identified units range in size

from large river basins to minor coastal streams and tributaries. A second problem is the

definition of categories used to classify population status. Only Nehlsen et al. (1991) used

categories intended to relate to ESA threatened or endangered status, and they applied their

own interpretations of these terms to individual populations, not to ESUs as defined here.

WDF et al. (1993) used general terms describing the status of populations that cannot be

directly related to the considerations important in ESA evaluations. For example, the WDF et

al. (1993) definition of healthy could conceivably include a population that is at substantial

extinction risk due to loss of habitat, hatchery fish interactions, and/or environmental

variation, although this does not appear to be the case for any pink salmon population. A third

problem is the selection of populations or stocks included in the review. Nehlsen et al. (1991)

did not evaluate (or even identify) populations not perceived to be at risk, so it is difficult to

determine the proportion of populations they considered to be at risk in any given area. WDF

et al. (1993) included all natural Washington populations of pink salmon in their assessment,

as they considered all of these to be substantially “wild.”

Data Evaluations

Quantitative evaluations of data included comparisons of current and historical

abundance of pink salmon, calculation of recent trends in escapement, and evaluation of the

proportion of natural spawning attributable to hatchery fish. Historical abundance information

for these ESUs is largely anecdotal. Time-series data are available for many populations, but

the amount and quality of the data varied among ESUs. We compiled and analyzed this

information to provide several summary statistics of natural spawning abundance, including

(where available) recent total spawning run size and escapement, percent annual change in

total escapement, recent naturally produced spawning run size and escapement, and average

percentage of natural spawners of hatchery origin.

Although our evaluation used the best data available, these data have several

limitations, and not all summary statistics were available for all populations. For example, we

generally did not measure spawner abundance directly for all populations; rather, we often

had to estimate abundance from catch (which itself may not always have been measured

accurately) or from limited survey data. In many cases, it was difficult to separate hatchery

production from natural production.

Quantitative methods--Information on population abundance was compiled from a

variety of state, federal, and tribal agency records. We believe it to be complete in terms of

long-term adult abundance records for pink salmon in the region covered here. Principal data

sources were fishery statistics and stream surveys. Neither of these provides a complete

measure of abundance for any of the streams. Specific problems are discussed below for each

data type.

Data types--There are two primary sources of abundance data for pink salmon:

fishery statistics and spawning escapement surveys. Fishery data span a longer series, but
87

landings in Washington, Oregon, and California are dominated by Fraser River fish and do

not accurately reflect abundance of local pink salmon populations. In addition, fisheries

harvest mixed populations and no systematic marking or tagging programs can be used to

attribute fishery landings to streams of origin consistently. Landings from areas covered by

the Pacific Salmon Treaty (PST) have been partitioned by country of origin with genetic stock

identification (GSI) techniques since 1985, and prior to that were allocated by assuming that

U.S. populations provided a constant percentage of the landings in treaty catch areas (J.

Woodey29) . These GSI techniques are used to estimate landings of fish originating from 23

stocks, but harvest management is currently based on the analysis of contributions from 3

major groups—Fraser River, non-Fraser River British Columbia, and Puget Sound (B.

White30) . Landings within Puget Sound and the U.S. origin catches from U.S. PST catch

areas are allocated among individual populations on the basis of the location of the fisheries

and the relative abundance, of the populations believed to contribute to each catch area.

Implicit in this methodology is the assumption that populations contribute to fisheries

in direct proportion to their run size. However, shifts in the timing and migratory pathways of

returning populations can substantially alter their contribution rate to preterminal fisheries.

Because the Fraser River typically produces many more pink salmon than Puget Sound, this

system of run reconstruction inaccurately estimates fishery exploitation rates on individual

populations, especially for smaller populations. For these reasons, spawning escapement

estimates are the most reliable estimates of population abundance, although they also have

inaccuracies and reflect abundance only after the populations have been subjected to variable

domestic exploitation and foreign interception rates.

Fishery landings of pink salmon are summarized in the Northwest Indian Fisheries

Commission (NWIFC) run reconstruction database (Big Eagle & Assoc. and LGL Ltd. 1995).

Run reconstruction attributes catches to stream of origin on the basis of geographic location

and assumed migration pathways, but the process is an approximation at best and can provide

only reasonably accurate estimates for individual populations. Nevertheless, estimates of

Puget Sound exploitation rates for individual populations can be constructed from these data.

The most comprehensive attempt to attribute historical harvest to area of origin was

made by Canadian Department of Fisheries and Oceans (CDFO) biologists who reconstructed

estimates of landings from many sources using a variety of methods and synthesized a time

series of harvest for the United States that spans the period from 1889 through 1981 (Shepard

et al. 1985). They also estimated the harvest of U.S. (excluding Alaska) pink salmon from

U.S. landings by adding in Canadian interceptions of U.S. salmon and subtracting U.S.

29J. Woodey, Pacific Salmon Commission, 600-1155 Robson Street, Vancouver, B.C.

V6E 1B5. Pers. commun., March 1995.

30B. White, Pacific Salmon Commission, 600-1155 Robson Street, Vancouver, B.C.

V6E 1B5. Pers. commun., February 1996.
88

interceptions of Canadian salmon. Since there is practically no domestic production of pink

salmon outside of Puget Sound, these landings can be attributed to Puget Sound production.

However, the partitioning of U.S. and British Columbia landings by country of origin requires

a number of assumptions and is therefore imprecise. It is possible to calculate exploitation

rates on Puget Sound pink salmon by dividing catch by catch plus escapement for the entire

Puget Sound for the years in which both estimates are available. These estimated exploitation

rates show an increasing trend with a low of about 35% in 1969 to a high of about 90% in

1981, but, the accuracy of these estimates is questionable.

In Puget Sound, most spawning escapement estimates have been made with a few

standard methods (see Vernon et al. 1964, Hourston et al. 1965). In the early 1960s an

intensive effort was made to estimate the size of pink salmon runs in Puget Sound. Pink

salmon were captured near the mouths of rivers and marked with external tags. Spawning

grounds were surveyed and spawners were sampled throughout the river systems; effort was

concentrated in areas of heaviest spawning. The spawner distribution was used to establish

index areas. Carcasses were examined for tags, and Petersen mark-recapture estimates

(Ricker 1958) of the total numbers of spawners were made. The Petersen estimate simply

expands the number of tags applied to fish by the ratio of unmarked to marked fish observed

in the carcass surveys to estimate the number of unmarked fish in the spawning run

(Caughley 1977). This procedure assumes that the marked fish are randomly distributed in the

spawning population, that they have the same survival rate as unmarked fish or that spawners

have an equal probability of being in the sample, that no tags are lost, and that all marked fish

encountered in the carcass surveys are recognized.

Violation of these assumptions reduces the accuracy of estimates and tends to bias the

estimates upward. Attempts were made by WDF to reduce biases due to mortality of tagged

fish and tag loss by rounding down the Petersen estimates (D. Hendrick31; see Vernon et al.

1964, Hourston et al. 1965). These Petersen estimates of total spawning escapement are the

best estimates available for Puget Sound, and they became the base-year data for subsequent

escapement estimates (Johnson et al. 1968, J. Ames32)., In years following the Petersen

estimates, spawning escapement has typically been estimated by multiplying the base-year

spawning escapements by the ratio of counts of total live plus dead fish observed at the peak

of the run (peak counts) in index reaches to peak counts in the base years. Historical estimates

for northern Puget Sound rivers were usually generated by comparing the total number of

carcasses counted in index areas to the total number of carcasses in the same areas during the

31D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., April 1995.

32J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., December 1994.
89

tagging studies. (Except for the Nooksack River, consistent live counts were not made during

the tagging years; D. Hendrick).

Since the mid-1970s, area-under-the-curve (AUC) estimates have been used instead of

peak counts to scale the base-year Petersen estimates (Ames 1984). These estimates are

currently compared for the Nooksack and Stillaguamish Rivers (D. Hendrick). These AUC

estimates are made from repeated surveys of the spawning grounds; the sequential counts are

plotted against time and used to generate an escapement curve. The area under the curve is

calculated to provide an estimate of the number of fish-days composing the spawning run in

an index reach.

Computed statistics--To represent current run size or escapement where recent data

were available, we have computed the geometric mean of the most recent 5 years reported (or

fewer years if the data series is shorter than 5 years). We tried to use only estimates that

reflect the total abundance for an entire river basin or tributary, and avoided index counts or

dam counts that represent only a small portion of available habitat.

As an indication of overall trend in pink salmon populations in individual streams, we

calculated average (over the available data series) percent annual change in adult spawner

indices within each river basin. Trends were calculated as the slope (a) of the regression of

loge

(abundance) against years corresponding to the biological model N(t) = beat, where N(t) is

population size in year t, b is a scalar coefficient, and e is the base of the natural logarithm.

Slopes significantly different from zero (P < 0.05) were noted. The regressions provided

direct estimates of mean instantaneous rates of population change (a); these values were

subsequently converted to percent annual change, calculated as 100(ea - 1). No attempt was

made to account for the influence of hatchery produced fish on these estimates, so the

estimated trends included any supplementation effect of hatchery fish.

In reviewing the status of individual ESUs of pink salmon in Washington and

southern British Columbia, we considered the risks posed by artificial propagation to be less

important than other risk factors, such as habitat degradation, indicating declines in

abundance. This factor was a consideration in the BRT’s conclusions that the ESUs for pink

salmon are not at risk of extinction or endangerment. However, the BRT’s conclusions on this

issue should be regarded as preliminary because information about the degree of interactions

that actually occur between hatchery and natural fish is still incomplete.

33D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., April 1995.

34D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., April 1995.
90

Analysis of Extinction Risk by ESU

Several data series of pink salmon spawner abundance in northwestern Washington

exist, but the ultimate sources for all quantitative estimates of spawning escapements are

WDFW for data from Washington and CDFO for data from British Columbia. These data

have been compiled in an electronic database and submitted to the ESA administrative record

(Big Eagle & Assoc. and LGL Ltd. 1995). These data are summarized for even- and odd-year

pink salmon in Figures 18-20. Trends and recent averages for spawning escapements of even

and odd-year pink salmon populations in Washington and British Columbia are given in

Tables 8 and 9. Additional information on individual pink salmon streams is summarized

below.

Even-year ESU

Snohomish River--There are anecdotal and sporadic accounts of even-year runs for

some northern Puget Sound rivers (D. Hendrick35, W. Waknitz36) , but the only river for which

an even-year population has been documented is the Snohomish River (WDF et al. 1993).

The run sizes were estimated by aerial counts of redds, and these estimates were used to scale

Snohomish River base-year estimates from odd-year runs. This run has been documented

every even year since 1980, but no run-size estimate was made in 1982. The distribution of

spawning is thought to be far more restricted for even-year pink salmon than for odd-year

pink salmon, with most spawning activity occurring in the mainstem Snohomish River.

Scattered redds have been observed in the Skykomish River as far upstream as Sultan. In

general, this run has been increasing since 1980. Estimated escapement for 1994 was

approximately 1,600 fish, which is less than 1990 and 1992 estimates but greater than those

for 1986 and 1988. A few adults are occasionally reported in even years in the Nooksack,

Stillaguamish, and Skagit Rivers, but the numbers are very small, and surveys are not

conducted in these systems in even years.

British Columbia--All of the Canadian even-year populations for which we received

escapement estimates are located in rivers draining into the northern Strait of Georgia or

Johnstone Strait. Additional populations may occur on the west coast of Vancouver Island as

far south as the Strait of Juan de Fuca (Aro and Shepard, 1967), but if so these populations

are probably very small.

35D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., January 1995.

36W. Waknitz, NMFS Northwest Fisheries Science Center. Unpubl. observation.
91

Figure 18. Spawning escapements for odd- and even-year pink salmon populations in

Washington. For each population, an exponential trend line is fitted to the

spawning escapements (see Tables 8 and 9 for statistical significance of trend

estimates). All populations are odd-year except for Snohomish River pink salmon.

In the Nisqually River from 1981 to 1985 and in 1993, escapements were not

estimated and a value of 500 was assigned for each of these years for run

reconstruction. Escapements in the Elwha river in 1977 and 1979 were assumed to

be 14.25% of the Dungeness River escapement (see text for discussion).
92

Figure 18. Continued.
93

Figure 19. Spawning escapements for selected even-year pink salmon populations in British

Columbia. For each population, an exponential trend line is fitted to the spawning

escapement (see Table 8 for statistical significance of trend estimates).
94

Figure 19. Continued.
95

Figure 20. Spawning escapements for selected odd-year pink salmon poulations in British

Columbia. For each population, an exponential trend line is fitted to the spawning

escapement (see Table 9 for statistical significance of trend estimates).
96

Figure 20. Continued.
97

Table 8. Average spawning escapement estimates and trends for even-year pink salmon

populations in Washington and British Columbia. Average escapements are

geometric means calculated from the five most recent spawning escapement

estimates. For each system, annual percentage change is calculated for the periods

shown in Figures 18-20. See text for further explanation.
98

Table 9. Average spawning escapement estimates and trends for odd-year pink salmon

populations in Washington and British Columbia. Average escapements are

geometric means calculated from the five most recent spawning escapement

estimates. The annual percentage change, calculated for the periods shown in

Figures 18-20, includes the effect of the unusually high odd-year escapements

observed in 1963 in Washington. See text for further explanation.
99

Odd-year ESU

Nooksack River--Because the Nooksack River is fed by glacial meltwater and the

fish cannot be counted reliably in the main stem because of the high turbidity, escapement

estimates for the Nooksack River are the least reliable in northern Puget Sound. Data

collection began in 1959, and Petersen estimates were made in 1959, 1961, and 1963. These

base-year estimates have subsequently been scaled by peak counts and AUC estimates. In the

base years, most fish spawned in the main stem. This may still be the case, as tributary

spawning alone cannot account for total production from the system, but only clear water

tributaries are surveyed due to the difficulty observing spawners in the main stem. Because

these tributaries contain a relatively small and variable fraction of the spawning escapement,

the escapement estimates have potentially large errors.

Skagit River--Skagit River run sizes were estimated in the main stem by comparing

total carcasses in mainstem index areas to the number of carcasses sampled during tagging to

construct the Peterson estimates in the base years 1959 through 1963. AUC estimates were

used in tributaries. Since the base years, the distribution of spawners has shifted somewhat.

There is presently more spawning in upper reaches of the river than occurred in the base

years, so recent runs may be underestimated. However, this bias should be minimal because

tagging year data are available for the entire main stem and because WDFW currently surveys

nearly 65 km of the river’s length (D. Hendrick).

Stillaguamish River--Escapement estimates are again based on AUC estimates of

observed live spawners. Base years are 1959- through 1965, with additional Petersen

estimates, from 1967 and 1987. In the original base years the majority of fish spawned in the

North Fork Stillaguamish River. This remained the case until 1987, when the Washington

Department of Fisheries (WDF) conducted a mark-recapture study on the Stillaguamish River

(D. Hendrick). Drought conditions in that year limited spawning in the North Fork, and

substantial numbers of fish spawned in the South Fork. WDF biologists did not realize where

the fish were until after the peak of spawning occurred, so their use of the 1987 AUC estimate

for the South Fork in scaling subsequent escapements is questionable. Since 1989, the run in

the North Fork has been rebuilding, but the South Fork still has the majority of spawning

activity.

Snohomish River--Runs were estimated by AUC scaling of base-year Petersen

estimates for 1959 through 1963 and 1967. Index reaches were in the Snohomish River and

the Skykomish River, with a few observational surveys made in the Snoqualmie River. The

37D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., January 1995.

38D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., January 1995.
100

portion of the run using the Snoqualmie River is unknown but may be increasing. In some

years, considerable numbers of spawners have been reported in the Tolt River, but the run is

inconsistent and is therefore believed to be just a component of the Snoqualmie River run.

Spawning distribution has expanded since the base years. There is presently more spawning

in intertidal areas, the Snoqualmie River, and in upper reaches of the Skykomish River and its

tributaries (D. Hendrick39). Because of this shift, the index reaches may contain a smaller

fraction of the escapement than they did in the base years, and recent estimates may be biased

downward.

Lake Washington--There is no evidence of sustained runs of pink salmon in the Lake

Washington watershed.

Southern Puget Sound and Hood Canal--Recent spawning escapement estimates

for southern Puget Sound and Hood Canal are based on AUC estimates of total live spawners.

Data series are of variable length, and early estimates were the sum of live and dead fish

observed during the peak of the spawning run. Except for the Nisqually River, which is

surveyed by Nisqually tribal biologists, spawning ground surveys are generally conducted by

WDFW biologists, and the AUC estimates are made by WDFW from WDFW and tribal data.

Data are generally reliable, except for those from surveys in the Nisqually River for 1981-85

and 1993 (see below).

The Nisqually River is glacially influenced with a few clear water tributaries, and

consequently has presented some special problems, in estimating escapement. Escapements

have been estimated with several methods. Before 1981, escapements were estimated from

visual surveys in the main stem and tributaries. From 1987 to 1991, estimates were made

from a combination of mark-recapture studies, visual surveys in tributaries, and fishery

catches. Estimates from the tributary surveys are expanded, somewhat arbitrarily, to account

for mainstem spawning. In 1981, 1983, and 1985, conditions were unfavorable in the

tributaries and the vast majority of fish spawned in the main stem. The number of spawners in

the main stem was unknown, but very few fish were seen in the tributary surveys. Peak counts

in those years ranged from three to nine fish. In 1993, no pink salmon data were recorded

during stream surveys. Thus, for odd years from 1981 to 1985 and for 1993, an escapement of

500 was assigned as a placeholder for run reconstruction (J. Ames40, J. Uehara41). For all four

of these years, actual spawning escapement is unknown and should be considered missing

values.

39D. Hendrick, Washington Department of Fish and Wildlife, 333 E. Blackburn Rd.,

Mount Vernon, WA 98273. Pers. commun., January 1995.

40J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., April 1995.

41J. Uehara, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., April 1995.
101

Dungeness River--The Dungeness River supports two different populations of pink

salmon: an early run that enters the river in July and August and ascends to areas above RKm

16, and a late run that enters the river in late August and September and spawns below RKm

5. Until 1981, a hatchery rack at about RKm 16 was used to enumerate the early run. The

lower (late) run was not surveyed regularly and was assumed to be a fixed proportion of the

early run in some years. When the rack was removed in 1981, WDF had to change their

estimation method, a change that coincided with the effects of a major winter flood in 1980

on the incubating 1979 brood. WDFW biologists do not believe that the visual survey method

significantly underestimates the run size in this case, and it seems unlikely that

underestimation could fully account for the observed drop in run size. Survey conditions are

consistently good in the Dungeness River when spawner counts are made (J. Ames42).

Since 1981, the spawning ground surveys have attempted to estimate the entire run by

AUC estimates. Runs were relatively stable until 1981, when 1979-brood fish affected by the

1980 winter flood returned43. Both runs have been depressed since that time, with the lower

run exhibiting a continued decline. Both runs on the Dungeness River exhibit statistically

significant downward trends in spawner abundance.

Elwha River--Data extend back to 1959 and tend to become less reliable in recent

years. Estimates in 1959, 1961, and 1963 were based on visual surveys made by WDF as part

of an extensive marking program at that time (J. Ames44). In 1975, the escapement estimate of

1,500 was based on a single float survey in which it was estimated that 300 spawners were

seen. In 1977 and 1979, the Elwha River was not surveyed, but its escapement was estimated

to be 14.25% of the total escapement to the Dungeness River. This was based on the average

ratio of escapements to the two rivers in the preceding five spawning runs. As did the

Dungeness River, the Elwha River experienced severe flooding in the winter of 1979-80.

Since 1981, the Elwha River has been surveyed every run year with 5 to 18 surveys

conducted each year. These surveys, which were made primarily for chinook salmon,

incorporated multiple breakout counts for different river sections. More intensive surveys in

1991 and 1993 failed to find any pink salmon in the Elwha River. As noted earlier in this

report, WDFW’s management biologists for this area believe the Elwha River run of pink

salmon to be extinct.

British Columbia--Data on run sizes for Fraser River populations and populations in

the Strait of Georgia and Johnstone Strait have been received -from CDFO (Big Eagle &

42J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., April 1995.

43A large slide on Gold Creek, a tributary of the upper Dungeness River, during the

winter of 1968-69 apparently reduced productivity of the upper Dungeness River population

during the early 1970s (Johnson 1973).

44J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., January 1995.
102

Assoc. and LGL Ltd. 1995). Spawning escapements were estimated with a variety of

methods, and managers have been required to provide escapement numbers regardless of the

quality of the estimates (Big Eagle & Assoc. and LGL Ltd. 1995). In addition, escapement

data from western Vancouver Island may be collected only incidentally during surveys for

other species. For these reasons, several escapement estimates for British Columbia

populations are of questionable quality. Nevertheless, pink salmon escapement data collected

over the last several years by Canadian Department of Fisheries and Oceans staff suggest that

western Vancouver Island escapements have declined significantly since the 1970s. Current

escapement levels on the west coast of the island are typically small, that is, a hundred to a

few thousand adults. Indirect evidence points to declining trends in some populations along

the southwestern coast of Vancouver Island, but this evidence is weak because the

escapement data are not robust (W. Luedke45). Tables 8 and 9 summarize the escapement data

that Canadian. biologists felt were the most reliable for runs in central and southern British

Columbia.

Conclusions

There is no evidence of strong or sustained recent declines in abundance for most pink

salmon populations in Washington and southern British Columbia. However, both odd-year

pink salmon populations in the Dungeness River are depressed, and the lower river

population shows a strong declining trend. Although this latter population also declined

substantially from 1973 to 1979, major flooding during the winter of 1979-80 appears to have

been an important factor leading to its current, severely depressed state. This flooding in fact

appears to have influenced all the Washington odd-year pink salmon populations along the

Strait of Juan de Fuca, including the Elwha River population. The single U.S. population of

even-year pink salmon in the Snohomish River is small, and although it has been increasing

in size over the last decade, the estimated 1994 escapement was a substantial drop over that in

1992.

In addition to abundance, two ecological factors relating to the status of pink salmon

populations were of concern to the BRT: low-water conditions upon river entry and spawning,

which can limit spawner distribution to suboptimal center-channel areas; and subsequent

highwater conditions, which can erode the quality of spawning and incubation habitat and

may adversely affect embryonic development. These factors may have been exacerbated by

water withdrawals for irrigation and by structures erected for flood control, particularly on the

lower Dungeness River (Lichatowich 1993, K. Lutz46). In addition, flooding can reduce

45W. Luedke, Canadian Department of Fisheries and Oceans, Fisheries Branch, South

Coast Division, 3225 Stephenson Point Road, Nanaimo, B.C. V9T 1K3. Pers. commun.,

March 1995.

46K. Lutz, Northwest Indian Fisheries Commission, 6740 Martin Way E., Olympia,

WA 98516. Pers. commun., April 1995.
103

substrate stability and permeability and subsequent pink salmon productivity (Wickett 1962).

Extensive severe flooding in several Puget Sound rivers caused by heavy rains in winter

1995-96 may have substantially reduced the productivity of the 1995 brood in these systems

through the mortality of embryos and hatchlings.

Other possible threats to pink salmon in the Puget Sound region include predation on

juvenile pink salmon by wild (Hiss 1994) and hatchery (Hiss 1995) coho salmon, and,

perhaps in some locations, predation by marine mammals (Knudsen et al. 1990, J. Ames47). In

addition, the population dynamics of pink salmon are not well understood, and may be

affected by intra- and interspecific interactions involving pink and chum salmon (Gallagher

1979, Smoker 1984, Heard 1991). Consequently, the possibility that hatchery production of

pink and chum salmon can limit the viability of some Washington populations of pink salmon

cannot be excluded.

Finally, oceanic conditions may also affect pink salmon abundance (Davidson and

Vaughan 1941; Mysak et al. 1982; Blackbourn 1985, 1990; Mysak 1986; Heard 1989). The

widespread declines observed in pink salmon body size (Ricker et al. 1978, Ricker 1981,

Marshall and Quinn 1988, Ricker 1989; Table 3) may have resulted from increased salmon

density, reduced ocean productivity, or directional selection on body size in both net and troll

fisheries. From analysis of the southeastern Alaska pink salmon fishery between 1895 and

1940, Davidson and Vaughan (1941) identified an inverse relationship between the abundance

(measured as total pack) of these fish and adult body size, and they suggested that this

relationship resulted from greater competition for marine prey. Small adult body size is a

cause for concern because it limits reproductive potential (Skud 1973), and there is some

evidence for a strong genetic component to body size (Smoker et al. 1994). Growth at sea or

the subsequent body sizes of adults -may also affect the timing of their spawning migration

(Davidson and Vaughan 1941), which in turn may affect fry recruitment. Skud (1973)

suggested that the interaction between these factors tends to yield higher fry survival in years

when spawners are larger and spawn earlier than in years when spawners are smaller and

spawn later. Conclusions for each of the proposed ESUs are summarized below.

Even-year ESU

Because it is unclear whether populations other than that in the Snohomish River are

in the even-year pink salmon ESU, the BRT first considered the status of this ESU under the

assumption that it included only the single U.S. population. Based on available information,

which shows a relatively small population with a generally increasing trend in abundance in

recent years, the BRT concluded that this ESU is not at risk of imminent extinction or

endangerment. Because even-year populations in British Columbia are generally stable or

increasing and are apparently not at low levels compared to historical abundance, the BRT

47J. Ames, Washington Department of Fish and Wildlife, P.O. Box 43151, Olympia,

WA 98501. Pers. commun., October 1994.
104

also concluded that an ESU that included populations in British Columbia would not

currently be at risk of extinction or endangerment.

However, three factors prompted considerable concern among BRT members about

risks the Snohomish River population might face in the near future: 1) it may be strongly

isolated from all other even-year populations; 2) although the population has generally been

increasing in recent years, it remains at low abundance; and 3) the invariant age structure in

pink salmon, coupled with considerable interannual variability in abundance, increases risks

faced by small, isolated populations. Clearly, these concerns would be greatest for an ESU

that included only the single U.S. population; however, it is also likely that the Snohomish

River population would be considered an important part of a larger ESU that contained

populations from British Columbia. Therefore, the BRT concluded that the Snohomish River

even-year pink salmon population should be closely monitored so that if any factors arise that

substantially increase risk faced by this population, they can be identified at an early stage.

Odd-year ESU

Most populations in the odd-year pink salmon ESU appear to be healthy, and overall

abundance appears to be close to historical levels. The two most distinctive Puget Sound

populations (from the Nooksack and Nisqually Rivers) both show nonsignificant trends in

recent abundance (Nooksack River slightly increasing, Nisqually River slightly decreasing),

and no other factors were found that would suggest that either of these populations is at

immediate risk. The BRT therefore concluded that the ESU for odd-year pink salmon as a

whole is not at significant risk of becoming extinct or endangered.

However, two populations on the Strait of Juan de Fuca are clearly at risk, and an

additional population (in the Elwha River) already appears to be extinct. These populations

contribute substantially to the ecological and genetic diversity of the ESU, and the BRT

expressed concern that further erosion of individual populations might result in future risk to

a significant portion of the ESU as a whole.

The BRT also identified risk factors that should be monitored in the future. Some

evidence exists for recent declines in body length of odd-year fish in Washington, which

raises concern about the ability of natural populations (notably those in the Strait of Juan de

Fuca) to recover naturally. The BRT was unable to review data on body size in odd-year

British Columbia pink salmon since the studies by Ricker et al. (1978) and Ricker (1989) to

ascertain whether body size in these populations has been declining to levels similar to those

observed in Washington fish in recent years. However, the decline in body length of odd-year

Washington pink salmon indicated by the data in Table 3 is qualitatively similar to a decline

in length observed in pink salmon returning to Auke Creek, Alaska over the last 20 years
105

(W. Smoke48). Data estimated from catches of southeastern Alaska pink salmon suggest

similarly declining trends over an even longer period (Marshall and Quinn 1988).

Collectively, these patterns suggest that pink salmon from populations over wide geographic

areas have been experiencing conditions at sea that restrict adult body size and, consequently,

reproductive potential.

48W. Smoker, Juneau Center School of Fisheries and Ocean Sciences, University of

Alaska Fairbanks, 11120 Glacier Hwy., Juneau, AK 99801. Pers. commun., March 1995.
106

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Appendix

Glossary
126
127

GLOSSARY

allele

An allele is an alternate form of a gene (the basic unit of heredity passed from parent

to offspring). By convention, the “100 allele” is the most common allele in a population and

is the reference for the electrophoretic mobility of other alleles of the same gene. Other

genetic terms used in this document include allozymes (alternate forms of an enzyme

produced by different alleles and often detected by protein electrophoresis); gene locus (pl.

loci; the site on a chromosome where a gene is found); genetic distance (D) (a quantitative

measure of genetic differences between a pair of samples); and introgression (introduction of

genes from one population or species into another). See also DNA, electrophoresis,

phenogram, and multidimensional scaling.

artificial propagation

See hatchery.

Biological Review Team (BRT)

A team of scientists from National Marine Fisheries Service formed to conduct the

status review.

broodline

The generation of pink salmon that reproduces every other year. Because of the lack of

variable age structure in this species, even-year pink salmon are reproductively isolated

from odd-year pink salmon.

coded-wire tag (CWT)

A small piece of wire, marked with a binary code, that is normally inserted into the

nasal cartilage of juvenile fish. Because the tag is not externally visible, the adipose fin of

coded wire-tagged fish is removed to indicate the presence of the tag. Groups of thousands to

hundreds of thousands of fish are marked with the same code number to indicate stock, place

of origin, or other distinguishing traits for production releases and experimental groups.

DNA (deoxyribonucleic acid)

DNA is a complex molecule that carries an organism’s heritable information. The two

types of DNA commonly used to examine genetic variation are mitochondrial DNA

(mtDNA), a circular molecule that is maternally inherited, and nuclear DNA, which is

organized into a set of chromosomes. See also allele and electrophoresis.
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electrophoresis

Electrophoresis refers to the movement of charged particles in an electric field. It has

proven to be a very useful analytical tool for biochemical characters because molecules can

be separated on the basis of differences in size or net charge. Protein electrophoresis, which

measures differences in the amino acid composition of proteins from different individuals,

has been used for over two decades to study natural populations, including all species of

anadromo,us Pacific salmonids. Because the amino acid sequence of proteins is coded for by

DNA, data provided by protein electrophoresis provide insight into levels of genetic

variability within populations and the extent of genetic differentiation between them. Genetic

techniques that focus directly on variation in DNA also routinely use electrophoresis to

separate fragments formed by cutting DNA with special enzymes (restriction

endonucleases). See also allele and DNA.

ESA

The U.S. Endangered Species Act.

escapement

The number of fish that survive to reach the spawning grounds or hatcheries. The

escapement plus the number of fish removed by harvest form the total run size.

even-year pink salmon

Pink salmon that spawn in even-numbered years. The distribution of these fish is

variable, but their abundance tends to increase. at higher latitudes in both Asia and North

America. Even-year pink salmon spawning regularly south of British Columbia are found

only in the Snohomish River, Washington.

evolutionarily significant unit (ESU)

A “distinct” population of Pacific salmon, and hence a -species, under the Endangered

Species Act.

F

ST

A measure of population structure that estimates the variance of allele frequencies

among populations, standardized relative to the maximum value possible given the observed

mean allele frequency.
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gene diversity analysis

A hierarchical analysis of the genetic variation observed at polymorphic loci (see

allele) in a set of samples that partitions this variation into several, typically geographic,

components. Diversity analysis commonly estimates the proportions of observed variation

expressed 1) among areas or regions, 2) among populations within areas, and 3) within

populations. The total of these proportions equals 1.

hatchery

Salmon hatcheries typically spawn adults in captivity and raise the resulting progeny

in fresh water for release into the natural environment. In some cases, fertilized eggs are

outplanted (usually in “hatch-boxes”), but it is more common to release fry (young juveniles)

or smolts Ouveniles that are physiologically prepared to undergo the migration into salt

water). Pink salmon are unusual among Pacific salmon in that they are “smolts” upon

emergence from the gravel and do not require extensive freshwater rearing before migrating

to the ocean.

The fish are released either at the hatchery (on-station release) or away from the

hatchery (off-station release). Releases may also be classified as within basin (occurring

within the river basin in which the hatchery is located or the stock originated from) or out-of

basin (occurring in a river basin other than that in which the hatchery is located or the stock

originated from).

The broodstock of some hatcheries is based on adults that return to the hatchery each

year; others rely on fish or eggs from other facilities, or capture adults in the wild each year.

island model of migration

An equilibrium model of gene flow and genetic. drift that is applied under the

assumption that a species (or operational taxonomic unit or ESU) is subdivided into

populations of equal size, all of which exchange migrants at a constant rate, with migrants

coming with equal probability from all other populations.

minimum spanning tree

A means of depicting nearest genetic neighbors. The tree is an undirected network of

smallest genetic distances between genetic samples superimposed on multidimensional

scaling graphs to reveal local distortion (pairs of points which look close together in one

dimension, but which are far apart in other dimensions). See also multidimensional scaling.
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multidimensional scaling

A nonmetric ordination technique used to visualize genetic relationships among

populations in two or three dimensions. This technique requires that the distances between

samples in two- or three-dimensional graphs have monotonic relationships to the original

genetic distances between pairs of samples. See also minimum spanning tree and

phenogram.

odd-year pink salmon

Pink salmon that spawn in odd-numbered years. The distribution of these fish is

variable, but their abundance tends to increase at lower latitudes in both Asia and North

America. Odd-year pink salmon are common in both southern British Columbia and

Washington.

phenogram

A graphical means of depicting genetic relationships among populations in the form

of

a branching “tree” (also often referred to as a dendrogram). The phenograrn is generated

from summary statistics, such as genetic distances or similarities, and shows the.results of

clustering these populations based on these statistics. A clustering algorithm commonly used

to generate phenograms from genetic distances or similarities is the unweighted pair group

method with averages (UPGMA). See also multidimensional scaling.

polymorphic

Having more than one form (e.g., polymorphic gene loci have more than one allele).

recruit-to-spawner ratio

Several measures are employed to estimate the productivity of salmon populations.

The recruit-to-spawner ratio estimates the number of recruits (fish. that are available for

harvest in addition to those that escape the fishery to spawn) produced by the previous

generation’s spawners. The spawner-to-spawner ratio estimates the number of spawners

(those fish that reproduced or were expected to reproduce) in one generation produced by the

previous generation’s spawners. A spawner-to-spawner ratio of 1.0 indicates that, on average,

each spawner produced one offspring that survived to spawn; the size of such a population

would remain unchanged over that generation.

river kilometer (RKm)

Distance, in kilometers, from the mouth of the indicated river. Usually used to identify

the location of a physical feature, such as a confluence, dam, waterfall, or spawning area.
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spawner surveys

Spawner surveys utilize counts of redds (nests dug by females in which they deposit

their eggs) and fish carcasses to estimate spawner escapement and identify habitat being used

by spawning fish. Annual surveys can be used to compare the relative magnitude of spawning

activity between years. Surveys are conducted on a regular basis on standard stream

segments, groups of which form a spawner index, and are occasionally conducted on

supplemental stream segments (those that are not part of the standard surveying plan).

Several methodologies have been used to estimate trends in spawner abundance based

on the results of redd counts or spawner surveys. The peak count (PC) methodology simply

uses the largest number of fish observed during the peak of spawning activity. The area

under the curve (AUC) approach estimates the number of “fish days” (one “fish day” is

equal to one fish (spawner) present on the spawning ground for one day) for a given stream

segment; AUC is calculated from the total number of spawners observed over the course of

the season, divided by the average residence time of spawners on the spawning ground.

Stratified random sampling (SRS) provides an estimate of the number of spawners in a

given area based on spawner counts in both standard and supplemental surveys.

Strait of Georgia

The body of water separating the southern portion of Vancouver Island and the British

Columbia mainland. The strait extends from Cortes Island and Desolation Sound in the north

to the San Juan Islands in the south.

Strait of Juan de Fuca

The body of water separating the southern portion of Vancouver, Island and the

Olympic Peninsula in Washington. The strait extends from the Pacific Ocean east to the San

Juan and Whidbey Islands. The Dungeness and Elwha Rivers on the Olympic Peninsula drain

into the Strait of Juan de Fuca.

west coast pink salmon

For the purposes of this document, west coast pink salmon are defined as pink salmon

originating from fresh waters of southern British Columbia, Washington, Oregon, and

California.