U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

NOAA Technical Memorandum NMFS-NWFSC-62

2004 Status Review

of Southern Resident

Killer Whales (Orcinus orca)

under the Endangered Species Act

December 2004
NOAA Technical Memorandum

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Technical Memorandum NMFS series to issue informal scientific and technical publications when complete formal review and editorial processing are not

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the Northwest Fisheries Science Center continues the

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has since been split into the Northwest Fisheries

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Center. The NMFS-AFSC Technical Memorandum

series is now being used by the Alaska Fisheries

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Reference throughout this document to trade names

does not imply endorsement by the National Marine

Fisheries Service, NOAA.

This document should be cited as follows:

Krahn, M.M., M.J. Ford, W.F. Perrin, P.R. Wade, R.P.

Angliss, M.B. Hanson, B.L. Taylor, G.M. Ylitalo,

M.E. Dahlheim, J.E. Stein, and R.S. Waples. 2004.

2004 Status review of Southern Resident killer whales

(Orcinus orca) under the Endangered Species Act.

U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-62, 73 p.
NOAA Technical Memorandum NMFS-NWFSC-62

2004 Status Review

of Southern Resident

Killer Whales (Orcinus orca)

under the Endangered Species Act

Margaret M. Krahn, Michael J. Ford, William F. Perrin2,

Paul R. Wade1, Robyn P. Angliss1, M. Bradley Hanson,

Barbara L. Taylor2

, Gina M.Ylitalo, Marilyn E. Dahlheim1,

John E. Stein, and Robin S. Waples

Northwest Fisheries Science Center

2725 Montlake Boulevard East

Seattle, Washington 98112

Alaska Fisheries Science Center

7600 Sand Point Way Northeast

Seattle, Washington 98115

Southwest Fisheries Science Center

8604 LaJolla Shores Drive

LaJolla, California 92037

December 2004

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

National Oceanic and Atmospheric Administration

Vice Admiral Conrad C. Lautenbacher, Jr. USN (Ret), Administrator

National Marine Fisheries Service

William T. Hogarth, Assistant Administrator for Fisheries

1

2
Most NOAA Technical Memorandums NMFS-NWFSC

are available online at the Northwest Fisheries Science

Center web site (http://www.nwfsc.noaa.gov)

Copies are also available from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone orders (1-800-553-6847)

e-mail orders (orders@ntis.fedworld.gov)

ii
Table of Contents 

List of Figures...............................................................................................................................................v

List of Tables ..............................................................................................................................................vii

Executive Summary .....................................................................................................................................ix

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

1.1. Scope and Intent of the Status Review Update...............................................................................1

1.2. History of the Status of Southern Resident Killer Whales.............................................................1

1.2.1. Petition to List—2001...........................................................................................................1

1.2.2. Status Review—2001/2002 ..................................................................................................2

1.2.3. NMFS’s “Not Warranted” Decision under ESA—2002.......................................................2

1.2.4. Legal Challenge in the U.S. District Court—2002 ...............................................................3

1.2.5. Court’s Decision—2003 .......................................................................................................3

1.2.6. BRT Reconvened—2004......................................................................................................4

1.3. Key Questions in ESA Evaluations................................................................................................4

1.3.1. The “Species” Question ........................................................................................................4

1.3.2. The “Extinction Risk” Question ...........................................................................................4

2. Updates on the Biology, Taxonomy, Habitat, Ecology, and Potential Risk Factors for Southern 

Resident Killer Whales.................................................................................................................................6

2.1. General Killer Whale Biology........................................................................................................6

2.1.1. Identifying Characteristics....................................................................................................6

2.1.2. North Pacific Killer Whale Populations................................................................................6

2.1.3. Feeding Ecology and Food Requirements............................................................................8

2.1.4. Diving Behavior....................................................................................................................9

2.1.5. Social Structure.....................................................................................................................9

2.1.6. Behavioral and Cultural Diversity ........................................................................................9

2.2. Genetics of Killer Whales ............................................................................................................10

2.2.1. Summary of the 2002 Status Review..................................................................................10

2.2.2. Additional Genetic Information Available to the 2004 BRT..............................................10

2.2.3. Summary and Conclusions .................................................................................................15

2.3. Taxonomy of Killer Whales.........................................................................................................16

2.3.1. Current Status......................................................................................................................16

2.3.2. Nomenclature......................................................................................................................18

2.4. Ecology of Southern Resident Killer Whales...............................................................................19

2.4.1. Current Range and Distribution ..........................................................................................19

2.4.2. Population Dynamics..........................................................................................................22

2.5. Potential Risk Factors...................................................................................................................29

2.5.1. Prey Resources....................................................................................................................29

2.5.2. Marine Noise/Disturbance ..................................................................................................33

2.5.3. Disease ................................................................................................................................35

2.5.4. Environmental Contaminants..............................................................................................35

2.5.5. Oil Spills.............................................................................................................................37

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3. Determination of the Taxon ...................................................................................................................38

3.1. Species..........................................................................................................................................38

3.1.1. Arguments for a Single Species..........................................................................................38

3.1.2. Arguments for Multiple Species.........................................................................................38

3.1.3. Conclusions of the BRT on Species....................................................................................39

3.2. Subspecies....................................................................................................................................39

3.2.1. Evidence for Subspecies Status...........................................................................................39

3.2.2. Conclusions of the 2004 BRT on Subspecies.....................................................................40

4. Determination of DPS............................................................................................................................42

4.1. Taxonomic Uncertainty................................................................................................................42

4.2. Additional Information Available to the 2004 BRT.....................................................................42

4.3. Data Relevant to Determining ESA Discreteness and Significance.............................................43

4.4. Evaluation of ESA Discreteness...................................................................................................43

4.5. Evaluation of ESA Significance...................................................................................................44

4.5.1. Ecological Setting ...............................................................................................................44

4.5.2. Range ..................................................................................................................................45

4.5.3. Genetic Differentiation .......................................................................................................45

4.5.4. Behavioral and Cultural Diversity ......................................................................................45

4.6. Conclusions for DPS Determination ............................................................................................45

5. Assessment of Extinction Risk ..............................................................................................................47

5.1. Population Viability Analysis.......................................................................................................47

5.1.1. PVA Results........................................................................................................................48

5.1.2. Discussion and Conclusions ...............................................................................................55

5.1.3. Comparison of Parameters Used in the 2002 and 2004 PVA Models................................55

5.2. Application of IUCN Criteria.......................................................................................................57

5.3. Extinction Risk—Summary of BRT Concerns ............................................................................58

5.3.1. Population Size ...................................................................................................................58

5.3.2. Population Trends...............................................................................................................59

5.3.3. Sex and Age Class Structure...............................................................................................60

5.3.4. Fecundity ............................................................................................................................60

5.3.5. Survivorship........................................................................................................................60

5.3.6. Conclusions.........................................................................................................................61

6. Conclusions of the Status Review..........................................................................................................62

7. References..............................................................................................................................................65

iv
List of Figures 

Figure 1. Ranges of resident killer whales in the eastern North Pacific. .....................................................7

Figure 2. MtDNA haplotype tree. ..............................................................................................................14

Figure 3. Southern Resident killer whale population size through time. ...................................................22

Figure 4. Best fitting model of crude survival, 7-year periods of constant survival, starting with a 6-year 

period in 1974. Also shown are annual estimates of survival....................................................................24

Figure 5. Model-averaged estimates of crude survival. .............................................................................25

Figure 6. Southern Resident killer whale annual survival estimates by pod..............................................25

Figure 7. Southern Resident killer whale annual survival estimates by age and sex category over the years 

1974 to 2002. ..............................................................................................................................................27

Figure 8. Best fitting model of fecundity, a periodic function with 3 years constant periods. Also shown 

are annual fecundity and the model average fecundity from 1974 to 2002. ...............................................29

v
vi
List of Tables 

Table 1. Summary of genetic analyses prior to 2002.................................................................................10

Table 2. Summary of new genetic data considered by the BRT................................................................11

Table 3. Estimates of genetic divergence and gene flow among eight killer whale populations based on 

microsatellite DNA divergence...................................................................................................................12

Table 4. Summary of known and potential sightings of Southern Resident killer whales along the outer 

Pacific Ocean coast. Also listed are known sightings of Southern Resident killer whales in “winter” 

(December–April) in the inside waters of British Columbia and Washington (the Strait of Juan de Fuca 

and east). .....................................................................................................................................................20

Table 5. Summary of historical and recent estimates of numbers of salmon produced by North American 

west coast river systems between the Strait of Georgia and Central California. ........................................30

Table 6. Survival Scenario A, using all 29 years of data and S(G+7c) best survival model, 7-year groups, 

modeled to extinction..................................................................................................................................49

Table 7. Survival Scenario A(Q), using all 29 years of data and S(G+7c) best survival model, 7-year 

groups, modeled to a quasi-extinction threshold. .......................................................................................50

Table 8. Survival Scenario B, using the last 14 years of data and survival model S(4t c), assuming four 

4-year periods, modeled to extinction. ........................................................................................................52

Table 9. Survival Scenario B(Q), using the last 14 years of data and survival model S(4t c), assuming 

four 4-year periods, modeled to a quasi-extinction threshold.....................................................................53

Table 10. Survival Scenario C, using last 10 years of survival estimates from model S(4t c), assuming 

two 4-year periods and one 2-year period, modeled to extinction..............................................................54

Table 11. Survival Scenario C(Q), using last 10 years of survival estimates from model S(4t c), assuming 

two 4-year periods and one 2-year period, modeled to a quasi-extinction threshold..................................56

vii
viii
Executive Summary 

Background 

On 18 December 2002, the Center for Biological Diversity and other plaintiffs initiated 

a motion for summary judgment in U.S. District Court, Western District of Washington, 

challenging the National Marine Fisheries Service (NMFS) 2002 decision indicating that listing 

of Southern Resident killer whales (Orcinus orca) as threatened or endangered under the 

Endangered Species Act (ESA) was not warranted at that time. The plaintiffs asserted that 

NMFS’s policy that considers the population=s “significance” in determining whether a 

population should be considered a distinct population segment (DPS) is not permitted by the 

ESA. In addition, the plaintiffs stated that NMFS’s reliance on the “outdated and discredited” 

species O. orca as the taxon violated the best available science standard. 

On 17 December 2003, U.S. District Court Judge Robert Lasnik found that the DPS 

policy is not contrary to congressional intent regarding the ESA and that including an assessment 

of a population’s “significance” is one component of a reasonable interpretation of the term DPS. 

Judge Lasnik also held that NMFS erred by using the “inaccurate” global species O. orca when 

considering whether the Southern Resident killer whales are a DPS. The court set aside NMFS’s 

“not warranted” finding and remanded the matter back to NMFS for determining whether the 

Southern Resident killer whales should be listed under the ESA. NMFS was required to issue a 

new finding consistent with Judge Lasnik’s order by 17 December 2004. 

NMFS decided that, in order to address the court order in a timely manner, the Biological 

Review Team (BRT) should be reconvened (referred to as the 2004 BRT). 

Status of the Southern Resident Killer Whale Population 

In May and June of each year since 1973/74, the Center for Whale Research, Friday 

Harbor, Washington, has taken photographs that identify every Southern Resident individual. As 

a result, the annual survey amounts to a census of the entire population. This census allows a 

detailed examination of the population dynamics of the Southern Resident community, including 

the survival and fecundity of individual animals of known age. In 1974 the population 

comprised 71 whales, whereas the most recent census in the summer of 2003 counted 83 whales, 

representing an overall annual increase of 0.4% per year. However, the population has 

fluctuated considerably over the 29 years of the study (Figure ES-1). Using the maximum

recorded population size of 97 animals in 1996, the Southern Resident killer whale population 

declined by 2% per year between 1996 and 2003. 

Large differences exist in survival rates of Southern Residents among different age and 

sex categories. Reproductive-age females had the highest survival rate, followed by juveniles, 

post-reproductive-age females, and young males. Calves and old males had the lowest survival 

ix
40

50

60

70

80

90

100

110

120

1973 1977 1981 1985 1989 1993 1997 2001

Year

Population siz

e

71

97

79

74

11% decline from 1980 to 1984 (4 years)

20% decline from 1996 to 2001 (5 years)

83 83

Figure ES-1. Southern Resident killer whale population size through time. (Note: The number 78 for 

year 2001 in Figure ES-1 of Krahn et al. 2002 was revised to 79 above to include L98, the 

juvenile male separated from his pod and living in Canadian waters.) 

rates. In addition, there have also been large changes in survival rates through time for all age 

and sex categories. Survival has shifted from relatively high levels in the 1970s, to low levels in 

the early 1980s, to high levels again in the late 1980s and early 1990s, then returned to low levels 

through 2000. Survival rates improved in 2001 and 2002, but they were not as high as in 

previous periods of relatively high survival. 

Genetic Data 

The understanding of killer whale population genetic structure has expanded considerably 

since the last status review in 2002. In particular, the mitochondrial DNA (mtDNA) 

differentiation among eastern North Pacific resident, transient, and offshore populations can now 

be seen in the context of variation worldwide (shown in the mtDNA haplotype tree in Figure 2 of 

this status review). The most notable result from the new mtDNA data is the lack of strong 

mtDNA structure worldwide, suggesting that the current distribution of killer whales populations 

may be relatively young on an evolutionary scale (e.g., several hundred thousand years compared 

to the ≈5-million-year-old age of the Orcinus genus and possibly associated with a population 

bottleneck followed by a worldwide expansion). With regard to identifying conservation units, 

one of the implications of the new data is that the relative degree of mtDNA divergence among 

populations is not necessarily a good predictor of the length of time that the populations have 

evolved independently. For example, animals with the “southern resident” haplotype have been 

found in populations from Washington (the Southern Residents), Alaska, Russia, Newfoundland, 

and the United Kingdom. Evolutionarily, these populations are almost certainly more closely 

related to other geographically proximate populations than to each other (a hypothesis supported 

by the microsatellite data), and therefore share an mtDNA haplotype purely by chance. Thus it 

would be inappropriate to rely heavily on simple mtDNA divergence as a criterion for 

x
identifying conservation units, especially on a global scale. On a local scale, however, mtDNA 

remains useful for helping to identify populations, especially when combined with other types of 

information. 

In addition to more mtDNA data, the amount of nuclear microsatellite data has expanded 

greatly in the last 2 years, both in terms of numbers of whales and loci analyzed (shown in the 

summary of new genetic data in Table 2 of this report). Within the eastern North Pacific, both 

the mtDNA and microsatellite data remain consistent with a hypothesis of 4–5 resident 

populations, at least 2–3 transient populations, and at least 1 offshore population. The issue of 

whether any contemporary gene flow occurs among eastern North Pacific populations remains 

unresolved, but the microsatellite data are consistent with low levels of gene flow (at most a few 

mating events among populations per generation). Despite some uncertainty about the 

evolutionary history that produced the current patterns of variation, both the mtDNA and the 

microsatellite data indicate a high degree of contemporary reproductive isolation among eastern 

North Pacific killer whale populations. 

Taxonomic Information

The taxonomy of the killer whales is in a state of flux, as viewed by experts at the recent 

Workshop on the Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation 

and Management, April 30–May 2, 2004, La Jolla, California (referred to as the Cetacean 

Taxonomy Workshop). The previous prevailing concept of a single species has recently evolved 

into a diversity of views that include the possibility of multiple species. Recent new 

observations and data on morphology and genetics of both the Antarctic and North Pacific killer 

whales have reopened the question, and two divergent bodies of expert opinion have emerged. 

Under one line of reasoning, killer whales comprise a single highly variable species, with locally 

differentiated ecotypes representing recently evolved and relatively ephemeral forms not 

deserving species status. According to the opposing body of opinion, congruence of several lines 

of evidence for the distinctness of sympatrically occurring forms speaks for multiple species. 

For the Antarctic, new observations of color pattern, size, habitat, and feeding ecology 

have led to the conclusion that there are three types of killer whales—one in open waters (the 

“ordinary” killer whale), one in the pack ice, and a third in leads in the fast ice. The types are 

distinguishable on the basis of body size, the size and shape of a white patch behind the eye, 

habitat, and feeding habits. Genetic relationships among the three forms, determined from

mtDNA from biopsy samples, are congruent with their morphological and ecological 

distinctiveness. 

A similar situation occurs for killer whales in the North Pacific. The seasonally 

sympatric resident and transient forms show consistent differences in mitochondrial and nuclear 

genetic markers, coloration, acoustic calls, and foraging habits. Preliminary data show

differences in their cranial skeletons as well, although sample sizes remain small. The majority 

of experts participating in the killer whale working group at the Cetacean Taxonomy Workshop 

believed that the three Antarctic forms, as well as the resident and transient ecotypes in the North

Pacific, may be distinct species or subspecies. 

xi
Determination of the Taxon 

Species 

The 2004 BRT first considered whether killer whales comprise a single species or 

multiple species, reviewing new information and the competing lines of evidence cited during 

the Cetacean Taxonomy Workshop. After discussion of this information, the BRT reached 

consensus that—although multiple species may exist and may be confirmed in the future—the 

present data do not adequately support designation of any new species. In particular, the BRT 

concluded that, provisionally, North Pacific transients and residents should be considered to 

belong to a single species. 

Subspecies 

The 2004 BRT next considered the question of whether Southern Residents and transients 

belong to different subspecies. A number of differences between residents and transients have 

been suggested to support subspecific separation. 

• Residents and transients differ on average in external morphology, including dorsal-fin 

size and shape, saddle-patch shape, and pigmentation. 

• Differences between the two ecotypes have been found in skull features, although the 

sample size is still small and uncontrolled for age and sex. 

• Residents and transients are sympatric in the summer range, but no intermingling or 

interbreeding has ever been observed. 

• The two groups have markedly different feeding specializations and social organization. 

• The two ecotypes exhibit markedly different acoustic dialects and acoustic practices that 

may relate to differences in feeding ecology. 

• The two forms are genetically divergent at both mtDNA and nuclear DNA markers. The 

level of divergence between the residents and transients is higher than the average level 

of divergence within populations of either group. 

• Residents and transients fall into two different global mtDNA clades. 

The 2004 BRT agreed that if the Southern Residents belong to a subspecies separate from

that of the transients, the subspecies would include the Southern Residents and the Northern 

Residents, as well as the resident killer whales of Southeast Alaska, Prince William Sound, 

Kodiak Island, the Bering Sea and Russia. In short, the subspecies would include all of the 

resident, fish-eating killer whales of the North Pacific. The rationale for this decision was that 

all of these groups are apparently fish-eating specialists, occupy relatively similar habitats, and 

appear to be genetically more closely related to each other than to sympatric transient 

populations. 

The BRT also considered whether the offshore form would be included in a subspecies 

with the residents (if such a subspecies were agreed to exist). A number of differences exist 

between North Pacific residents and offshores, including distribution, diet (as indicated by 

xii
analyses of stable isotopes, fatty acids and contaminants, and differential tooth wear in whales 

with sharks in stomach contents), mtDNA haplotypes, nuclear DNA, external morphology 

(saddle patch and degree of sexual dimorphism, although data have not yet been well quantified), 

group size, and acoustic dialects. 

The possible inclusion of killer whales of the eastern Tropical Pacific with North Pacific 

residents in a potential subspecies was also discussed. Differential characteristics of these 

whales include small group size (up to 20, but mostly 3–8), indistinct saddles, multiple 

haplotypes within sampled groups, vocal patterns that do not match those of the North Pacific, 

and prey that include large baleen whales. 

After considering the arguments for existence of subspecies and the conclusions of the 

Cetacean Taxonomy Workshop, the BRT decided (by a 5-to-1 margin) that the taxon to use for 

determining a DPS under the ESA should be the North Pacific residents, an unnamed subspecies 

of O. orca. Including the North Pacific offshore or eastern Tropical Pacific killer whales in the 

same taxon as the North Pacific residents was rejected by a 3:2 and a 7:3 margin, respectively. 

Determination of DPS 

Evaluation of ESA Discreteness 

The 2004 BRT unanimously concluded that the Southern Residents are discrete from

other North Pacific resident killer whale populations. In particular, all available data—including 

behavior, demography, and core and summer ranges, as well as genetics—indicated that the 

Southern Residents are an independent population that is distinct from other populations. 

Evaluation of ESA Significance 

The BRT discussed at length the significance of the Southern Residents with respect to 

the North Pacific resident taxon. The BRT concluded by a 2-to-1 margin that the Southern 

Residents are significant with regard to the North Pacific resident taxon and therefore should be 

considered a DPS. The BRT also concluded by a 3-to-2 margin that the Southern Residents 

would be a DPS of a taxon consisting of both North Pacific residents and offshores. The 

arguments favoring significance under both taxonomic scenarios were as follows. 

Ecological setting 

The Southern Residents appear to occupy an ecological setting distinct from the other 

North Pacific resident populations. In particular, the Southern Residents are the only North 

Pacific resident population to spend a substantial amount of time in the California Current 

ecosystem, an ocean habitat that differs considerably from the Alaskan Gyre occupied by the 

Alaska Residents and Northern Residents. There is some evidence of differences in prey 

utilization, with Southern and Northern Residents favoring Chinook salmon (Oncorhynchus 

tshawytscha) and certain Alaska Residents also eating groundfish such as halibut and turbot. 

xiii
Range 

The BRT discussed data related to both the Southern Residents’ year round and summer 

core ranges and concluded that loss of the Southern Residents would result in a significant gap in 

the range of the North Pacific resident taxon. In particular, the Southern Residents are the only 

North Pacific resident population to be sighted in the coastal areas off of California, Oregon, and 

Washington, and are the only population to regularly inhabit Puget Sound. Based on knowledge 

of other cetaceans, the BRT found little reason to believe that these areas would be repopulated 

by other North Pacific resident populations in the foreseeable future should the Southern 

Resident population become extinct. 

Genetic differentiation

The Southern Residents differ markedly from other North Pacific resident populations at 

both nuclear and mitochondrial genes. The Southern Residents also differ from other North 

Pacific resident populations in the frequency of certain saddle-patch variants, a trait believed to 

have a genetic basis. 

Behavioral and cultural diversity 

The BRT noted that culture (knowledge passed through learning from one generation to 

the next) is likely to play an important role in the viability of killer whale populations. For 

example, the Southern Residents may possess unique knowledge of the timing and location of 

salmon runs in southern part of the North Pacific residents’ range. The BRT also noted that there 

was some evidence that cultural traditions, such as greeting behavior, beach rubbing, and 

utilization of prey from longlines, differed among the resident populations. 

Conclusions for DPS Determination 

The BRT concluded that the Southern Residents are likely to be a DPS of the North 

Pacific resident taxon. Despite some uncertainty, the 2004 BRT was considerably more 

confident than the 2002 BRT about its conclusion. For example, the 2002 BRT was almost 

evenly split on the question of whether or not the Southern Residents are a DPS of the North 

Pacific resident taxon and gave only minor support to the idea that Southern Residents would be 

a DPS of a taxon consisting of North Pacific residents and offshores. In contrast, the 2004 BRT 

was fairly confident that the Southern Residents should be considered a DPS under both of these 

scenarios. The 2004 BRT discussed this increase in support for the Southern Residents as a DPS 

and attributed it primarily to the amount of new information that has been collected over the last 

couple of years. For example, knowledge about worldwide patterns of genetic variation in killer 

whales has increased dramatically and has demonstrated that sharing a similar mtDNA haplotype 

does not necessarily indicate a close evolutionary relationship between two populations. This is 

important, because the offshores and Southern Residents are characterized by very similar 

mtDNA haplotypes, a factor that influenced the conclusions of the 2002 BRT. In addition, the 

2004 BRT was aware of recently collected information about the social structure, morphology, 

behavior, and diet of offshore killer whales that was unavailable at the time of the 2002 status 

review. This information tends to suggest that the offshores are more distinct from resident killer 

whales than was appreciated by the 2002 BRT. Finally, knowledge about ecological and 

xiv
behavioral diversity within killer whales has increased as a result of ongoing studies in British 

Columbia, Alaska, and the Russian Far East. The BRT generally concluded that this new 

information tended to suggest substantial ecological differentiation between the Southern 

Residents and other populations. 

Risk Assessment 

Risk Factors 

The 2004 BRT considered whether factors that currently pose a risk for Southern 

Residents might continue in the future. Concern remains about whether reduced quantity or

quality of prey are affecting the Southern Resident population. In addition, levels of 

organochlorine contaminants are not declining appreciably and those of many newly emerging 

contaminants (e.g., brominated flame retardants) are increasing, so Southern Residents are likely 

at risk for serious chronic effects similar to those demonstrated for other marine mammal species 

(e.g., immune and reproductive system dysfunction). Other important risk factors that may 

continue to impact Southern Residents are oil spills and noise and disturbance from vessel 

traffic. 

Population Viability Analysis 

A population viability analysis (PVA) was conducted to synthesize the potential 

biological consequences of a small population size, a slowly increasing or a declining population 

trend, and potential risk factors. The probability of the Southern Resident population going 

extinct was estimated using demographic information from the yearly census. Both the 

probability of extinction (defined as <1 male or female) as well as the probability of “quasiextinction” (defined as < 10 males or females) were determined, because the BRT believed that a 

population at the quasi-extinction level would be “doomed” to extinction, even though literal 

extinction might still take decades for long-lived killer whales. Under the assumption that 

growth rates in the future will accurately be predicted by the full 29-year time series of available 

data (the most optimistic scenario considered), the model predicted the probability that Southern 

Resident would become extinct was <0.1–3% in 100 years and 2–42% in 300 years (Figure 

ES-2). If a quasi-extinction threshold was used instead of actual extinction, the predicted 

probability of meeting the threshold ranged 1–15% in 100 years and 4–68% in 300 years. For 

both scenarios, the higher percentages in each range were associated with higher probability and 

magnitude of catastrophic mortality events (e.g., oil spills), as well as with a smaller carrying 

capacity (i.e., K = 100). When it was assumed that the population survival for the last 10 years 

would best predict the future (most pessimistic model), the analysis predicted a probability of

extinction of 6–19% in 100 years and 68–94% in 300 years. If a quasi-extinction threshold was 

used in lieu of actual demographic extinction, the predicted probability of meeting the threshold

ranged from 39–67% in 100 years to 76–98% in 300 years (Figure ES-2). 

Summary of BRT Concerns 

The population dynamics of the Southern Residents describe a population that is at risk 

for significant decrease, due either to incremental small-scale impacts over time (e.g., reduced 

fecundity or subadult survivorship) or to a major catastrophe (e.g., disease outbreak or oil spill). 

xv
0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

All 29 years survival

No catastrophes

K = 400

All 29 years survival

Max. catastrophes

K = 100

Last 10 years survival

No catastrophes

K = 400

Last 10 years survival

Max. catastrophes

K = 100

Probability of extinction

100 years

200 years

300 years

100 years (Q)

200 years (Q)

300 years (Q)

Figure ES-2. Estimated risk of extinction (<1 male or female) or quasi-extinction (Q; <10 males or 

females) at 100, 200, and 300 years for the Southern Resident population, assuming 1974–2003 

(29-year) survival rates continue, with no catastrophes and with the maximum probability of 

catastrophe (two catastrophes every 100 years, with a 20% decline in the population following the 

catastrophes); or assuming survival rates for the last 10 years continue, with no catastrophes and 

with the maximum probability of catastrophe. 

Additionally, the small size of this killer whale population makes it potentially vulnerable to 

Allee effects (e.g., inbreeding depression) that could cause a major decline. Furthermore, the 

small number of breeding males, as well as possible reduced fecundity and subadult survivorship 

in L Pod, may limit the population’s potential for rapid growth in the near future. Although the 

Southern Resident population has demonstrated the ability to recover from lower levels in the 

past, the factors responsible for the recent decline are unclear, may still exist, and may continue 

to persist, precluding a substantial population increase. 

Conclusions of the Status Review 

• Although multiple species of killer whales may exist and may be confirmed in the future, the 

2004 BRT concluded that present data do not adequately support designation of any new 

species, so North Pacific transients and residents should be considered to belong to a single 

species. 

• The BRT agreed (by a 5-to-1 margin) that Southern Residents belong to a subspecies 

separate from that of the transients and this subspecies includes the Southern and Northern 

Residents, as well as the resident killer whales of Southeast Alaska, Prince William Sound, 

xvi
Kodiak Island, the Bering Sea, and Russia (but not the offshores). Thus the taxon to use for 

determining a DPS under the ESA would be resident killer whales in the North Pacific, an 

unnamed subspecies of O. orca. 

• The BRT unanimously concluded that the Southern Residents are discrete from other North 

Pacific resident killer whale populations. The BRT also concluded (by a 2-to-1 margin) that 

the Southern Residents are significant with respect to the North Pacific resident taxon and 

therefore should be considered a DPS. 

• Factors that might pose a future risk to the Southern Resident population are: reduced 

quantity and quality of prey, persistent pollutants that could cause immune or reproductive 

system dysfunction, oil spills, and noise and disturbance from vessel traffic. 

• A PVA was conducted and the most optimistic model (29-year data set) predicted that the 

probability that Southern Resident would become extinct was <0.1–3% in 100 years and 

2–42% in 300 years. Using the most pessimistic model (the last 10 years; quasi-extinction 

threshold), the probability of meeting the threshold ranged from 39–67% in 100 years to 

76–98% in 300 years. 

• Overall, the BRT was concerned about the viability of the Southern Resident population. 

The population is at risk for extinction, due either to small-scale impacts over time (e.g., 

reduced fecundity or subadult survivorship) or to a major catastrophe (e.g., disease outbreak 

or oil spill). Additionally, the small size of this killer whale population makes it potentially 

vulnerable to Allee effects (e.g., inbreeding depression). 

xvii
xviii
1. Introduction 

1.1. Scope and Intent of the Status Review Update 

Following a 2002 review of the status of the Southern Resident population of killer 

whales (Orcinus orca) in the eastern North Pacific, the National Marine Fisheries Service 

(NMFS) determined that listing this killer whale population as a threatened or endangered 

species was not warranted because Southern Resident killer whales did not constitute a species, 

subspecies or distinct population segment (DPS) as defined by the Endangered Species Act 

(ESA). A legal challenge of the determination followed. Then the U.S. District Court, Western 

District of Washington, issued an order that set aside the NMFS finding and remanded the matter 

back to NMFS for redetermination of whether the Southern Resident killer whales should be 

listed under the ESA. NMFS reconvened a Biological Review Team (referred to as the 2004 

BRT) to review and evaluate the most recent scientific and commercial information available on 

Southern Resident killer whales. This technical memorandum details the 2004 BRT’s evaluation 

of the status of the Southern Resident killer whale population under the ESA. 

1.2. History of the Status of Southern Resident Killer Whales 

1.2.1. Petition to List—2001 

On 2 May 2001, NMFS received a petition from the Center for Biological Diversity and 

11 co-petitioners (Plater 2001) to list Southern Resident killer whales as threatened or 

endangered and to designate critical habitat for them under the ESA. The petitioned whale 

population, consisting of three pods (J, K, and L), inhabits the inland waterways of Puget Sound, 

Strait of Juan de Fuca, and Georgia Strait during the spring, summer, and fall. The primary 

impetus behind the petition was a rapid decline in the population from 97 animals in 1996 to 78 

animals in 2001. 

The petition highlighted key issues for NMFS’s consideration, including: 1) genetic, 

behavioral, and ecological evidence indicating that Southern Resident killer whales might meet 

the criteria for being a DPS as defined by the ESA, 2) population data documenting a recent 

decline in Southern Resident killer whales and analyses indicating that these whales might be at 

risk of extinction, and 3) an array of threats that might account for the decline in Southern 

Resident killer whales. On 26 July 2001, NMFS received additional information from the lead 

petitioner, including an updated population viability analysis (PVA) and a report on the July 

2001 census of Southern Resident killer whales returning to the inland waters of Washington and 

southern British Columbia (Taylor and Plater 2001). 

On 13 August 2001, NMFS (2001) provided notice of its determination that the petition 

presented substantial information indicating that a listing might be warranted and that it would 
initiate a status review to determine if Southern Resident killer whales would warrant listing 

under the ESA. 

1.2.2. Status Review—2001/2002 

To conduct the status review, NMFS formed a BRT (referred to as the 2002 BRT) 

consisting of scientists from the agency’s Alaska, Northwest, and Southwest Fisheries Science 

Centers. Because the ESA requires that NMFS make a listing determination based upon the best 

available scientific and commercial information, the agency solicited pertinent information on 

killer whales (NMFS 2001) and convened a meeting on 26 September 2001 to gather technical 

information from co-managers, scientists, and individuals having research or management 

expertise pertaining to killer whale stocks in the North Pacific Ocean. In addition, in March 

2002 the BRT received comments from the Marine Mammal Commission and Washington, 

Tribal, and Canadian co-managers on a preliminary draft of the BRT’s status review findings. 

These comments were evaluated by the BRT, which then prepared a final status review 

document for Southern Resident killer whales (NMFS 2002c) that was subsequently published as 

a NOAA technical memorandum (Krahn et al. 2002). 

1.2.3. NMFS’s “Not Warranted” Decision under ESA—2002 

NMFS reviewed the petition, the 2002 BRT report (NMFS 2002c), co-manager 

comments, and other available information, and consulted with species experts and other 

individuals familiar with killer whales. The best available scientific and commercial information 

was inconclusive regarding a determination about whether the petitioned group of killer whales 

constituted a DPS of the currently recognized species O. orca. 

NMFS found that the status review revealed uncertainties regarding the taxonomic status 

of killer whales worldwide. The taxonomy of killer whales published in the scientific literature 

described only a single species that included all killer whales globally. The BRT had discussed 

the more recent but inconclusive evidence that the cosmopolitan species O. orca should be 

subdivided into two or more species or subspecies. The BRT had recognized that taxonomists 

might be conservative or liberal in assigning new species and that the relevance of the new 

information would have to be debated widely before it could be generally accepted by the 

scientific community. Because the recent information related to the taxonomy of killer whales 

had not been subjected to that scientific debate, NMFS considered that the published standard 

(Rice 1998) of a single, global species was the best available scientific information. NMFS 

found that Southern Resident killer whales were not a species under the ESA. Consequently, 

NMFS found that listing Southern Resident killer whales as threatened or endangered was not 

warranted at that time (NMFS 2002a). 

As noted in the 2002 BRT report, the BRT also investigated alternative DPSs to which 

Southern Residents might belong. Although a DPS could not be identified clearly, the BRT 

evaluated the risk of extinction for potential DPSs by aggregating logical units. As a first logical 

step in aggregating units of killer whales, the BRT combined the Southern, Northern, and Alaska 

Residents as a potential DPS to which the Southern Resident killer whales might belong and 

estimated the risk of extinction for this aggregation. Simulation results predicted that the 

extinction risk of that initial aggregation was negligible. Therefore, NMFS could not identify a 

2
DPS to which Southern Residents might belong that was in danger of extinction throughout all or 

a significant portion of its range or likely to become endangered in the foreseeable future. 

NMFS noted at the time of the “not warranted” decision that the agency was concerned 

about the recent decline in the Southern Residents1

 and would continue to seek new information 

on the taxonomy, biology, and ecology of these whales, as well as potential threats to their 

continued existence. In addition, NMFS stated that the agency would reconsider the taxonomy 

of killer whales within 4 years. If after 4 years the species O. orca had been subdivided in a 

manner that might allow Southern Resident killer whales to be identified as a DPS, NMFS 

indicated it would reconvene a BRT to reassess the status of these whales under the ESA. 

1.2.4. Legal Challenge in the U.S. District Court—2002 

On 18 December 2002 the Center for Biological Diversity and other plaintiffs initiated a 

motion for summary judgment in U.S. District Court challenging the NMFS “not warranted” 

finding. The plaintiffs asserted that NMFS’s policy that considers the population’s 

“significance” in determining whether a population should be considered a DPS is not permitted 

by the ESA. In addition, the plaintiffs stated that NMFS’s reliance on the “outdated and 

discredited” species O. orca as the taxon violated the best available science standard. 

1.2.5. Court’s Decision—2003 

On 17 December 2003, U.S. District Court Judge Robert Lasnik found that the DPS 

policy (see subsection 1.3 below) is not contrary to congressional intent regarding the ESA and 

that including an assessment of a population’s “significance” is one component of a reasonable 

interpretation of the ambiguous DPS term. Judge Lasnik also held that NMFS erred by using the 

“inaccurate” global species O. orca when considering whether the Southern Resident killer 

whales are a DPS. The court set aside the NMFS “not warranted” finding and remanded the 

matter back to NMFS for determining whether the Southern Resident killer whales should be 

listed under the ESA. NMFS was required to issue a new finding consistent with Judge Lasnik’s 

order by 17 December 2004. 

The decision upheld the DPS policy—particularly the “significance” inquiry. However, 

the decision also mandated that NMFS consider the classification of Southern Resident killer 

whales using the best data available on the global species taxonomy, regardless of whether the 

scientific debate about killer whale taxonomy has been concluded, instead of defaulting to the 

currently recognized global species. 

 

1

 The scientific information evaluated during the ESA status review indicated that Southern Resident killer whales 

might be depleted under the Marine Mammal Protection Act (MMPA). NMFS initiated consultation with the 

Marine Mammal Commission (Commission) in a letter dated 25 June 2002 and published an advance notice of

proposed rulemaking on 1 July 2002 (NMFS 2002b) to request pertinent information regarding the status of the 

stock and potential conservation measures that might benefit these whales. After considering comments received in 

response to the advance notice and from the Commission, NMFS published a proposed rule to designate the 

Southern Resident stock of killer whales as depleted (NMFS 2003a) and solicited comments on the proposal. Based 

on the best scientific information available and consultation with the Commission, NMFS determined that the 

Southern Resident stock of killer whales was depleted under the MMPA (NMFS 2003b) and announced its 

intentions to prepare a conservation plan. 

3
1.2.6. BRT Reconvened—2004 

NMFS decided that, in order to address the court order in a timely manner, the BRT 

should be reconvened. Most of the 2002 BRT members also served on this new panel, the 2004 

BRT. Returning panel members and their areas of expertise were: NWFSC—Dr. Peggy Krahn 

(Team Leader; contaminants/feeding ecology), Dr. John Stein (toxicology), Gina Ylitalo 

(contaminants), Dr. Robin Waples (genetics), Dr. Brad Hanson (habitat/foraging ecology/whale 

watching); AFSC—Dr. Paul Wade (Lead, risk assessment; population dynamics/risk modeling), 

Dr. Robyn Angliss (conservation biology) and Dr. Marilyn Dahlheim (conservation 

biology/photo-identification/killer whale biology); and SWFSC—Dr. Barbara Taylor 

(genetics/risk modeling). Dr. Michael Ford (Lead, DPS; genetics) replaced a former panel 

member, Dr. Steven Kalinowski, who had taken a position outside NOAA. In addition, Dr. 

William Perrin from the SWFSC (Lead, cetacean taxonomy), joined the BRT to provide 

additional expertise on cetacean taxonomy and biology. 

1.3. Key Questions in ESA Evaluations 

1.3.1. The “Species” Question 

For the purpose of the ESA, Congress has defined a species as “any subspecies of fish or 

wildlife or plants, and any distinct population segment of any species of vertebrate fish or 

wildlife which interbreeds when mature.” As amended in 1978, the ESA allows listing of 

“distinct population segments” of vertebrates, as well as named species and subspecies. 

Guidance on what constitutes a DPS is provided by the joint NMFS-U.S. Fish and Wildlife 

Service (USFWS) interagency policy on vertebrate populations (USFWS and NMFS 1996). To 

be considered “distinct,” a population, or group of populations, must be “discrete” from other 

populations and “significant” to the taxon (species or subspecies) to which it belongs. Details of 

this joint DPS policy, including the specific considerations necessary for a population to be 

designated a DPS, are reviewed in subsection 4.3. 

1.3.2. The “Extinction Risk” Question 

The ESA 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.” The ESA states that a variety of 

information should be used in evaluating the level of risk faced by a species or a DPS. Important 

considerations include: 

• the present or threatened destruction, modification, or curtailment of its habitat or range, 

• overutilization for commercial, recreational, scientific, or educational purposes, 

• disease or predation, 

• the inadequacy of existing regulatory mechanisms, or 

• other natural or man-made factors affecting its continued existence. 

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 on its current 

4
status, after taking into consideration conservation measures that are proposed or are in place. 

The BRT’s mandate was to identify the DPS to which the Southern Residents belong and to 

evaluate the risk of extinction of that DPS. Evaluation of conservation measures and making a 

final listing recommendation for Southern Residents will be done by the NMFS Northwest 

Regional Office. 

Additional details on ESA evaluations can be found in subsection 4.3 of this report, as 

well as in subsection 1.2, “Key Questions in ESA Evaluations,” in the 2002 Status Review report 

(NMFS 2002c) and NOAA technical memorandum (Krahn et al. 2002). 

5
2. Updates on the Biology, Taxonomy, Habitat,

Ecology, and Potential Risk Factors for Southern 

Resident Killer Whales 

This section has been limited to new information that was not reviewed by the 2002 BRT. 

Additional information on each topic can be found in section 2 of Krahn et al. (2002) or in Wiles 

(2004). 

2.1. General Killer Whale Biology 

2.1.1. Identifying Characteristics 

Color patterns 

Recently, Pitman and Ensor (2003) described three forms of killer whales in the Antarctic 

based on field observations and a review of available photographs. Identifications were based on 

the relative size and orientation of the white eyepatch and the presence of a dorsal cape. They 

concluded that, in addition to O. orca, two different types of killer whales occur in Antarctic 

waters. Visser (2000) also described variations in the eye-patch shape of killer whales in New 

Zealand waters. 

Internal anatomy—skeleton 

Killer whale skulls and associated skeletal material from a number of different museum 

collections have recently been measured. A preliminary comparison of these measurements 

suggested anatomical differences between resident and transient ecotypes (Fung and BarrettLennard 2004), but the sample size was small and uncontrolled for age and sex. 

2.1.2. North Pacific Killer Whale Populations 

Resident killer whales 

The BRT recognized that there are five populations of resident killer whales in the North 

Pacific: Southern, Northern, Southern Alaska (to include Southeast Alaska and Prince William

Sound), and Western Alaska Residents (Figure 1). Resident killer whales from Russian waters 

have also been described (Wiles 2004). 

Southern Residents—The occurrence of Southern Residents has been documented in the 

coastal waters off Washington State, Vancouver Island, and more recently off the coast of central 

California and the Queen Charlotte Islands. 

Northern Residents—Northern Resident killer whales are frequently seen in the waters 

of Southeast Alaska. Although Northern Residents are seen in close proximity to Southeast 

6
Figure 1. Ranges of resident killer whales in the eastern North Pacific (map from National Marine 

Mammal Laboratory). 

Alaska Residents (less than 1⁄4 nautical mile), the two groups have never been seen to intermix. 

Southeast Alaska whales have never been observed to the south in British Columbian waters. 

Southern Alaska Residents—Southern Alaska Residents include those whales from 

both the Southeast Alaska and Prince William Sound/Kenai Fjords areas. Southeast Alaska 

whales frequently travel north and west into the waters of Prince William Sound. Intermixing 

between Prince William Sound and Southeast Alaska Residents has been documented. On one 

occasion in July 2001, a large group of killer whales was seen just south of Kodiak Island 

(Dahlheim unpubl. data). This grouping contained whales from Southeast Alaska, Gulf of 

Alaska, and the Bering Sea (Figure 1). 

Western Alaska Residents—In 1992/93, large groups of resident whales from Kodiak

Island westward to the Aleutian Islands and the Bering Sea shelf were first described (Dahlheim

1997). Recent studies (2001 to present) verified the resident form through genetic investigations. 

Preliminary counts, based on photo-identification studies, suggest a minimum of 800 individual 

resident whales inhabiting this region. 

Western North Pacific Residents—Photo-identification studies conducted by the 

National Marine Mammal Laboratory (V. Burkanov and M. E. Dahlheim), as well as 

independent data collected and analyzed by the Alaska SeaLife Center (Seward, S. Burdin), have 

7
documented the presence of resident killer whales off the coast of Russia. Genetic data from

Russian killer whales collected through the efforts of V. Burkanov also confirm this resident 

ecotype (Hoelzel et al. 2002b). It is likely that resident killer whales also occur along the 

coastline of Japan, but additional information is required to confirm this hypothesis. 

Transient killer whales 

Information on transient whales is provided in Krahn et al. (2002). 

Offshore killer whales

Offshore killer whales can be distinguished from resident and transient whales (Dahlheim

unpubl. data), because offshores appear to be smaller in overall size and their dorsal fins

typically are more rounded than that of the resident form. In addition, less sexual dimorphism

has been observed between adult males and females (Dahlheim unpubl. data), but this needs to 

be quantified. Offshore whales have multiple nicks on the trailing edge of the dorsal fin, 

possibly a result of the type of prey being targeted or the social interactions that may occur 

among members of this offshore group. Offshore group size is considerably larger—up to 200 

whales—than reported for resident and transient whales. Offshore whales have not been seen to 

intermix with the resident or transient ecotypes, but there does appear to be a considerable 

amount of mixing of individual whales within the offshore groups. When comparing the overall 

range of the three ecotypes, offshore whales have significantly larger home ranges (Dahlheim

unpubl. data). They also have suggested distinct differences in acoustical behavior.2

2.1.3. Feeding Ecology and Food Requirements 

Information about the feeding ecology of the Southern and Northern Residents can be 

found in Krahn et al. (2002) and Wiles (2004). 

When observed within inland waterways of Southeast Alaska and Prince William Sound, 

Southern Alaska Resident whales were primarily targeting salmon (Dahlheim unpubl. data). 

These feeding observations have been limited to the months of May to October, so the feeding 

habits of Southern Alaska Resident whales are not known for the winter periods. Little is known 

about the feeding habits of Western Alaska Resident whales. Given that major runs of salmon 

occur in this region, Western Alaska Resident whales may also be targeting salmon. Again, our 

data are limited to a 3–4 month period and nothing is known about feeding ecology in the fall to 

early spring period. However, in every month of the year, Western Alaska Resident whales have 

been documented to feed on fish from longlines (Yano and Dahlheim 1995). Based on a few 

observations, Russian resident killer whales also appear to be targeting salmon as prey.3

Based on only a few direct observations, offshore whales appear to be targeting fish. 

Sharks may also be consumed by this offshore ecotype. If offshore whales are following 

migratory fish, this may provide an explanation for the extensive movements of these whales 

between California and Alaska (Dahlheim unpubl. data). 

 

2

 J. K. Ford, DFO Canada, Science Branch, Conservation Biology Section, Pacific Biological Station, Nanaimo, BC. 

Pers. commun., 2004. 3

 V. Burkanov, AFSC, National Marine Mammal Laboratory, Seattle. Pers. commun., 2004. 

8
2.1.4. Diving Behavior 

From 1993 to 2002, 40 time-depth recorder tags were attached by suction cups to 

Southern Resident killer whales and these data from the study are still being analyzed (Baird and 

Hanson 2004). Although whales regularly dive to greater than 150 m, there appears to be a trend 

toward a greater frequency of shallower dives in recent years. In addition, the data have shown 

that males dive deeper than females do. 

2.1.5. Social Structure 

Ford and Ellis (2004) recently suggested that the most useful definitions of social 

structure within a resident killer whale community are the matriline and clan. The term pod 

should perhaps be used as a generic description of any aggregation of whales without implication 

of structure, or alternatively as a synonym for the matriline. 

2.1.6. Behavioral and Cultural Diversity 

When Southern Resident pods approach each other after being separated for some time, 

the pods have a unique “greeting” behavior that has not been described for other populations. 

The pods will form two tight lines and approach each other head on. When the groups are within 

10–20 m of each other, they stop motionless at the surface and hover, facing each other for 

10–30 seconds (Osborne 1986). Intermingling typically follows this greeting ceremony. 

Intermingling is characterized by slow-moving and tight-milling concentrations of whales. 

Many of the whales are in physical contact and roll and brush against each other at or near the 

surface. 

Northern Residents also exhibit a somewhat unusual behavior. Northern Resident whales 

have entered shallow water along the coast and rubbed against the rocks along the bottom

(Dahlheim unpubl. data). It is believed that this “beach rubbing” behavior aids the whales in 

sloughing dead skin. Because Northern Residents are frequently seen exhibiting this behavior, 

the beach rubbing areas are protected by the Canadian government. Beach rubbing by other 

resident whales, although extremely rare, has also been seen in Prince William Sound (Angliss 

unpubl. data). 

In western Alaska, along the Aleutian Islands and Bering Sea shelf break, several pods of 

killer whales are known to actively depredate on longline-caught fish (Yano and Dahlheim

1995). These whales target sablefish and Greenland turbot. The extent and magnitude of these 

interactions appears to be expanding into the central and western Aleutians (Yano and Dahlheim

1995). In Prince William Sound, two killer whale pods (AB and AI Pods) are also known to 

depredate on longline-caught fish. In the late 1990s, AF Pod (resident pod from southeast 

Alaska) damaged longline-caught fish (Dahlheim unpubl. data). Given that AF Pod has been 

seen in association with the Prince William Sound resident pods, it is possible that AF Pod 

learned this behavior from observing the Prince William Sound resident whales. 

9
2.2. Genetics of Killer Whales 

2.2.1. Summary of the 2002 Status Review

The genetic information evaluated by the 2002 status review consisted primarily of 

mitochondrial DNA (mtDNA) sequences and microsatellite genotypes from samples collected in 

the eastern North Pacific and a small number of samples from other parts of the world (Table 1). 

The then current understanding of patterns of killer whale genetic variation was as follows: the 

resident and transient killer whale ecotypes in the eastern North Pacific were clearly 

differentiated by multiple (5-6/1000) fixed base pair differences in the mtDNA control region 

and relatively high divergence at nuclear microsatellite loci (FST estimates ranged from 0.23 to 

0.43) depending on the specific populations compared (Barrett-Lennard 2000). 

Only two mtDNA haplotypes had been found among eastern North Pacific residents, 

which differed from each other by a single base pair substitution. The Northern Residents were 

fixed for one haplotype and the Southern Residents for the other. The Southern Alaska 

Residents had both haplotypes, split along acoustical clans. The AB clan had the “northern 

resident” haplotype and the AD clan the “southern resident” haplotype. Offshores had only one 

haplotype, which differed from the southern resident haplotype by a single base pair substitution. 

Resident populations were strongly differentiated from offshores at microsatellite loci (estimates 

of FST were ≈0.30), and moderately differentiated from each other (FST estimates ranged from

0.076 to 0.187). The small number of Atlantic samples that had been analyzed had mtDNA 

haplotypes more similar to residents than to transients. The 2002 status review also noted that 

the level of microsatellite diversity in the small sample (n = 8) of Southern Residents that had 

been analyzed was similar to that observed in a much larger sample of Northern Residents 

(n = 126), suggesting the possibility that the Southern Resident population had once been much 

larger than its current size. 

2.2.2. Additional Genetic Information Available to the 2004 BRT 

Since the 2002 status review, additional mtDNA and microsatellite data have been 

collected for killer whales from various places around the world (Table 2), including one 

published paper (Hoelzel et al. 2002a) and five unpublished reports prepared as part of the 

NOAA-sponsored Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs of 

Table 1. Summary of genetic analyses prior to 2002. 

Study Geographic focus

Number of 

samples Type of data 

Stevens et al. 1989 Eastern North Pacific, Atlantic 20 mtDNAa

Hoelzel and Dover 1991 Eastern North Pacific, 

Atlantic, southeastern Pacific 

17 MtDNA,

b

 nuclear 

fingerprinting 

Hoelzel et al. 1998 Eastern North Pacific 73 MtDNA,b

 microsatellites 

Barrett-Lennard 2000 Eastern North Pacific 130 MtDNA,b

 microsatellites 

a Restriction fragment length polymorphism

b Control region sequence 

10
Table 2. Summary of new genetic data considered by the BRT. 

Study Geographic focus

Number of 

samples Type of data 

Hoelzel et al. 2002a Worldwide 102 mtDNA, microsatellites

Hoelzel 2004 Worldwide 211 mtDNA, microsatellites 

LeDuc and Pitman 2004 Antarctic 49 mtDNA 

LeDuc and Taylor 2004 Worldwide 219 mtDNA 

Morin et al. 2004 Eastern North Pacific (historic 

samples) 

30 mtDNA

Mesnick and EscorzaTreviño 2004Eastern Tropical Pacific 13 mtDNA, microsatellites 

Conservation and Management, April 30–May 2, 2004, La Jolla, California (designated the 

Cetacean Taxonomy Workshop). Each of these documents is summarized below. 

Hoelzel et al. (2002a) sequenced the mtDNA control region from 102 whales, including 

47 from the eastern North Pacific, 45 from the eastern North Atlantic, 5 from the western North 

Atlantic (Argentina), 3 from the western South Pacific (New Zealand), 1 from the western North 

Atlantic (Newfoundland), and one from Antarctica (Ross Sea). The total level of variation 

within the worldwide samples was low compared to other cetacean species. On average, 

randomly selected pairs of killer whale mtDNA control region sequences differed by only 5/1000 

base pairs, a value near the low end of the range observed among marine mammals (Hoelzel et 

al. 2002b). The study found little evidence of geographic structure on a global scale. For 

example, the southern resident haplotype was observed not only in Southern and Alaskan 

Residents, but was also found in animals from the Atlantic sampled off the British Isles and 

Newfoundland. Similarly, another haplotype was shared between samples from New Zealand 

and Iceland. The overall pattern of variation is described by a “star phylogeny,” in which most 

sequences are more or less equally divergent from most other sequences. The distribution of 

differences among all pairs of sequences was unimodel, a pattern often associated with an 

expanding population. Hoelzel et al. (2002a) concluded that the low levels of diversity, lack of 

geographic structure, and distribution of pairwise differences all suggested that killer whales had 

gone through a genetic bottleneck. Based on the level of divergence among haplotypes, they 

suggested that if such a bottleneck occurred, it probably happened around 145,000 to 210,000 

years ago. The study also examined microsatellite variation at eight loci, and found low levels of 

heterozygosity compared to other cetacean species. Patterns of microsatellite variation among 

the three groups of eastern North Pacific whales in the study (Southern and Alaskan Residents 

and transients) were generally similar to those reported by Barrett-Lennard (2000). 

Hoelzel (2004) expanded his earlier study to include 211 samples, primarily from the 

eastern North Pacific, southeast Alaska, the Bering Sea, Kamchatka Peninsula in Russia, and 

southeast Iceland. In addition to mtDNA analysis (conducted on a subset of 188 samples), these 

samples were scored for 17 microsatellite loci. The increased number of mtDNA samples 

contained several additional haplotypes, including three previously unknown transient 

haplotypes. Patterns of mtDNA variation remained largely as described above, however, with 

the transients haplotypes forming one divergent group and all other haplotypes from around the 

11
world another group. Patterns of microsatellite divergence among eastern North Pacific 

population were largely consistent with Barrett-Lennard (2000), although the absolute level of 

divergence was lower (FST ranged from 0.03 between Bering Sea and Alaskan Residents to 0.25 

between the samples from Russia and Iceland) (Table 3). The estimates of FST among pairs of 

resident populations were on average lower than estimates between resident and transient 

populations (0.03–0.125 within residents compared to 0.122–0.168 between residents and 

transients). Average heterozygosity and allelic richness (number of alleles corrected for sample 

size) were similar among the four resident populations in the study (Southern, Southeast 

Alaskan, Bering Sea, and Russian), and all four of the resident samples were less variable than 

the transient samples (heterozygosities ranged 0.387–0.507 for the residents and 0.652–0.668 for 

the transients). There was no evidence that the Southern Residents were less genetically diverse 

than other resident populations. 

Hoelzel (2004) conducted several analyses aimed at estimating the level of migration 

among populations. These included estimating the number of migrants per generation under an 

equilibrium island migration model using the private allele method of Slatkin (1985) and an 

asymmetric migration model (Beerli and Felsenstein 2001, Beerli 2002). Both models produced 

roughly similar estimates of migration rate, ranging from less than one migration per generation 

between Icelandic samples and the Pacific samples (private alleles method, Table 3) to 

approximately eight migrants per generation from the Southern Residents to the Alaskan 

transients (Beerli method). It is important to note these estimates were obtained using models 

that are not designed to distinguish between current and historical gene flow, and the data could 

therefore potentially also be consistent with models assuming no contemporary migration but 

varying divergence times among populations (see extensive discussion of this issue in Nielsen 

and Wakeley 2001). 

Hoelzel (2004) also approached the migration question by employing a population 

assignment method developed by Pritchard and Donnelly (2000). The method works by 

Table 3. Estimates of genetic divergence (FST) and gene flow (migrants per generation, private allele 

method) among eight killer whale populations based on microsatellite DNA divergence. 

(Reproduced with permission from Hoelzel 2004.) 

SRa RU AR BS OS AT CT ICE

SR – 1.69 2.53 2.07 0.45 1.50 1.59 0.98

RU 0.125***b – 2.18 2.06 0.48 0.90 0.79 0.48

AR 0.061  0.095** ** – 3.38 1.06 1.34 0.97 0.69

BS 0.089*** 0.052*** 0.029** – 0.53 1.21 0.72 0.62

OS 0.122* 0.201* 0.186** 0.208 – 1.34 0.93 0.68

AT 0.122  0.132** ** 0.156  0.143** * 0.106* – 2.56 0.94

CT 0.131**** 0.152  0.168** ** 0.166** 0.130* 0.035**** – 1.03

ICE 0.141  0.245** ** 0.154  0.205** * 0.148** 0.145  0.136** ** – 

a

 Abbreviations are: SR = Southern Resident, RU = Russian, AR = Southeast Alaskan Resident, BS = Bering Sea 

Resident, OS = offshore, AT = Alaskan transient, CT = California transient, ICE = Iceland. 

b

 Asterisks indicate degree of statistical significance:   = p < 0.001, ** * = p < 0.005, ** = p < 0.01, * = p < 0.05. 

(See Hoelzel 2004 for details.) 

12
partitioning the entire sample set into a preselected number of populations by maximizing the fit 

to multi-locus Hardy-Weinberg equilibrium expectations. Each individual sampled can then be 

assigned to its most likely population of origin. Individuals that assign with high probability to a 

population different from their sampling population can be identified as possible migrants or 

recent descendants of migrants. Hoelzel applied this analysis to the microsatellite data from the 

eastern North Pacific and Icelandic samples, and found that each initially identified population 

was strongly supported except for the Bering Sea Resident sample, which appeared to be a 

mixture of two or more populations. The analysis identified only three potential migrants—one 

Southeast Alaska Resident that genetically appeared to be Russian, an offshore sample that 

genetically appeared to be a California transient, and an Alaskan transient that genetically 

appeared to be a California transient. 

Morin et al. (2004) reported on preliminary findings of a study examining patterns of 

mtDNA diversity in historical (pre-1980) samples of killer whales from California and 

Washington. The purpose of the study was to determine if there is evidence that the Southern 

Residents may have historically inhabited the California coast, especially the Sacramento River 

estuary, to take advantage of the historically large runs of Chinook salmon (Oncorhynchus 

tshawytscha) in that area. The presence of whales with the southern resident mtDNA haplotype 

would suggest that historically the Southern Residents inhabited the area, whereas the absence of 

this haplotype would tend to suggest they did not. The preliminary analyses from 30 samples, 

some dating from as early as the mid-1800s, found no evidence of haplotypes outside of their 

contemporary ranges. The whales sampled from the California coast all contained haplotypes 

currently associated with transients or offshores, and haplotypes currently associated with 

Southern Residents were found only in Puget Sound or the Strait of Juan de Fuca. Neither 

outcome was expected to be conclusive, however, because the absence of southern resident 

haplotypes in a small sample does not prove they were not there, and the presence of the 

southern resident haplotype does not conclusively prove that the whales carrying the haplotype 

were part of what is now considered the Southern Resident population. 

LeDuc and Taylor (2004) reported on a large (n = 219) data set of killer whale mtDNA 

control region sequences. In addition, they combined their data with the published mtDNA 

sequences of Hoelzel et al. (2002b) to create the largest existing data set of killer whale mtDNA 

sequences. Their results can be summarized as follows: 

1. The number of unique haplotypes has grown dramatically since the last status review was 

conducted as sample sizes have increased and new areas have been sampled. In total, 54 

different haplotypes have now been found. 

2. A large number of new haplotypes have been found in samples from Antarctica and the 

eastern Tropical Pacific.

3. The haplotypes form two major clades, named the R and T clades by LeDuc and Taylor 

(Figure 2). 

The R clade is more diverse, and contains a large number of haplotypes from around the world, 

including the southern resident and northern resident haplotypes and the offshore haplotype. The 

T clade is limited to the Pacific Ocean and Antarctica, and contains the original transient 

haplotypes as well as many previously unsampled haplotypes. All known fish specialists (such 

as the eastern North Pacific residents) are found in the R clade, but both clades contain animals 

13
Figure 2. MtDNA haplotype tree (provided by R. LeDuc based on data described in LeDuc and Taylor 

2004). ETP = eastern Tropical Pacific, NR = Northern Residents, SR = Southern Residents, 

WCT = West Coast transients, GAT = Gulf of Alaska transients, and AT1 = the AT1 Pod of 

transients in Alaska. 

14
observed to feed on either fish or marine mammals or both (i.e., the two clades do not cleanly 

correspond to any known ecological specialization). LeDuc and Taylor (2004) did not report 

levels of nucleotide diversity, but as all of the new haplotypes are closely related to previously 

known haplotypes, it appears unlikely that the low levels of diversity found by Hoelzel (2002b) 

will change substantially. On a global scale, there is little geographic structure apparent in the 

data, but some local structure is apparent. In particular, the B and C forms from Antarctica share 

a group of closely related haplotypes, as do some animals from the eastern Tropical Pacific 

(Figure 2). 

LeDuc and Pitman (2004) described recent mtDNA sequence data from Antarctic killer 

whales. They analyzed 49 samples, which included 7 samples identified a priori as Type A, 15 

as Type B, and 18 as Type C. The 49 samples contained 24 variable sites, yielding 16 unique 

haplotypes. The ice inhabiting forms (B and C) were characterized by a group of closely related 

haplotypes, differing from Type A forms by three fixed differences. The Type A forms 

contained a large number of highly diverse haplotypes similar to others found from throughout 

the world (Figure 2). The total diversity present in Antarctica alone is comparable to what is 

found throughout the rest of the world. 

Mesnick and Escorza-Treviño (2004) analyzed microsatellite and mtDNA variation 

within 13 killer whales sampled from five groups, defined as animals seen swimming together in 

a coordinated manner. Four of the groups were from the eastern Tropical Pacific, and one was a 

transient group from the Bering Sea. The goal of the study was to use patterns of genetic 

variation within groups to infer characteristics of their social structure. For example, the wellstudied eastern North Pacific resident groups are characterized by a lack of mtDNA variation 

within pods, consistent with observations of no dispersal from natal groups. In contrast, at least 

one transient pod from the Gulf of Alaska has been found with two mtDNA haplotypes within 

the pod (Barrett-Lennard 2000). Killer whales in the eastern Tropical Pacific are much less 

studied than the eastern North Pacific whales, and could potentially have quite different social 

structures than have been previously observed. In their preliminary study, Mesnick and EscorzaTreviño found that animals within groups shared on average twice as many microsatellite alleles 

as animals compared from different groups, consistent with a high degree of relatedness within 

groups. Two of the eastern Tropical Pacific samples were each fixed for a single mtDNA 

haplotype, similar to what has been observed among eastern North Pacific resident groups. The 

other two eastern Tropical Pacific groups, however, each contained two mtDNA haplotypes, 

similar to what has been observed in some transient groups. In one of these groups, one of the 

two haplotypes was from the R side of the haplotype tree and the other from the T side (Figure 

2). These results are preliminary and Mesnick and Escorza-Treviño are reanalyzing some

samples to confirm the results, but they do provide some suggestion that the eastern Tropical 

Pacific killer whales may exhibit at least two of the social structures that have been observed in 

the eastern North Pacific. 

2.2.3. Summary and Conclusions 

The understanding of killer whale population genetic structure has expanded considerably 

since the 2002 status review. In particular, the mtDNA differentiation among eastern North 

Pacific resident, transient, and offshore populations can now be seen in the context of variation 

worldwide. The most notable result from the new mtDNA data is the lack of strong mtDNA 

15
structure worldwide, suggesting that the current distribution of killer whales populations may be 

relatively young on an evolutionary scale (e.g., several hundred thousand years compared to the 

≈5-million-year-old age of the Orcinus genus [Waples and Clapham 2004]) and possibly 

associated with a population bottleneck followed by a worldwide expansion. With respect to 

identifying conservation units, one of the implications of the new data is that the relative degree 

of mtDNA divergence among populations is not necessarily a good predictor of the length of 

time that the populations have evolved independently. For example, killer whales with the same

haplotype as in Southern Residents have also been found in Alaska, Russia, Newfoundland, and 

the United Kingdom (Figure 2). Evolutionarily, these whales with the southern resident 

haplotype are almost certainly more closely related to other geographically proximate 

populations than to each other (a hypothesis supported by the microsatellite data, Table 3) and 

therefore, share a mtDNA haplotype purely by chance. Because of this finding, it would be 

inappropriate to rely heavily on simple mtDNA divergence as a criterion for identifying

conservation units, especially on a global scale. On a local scale, however, mtDNA clearly 

remains useful for helping to identify populations, especially when combined with other types of 

information. 

In addition to more mtDNA data, the amount of nuclear microsatellite data has expanded 

greatly in the last 2 years, both in terms of whales and loci analyzed. Within the eastern North 

Pacific, both the mtDNA and microsatellite data remain consistent with a hypothesis of four to 

five resident populations, at least two to three transient populations and at least one offshore 

population (Figure 1). The issue of whether any contemporary gene flow occurs among eastern 

North Pacific populations remains unresolved, but the microsatellite data are consistent with 

either low levels of gene flow (at most a few mating events among populations per generation) or 

divergence times of at least several hundred to several thousand years (M. Ford 2004, Hoelzel 

2004). Despite some uncertainty about the evolutionary history that produced the current 

patterns of variation, both the mtDNA and the microsatellite data indicate a high degree of 

contemporary reproductive isolation among eastern North Pacific killer whale populations. 

2.3. Taxonomy of Killer Whales 

2.3.1. Current Status 

The taxonomy of the killer whales is in a state of flux. The previous prevailing concept 

of a single species has recently evolved into a diversity of views that include the possibility of 

multiple species. In 1758, Linnaeus described the species O. orca. Subsequently, some 25 

additional species were described. Following a century or so of general “lumping” of zoological 

species described in Victorian times, the consensus of scientific opinion—until recently—was 

that a single global killer whale species exists (Rice 1998). Despite this consensus, new 

“species” of killer whales occasionally continue to be described. For example, in 1982 two 

Russian whale biologists described Orcinus glacialis based on large numbers of a small and 

distinctively patterned killer whale they encountered in the pack ice of Antarctica (Berzin and 

Vladimirov 1982, 1983). This “species” was not generally accepted by the scientific community 

because of the then-prevailing consensus of a single global species of killer whale and because of 

the loss of the holotype specimen. However, recent new observations and data on morphology 

and genetics of both the Antarctic and North Pacific killer whales have reopened the question 

and two divergent bodies of expert opinion have emerged (Waples and Clapham 2004). Under 

16
one line of reasoning, killer whales comprise a single highly variable species, with locally 

differentiated ecotypes representing recently evolved and relatively ephemeral forms not 

deserving species status. According to the opposing body of opinion, congruence of several lines 

of evidence for the distinctness of sympatrically occurring forms speaks for multiple species. 

For the Antarctic, new observations of color pattern, size, habitat, and feeding ecology 

have led to the conclusion that there are three types of killer whales—one in open waters (the 

“ordinary” killer whale), one in the pack ice, and a third in leads in the fast ice (Pitman and 

Ensor 2003). The types are distinguishable on the basis of body size, size and shape of a white 

patch behind the eye, habitat, and feeding habits. Genetic relationships among the three forms, 

determined from mtDNA from biopsy samples, are congruent with their morphological and 

ecological distinctiveness (see subsection 2.2). Although loss of the holotype specimen of O. 

glacialis will complicate determining the correct nomenclature for the three forms (Perrin and 

Reeves 2004), the majority opinion in an expert working group on killer whales at the recent 

Cetacean Taxonomy Workshop was that, although more data are needed to evaluate species 

status, the three forms may represent two or possibly three species or subspecies (Reeves et al. 

2004, Waples and Clapham 2004). 

A similar situation occurs for killer whales in the North Pacific. The seasonally 

sympatric resident and transient forms show consistent differences in mitochondrial and nuclear 

genetic markers, coloration, acoustic calls, and foraging habits (Waples and Clapham 2004 and 

also subsections 2.1 and 2.2). Preliminary data show osteological differences as well, although 

sample sizes remain small (Fung and Barrett-Lennard 2004). The offshore form is also distinct, 

but shares some characteristics with the resident form. Similar to the case for the Antarctic killer 

whales, the majority of experts participating in the killer whale working group at the Cetacean 

Taxonomy Workshop believed that the resident and transient killer whales in the North Pacific 

may be distinct species or subspecies (Reeves et al. 2004, Waples and Clapham 2004). 

Participants in the Cetacean Taxonomy Workshop agreed on guidelines for recognition of 

a cetacean subspecies: 

In addition to the use of morphology and genetics to define subspecies, the 

subspecies concept should be understood to embrace groups of organisms that 

appear to have been on independent evolutionary trajectories (with minor 

continuing gene flow), as demonstrated by morphological evidence or at least one 

line of appropriate genetic evidence. Geographical or behavioral differences can 

complement morphological and genetic evidence for establishing subspecies. As 

such, subspecies could be geographical forms or incipient species. 

The Cetacean Taxonomy Workshop recognized that applying these standards may result 

in cases where subspecies status is given to entities that later prove to be full species, as has often 

happened in the past. Under the guidelines proposed, the participants concluded that recognition 

and formal description of subspecies of killer whales in the Antarctic (types A, B, and C) and 

North Pacific (residents and transients) would be appropriate, with the understanding that further 

research may result in elevation of some or all of them to the species level, or alternatively, in the 

determination that species status is not warranted.

17
2.3.2. Nomenclature 

If it is decided that the resident killer whales of the North Pacific should be considered a 

subspecies of O. orca (see subsection 3.2), naming this taxon (and other killer whale taxa 

identified in a potential global review) becomes a problem. It must be emphasized that the 

nomenclatural work, if any is required, cannot commence until the biological work is completed, 

that is, after globally identifying the number of valid species or subspecies and their diagnostic 

characters. 

The first step in assigning the various nominal species and subspecies names (some 25 in 

the literature since 1758, draft list in Perrin 2004) to biologically determined species or 

subspecies is determining the species or subspecies identity of type specimens. Some holotype 

specimens may be identifiable to species or subspecies from the figures and characters given in 

the description or from data published by earlier workers who examined the specimen. Others 

may require a visit to the collection holding the specimen to measure and photograph it. If the 

morphological characters are not fully diagnostic (including at all life stages in the case of an 

immature holotype), or if the specimen is incomplete or damaged such that the diagnostic 

characters cannot be examined, it may be necessary to collect a tooth or bone sample for genetic 

analysis. Alternatively, it may be possible to obtain a tooth or bone sample from the specimen 

without visiting the collection. In this case, the identification would hinge entirely on the 

molecular diagnosis. If all attempts to identify the holotype specimen to species or subspecies 

fail, the nominal species (the name) must be relegated to uncertain status (nomen dubium). If 

future, more powerful, analyses are able to identify the specimen, then the name will come back 

into play as a valid (junior or senior) synonym. 

Holotype specimens of killer whales are thought to be held in the following collections: 

1. Museum of the College of Surgeons, (may now be at British Museum), London, United 

Kingdom: Orca capensis. 

2. British Museum, London, United Kingdom: Orca stenorhynchus, O. latirostris, O. 

pacifica. 

3. Muséum National d’Histoire Naturelle, Paris, France: O. gladiataor europoeus. 

4. Copenhagen Museum, Denmark: Orca eschrichtii, O. gladiator arcticus. 

5. Bergen Museum, Norway: Orca schlegelii. 

6. Naturistorika Museum, Göteborg, Sweden: Orca minor.

7. Buenos Aires Museum, Argentina: Orca magellanica.

As noted above, some of these may be identifiable to species based on information in the 

description or data published by earlier workers who examined the specimen. 

If it is decided (as recommended by the Cetacean Taxonomy Workshop) that the North 

Pacific resident form constitutes a subspecies (see subsection 3.2), until a global review of 

holotypes and species descriptions can be accomplished, this subspecies would best remain 

unnamed. There is a precedent for such provisional recognition of cetacean subspecies (Rice 

1998). For example, the dwarf southern-hemisphere form of the common minke whale 

(Balaenoptera acutorostrata) and the Kerguelen Island form of Commerson’s dolphin 

(Cephalorhynchus commersonii) are recognized and managed by the International Whaling 

Commission as “unnamed subspecies.” 

18
2.4. Ecology of Southern Resident Killer Whales 

2.4.1. Current Range and Distribution 

Since the early 1970s, the range of Southern Resident killer whales has been determined 

from strandings or opportunistic resightings of photo-identified individuals. Some Southern 

Resident killer whale pods use different summer and winter habitats, and the amount of 

information available to determine the extent of their seasonal ranges is very limited. For 

example, over a 20-year period, only 27 confirmed sightings of Southern Residents have been 

documented outside the Puget Sound region (Table 4). 

Summer 

Additional studies in 2003 demonstrated that there are seasonal and temporal differences 

in habitat use by the three Southern Resident pods in Puget Sound (Hauser unpubl. data). The 

west side of San Juan Island and Haro Strait is the most commonly used area among all three 

pods, but other regions (e.g., the south end of Vancouver Island) are used in varying extents by 

the pods. 

Fall, winter, and spring 

Although the range of the Southern Residents outside Puget Sound is not well 

documented, recent studies indicate that, during nonsummer months, J Pod is sighted more 

frequently in Puget Sound than the other two pods (Wiles 2004). Expanded volunteer sighting 

efforts along the coasts of Washington, Oregon, and northern California, and a dedicated NMFS 

research cruise in February–March 2004 resulted in seven new confirmed Southern Resident 

sightings from April 2002 to April 2004 (Table 4). From these data, it appears that the current 

range of Southern Residents extends further south and north than previously documented. For 

example, the March 2003 sighting of K and L Pods off Monterey Bay, California4

—in addition 

to the previously reported sighting there in January 2000—suggests that their current range may 

extend to central California. The sighting of L Pod off Langara Island in the northern Queen 

Charlotte Islands in May 2003 extended the northern range of the Southern Residents. This 

sighting, combined with earlier sightings of the pods returning to Georgia Strait through 

Johnstone Strait, suggests that this region may be a customary part of their range. 

Multiple sightings have occurred over the years in a few locations and may provide new 

information on the habitat use and prey resources that are important to the Southern Residents 

during the winter and spring months. A sighting of L Pod off Tofino on the west coast of 

Vancouver Island in May 2004 was the fifth occurrence of Southern Residents in this area. 

During the 2004 research cruise, J Pod was observed at the entrance of the Strait of Juan de Fuca, 

heading toward the outer coast, and L Pod was sighted off Westport, Washington, the fourth 

occurrence in this area. The L Pod sighting coincided with the start of the spring Chinook 

salmon run in the Columbia River, but it is not known if salmon or other potential prey were in 

the area at the time of the J Pod sighting. 

 

4

 N. A. Black, Monterey Bay Cetacean Project, Pacific Grove, CA. Pers. commun., 2004. 

19
Table 4. Summary of known and potential sightings of Southern Resident killer whales along the outer 

Pacific Ocean coast. Also listed are known sightings of Southern Resident killer whales in 

“winter” (December–April) in the inside waters of British Columbia and Washington (the Strait 

of Juan de Fuca and east).* 

Date Location Identification Source Comments

British Columbia outer coast

31 Jan 1982 Barkley Sound, west

coast of Vancouver 

Island

L Pod Ford et al. 2000 and 

J. Ford, PBS/DFO 

Off shore of Sound

21 Oct 1987 Coal Harbor, 

north Vancouver Island

Part of L Pod J. Ford, PBS/DFO Were way up inlet a 

long distance from

open ocean 

3 May 1989 Tofino, west coast of 

Vancouver Island 

K Pod WMSA 

Jun 1995 Hippa Is., south Queen 

Charlotte Islands 

Southern

resident

haplotype 

J. Ford, PBS/DFO Carcass found on 

beach, ID only by 

genetics 

May 1996 Cape Scott, north 

Vancouver Island 

Southern

resident

haplotype 

J. Ford, PBS/DFO Carcass found on 

beach, ID only by 

genetics 

4 Sep 1997 Off Carmanah Point L Pod Observed by P.

Gearin, NMML

Identified by D. 

Ellifret 

14 Apr 2001 Tofino, west coast of

Vancouver Island 

L Pod J. Ford, PBS/DFO 

27 Apr 2002 Tofino, west coast of 

Vancouver Island 

L Pod J. Ford, PBS/DFO 

12 May 2002 Tofino, west coast of 

Vancouver Island 

L Pod J. Ford, PBS/DFO 

30 May 2003 Langara Is., Queen 

Charlotte Islands 

L Pod M. Joyce, DFO 

17 May 2004 Tofino, west coast of 

Vancouver Island 

L Pod M. Joyce, DFO 

Washington outer coast

4 Apr 1986 Westport/Grays Harbor L Pod Bigg et al. 1990 and 

J. Ford, PBS/DFO 

13 Sep 1989 Off Cape Flattery L Pod J. Calambokidis, 

Cascadia Research 

Photos were sent to 

K. Balcomb 

17 Mar 1996 Grays Harbor L Pod R. Osborne, WMSA 2 mi. off outer coast

20 Sep 1996 Off Sand Point L Pod Observed by P.

Gearin, NMML

Identified by D. 

Ellifret 

15 Apr 2002 Long Beach L60 D. Duffield, 

Portland State Univ. 

Stranded whale 

identified by K. 

Balcomb, CWR

11 Mar 2004 Grays Harbor L Pod B. Hanson, NWFSC

Oregon

Apr 1999 Depoe Bay L Pod J. Ford, PBS/DFO

Mar 2000 

(week of 20th)

Yaquina Bay L Pod J. Ford, PBS/DFO

14 Apr 2000 Depoe Bay Southern

Residents 

K. Balcomb, CWR 

20
Table 4 continued. Summary of known and potential sightings of Southern Resident killer whales along 

the outer Pacific Ocean coast. Also listed are known sightings of Southern Resident killer whales 

in “winter” (December–April) in the inside waters of British Columbia and Washington (the 

Strait of Juan de Fuca and east).* 

Date Location Identification Source Comments

California

29 Jan 2000 Monterey Bay K and L Pods N. Black, MBWW Seen and 

photographed feeding 

on fish (Chinook?)

13 Mar 2002 Monterey Bay L Pod N. Black, MBWW 

Inside waters of Washington and British Columbia

26 Feb 1975 Chatham Point, BC,

central east coast 

Vancouver Island 

L Pod J. Ford, PBS/DFO 

1 Feb 1976 Beecher Bay, BC, 

Strait of Juan de Fuca, 

10 mi. west of Victoria,

BC 

K and L Pods J. Ford, PBS/DFO 

17 Apr 1976 Victoria, BC K and L Pods J. Ford, PBS/DFO Off Victoria 

3 Feb 1982 Victoria, BC K and L Pods J. Ford, PBS/DFO Off Victoria 

13 Mar 2004 Off Cape Flattery J Pod B. Hanson, NWFSC Whales were outbound

Possible sightings of Southern Residents on outer coast

15 Aug 1994 10–20 mi. off Westport, 

WA 

3–5 whales R. Osborne, WMSA Photos taken 

11 Apr 1997 Mouth of the Columbia 

River 

Large pod R. Osborne, WMSA

18 Apr 1997 Off La Push, WA 18 whales R. Osborne, WMSA

20 Jul 2000 14 mi. west of Ucluelet, 

west coast Vancouver 

Island

50+ whales R. Osborne, WMSA No Southern Residents 

were known to be in

inland waters at the 

time

26 Jul 2001 Off La Push, WA 10–20 whales R. Osborne, WMSA Possible Southern

Resident

29 Jul 2001 Off Cape Flattery, WA 20–30 whales R. Osborne, WMSA

* Dates of new sightings (since the 2002 status review) are in bold. Observations are from a variety of sources. 

PBS/DFO is the Pacific Biological Station, Dept. Fisheries and Oceans Canada, Nanaimo, BC. NMML is the 

AFSC’s National Marine Mammal Laboratory, Seattle, WA. WMSA is the Whale Museum Sighting Archives 

(1978–2001), Friday Harbor, WA. CWR is the Center for Whale Research, Friday Harbor, WA. MBWW is

Monterey Bay Whale Watch, Pacific Grove, CA. 

21
2.4.2. Population Dynamics 

Since 1973/74, the Southern Resident killer whale pods have been photo-identified 

annually by the Center for Whale Research (Hammond et al. 1990). In order to identify 

individual whales, photographs are taken of a lateral view of a whale’s dorsal fin and saddle 

patch. The shape of the dorsal fin and the coloration pattern of the saddle patch, as well as 

distinctive scratches, nicks or other marks, allows individual whales to be identified. In May and 

June of each year, sufficient photographs are taken to identify every Southern Resident

individual, so the annual survey amounts to a census of the entire population. This census allows 

a detailed examination of the population dynamics of the Southern Resident community, 

including the survival and fecundity of individual animals of known age. 

Age-specific information on survival and fecundity of individuals in the Southern 

Resident pods was analyzed to determine patterns in vital rates and to provide parameters for a 

PVA that examined possible population trajectories, given certain initial conditions and a range 

of plausible environmental parameters. The analyses of population dynamics here, as well as the 

PVA presented in subsection 5.1, update the analyses documented in the previous status review 

(Krahn et al. 2002). 

Results from new analyses 

Annual counts of the total population size showed fluctuations in the Southern Resident 

population from 1974 to 2003 (Figure 3). With a time series of 29 years, it is possible to look for 

changes in survival and fecundity rates (conditional on the survival of the adult female) over 

time and among age and sex classes, thus allowing an investigation into demographic factors that 

may have contributed to the fluctuations. 

40

50

60

70

80

90

100

110

120

1973 1977 1981 1985 1989 1993 1997 2001

Year

Population siz

e

71

97

79

74

11% decline from 1980 to 1984 (4 years)

20% decline from 1996 to 2001 (5 years)

83 83

Figure 3. Southern Resident killer whale population size through time. (Note: The number 78 for year 

2001 in Figure 3 of Krahn et al. 2002 was revised to 79 above to include L98, the juvenile male 

separated from his pod and living in Canadian waters.) 

22
Population abundance and trends 

In the 1974 census, the population comprised 71 whales, whereas the most recent census 

in the summer of 2003 counted 83 whales, representing an overall annual increase of 0.4% per 

year. However, the population has fluctuated over the 29 years of the study: increasing from

1974 to 1980 at 2.6% per year, then declining at –2.8% per year until 1984, then increasing again 

at 2.3% per year until 1996, declining at –4.3% per year through 2001, and finally increasing by 

2.5% per year in 2002–2003 (Figure 3). On average, there have been 3.0 births and 2.7 

mortalities per year. The whale L98 (known to be alive, but separated from L Pod) was included 

in these analyses.

Estimates of survival 

A complete census of the population is made each year. Therefore, the realized survival 

rate of the population can be examined by calculating the fraction of animals that survive from

one year to the next. Survival rate in year t is defined here as the probability of surviving from

the summer of year t until the summer of year t + 1. For example, the survival rate in year 1990 

is the proportion of animals that survived from the summer of 1990 until the summer of 1991. 

With 30 years of census data available, a total of 29 survival rates (for the years 1974–2002) can 

be calculated. 

Crude (total population) survival rates 

When every animal is seen in each year, the mark-recapture literature refers to this 

situation as “known fate” data. The survival rate in any given year is estimated as the number of 

animals in the group that survive from time t to t + 1 divided by the number alive in the group at 

time t. The “known fate” option in the program MARK (White and Burnham 1999) was used to 

analyze the data. This allowed a comparison between different models of survival and the 

selection of the model that provided the best fit to the data. Survival can be modeled over time

in several different ways. A particular survival model is described by whether survival is 

different among groups (the six age and sex categories given in the “Age- and sex-specific 

survival models” subsection below) and how it changes over time. Models for survival over time 

included: 

1. S(.) = a constant survival rate over all 28 years (1 parameter) 

2. S(T) = a trend in survival (2 parameters) 

3. S(t) = different survival rate in each year (29 parameters) 

4. S(mt) = a different constant survival rate for each of m consecutive years (e.g., S(5t) 

would have one survival rate for the first 5 years, another survival rate for the second 5 

years and so forth, for a total of 5 different parameters) 

Values of m from 2 to 10 were used, ranging from a 14-parameter model to a 3-parameter 

model. As an additional complication, all possible starting permutations were considered: a full 

period starting in 1974 was given the letter “a” designation, a starting period 1 year less than a 

full period was given the letter “b” designation, and so on. For example, S(7t a) was a fiveparameter model that had constant survival for five periods of 7, 7, 7, 7, and 1 year duration, 

S(7t b) had constant survival for five periods of 6, 7, 7, 7, and 2 years duration, and S(7t c) had 

constant survival for five periods of 5, 7, 7, 7, and 3 years duration. 

23
The models were compared using Akaike’s Information Criterion (AIC), which is based 

on the maximum likelihood estimates for the parameters. AIC provided a measure of which 

model best fits the data. 

The best fitting models for crude survival were, in order, S(7t b), S(7t c), S(8t f), and 

S(4t b). Although these appear to be different models, in reality they provided a very similar 

picture of trends in survival through time, with the exception of some differences in single years. 

The best model, S(7t b), showed the overall pattern with alternating periods of relatively high 

and relatively low survival rates, ending with higher survival rates in the last 2 years (Figure 4). 

However, the three other models mentioned fit the data nearly as well. One was another model 

with constant 7-year periods, starting with a 5-year period in 1974, and the other was a model 

with 8-year constant periods, starting with a 3-year period in 1974. Both model S(8t f) and 

model S(4t b) started with a 3-year initial period in 1974; the difference between the two models 

was that the model S(4t b) allowed the 8-year periods in S(8t f) to be broken into 4-year periods 

with slightly different survival rates.

In cases where several models fit the data well, it is appropriate to average across models, 

where each model is weighted by its AIC value. Model averaging was done using the program

MARK. The model-averaged estimates of survival show the distinct patterns through time 

(Figure 5). Survival rates were relatively high from 1974 to 1979, relatively low from 1980 to 

1984, relatively high from 1985 to 1992, and relatively low again from 1993 to 2000 (Figure 4). 

Recent data showed an increase in survival from 2000 to 2003, but the observed increase was 

less than that seen during previous oscillations in survival rates. 

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Survi

val

S(7t b) S(t)

Figure 4. Best fitting model S(7t b) of crude (total population) survival (line), 7-year periods of constant 

survival, starting with a 6-year period in 1974. Also shown are annual estimates of survival 

(triangles). 

24
0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Survi

val

Model average S(t)

Figure 5. Model-averaged estimates of crude (total population) survival. 

Crude survival by pod 

An additional analysis was done to investigate whether there were differences in survival 

rates among J, K, and L Pods of Southern Residents (Figure 6). No differences in temporal 

patterns were found among the pods, and all three pods showed the same temporal trends seen in 

the crude survival analysis described above. Indeed, the decline in survival in the early 1980s, as 

well as in the 1990s, can be seen in each pod. However, L Pod has consistently had lower 

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1972 1976 1980 1984 1988 1992 1996 2000 2004

Survival

Year

J Pod

K Pod

L Pod

Figure 6. Southern Resident killer whale annual survival estimates by pod. 

25
survival rates than either J or K Pod. The difference in the magnitude of survival among pods 

was sufficiently large that the AIC value considered the best pod survival model to be a better fit 

to the data than the best crude survival model that ignored pods. 

Age- and sex-specific survival models 

All mammals tend to have differences in survival with age, with relatively low early 

survival (infants and young juveniles), high adult survival and declining survival in older 

individuals (Caughley 1966). Killer whales have been shown to follow this pattern, as well as to 

exhibit differences in survival between sexes (Olesiuk et al. 1990). Olesiuk et al. (1990) reported 

that most births take place from October to March. Newly born whales are not counted until 

they are seen during the summer field season (typically May and June). The “calf” survival rate 

estimated here is for survival from the first summer to the second summer. For example, calf 

survival for a six-month old calf first seen in June will be survival from six months to 18 months 

of age. 

Some individual killer whales do not have their sex identified until they are 

approximately 10 years old, although other individuals are identified at a much earlier age. 

Therefore, all males, females, and unknown sex whales aged 1 to 10 were assigned to the 

“juvenile” age class. Age 10 also provides a useful break point for females, because the 

youngest female to give birth in this population was age 12, meaning she was sexually mature at 

age 11. Whales older than age 10 were considered “adult” for this study, even though it is 

recognized that males do not reach sexual maturity until age 15 (on average) and may not reach 

physical maturity until age 20 or greater (Olesiuk et al. 1990). The oldest female to give birth 

was estimated to be 41 years old. Therefore, females from age 11 to 41 were placed into a single 

category “reproductive-age females” and those 42 and older were designated “post-reproductiveage females.” However, a few females in this category have not been observed with a calf, so 

membership in this category does not imply that the animal is reproductively active or 

successful. Males from age 11 to 21 were placed into another category, called “young males.” 

The age 21 was chosen as the upper bound because this is the average age at which physical 

maturity is attained. Males aged 22 and older were designated “old males.” Six different age 

and sex classes were examined for survival: 

• calves (age 0, whales seen in their first summer), 

• juveniles (ages 1–10), 

• females (ages 11–41, reproductive-age females), 

• females (ages 42+, post-reproductive-age females), 

• males (ages 11–21, young males), and 

• males (ages 22+, old males). 

The influence of the different age and sex classes was investigated by two different types 

of models for group effects. In the “times” models, each of the six groups had their own survival 

parameters that were independent from the other groups. This allowed for the possibility of each 

class (group) having its own unique temporal trend in survival. These models allowed more 

flexibility, but had more parameters to estimate than did simpler models. For example, 

26
combining a “times” model with a S(7t) temporal survival model led to 5 × 6 = 30 total 

parameters for estimating survival. 

The second type of group effect models were “additive” models, where each age and sex 

class would have the same temporal trend (not independent), but each class could be scaled 

differently to account for different average survival rates seen between different age and sex 

classes. These models require the parameters that describe the temporal trend and just one 

additional parameter to scale each group (except for the first group). For example, an additive 

model with an S(7t) temporal survival model leads to five parameters for the temporal trend and 

then five more parameters to scale the other five groups, for a total of 10 parameters. 

The results showed that “additive” models had the best (lowest) AIC values and these 

were much lower than models that ignored sex and age structure. In other words, the large 

differences in average survival among the age and sex classes was an important difference to 

take into account. The “additive” model also indicated that all the age and sex classes were 

experiencing similar patterns in survival through time, so more than one or two age and sex 

classes were affected when survival rates declined. 

In this sex and age structured analysis, the best fitting models provided temporal trends 

similar to those from the best models in the crude survival analysis. The best four models all had 

similar AIC values—models S(7t c), S(7t b), S(8t f), and S(4t b). The model-averaged estimates 

of survival by age and sex class are shown in Figure 7. Although the averaging was done across 

all models, the results were dominated by the best four models mentioned above. Reproductiveage females had the highest survival rate, followed by juveniles, post-reproductive-age females 

and young males. Calves and old males had the lowest survival rates. 

0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Survival 

Calves

Juveniles

Reproductive females

Post-reproductive females

Young males

Old males

Figure 7. Southern Resident killer whale annual survival estimates by age and sex category over the years 

1974 to 2002. These are the model-averaged estimates of survival. 

27
Thus there were large differences in survival rates of Southern Resident killer whales 

among different age and sex categories, but there have also been large changes in survival rates 

through time. These changes have been characterized by periods of relatively constant survival 

for approximately 7 years, followed by a shift to a different, relatively constant, level of survival 

for the next 7 years, and so on. Survival has shifted from relatively high levels in the 1970s, to 

low levels in the early 1980s, to high levels in the late 1980s and early 1990s, then back to low 

levels through 2000, when survival began to improve. Although survival rates improved in 2001 

and 2002, they were not as high as in previous periods of relatively high survival. 

The risk factors that might account for differential survival among the age and sex classes 

were detailed in the previous status review (Krahn et al. 2002) and have been updated in 

subsection 2.5. 

Estimates of fecundity 

All calculations of fecundity were made for “recruited” calves (Olesiuk et al. 1990), 

which are defined as calves that survive until their first summer. Therefore, the fecundity rates 

reported here are likely to be much less than the true birth rate, because the fecundity rate is a 

product of the birth rate and the neonate survival rate. 

The number of recruited calves as a percent of total population size (the gross annual 

reproductive rate, or GARR) was on average 3.5%, with a high of 11.3% (8 calves in 1976) and a 

low of 0%. From 1974 to 2000, the average observed calving interval (years between recruited 

calves) was 5.65. The reciprocal of the calving interval can be used to estimate the fecundity 

rate (Olesiuk et al. 1990). However, in this case it would overestimate the fecundity rate of 

reproductive age females (11–41), because it is based on the observed calving intervals that 

eliminate the years before and after the first and last observed calves. Fecundity was directly 

estimated from the number of recruited calves per reproductive-age female as 12%, with a high 

of 38% and a low of 0%. The reciprocal of 12% (0.12) is 7.7 years, which represents the average 

interval between recruited calves for every female from age 11 to 41. 

To investigate temporal trends in fecundity, various models were fit to the fecundity data 

and compared using AIC, in a similar way as for the survival analysis. The two models that fit 

the data best were models with 3- or 4-year constant periods (the 3-year model was slightly 

better and is shown in Figure 8). However, given that several models had similar AIC values, it 

is again most appropriate to consider a model averaged across the best models as the best 

representation of fecundity through time for this population. The model-averaged estimates of 

fecundity represent a roughly periodic function that ranged between 0.052 and 0.187, with 

approximately 8 years between peaks (Figure 8). This corresponded well to the estimated 

calving interval of 7.7 years calculated above. Low points in the periodic model occurred in 

1981, 1987, and 1996 and high points occurred in 1976, 1984, and 1992–1995. 

A trend model was considered but did not provide a good fit to the data. Therefore, there 

was no evidence of a decline in fecundity rates over the study period. Two of the low periods in 

fecundity were coincident with the two low periods in survival rates. These drops in survival 

and fecundity in the early 1980s and the late 1990s suggested that environmental factors, such as 

a reduced supply of prey (Krahn et al. 2002), might have been responsible. 

28
0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Fecundity

Model average f(t) f(3y c)

Figure 8. Best fitting model of fecundity (recruited calves per reproductive-age female), a periodic 

function with 3 years constant periods (gray line). Also shown are annual fecundity (triangles) 

and the model average fecundity from 1974 to 2002 (black line). 

2.5. Potential Risk Factors 

2.5.1. Prey Resources 

There is little new information on the diet of Southern Resident killer whales since the

Washington State Status Report for the Killer Whale (Wiles 2004) and the previous NMFS status 

review (Krahn et al. 2002). Salmon, particularly Chinook, are considered the major prey of 

Southern Residents, although information on food habits outside the Puget Sound region is very 

limited. There is some new unpublished information on the presence of Southern Residents 

during certain salmon runs in coastal waters. In 2003, the whales were observed in the Monterey 

Bay area feeding on Chinook salmon.5

 In March 2004, L Pod was foraging on salmon off 

Westport, Washington, during the spring Chinook salmon run in the Columbia River (Hanson 

unpubl. data). 

Trends in salmon abundance 

Most West Coast salmon populations have declined significantly since the 1950s. 

Currently 26 evolutionarily significant units (ESUs) on the West Coast are listed as threatened 

(21) or endangered (5) out of the 52 recognized ESUs. Adult returns for some populations have 

increased since 2000 (see Table 5 for updated information on salmon abundance), but it is 

unclear if these reflect a long-term trend. 

 

5 See footnote 4. 

29
Table 5. Summary of historical and recent estimates of numbers of salmon produced by North American west coast river s

Strait of Georgia and Central California (numbers in thousands, ND = no data). 

Species 

Region Time period Chinook Coho Sockeye Pink Chum 

Mid–late 1800s 750a 1,230a 925–40,200n 23,850a 800a Fraser 

River Mid 1900s 150a 160a 967–18,800n 1,900–18,700o 390a 

Mid 1980s–early 1990s 140–280b 40–100a 3,770–22,000n 7,200–22,180o ≈1,30

Mid 1990s–current 140–350b Increasingc 3,640–23,600n 3,600–21,200o 13× g

since 

Mid–late 1800s 250–700e 700–2,200e 1,000–22,000e 1,000–16,000e 500–1

Puget Sound Mid 1900s 40–100e 250–600e, f 150–400f 350–1,000f 300–6

Mid 1980s–early 1990s 80–140f 300–800f 92–621p 1,000–1,930p 1,040

Mid 1990s–current 56–92f, r, x 200–500f 35–548p 440–3,550p 570–3

Mid–late 1800s 190w Coastal ND ND ND 

Washington Mid 1900s ND ND 20–130f 80–10

Mid 1980s–early 1990s 30–115f 40–130f 15–80f 10–32

Early 1990s–current 50–65f 30–70f 20–80f 60–17

Columbia Mid–late 1800s 5,000–9,000g 900–1,700g 2,600–2,800g 500–1River Mid 1900s 565–1,410s 21–272s 43–335s 1–425

Mid 1980s–early 1990s 410–1,140s 43–1,575s 47–201s 1–5s 

Mid 1990s–current 360–630s 89–624s 9–94s 1–3s Mid–late 1800s 300–600i 1,000–2,000i ND 

Mid 1900s 192h ND 130i 

Mid-northcoastal Oregon Mid 1980s–early 1990s 200–300i 100i 29i 

Mid 1990s–current ND ND ND 

Mid–late 1800s 300w 1,200j North coast 

California Mid 1900s 256j 200–500l 

Mid 1980s–early 1990s ND 13l 

Mid 1990s–current ≈10–50k ND 

30
Table 5 continued. Summary of historical and recent estimates of numbers of salmon produced by North American west co

between the Strait of Georgia and Central California (numbers in thousands, ND = no data). 

Species 

Region Time period Chinook Coho Sockeye Pink Chum 

Mid–late 1800s 1,000–2,000m ND Mid 1900s 121–610m ND 

Central ValleyCalifornia Mid 1980s–early 1990s 125–386m ND 

Mid 1990s–current 207–415m ND 

a Northcote and Atagi 1997; catch and escapement m Yoshiyama et al. 1998 b DFO 1999; catch and escapement n I. Guthrie unpubl. data c DFO 2002a o B. White unpubl. datad DFO 2001 p J. Ames unpubl. datae Bledsoe et al. 1989; catch only q WDFW no date; escapement f Johnson et al. 1997; wild run sizes only r B. Sanford unpubl. datag Northwest Power Planning Council 1986 s WDFW and ODFW 2001h Nicholas and Hankin 1989 t Busby et al. 1996i Nickelson et al. 1992 u California Trout no datej California Dept. Fish and Game 1965 v Simon Fraser Univ. 1998 k Mills et al. 1997 w Meyers et al. 1998l Brown et al. 1994 x S. Thiesfeld unpubl. data

31
Chinook salmon—Chinook salmon is the least abundant species in the Northwest 

region. Total abundance of Chinook salmon along the Washington and Oregon coasts is 

relatively high and long-term population trends are generally upward, but a number of runs have 

had severe declines recently. In British Columbia, Chinook escapements in the early 1990s were 

higher than at any time since the 1950s, but concern still exists about the depressed status of 

stocks in southern British Columbia (Northcote and Atagi 1997, Henderson and Graham 1998). 

The status of California stocks is variable, with some in poor condition and others fairly 

abundant. 

Chum salmon—In British Columbia, chum salmon (Oncorhynchus keta) populations 

have large annual fluctuations. Overall, the populations have been slowly increasing since the 

1950s (Henderson and Graham 1998). Puget Sound runs are at or near historical levels, with 

about 3.4 million fish returning in 2002 (WDFW no date). Columbia River runs have been 

extremely low (<1% of historical) since the 1950s (WDFW and ODFW 2001). Stocks along the 

Washington coast remain variable and Oregon stocks are low. 

Coho salmon—Coho (O. kisutch) populations in British Columbia, the Columbia River, 

and coastal waters of Washington and Oregon remain low. In contrast, Puget Sound and Strait of 

Georgia populations are near historical high levels, due to large numbers of hatchery fish 

(Weitkamp et al. 1995). 

Sockeye salmon—Sockeye (O. nerka) is the second most common species of salmon in 

the eastern Pacific (Wydoski and Whitney 2003). Populations in British Columbia are 

increasing, with runs as large as 23.6 million fish. The largest run is in the Fraser River. In 

contrast, the run size in the Lake Washington system has averaged 230,000 fish. In addition, 

Columbia River and other Washington runs are low. 

Pink salmon—Pink (O. gorbuscha) is the most abundant salmon species. Runs in Puget 

Sound have been high (up to 7.4 million fish), whereas those in the Fraser River have been 

higher (up to 22 million fish). The southern limit of their spawning range is Puget Sound. 

Steelhead—Although Columbia River steelhead (O. mykiss) summer runs have increased 

since the 1970s, winter runs have declined (WDFW and ODFW 2001). Wild coastal populations 

are considered healthy in Washington (WDFW 2002), but Oregon and northern California 

populations are in decline (Busby et al. 1996). Stocks in Washington are heavily supplemented 

with hatchery fish. 

Trends in herring abundance 

Herring have been identified as prey of Southern Resident killer whales.6

 Stocks in 

Georgia Basin and Puget Sound recovered in the late 1970s (DFO 2002b), but certain 

subpopulations in Puget Sound and off Vancouver Island have declined (DFO 2001, Stout et al. 

2001). 

 

6 See footnote 2. 

32
2.5.2. Marine Noise/Disturbance 

Marine mammal populations are experiencing ever-increasing amounts of disturbance 

through contact with anthropogenic sources of marine noise and presence of vessel traffic (see 

detailed review in Wiles 2004). Underwater noise pollution originates from a variety of sources, 

including general shipping and boating traffic, industrial activities (e.g., dredging, drilling, 

marine construction, and seismic testing of the sea bottom), and military and other vessel use of 

sonar (Richardson et al. 1995, Gordon and Moscrop 1996, NRC 2003). Many of these activities 

occur in coastal areas and overlap with the habitat used by most resident and transient killer 

whale populations. 

Killer whales rely on their highly developed acoustic sensory system for navigating, 

locating prey, and communicating with other individuals. Loud sounds are hypothesized to 

impair foraging and also to alter the movements of prey, which could affect foraging efficiency 

(Bain and Dahlheim 1994, Gordon and Moscrop 1996, Erbe 2002, Williams et al. 2002a, 

Williams et al. 2002b). Furthermore, chronic stress from noise exposure, as well as repeated 

disturbance from vessel traffic, can induce harmful physiological conditions (Gordon and 

Moscrop 1996), as well as increase energetic expenditures and cause temporary hearing 

threshold shifts. In extreme cases, high-intensity sounds (e.g., those from certain types of sonar) 

are potentially lethal by directly damaging body tissues (Gordon and Moscrop 1996). The 

threshold levels at which underwater noise becomes harmful to killer whales are unknown. In 

addition to the problem of noise, the physical presence of vessels can disrupt killer whale 

movements and normal behavioral patterns, resulting in increased energetic costs. Of the three 

pods, J Pod has the most exposure to whale watching and private vessels and L Pod has the least 

(Bain 2002, Koski7

). 

Commercial vessel traffic 

The Strait of Juan de Fuca and Haro Strait are primary shipping lanes for vessels entering 

the Strait of Georgia and Puget Sound, and these areas are used by Southern Resident killer 

whales. This commercial traffic—on the order of several thousand trips per month—is typified 

by large freighters, tugs, and barges. 

Commercial whale watching 

In Washington and British Columbia, killer whales are the focal species of the 

commercial whale-watching industry (Hoyt 2001). Killer whale watching in the transboundary 

region is centered primarily on the Southern Residents, which can be found more reliably than 

transients or offshores. Viewing activity occurs predominantly in and around Haro Strait, which 

is the summer core area of this resident community. 

There was a sharp increase in the number of whale-watching vessels between 1989 and 

1998, reaching a peak of 80 vessels. However, in 2003 there were about 37 commercial whalewatching companies with 73 boats; passenger levels were estimated at 450,000 people in both 

2001 and 2002.8

 Commercial whale-watching boats vary in size (7–30 m) and configuration 

 

7

 K. L. Koski, The Whale Museum, Friday Harbor, WA. Pers. commun., 2004. 8 See footnote 7. 

33
(6–280 passengers) and many routinely make two or three trips per day to view whales. In 

addition, at least one business offers airplane viewing. The San Juan Islands and adjacent waters 

also attract large numbers of private boaters for recreational cruising and fishing. Additionally, 

private floatplanes, helicopters, and small aircraft take regular advantage of opportunities to view 

whales (MMMP 2002). 

In recent years, not only do large numbers of boats accompany the whales for long 

periods of the day (9 a.m. to 9 p.m.), but there has also been a gradual lengthening of the viewing 

season (April–October), with some vessels present even in the winter and early spring. The 

mean number of vessels following groups of killer whales increased from five boats in 1990 to 

18–26 boats from 1996 to 2002 (Osborne 1999, Baird 2001, Erbe 2002, MMMP 2002, Osborne 

et al. 2002). Annual maximum counts of 72–120 boats were made near whales from 1998 to 

2002 (Osborne et al. 2002). Of these, as many as 35 were commercial whale-watching vessels 

with privately owned vessels comprising the remainder. Whale-watching vessels were mainly 

U.S.-based in the 1980s, but currently about 65% of the vessels are Canadian (Osborne et al. 

2002). 

Whale-watching vessels have the potential to produce high levels of underwater sound in 

close proximity to the animals. Noise levels vary with vessel engine or propulsion system and 

become louder as speed increases (Bain 2002, Erbe 2002). The Whale Watch Operators 

Association Northwest was established in 1994 to establish guidelines for commercial operators 

to ensure consistency in practices and reduce impacts on the whales. 

Recreational boating 

Protected inland waters of Washington and British Columbia are popular cruising and 

recreational boating destinations for the general public. Opportunistic encounters between 

private boaters and whales are common (Osborne et al. 2002). Private boaters are more likely 

than commercial operators to approach too closely or otherwise operate their vessel in a manner 

that would potentially harass the whales.9

Commercial fishing 

The summer range of Southern Resident killer whales was historically a region of intense 

fishing operations, particularly for salmon. Changes in fishing regulations and declines in 

salmon abundance have resulted in a significant reduction of commercial fishing vessels in this 

region. 

Recreational fishing 

Although reductions in many salmon populations have occurred, there are still seasonal 

openings for salmon sport fishing within the Southern Residents’ summer range. Although the 

boats are likely to co-occur in areas that the whales frequently use, they are relatively few and 

their activity (slow idle) generally does not appear to disrupt whale behavior. 

 

9 See footnote 7. 

34
Military operations 

The Puget Sound area is home to a large number of naval vessels. Although naval 

vessels represent a small fraction of the total traffic and are designed to operate quietly, these 

ships are large and some are equipped with high-output sonar equipment. A mid-frequency 

“sonar incident” occurred with the USS Shoup in Haro Strait in May 2003 when J Pod was 

present. Biologists there reported unusual behavior patterns of J Pod, including surface 

behaviors (e.g., tail slapping and spy hopping), less surfacing, and changing direction/milling.10

Effects of vessel noise/traffic 

In a model of vessel noise levels relative to killer whales’ hearing detection capabilities, 

Erbe (2002) predicted that the sounds of fast boats are audible to killer whales at distances of up 

to 16 km, can mask their calls up to 14 km away, can elicit behavioral responses within 200 m,

and may cause temporary hearing impairment after 30–50 min of exposure within 450 m.

Several other studies have linked vessel noise and traffic with short-term behavioral 

changes in Northern and Southern Resident killer whales ( Kruse 1991, Jelinski et al. 2002, 

Williams et al. 2002a, Williams et al. 2002b, Foote et al. 2004). Individuals can react in a 

variety of ways to the presence of whale-watching vessels. Some of these responses include 

increased swimming speed, unpredictable travel paths, alteration of dive times, movement into 

open water, and unusual surface pattern behaviors (Kruse 1991, Jelinski et al. 2002, Williams 

et al. 2002a). In a recent study, Foote et al. (2004) found an increase in call duration of Southern 

Resident whales associated with the increase in whale-watching traffic. 

2.5.3. Disease 

As a baseline for developing standard necropsy protocols, Gaydos et al. (2004) provided 

a review of the potentially important infectious diseases that occur in other marine mammals and 

may impact Southern Resident killer whales. Among the identified diseases, four high priority 

pathogens (marine Brucella, cetacean poxvirus, cetacean morbillivirus and herpesvirus) were 

targeted for further study. 

2.5.4. Environmental Contaminants 

Southern Resident killer whales are exposed to relatively high levels of persistent 

organochlorine contaminants (OCs, e.g., PCBs and DDTs) (Ross et al. 2000) and may be 

exposed to other classes of emerging contaminants that have been documented in freshwater and 

marine environmental samples. These new contaminants of concern include brominated flame 

retardants (BFRs), perfluorooctanoic sulfate (PFOS) and related compounds, endocrine 

disruptors (e.g., synthetic estrogens, phthalates, steroids) and current use pesticides (e.g., 

carbamates, chlorpyrifos) (Richardson 2003, Schnoor 2003). These contaminant classes vary in 

their chemical structures, half-lives in the environment, input sources (e.g., atmospheric 

transport, input from sewage treatment plants) and uses (e.g., pesticides, flame retardants, 

industrial compounds). Even though many of these chemicals have been found to be toxic to 

 

10 K. Balcomb, the Center for Whale Research, Friday Harbor, WA; R. Osborne, The Whale Museum, Friday 

Harbor, WA; and D. Bain, Univ. Washington, Seattle. Pers. commun., 2004. 

35
wildlife, most are still being manufactured and used as agricultural and industrial chemicals in 

many countries throughout the world (de Wit et al. 2004). 

Polybrominated diphenyl ethers (PBDEs) are a class of environmental BFRs that are 

quickly gaining the attention of regulatory agencies. These compounds are added to plastics, 

textiles, clothing, electronic circuit boards, and other materials as flame retardants. Similar to 

PCBs, PBDEs are ubiquitous lipophilic compounds that have been shown to bioaccumulate, 

especially in top-level predators such as marine mammals. The European Union has banned the 

use of two PBDE mixtures (penta- and octa-BDEs) and California will ban products that contain 

these two mixtures in 2008 (Raloff 2003). However, until PBDEs are discontinued globally, 

humans and wildlife will continue to be exposed to increasing levels of these compounds. 

Boon et al. (2002) found that largest biomagnification of PBDEs occurred from predatory 

fish (cod) to marine mammals (harbor porpoise and harbor seal) in the North Sea food web. 

Furthermore, in North America and northern Europe, concentrations of PBDEs have been 

increasing since the 1970s in humans, as well as in freshwater and marine biota (de Wit 2002, 

Hites 2004). For example, levels of summed PBDEs measured in pooled human breast milk 

samples of Swedish mothers from the Stockholm region collected from 1972 through 1997 

doubled every 5 years (Noren and Meironyte 2000). 

Various studies have shown that some PBDE congeners may induce various toxicological 

effects in laboratory animals, including immune dysfunction, liver toxicity, and thyroid 

disruption (de Wit 2002). Hall et al. (2003) investigated the relationship between PBDE 

exposure and circulating levels of albumin, thyroid hormones, and cholesterol in gray seal pups 

from the east coast of the United Kingdom. The results suggested a link (although not a causeand-effect relationship) between serum thyroid hormone, albumin, and cholesterol 

concentrations and exposure to PBDEs (approximate range: 56–1,600 ng/g, lipid) in the gray 

seals during their first year of life. Blubber of a reproductive female Southern Resident killer 

whale (L60) that stranded near Long Beach, Washington, in April 2001 was recently analyzed 

and found to contain a ∑PBDE concentration (1,300 ng/g, lipid, Ylitalo unpubl. data) in the same

range that was associated with thyroid hormone disruption in the gray seal pups (Hall et al. 

2003). 

Exposure to various classes of contaminants, including OCs, PBDEs, and endocrine 

disrupters, may compromise the health of Southern Resident killer whales. Although these 

whales may be exposed to various classes of new contaminants of concern, measuring exposure 

in free-ranging whales is difficult because many of these contaminants are not as lipophilic as 

OCs and therefore are not stored in their blubber. In addition, some of these emerging 

contaminants have shorter half-lives and are more readily metabolized than OCs, so measuring 

the parent compounds in tissues is difficult. For example, steroids and pharmaceuticals are 

routinely measured in wastewater constituents and sediment samples in relatively low 

concentrations (low ng/L) (Richardson 2003, Vanderford et al. 2003), but few analytical methods 

have been developed to measure these compounds or their metabolites in tissues of wildlife. 

36
2.5.5. Oil Spills 

On 30 December 2003, approximately 4,800 gallons of #6 fuel oil (Bunker C) was spilled 

at the Chevron Texaco terminal at Point Wells, Washington. No Southern Resident killer whales 

were seen in the vicinity during this recent spill. 

37
3. Determination of the Taxon 

3.1. Species 

The BRT first considered whether killer whales comprise a single species or multiple 

species, reviewing new information and the competing lines of evidence cited in the recent 

Cetacean Taxonomy Workshop (Reeves et al. 2004, Waples and Clapham 2004). 

3.1.1. Arguments for a Single Species 

• Patterns of divergence in mtDNA (the Antarctic [LeDuc and Pitman 2004], North Pacific 

[LeDuc and Taylor 2004], and worldwide [Hoelzel et al. 2002a]) could be explained by 

incomplete lineage sorting following a worldwide expansion. The mtDNA data do not 

clearly identify different lineages corresponding to ecotypes, and therefore suggest that the 

ecological specializations (e.g., fish eating versus marine mammal eating) may have 

developed several times (Hoelzel et al. 2002a, Hoelzel 2004). 

• The nuclear genetic divergences are consistent with evolutionarily recent (hundreds to low 

thousands of years) divergence between resident and transient ecotypes in the eastern North 

Pacific (Hoelzel et al. 2002a, 2004). These groups may therefore be relatively short-lived 

compared to the age of the Orcinus genus (estimated at 5 million years [Waples and Clapham

2004]). One hypothesis is that the ecotypes originated in the Pleistocene as glaciers retreated 

and new foraging niches became available ( Hoelzel et al. 2002a, Barrett-Lennard and Heise 

2004, Hoelzel 2004). 

• Foraging specializations and other behavioral characteristics such as distinct vocalizations 

may be learned and therefore are not good indicators of species status (Barrett-Lennard and 

Heise 2004). 

• Morphological differences similar in scale to those provisionally observed among the killer 

whale ecotypes occur within species of other animals, such as wolves and other canids, and 

therefore are not compelling indicators of species-level difference (Waples and Clapham 

2004). 

• The morphological differences so far observed among the Antarctic or eastern North Pacific 

ecotypes have not yet been sufficiently quantified to serve as a basis for a taxonomic decision 

at the species level (Waples and Clapham 2004). 

3.1.2. Arguments for Multiple Species 

• For residents and transients in the North Pacific, there is congruence among patterns of 

genetic variation, acoustics, color pattern, and foraging specialization (Krahn et al. 2002). 

38
• There is no direct evidence of interbreeding or even interaction between the resident and 

transient whales in the eastern North Pacific. The genetic data are subject to multiple 

interpretations and are consistent with a fairly high degree of contemporary reproductive 

isolation between the resident and transient ecotypes (see subsection 2.2 above). 

• Diagnostic differences in mtDNA exist between the resident and transient ecotypes in both 

the Antarctic and Pacific Northwest, despite the variation within them (Section 2 of Krahn 

et al. 2002). 

• All available genetic and observational data show no evidence of any female migration or 

gene flow among killer whale ecotypes, either in the eastern North Pacific or the Antarctic 

(Waples and Clapham 2004). 

• For the Antarctic killer whales, the data on differences in morphology (body size, size and 

orientation of postocular patch), genetics, and ecological specialization suggest existence of

two or possibly three species in the region, with types B and C representing forms not found 

elsewhere in the world (Pitman and Ensor 2003, LeDuc and Pitman 2004). 

Overall, in the opinion of the participants in the Cetacean Taxonomy Workshop who 

favored the concept of multiple species, the data suggest existence of at least four new species: 

residents and transients in the North Pacific and Types B and C in the Antarctic. 

3.1.3. Conclusions of the BRT on Species 

After discussion of information relating to these arguments in the North Pacific, the BRT 

reached consensus that—although multiple species may exist and may be confirmed in the 

future—the present data are not adequate to support designation of any new species. In 

particular, the BRT concluded that, provisionally, North Pacific transients and residents should 

be considered to belong to a single species. 

3.2. Subspecies 

The BRT next considered the question of whether Southern Residents and transients 

belong to different subspecies. 

3.2.1. Evidence for Subspecies Status 

As noted above (subsection 2.3.1), the majority of participants in the Cetacean Taxonomy 

Workshop agreed that North Pacific residents and transients probably belong to different 

subspecies. A number of differences between residents and transients have been suggested to 

support subspecific separation. 

• Residents and transients differ on average in external morphology, including dorsal-fin 

size and shape, saddle-patch shape, and pigmentation (Krahn et al. 2002, Waples and 

Clapham 2004). 

39
• Differences between the two ecotypes have been found in skull features (Fung and 

Barrett-Lennard 2004), although the sample size is still small and uncontrolled for age 

and sex (Reeves et al. 2004, Waples and Clapham 2004). 

• Residents and transients are sympatric in the summer range, but no intermingling or 

interbreeding has ever been observed, suggesting that the two groups meet the 

operational definition of species (let alone subspecies) under the biological species 

concept (Mayr 1963). 

• The two groups have markedly different feeding specializations and social organization 

(Barrett-Lennard and Heise 2004); also see subsection 2.1, as well as relevant sections of 

Krahn et al. (2002) and Wiles (2004). 

• The two ecotypes exhibit markedly different acoustic dialects and acoustic practices that 

may relate to differences in feeding ecology (J. K. Ford 2004). 

• The two forms are genetically divergent at both mtDNA and nuclear DNA markers. The 

level of divergence between the residents and transients is higher than the average level 

of divergence within populations of either group (subsection 2.2). 

• Residents and transients fall into two different global mtDNA clades (the R and T clades 

in Figure 2 [LeDuc and Taylor 2004]). One theory is that the two clades arose in 

different ocean basins, with movement of R-clade whales from the Atlantic to the Pacific 

following the last glacial period. 

3.2.2. Conclusions of the 2004 BRT on Subspecies 

The 2004 BRT agreed that if the Southern Residents belonged to a subspecies separate 

from that of the transients, the subspecies would include the Southern Residents and the 

Northern Residents, as well as the resident killer whales of Southeast Alaska, Prince William

Sound, Kodiak Island, the Bering Sea, and Russia. In short, the subspecies would include all of 

the resident, fish-eating killer whales of the North Pacific. The rationale for this decision was 

that all of these groups are apparently fish-eating specialists, occupy relatively similar habitats, 

and appear to be genetically more closely related to each other than to sympatric transient 

populations. 

The 2004 BRT also considered whether the offshore form would be included in a 

subspecies with the residents (if such a subspecies were agreed to exist). A number of 

differences exist between North Pacific residents and offshores, including distribution, diet (as 

indicated by analyses of stable isotopes, fatty acids and contaminants, and differential tooth wear 

in whales with sharks in stomach contents), mtDNA haplotypes, nuclear DNA, external 

morphology (saddle patch and degree of sexual dimorphism, although data have not yet been 

well quantified), group size, and acoustic dialects (Krahn et al. 2002, J. K. Ford 2004). 

The possible inclusion of killer whales of the eastern Tropical Pacific with residents in a 

potential subspecies was discussed. Differential characteristics of these whales include small 

group size (up to 20, but mostly 3–8), indistinct saddles, multiple haplotypes within sampled 

groups, vocal patterns that do not match those of the North Pacific, and prey that includes large 

baleen whales (Mesnick and Escorza-Treviño 2004, Waples and Clapham 2004). 

40
It was noted that other fish-eating whales of the R-clade (e.g., herring eaters in Norway) 

occur in regions remote from the North Pacific (i.e., the North Atlantic, Australasian region, and 

Antarctic [Hoelzel et al. 2002a, Hoelzel 2004]). However, it was decided that inclusion of these 

in a potential subspecies would only be considered if the adjacent eastern Tropical Pacific whales 

were included, as subspecies designations in taxonomy are traditionally geographically coherent 

(Winston 1999). 

The BRT concluded that there was the potential for considerable uncertainty regarding 

the taxonomic status of eastern North Pacific killer whales. In order to characterize that 

uncertainty, the BRT used the 10-point likelihood voting method described by Krahn et al. 

(2002). Briefly, for each taxonomic question, each BRT member distributed 10 likelihood votes 

among the possible alternatives in proportion to the relative likelihood the member assigned to 

each alternative. The following questions were put to likelihood votes (overall likelihood scores 

in parentheses): 

1. Do North Pacific residents and transients belong to a separate subspecies? (84 yes, 

16 no) 

2. If the North Pacific residents belong to a separate subspecies, does the subspecies 

include: 

a. North Pacific offshores? (42 yes, 58 no) 

b. Eastern Tropical Pacific killer whales? (29 yes, 71 no) 

After considering the arguments for existence of subspecies, the conclusions of the Cetacean 

Taxonomy Workshop, and the results of the likelihood votes, the BRT decided that the taxon to 

use for determining a DPS under the ESA should be the North Pacific residents, an unnamed 

subspecies of O. orca. 

41
4. Determination of DPS 

4.1. Taxonomic Uncertainty 

Uncertainty about the taxonomic status of killer whales was a problem for the DPS 

determinations in the 2002 status review. In particular, the 2002 BRT noted that there was 

increasing evidence to suggest that the currently recognized species Orcinus orca should be split 

into more than one species or subspecies, but authorities on killer whale taxonomy generally 

viewed that evidence as insufficient (see subsection 2.3). Getting the taxonomy right is an 

important part of the status review process, because the significance criterion of a DPS is made 

with reference to the taxon to which it belongs (USFWS and NMFS 1996). 

The 2002 BRT emphasized the uncertainty surrounding killer whale taxonomy, but also 

found that no clear taxonomic alternatives had been proposed and widely accepted, particularly 

for the eastern North Pacific. Lacking the information necessary to revise the taxonomy, the 

BRT explored whether or not the Southern Residents would be considered a DPS under several 

plausible taxonomic scenarios. The scenarios ranged from the currently recognized global 

species to a taxon containing only North Pacific residents. The 2002 BRT considered the 

Southern Residents likely (48% of likelihood votes) to be a DPS only if the North Pacific 

residents were themselves considered to be the taxon of reference (species or subspecies) (see 

Table 8 in subsection 3.4.2 of Krahn et al. 2002). 

4.2. Additional Information Available to the 2004 BRT 

In part due to the uncertainty highlighted by the 2002 status review, the Southwest and 

Northwest Fisheries Science Centers sponsored the Cetacean Taxonomy Workshop in 2004 

(Perrin and Reeves 2004). The results of that workshop vis-a-vis killer whale taxonomy are 

summarized in subsection 2.3. In addition to addressing taxonomic questions, another goal of 

the workshop was to review and summarize “existing information on the characteristics, ecology, 

and behavior of killer whales worldwide and attempt to resolve biological relationships within

the genus Orcinus at all levels from species to local breeding populations” (Waples and Clapham

2004). The workshop did not address the particular question of whether or not the Southern 

Residents are a DPS, but it provided a useful forum for experts in killer whale biology to discuss 

and summarize information relevant to this question. 

The 2004 BRT benefited from considerable new information on killer whale taxonomy 

(summarized in subsection 2.3), allowing the team to focus on a much more limited range of 

scenarios compared to the 2002 BRT. In particular, the 2004 BRT concluded that it was likely 

that North Pacific residents were a subspecies distinct from both transients and offshores. The 

unnamed North Pacific resident subspecies was considered to include killer whales from

throughout the Pacific Rim, ranging from Puget Sound to the Russian Far East (Figure 1). The 

BRT focused most of its efforts on determining if the Southern Residents were a DPS of this 

unnamed North Pacific resident subspecies. In addition, the BRT considered the question of 

42
whether the Southern Residents were a DPS of a hypothetical subspecies that included both 

North Pacific resident and offshore killer whales, a taxonomic hypothesis that received some

minority support from the BRT (subsection 2.3). 

4.3. Data Relevant to Determining ESA Discreteness 

and Significance 

Joint NOAA/USFWS policy defines a population to be a DPS if it is both discrete and 

significant relative to the taxon to which it belongs (USFWS and NMFS 1996). Under the 

policy, a population may be considered discrete if is satisfies either one of the following 

conditions: 

• It is markedly separated from other populations of the same taxon as a consequence of 

physical, physiological, ecological, or behavioral factors. Quantitative measures of 

genetic or morphological discontinuity may provide evidence of this separation. 

• It is delimited by international governmental boundaries within which differences in 

control of exploitation, management of habitat, conservation status, or regulatory 

mechanisms exist that are significant in light of Section 4(a)(1)(D) of the ESA. 

Data relevant to the distinctiveness question include the physical, ecological, behavioral, and 

genetic data that are summarized in Krahn et al. (2002) and updated in section 2 above. 

If a population segment is considered discrete, NMFS must then consider whether the 

discrete segment is “significant” to the taxon to which it belongs. Criteria that can be used to 

determine whether the discrete population segment is significant include: 

• persistence of the discrete segment in an ecological setting unusual or unique for the 

taxon, 

• evidence that loss of the discrete segment would result in a significant gap in the range of 

the taxon, 

• evidence that the discrete segment represents the only surviving natural occurrence of a 

taxon that may be more abundant elsewhere as an introduced population outside its 

historical range, or 

• evidence that the discrete segment differs markedly from other populations of the species 

in its genetic characteristics. 

A discrete population segment needs to satisfy only one of these criteria to be considered 

significant. The policy also allows for consideration of other factors if they are appropriate to 

the biology or ecology of the species. Data relevant to the significance question include the 

morphological, ecological, behavioral, and genetic data summarized in Krahn et al. (2002) and 

updated in section 2 above. 

4.4. Evaluation of ESA Discreteness 

The BRT unanimously concluded that the Southern Residents are discrete from other 

North Pacific resident killer whale populations. In particular, all available data, including 

43
behavior, demography, and core and summer ranges (subsection 2.1), as well as genetics 

(subsection 2.2), indicated that the Southern Residents are an independent population that is 

distinct from other populations. 

4.5. Evaluation of ESA Significance 

The BRT discussed at length the significance of the Southern Residents with respect to 

the North Pacific resident taxon. In particular, the BRT focused on the following four factors: 

• the ecological setting of the Southern Residents, including diet and habitat, and how it 

differs from that of other North Pacific resident populations, 

• information related to the range of the Southern Residents and other North Pacific 

resident populations, and whether loss of the Southern Residents would result in a 

significant gap in the range of the unnamed North Pacific resident subspecies (taxon), 

• genetic information, including both molecular and morphological differences among 

North Pacific resident populations, and 

• behavioral and cultural diversity within the North Pacific resident and what role the 

Southern Residents play in maintaining this diversity. 

During these discussions, most BRT members expressed some uncertainty regarding whether or 

not the Southern Residents met the significance criterion as it is defined in the DPS policy. To 

quantify this uncertainty, the BRT employed the same 10-point voting system it used for making 

the taxonomic determinations (subsection 3.2). 

The BRT concluded by a 2-to-1 margin of likelihood points that the Southern Residents 

are significant with respect to the North Pacific resident taxon, and therefore should be 

considered a DPS. The BRT also concluded by a 3-to-2 margin of likelihood points that the 

Southern Residents would be a DPS of a taxon consisting of both North Pacific residents and 

offshores. The arguments favoring significance under both taxonomic scenarios were as follows. 

4.5.1. Ecological Setting 

The Southern Residents appear to occupy an ecological setting distinct from the other 

North Pacific resident populations (see subsections 2.3 and 2.4 in Krahn et al. 2002 and updates 

in subsection 2.4 above). In particular, the Southern Residents are the only North Pacific 

resident population to spend a substantial amount of time in the California Current ecosystem, an 

ocean habitat that differs considerably from the Alaskan Gyre occupied by the Alaska Residents 

and (to a lesser extent) by Northern Residents. There is some evidence of differences in prey 

utilization (see subsection 2.1.3 above), with Southern and Northern Residents favoring Chinook 

salmon and certain Alaska resident populations also eating groundfish such as halibut and turbot. 

Southern Residents and Western Alaska Residents (west of 170oW) also differ in their stable 

isotope signatures (Herman unpubl. data), which suggests that they are consuming different prey. 

There are reasons to believe that the Southern Residents may have historically utilized the large 

salmon runs to the Columbia and perhaps Sacramento Rivers as a major source of prey, 

consistent with an ecological specialization for Chinook salmon. 

44
4.5.2. Range 

The BRT discussed data related to both the Southern Residents’ year round and summer 

core ranges (see subsection 2.4.1 in Krahn et al. 2002 and updates in subsection 2.4.1 above), 

and concluded that loss of the Southern Residents would result in a significant gap in the range 

of the North Pacific resident taxon. In particular, the Southern Residents are the only North 

Pacific resident population to be sighted in the coastal areas off of California, Oregon, and 

Washington, and are the only population to regularly inhabit Puget Sound. Based on experience 

from other cetaceans, the BRT found little reason to believe that these areas would be 

repopulated by other North Pacific resident populations in the foreseeable future should the 

Southern Resident population become extinct (see subsection 3.2.1 in Krahn et al. 2002). 

4.5.3. Genetic Differentiation 

The Southern Residents differ markedly from other North Pacific resident populations at 

both nuclear and mitochondrial genes (subsection 2.2 above). The Southern Residents also differ 

from other North Pacific resident populations in the frequency of certain saddle-patch variants, a 

trait believed to have a genetic basis (see subsection 2.2 in Krahn et al. 2002). 

4.5.4. Behavioral and Cultural Diversity 

The BRT noted that culture (knowledge passed through learning from one generation to 

the next) is likely to play an important role in the viability of killer whale populations (see 

subsection 2.1.6 in Krahn et al. 2002). Although the importance of culture has not been directly 

quantified in killer whales, it has been demonstrated to affect the survival of other highly social 

mammalian species such as elephants (McComb et al. 2001) and humans (Lahdenpera et al. 

2004). It is a reasonable hypothesis, therefore, that the cultural knowledge that may be possessed 

by the Southern Resident killer whales could be important for the survival of the North Pacific 

resident taxon as a whole. For example, the Southern Residents may possess unique knowledge 

of the timing and location of salmon runs in the southern part of the North Pacific residents’ 

range. The BRT also noted that there was some evidence that cultural traditions, such as 

greeting behavior, beach rubbing, and utilization of prey from longlines, differed among the 

resident populations. 

4.6. Conclusions for DPS Determination 

The 2004 BRT concluded that the Southern Residents are likely to be a DPS of the 

unnamed North Pacific resident subspecies (taxon). Although the BRT believed that the weight 

of evidence supported recognizing the Southern Residents as a DPS, nearly all BRT members 

put some likelihood points into the “not a DPS” category as well. The primary reason for this 

uncertainty was that much of the data bearing on the significance question is preliminary and 

unpublished, particularly recent data on the ecology and behavior of the offshores and the 

western Alaska populations. Some BRT members also expressed some uncertainty about how to 

evaluate behavioral and cultural traits with respect to the significance criterion. 

Despite some uncertainty, the 2004 BRT was considerably more confident than the 2002 

BRT that the Southern Residents should be considered a DPS. For example, the 2002 BRT was 

45
almost evenly split on the question of whether or not the Southern Residents are a DPS of the 

North Pacific resident taxon and gave only minor support to the idea that Southern Residents 

would be a DPS of a taxon consisting of North Pacific residents and offshores (Table 8 of Krahn 

et al. 2002). In contrast, the 2004 BRT was fairly confident that the Southern Residents should 

be considered a DPS under both of these scenarios. The 2004 BRT discussed this increase in 

support for the Southern Residents as a DPS and attributed it primarily to the amount of new 

information that has been collected over the last couple of years. For example, knowledge about 

worldwide patterns of genetic variation in killer whales has increased dramatically over the last

couple of years, and has demonstrated that sharing of a similar mtDNA haplotype does not 

necessarily indicate a close evolutionary relationship between two populations (subsection 2.2 

above). This is important, because the offshores and Southern Residents are characterized by 

very similar mtDNA haplotypes, a factor that influenced the conclusions of the 2002 BRT. In 

addition, the 2004 BRT was aware of recently collected information about the social structure, 

morphology, behavior, and diet of offshore killer whales that was unavailable at the time of the 

2002 status review, and this information tends to suggest that the offshores are more distinct 

from resident killer whales than was appreciated by the 2002 BRT (subsection 2.1). Finally, 

knowledge about ecological and behavioral diversity within killer whales has increased as a 

result of ongoing studies in British Columbia, Alaska, and the Russian Far East (subsection 2.1). 

The BRT generally concluded that this new information tended to suggest substantial ecological 

differentiation between the Southern Residents and other populations. 

46
5. Assessment of Extinction Risk 

5.1. Population Viability Analysis 

The 2002 BRT developed a PVA that modeled combinations of a variety of parameters to 

estimate the probability that the Southern Resident killer whale population would go extinct over 

a specific timeframe (Krahn et al. 2002). The 2002 model and analysis have been updated for 

this report and new results are presented. The updated results incorporate data on the Southern 

Resident population collected through 2003. 

Although excellent information is available on age-specific survival and fecundity of the 

Southern Resident killer whale population, there are other parameters needed for the model that 

are less well understood. Necessary model parameters (e.g., carrying capacity and the 

probability of occurrence of a catastrophic mortality event) are unknown, so a variety of 

scenarios were analyzed in order to understand the implications of these parameters on the 

probability that the population would go extinct. Carrying capacities ranging from 100 to 400 

animals were chosen to bracket the range of likely values: 100 whales represents the approximate 

size of the largest population that has been observed for Southern Residents and 400 whales 

represents a reasonable maximum value. Additionally, Krahn et al. (2002) showed that using a 

carrying capacity higher than 400 gave results identical to using the value of 400. The frequency 

of large mortality events or catastrophes was set at 0 (no catastrophes), 0.01 (one catastrophe on 

average every 100 years), or 0.02 (two catastrophes on average every 100 years). Potential 

sources of catastrophic mortalities include major oil spills or disease epidemics. 

The only substantial change from the 2002 PVA (Krahn et al. 2002) was the use of 

updated information on survival and fecundity, using the results of subsection 2.4.2 above. 

Three different scenarios of assumed survival rates were examined. The model-averaged 

estimates of fecundity were used, and were assumed to continue cycling through the same 29-

year pattern indefinitely. The three survival scenarios used are described in detail below. 

One addition to the 2002 PVA (Krahn et al. 2002) was examination of both the 

probability of extinction (defined as <1 male or female) and the probability of “quasi-extinction” 

(defined as <10 males or females). The BRT strongly believed that a population that included 

less than 10 males or females was highly unlikely to persist, and so this would provide a 

conservative threshold below which populations would not be expected to persist over the longterm, even though literal extinction might still take decades or more because individual killer 

whales can live for a long time. Therefore, for all three survival scenarios the probability that the 

current population would decline to this quasi-extinction threshold was also calculated. The 

following describes the results of all of these PVA scenarios. Note that the probabilities given in 

Tables 6–11 are not given as percentages. 

47
5.1.1. PVA Results 

Scenario A, all 29 years of data, modeled to extinction 

Scenario A involved using the best fitting model for survival and the entire 29-year 

sequence of estimates. This was the additive group effect model with a temporal trend S(7t c) 

(subsection 2.4.2 above). In other words, the temporal trend model had constant survival periods 

of length 5, 7, 7, 7, and 3 years, but the survival rates were scaled differently for each age and 

sex class. In this scenario, the full 29 years of survival estimates were assumed to be the best 

predictor of future survival rates over the next 100–300 years. This scenario gave the highest 

average survival rate and can therefore be considered the most optimistic of the three survival

scenarios considered. 

As expected, carrying capacity had a strong influence on the estimated risk of extinction 

of Southern Resident killer whales (Table 6). Most sets of parameters resulted in a probability of

extinction of less than 1% in 100 years if the carrying capacity was between 200 and 400 

animals, and a probability of extinction of from less than 0.1% to 3% in 100 years if the carrying 

capacity was 100 animals. When the model results were examined for 200 and 300 years, the 

pattern remained—a large carrying capacity resulted in a substantially lower probability of 

extinction at 200 and 300 years than a small carrying capacity. 

The probability of a catastrophic mortality event and the severity of that event also had a 

major impact on the probability that the modeled population would go extinct. Under the 

assumption that there were no catastrophic mortality events (Scenario A1), simulations with a 

carrying capacity of 200–400 animals had nearly identical results—the risk of extinction was less 

than 0.1% at 100 years, approximately 0.6% after 200 years, and approximately 2% after 300 

years. When carrying capacity was reduced to 100, the risk of extinction remained at less than 

0.1% at 100 years, but rose to 2% in 200 years and 12% after 300 years 

When a 1% probability of a mortality event with a magnitude that reduced survival by

10% was included (Scenario A2), there was still little chance of extinction after 100 years at any 

carrying capacity. However, with carrying capacity at 200 or more, the chance of extinction was 

approximately 1% after 200 years and 3–4% after 300 years. At a carrying capacity of 100, the 

chance of extinction rose to 3% after 200 years and 17% after 300 years. At the highest 

catastrophe rates and magnitudes, the risk of extinction rose to 17% after 200 years and 42% 

after 300 years (Scenario A4). 

Scenario A(Q), all 29 years of data, modeled to a quasi-extinction threshold 

These calculations used the same survival and fecundity as in Scenario A described 

above, but estimated the probability the population will fall below the quasi-extinction threshold. 

Again, carrying capacity had a strong influence on the estimated risk of meeting the threshold 

(Table 7)—all scenarios had substantially higher risks at 100 years when the carrying capacity 

was set at 100 animals than when the carrying capacity was higher. For the most optimistic of 

these scenarios (Scenario A(Q)1), a carrying capacity of 100 animals resulted in a probability of 

meeting the quasi-extinction threshold of 2% at 100 years, 12% at 200 years, and 31% at 300 

years. When catastrophic mortality events were included (Scenarios A(Q)2–4), the probability 

48
Table 6. Survival Scenario A, using all 29 years of data and S(G+7c) best survival model, 7-year groups, 

modeled to extinction.a

Catastrophe Probability of extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario A1 

400 0.000 1.000 <0.001 0.006 0.019

300 0.000 1.000 <0.001 0.005 0.018

200 0.000 1.000 <0.001 0.007 0.020

175 0.000 1.000 <0.001 0.007 0.024

150 0.000 1.000 <0.001 0.006 0.031

125 0.000 1.000 <0.001 0.009 0.047

100 0.000 1.000 <0.001 0.021 0.121

Scenario A2 

400 0.010 0.900 0.001 0.012 0.034

300 0.010 0.900 <0.001 0.013 0.037

200 0.010 0.900 <0.001 0.012 0.038

175 0.010 0.900 0.001 0.013 0.044

150 0.010 0.900 0.001 0.014 0.046

125 0.010 0.900 <0.001 0.015 0.075

100 0.010 0.900 0.001 0.030 0.165

Scenario A3 

400 0.010 0.800 0.005 0.037 0.081

300 0.010 0.800 0.005 0.034 0.081

200 0.010 0.800 0.006 0.037 0.088

175 0.010 0.800 0.006 0.034 0.091

150 0.010 0.800 0.005 0.039 0.108

125 0.010 0.800 0.007 0.042 0.139

100 0.010 0.800 0.008 0.072 0.244

Scenario A4 

400 0.020 0.800 0.024 0.104 0.210

300 0.020 0.800 0.024 0.107 0.211

200 0.020 0.800 0.024 0.111 0.230

175 0.020 0.800 0.024 0.113 0.232

150 0.020 0.800 0.026 0.115 0.250

125 0.020 0.800 0.025 0.128 0.304

100 0.020 0.800 0.028 0.166 0.424

a

 Extinction defined as <1 male or female. b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

49
Table 7. Survival Scenario A(Q), using all 29 years of data and S(G+7c) best survival model, 7-year 

groups, modeled to a quasi-extinction threshold.a

Catastrophe Probability of quasi-extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario A(Q)1 

400 0.000 1.000 0.010 0.024 0.036

300 0.000 1.000 0.009 0.022 0.035

200 0.000 1.000 0.010 0.024 0.044

175 0.000 1.000 0.010 0.024 0.052

150 0.000 1.000 0.010 0.027 0.077

125 0.000 1.000 0.009 0.044 0.138

100 0.000 1.000 0.019 0.123 0.311

Scenario A(Q)2 

400 0.010 0.900 0.016 0.042 0.063

300 0.010 0.900 0.017 0.043 0.065

200 0.010 0.900 0.017 0.043 0.074

175 0.010 0.900 0.018 0.045 0.087

150 0.010 0.900 0.020 0.051 0.121

125 0.010 0.900 0.017 0.072 0.198

100 0.010 0.900 0.037 0.175 0.392

Scenario A(Q)3 

400 0.010 0.800 0.043 0.092 0.130

300 0.010 0.800 0.039 0.088 0.129

200 0.010 0.800 0.042 0.091 0.147

175 0.010 0.800 0.039 0.094 0.161

150 0.010 0.800 0.045 0.105 0.208

125 0.010 0.800 0.042 0.132 0.288

100 0.010 0.800 0.065 0.252 0.492

Scenario A(Q)4 

400 0.020 0.800 0.105 0.212 0.298

300 0.020 0.800 0.101 0.217 0.303

200 0.020 0.800 0.105 0.226 0.337

175 0.020 0.800 0.105 0.227 0.347

150 0.020 0.800 0.107 0.242 0.398

125 0.020 0.800 0.107 0.291 0.494

100 0.020 0.800 0.146 0.427 0.677

a

 Quasi-extinction threshold defined as <10 males or females. 

b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

50
of meeting the threshold increased from approximately 2% in 100 years (K > 125, 1% 

probability and 0.90 magnitude of a catastrophe) to as high as 43% after 200 years and 68% after 

300 years with the highest catastrophe rate and magnitude (Scenario A(Q)4). 

Scenario B, 14 years of data, modeled to extinction 

Scenario B (Table 8) involved using the best fitting model with a shorter time sequence, 

the S(4t c) temporal model and using only the survival estimates over the last four time periods, a 

total of 14 years. The last time period of 2 years was assumed to be the beginning of an eventual 

4-year period, so it was extended to 4 years. Therefore, this scenario had two 4-year periods 

with relatively high survival and two 4-year periods with relatively low survival. However, the 

average survival for the 14 years was lower than the overall average survival used in Scenario A, 

so this scenario was more pessimistic. This scenario was used to investigate the assumption that 

survival will continue to cycle for about equal periods of relatively low and high survival—but at 

the overall lower average level seen the last 14 years—instead of assuming that the overall 

average survival seen over 29 years would prevail. Thus this scenario carried an assumption that 

the environment has gotten worse for this population than it was in the initial period the 

population was monitored. 

Scenario B was the “average” scenario that was expected to give results between the most 

(A) and least (C) optimistic scenarios. This scenario’s most optimistic forecast (for all values of 

K, no catastrophes; Scenario B1) resulted in a risk of extinction in 100 years of about 0.3% 

(Table 8). For the worst case, the 300-year extinction risk was 66% (K = 100 and the highest 

probability and magnitude of a catastrophe; Scenario B4). 

Scenario B(Q), 14 years of data, modeled to a quasi-extinction threshold 

Scenario B(Q) (Table 9) used the same survival rates found in Scenario B. Assuming the 

quasi-extinction Scenario B(Q), the most optimistic 100-year forecast (for all K values, no 

catastrophes; Scenario B(Q)1) had a risk of meeting the quasi-extinction threshold of 6–8%. The 

highest risk, 85% in 300 years, resulted from Scenario B(Q)4 with a carrying capacity of 100 and 

two catastrophes every 100 years that each reduced the population by 20%. 

Scenario C, last 10 years of data, modeled to extinction 

Scenario C (Table 10) used the same survival model as Scenario B, S(4t c), but only used 

the last 10 years of survival data. The last 10 years had two 4-year periods of relatively low 

survival, with just the last 2-year period having relatively higher survival. This scenario, the 

most pessimistic, was designed to investigate the assumption that the survival rates for the 

population observed most recently were most representative of the population’s dynamics and 

would continue into the future. The most optimistic forecast of extinction risk for Scenario C 

(K = 400, no catastrophes; Scenario C1) had a risk of extinction of 5–6% in the next 100 years. 

The highest extinction risk, 94% in 300 years, resulted from a modeled population with a 

carrying capacity of 100, two catastrophes of magnitude 0.8 every 100 years (Scenario C4). 

51
Table 8. Survival Scenario B, using the last 14 years of data and survival model S(4t c), assuming four 

4-year periods, modeled to extinction.a

Catastrophe Probability of extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario B1 

400 0.000 1.000 0.002 0.054 0.144

300 0.000 1.000 0.003 0.059 0.145

200 0.000 1.000 0.003 0.052 0.138

175 0.000 1.000 0.003 0.057 0.149

150 0.000 1.000 0.002 0.055 0.157

125 0.000 1.000 0.003 0.064 0.202

100 0.000 1.000 0.003 0.086 0.303

Scenario B2 

400 0.010 0.900 0.004 0.083 0.195

300 0.010 0.900 0.004 0.082 0.200

200 0.010 0.900 0.005 0.085 0.199

175 0.010 0.900 0.006 0.087 0.210

150 0.010 0.900 0.004 0.084 0.211

125 0.010 0.900 0.005 0.094 0.258

100 0.010 0.900 0.006 0.126 0.370

Scenario B3 

400 0.010 0.800 0.015 0.144 0.289

300 0.010 0.800 0.014 0.144 0.288

200 0.010 0.800 0.017 0.147 0.298

175 0.010 0.800 0.013 0.150 0.312

150 0.010 0.800 0.016 0.147 0.318

125 0.010 0.800 0.015 0.151 0.353

100 0.010 0.800 0.017 0.191 0.481

Scenario B4 

400 0.020 0.800 0.048 0.275 0.483

300 0.020 0.800 0.046 0.274 0.490

200 0.020 0.800 0.045 0.272 0.486

175 0.020 0.800 0.046 0.277 0.502

150 0.020 0.800 0.044 0.277 0.516

125 0.020 0.800 0.043 0.292 0.562

100 0.020 0.800 0.052 0.343 0.656

a

 Extinction defined as <1 male or female. b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

52
Table 9. Survival Scenario B(Q), using the last 14 years of data and survival model S(4t c), assuming 

four 4-year periods, modeled to a quasi-extinction threshold.a

Catastrophe Probability of quasi-extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario B(Q)1 

400 0.000 1.000 0.061 0.152 0.214

300 0.000 1.000 0.064 0.153 0.214

200 0.000 1.000 0.056 0.142 0.214

175 0.000 1.000 0.061 0.157 0.241

150 0.000 1.000 0.060 0.160 0.274

125 0.000 1.000 0.064 0.199 0.363

100 0.000 1.000 0.082 0.305 0.548

Scenario B(Q)2 

400 0.010 0.900 0.089 0.205 0.281

300 0.010 0.900 0.092 0.209 0.293

200 0.010 0.900 0.091 0.208 0.300

175 0.010 0.900 0.092 0.214 0.314

150 0.010 0.900 0.084 0.215 0.343

125 0.010 0.900 0.093 0.252 0.439

100 0.010 0.900 0.122 0.381 0.618

Scenario B(Q)3 

400 0.010 0.800 0.140 0.296 0.389

300 0.010 0.800 0.138 0.296 0.392

200 0.010 0.800 0.145 0.302 0.414

175 0.010 0.800 0.150 0.316 0.444

150 0.010 0.800 0.139 0.314 0.467

125 0.010 0.800 0.141 0.350 0.550

100 0.010 0.800 0.181 0.488 0.720

Scenario B(Q)4 

400 0.020 0.800 0.251 0.481 0.605

300 0.020 0.800 0.250 0.483 0.609

200 0.020 0.800 0.245 0.478 0.617

175 0.020 0.800 0.255 0.490 0.644

150 0.020 0.800 0.245 0.498 0.676

125 0.020 0.800 0.250 0.542 0.739

100 0.020 0.800 0.298 0.654 0.853

a

 Quasi-extinction threshold defined as <10 males or females. 

b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

53
Table 10. Survival Scenario C, using last 10 years of survival estimates from model S(4t c), assuming 

two 4-year periods and one 2-year period, modeled to extinction.a

Catastrophe Probability of extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario C1 

400 0.000 1.000 0.056 0.453 0.682

300 0.000 1.000 0.051 0.454 0.677

200 0.000 1.000 0.055 0.451 0.681

175 0.000 1.000 0.056 0.460 0.680

150 0.000 1.000 0.053 0.450 0.681

125 0.000 1.000 0.056 0.454 0.703

100 0.000 1.000 0.052 0.475 0.752

Scenario C2 

400 0.010 0.900 0.074 0.534 0.757

300 0.010 0.900 0.070 0.535 0.760

200 0.010 0.900 0.069 0.534 0.750

175 0.010 0.900 0.075 0.533 0.756

150 0.010 0.900 0.071 0.537 0.763

125 0.010 0.900 0.069 0.530 0.767

100 0.010 0.900 0.072 0.546 0.813

Scenario C3 

400 0.010 0.800 0.107 0.620 0.816

300 0.010 0.800 0.105 0.607 0.812

200 0.010 0.800 0.108 0.617 0.817

175 0.010 0.800 0.110 0.613 0.823

150 0.010 0.800 0.104 0.607 0.816

125 0.010 0.800 0.105 0.610 0.832

100 0.010 0.800 0.106 0.636 0.870

Scenario C4 

400 0.020 0.800 0.186 0.735 0.904

300 0.020 0.800 0.176 0.741 0.906

200 0.020 0.800 0.182 0.742 0.904

175 0.020 0.800 0.184 0.748 0.911

150 0.020 0.800 0.179 0.742 0.911

125 0.020 0.800 0.182 0.742 0.914

100 0.020 0.800 0.187 0.765 0.942

a

 Extinction defined as <1 male or female. b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

54
Scenario C(Q), last 10 years of data, modeled to a quasi-extinction threshold 

Scenario C(Q) (Table 11) used the same survival assumption as Scenario C, but 

examined the probability the population would fall below the quasi-extinction threshold. The 

most optimistic scenario involved no catastrophes over 100 years; the estimated probability of 

meeting the threshold in that case was approximately 40% at all carrying capacities (Scenario 

C(Q)1). The highest risk, 98% in 300 years, resulted from a modeled population with a carrying 

capacity of 100 and two catastrophes every 100 years that each reduced the population by 20% 

(Scenario C(Q)4). 

5.1.2. Discussion and Conclusions 

The PVAs were conducted using available demographic information for Southern 

Resident killer whales. Under the assumption that population growth rates in the future will 

more accurately be predicted by the full (29-year) time series of data (most optimistic model), 

the extinction model predicted a risk of <0.1–3% in 100 years and 2–42% in 300 years 

(Scenarios A1–A4). If a quasi-extinction threshold was used instead of actual extinction, the 

predicted probability of meeting the threshold ranged 1–15% in 100 years and 4–68% in 300 

years, with the higher values associated with higher probability and magnitude of catastrophic 

mortality events (Scenarios A(Q)1–A(Q)4). 

When it was assumed that the population survival for last 10 years would best predict the 

future (most pessimistic model), the analysis predicted a probability of extinction of 6–19% in 

100 years and 68–94% in 300 years (Scenarios C1–C4). If a quasi-extinction threshold was used 

in lieu of actual demographic extinction, the predicted probability of meeting the threshold 

ranged from 40–67% in 100 years to 76–98% in 300 years (Scenarios C(Q)1–C(Q)4). 

The estimated risk of extinction was, therefore, very sensitive to the assumption 

regarding survival rates in the future. If the assumption was made that the last 29 years are a 

good indicator of future population trends, then the estimated probability of extinction was much 

lower than if a more pessimistic assumption was made that the last 10 years are a good indicator 

of the future. Under the pessimistic assumption, uncertainties with respect to the level of 

carrying capacity, as well as the rate and magnitude of catastrophes, had relatively little effect on 

the extinction probability (i.e., it was high regardless). In contrast, under the more optimistic 

prediction using the 29-year series of survival rates, the risk of extinction was strongly 

influenced by the assumption made about carrying capacity and was to a lesser extent influenced 

by the level and magnitude of catastrophes. 

5.1.3. Comparison of Parameters Used in the 2002 and 2004 PVA Models 

There were many similarities and only a few differences between the PVAs developed by 

the 2002 BRT (Krahn et al. 2002) and the current BRT. The same basic killer whale population 

parameters, such as life span and the youngest female to give birth, were used in both models 

and were based on information reported in Olesiuk et al. (1990). Demographic and 

environmental variances were modeled identically in both PVAs. In addition, both models 

incorporated an Allee effect in the same manner and gradually incorporated density-dependent 

changes in survival and fecundity when the modeled killer whale populations were above an 

55
Table 11. Survival Scenario C(Q), using last 10 years of survival estimates from model S(4t c), assuming 

two 4-year periods and one 2-year period, modeled to a quasi-extinction threshold.a

Catastrophe Probability of quasi-extinction (years) 

K Probability Magnitudeb 100 200 300

Scenario C(Q)1 

400 0.000 1.000 0.394 0.667 0.761

300 0.000 1.000 0.396 0.667 0.761

200 0.000 1.000 0.394 0.671 0.770

175 0.000 1.000 0.394 0.670 0.769

150 0.000 1.000 0.388 0.670 0.778

125 0.000 1.000 0.395 0.680 0.810

100 0.000 1.000 0.399 0.736 0.877

Scenario C(Q)2 

400 0.010 0.900 0.465 0.745 0.831

300 0.010 0.900 0.460 0.743 0.833

200 0.010 0.900 0.455 0.740 0.828

175 0.010 0.900 0.467 0.741 0.836

150 0.010 0.900 0.462 0.750 0.846

125 0.010 0.900 0.454 0.747 0.865

100 0.010 0.900 0.472 0.796 0.916

Scenario C(Q)3 

400 0.010 0.800 0.535 0.799 0.880

300 0.010 0.800 0.525 0.794 0.875

200 0.010 0.800 0.537 0.806 0.879

175 0.010 0.800 0.534 0.808 0.886

150 0.010 0.800 0.528 0.801 0.890

125 0.010 0.800 0.527 0.809 0.912

100 0.010 0.800 0.542 0.856 0.952

Scenario C(Q)4 

400 0.020 0.800 0.653 0.888 0.947

300 0.020 0.800 0.652 0.890 0.948

200 0.020 0.800 0.661 0.889 0.946

175 0.020 0.800 0.665 0.897 0.953

150 0.020 0.800 0.655 0.891 0.954

125 0.020 0.800 0.652 0.898 0.959

100 0.020 0.800 0.665 0.927 0.983

a

 Quasi-extinction threshold defined as <10 males or females. 

b

 The magnitude shows the fraction of the population remaining following the catastrophe; the SE 

of the magnitude is 0.020.

56
assumed carrying capacity. In both models, the same range of carrying capacity values were 

used to reflect the range of possible population carrying capacities. Finally, both modeling 

efforts examined what increase in the risk of extinction could occur if 0, 1, and 2 catastrophes 

over 100 years, on average, affected the survival rates of individuals. 

There were two major differences between the 2002 PVA (Krahn et al. 2002) and the 

current PVA. First the current modeling effort updated the 2002 population parameters by 

adding an additional 3 years to the information on survival and fecundity rates. Thus survival 

and fecundity rates from 1974 to 2000 have been updated and the 2004 PVAs included an 

analysis of survival and fecundity rates from 1974 to 2003. 

Some members of the BRT believed strongly that the 2004 PVA should reflect the 

probability of the population reaching some very low number of animals, but one that is above 

the level identified as “extinction” (defined as <1 male or female). This level, called the “quasiextinction” threshold, was set as the number of animals at which the BRT was reasonably certain 

that the population would be “doomed” to extinction. The BRT believed that if there were <10 

males or 10 females, the population would likely not persist longer than the lifespan of those 

animals. PVA scenarios were then examined that incorporated both extinction and the quasiextinction threshold. 

5.2. Application of IUCN Criteria 

Although the IUCN (International Union for the Conservation of Nature and Natural 

Resources or “the World Conservation Union”) criteria were originally created to measure the 

global risk to all species, there was such widespread need for measures of risk on smaller scales 

that the IUCN created guidelines for regional applications of their criteria. The guidelines 

(IUCN 2001) suggest using the criteria unmodified if the group under consideration meets the 

following definition for subpopulations: 

Geographically or otherwise distinct groups in the (global) population between 

which there is little demographic or genetic exchange (typically one successful 

migrant individual or gamete per year or less [IUCN 2001]); a subpopulation may 

or may not be restricted to a region. 

Assuming a generation time of 20 years and using the estimated genetic differentiation between 

Southern and Northern Resident populations (FST = 0.144) (Barrett-Lennard 2000) and using 

Wright’s formula of Fst = 1/(4Nm + 1), the number of migrants/generation is 1.49 or 0.074/year. 

Thus by the IUCN criteria, the Southern Residents qualify as a subpopulation. 

The IUCN “Redlist” criteria classify species into four different risk categories—critically 

endangered, endangered, vulnerable, and least concern—using five criteria: 

A. magnitude of population reduction, 

B. geographic range, 

C. abundance and trends in abundance, 

D. abundance alone (population size numbers fewer than 50 mature individuals), and 

E. quantitative estimate of the probability of extinction. 

57
Qualification for a risk category depends on meeting any one of these criteria. For killer whales, 

historical range and abundance are so poorly known that data-driven assessments cannot be 

made. The Redlist guidelines base classification on the highest risk category for which the 

“species” can qualify. In this case, Southern Residents would qualify as “critically endangered” 

under criterion D. The IUCN defines mature individuals as “the number of individuals known, 

estimated or inferred to be capable of reproduction.” There are currently no more than 41 mature 

individuals in the Southern Resident population, thus this population is below the threshold for 

“critically endangered” using criterion D. 

It is worth noting that, although the listing would be based on criterion D above, Southern 

Residents may qualify as either “critically endangered” or “endangered” under criterion C1. 

To meet the C1 criterion at the ‘critically endangered’ level: Population size 

estimated to number fewer than 250 mature individuals and an estimated 

continuing decline of at least 25% within 3 years or one generation, whichever is 

longer (up to a maximum of 100 years in the future). 

The removals of the Southern Residents for oceanaria in the late 1960s and early 1970s, coupled 

with recent declines, may make the reduction in mature individuals more that 25% in the last 

generation. 

To meet the C1 criterion at the ‘endangered’ level: Population size estimated to 

number fewer than 2,500 mature individuals and an estimated continuing decline 

of at least 20% within 5 years or two generations, whichever is longer (up to a 

maximum of 100 years in the future). 

5.3. Extinction Risk—Summary of BRT Concerns 

The Southern Resident killer whale population is a relatively small, substantially 

reproductively isolated population in the eastern North Pacific Ocean. Although its historical 

population size is unknown, the development of photo-identification techniques in the 1970s has 

led to comprehensive documentation of population size, survivorship, and reproductive success 

of individuals. To assess risk, the BRT evaluated population size, population trends, age 

structure, social structure, diversity, recent fecundity, and survivorship, as well as external risk 

factors such as habitat degradation or potential catastrophic events. Due to the long life span of 

this species, the BRT believed that it is important to consider the risk of extinction using a 

relatively long time frame (e.g., hundreds of years). Populations of long-lived animals can have 

considerable demographic inertia; thus a nonviable population has the potential to persist for 

many decades simply due to the long life spans of its existing members. 

5.3.1. Population Size

In comparison to most other marine mammal stocks, the Southern Resident killer whale 

population is extremely small (Angliss and Lodge 2002, Carretta et al. 2002). Although the 

historical population size is unknown, the current population is only slightly higher than its level 

in the early 1970s after being reduced by about one-third by collections for oceanaria. The 

Southern Resident population has been able to persist at a relatively low level over the past 30 

years, but the relatively long life span of this species may be masking its future viability. 

58
Resident killer whales of the North Pacific have a highly structured social organization 

with matrilineal groups as the basic structural element. The Southern Residents killer whale 

community consists of three generally separate pods (J, K, and L), each containing several 

matrilineal groups. Because individual killer whales are most often in proximity to their pod, 

any event that reduces survival (e.g., disease outbreak, oil spill) could adversely impact the entire 

pod. Thus the combination of small population size and their occurrence in socially cohesive 

groups puts the Southern Residents at risk for a significant population decrease resulting from

catastrophic events. 

A well-recognized factor that may have an adverse impact on an already small population 

is the Allee effect of inbreeding depression. Inbreeding depression is more likely to be 

manifested as the population size decreases. The IUCN suggests that if the number of 

reproductive animals is fewer than 50, the potential for impacts associated with inbreeding 

depression increases substantially. Given that the population of Southern Resident killer whales 

currently has a small number of reproductive females (28, ages 11–41) and an even smaller 

number of reproductive males (9, ages 15 and older) it could be approaching the level at which 

the effects of inbreeding depression may start to be a factor impacting the population’s ability to 

maintain itself or increase. 

A too-small population could also experience a breakdown of social structure. Although 

certain cultural and behavioral aspects of the Southern Resident killer whale community have 

been described, the mechanisms by which they contribute to the viability of the population are 

not yet well understood. However, the situation of the killer whale population may be analogous 

to those of the few other large mammal populations in which females live far beyond their 

reproductive span (e.g., elephants, higher primates, and other toothed cetaceans such as pilot 

whales) (McComb et al. 2001, Lahdenpera et al. 2004). The loss of only a few key individuals—

primarily the older, post-reproductive females in this matriarchal society—could result in a 

significant loss of inclusive fitness conveyed by “aunting” behavior (i.e., assistance in care of the 

young of other females in the pod). In addition, cultural knowledge (e.g., about how to cope 

with environmental changes occurring on decadal scales) could be lost, leading to reduced 

survival or fecundity of some or all age classes. This factor may have contributed to the decline 

observed in the AB Pod in Alaska (Matkin et al. 2003). 

5.3.2. Population Trends 

Over the past 30 years the population size has fluctuated, with two increasing and two 

decreasing periods. Following the removal of approximately a third of the population for 

displays in oceanaria in the late 1960s and early 1970s, the Southern Resident population 

increased, demonstrating its ability to recover following a significant “mortality event” (i.e., 

removing subadults from the population). From 1980 to 1984, the population declined by 11%, 

but the decline was followed by a steady increase from 74 to 97 animals (31% increase) between 

1985 and 1996. Then, another sharp decline (20%) followed between 1997 and 2001, but the 

factors responsible for this recent decline are not clear. Although the population has increased 

since 2001 and is at a level that is slightly higher today than it was 30 years ago, it is unknown 

whether this trend will continue. These trends are in contrast to the population of Northern 

Resident killer whales which increased steadily until the late 1990s before undergoing a 7% 

59
decline. The apparent inability of Southern Resident killer whales to recover to preharvest 

(presumably higher) levels is of concern. 

5.3.3. Sex and Age Class Structure 

Although the breeding system in killer whales is not fully understood, previous research 

on Northern Resident killer whales has indicated that breeding occurs only between pods 

(Barrett-Lennard 2000). In addition, the observed sexual dimorphism of the resident whales 

suggests some selection pressure is being exerted, either through female choice or male-male 

competition.

The sex and age class structure of the Southern Residents differs from that of other killer 

whale populations. The proportion of adult males, particularly in J and K Pods, appears to be 

lower than found for other resident killer whale populations in the eastern North Pacific Ocean 

(Wade unpubl. data). In the early 1990s there were five adult males total in J and K Pods. By 

1997 the last male in K Pod had died and by 2000, when a J Pod male died, there was only one 

adult male (J1) remaining in these two pods. It is only within the last 2 years that a male in 

K Pod appears to be attaining sexual maturity. Consequently, the pool of males available to 

breed with females in L Pod appears to be extremely limited. Furthermore, L Pod has a greater 

proportion of post-reproductive females (9 compared to 2 and 3 in J and K Pods, respectively). 

The lack of reproductive males or post-reproductive females can have substantial 

consequences to the population. If loss of the sexually mature males from J and K Pod were to 

occur, the reproductive output of L Pod could potentially be suspended, perhaps for as few as 2 

years or as many as 7 years, until other J Pod or K Pod males become physically and socially 

mature. The likelihood of these two males dying in the near future is relatively high, because J1 

is the oldest male (50+ years) in the Southern Resident population and K21, at age 18, is nearing 

the age (20–25 years) when a substantial portion of the male population has died. Additionally, 

because post-reproductive whales have a higher mortality rate than other age classes, deaths of 

members of this class may result in a faster decline in L Pod than in the other pods. 

5.3.4. Fecundity 

In addition to a large proportion of post-reproductive females, L Pod also currently has a 

smaller proportion of reproductive-age females compared to J and K Pods (17% versus 26% and 

27%, respectively). Although several females in L Pod have recently reached reproductive age, 

none have produced viable calves. Furthermore, in a comparison of females that have given 

birth to their first calf since 1972, 7 of the 16 females in L Pod had an average inter-calf interval 

greater than 6 years compared to only 3 of 13 females in J and K Pods combined. In the past 5 

years, L Pod has had the lowest birth rate of viable calves (4 for the 9 reproductive age females 

>15 years old). Although the average fecundity of the Southern Residents has not declined (see 

subsection 2.4.2), these anomalies found for L Pod may affect the population’s future ability to 

grow. 

5.3.5. Survivorship 

Although mortality patterns through time are similar among the three Southern Resident 

pods, L Pod has had a lower survival rate (Figure 6) than the other two pods, particularly during 

60
the most recent decline. When compared to J and K Pods, L Pod has lost about a third more of 

its adult whales and, perhaps more significantly, has also lost about a third more subadults and 

calves. This loss of subadults may impact this pod’s future reproductive potential. Because the 

factors associated with mortality in L Pod are unclear—particularly for subadults and young 

adults—the uncertainty about the viability of L Pod has increased substantially. 

5.3.6. Conclusions 

Taken together, the population dynamics of the Southern Residents describe a population 

that is at risk for extinction, due either to incremental small-scale impacts over time (e.g., 

reduced fecundity or subadult survivorship) or to a major catastrophe (e.g., disease outbreak or 

oil spill). Additionally, the small size of this killer whale population makes it potentially 

vulnerable to both Allee effects (e.g., inbreeding depression) and loss of post-reproductive 

females that could cause a major decline. Although this population has demonstrated the ability 

to recover from lower levels in the past, the factors responsible for the recent decline are unclear, 

may still exist, and may continue to persist, precluding a substantial population increase. 

Furthermore, the small number of breeding males, as well as possible reduced fecundity and 

subadult survivorship in L Pod, may limit the population’s potential for rapid growth in the 

future. 

61
6. Conclusions of the Status Review 

Although multiple species of killer whales may exist and may be confirmed in the future, 

the 2004 BRT concluded that present data do not adequately support designation of any new 

species. In particular, the BRT concluded that North Pacific transients and residents should be 

considered to belong to a single species. 

The 2004 BRT agreed (by a 5-to-1 margin) that Southern Residents belong to a 

subspecies separate from that of the transients. That subspecies would include the Southern 

Residents and the Northern Residents, as well as the resident killer whales of Southeast Alaska, 

Prince William Sound, Kodiak Island, the Bering Sea, and Russia (but not the offshores). Thus 

the taxon to use for determining a DPS under the ESA would be resident killer whales in the 

North Pacific, an unnamed subspecies of O. orca. 

The 2004 BRT unanimously concluded that the Southern Residents are discrete from

other North Pacific resident killer whale populations. In particular, all available data—including 

behavior, demography, and core and summer ranges, as well as genetics—indicated that the 

Southern Residents are an independent population that is discrete with respect to other 

populations. 

The BRT concluded (by a 2-to-1 margin) that the Southern Residents are significant with 

respect to the unnamed North Pacific resident subspecies (taxon) and therefore should be 

considered a DPS. The BRT also concluded (by a 3-to-2 margin) that the Southern Residents 

would be a DPS of a taxon consisting of both North Pacific residents and offshores. Arguments 

favoring significance under both taxonomic scenarios were as follows: 

• The Southern Residents appear to occupy an ecological setting, the California Current 

ecosystem, distinct from the other North Pacific resident populations. There is also some

evidence of differences in prey utilization. 

• The loss of the Southern Residents would result in a significant gap in the range of the 

North Pacific resident taxon, because the Southern Residents are the only North Pacific 

resident population to be sighted in the coastal areas off of California, Oregon, and 

Washington and are the only population to regularly inhabit Puget Sound. 

• The Southern Residents differ markedly from other North Pacific resident populations at 

both nuclear and mitochondrial genes, as well as in the frequency of certain saddle-patch 

variants. 

• Culture (knowledge passed through learning from one generation to the next) is likely to 

play an important role in the viability of killer whale populations. For example, the 

Southern Residents may possess unique knowledge of the timing and location of salmon 

runs in the southern part of the North Pacific residents’ range. There was some evidence 

that cultural traditions (e.g., greeting behavior, beach rubbing, and utilization of prey 

from long-lines) differed among the resident populations. 

62
The 2004 BRT considered whether certain factors that currently pose a risk for Southern 

Residents might continue in the future. Concern remains about whether reduced quantity or

quality of prey are adversely affecting the Southern Resident population. In addition, 

concentrations of OC contaminants are not declining appreciably and those of many newly 

emerging contaminants (e.g., PBDE flame retardants) are increasing, thus Southern Residents are 

likely at risk for chronic effects, similar to those demonstrated for other marine mammal species 

(e.g., immunotoxicity in harbor seals). Other serious risk factors that may impact Southern 

Residents are oil spills, as well as noise and disturbance from vessel traffic. 

A PVA was conducted to synthesize the potential biological consequences of a small 

population size, a slowly increasing or a declining population trend, and potential risk factors. 

Using the most optimistic model (29-year data set), the model predicted that the probability that

Southern Residents would become extinct was from less than 0.1% to 3% in 100 years and 2–

42% in 300 years. If a quasi-extinction threshold was used instead of actual extinction, the 

predicted probability of meeting the threshold ranged 1–15% in 100 years and 4–68% in 300 

years. For both scenarios, the higher percentages in each range were associated with higher 

probability and magnitude of catastrophic mortality events (e.g., oil spills), as well as with a 

smaller carrying capacity (i.e., K = 100). When the most pessimistic model was used (the last 10 

years), the analysis predicted a probability of extinction of 6–19% in 100 years and 68–94% in 

300 years. If a quasi-extinction threshold was used in lieu of actual demographic extinction, the 

predicted probability of meeting the threshold ranged from 40–67% in 100 years to 76–98% in 

300 years. 

Overall, the 2004 BRT was concerned about the viability of the Southern Resident 

population of killer whales. The population dynamics describe a population that is at risk for 

extinction, due either to incremental small-scale impacts over time (e.g., reduced fecundity or 

subadult survivorship) or to a major catastrophe (e.g., disease outbreak or oil spill). 

Additionally, the small size of this killer whale population makes it potentially vulnerable to 

Allee effects (e.g., inbreeding depression). Furthermore, the small number of breeding males, as 

well as possible reduced fecundity and subadult survivorship in L Pod, may limit the 

population’s potential for rapid growth in the future. Although the Southern Resident population 

has demonstrated the ability to recover from lower abundance levels in the past, the factors 

responsible for the recent decline are unclear, may still exist and may continue to persist, 

precluding the likelihood of a substantial population increase. 

63
64
7. References 

Ames, J. Unpubl. data. Data attached to e-mail dated 29 August 2003 from Rich Lincoln to Gary Wiles. 

(Available from J. Ames, Washington Dept. Fish and Wildlife, 600 Capitol Way N., Olympia, 

WA 98501.) 

Angliss, R. P. Unpubl. data. Field observations. (Available from R. P. Angliss, AFSC, 7600 Sand Point

Way NE, Seattle, Washington 98115.) 

Angliss, R. P., and K. L. Lodge. 2002. Alaska marine mammal stock assessments, 2002. U.S. Dept. 

Commer., NOAA Tech. Memo. NMFS-AFSC-133. 

Bain, D. E., and M. E. Dahlheim. 1994. Effects of masking noise on detection thresholds of killer 

whales. In T. R. Loughlin (ed.), Marine mammals and the Exxon Valdez, p. 243–256. Academic 

Press, San Diego, CA. 

Bain, D. E. 2002. A model linking energetic effects of whale watching to killer whale (Orcinus orca) 

population dynamics. University of Washington, Friday Harbor Laboratories, Friday Harbor, 

WA. Report Sponsored by the Orca Relief Citizens Alliance. Online at 

http://www.nwfsc.noaa.gov/research/divisions/sd/kwworkshops/boatpubs.cfm [accessed 27 

September 2004]. 

Baird, R. W. 2001. Status of killer whales, Orcinus orca, in Canada. Can. Field-Nat. 115:676–701. 

Baird, R. W., and M. B. Hanson. 2004. A progress report on diving behavior of Southern Resident killer 

whales. Contract report under Order No. AB133F-03-SE-1070. (Available from M. B. Hanson, 

NWFSC, 2725 Montlake Blvd. East, Seattle, WA 98112.) 

Barrett-Lennard, L. G. 2000. Population structure and mating patterns of killer whales as revealed by 

DNA analysis. Doctoral thesis. Univ. British Columbia, Vancouver, BC, Canada. 

Barrett-Lennard, L., and K. Heise. 2004. Influences of ecology, cultural traditions, and social 

organization on the genetic population structure and systematics of killer whales. Meeting 

document LJ/04/KW1. Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs 

of Conservation and Management, April 30–May 2, 2004, La Jolla, California. (Available from

S. Mesnick, SWFSC, 8604 La Jolla Shores Dr., La Jolla, CA 92037.) 

Beerli, P. 2002. Migrate: Documentation and program, part of Lamarc. Version 1.6. Revised August 

23, 2002. Distributed online at http://evolution.genetics.washington.edu/lamarc.html [accessed 

23 September 2004]. 

Beerli, P., and J. Felsenstein. 2001. Maximum likelihood estimation of a migration matrix and effective 

population sizes in n subpopulations by using a coalescent approach. Proc. Natl. Acad. Sci. USA 

98:4563–4568. 

Berzin, A. A., and V. L. Vladimirov. 1982. A new species of killer whale from the Antarctic. Priroda 

6:31. 

65
Berzin, A. A., and V. L. Vladimirov. 1983. A new species of killer whale (Cetacea, Delphinidae) from

Antarctic waters. Zool. Zh. 62:287–295.

Bigg, M. A., P. F. Olesiuk, G. M. Ellis, J. K. B. Ford, and K. C. Balcomb III. 1990. Social organization 

and genealogy of resident killer whales (Orcinus orca) in the coastal waters of British Columbia

and Washington State. Rep. Int. Whal. Commn (Spec. Issue) 12:386–406. 

Bledsoe, L. J., D. A. Somerton, and C. M Lynde. 1989. The Puget Sound runs of salmon: An 

examination of the changes in run size since 1896. Can. Spec. Publ. Fish. Aquat. Sci. 105:50–61. 

Boon, J. P., W. E. Lewis, M. R. Tjoen-A-Choy, C. R. Allchin, R. J. Law, J. DeBoer, C. C. Ten HallerTjabbes, and B. N. Zegers. 2002. Levels of polybrominated diphenyl ether (PBDE) flame 

retardants in animals representing different trophic levels in the North Sea food web. Environ. 

Sci. Technol. 36:4025–4032. 

Brown, L. R., P. B. Moyle, and R. M. Yoshiyama. 1994. Historical decline and current status in coho

salmon in California. No. Am. J. Fish. Manage. 14:237–261. 

Busby, P. J., T. C. Wainwright, G. J. Bryant, L. J. Lierheimer, R. S. Waples, F. W. Waknitz, and I. V. 

Lagomarsino. 1996. Status review of West Coast steelhead from Washington, Idaho, Oregon, 

and California. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-27. 

California Dept. Fish and Game. 1965. California Fish and Wildlife Plan. Volume III, Supporting data; 

Part B, Inventory (Salmon-Steelhead and Marine Resources). California Dept. Fish and Game,

Sacramento, CA. 

California Trout. No date. Steelhead recovery overview. Online at http://www.caltrout.org/consact/ 

Steelhead_Overview.html [accessed 14 October 2004].

Carretta, J. V., M. M. Muto, J. Barlow, J. Baker, K. A. Forney, and M. Lowry. 2002. U.S. Pacific marine 

mammal stock assessments: 2002. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-SWFSC346. 

Caughley, G. 1966. Mortality patterns in mammals. Ecology 47:906–918. 

Dahlheim, M. E. 1997. A photographic catalog of killer whales, Orcinus orca, from the Central Gulf of 

Alaska to the southeastern Bering Sea. U.S. Dept. Commer., NOAA Tech. Rep. NMFS 131, 

Seattle. 

Dahlheim, M. E. Unpubl. data. Field observations. (Available from M. E. Dahlheim, AFSC, 7600 

Sand Point Way NE, Seattle, Washington 98115.) 

de Wit, C. A. 2002. An overview of brominated flame retardants in the environment. Chemosphere 

46(5):583–624. 

de Wit, C., A. Fisk, K. Hobbs, D. Muir, G. Gabrielsen, R. Kallenborn, M. M. Krahn, R. Norstrom, and J. 

Skaare. 2004. AMAP assessment 2002: Persistent organic pollutants in the Arctic. Arctic 

Monitoring and Assessment Program, Oslo, Norway. 

DFO (Dept. Fisheries and Oceans Canada). 1999. Fraser River Chinook salmon. DFO science stock 

status report D6-11. Dept. Fisheries and Oceans Canada, Pacific Region, Nanaimo, BC. 

66
DFO (Dept. Fisheries and Oceans Canada). 2001. 2000 Pacific Region state of the ocean status report 

2001-01. Dept. Fisheries and Oceans Canada, Pacific Region, Nanaimo, BC. 

DFO (Dept. Fisheries and Oceans Canada). 2002a. Interior Frasier River coho salmon. DFO science 

stock status report D6-08. Dept. Fisheries and Oceans Canada, Pacific Region, Nanaimo, BC. 

DFO (Dept. Fisheries and Oceans Canada). 2002b. Strait of Georgia herring. DFO science stock status 

report B6-05. Dept. Fisheries and Oceans Canada, Pacific Region, Nanaimo, BC. 

Erbe, C. 2002. Underwater noise of whale-watching boats and potential effects on killer whales (Orcinus

orca), based on an acoustic impact model. Mar. Mamm. Sci. 18(2):394–418. 

Foote, A. D., R. W. Osborne, and A. R. Hoelzel. 2004. Whale-call response to masking boat noise. 

Nature 428(6986):910. 

Ford, J. K. 2004. The role of acoustics in defining killer whale populations and societies. Meeting 

document LJ/04/KW4. Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs 

of Conservation and Management, April 30–May 2, 2004, La Jolla, California. (Available from

S. Mesnick, SWFSC, 8604 La Jolla Shores Dr., La Jolla, CA 92037.) 

Ford, J. K., and G. M. Ellis. 2004. Reassessing the social organization of resident killer whales in British 

Columbia. Meeting document LJ/04/KW5. Workshop on Shortcomings of Cetacean Taxonomy

in Relation to Needs of Conservation and Management, April 30–May 2, 2004, La Jolla, 

California. (Available from S. Mesnick, SWFSC, 8604 La Jolla Shores Dr., La Jolla, CA 92037.) 

Ford, J. K. B., G. M. Ellis, and K. C. Balcomb. 2000. Killer whales: The natural history and genealogy

of Orcinus orca in British Columbia and Washington State. Second edition. University of 

British Columbia Press, Vancouver, BC, Canada. 

Ford, M. 2004. How old are the Southern Residents? Meeting document LJ/04/KW6. Workshop on 

Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation and Management, 

April 30–May 2, 2004, La Jolla, California. (Available from S. Mesnick, SWFSC, 8604 La Jolla 

Shores Dr., La Jolla, CA 92037.) 

Fung, C. W., and L. G. Barrett-Lennard. 2004. Does cranial morphology reflect adaptive evolutionary

divergence of sympatric killer whale (Orcinus orca) ecotypes? In Symposium on cetacean 

systematics: Approaches in genetics, morphology and behavior, 28–29 April 2004, La Jolla,

California, Abstracts, p. 20. SWFSC, La Jolla, CA. 

Gaydos, J. K., K. C. Balcomb III, R. W. Osborne, and L. Dierauf. 2004. Evaluating potential infectious 

disease threats for Southern Resident killer whales, Orcinus orca: A model for endangered 

species. Biol. Cons. 117:253–62. 

Gordon, J., and A. Moscrop. 1996. Underwater noise pollution and its significance for whales and 

dolphins. In M. P. Simmonds and J. D. Hutchinson (eds.), The conservation of whales and 

dolphins: Science and practice, p. 281–319. John Wiley & Sons, Chichester, United Kingdom. 

Guthrie, I. Unpubl. data. Data attached to e-mail dated 29 August 2003 from Rich Lincoln to Ian 

Guthrie. (Available from I. Guthrie, Pacific Salmon Commission, 600–1155 Robson St., 

Vancouver, BC, Canada V6E 1B5.) 

67
Hall, A. J., O. I. Kalantzi, and G. O. Thomas. 2003. Polybrominated diphenyl ethers (PBDEs) in grey

seals during their first year of life—Are they thyroid hormone endocrine disrupters? Environ. 

Pollut. 126(1):29–37. 

Hammond, P. S., S. A. Mizroch, and G. P. Donovan (eds.). 1990. Individual recognition of cetaceans: 

Use of photo-identification and other techniques to estimate population parameters: Incorporating 

the proceedings of the Symposium and Workshop on Individual Recognition and the Estimation 

of Cetacean Population Parameters. Report of the International Whaling Commission (Spec. 

Issue 12). International Whaling Commission, Cambridge, United Kingdom. 

Hanson, M. B. Unpubl. data. Field observations. (Available from M. B. Hanson, NWFSC, 2725 

Montlake Blvd. East, Seattle, WA 98112.) 

Hauser, D. D. Unpubl. data. Presentation to The Marine Mammal Program, NWFSC, dated 11 

December 2003. (Available from D. D. Hauser, NWFSC, 2725 Montlake Blvd. E., Seattle, WA 

98112.) 

Henderson, M. A., and C. C. Graham. 1998. History and status of Pacific salmon in British Columbia. 

In D. W. Welch, D. M. Eggers, K. Wakabayashi, and V. K. Karpenko (eds.), Assessment and 

status of Pacific Rim salmonid stocks, p. 13–22. Bulletin No. 1. North Pacific Anadromous Fish 

Commission, Vancouver, BC, Canada. 

Herman, D. P., D. G. Burrows, P. Wade, J. Durban, R. G. LeDuc, C. Matkin, and M. M. Krahn. Unpubl. 

data. Ecotype classification and prey preferences of eastern North Pacific killer whale 

populations from fatty acid, stable isotope, and organochlorine analyses of blubber biopsies. 

Paper SC/56/E14, IWC Scientific Committee, 2004. (Available from D. P. Herman, NWFSC, 

2725 Montlake Blvd. East, Seattle, WA 98112.) 

Hites, R. A. 2004. Polyhrominated diphenyl ethers in the environment and in people: A meta-analysis of 

concentrations. Environ. Sci. Technol. 38(4):945–56.

Hoelzel, A. R. 2004. Report on killer whale population genetics for the BRT review on the status of the 

Southern Resident population. Unpubl. report to BRT. (Available from L. Barre, NMFS, NWR, 

7600 Sand Point Way NE, Seattle, WA 98115.) 

Hoelzel, A. R., M. Dahlheim, and S. J. Stern. 1998. Low genetic variation among killer whales (Orcinus

orca) in the eastern North Pacific and genetic differentiation between foraging specialists. J. 

Hered. 89(2):121–128. 

Hoelzel, A. R., and G. A. Dover. 1991. Genetic differentiation between sympatric killer whale 

populations. Heredity 66:191–195. 

Hoelzel, A. R., S. D. Goldsworthy, and R. C. Fleischer. 2002b. Population genetic structure. In A. R. 

Hoelzel (ed.), Marine mammal biology: An evolutionary approach, p. 325–52. Blackwell 

Science Ltd, Oxford, United Kingdom. 

Hoelzel, A. R., A. Natoli, M. E. Dahlheim, C. Olavarria, R. W. Baird, and N.A. Black. 2002a. Low 

worldwide genetic diversity in the killer whale (Orcinus orca): Implications for demographic 

history. Proc. R. Soc. Lond. B. Biol. Sci. 269(1499):1467–1473. 

Hoyt, E. 2001. Whale watching 2001: Worldwide tourism numbers, expenditures, and expanding 

socioeconomic benefits. International Fund for Animal Welfare, Yarmouth, MA.

68
IUCN (World Conservation Union). 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN, 

Species Survival Commission, Gland, Switzerland, and Cambridge, United Kingdom. 

Jelinski, D. E., C. C. Krueger, and D. A. Duffus (eds.). 2002. Geostatistical analyses of interactions 

between killer whales (Orcinus orca) and recreational whale-watching boats. Appl. Geogr. 

22:393–411. 

Johnson, T. H., R. Lincoln, G. R. Graves, and R. G. Gibbons. 1997. Status of wild salmon and steelhead

stocks in Washington State. In D. J. Stouder, P. A. Bisson, and R. J. Naiman (eds.), Pacific 

salmon and their ecosystems: Status and future options, p. 127–144. Chapman & Hall, New 

York. 

Krahn, M. M., P. R. Wade, S. T. Kalinowski, M. E. Dahlheim, B. L. Taylor, M. B. Hanson, G. M. Ylitalo, 

R. P. Angliss, J. E. Stein, and R. S. Waples. 2002. Status Review of Southern Resident killer 

whales (Orcinus orca) under the Endangered Species Act. U.S. Dept. Commer., NOAA Tech.

Memo. NMFS-NWFSC-54. 

Kruse, S. 1991. The interactions between killer whales and boats in Johnstone Strait, B.C. In K. Pryor 

and K. S. Norris (eds.), Dolphin societies: Discoveries and puzzles, p. 149–159. University of 

California Press, Berkeley. 

Lahdenpera, M., V. Lummaa, S. Helle, M. Tremblay, and A. F. Russell. 2004. Fitness benefits of 

prolonged post-reproductive lifespan in women. Nature 428:178–181. 

LeDuc, R. G., and R. L. Pitman. 2004. Genetic and morphological evidence supports multiple species of 

killer whales in Antarctica. Meeting document LJ/04/KW8. Workshop on Shortcomings of 

Cetacean Taxonomy in Relation to Needs of Conservation and Management, April 30–May 2, 

2004, La Jolla, California. (Available from S. Mesnick, SWFSC, 8604 La Jolla Shores Dr., La 

Jolla, CA 92037.) 

LeDuc, R. G., and B. L. Taylor. 2004. Revision of meeting document LJ/04/KW7, Mitochondrial 

sequence variation in North Pacific killer whales, Workshop on Shortcomings of Cetacean 

Taxonomy in Relation to Needs of Conservation and Management, April 30–May 2, 2004, La

Jolla, California. Unpubl. report to BRT. (Available from L. Barre, NMFS, NWR, 7600 Sand 

Point Way NE, Seattle, WA 98115.) 

Matkin, C. O., G. Ellis, L. B. Lennard, H. Yurk, E. Saulitis, D. Scheel, P. Olesiuk, and G. Ylitalo. 2003. 

Photographic and acoustic monitoring of killer whales in Prince William Sound and Kenai Fjords. 

Exxon Valdez Oil Spill Restoration Project Number 030012 Final Report. (Available from C. O. 

Matkin, North Gulf Oceanic Society, P.O. Box 15244, Homer, AK 99603.) 

Mayr, E. 1963. Animal species and evolution. Harvard University Press, Cambridge, MA. 

McComb, K., C. Moss, S. M. Durant, L. Baker, and S. Sayialel. 2001. Matriarchs as repositories of 

social knowledge in African elephants. Science 292:491–494. 

Mesnick, S. L., and S. Escorza-Treviño. 2004. Social structure in eastern tropical Pacific killer whales: 

Preliminary report to the Biological Review Team. Unpubl. report to BRT. (Available from L. 

Barre, NMFS, NWR, 7600 Sand Point Way NE, Seattle, WA 98115.) 

69
Mills, T. J., D. R. McEwan, and M. R. Jennings. 1997. California salmon and steelhead: Beyond the 

crossroads. In D. J. Stouder, P. A. Bisson, and R. J. Naiman (eds.), Pacific salmon and their 

ecosystems: Status and future options, p. 91–111. Chapman & Hall, New York. 

MMMP (Marine Mammal Monitoring Project). 2002. Annual report, 2001–2002. Marine Mammal 

Monitoring Project, Victoria, BC, Canada. 

Morin, P. A., R. G. LeDuc, K. M. Robertson, N. M. Hedrick, W. Perrin, P. Wade, and B. L. Taylor. 

2004. Genetic analysis of killer whale (Orcinus orca) historic samples for evidence of southern 

resident haplotypes along the western U.S. Unpubl. report to BRT. (Available from L. Barre, 

NMFS, NWR, 7600 Sand Point Way NE, Seattle, WA 98115.) 

Myers, J. M., R. Kope, G. Bryant, D. Teel, L. Lierheimer, T. Wainwright, W. S. Grant, F. W. Waknitz, K. 

Neely, S. Lindley, and R. Waples. 1998. Status review of Chinook salmon from Washington, 

Idaho, Oregon, and California. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-35. 

Nicholas, J. W., and D. G. Hankin. 1989. Chinook salmon populations in Oregon coastal basins: 

Description of life histories and assessment of recent trends in run strengths. 2nd edition. 

Oregon Dept. Fish and Wildlife, Corvallis. 

Nickelson, T. E., J. W. Nicholas, A. M. McGie, R. B. Liday, D. L. Bottom, R. J. Kaiser, and S. E. Jacobs. 

1992. Status of anadromous salmonids in Oregon coastal basins. Oregon Dept. Fish and 

Wildlife, Corvallis. 

Nielsen, R., and J. Wakeley. 2001. Distinguishing migration from isolation: A Markov Chain Monte 

Carlo approach. Genetics 158:885–896.

NMFS (National Marine Fisheries Service). 2001. Listing endangered and threatened species and 

designating critical habitat: Petition to list Southern Resident killer whales. Federal Register 

[Docket No. 010731194-1194-01, I.D. 070601B, 13 Aug. 2001] 66:42499. 

NMFS (National Marine Fisheries Service). 2002a. Endangered and threatened wildlife and plants: 12-

month finding for a petition to list Southern Resident killer whales as threatened or endangered 

under the Endangered Species Act (ESA). Federal Register [Docket No. 020603138-2138-01, 

I.D. 042502B, 1 July 2002] 67:44133. 

NMFS (National Marine Fisheries Service). 2002b. Regulations governing the taking and importing of 

marine mammals; eastern North Pacific Southern Resident killer whales. Federal Register 

[Docket No. 020603140-2140-01, I.D. 050102G, 1 July 2002] 67:44132. 

NMFS (National Marine Fisheries Service). 2002c. Status review under the Endangered Species Act: 

Southern Resident killer whales (Orcinus orca). (Available from M. M. Krahn, NWFSC, 2725 

Montlake Blvd. East, Seattle, WA 98112.) 

NMFS (National Marine Fisheries Service). 2003a. Regulations governing the taking and importing of 

marine mammals; eastern North Pacific Southern Resident killer whales. Federal Register 

[Docket No. 020603140-3010-02, I.D. 050102G, 30 January 2003] 68:4747. 

NMFS (National Marine Fisheries Service). 2003b. Regulations governing the taking and importing of 

marine mammals; eastern North Pacific Southern Resident killer whales. Federal Register 

[Docket No. 020603140-3129-03, I.D. 050102G, 29 May 2003] 68:31980. 

70
Noren, K., and D. Meironyte. 2000. Certain organochlorine and organobromine contaminants in 

Swedish human milk in perspective of past 20–30 years. Chemosphere 40(9–11):1111–1123. 

Northcote, T. G., and D. Y. Atagi. 1997. Pacific salmon abundance trends in the Fraser River watershed 

compared with other British Columbia River systems. In D. Stouder, P. Bisson, and R. Naiman 

(eds.), Pacific salmon and their ecosystems, p. 199–222. Chapman & Hall, New York. 

Northwest Power Planning Council. 1986. Council staff compilation of information on salmon and 

steelhead losses in the Columbia River Basin. Northwest Power Planning Council, Portland, OR. 

NRC (National Research Council). 2003. Ocean Noise and Marine Mammals. National Academies 

Press, Washington, DC. 

Olesiuk, P. F., M. A. Bigg, and G. M. Ellis. 1990. Life history and population dynamics of resident killer 

whales (Orcinus orca) in the coastal waters of British Columbia and Washington State. Rep. Int. 

Whal. Commn. (special issue) 12:209–244. 

Osborne, R. W. 1986. A behavioral budget of Puget Sound killer whales. In B. Kirkevold and J. S. 

Lockard (eds.), Behavioral biology of killer whales, p. 211–249. Alan R. Liss, Inc., New York. 

Osborne, R. 1999. A historical ecology of Salish Sea resident killer whales (Orcinus orca): With 

implications for management. Doctoral dissertation. Univ. Victoria, Victoria, BC, Canada. 

Osborne, R., K. Koski, and R. Otis. 2002. Trends in whale-watching traffic around Southern Resident 

killer whales. The Whale Museum, Friday Harbor, WA. 

Perrin, W. F. 2004. Nomenclature of killer whales. Meeting document LJ/04/KW3. Workshop on

Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation and Management, 

April 30–May 2, 2004, La Jolla, California. (Available from S. Mesnick, SWFSC, 8604 La Jolla 

Shores Dr., La Jolla, CA 92037.) 

Perrin, W. F., and R. R. Reeves (eds.). 2004. Appendix 5: Report of the Working Group on Species- and 

Subspecies-Level Taxonomy. In R. R. Reeves, W. F. Perrin, B. L. Taylor, C. S. Baker, and S. L. 

Mesnick (eds.), Report of the Workshop on Shortcomings of Cetacean Taxonomy in Relation to 

Needs of Conservation and Management, April 30–May 2, 2004, La Jolla, California, p. 26–61. 

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-SWFSC-363. 

Pitman, R. L., and P. Ensor. 2003. Three forms of killer whales (Orcinus orca) in Antarctic waters. J. 

Cetacean Res. Manage. 5:131–139. 

Plater, B. 2001. Petition to list the Southern Resident killer whale (Orcinus orca) as an endangered 

species under the Endangered Species Act. The Center for Biological Diversity, Berkeley, CA. 

Pritchard, J. K., and S. M. Donnelly. 2000. Inference of population structure using multilocus genotype 

data. Genetics 155:945–959. 

Raloff, J. 2003. New PCBs? Sci. News 164:266–268. 

Reeves, R. R., W. F. Perrin, B. L. Taylor, C. S. Baker, and S. L. Mesnick (eds.). 2004. Report of the 

Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs of Conservation and 

Management, April 30–May 2, 2004, La Jolla, California. U.S. Dept. Commer., NOAA Tech. 

Memo. NMFS-SWFSC-363. 

71
Rice, D. W. 1998. Marine mammals of the world. Systematics and distribution. Allen Press, Lawrence, 

KS. 

Richardson, S. D. 2003. Water analysis: Emerging contaminants and current issues. Anal. Chem. 

75(12):2831–2857. 

Richardson, W. J., C. R. Greene, C. I. Malme, and D. H. Thomson. 1995. Marine mammals and noise. 

Academic Press, San Diego, CA. 

Ross, P. S., G. M. Ellis, M. G. Ikonomou, L. G. Barrett-Lennard, and R. F. Addison. 2000. High PCB 

concentrations in free-ranging Pacific killer whales, Orcinus orca: Effects of age, sex ,and dietary

preference. Mar. Pollut. Bull. 40(6):504–515. 

Sanford, B. Unpubl. data. Data attached to e-mail dated May 2004 to M. B. Hanson. (Available from 

M. B. Hanson, NWFSC, 2725 Montlake Blvd. East, Seattle, WA 98112.) 

Schnoor, J. L. 2003. Emerging chemical contaminants. Environ. Sci. Technol. 37(21):375A. 

Simon Fraser Univ. 1998. Thompson River steelhead: A resource in crisis? Online at 

http://www.sfu.ca/cstudies/science/salmon/thompson.pdf [accessed 14 October 2004]. 

Slatkin, M. 1985. Rare alleles as indicators of gene flow. Evolution 39:53–65. 

Stevens, T. A., D. A. Duffield, E. D. Asper, K. G. Hewlett, A. Bolz, L. J. Gage, and G. D. Bossart. 1989. 

Preliminary findings of restriction fragment differences in mitochondrial DNA among killer 

whales (Orcinus orca). Can. J. Zool. 67:2592–2595.

Stout, H., R. G. Gustafson, W. H. Lenarz, B. B. McCain, D. M. V. Doornik, T. L. Builder, and R. D. 

Methot. 2001. Status review of Pacific herring (Clupea pallasi) in Puget Sound, Washington.

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-45. 

Taylor, M., and B. Plater. 2001. Population viability analysis for the Southern Resident population of the 

killer whale (Orcinus orca). The Center for Biological Diversity, Tucson, AZ. 

Thiesfeld, S. Unpubl. data. Data attached to e-mail dated November 2004 to M. B. Hanson. (Available 

from M. B. Hanson, NWFSC, 2725 Montlake Blvd. East, Seattle, WA 98112.) 

USFWS and NMFS (U.S. Fish and Wildlife Service and National Marine Fisheries Service). 1996. 

Policy regarding the recognition of distinct vertebrate population segments under the Endangered 

Species Act. Federal Register [Docket I.D. fr07fe96-107, 7 February 1996] 61:4722. 

Vanderford, B. J., R. A. Pearson, D. J. Rexing, and S. A. Snyder. 2003. Analysis of endocrine 

disruptors, pharmaceuticals, and personal care products in water using liquid 

chromatography/tandem mass spectrometry. Anal. Chem. 75(22):6265–6274. 

Visser, I. N. 2000. Variation in eye-patch shape of killer whales (Orcinus orca) in New Zealand waters. 

Mar. Mamm. Sci. 16(2):459–69. 

Wade, P. R. Unpubl. data. Field observations. (Available from P. R. Wade, AFSC, 7600 Sand Point

Way NE, Seattle, WA 98115.) 

Waples, R., and P. Clapham. 2004. Appendix 6: Report of the Working Group on Killer Whales as a 

Case Study. In R. R. Reeves, W. F. Perrin, B. L. Taylor, C. S. Baker, and S. L. Mesnick (eds.), 

72
Report of the Workshop on Shortcomings of Cetacean Taxonomy in Relation to Needs of 

Conservation and Management, April 30–May 2, 2004, La Jolla, California, p. 62–73. U.S. Dept. 

Commer., NOAA Tech. Memo. NMFS-SWFSC-363. 

WDFW (Washington Dept. Fish and Wildlife). 2002. 1999–01 Biennial Report. Washington Dept. Fish 

and Wildlife, Olympia. 

WDFW and ODFW (Washington Dept. Fish and Wildlife and Oregon Dept. Fish and Wildlife). 2001. 

Status report: Columbia River fish runs and fisheries, 1938–2000. Washington Dept. Fish and 

Wildlife and Oregon Dept. Fish and Wildlife, Olympia, WA, and Clackamas, OR. 

WDFW (Washington Dept. Fish and Wildlife). No date. Chum salmon. Online at 

http://www.wdfw.wa.gov/fish/chum/ [accessed 27 September 2004].

Weitkamp, L. A., T. C. Wainwright, G. J. Bryant, G. B. Milner, D. J. Teel, R. G. Kope, and R. S. Waples. 

1995. Status review of coho salmon from Washington, Oregon, and California. U.S. Dept. 

Commer., NOAA Tech. Memo. NMFS-NWFSC-24. 

White, B. Unpubl. data. Data attached to email dated 29 August 2003 from Rich Lincoln to Gary Wiles. 

(Available from B. White, Pacific Salmon Commission, 600–1155 Robson St., Vancouver, BC, 

Canada V6E 1B5.) 

White, G. C., and K. P. Burnham. 1999. Program MARK: Survival estimation from populations of 

marked animals. Bird Study 46(Suppl.):120–138. 

Wiles, G. J. 2004. Washington State status report for the killer whale. Washington Dept. Fish and 

Wildlife, Olympia. 

Williams, R., D. E. Bain, J. K. B. Ford, and A. W. Trites. 2002b. Behavioural responses of male killer 

whales to a “leapfrogging” vessel. J. Cetacean Res. Manage. 4:305–310. 

Williams, R., A. W. Trites, and D. E. Bain. 2002a. Behavioural responses of killer whales (Orcinus 

orca) to whale-watching boats: Opportunistic observations and experimental approaches. J. Zool. 

256:255–270.

Winston, J. E. 1999. Describing species. Columbia University Press, New York. 

Wydoski, R. S., and R. R. Whitney. 2003. Inland fishes of Washington. 2nd edition. University of 

Washington Press, Seattle. 

Yano, K., and M. E. Dahlheim. 1995. Killer whale (Orcinus orca) depredation on long-line catches of 

bottomfish in the southeastern Bering Sea and adjacent waters. Fish. Bull. 93:355–373. 

Ylitalo, G. M. Unpubl. data. (Available from G. M. Ylitalo, NWFSC, 2725 Mountlake Blvd. East, 

Seattle, WA 98112.) 

Yoshiyama, R. M., F. W. Fisher, and P. B. Moyle. 1998. Historical abundance and decline of Chinook 

salmon in the Central Valley region of California. N. Am. J. Fish. Manage. 18(3):487–521. 

73

Most NOAA Technical Memorandums NMFS-NWFSC are available online at the

Northwest Fisheries Science Center web site (http://www.nwfsc.noaa.gov).

Recent NOAA Technical Memorandums NMFS

published by the

Northwest Fisheries Science Center

NOAA Tech. Memo.

NMFS-NWFSC61 Berejikian, B.A., and M.J. Ford. 2004. Review of relative fitness of hatchery and natural salmon. U.S.

Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-61, 28 p. NTIS number pending.

60 Ford, M.J., T.A. Lundrigan, and P.C. Moran. 2004. Population genetics of Entiat River spring Chinook

salmon. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-60, 45 p. NTIS PB2004-107039.

59 Sloan, C.A., D.W. Brown, R.W. Pearce, R.H. Boyer, J.L. Bolton, D.G. Burrows, D.P. Herman, and

M.M. Krahn. 2004. Extraction, cleanup, and gas chromatography/mass spectrometry analysis of

sediments and tissues for organic contaminants. U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-59, 47 p. NTIS PB2004-105739.

58 Beechie, T.J., E.A. Steel, P. Roni, and E. Quimby (editors). 2003. Ecosystem recovery planning for

listed salmon: an integrated assessment approach for salmon habitat. U.S. Dept. Commer., NOAA Tech.

Memo. NMFS-NWFSC-58, 183 p. NTIS PB2004-105734.

57 Rogers, J.B. 2003. Species allocation of Sebastes and Sebastolobus sp. caught by foreign

countries from 1965 through 1976 off Washington, Oregon, and California, USA. U.S. Dept. Commer.,

NOAA Tech. Memo. NMFS-NWFSC-57, 117 p. NTIS PB2004-105737.

56 MacCall, A.D., and T.C. Wainwright (editors). 2003. Assessing extinction risk for West Coast salmon.

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-56, 198 p. NTIS PB2003-104642.

55 Builder Ramsey, T., et al. 2002. The 1999 Northwest Fisheries Science Center Pacific West Coast upper

continental slope trawl survey of groundfish resources off Washington, Oregon, and California. U.S. Dept.

Commer., NOAA Tech. Memo. NMFS-NWFSC-55, 143 p. NTIS PB2003-104641.

54 Krahn, M.M., et al. 2002. Status review of Southern Resident killer whales (Orcinus orca) under the

Endangered Species Act. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-54, 133 p. NTIS

PB2003-104520.

53 Waknitz, F.W., T.J. Tynan, C.E. Nash, R.N. Iwamoto, and L.G. Rutter. 2002. Review of potential

impacts of Atlantic salmon culture on Puget Sound chinook salmon and Hood Canal summer-run chum

salmon evolutionarily significant units. U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-53,

83 p. NTIS PB2002-108143.

52 Meador, J.P., T.K. Collier, and J.E. Stein. 2001. Determination of a tissue and sediment threshold for

tributyltin (TBT) to protect prey species of juvenile salmonids listed under the Endangered Species Act.

U.S. Dept. Commer., NOAA Tech. Memo. NMFS-NWFSC-52, 21 p. NTIS PB2002-103161.