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INTRODUCTION
The easily recognizable “killer whale” is known throughout the world. With its large size
and distinctive black and white markings it is hard to miss. Displayed in aqua parks such
as Sea World, they have quickly replaced dolphins as the main attraction. With the name
“killer whale”, their massive build and ferocious looking teeth they elicit a perverse
fascination, especially when it appears these fearsome beasts have been tamed to perform
like our pets. The reality is somewhat different. Our knowledge of these intelligent
creatures is extremely limited. It should be noted that the killer whale is not the maniacal
killer its name implies. There are no reported attacks by a killer whale upon a human.
The name "killer whale" arose from their predation on other whales and dolphins. Early
Spanish whalers referred to it as the "whale killer". Through time, this has been
transposed to killer whale (Poncelet internet site, The Marine Mammal Center internet
site). Their intelligence has been ranked extremely high, comparable to the bottlenose
dolphin. In fact, the killer whale or orca, is the largest of the dolphin family
(Delphinidae) and a member of the toothed whale (Odontoceti) suborder. The orca is
found in all of the world’s oceans, but most often in the colder waters rather than the
tropics and subtropics. It is considered the most widely distributed marine mammal in
the world. This raises the question, are all of the world’s orcas the same species? Can
different species evolve even in the same geographical area? This paper reviews the
available literature studying the orca populations that inhabit the Pacific Northwest and
will explore the possibility that the orca is more than the one species (“Orcinus orca”)
recognized in the scientific community today.
Physical Characteristics
Orcas are characterized by a robust, heavy body with a rounded head that tapers to a
point. Their teeth are large, sharp and conical with interlocking, massive jaws that are
used to seize prey and, on occasion, tear flesh from their prey. Their skin is black on the
back and sides with white undersides, with a white patch extending up the mid flanks and
an elliptical white patch behind each eye. A gray patch over the back, behind the dorsal
fin is variable in shape and is called a “saddle patch”. Their flippers are paddle shaped
and grow with age, up to one-fifth of the body length on older adult males. Adult males
range in size from 22 – 31 feet long and weigh between 8,800 – 9,920 pounds. The adult
females range from 20 – 27 feet long and weigh between 5,500 – 6,600 pounds. The
dorsal fin is located slightly forward of center and on females or juveniles it is sickle–
shaped and approximately two feet high. On the adult males however, the dorsal fin is
one of their most distinct features, standing up to six feet (1.8 meters) tall, with a
somewhat triangular shape (Carwindine, 1995; Bateman, 1984). Females attain adult size
at about 10 years and give birth to their first calf at around age 15 (Bigg, 1990). It is
believed that in order to prevent inbreeding, cross pod mating occurs (Heimlich-Boran,
1990). The females become reproductively senescent at approximately 40 years of age
although they can live to be as old as 80 – 90 years (Bigg, 1990). Gestation is believed to
be about 15 - 16 months. The birth rate has been estimated at 9.5 % per year. With the
very low observed death rate the populations tend to remain quite stable (Bigg, 1980).
Males are larger and reach the size of younger adult female by 8 years of age, at which
time they are most likely sexually mature. Their dorsal fins are much larger and it
continues to grow until about 21 years of age. Male orcas can live for 50 – 60 years
(Bigg, 1990). Orcas have no known natural predators.
Social Organization
The social organization of the orca centers on the female (Hoelzel, 1993). A matrilineal
group is the foundation, or basic unit of orcas, and consists of a female and her offspring.
Even though females make up the hierarchy of social structure, males traditionally stay
with their mothers throughout their lives — a trait unique to mammalian social systems.
Occasionally, males have been sighted to stray from their groups into another group,
possibly for mating reasons, which helps to avoid inbreeding. Orca social structure is
broken into a series of progressively smaller groups. The largest aggregation is called a
“community” or sometimes referred to as a “super pod”. A “community” is defined as a
group of individuals that live in the same area and associate periodically with each other.
A “clan” consists of pods with vocal dialects that are related to one another. The next
smaller grouping is called a “pod”. A “pod” is defined as a cohesive group of individuals
within a community, that, for the majority of time travel together. The pods are usually
family groups based on maternal bonds. The “subpod” is the next smaller grouping and
is defined as a group of individuals from the same pod that break into a smaller stable
group. A subpod can either form for a short period of time (less than a month) or are
often formed when daughters in a pod have their own offspring and form new maternal
groups (Bigg, 1990). Subpods may grow into a new pod. The last and smallest grouping
is called a “intra-pod” group, and is defined as a discrete and very cohesive group within
the sub-pod, that travels together. Individuals are rarely separated from its intra-pod
group for more than a few hours.
Feeding Strategies
The orca has gained notoriety for its predation on other marine mammals, but
observations and inspection of stomach contents indicate that they feed on a wide array of
marine vertebrates and invertebrates, including many species of whales, dolphins and
porpoises, fish, sea turtles, birds and cephalopods. A list of known prey was compiled in
1984 and included 24 species of cetaceans (whale & dolphins), 14 species of pinnipeds
(seals), 31 species of fish, 9 species of birds, 2 species of cephalopods, 1 species of turtle
and 1 species of otter (Fellerman, 1991). The orca feeding strategies appear to be
opportunistic in that they vary their diet in response to the availability of prey, but are
selective in the prey that they seek. (Fellerman 1991) Several studies hypothesize that
they may specialize on a preferred prey for a given location, even shifting prey
preferences in response to seasonal variations in prey availability and density.
(Heimlich-Boran, 1988, Baird, 1995) It has been documented that orcas move through
their range in response to seasonal prey. Cooperation among the orcas is almost always
evident and sharing prey will sometimes occur, depending on what type of prey was
captured. It is also believed and supported by observations that foraging strategies are
learned behaviors and the knowledge is passed from mother to her offspring.
Vocalizations
Orcas have very distinct and complex methods of communicating. Two types of
underwater vocalizations have been identified, echolocation and communication (Bigg,
1987). For echolocation, orcas produce a series of short clicking sounds from air sacks in
the nasal passages. The sound waves travel through the water, bounce off the
surrounding objects, are received by receptors in the lower jaw and conducted to the
inner ear. From the ear they then sent to the brain through the auditory nerve. It is
assumed that orcas can determine distance, movement and speed of objects, if not
identity of organisms in the water. It has been shown that dolphins use this echolocation
to detect food sources. They have the ability to estimate the size of fish and perhaps the
species of fish they are chasing (Dolphin Research Center, personal communication).
Communication sounds are used for social contact within and between groups of whales.
Whistles and variable calls, such as squeaks, squawks, and screams, seem to be used
when orca groups are socializing. Orcas also produce “discrete calls”, which sound the
same each time they are used. Discrete calls are of particular interest because it has been
shown that each group of orcas (of the same matriarchal lineage) usually produce a
specific number and type of these calls which are unique to and make up each group's
dialect. It appears that the dialect is learned and retained by the individuals of the
population. Distinctive dialects are used to recognize particular groups of whales and the
relationships between groups and populations (Bigg, 1987). It is interesting to note that
while human language and dialect occur through geographical isolation, orcas seem to
develop theirs through social isolation (Bigg, 1987).
Study Area
An area that has several populations of orcas that have been thoroughly evaluated is the
area of the coastal waters and the Pacific Ocean along the border of the United States
(Washington State) and Canada (British Columbia) lying between 47° N and 51° N
latitudes. The region has a varied bottom profile with an average depth of 100 to 150
meters. Two high and low tides and an average current speed of approximately 50
cm/sec characterize the area. Salmon is abundant in the area during its migration period
of June through September. Several other fish, including steelhead and cutthroat trout,
are found during the winter. Two species of marine mammals (which are also orca prey)
are found year round; the Dall’s and harbor porpoise with several others migrating
through. Harbor seals are resident year round with other pinnipeds occurring seasonally,
such as elephant seals and California and Stellar sea lions. (Fellerman 1991)
Study Area Population
Three distinct forms of orca occur in the study area, these are: the “resident” population;
the “transient” population; and the “offshore” population.
The resident population is the most abundant and most extensively studied. The residents
are divided into two nonoverlapping (“allopatric”) communities: the “northern” and
“southern” (see figure 1). The northern community, which ranges from the midpoint of
Vancouver Island, north to southeast Alaska, including the Queen Charlotte Islands,
contains approximately 16 pods with about 250 whales. The southern community
inhabits the inshore waters of southern half of Vancouver Island and Puget Sound and
totals approximately 100 orcas in 3 pods (Vancouver Aquarium internet site). See figure
1 below.
Figure 1
Pacific Northwest “Resident” Orca Distribution
The transient community travels throughout the range of both resident groups (making
the two groups sympatric), travelling as far south as northern California and as far north
as southeast Alaska. In the early 1990’s their population numbers were calculated to be
79 orcas in 30 pods (Fellerman 1991).
The offshore population was identified in 1991 when a field study led by Dr. John Ford
of the Vancouver Aquarium Marine Science Center identified 54 killer whales off the
Queen Charlotte Islands that did not match identification photos of any transients or
residents known in the Pacific Northwest. Offshore orcas tend to be seen in large groups
of 30 to 60 individuals, and are seldom seen in protected coastal waters. As of 1993,
about 200 offshore orcas have been identified in the Queen Charlotte Islands and
surrounding waters (Vancouver Aquarium internet site). Little is known about this
population of orcas.
REVIEW OF EVIDENCE
Taxonomy - Species vs. Subspecies
Taxonomy is “the theory and practice of classifying organisms” (Mayr, 1969). Ernst
Mayr defines “Species” as “groups of actually (or potentially) interbreeding natural
populations which are reproductively isolated from other such groups”. The first
indication that a separate species has evolved is usually provided by behavioral,
ecological or distributional data. The amount of differences among the group in
comparison to the differences between the groups is often evidence, or not, of separate
species status. However, better defining evidence for species status is based upon a
review of the area of sympatry of the species and observations of the evidence of
phenotypic (visible) differences. If the differences are not obvious enough to resolve all
doubt, Mayr recommends that it is preferable to treat the group as a subspecies. Phenetic
differences are only indicative and not usually determinative of species status. In
addition, according to Mayr, allopatric populations (a group of a species that inhabit
mutually exclusive but usually adjacent geographical areas) that are in contact but do not
interbreed (or do so occasionally) are to be treated as different species. The failure to
interbreed is indicative of reproductive isolation and therefore the classification of a
species (Mayr, 1969).
Orca Population Differences
I. Physical Differences
A. Dorsal Fin
The appearance and positioning of the dorsal fin differs between the resident and
transient orcas. The dorsal fins of the resident orcas in both communities tend to be
rounded and positioned over the posterior insertion of the fin to the back. The transient
dorsal fin is usually pointed and positioned in the center of the posterior and anterior
insertions of the fin (Baird 1988). The offshore orcas have physical characteristics more
similar to resident whales than to transients, with continuously rounded dorsal fins,
lacking the sharp angle at the rear corner (Vancouver Aquarium internet site). See figure
2.
Figure 2
Dorsal Fin & Saddle Patch Differences
B. Saddle Patch Pigmentation Pattern
A review of the saddle patch pattern, including its coloration, reveals interesting
differences between the resident and transient populations. Five types of saddle patch
patterns have been determined by the pigmentation line separating the upper saddle patch
and have been categorized for orcas. The types are: vertical notch; horizontal notch;
smooth; hook; and bump. All five types are found among resident populations. Patterns
were similar among resident pods but showed variation between the different
communities.
The transient orcas display only two pattern types and most
(approximately 90%) were the smooth pattern (Baird, 1988). The offshore populations’
saddle patch pattern variations have not been observed (Vancouver Aquarium internet
site). Baird and Stacey, the authors of the study, theorize that the patterns are inheritable
and that the differences in the patterns suggest genetic isolation of the populations (Baird
1988). See Figure 2.
II. Behavioral Differences
A. Pod Size and Dynamics
Both resident communities are organized around large pod size, typically 5 – 50
individuals (Baird 1988). The resident orca pod are extremely stable units. Since the
early 1970’s, observations of resident groups have shown no evidence of immigration or
dispersal (Hoelzel, 1993). The transients live in smaller, less stable pods, typically 1 to 7
individuals (Baird 1988). The smaller size seems related to their prey choice. The
greatest foraging efficiency in hunting marine mammals occurs with a group size of 3
orcas, which may explain why dispersal occurs in the transient population but not in the
resident population (Baird, 1990). The size, behavior, schooling tendencies and
distribution of prey seems to effect the size of the orca group by allowing the most
successful foraging strategy to evolve (Fellerman, 1990).
B. Diet
Diet is perhaps the most obvious aspect of orca behavior that distinguishes resident from
transient orcas. Residents are fish-eating whales, coordinating their movements
throughout the year with migrating salmon (Oncorhynchus spp.) routes, which constitutes
90% of their prey. They also eat halibut, herring, hake, lingcod, rockfish and herring
(Baird, 1992, Bigg, 1987). There are only a few instances of residents eating marine
mammals. The resident orcas appear to use the bathymetry of the area as barriers to aid
in the collection of fish. They also exhibit loosely coordinated prey searching and,
perhaps, herding (Heimlich-Boran, 1988). However, the capture of the prey is
undertaken individually.
Transients’ principal prey are marine mammals, especially harbor seals (Phoca vitulina),
but also the elephant seal (Mirounga angustirostris), the Steller sea lion (Eumetopias
jubatus) and the California sea lion (Zalophus californianus). They may also eat some
fish, although this has not been observed (Bigg, 1987). The northern fur seal
(Callorhinus ursinus), which inhabits the subject area has not been recorded as prey, but
the possibility exists as it is known that orcas in Alaska feed on them (Baird, 1992). The
transients also feed upon porpoises, especially the Dall’s porpoise (Phocoenoides dalli)
and the harbor porpoise (Phocoena phocoena) (Baird, 1992, Bigg, 1987). Coordinated
attacks were usually observed and prey sharing occurred at more than half of the kills,
with active prey division or transfers occurring on several occasions (Baird, 1995).
It is believed than the offshore population feeds on the schools of fish found offshore,
principally salmon, like the residents, but this has not been confirmed (Vancouver
Aquarium internet site).
C. Travel and Foraging Patterns
As stated above there are obvious group size differences between the residents and
transients. It is believed that these developed in response to the ability to capture and
share prey. Resident orcas can herd, corral and take fish with a large group and the
capture of a fish by any individual does not effect the ability of the group or any
individual to capture another fish. Also, residents use echolocation to locate and capture
fish. Emitting these sounds does not seem to alert the fish and diminish the chances of
capture. . Residents therefore maximize their group size and are not concerned with
being detected by their prey.
Transients eat primarily seals, which due their size and agility need extensive handling to
be subdued, the capture of one limits the ability to capture subsequent prey. Seals are
extremely aware of their environment and are able to detect noises and movements and
take evasive action. Therefore, the transients are largely silent when hunting, even
modifying their respiratory rate and amplitude to avoid detection and limit their group
size in response to the number needed to capture the prey (Baird, 1992).
Resident orcas tend to travel on predictable routes, along the middle of the channels and
into the current. They have a consistent dive pattern of 3 – 4 short dives of about 15
seconds, followed by a longer 3 – 4 minute dive, whereas the transients often remain
underwater for longer periods of time. The travel patterns of the transient orcas covers a
wide range and is often unpredictable, changing travel direction suddenly even when
seemingly not in search of prey. They are found primarily around seal haulout sites or in
open water. Also, they tend to enter small bays not entered by resident orcas (Baird,
1995). See figure 3 below.
Although sympatric, resident and transient pods have not been seen travelling together, in
fact it has been observed that transients will change course and direction when within 100
meters of a resident group. It is believed that due to the transients being “silent” feeders
they usually detect the resident orcas, which vocalize frequently, before they are detected
themselves (Baird, 1995, Bigg, 1987). On one occasion a group of resident orcas was
observed attacking and chasing a group of transients (Baird, 1995).
Figure 3
Orca Travel Routes
(Green = resident pod,
Red = transient pod)
(Scheel, David, Prince William Sound Science Center internet site)
D. Acoustical Differences
Residents use echolocation to aid in foraging and constantly use communication sounds.
Transients, on the other hand are usually silent while hunting so as not to be detected by
their prey (Fellerman, 1991). They produce sounds infrequently and have a much smaller
repertoire of discrete sounds, as discussed below (Ford, 1990).
1. Dialects and Communication
The distinctive dialects, show that residents may have a repertoire of up to 17 calls used
for everything from contact signals to coordinating group behavior, whereas transients
produce only 4 to 7 calls (Ford, 1990). While all transients share the same dialect, the
southern and northern residents are grouped into four distinct dialect groups. Offshore
groups have a completely different dialect, seemingly unrelated to that of any resident or
transient pod previously recorded on the British Columbia coast. This seems to support
the contention that it is a completely distinct population (Vancouver Aquarium internet
site).
E. Genetic Differences
Of the studies performed on the orca populations there are indications that there is a
significant level of genetic differentiation (Hoelzel, 1998). The greatest genetic
difference was between the resident and transient groups, while the two resident
communities had only a slight difference between them. Interestingly, samples from
three whales from a known offshore community shared the same genetic make-up as the
southern resident orcas. The limited genetic variation within the resident and transient
populations indicates that mating occurs primarily within the individual populations. The
authors of this study suggest that the genetic differentiation evolved by behavioral
isolation based on different foraging strategies (Hoelzel, 1998).
CONCLUSIONS
Only one species of Orca is presently recognized by the scientific community, however,
several localized orca groups have been documented as having different behavioral,
physical and other biological traits (Bigg, 1987). Throughout history scientists have
attempted to convince the scientific community to designate new species of orcas. Most
recently Russian scientists had proposed a second orca species, Orcinus glacialis, for a
group of Antarctic orcas, but this designation has not been accepted. The Orcinus
glacialis orcas seem much the same as the resident populations of the Pacific Northwest
(Heimlich-Boran, 1988). The documented differences between the resident and transient
orcas suggest that despite their being sympatric, these groups have been reproductively
isolated for a long time (Bigg, 1987). One explanation of this separation of groups could
be human presence, exploitation and interaction with the orcas. Evidence collected thus
far seems to indicate that while human presence does occasionally affect the foraging and
socializing of orcas (Kruse, 1991), especially the transient groups, the impact seems
minimal (Baird, 1995). In fact the “southern” resident population has increased their use
of the Haro Strait in spite of an increase in commercial boat traffic (Baird, 1995). This
suggests that human interaction has not negatively the orcas.
The more realistic theory is the resources of the area were divided among the same
species and that in becoming more prey-specific, morphological differences evolved.
Rather than both being generalists that competed with each other, this partitioning of the
resources is mutually beneficial to the existence of both groups (Baird, 1992).
As different foraging tactics developed in response to different prey and their
accompanying variations in size, habits and habitat, the orcas developed different
behavioral strategies. Each orca group adjusted its group size and composition, and
developed physical adaptations. No specific explanation for the physical changes
(differences in dorsal fins size, saddle patch patterns and coloration or body size), have
been given although it appears clear that such is due to genetic transfer within the
communities, which seems to be supported by the genetic studies done to date. One
study seems to point to the conclusion that such changes evolved due to the different
foraging strategies and they are adaptations to make those strategies more efficient and
successful. In this study indications were found that differences in the thickness of the
area of attachment of the jaw might have developed in a group of Antarctic orcas. The
importance of this variation is that it might be an adaptation reflecting the need to
increase the thickness (the strength) of the bone to withstand the forceful movements of a
large prey, or decrease the thickness to enhance the reception of sound for echolocation
(Baird, 1992).
These behavioral and physical changes seem to have lead to differences in reproductive
strategies, which then leads to reproductive isolation (Hoelzel, 1998). As Mayr indicated,
the failure to interbreed is indicative of reproductive isolation and therefore the
classification of a species (Mayr, 1969). The genetic data seems to support this.
Examining the definition of “species” stated above, in conjunction with the number of
significant differences found between the resident and transient orca groups, such as
differences in: diet; foraging behaviors and group dynamics; differences in saddle patch
and dorsal fin shapes; vocalizations and dialects; and genetics, the evidence seems
overwhelming. These differences taken in comparison to the differences between the
individuals of a particular orca community show that there is definite evidence of
separate species status.
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Baird, Robin William and Stacey, Pam Joyce, (1988). Variation in saddle patch
pigmentation of killer whales (Orcinus orca) from British Columbia, Alaska, and
Washington State. Can. J. Zool. 66:2582 - 2585
Baird, Robin W., Lawrence M. Dill and Pam Joyce Stacey, (1990). Group Size-Specific
Foraging Efficiency in Transient Killer Whales (Orcinus orca) Around Southern
Vancouver Island. In: Abstracts of the Third International Orca Symposium, March
1990, Victoria, B.C. p.3
Baird, Robin W., Peter A. Abrams, and Lawrence M. Dill (1992). Possible indirect
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foraging specializations in the genus Orcinus. Oecologia 89: 125 - 132
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killer whales: seasonal and pod-specific variability, foraging behaviour, and prey
handling. Can. J. Zool. 73: 1300 - 1311.
Bateman (Project Editor) 1984. Sea Mammals, All The World’s Animals Series, Tostar
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Bigg, M.A. (1980). The life cycle of killer whale pods in British Columbia. Orca
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Columbia and Washington State. Phantom Press & Publishers, Inc., Nanaimo, British
Columbia, Canada 79 pp.
Carwardine, Mark, (1995). Whales Dolphins and Porpoises, DK Publishing, Inc. 1995,
pp. 152 – 155.
Fellerman, Fred and Elizabeth Miller (1990). Ecological Influences on Group Size in
Killer Whales (Orcinus orca). In: Abstracts of the Third International Orca Symposium,
March 1990, Victoria, B.C. p.6
Fellerman, F.L., Heimlich_Boran, J.R., and Osborne, R.W. (1991). The feeding ecology
of killer whales(Orcinus orca) in the Pacific Northwest. In Dolphin societies –
discoveries and puzzles. Edited by K. Pryor and K.S. Norris. University of California
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Heimlich-Boran, (1988). Behavioral ecology of killer whales (Orcinus orca) in the
Pacific Northwest. Can. J. Zool. 66:565 – 578.
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Hoelzel, A.R., M. Dahlheim, and S. J. Stern (1998). Low Genetic Variation among Killer
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INTERNET SITES
The Marine Mammal Center internet site (http://www.tmmc.org/orca.htm)
Poncelet, Eric. Killer Whale Biology internet site
(http://orca.citeweb.net/contents.htm#classification)
Vancouver Aquarium internet site (http://www.vancouver-aquarium.org)
Scheel, David, Prince William Sound Science Center
(http://www.pwssc.gen.ak.us/~dls/kw/kwfeed.html)