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INTRODUCTION
The feeding behavior and diets of orcas (Orcinus orca) have been described in numerous
scientific and popular literature. The first view of the diet of killer whales’ came from an
animal stranded in Denmark in the 1800s. The stomach content analysis showed the
primary prey to be marine mammals (Baird, 2002). This led to the thought that all orcas
were voracious hunters. The misconception that orcas are “killer” whales that only feed
only on other marine mammals has since been disproved. Martinez and Klinghammer
(1970) were the first to attempt to describe orca foraging behavior by reviewing the
literature current at that time. They described various prey species and cooperative
hunting. Since then, several long-term studies have emerged. The past 30 years of
research are revealing that orcas, which inhabit all the worlds oceans, are divided into
distinct populations specializing on particular prey that differ among populations.
Since the initial studies on wild orcas in the Northeastern Pacific Ocean (Bigg
1982, Bigg et al 1987), other similar studies have taken place and group specific prey
specializations are being documented worldwide. While Bigg and his colleagues (1987)
classified two discrete orca populations in British Columbia and Washington State
waters, the transients (or marine mammal eating orcas) and the residents (or fish eating
orcas), other populations have not been classified as such. While the type of prey
consumed depends largely upon the type of killer whale, many other geographic groups
seem to be solely fish eating populations. In Russia, the primary prey has been identified
as fish, primarily herring, mackerel and salmon (Tarasyan et al., 2002). In the Northeast
Atlantic, killer whale diets primarily consist of herring (Jonsgard 1970, Simila 1997). In
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Gibraltar Strait, killer whales have been feeding on tuna from the local fishery’s long
lines (de Stephanis et al., 2002). However, there has been documentation of mixed diets.
A population in the Northeastern Pacific Ocean, identified as “offshore” orcas, is thought
to feed on telost fish and elasmobranchs (Bain, pers.comm.). In Argentina, Brazil, the
Crozet Islands, New Zealand and Norway (one group) there has been documentation of a
mixed diet of both fish and marine mammals (Lopez et al. 1985, Guinet 1991, Guinet et
al. 1997, Simila 1997). There has also been documentation of orcas feeding on pelagic
sharks, 9 species of birds, 2 species of cephalopods, 1 species of turtle (Hoyt, 1984), 20
species of cetaceans 14 species of pinnepeds, dugongs (Nishiwaki et al. 1958, Jefferson
et al. 1991) and sea otters (Jefferson et al. 1991, Estes et al. 1998). While further research
is clearly warranted to determine killer whales year round diets, it has long been clear that
fish are important prey for many different populations of killer whales.
A clear benefit of specializing on a certain type of prey is the ability to refine
foraging skills. However, the costs of being a specialist may outweigh the benefits if they
are not able to adapt quickly enough to changing prey resources. Distribution of prey
resources will have strong effects on the gains and costs of foraging (Tiselius et al. 1993).
If the cost of searching for another type of prey is greater energy expenditure and the
predator population already has additional stressors on it, it will clearly result in a decline
in the predator population.
Stephen and Kreb’s (1986) foraging and optimality models address such issues as
“constraint assumptions”. They further describe these constraints as extrinsic and
intrinsic. An extrinsic constraint is one that is put on the animal by its environment.
Intrinsic constraints are limitations in the ability and tolerances of the animals. From the
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available evidence, limitations on orca diving depths (an intrinsic constraint) are
probably of little concern (Simila 1997, Baird et al. 1998, Baird 2002, Baird et al. 2003).
However, search time at certain depths may be a physiological limitation. The longer an
orca is required to hold its breath at certain depths while searching for prey, may affect
their ability to locate prey. Handling time, or the amount of time it takes for an orca to
catch and consume its prey, will also be a factor. The longest recorded dive for a marinemammal eating killer whale in the Pacific Northwest was seventeen minutes (Erickson,
1978). Less than 20 of 1365 dives exceeded 11 minutes his study. Thus, extrinsic
constraints, such as the availability and spatial distribution of prey, may be essential to
killer whale populations. Since many groups may specialize on certain types of prey and
because of a downward trend in abundance of many marine species worldwide (e.g.
Megrey 1991, Estes et al. 1998, Hutchings 2001, Greenwood et al. 2002, Trites et al.
2003, Kesser et al., 2003), knowledge of orcas’ diets is becoming increasingly important.
Further, Stephen and Kreb’s describe “decision assumptions” that the animal is assumed
to make (or natural selection has made for it). These “decisions” may either limit a
predator to one type of prey or cause an animal to change to another prey source if its
primary resources are limited. In considering these decision assumptions, further
attention should be warranted to the viability of many orca populations worldwide and/or
effects that may occur on ecological levels because of these whales altering their prey.
In the Pacific Northwest, an analysis by Ford et al. (1998) showed that salmoneating Pacific Northwest killer whales chose chinook (Oncorhynchus tshawytscha) even
in areas where pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon
were abundant. Chinook, however, have seen the greatest decline in wild salmon
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populations. Conversely, western Alaska marine-mammal eating killer whales are
expanding their diets to include sea otters because of a precipitous decline in pinneped
numbers across the western North Pacific (Estes et al. 1998). This study showed that as
few as 3.7 killer whales could have caused the 25-76% decline in sea otter populations
observed since the 1990’s. Because their prey base has been altered, many ecosystem
changes, such as freeing urchin populations from sea otter predation resulting in
overgrazing on kelp forests, are being documented in western Alaskan marine habitats.
Concern is warranted, not only based on orca conservation, but based on larger
ecological issues. In the present study, the hypothesis is that a Pacific Northwest
population of orcas is being affected by the spatial and temporal dynamics of its declining
prey base.
Case Study-The Southern Resident Community
The fish-eating (or resident) populations in the waters of British Columbia and
Washington State have been studied since the 1970’s and are some of the most well
known killer whales worldwide. Many studies have revealed information concerning
genetics, foraging behavior, preferred prey, toxicology and genealogy (e.g. Bigg et al.
1987, Ford et al. 1998, Ross et al. 2000, Barrett-Lenard 2000). Because of previous data,
these whales provide a unique opportunity to address long-term issues, build on previous
data and provide framework for other studies that may be applied to killer whale
populations worldwide.
These whales have been divided into two distinct groups: the Northern Resident
Community and the Southern Resident Community. The Northern Residents are found
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primarily north of central Vancouver up to Southeast Alaska. The Southern Residents,
the focus of this thesis, are found primarily south of central Vancouver Island and
throughout the inland and coastal waters of Washington (Figure 1) from May through
October. This population is divided into 3 distinct pods, J, K and L pods.
Figure 1. Typical Range of the Southern Resident Community Orcas
from May through October. Arrows show typical whale routes.
Map by Jones Maps & Diagrams, LTD. Ladner, B.C.
The Southern Residents primary prey from May through October is most likely
salmon (Balcomb et al. 1979, Fellemen 1986, Heimlich Boran 1986, Bigg et al.1987,
Hoezel 1993 , Ford et al. 1998). Correlations of salmon abundance with whale presence
have been well documented (Heimlich-Boran 1986, Nichol et al. 1996). Fraser River
salmon may provide much of the Southern Residents’ diets through out the spring and
summer (Heimlich-Boran, 1986) and there is a high correlation of whale presence with
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runs of chum salmon (Oncorhynchus keta) in the fall (Osborne, 1999). Winter foraging
areas have not been researched with the exception of one sonar sample described in this
thesis.
Because of a decrease in salmon populations (e.g. Nehlsen et al. 1991, Hare et al.
1999, NOAA 2000, State of Wa. Salmon Recovery Office 2002, Pacific Salmon
Commission 2003) it has been suggested that Southern Resident orcas are foraging for
different types of prey or increasing their search area (Black et al. 2002, Balcomb
pers.comm.). Recently, the Southern Residents have been seen as far south as Monterey
Bay, California (Center for Whale Research, 1998, 2002). Even though this population
has been continuously observed since the 1970s, it is not known if the Monterey Bay
“trips” are rare occurrences. While large groups of orcas have been seen off the coast of
California (Dohl et al., 1983), these two documented events of Southern Residents as far
south as California are the only verified occurrences in the last 30 years. This is a
distance of over 1200 km from their known summer range. They were also spotted in the
Queen Charlotte Islands, B.C in 2002, a known range for Northern Residents but not for
Southern Residents (Center for Whale Research, 2003). In addition, they have been
observed in the inland waters of Puget Sound on a more frequent basis during the winter
months (December and January) in the last few years (Center for Whale Research, 2003).
Population Decline
The population of Southern Residents has seen significant declines (20%) in
recent years (Krahn et al. 2002, Baird 2001, Wade et al. 2000). The population as of
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December 2003 is 84 whales, down from a peak of 96 whales in 1995. This current
number does not include a three-year-old calf that has been separated from L-Pod and is
inhabiting a bay in Canada. While the population has increased from 78 to 84 over the
past two years, historically a population decline like the one observed from 1996 to 2001
has never been seen except when many of the whales were captured for the marine
aquarium industry. There are three main hypotheses for the decline: 1) the loss of
primary prey; 2) immunosuppression and reproductive impairment due to high levels of
polychlorinated biphenyls (PCB’s) and other toxins; and 3) acoustic disturbances of
various kinds associated with vessel traffic. These hypotheses are not mutually
exclusive of one another. The latter is not thought to be directly related to deaths of any
individuals although one recent study has shown a correlation between the population
decrease and the number of whale watch vessels from 1991 to 2000 (Bain et al. 2003,
submitted for publication). However, the authors recognize that this may not be a causal
relationship and that other variables must be recognized. Alternatively, the hypothesis
that the decline is due to the loss of primary prey with the combination of the deleterious
effects of polychlorinated biphenyls may be of great concern for the conservation of these
whales (Reijnders 1994, O'Niell et al. 1998, Ross et al. 2000, Ylatalo et al. 2001, Ross et
al. 2002, Balcomb pers.comm.). Under the assumption that population declines continue
like the one observed from 1996 through 2001, a population viability analysis has
predicted the probability of extinction to be 86-98% in 300 years (Krahn et al. 2002).
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Salmon Prey Availability, Distribution and Requirements
Availability
From current and past research, salmon resources may provide the best estimate
of prey availability for the Southern Resident Community. Salmon are found throughout
the year in the inland waters of Washington and British Columbia. Unfortunately, all five
salmon species that spawn in regional waters have seen a downward trend in abundance
since the 1980’s (Nehlsen et al. 1991, Hare et al. 1999, State Washington’s Salmon
Governor’s Report 2002, Pacific Salmon Commission 2003). From Washington to
California there are two stocks of chinook and one stock of sockeye that are endangered.
In addition, 8 stocks of chinook, 5 stocks of coho (Oncorhynchus kisutch), 2 stocks of
chum (Oncorhynchus keta) and one stock of sockeye (Oncorhynchus nerka) are
threatened or candidates for listing (NOAA, 2000). There is no estimate of the total
number of stocks that could be available to the Southern Resident Community, although
the Fraser River stocks are probably of importance (Heimlich-Boran, 1986). Although the
Fraser River is the largest salmon producer in the world (Northcote et al. 1999), many of
these stocks have also seen declines (Pacific Salmon Commission, 2003). In addition,
Heimlich-Boran (1986) showed no correlation with Fraser River salmon catch estimates
(i.e. abundance) and killer whale presence.
Assessing the actual number of salmon available to the Southern Residents is
challenging because of a number of factors. While most west coast Pacific salmon have
declined significantly over the last 150 years, there is a lack of current, consistent and
uniform estimates of total stock sizes. Some data are based on both catch and
escapement estimates, while other data are based on only one of these to estimate total
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stock size. As well, catch estimates are from different sources including harvest data
from commercial , recreational, and tribal fisheries. Some studies include both wild and
fish hatchery fish, while others include only one type. In addition, many of the stock
estimates are based on a large geographic range and are not compatible with specific
groups of killer whales, such as the Southern Residents. Since the winter geographic
range of the Southern Residents is largely unknown and may be changing, estimating the
number of stocks that are available is further complicated. One estimate would likely
have to include all of the stocks associated with the Puget Sound. While fish hatcheries
and fishery managers have implemented “extended rearing programs” for chinook and
coho, theoretically increasing the number of salmon available (Weitkamp in Bain et al.
2002) and increasing harvest and escapement abundances in some instances (Bigler et al.,
1994), there is a lack of evidence that this is increasing the salmon available to the
Southern Residents. Compounding factors such as predation from other species, sports,
tribal and commercial fisheries and seasonal availability will have an affect on the whales
available prey.
Distribution
All salmon species except chum have their highest abundance in the inland
marine waters during summer and fall. Chums reach their maximum in October and
November in the Puget Sound. Excepting chinook, all salmon species tend to stay in the
upper 20 meters of the water column. Chinook fall and winter runs tend to occupy depths
of 30 to 80 meters while spring and summer runs tend to stay within 15 meters of the
surface (Candy et al., 1999). As salmon are returning from the Pacific to their natal
stream in the inland waters of Washington and British Columbia, they tend to concentrate
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and migrate toward their spawning river in consecutive waves that can last for days,
weeks or months. Resident stocks may also be available. Yet since the geographic
distribution of salmon is dynamic because of habitat loss, hatcheries and natural events,
determining specific stocks of importance to the Southern Residents will be challenging.
More winter observations, as in this study, will help facilitate an understanding of the
geographic distribution and spatial distribution of their prey.
Requirements
The dietary requirements of orcas have been estimated by Osborne (1999) based
on Kriete’s (1995) analysis of orca bioenergetics. Considering caloric values and average
body mass of all five species of salmon and the age and sex of all the orcas at the time of
his analysis, Osborne estimated a mean requirement of 25 adult salmon per day per orca.
All salmon species provide approximately 1 to 2000 kcal per kg of fish (Weitkamp,
pers.comm.). Based on his estimates of 85,000 to 200,000k/cals per day per orca and the
quantity of certain salmon species for age and sex classes, juvenile orca would require
eight 5 to 6kg chinook a day while adult males would require twenty 5 to 6kg chinook a
day. Overall, the current population of Southern Resident orcas would need
approximately 750,000 average adult salmon per year, from these estimates.
Most North Pacific adult salmon, however, have decreased in both weight and
length from 1973 to 1993. (e.g. Ishida et al. 1993, Bigler et al. 1994, Helle et al. 1998).
Chinook salmon have seen size decreases in both Washington (18.44%, <4kg
respectively) and Oregon (10.09% and 46.7%, <4kg respectively). All other four salmon
species have seen decreases in California, Oregon, Washington and British Columbia
ranging from 1.16 to 30.86%. Yet, Chinook have increased in size in California (24.70%,
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>5kg) and British Columbia (45.54%, >5kg), areas where Southern Residents have
been recently observed. The Southern Residents were feeding on chinook in California
when they were sighted (Black et al. 2002). Because of the decrease in size of many
North Pacific stocks of salmon, the actual number which would be required by the
Southern Resident Community may be much greater than 750,000.
The quality of prey will also be a factor. Of the five salmon species, chinook
salmon provide the highest amount of fat and Kcal/fish (NWAFC, 1977). This may be
important to maintain body fat stores required for marine mammal survival in the wild
(Kirsch, et al. 2000).
Foraging Research Techniques
Determining prey species of cetaceans has historically been done by stomach
content analysis, observation of surface feeding behavior and analysis of stable isotopes
and fatty acids from biopsies (e.g. Ackerman et al., 1987, Ford et al. 1998). Direct
observations are very rare since cetaceans spend the majority of their life below the
surface. Scuba divers and underwater cameras have been used but have some
methodological limitations. Scuba divers may modify the activity of the cetaceans and
water visibility is rarely sufficient for underwater cameras. Over the last decade
telemetric studies, such as satellite tags and depth recorders have provided researchers
with valuable insights into dive depths (e.g. Baird et al. 2003, Hindell et al. 1991), heart
rate (e.g. Thompson et al., 1993) and location at sea (e.g. Martin et al. 1994). Yet, direct
real-time observations are still needed for many situations, including prey and predator
distribution and for animals that are not easily tagged or handled.
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Ford et al. (1998) have described the prey species of the Northern and
Southern Resident Community orcas by fish scale analysis, observations of predatory
events and beached carcasses. This study identified several other species of fish prey
based upon 161 feeding events of the Northern and Southern Residents. Their analysis
included observations of predatory events, necropsies on beached carcasses and netting
and analysis of fish scales after surface-associated kills. The study incorporated data
collected over a 22-year period, from 1973 through 1996. Although the study showed a
93% preference for Pacific salmon (Oncoryhynchus spp.), other fish species that were
identified included Pacific herring (Clupea pallassi), yelloweye rockfish (Sebestes
ruberrimus), Pacific halibut (Hippocampus stenolepis) and an unidentified flatfish. In
addition, two carcasses of Southern Resident whales showed the remains of eight armed
squid.
It is important to note that of the 161 feeding events pooled over a 22 year period
only 5 of the stomachs analysis and 33 of the fish scale analysis were from Southern
Resident whales (Baird et al., 2003). Many have recognized that this sample is small and
the potential bias in terms of the sampling season and geographic area is large (Ford et al.
1998, Osborne 1999, Baird et al. 2003).
Baird and his colleagues (1998, 2003) recently obtained TDR recordings on the
Southern Resident Community orcas while the whales were suspected to be foraging.
These data revealed that the orcas were making repeated long dives, maximum depth of
201 meters, which are beyond the typical range of salmonids (e.g. Quinn, 1990). Besides
these TDR studies, there is little information about the depths the Southern Residents are
diving while foraging.
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The merits of TDR data, scale sampling, and surface observations to help
clarify prey and foraging behavior have been well documented. The limitation of each of
these methods is that they cannot look at prey or whale distribution. Further, scale
sampling may under represent prey consumed at depths.
Echosounders as Tools for Research
Echosounders can provide the opportunity to monitor real time underwater
observations and help determine prey and predator distributions. The use of echosounder
equipment is a relatively new tool for cetacean researchers. Echosounders have been used
in only a few recently published studies (Benoit-Bird 2003, Simila 1997, Guinet et al.
1997), one that focused on orca/prey interactions in Norway. However, it is currently
being used by a number of cetacean researchers worldwide (e.g. Benoit-Bernard 2003,
Weinrich, Dolphin, Sharpe, Lusseau pers.comm., Keeney pers.comm., Sanino
pers.comm.). These tools are being used because of visibility limitations typical of
submarine habitats in many areas of the world, and because they can be operated at
greater distances from the animals than a videocamcorder or TDR’s, minimizing
behavioral changes in the animals. In addition, echosounder observations may provide a
thorough quantitative assessment of all prey available when the whales are present and
foraging. They may also build upon previous fish scale analysis, necropsy and TDR data.
These studies will be very useful when done in conjunction with TDR studies, crittercams
(underwater cameras attached to the animal) and fish scale analysis.
Echosounder technology has been widely used in the fisheries sciences and
numerous studies have contributed to the understanding of acoustic measurements in fish
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(e.g. Love 1979, Barans et al. 1983, Rose et al. 1988, Horne et al. 1994, Petitgas et al.
1996, Swartzman et al. 1999). The observations and measurement of fish and fish
abundance have been done by echo counting and echo integration of target strengths.
Target strengths are numbers that indicate the strength of the echoes and the fish’s swim
bladder is the predominant sound reflector. For a marine mammal, the primary sound
reflector will be its lungs. Although acoustical measurements on cetaceans are limited,
many marine mammal researchers are beginning to understand the capabilities and
constraints of sonar.
Echosounders can be operated in low visibility areas with minimal impact on the
behaviors of the targeted animals, as long as the acoustic frequency of the sonar is well
out of the animal’s hearing range. Sonar can provide excellent resolution and good range.
Acoustic measurements also provide information about spatial and temporal components
of marine mammals and their habitat.
Acoustic measurements have many potential sources of variability and error.
Factors contributing to error include variable orientation of target animals to the
transducer, depth of dive, frequency of the sonar (MacLennan et al. 1992, Au 1996), and
temperature and salinity structure of the water column (MacLennan et al. 1992). Au
measured the target strength of a captive Atlantic bottlenose dolphin (Tursiops
truncatus). Maximum target strength was reflected from the dolphin’s lungs, or between
the dorsal and pectoral fins, when measured broadside. All target strengths from other
orientations were at least 10 dB lower than the lungs, with the minimum target strength
reflected from behind at the fluke. However, the results of this study may only be
applicable to cetaceans near the surface. Cetacean lung volume decreases in response to
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increasing ambient pressure associated with increasing depths of dives. The decrease
in air volume may make the target strength decrease.
Benoit-Bird (2001, 2003) used target strength measurements and echo integration
methods to measure the abundance of wild spinner dolphins and their prey. She found
overall target strength of the dolphins was independent of depth. The number of echoes
obtained from the dolphin was consistent in both the horizontal and vertical directions.
Large cetaceans, such as orcas, may or may not exhibit this consistency.
Fellemen and Thomas (1987) were the first to attempt to use sonar technology
with the Southern Resident Community orca. A 70kHz sonar was used to observe prey
distributions. More than 85% of single target fish and schooling fish were found within
the upper 30 meters of the water column.
There is no information on the subsurface spatial distribution of the Southern
Resident orcas while they are foraging and little information on their prey distribution.
Thus, the present study used a 200kHz sonar to determine prey distribution and
abundance of single target fish and fish masses while simultaneously looking at orca
distribution. Orca foraging dive times were also analyzed based on recorded surface
observations and focal sampling. The integration of these methods with other available
technology will undoubtedly be important to clarify prey species and distribution.
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METHODS
Equipment
Surface foraging behavior was recorded by a digital videocamcorder (Canon
2000, JVC 250X digital zoom) allowing us to take multiple continuous focal samples of
photographically identified individuals (Mann, 1999). From the digital tapes, foraging
dive times were systematically recorded. Based on photographic catalogues of the
Southern Residents (Bigg et al. 1987, Ford et al. 2000), individuals were identified in the
field or from the digital tapes later.
Subsurface acoustical images of the whales and their possible prey were recorded
on an Interphase PC View sonar deployed on a small autonomous catamaran (Figure 2)
off of a 30m whale watching vessel in 2001 and a 9m vessel in 2002. The sonar was
deployed manually off a 7m vessel in the winter of 2003 and off a 5m vessel in the spring
of 2003. The PC view sonar operates at 200kHz, well above the hearing range for killer
whales (Szymanski et al. 1999, Bain and Dalheim 1994, Bain et al., 1993).
All images and events were quantified by counting the number of individual fish
or the total area of possible prey, the depth of prey, the number of focal whales we
sampled, depth of dives and the possible predator/prey interactions. Sonar observations
were correlated with the videotaped surface observations to determine the reliability of
the sonar readings. More specifically, based on the whales range from the research vessel,
the sonar image and its range from the transducer and having the sonar and
videorecorders times synchronized, a whale at the surface could often be verified as the
same whale on the sonar.
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Figure 2. Autoboat and Echosounder being Deployed
from research vessel, July 2001
Photo by Leo Shaw
The Interphase P.C View is a phased-array echosounder that can be set to scan
over 90 degree sectors. The scanning beam is conical in shape and has an effective beam
angle of 12 degrees. Although the echosounder has a potential range of 1200 feet (366
meters) horizontally and 800 feet (244 meters) vertically, scans were primarily taken at
600 feet (183 meters) for quicker and clearer images. The echosounder attaches to a
laptop computer’s parallel port for direct data storage (Figure 3). The transducer was
mounted in front of the autoboat in 2001 and 2002 and operated manually off the
research vessels in 2003. Data were captured on the screen in 20 to 30-second intervals.
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Figure 3. Interphase P.C. View Sonar.
Images are stored directly onto the laptop.
July 2001
Photo by Leo Shaw
The autoboat is a prototype radio controlled vessel. The boat is a double-hulled
catamaran, 2 meters in length with a 1-meter beam. This unmanned vessel has a speed of
2-4 knots, is virtually silent and has a range of approximately 0.8km from the radio
controller. While it was not used in 2003 due to space limitations on board the research
vessel, a clear advantage was that it allowed the research vessel to keep a greater
distance, thus minimizing any behavioral changes that could occur due to the research
vessel.
Collection of Data
Data collection occurred from June 2001 through May 2003. Over 300 hours of
observation time was logged. Data collection occurred in the inland waters of
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Washington and British Columbia. Data collection started only when the whales began
to forage, as defined by Osborne (1986).
Although echosounder data were collected prior to 2003, a USB wireless
connection from the sonar computer aboard the autoboat to the computer on board the
manned vessel was not established until 2002. Because we could not see the data as they
were being collected in 2001 and we did not encounter the whales while they were
Figure 4. Echosounder Data Collection, Vicinity Map
Map courtesy of the Whale Museum
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foraging in 2002, we did not use any sonar data prior to 2003. Sonar data were
collected north of Elliot Bay in January 2003 on K and L pod and south of Henry Island,
north of Eagle Point and south of Lime Kiln in May of 2003 on J pod (Figure 4).
All foraging dive data were collected on the West Side of San Juan Island from
May through September of 2001. Foraging dive data were recorded on a digital
videorecorder for analysis. Focal whales were identified and followed systematically
as described by Mann (1999). A total of 22 focal samples were taken in 2001. Durations
of individual samples ranged from 5 to 62 minutes. All individuals were from L pod, the
largest of the three resident pods.
Analysis of Data
Orcas were identified based on the size of the image, target strength and by
correlating surface videorecorded observations with the sonar images. Single target fish
and aggregations of fish were identified based on the size of the image, the strength of the
target (color) and its vertical and horizontal distribution in relationship to the whales
images.
We obtained sonar data for foraging whales on five occasions. From each of the
five foraging bouts, four on May 11th and one on January 11th, 2003, images of prey and
orca distribution were saved onto the sonar computer every 30 seconds. Because there
were only 11 minutes of time between two late morning samples and 25 minutes between
the two afternoon samples in May, these four spring samples were combined into one
morning sample and one afternoon sample, totaling 3 samples or foraging bouts. Because
these foraging bouts were short and the orcas moved less than 3 miles, approximately, a
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longer sample period was analyzed to present less bias. However, between these
samples, there was clear indication (e.g. cessation of foraging behavior, grouping
together, slow traveling away from the area and no sonar images) that the whales were
moving to forage in a different area.
Each of those samples was then divided and averaged over parts of the sample
where there was not a high degree of variability in the depth distribution of the single fish
or aggregation of fish, constituting twelve sub-samples that ranged from a minimum of 2
minutes and maximum of 10 minutes (median 6 minutes). For example, if a new
aggregation appeared that was in a different depth distribution, another sub-sample
began. If the aggregation changed in size but not in depth distribution, the sub- sample
continued. Total single fish targets, aggregations of fish, and their depth distribution were
averaged, respectively, over all of the 30 seconds scans within the sub-sample analyzed.
The sub-samples were then averaged over the whole foraging bout as a simple average
rather than a weighted average because the time difference, considering the scope of the
samples, was not substantial.
To determine whether the number of orca sonar images were reliable and
associated with the number of whales observed at the surface before, during or after a
foraging bout, visual surface counts were regressed on orca sonar counts over each of the
five foraging bouts. To look at orca spatial distribution while the whales were foraging
and to examine indications of cooperative foraging, the depth of the shallowest orca was
regressed on the depth of the deepest orca at the time an aggregation of fish was at its
largest.
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RESULTS
Foraging Dive Times
Mean foraging dive times for individuals varied from 63 seconds maximum for an adult
male, L-57, to 7 seconds for an unidentified juvenile (Figure 5). Juveniles’ (1-11 years
old) and females’ foraging dive times averaged 21 seconds while males’ foraging dive
times averaged 33 seconds (Figure 6). Foraging dive duration of males was 64% longer
than females and juveniles. The average foraging dive time of all the individuals samples
Dive Time (seconds)
was 28 seconds (n=22, SD=14).
72.0
57.4
43.1
28.5
14.2
00.0 L58 L41
L79 L57
L77,U, L85,L94, juv,U,L32,L12
Figure 5. Individual Orca’s Foraging Dive Times
Grey bars are males, black bars are females and
juveniles (1-11years old). U=unidentified individual,
juv=juvenile.
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Dive times (seconds)
50.0
40.0
30.0
20.0
10.0
0.0
Figure 6. Average Foraging Dive Times
Light grey bar is males, dark grey bar is females and
juveniles (1-11 years old)
Echosounder Data
A total of 80 minutes and 30 seconds of foraging sonar data were recorded from five
foraging bouts. The average foraging bout from sonar samples was 16.06 minutes (n=5),
maximum 23 minutes, and minimum 10. An example of sonar images from whales (Jpod individuals) is shown in Figure 7. A series of sonar images of whales possibly
feeding on single target fish and an aggregation of fish are shown in Figure 8.
Whales
Figure 7. Echosounder image of whales
Southern Resident Orcas, J pod, 10 individuals. Traveling not foraging.
One-30 second image, for illustrative purposes only. May 12, 2003
24
25
Vertical distribution of single fish targets and aggregations of fish are shown in
Tables 1-3. In the winter sample, only 11.5% of single target fish were found in the
upper 30 meters. The remaining 88.5% of single target prey were found from 91 to 120
meters. Overall, in the spring samples 40% of single target fish were found from 0 to 30
meters. When the spring samples are divided into morning (Table 2) and afternoon (Table
3), the morning sample shows that 75% of single target fish were found from 31 to 90
meters and the afternoon sample shows that 75% of single target fish were found from 0
to 30 meters. The highest percentages of aggregations of fish were found from 0-30
meters in both the winter and spring samples.
Table 1. Vertical distribution of single fish targets and aggregations of fish.
K and L pods foraging, Elliot Bay, January 2003
sf=single fish measured as an average over sub-samples
af=aggregation of fish measured in m2
Standard deviations shown where the sample size is large enough (n=4)
1/11/03
1/11/03
1/11/03
14:38:13 to 14:47:13
14:47:43 to 14:54:43
14:55:13 to 14:59:43
Depth
(meters)
sf
af
sf
0 to 30
0
442.1
sf
af
Total %
sf
af
3
0
0
486.44
11.5% 100%
31 to 60
0
0
6
0
0
0
23.1%
0
61 to 90
0
0
6
0
0
0
23.1%
0
0
11
0
0
0
42.3%
0
0
0
0
0
0
0
0
 317.7
af
833.66
91 to 120
121 to
150
0
26
Table 2. Vertical distribution of single target fish and aggregates of fish.
J Pod foraging, in the late morning of May 11, 2003.
North of Lime Kiln, South Henry Island. San Juan Islands
sf=single fish measured as an average over sub-samples,
af=aggregation of fish measured in m2
Standard deviations shown where the sample size is large enough (n=4)
5/11/03
5/11/03
5/11/03
5/11/03
5/11/03
10:15:52
to
10:20:21
10:20:51
to
10:27:51
10:38:59to
10:40:59
10:41:29
to
10:47:59
10:48:29
to
10:54:59
Depth
sf
af
sf
af
sf
af
sf
(meters)
0 – 30
af
sf
af
Total %
sf
af
1.33
74.2
1
0
1.5
0
2.5
588.38
4.4
297.91
25%
43%
31 – 60
3
0
1.5
0
3
0
4.7
0
6
255.61
45%
29%
61 – 90
2.6
0
3.2
288.15
4
418.28
1.5
0
1
0
30%
29%
91 -120
0
0
0
0
0
0
0
0
0
0
0
0
121-150
0
0
0
0
0
0
0
0
0
0
0
0
 398..3
 227..9
Table 3. Vertical distribution of single target fish and aggregates of fish.
J Pod foraging in the afternoon of May 11, 2003.
South of Lime Kiln. San Juan Islands
sf=single fish measured as an average over sub-samples,
af=aggregation of fish measured in m2
Standard deviations shown where the sample size is large enough (n=4)
Depth
sf
5/11/03
5/11/03
5/11/03
5/11/03
13:39:04
to
13:49:04
14:16:45
to
14:26:44
14:27:14
to
14:33:44
14:34:14
to
14:39:04
af
sf
362.51
3.8
1.67
0
1.5
0
(meters)
0 – 30
1.75
31 – 60
61 – 90
 422.9
af
sf
139.43
3.5
0
0
0
0
0
0
 93.1
af
sf
af
250.0
3.5
0
75%
50%
353.21
0
0
16%
16%
646.01
0
0
9%
33%
 273.8
 6.6
Total %
sf
af
1022.46
91 –120
2.2
0
0
0
0
0
0
0
0
121-150
0
0
0
0
0
0
0
0
0
27
Overall, all the foraging samples showed that the Southern Resident orca are
spending only 43.7% in the upper 30 meters of the water column. When divided into the
one winter sample versus the four spring samples, 43.5% and 63.7% are spent in the
upper 30 meters respectively. Overall, the percentages of time orcas spent at different
depth distributions in the spring and winter are shown in Figures 9 and 10.
Two statistical analyses were run that included data from the five foraging bouts.
To determine whether the number of orca sonar images was reliable and associated with
the number of whales observed at the surface before, during or after a foraging bout,
visual counts were regressed on orca surface counts. This yielded significant correlations
(r2 =0.860, p<.023), offering support to number of whales that were identified from the
sonar images. Visual surface counts were further verified by videotape. Examining
indications of cooperative foraging, by regressing the depth of the shallowest orca on the
depth of the deepest orca at the time an aggregation of fish was at its largest, showed a
weak correlation (r2 = 0.144, p<0.529).
28
70
60
Percentage
50
40
30
20
10
0
0-30
31-60
61-90
91-120 121-150
Depth (meters)
Figure 9. Foraging Depth Distribution of the Southern
Resident Community Orca, May 2003
70
60
Percentage
50
40
30
20
10
0
0-30
31-60
61-90
91-120 121-150
Depth (meters)
Figure 10. Foraging Depth Distribution of the Southern
Resident Community Orca, January 2003
29
DISCUSSION
Foraging Dive Duration
Foraging dive duration is shorter than the average foraging dive time that Ford
(1989) showed with resident whales, 34 seconds (n=89) versus 28 seconds. This is
shorter (18%) than his findings. However, the current study’s sample is small (n=22) and
is only based on summer observations with L pod individuals. In addition, Ford’s
analyses are primarily based on observations with the Northern Resident Community.
Yet, since the Northern Residents and Southern Residents have similar prey, group
dynamics and ranges (Ford et al., 2000), it should be expected that foraging dive times
would be similar. The explanation for this difference is unknown but may be due to the
smaller sample size.
The results of adult males averaging longer dives than females is not surprising
based on past research and observations of these killer whales. Adult males stayed on the
outer perimeter of the group while foraging, which is also consistent with previous
information on the Southern Residents. During many of the foraging bouts observed with
L-pod in the summer, there was often one adult male with a younger sibling whose dive
time was shorter in duration.
Dive duration was not analyzed by focal sampling during the winter or spring of
2003 because of limited assistance in the field. Yet, based on visual observations and
echosounder observations of prey distribution, dive times of K and L pod individuals in
the winter appeared longer in duration than the summer. Further, north of Elliott Bay, the
area L pod was foraging during sonar data collection, is known for juvenile chinook
30
(blackmouths) in the winter months (Sears, pers. comm.). The depth distribution (30 to
80m) of these fall and winter chinook (Quinn, 1990) suggests that orca dive durations
may be longer.
Surface observations alone may provide some information on the spatial
distribution of prey (e.g. Alejandro et al., 2000) and provide a reliable way to assess dive
duration (Leyssen et al, 2002). Yet, ultimately cetaceans movements are three
dimensional and the integration of data from recorded surface observations, TDR data
and echosounder data will provide a fairly novel approach to clarify both prey and
predator distribution.
Distribution of Whales and their Prey
Echosounder data indicate that the Southern Residents are spending less time in
the upper 30m in the winter (43.5%) than the spring (63.7%) while they are foraging. The
orca spent over 26% of their time from depths of 61 to 90m in the winter and only 11%
of their time in this depth distribution in the spring. Baird et al.’s (1998) TDR study
showed that the whales spent less than 2.5% of their time at depths greater than 50
meters. It is important to clarify that their analysis included depths of dives over all
behavioral states, not just foraging. Further, it was conducted only in the summer months.
The current study indicates that the whales may be spending greater than 20% of their
time from depths ranging from 61 to 150m while foraging. In the winter months, this
may be greater than 35% of their time. However, the depth of the water column was
sometimes beyond the sonar’s set range. Baird et al. (2003) recorded a dive that
exceeded 201m (the depth limit of the TDR). It is probable that they are not staying at
31
these depths and that these dives are at a high velocity as were recorded by these TDR
studies.
The majority of single prey targets (88.5%) were found from 31 to 120m during
the winter. These depths are fairly consistent with fall/winter Chinook runs that are found
from 30-80 meters. It is possible that the orcas were coming up from below the salmon
to chase them to the surface or conversely, may have chased them to greater depths than
80 meters. The echosounder images indicate that the whales may have been herding or
consuming prey at depths ranging from 30 to 150 meters.
In the afternoon spring data set, most single prey targets (75%) were found from 0
to 30 meters. Yet, in a late morning spring sample 75% of the single fish targets were
found from 31-90 meters. Since most salmon runs, excepting chinook, are found within
the upper 15 to 20m of the water column and rarely descend beyond 50 m (e.g. Candy et
al. 1999, Walker et al. 2000, Ishida et al. 2001), it may be that they were feeding on
other types of prey. Besides Ford et al’s (1998) study, it is unknown what other fish
species, other than salmon, are contributing to their diets. This will undoubtedly be
important to the conservation of the Southern Resident Community orcas.
Sonar observations of foraging bouts were comparable to Simila’s (1997) sonar
observations with killer whales in Norway. She recorded 10 foraging events ranging
from 3.13 minutes to 80.23 minutes, mean 20.78 minutes. In the current study, the
longest foraging bout lasted 23 minutes during the winter. The minimum foraging bout
was 10 minutes, the mean 16.06 minutes. Yet, in the summer observations with L-Pod the
maximum-recorded time for an individual foraging, based on visual-recorded
observations, was 62 minutes.
32
During this study, the whales always began slow traveling after foraging. With
all sonar samples at the end of a foraging bout, there were fewer sonar images. As the
whales moved out of range, no sonar images were apparent. The whales surface
behavior, grouping together and slow traveling (Osborne, 1986) away from the area, as
well as the lack of sonar images, suggests that all the fish were consumed. Fishermen
over the years have reported that catches, after killer whale presence, were non-existent.
While the fish may be actively avoiding these predators or may not have been in
echosounder’s beam, it was clear that the whales had stopped actively foraging in all the
samples.
Finally, it is important to note that there were no observable behavioral
differences over the course of 3 years when the 200kHz echosounder was operating.
Echosounders below 100kHz are not recommended because of the hearing ability of
killer whales and their potential impact on the animals.
Cooperative Foraging
Cooperative foraging has been seen with many other groups of killer whales and other
dolphin species (e.g. Norris et al., 1980, Simila, 1997, Guinet 2000, Donenici et al.
2000). The feeding behavior of the Southern Residents has also been characterized as
cooperative based on the movement patterns and synchronized respirations while chasing
prey (Fellemen et al., 1991). Although Hoezel’s (1993) study suggested that the
Southern Residents may search for food cooperatively but feed independently, many
aggregations were often seen near the end of the foraging bout. In addition, the greatest
percentages of aggregations of fish were found in the upper 30 meters in all samples,
33
independent of season. While the correlations between the depths of the shallowest and
deepest orca were not significant, indicating the whales were moving independently,
further analyses on current and future data are warranted. Because the spatial distribution
of prey tended to concentrate over the whales foraging bouts, the possibility that the orcas
are herding prey and feeding together below the surface where they cannot be observed
should not be overlooked.
Sources of Error
The use of active acoustic techniques has several limitations with regards to
determining prey abundance and distribution. These include the potential bias when
assuming incorrect target strengths, the detection of targets near the surface or the
bottom, and determining species (MacLennan, 1992). Because of the inferences made
from the sonar image (single target fish, aggregates of fish, or whale) in this study, these
results must be taken with caution.
This current study’s sample size using an echosounder was small in comparison to
the amount of data that can be collected by TDR studies. Yet, in the near future
echosounder studies will still probably yield much less data than TDR studies because of
their novelty with marine mammal researchers and technological limitations.
Future Work
Future echosounder work must incorporate target strength and echo-energy
integration analysis as described by MacLennan and Simmonds (1992) and Benoit-Bird
(2003). While this study could not incorporate echo-energy integration analysis, a
34
necessity for future sonar work, we were able to recognize high, medium and low target
strengths based on the color of the image. Also, unlike Benoit-Bird’s study where there
was limited knowledge of the prey species prior to her study, the abundance, distribution,
habitat use and acoustical qualities of Pacific Northwest salmon have been well studied
(e.g. Candy et al., 1999, Quinn 1990, Thorne 1979). Yet, further acoustical assessments
of all possible prey, including salmon, should be conducted prior to data collection on
foraging whales.
Echosounder equipment must be able to assess specific numerical target strengths
rather than undefined target strengths. In addition multibeam echosounders will be much
more efficient, yet more expensive. The Interphase P.C view’s ease in operation
(mobility) and the storage of data directly onto a laptop is a necessity when the whales
foraging bouts are short, as in this study.
Videotaping the whales at the surface and correlating those observations with
echosounder observations is essential. This study was able to confirm many sonar
images as whales from videotaped surface observations. If possible, TDR studies and fish
scale analysis should be done in conjunction with echosounder studies. Finally, the use
of a radio controlled autoboat has the clear advantage of being able to approach the
whales without having to operate the research vessel around the whales, thus minimizing
any behavioral changes that the vessel may have caused.
35
BIBLIOGRAPHY
Ackerman, R.G., Lamothe, F., 1989.
Marine Mammals. In Ackerman, R.G. (ed.) Marine biogenic lipids, fats and oils.
Vol II CRC Press. Boca Raton, Florida: 179-381
Alejandro, A.G, Parker, N., 2000
“Surface Behavior of Bottlenose Dolphins is Related to Spatial Arrangement of
Prey.” Marine Mammal Sci. 16(2) 287-298.
Au, W.L.W, 1996.
“Acoustic reflectivity of a dolphin.” J.Acoust.Soc.Am. 99(6): 3844- 3848
Bain, D.E., Kreite, B., Dalheim, M. 1993.
"Hearing Abilities of Killer Whales (Orcinus orca)." J. Acoust. Soc.Am.
94(2):1829
Bain, D.E., Dalheim, M.E., 1994.
“Effects of masking noise on detection thresholds of killer whales.” In T.R.
Loughlin (ed.) Marine Mammals of the Exxon Valdez, p.243-256. Academic
Press, San Diego, CA. 395p.
Bain, D.E., Anderson, W., Fellemen, F., Harris, M., Higgins, P., 2002.
In “Orca Recovery Conference Report.” University of Washington, Seattle, WA.
Report available at www.earthisland.org/immp/orca/orcareportfinal.pdf
Bain, D.E., Williams, R., Trites, A.W., 2003.
“Potential Impacts of Whale Watching on Killer Whales (Orcinus orca)
Population Dynamics: Insights from Three Models.” Marine Mammal Science.
Submitted for review
Baird, R., Hanson, B., Ashe, E., Heithaus, M., Marshall, G., 2003.
“Studies of Foraging in “Southern Resident” Killer Whales During July 2002:
Dive depths, Bursts in Speed, and the Use of a “Crittercam” System for
Examining Sub-surface Behavior.” NMFS report, AB133F-02-SE-1744.
Baird, R., 2002. Killer Whales of the World. Voyageur Press, Inc. 131pg.
Baird, R. 2001.
“Status of Killer Whales (Orcinus orca) in Canada.” Canadian Field Naturalist.
115: 676-701
Baird, R, Dill, L.M., Hanson, M.B, 1998.
"Diving Behavior of Killer Whales." Abstract of paper presented at the World
Marine Mammal Conference, Monaco, January, 1998.
36
Balcomb, K.C., Boran, J.R., Osborne, R.W., Haenel, N.J, 1979.
“Observations of killer whales (Orcinus orca) in greater Puget Sound, State of
Washington. Marine Mammal Commission, Washington D.C.
Barans, C.A., Holliday, D.V., 1983.
“A Practical Technique for Assessing some Snapper/Grouper Stocks.” Bull.of
Marine Science. 33 (1): 176-181
Barrett-Lennard, L.G., 2000.
“Population Structure and mating patterns of killer whales as revealed by DNA
analysis.” PhD thesis, University of British Columbia, Vancouver B.C.
Benoit-Bird, K.J. 2003.
“Dynamics of the Hawaiian Mesopelagic Boundary Community and their Effects
on Predator Foraging.” PhD Thesis, University of Hawaii.
Benoit-Bird, K.J., Au, W.L. 2001.
“Target strength measurements of Hawaiian mesopelagic boundary
community animals.” J. Acoust.Soc. Am. 110:812-819.
Bigg, M.A., Ellis, G.M., Ford, J.K.B., Balcomb III K.C., 1987.
“Killer Whales. A Study of their Identification, Genealogy & Natural History in
British Columbia and Washington State.” Phantom Press. Nanaimo, British
Columbia. 79pg.
Bigg, M.A. 1982.
“The Assessment of Killer Whale (Orcinus orca) Stocks off Vancouver Island,
British Columbia.” Rep. Intl. Whale Comm. 32: 655-66
Bigler, B., Helle, J.H., 1994.
“Decreasing size of North Pacific salmon (Oncorhynchus sp.). Possible causes
and consequences.” In Annual Meeting of the North Pacific Anadromous Fish
Commission. Vladivostok, Russia. 34p. Wards Cove Packing Company, P.O. Box
C-5030, Seattle, Washington 98105.
Black, N., Ternullo, R.,Schulman-Janiger, A., Ellis, G., Dahlheim, M., 2002.
"Behavior and Ecology of Killer Whales in Monterey Bay, California." Fourth
Intl. Orca Symposium and Workshop: 40-43.
Candy, J.R., Quinn, T.P. 1999.
Behavior of Adult Chinook Salmon (Oncorhynchus tshawytscha) in British
Columbia waters determined from ultrasonic telemetry.” Can.Journal of Zoology.
77: 1161-1169
37
de Stephanis, R., Perez, G.N., Poncelot, E., Guinet, C., 2002.
“Interactions between Killer Whales and Red Tuna (Thymus Thynnus) Fishery in
the Strait of Gibralter.” Fourth Intl. Orca Symposium and Workshop: 138-142.
Dohl T.P., Guess, R.C., Duman, M.L., Helm, R.C. 1983.
“Cetaceans of Central and Northern California 1980-1983: Status, Abundance,
and Distribution.” Final Report Marine Mammal and Seabird Study, Central and
Northern California. Mineral Management Service, U.S. Department of Interior.
Contract #14-12-0001-29090
Domenici, P., Batty, R.S., Simila, T. , Ogam, E., 2000.
“Killer Whale (Orcinus orca) Feeding on Schooling Herring (Clupea Harengus)
Using Underwater Tail Slaps: Kinematic Anaylsis of Field Observations.” Journal
of Experimental Biology. 203: 283-294.
Erickson, A.W., 1978.
“Population studies of killer whales (Orcinus orca) in the Pacific Northwest: a
radio marked and tagged study of killer whales.” Contract PB-285-615, Marine
Mammal Commission, Washington D.C., 31p.
Estes, J.A., Tinker, M.T., Williams T.M., Doak, D.F., 1998
“Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Systems.”
Science. 282: 473-475.
Fellemen, F.L., 1986.
“Feeding Ecology of the Killer Whale (Orcinus orca).” M.Sc. Thesis,
College of Fisheries, University of Washington, Seattle, WA.
Fellemen, F.L., Thomas, G.L. 1987.
“Acoustic measurement of the fish assemblage beneath killer whale pods in the
Pacific Northwest.” Rit Fiskideildar, Journal of the Marine Institute: Vol X1: 276284.
Fellemen, F.L., Heimlich-Boran, J.R., Osborne, R.W., 1991.
“The feeding ecology of killer whales (Orcinus orca) in the Pacific Northwest.”
In K,Pryor and K.Norris (eds.), Dolphin societies: Discoveries and puzzles, p.
113-147. Univ. California Press, Berkeley.
Ford, J., 1989.
“Acoustic behaviour of resident killer whales (Orcinus orca) off Vancouver
Island, British Columbia.” Can.J.Zool. 67: 727-743.
Ford, J., Ellis, G.M., Barett-Lennard, L., Morton, A., Palm, R., Balcomb III, K., 1998.
“Dietary specialization in two sympatric populations of killer whales (Orcinus
orca) in coastal British Columbia and adjacent waters.” Can. J. Zool. 76: 14561471.
38
Ford, J., Ellis, G., Balcomb, K., 2000.
“Killer Whales: The natural history and genealogy of Orcinus orca in British
Columbia and Washington State.” Second edition Vancouver B.C., Canada. UBC
Press. 102pg.
Greenwood, M.F.D, Hill, A.S., McLusky D.S., 2002.
“Trends in abundance of benthic and demersal fish populations of the lower Forth
Estuary, East Scotland, from 1982-2001.” Journ. Fish Biology. 61(1): 90-104.
Guinet, C., Ridoux, V., Liret, C., Creton, P., Steenstrup, R., Beauplet, G., 1997.
“A Video Sonar as a New Tool to Study Marine Mammals in the Wild:
Measurements of Dolphin Swimming Speed.” Marine Mammal Science. 13(2):
196-206.
Guinet, C., Barrett-Lennard, L.G., Loyer, B., 2000.
“Coordinated Attack Behavior and Prey Sharing by Killer Whales at Crozet
Archipelago: Strategies for Feeding on Negatively Buoyant Prey.” Marine
Mammal Science. 16(4): 829-834.
Hare, S.R., Mantua, N.J., Francis, R.C., 1999.
“Empirical evidence for North Pacific regime shifts in 1977 and 1989.” Prog.
Oceanogr. 47:103-146.
Heimlich-Boran, J.R., 1986.
“Habitat Use Patterns and Behavioral Ecology of Killer Whales (Orcinus
orca) in the Pacific Northwest.” M.Sc.Thesis, Moss Landing Marine Laboratories
and the Department of Biological Sciences, San Jose State University, San Jose,
CA.
Helle, J.H., Hoffman, M.S., 1998.
“Changes in size at maturity of two North American stocks of chum salmon
(Oncorhynchus keta) before and after a major regime shift in the North Pacific
Ocean.” N.Pac.Anadr.Fish Comm. Bull. No. 1: 81-89.
Hindell, M.A., Slip, D.J., Burton, H.R., 1991.
“The diving behavior of adult male and female elephant seals (Miounga leonina,
(Pinnipedia: Phocidae). Australian Journal of Zoology. 39: 595-619.
Hoezel, A.R., 1993.
“Foraging behavior and social group dynamics in Puget Sound Killer Whales.”
Animal Behavior. 45: 581-591.
Horne, J., Clay, C.S.,1994.
Acoustic Models of fish: the Atlantic Cod (Gadus morus). J.Acoust. Soc. Am. 96:
1661-1668
39
Hoyt, E., 1984.
“The Whale Called Killer”. New York, E.P.Dutton. 287pg
Hutchings, J.A., 2001.
“Influence of population decline, fishing, and spawner variability on the recovery
of marine fishes.” Journal of Fish Biology 59(1) : 306-322.
Ishida, Y., Ito, S. Kaeriyama, M., McKinnel, S., Nagasawa, K., 1993.
“Recent changes in age and size of chum salmon (Oncorhynchus keta) in the
North Pacific Ocean and possible causes.” Can.J.Fish.Aquat.Sci. 50: 290-295.
Ishida, Y., Yano, A., Ban, M, Ogura, M., 2001.
“Vertical movement of a chum salmon (Oncorhynchus keta) in the western North
Pacific Ocean as determined by a depth-recording archival tag.” Fisheries Sci.
67(6): 1030
Jefferson, T.A., Stacey, P.J., Baird, R.W., 1991.
“A review of killer whale interactions with other marine mammals: Predation to
co-existence.” Mammal. Rev. 21(4): 151-180.
Jonsgard, A, Lyshoel, P.B., 1970.
“A contribution to the knowledge of the biology of the killer whale (Orcinus
orca). L.Nytt. Mag. Zool. 18:41-48.
Keser, M., Swenarton, J.T., Vozarik, J.M., Foertch, J.F., 2003.
“Decline in eelgrass (Zostera marina L.) in Long Island Sound near Millstone
Point, Connecticut (USA) unrelated to thermal input.” Journal of Sea Research,
49(1): 11-26.
Kirsch, P.E., Iverson, S.J., Bowen, W.D., 2000.
“Effect of Low-Fat Diet on Body Composition and Blubber Fatty Acids of
Captive Juvenile Harp Seals (Phoca groenlandica).” Physiological and
Biochemical Zoology. 73(1): 45-49.
Krahn, M.M., Wade, P.R., Kalinowski, S.T., Dahlheim, M.E., Taylor, B.L., Hanson,
B.M., Ylitalo, G.M., Angliss, R.P. Stein, J.E., Waples, R.S., 2002.
“Status Review of Southern Resident killer whales (Orcinus orca) under the
Endangered Species Act.” U.S. Dept. Commer., NOAA Tech. Memo. NMFSNWFSC-54, 133p.
Kriete, B. 1995.
“Bioenergetics in the Killer Whale, Oricinus orca.” PhD Thesis, University of
British Columbia.
40
Leyssen, T., Simila, T., Hanson, B., Holst, J.C., Oien, N., 2002.
“Surface Intervals of an Adult Male Killer Whale in Norway.” Fourth Intl. Orca
Symposium and Workshop. p. 89-91.
Lopez, J.C., Lopez, D., 1985.
“Killer Whales (Orcinus orca) of Patagonia and their behavior of intentional
stranding while hunting nearshore.” J. Mammal. 66: 181-183
Love, R.H. 1971.
“Dorsal aspect target strength of individual fish.” J.Acoust.Soc.Am: 49: 816-823.
MacLennan, D.N., Simmonds, E.J. 1992.
“Fishery Acoustics.” New York: Chapman and Hall.
Mann, J. 1999.
“Behavioral Sampling Methods for Cetaceans: A Review and Critique.” Marine
Mammal Science. 15(1): 102-122.
Martin, A., Kingsley, C., Ramsay, M., 1994. Diving behavior of narwhals (Monodon
monoceros) on their summer grounds.” Canadian Journal of Zoology. 72 :118125.
Megrey, B.A., 1991.
“Population dynamics and management of walleye pollock (Theragra
chalcogramma) in the Gulf of Alaska, 1976–1986.” Fisheries Research. 11(3,4):
321-354.
Martinez, D.R., Klinghammer E., 1970.
“The behavior of the Whale, Orcinus orca: A Review of the Literature.”
Zeitschrift fur Tierpsycholgoie 27: 828-39.
Nehlsen, W., Williams, J.E., Lichotowich, J.A., 1991.
“Pacific Salmon at the Crossroads. Stocks at Risk from California, Oregon, Idaho,
and Washington.” Fisheries. 15 (2): 4-21
Nichol, L.M, Shackelton, D.M. 1996.
“Seasonal movements and foraging behaviour of Northern Resident killer whales
(Orcinus orca) in relation to the inshore distribution of salmon (Oncorhynchus
spp.) in British Columbia.” Canadian Journal of Zoology 74: 983-991.
Nishiwaki, M, Handa, C., 1958.
“Killer Whales caught in coastal waters of Japan.” Sci. Rept. Whales Res. Intl. 13,
85-96.
41
NOAA, 2000.
APRIL 18 2000, Listing Status: Chinook (Oncorhynchus tshawytscha), Coho
(Oncorhynchus kisutch), Chum (Oncorhynchus keta), Pink (Oncorhynchus
gorbuscha), Sockeye (Oncorhynchus nerka). http.www.nwr.noaa.gov/1salmon
Northcote, T.G., Atagi, D.Y., 1997.
“Pacific salmon abundance trends in the Fraser River watershed compared with
other British Columbia river systems.” In D.Stouder, P.Bisson, R.Naimon (eds).
Pacific Salmon and their ecosystem. p. 199-222. Chapman and Hall, New York.
Norris, K.S., Dohl, T.P, 1980.
“The Structure and Function of Cetacean Schools.” In Cetacean Behavior:
Mechanisms and Functions, L.M. Herman (ed.). John Wiley and Sons, New York.
NFAFC, NOAA, 1977.
“Mean Caloric Values of Eastern North Pacific Food Fish.” Food Sciences report,
Northwest Alaska and Fisheries Center, National Marine Fishery Service.
National Oceanic and Atmospheric Association, Department of Commerce.
O’Neill, S.M., West, J.E., Hoeman, J.C., 1998.
“Spatial trends in the concentration of polychlorinated biphenyls (PCB’s in
Chinook (Oncorhyncus tshawytscha) and Coho salmon (O. kisutch) in Puget
Sound and factors affecting PCB accumulation.” Results for the Puget sound
Ambient Monitoring Program: Puget Sound Research ’98: 312-328.
Osborne, R.W. 1999.
“A Historical Ecology of Salish Sea “Resident” Killer Whales (Orcinus orca):
With Implications for Management.” PhD Thesis, University of Victoria.
Osborne, R.W. 1986.
“A behavioral budget of Puget Sound Killer Whales.” In Behavioral Biology of
Killer Whales. Ed. B. Kirkevold and J.S. Lockard. A.R. Liss, N.Y. 211-249.
Pacific Salmon Commission, March 2003.
Seventeenth Annual Report, Vancouver B.C., Canada. 1-179.
Petitgas, P., Levenez, J.J., 1996.
“Spatial organization of pelagic fish:echogram structure, spatial temporal
condition and biomass in Senegalese waters.” ICES Journal of Marine Sci. 53:
147-153
Quinn, T.P. 1990.
“Migratory behavior of Pacific Salmon in estuaries, recent results with ultrasonic
telemetry.” In C.A. Simmenstad (ed.) Effects of Dredging on Anadromous Pacific
Coast Fishes, WA. SeaGrant, Seattle, WA. 13-25.
42
Reijnders, P. 1994.
“Toxicokinetics of chlorobiphenyls and associated physiological responses in
marine mammals with particular reference to their potential for ecotoxicolgical
risk assessment.” The Science of the Total Environment. 154: 229-236.
Rose, G.A., Legget, W.C. 1988.
“Hydroacoustic Signal Classification of Fish School by Species.” Can.Jour.of
Fish and Aquatic Sci. 45: 597-604.
Ross, P., Ellis, G., Ford, J., Barrett-Lennard, L., 2002.
“Toxic Chemical Pollution and Pacific Killer Whales (Orcinus orca)”. Fourth
Intl. Orca Symposium and Workshop: 126-130.
Ross, P.S., Ellis, G.M., Ikonomou, M.G., Barett-Lennard, LG., Addison, R.F. 2000.
“High PCB concentrations in Free-Ranging Pacific Killer Whales (Orcinus
orca): Effects of Age, Sex, and Dietary Preference.” Marine Pollution Bulletin: 40
(6); 504-515.
Simila, T., 1997.
“Sonar observations of killer whales (Orcinus orca) feeding on herring schools.”
Aquatic Mammals: 23(3); 119-126.
Simila, T. 1997.
“Behavioral Ecology of Killer Whales in Northern Norway.” PhD Thesis,
Norwegian College of Fisheries Science, University of Tromso.
State of Washington’s Salmon Recovery Office, 2002.
2002, State of Salmon. 1-15
Stephens, D.W., Krebs, J.R., 1986.
“Foraging Theory.” Princeton University Press, Princeton New Jersey. p. 1-12.
Swartzman, G., Brodeur R., Napp, J., Walsh, D., 1999.
“Relating spatial distribution of acoustically determined patches of fish and
plankton.: Data viewing, image analysis and spatial proximity.” Can.Journal of
Fish and Aquatic Sci. 56: 188-198
Szymanski, M.D., Bain, D.E., Kiehl, K., Pennington, S., Wong, S., Henry, K.R, 1999.
“Killer whale (Orcinus orca) hearing: Auditory brainstem response and
behavioral audiograms.” J.Acoust. Soc. Am. 106(2): 1134-1141.
Tarasyan, K., Jikiya, E., 2002.
“What is the Favourite Prey? Foraging Ecology of Killer Whales at Avacha Gulf,
Russian Far East.” Fourth Intl. Orca Workshop and Symposium. 151.
43
Thompson, D., Hiby, A., Fedak, M., 1993.
“How fast should I swim? Behavioral implications of diving physiology.”
Symposium of the Zoological Society of London 66: 676-684.
Thorne, R.E. 1979.
“Hydroacoustic estimates of adult sockeye salmon (O.nerka) in Lake Washington.
1972-75. Journ.Fish Research Brd. Can. 1145-1149
Tiselius, P., Jonsson, P.R., Verity,P.G., 1993.
“A model evaluation of the impact of food patchiness on foraging strategy and
predation risk in zooplankton.” Bulletin of Marine Science. 53: 247-264.
Trites, A.W., Donnely, C.P., 2003.
“The decline of Stellar sea lions Eumetopias jubatus in Alaska: a review of the
nutritional stress hypothesis.” Mammal Rev. 33(1): 3-28.
Wade, P.R., Bain, D.E., Balcomb, K.C., 2000.
“Population dynamics of the Southern Resident Killer Whales.” Report SRKW11
to the Southern Resident Killer Whale Workshop. National Marine Mammal
Laboratory, Seattle, WA.
Walker, R.V., Myers, K.W., Davis, N.D., Aydin, K.Y., Friedland, K.D., Carlson, R.H.,
Boehlert, G.W., Urawa, S., Ueno, Y., Anma, G., 2000
“Diurnal variation in thermal environment experienced by salmonids in the North
Pacific as indicated by storage tags.” Fisheries Oceanogr. 9(2): 171
Ylitalo, G.M., Matkin, C.O., Buzitis, J., Krahn, M.M., Jones, L.L., Rowles, T., Stein,
J.E., 2001.
“Influence of life history parameters on organochlorine concentrations in freeranging killer whales (Orcinus orca) from Prince William Sound, AK.” Sci.Total
Environ. 281(1-3):183-203.
44