1 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 2 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 3 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 4 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 5 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 6 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 7 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). 8 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 9 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 10 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%, 11 >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. 12 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. 13 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 14 (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 15 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. 16 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. 17 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. 18 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 19 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 20 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 21 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. 22 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. 23 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. 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