Echolocation, calls and strategy used by Southern Resident Killer Whales (Orcinus orca) during foraging.
Wilfredo Santiago Benítez
Killer Whales around the world differ in prey, size, behavior, social organization and others that make them easy to identify. Some populations specialize on fish foraging while other specialize on marine mammals. But in general orcas are the top predator, with an extreme range in food items reported taken, including squid, octopus, bony and cartilaginous fish, including sharks, sea turtles, seabirds, sea and river otters, dugongs, pinnipeds, and cetaceans, as well as occasional reports of terrestrial mammals such as deer, moose, and pigs (Heyning and Dahlheim 1988; Guinet 1992; Jefferson et al. 1991 and Baird 2000).
Research on the acoustic of Killer Whale (Orcinus orca) echolocation and foraging have been rare during the years when these animals have been studied in the wild in the waters of Washington and British Columbia. Not until the late 1990’s did research begin to produce results about this unknown chapter on the orcas. Some populations specialize on fish foraging while other specialize on marine mammals. Orcas that forage on fish relay more on echolocation and calls that the ones who prey on marine mammals. Recent experiments that focus on echolocation (Au et al., 2003) concluded that the foraging behavior of Orcinus pursuing salmon is very different to the foraging behavior of killer whales feeding on herring on Norway (Nottestad et. al., 2002 and Au et. al., 2003). Even the strategies used to forage and the use of echolocation and calls are different. Barret-Lennard et al. (1996a) suggested that all of these differences arise from the differences in prey taken, since marine mammals can hear echolocation clicks and potentially evade capture while the fish generally cannot. Residents appear to locate prey underwater using a combination of echolocation and passive listening, and both vision and echolocation are probably important during prey capture (Barret-Lennard et al., 1996a).
The foraging strategy and which aspect the echolocation clicks used by the Southern Residents Killer Whales are ones of the unknown chapters of these animals. Since mammal-eating orcas have been known to hunt in pods, the fish-eating orcas are not been identified if they capture their prey like a pod or each member forage separately (Baird, pers. comm.). Southern Residents are known to travel and perform different social behaviors like a pod or even as a super pod (Baird, pers. comm.), but no pattern of foraging have been established to see if these pod hunt like a group or separately. Since the Chinook Salmon (Oncorhynchus tshawytscha), is the preferred prey in the Northwest Pacific area, cannot detect the echolocation clicks of the whales (Au et,al 2003), is very likely that are more easier to be hunted. Unlike mammal-eating killer whales who do not use too much echolocation to capture their prey, the fish-eating killer whales can perform this clicks in very good standard without been detected makes the foraging be more easier, but that strategy haven’t been established until this research was performed. To investigate this strategy, observations about the position of the whales, when foraging is identified, will be written by a certain amount of time for later be analyzed. Such analysis will reveal if the orcas have a certain pattern as a group or individually forage.
Also the questions on which way they use the echolocation have been a topic of discussion during the 1990’s. Some scientists have proposed that they relay their clicks for navigation; other said that is for foraging only. This study will determine the amount of clicks when foraging and traveling is performed to find a pattern and/or to reveal on which behavior is more likely for the whales to use their echolocation clicks.
This study will be done in the waters surrounding the San Juan Islands, Strait of Juan de Fuca and the Admiralty Inlet area during the last week of September to the end of October (Figure 1). A total of 5 weeks at sea will be the period of observations to answers the questions about foraging strategy and echolocation clicks usage among these cetaceans.
Figure 1. Area where observations were taken from late September to late October.
Materials and Methods
I propose the following procedure to get data regarding echolocations and to identify foraging strategy. A person will record the echolocation and calls that the whales produce during the event through a set of two hydrophones deployed in parallel position to one side of the boat (either port or starboard). The sound will be recorded on a Marantz Recorder Model PMD660 that later can be downloaded on a computer and later be analyzed on acoustic software called Audacity for Macintosh Apple Operating System. A spotter will be collecting data of foraging behavior and will write down the start and end of each minute when the whale travel and perform foraging behavior. Also a time of start and end time of each recording is taken for better localization of sounds in the specific period of time. (Should I mention the characteristics that for me mean foraging behavior?) Put the detail step of the amount of time of the Marantz record. Ask Laura about GPS map, appendix for paper.
For determine the foraging strategy, a person will observe, from the highest point on the vessel, the position on the surface of the whales. It will recorded that position on a special data sheet made for pin-point those position by minute during the entire observation of the whales. The data will be analyzed to determine a pattern of the whales during foraging, especially their strategy. Video and photo footage will be used to record their behavior on their surface before, during and after to be compared with the position data sheets. In case of night foraging, night vision equipment will be used to confirm their behavior on the surface. A specific person should carry this observation when it happens. Data regarding weather and environment are gone to be taken along with data info about the location, GPS coordinates, pod, etc. on a spreadsheet design for this purpose. Such data is going to be recorded by a person.
Additionally, a fish net, with a fine mesh, is going to be used in case that fish scales and/or remains are sighted in the surface after a foraging event. This evidence later is going to be identified to determine what species was hunted and in what area. (For now I have been unable to catch any fish scales, should I put this anyway?)
I compiled records from the area of study from October 3 to October 21. A total of 10 recording were made in various locations, especially on the west side of the San Juan Island. The observations were noted when the pods were spread out, performed a tail lobbing, multiples rapid changes in direction and speed and when sea birds gather around the whales. These characteristics enable to identify the foraging behavior and start making the recordings. Each recording was made by day and the same time divided in numbers of observations. The recordings are a minute long and were recorded on a ScanDisk card. Each time the card full, it was immediately downloaded, deleted and formatted to be used again. The recordings were analyzed on Audacity for later pick up the best recordings, one for foraging and one for traveling. The foraging analysis from October 6 reveal than in ten minutes of recording there were 4,162 clicks with an average of 416.2 per minute. Also the analysis reveals a pattern where the echolocation clicks are more tighter and in some points start in a very small amplitude which increase by each echolocation clicks is emitted (Figure 2). The whales during this observation were very spread out and changing direction and speed frequently. (Put pictures of these here and describe them. Also describe the figure)
The traveling analysis from October 21 reveal than in ten minutes of recording, there were 155 clicks with an average of 15.5 per minute. Each click got very large amplitude most of the time they were emitted (Figure 3). During this observation, the whales were traveling together with sometimes doing synchronized breathing and diving. (Put pictures of these here and describe them. Also describe the figure.)
The observations made for the foraging during four days of data reveal a pattern that the pod spread out even make small group while foraging. Males were usually saw alone or together on the offshore part (or facing the sea?) . Females of juveniles were seen together in-group of 2 to 4 members in a certain spot, usually between the inshore and offshore. Mothers and calves were also group separately with the company of another female more close to the shore. This final type of group was usually observed to be no more than 3. All groups performed rapid changes in direction and speed while foraging like been stated on Baird et, al. 2002. Also lots of tail lobbing was observed and lots of circling around a same spot was noted. The best evidence that a successful hunting was performed was when sea birds were around the whales and continued to be there after the whale presumably made his “kill”. (Add photos of sea birds with the whales and describe them)
Au, W.W.L., J.K.B. Ford, J.K. Horne and K.A. Newman-Allman. 2003. Echolocation signals of free-ranging killer whales (Orcinus orca)and modeling of foraging for Chinook salmon (Oncorhynchus tshawytscha). J. Acoust. Soc. Am. 115 (2). February, 2004.
Baird, R.W. 2000. The killer whale- foraging specializations and group hunting. Pages 127-153 in Cetecean societies: field studies of dolphins and whales. Edited by J. Mann, R.C. Connor, P.L. Tyack and H. Whitehead. University of Chicago Press.
Baird, R.W., M.B. Hanson, E.E. Ashe, M.R. Heithaus and G.J. Marshall. 2002. Studies of foraging in “southern resident” killer whales during July 2002: Dive depths, burst in speed, and the use of a “crittercam” system for examining sb-surface behavior. Report for the NMML, NMFS. February 28, 2003.
Barrett-Lennard, L.G., J.K.B. Ford, and K.A. Heise. 1996. The mixed blessing of echolocation: differences in sonar use by fish-eating and mammal-eating killer whales. Animal Behaviour. 51:553-565.
Nøttestad, L., A. Fernö, and B.E. Axelsen. 2002. Digging in the deep: killer whales’ advanced hunting tactic. Polar Biology 25:939-941.