PIs: Mark Johnson
Woods Hole Oceanographic Institution
Woods Hole, MA 02543
NOAA Program Manager: Deborah Palka, NMFS-NEFSC
Related NOAA Strategic Plan Goal: Goal 1 - Protect, Restore, and Manage the Use of Coastal and Ocean Resources Through Ecosystem-based Management
The MMS funded ‘Sperm Whales in the North Atlantic’ study was a cooperative effort between the Northeast Fisheries Science Center (NEFSC) of the National Marine Fisheries Service and the Woods Hole Oceanographic Institution (WHOI). The study built upon on-going survey work in the North Atlantic by NEFSC and a multi-year tagbased controlled exposure project in the Gulf of Mexico (the SWSS project) by WHOI. The goals in combining these two methodologies were:
1. to obtain baseline data on the behavior of sperm whales in the North Atlantic to compare against data from the Gulf of Mexico and the Mediterranean.
2. to assess the potential of the North Atlantic study area for controlled exposure experiments similar to those carried out in the Gulf of Mexico under the SWSS program.
3. to estimate the surface presence of sperm whales to improve survey-based population estimates.
The study centered on a cruise onboard the NOAA R/V Delaware in July 2003. A total of 12 sperm whales were tagged during the 4 week cruise yielding a substantial data set spanning both deep foraging and socializing. These tag recordings represent the first acquisition of sound and movement data from sperm whales in the North Atlantic. Visual and acoustic surveys were performed whenever weather permitted throughout the cruise and visual focal follows were made when tags were deployed. Complimentary data products included physical oceanographic measurements and skin and fecal samples from tagged and neighboring whales. The tag data set from the cruise has been examined using techniques developed on the SWSS program to parameterize foraging and social behaviors. The data set has also been integrated into a combined data set covering the Gulf of Mexico, North Atlantic and Mediterranean seas to enable comparative analyses. We find that the North Atlantic whales follow a foraging and socializing cycle similar to the Gulf of Mexico whales but dive significantly deeper to forage. Foraging largely occurs at 700-1100 m but a small amount of food may be taken as shallow as 300 m. A wide range of codas are produced but even fairly closely located groups appear to prefer distinct codas. Two factors make the study area undesirable for future controlled exposure trials with an air-gun source. First, an unusually high rate of breaching, possibly associated with tag attachment, limited the longevity of the tag. The maximum attachment duration of 6 hours in the study area compares unfavorably with 16 hours in the Gulf of Mexico and Mediterranean. Secondly, low frequency impulsive sounds from underwater explosions in a Navy test range were frequently heard and would provide a pre-exposure condition amongst whales in a large surrounding region.
The data collection systems and methodologies used for the DTAG component of the Delaware cruise were based on those developed for the SWSS’02 and ’03 cruises.
Detailed descriptions may be found in the reports to MMS for those cruises and only an overview is presented here. Focus here is on the tag-related data collection; the visual survey method is detailed in a companion report from NEFSC.
The DTAG was developed by WHOI principal investigators in 1999 with funding from ONR and WHOI endowment. Details on its design are in Johnson and Tyack (J. Oceanic Eng., Jan. 2003). This non-invasive tag records the sounds heard, and made, by the tagged whale together with its depth and orientation (i.e., pitch, roll, and heading), in a synchronized fashion throughout the dive cycle. The tag records data digitally for between 10 and 24 hours, depending on sampling rate, with enough resolution to track individual fluke strokes and is sensitive enough to record sounds from distant whales and ships. A new version of the DTAG, called DTAG-2, was used in the Delaware cruise and in the SWSS’03 cruise preceding it. This device has more recording capacity and a higher audio sampling rate and resolution than the original
version. It is also one half the size and weight (300g in air). The improved recording capacity is achieved using a loss-less compression algorithm to increase the storage efficiency of the audio data. This algorithm gives a consistent compression factor of between 3 and 4 (i.e., the effective memory capacity is 3-4 times the nominal value). With the 3GByte memories used on the 2003 DTAG-2s, it is possible to record 96 kHz, 16 bit audio for over 16 hours. The sensitivity of the DTAGs used in the SWSS’03 and Delaware cruises was approximately -193 dB re μPa (this is also the clipping level or loudest sound level accurately recorded by the tag).
The DTAG is housed in a plastic fairing and is attached to the whale with a set of four small suction cups. The tag has a low profile on the whale as exemplified by Fig. 1 to minimize the risk of tag removal by conspecific rubbing. The tag has been successfully deployed on more than 60 sperm whales, 25 pilot whales and 5 beaked whales, among other species, with deployment durations of up to 30 hours. In the SWSS’03 cruise in the Gulf of Mexico immediately prior to the Delaware cruise, tag attachments of up to 17 hours with an 8 hour average were achieved with the new tag. The tag has a VHF beacon which broadcasts a signal in the 2m band (148-150 MHz) every second for tracking and recovery of the tag. Data is off-loaded from the tag via an infra-red interface. The tag battery can be recharged while data is offloading maximizing the availability of the device.
1.2 Tagging Method:
Operations in the field are typically run from a research vessel with a high flying bridge for visual observations. Once whales are located and the research vessel has moved close to the animals, a rigid-hulled inflatable boat (RHIB) is deployed with a 3 or 4-person tagging team to attach DTAGs to whales. On the RHIB, a directional hydrophone is used to locate and close on sperm whales. Visual and acoustic observers on the research vessel support the tagging effort by providing surfacing positions and acoustic bearings of whales to the RHIB team. A 46’ cantilevered pole, made of carbon fiber, is used to deliver the tag allowing the approach vessel to remain well behind the flukes of the target animal. Intensive visual and acoustic observations from a nearby research vessel record the social and geographical context of the whales' behavior, before, during, and after tagging. After attaching a tag, the length of the whale is measured using photogrammetry and photographs of the fluke and other distinguishing features are taken for photoidentification. Whether a tag is attached or not, no more than three approaches are made to any individual or tight group of whales in keeping with the requirements of the NMFS permit issued to Peter Tyack. After each approach, the whale’s surfacing location is
inspected to search for feces or skin, and a data sheet is filled out detailing the position, approach number and response of the whale. Once a whale has been tagged and photographed, the RHIB either returns to the research vessel or attempts to tag another whale. No more than three whales are tagged at a time.
1.3 Visual and Acoustic Data Acquisition
Continuous visual and acoustic observation is critical not only to locate and close on sperm whales but also to provide a context for the data collected by the DTAG. Visual observations while following a tagged whale (i.e., during a focal follow) provide a surface track for the tagged whale, anchoring the movement data collected on the DTAG into a geographic frame. Visual and acoustic observations can also define the group size and distance between whales, important data for understanding the social behavior of the tagged whale. Acoustic tracking is also essential to stay with a tagged whale overnight or during bad weather.
For visual observations, we use high-power (‘Big Eye’) binoculars, mounted on tripods on the flying bridge of the research vessel. These are arranged to give a close-to 360 degree view. The visual and acoustics data are entered into logging software which also interfaces with the ship's navigation network to precisely locate each observation. Realtime displays of all the visual and acoustic contacts are maintained in both the acoustics laboratory and on the flying bridge to help the two teams communicate.
During the search phase of operations, sperm whales are located using visual and acoustic techniques. Visual observers scan for whales using the Big-Eye binoculars, and acoustic observers attempt to detect and locate sperm whales by listening for their vocalizations on a towed hydrophone array. Once whales are detected, the research vessel is steered toward the whales, and visual observers record the numbers and distribution of the group of animals. The acoustic observers commence to track submerged whales in preparation for tagging and record array signals to multi-channel audio recorders.
2. Cruise Summary
The field effort took place between the 7th and 31st of July, 2003, on board the R/V Delaware. Both WHOI and NEFSC personnel participated in the cruise. The WHOI
group of 7 included a tagging engineer, acoustic observers, and visual observers. WHOI also supplied a 24’ RHIB for tagging, a towed hydrophone array, and the visual and acoustic data collection hardware and software. The tag boat was a fiberglass-hulled Novurania, called the ‘Balena’, owned by the tagging group at WHOI. The Balena, has two counter-rotating 4-stroke Yamaha 110 hp outboard motors chosen for their low acoustic noise. The Balena was stowed on the aft deck of the Ewing and lowered over the starboard side using the main crane. The tight fit of the Balena on the deck made deployment difficult especially given the persistent roll of the R/V Delaware. However, there were no incidents during deployment or operation of the small boat. The Balena was captained by Wayne Hoggard from Southeast Fisheries Science Center, an expert boat operator with experience of approaching sperm whales gained during the MMSfunded SWAMP trials. DTAGs were delivered using the cantilever-pole method and Mark Johnson operated this system. The other tag-boat crew, Natacha Aguilar de Soto and Peter Madsen, performed the duties of acoustic tracking, permit data fulfillment and video camera operation. All approaches were made under a NMFS permit granted to Peter Tyack which lists Mark Johnson as a co-worker. In addition to tagging, the Balena crew took video for photo-identification and sizing of whales. Fecal samples were collected from diving whales and skin samples were preserved from recovered tags. As radio tracking of tags from the Delaware was impacted by strong interference, the Balena assisted with radio tracking of tagged whales and in recovering tags. Night time recoveries of tags were achieved fairly efficiently from the Delaware although this
required that the acoustic array be winched in.
Two hydrophone arrays were carried onboard the Delaware for acoustic tracking. The WHOI-supplied three-element hydrophone array was built for the SWSS program and deployed from the Delaware as a streaming array (i.e., without a depressor) using a mechanical capstan. The array was used throughout the experiment and performed well. Two software systems were used in parallel for acoustic tracking. The first, Rainbow Click from the International Fund for Animal Welfare (IFAW), provided reliable bearing estimates for distant sperm whales. The other program, developed by Walter Zimmer of the SACLANTCEN NATO Undersea Research Center in La Spezia, Italy, was most effective for close whales and was used during focal follows. Sound from the array was recorded continuously on an Alesis hard-drive recorder at a sampling-rate of 48 kHz while tracking and 96 kHz during focal follows. Acoustic observations were logged using custom software also developed by Zimmer. Sound samples were acquired digitally using Logger software from IFAW. A staff of 4 observers operated the hydrophone array providing 24 hour coverage throughout the cruise except in high sea states and during high speed transits. A summary of the tracklines covered by acoustic watches is shown in Fig. 3 indicating also where sperm whales were heard.
Visual observations were made from the flying bridge of the Delaware and conformed to one of two protocols. While sperm whales were not present, the visual effort was led by NEFSC in a survey study. When sperm whales were located, the visual effort operated in a focal follow mode, using a protocol and data logging system developed under the SWSS program. The data logger combined navigation and observation information into a database and provided a real-time display for both the visual and acoustic personnel. The software for this system was developed cooperatively by WHOI and SACLANTCEN and was managed by Marilena Quero of WHOI. The visual data collection effort operated well throughout the campaign with the results summarized in Fig. 2.
A total of 12 tags were delivered in 7 operational days with sperm whales with the results given in Table 1. Weather was the main limiting factor: only about 45% of available atsea days had sufficiently good weather for tagging. Considering that on many of the bad weather days sperm whales were located and tracked by the Delaware, the encounter rate of whales was excellent. Overall, we found the whales straightforward to approach - comparable to the most successful year in the Gulf of Mexico. 24 approaches were required to deliver 12 tags and only on one day of tagging attempts were we unable to deliver a tag. On a majority of days we delivered 2 or more tags. A summary of time expenditure on the cruise is given below.
With two exceptions, the attachment durations were fairly short (1.0-6.4 hours, see Table 2). This was, in part, due to a large number of breaches: 5 out of 12 tagged whales breached, in most cases ending the attachment. Similar high breaching rates were seen on the SWAMP’01 trial in the Gulf of Mexico whereas in other years, in the same area, few breaches were seen. It is not yet clear whether this was in response to the tag and, if so, what leads to this sort of heightened sensitivity. A high percentage (75%) of tags yielded skin samples. Two tags failed to yield a data-set: one was not recovered due to poor weather and a possible failed VHF transmitter. A second tag had a battery failure during deployment and did not record. The cause of this problem has now been identified and rectified in the design. A third tag remained attached for less than a minute due to a breach.
Despite the short attachments, we sampled each of the usual behavioral modes of sperm whales: foraging dives, socializing, resting, and traveling. The set of 18 deep dives provides a strong initial baseline for estimates of foraging success and energy expenditure using metrics developed in the SWAMP and SWSS programs. In addition to sperm whale vocalizations, the tags recorded sounds from other nearby odontocetes including pilot whales, bottlenose dolphins and spotted dolphins. The sounds of passing vessels and explosions from a distant naval exercise were also collected.
Overall we found the study area to be an exceptionally good site for sperm whale tagging. However the potential for poor weather and few long attachments make the area less attractive for controlled exposure experiments. Any such experiments would also need to examine the extent to which frequent naval exercises may have pre-exposed the population to impulsive sounds.
3. Data Summary
As shown in Table 1, a total of 12 DTAGs were deployed yielding 9 data sets. These were complimented by visual sightings and ship-board acoustic recordings. A full copy of all data was provided to NEFSC at the end of the Delaware cruise for archiving. The procedure for quality assurance, archiving and handling each data source is described in the following.
DTAG Data: The tag data comprises two streams: the audio recording and the sensor stream. Sound from the tag is archived to a sequence of audio files in WAV format. The sampling rate for all tags except sw212a was 96kHz and the resolution was 16 bits. The data in the WAV files corresponds to the raw analog acquisition: a magnitude of 32768 corresponds to a full-scale input on the analog-to-digital converter. The frequency range of the audio acquisition was from about 100Hz to 46kHz with a flat response from 400Hz to 45kHz. The format for audio data as stored on the tag contains a built-in quality check with regularly spaced repeated samples and cyclic-redundancy error checking. The sensor data from the tag is archived in a sequence of 12-channel WAV format files. Each channel corresponds to a physical sensor channel, namely: accelerometer x, y, and z axes, magnetometer x, y and z axes, depth, temperature, and 4 variables related to engineering variables within the tag. The sampling rate of each sensor channel is 50Hz. The raw tag data is archived on CDs in WHOI’s marine mammal center managed by Research Associate Amanda Hansen. The large WAV files are available on hard drives or can be regenerated from the raw data files on any PC. Sensor data are analyzed as described in Johnson and Tyack (2003) which also describes methods for quality assurance. Acoustic records are completely audited to produce a catalog of sounds produced by the tagged whale as well as other natural and man-made sounds recorded by the tag.
Permit Data/Close Observations from RHIB: During close approaches of the RHIB to whales, a range of data is collected for permit compliance, and for sizing and identifying individuals. These data include tagging location, reaction of the whale to tagging, tag placement, videogrammetry, and fluke identification photography. Visual observations are recorded on data sheets. Data sheets are copied in the field for archival and a copy is maintained in the WHOI marine mammal laboratory. Video recordings are streamed into a computer using FireWire and back-ups made on CD. Fluke-shots and other images are extracted as high-quality bit-map images and contributed to local identification catalogues where they exist. A description of each whale approach is generated for reporting purposes to NMFS.
Visual Data: The SACLANT-WHOI visual data collection system acquires ship location and heading at one second intervals and stores this along with visual observations in a Microsoft Access format database. The visual observation data include the range and bearing from the ship to a whale and the aspect (i.e., the heading) of the whale. This data is used to produce a surface track of focal whales (see, for example, Fig. 4) and to correct the dead-reckoned track derived from the tag data. Other visual data recorded include the species location and number of other species as well as the environmental conditions. Locations of whales sighted through the Big-Eye binoculars are determined from their relative bearing and reticle number. The standard algorithm is used to convert reticle number to range, based on the height from the water-line to the binoculars. The visual database is checked daily during the cruise to ensure that group ID’s are correct, and that focal whales were correctly identified. The database is archived on CDs held at the WHOI marine mammal lab. After the cruise, surfacing locations of whales are plotted in
MATLAB or Arcview and integrated with positions of the observation-boat. Acoustic Data: Acoustic data comprises recordings made on the Alesis recorders, audio
samples taken with Logger, and observations recorded with AcLogger. The recordings were backed up using external hard drives and these copies are maintained in the WHOI marine mammal lab. The start and end time of each recording is listed on a data sheet and the disks are sampled to check the recording quality. The AcLogger database was stored in Microsoft Access format and was periodically archived to CD during the cruise. A final copy is kept in the marine mammal lab. The acoustic recordings are used in afterthe- fact data analysis for passive tracking and to link acoustic activity to sounds recorded on the tag.
Skin and fecal samples: Feces and sloughed skin material are occasionally collected during close approaches to whales using a dip-net or small plankton tow-net. Skin is also sometimes found on the DTAG suction cups after tag recovery. Anticipating this, the suction cups are sterilized before each deployment. The location and ID of the animal from which the material was collected are recorded on data sheets. A total of 9 skin
samples and 2 fecal samples were collected from tags or during tagging on the Delaware cruise. Skin samples were stored in vials of DMSO during the cruise and then split for analysis by two separate laboratories. One set of samples was sent to Dan Englehaupt at the University of Durham to determine gender and relatedness. Dan has processed samples collected with DTAGs from the Gulf of Mexico and the Mediterranean and will examine relatedness of the North Atlantic whales with these populations. The other set of samples was analyzed at the NMFS laboratories to compare against samples from previous biopsy efforts in the North Atlantic. For samples with substantial material, excess material will be added to a library of genetic material maintained by NMFS. Fecal samples were first checked for skin which was removed and handled as above. Filtered fecal material was frozen and then taken by NEFSC for analysis.
Analysis of the tag and supporting data proceeds in two phases. The first phase consists of low level auditing of the data. In this phase, the sensor data is calibrated based on laboratory and field calibration values and checked for quality. The data from the orientation sensors (magnetometer and accelerometer) must also be corrected for the tag position on the whale which is estimated from visual sightings of whale aspect (i.e., compass heading) during surfacings as well as photographs and video taken from the tag boat. The tag position is then refined iteratively in order to maximize the consistency of the data. This technique, developed under the SWSS program, takes advantage of the fact that, in normal diving behavior, a sperm whale has a zero mean pitch and roll while at the surface and does not roll during the initial few seconds of a steep (i.e., non-social) dive. This method can also be used to detect a change in placement of the tag due to sliding. The end result is an accurate time series of the whale orientation parameterized by the Euler angles pitch, roll, and yaw. The accelerometer used to determine pitch and roll is inherently sensitive to sudden changes of movement as well as orientation and these give rise to an error in the orientation estimate. Fortunately the occasional episodes with strong dynamics due to sharp acceleration or turning can be readily identified in the data and flagged as inaccurate. The final step in the sensor data preparation is to combine the visual tracks with the DTAG pitch and roll time series to produce a dead-reckoned 3-dimensional track of the whale.
The initial processing of the audio data from the tag involves careful listening of the entire recording by expert listeners. A data sheet is used to record every vocalization from the tagged whale and other nearby whales as well as sounds from movement, vessels etc. Key features are entered into a database. These include creaks (fast click sequences associated with foraging), codas (stereotypical click sequences associated with socializing), and the start and end of regular clicking in each dive. The audio data is also inspected for echoes from the sea floor to determine the altitude of the whale. The second phase of data analysis is to examine the meta-data products produced in the first phase, described above, to determine behavioral states, estimate foraging efficiency, look for evidence of foraging specialization, and to examine social interactions. The same low-level processing has also been performed for tag data acquired during the SWSS and Mediterranean studies. The resulting meta-data has a well-defined format facilitating comparisons between data sets and so the analytic value of the North Atlantic tag data will extend well beyond the time frame of the current project.
We are in the process of preparing a paper based on the North Atlantic data and present here an overview of the two main behavioral states represented in the data: foraging and socializing.
4.1 Dive behavior
The North Atlantic tags recorded normal sequences of deep and shallow dives. We distinguish the deep, typically U-shaped, foraging dives and their accompanying brief surface interval from extended near-surface periods as shown in Fig. 5. Table 2 summarizes the North Atlantic data set in terms of the dive parameters in Fig. 5. The dive times and descent/ascent rates are typical of sperm whales in our other study areas (see Table 3). Dives were on average deeper than in the Gulf of Mexico: four of seven deepdiving whales in the North Atlantic dove below 1000m with a deepest dive depth of 1186m. This is more representative of diving behavior recorded from isolated large males in the Mediterranean where dives to 1250m have been recorded. According to the published bathymetry, the water depth at the North Atlantic tagging locations was between 1500m and 3000m. No bottom echoes have been found in the tag audio data indicating that the whales are at least 500m above the bottom and suggesting that the tagged whales were foraging in the mid-water column, like those in the Mediterranean deep water. In comparison, whales tagged in the Gulf of Mexico and in the Gulf of Genova in the Mediterranean often dove close to the bottom at a depth of between 600 and 1000m.
The tag audio recording was typical of that recorded in the Gulf of Mexico. Deep dives contained regular clicking with interspersed creaks while codas were common in shallow dives and during the near-surface portion of deep dives. The following sections describe the occurrence of sounds in these two dive classes in more detail.
4.2 Foraging Behavior
Table 4 lists the key acoustic features of the deep foraging dives recorded in the North Atlantic. Regular clicks start at normal depths, but some animals keep clicking on the ascent (see especially sw03_201b) which is highly unusual. Looking at the depth distribution of whales from the three study sites, shown in Fig. 6, it appears that the North Atlantic whales spend comparatively less time at the maximum dive depths and rather more at intermediate depths. This is in agreement with the observation that the North Atlantic profiles are somewhat more V-shaped than those seen elsewhere. Some example dive profiles are shown in Figs. 7-12 with acoustic features superimposed. Creaks also occur over a much broader depth range than normal in our other study sites. Although the majority of creaks still occur near the base of the dive, the occasional shallow creaks and continued clicking through the ascent may indicate opportunistic foraging at shallower depths perhaps taking advantage of dispersed layers of prey. This represents a point of difference with Gulf of Mexico and Mediterranean data in which foraging appears to be limited to the base of the dive or to several distinct deep layers. Sperm whales, although primarily teutophagus, are known to also eat fish. In future work, we plan to examine fisheries information for the North Atlantic to identify possible meso-pelagic prey species.
4.3 Social Behavior
As shown in Figs. 7-12, codas (stereotypical click patterns) were often heard near the surface. Codas were made both by deep-diving whales during the descent and ascent, and by whales performing shallow dives. A number of tag recordings made on the Delaware cruise contained extended periods with shallow (<50m) dives and many codas. Codas are considered strong indicators of social behavior and were frequently accompanied, in the tag recordings, by sounds from other nearby conspecifics (usually also codas) and rubbing sounds from body contact. Out of the nine DTAG recordings, four contained codas (see Table 5). Although it can be difficult to judge if a particular sound was made by the tagged whale or another nearby, codas were identified in two recordings that were unambiguously produced by the tagged whale. On average, there were 121 codas on a given tag, with 45 being assigned to the tagged whale.
Figs. 13-14 show the depth histogram of coda production in the three study sites divided according to whether the coda was produced by the tagged (focal) whale or the untagged (nonfocal) whale. Whales in the North Atlantic tended to produce most of their codas in the shallowest part of the foraging dive (i.e., at the very beginning and end of the dive). No codas were recorded below 300 m. In the Gulf of Mexico, whales tended to produce codas throughout the upper 50% of their foraging dives. Most codas were produced above 300 m, although two whales produced codas between 300 m and 400 m. Tagged whales in the Mediterranean produced codas at up to 70% of their maximum dive depth, far deeper than in the other two regions. Three Mediterranean whales produced codas between 500 m and 700 m.
Figure 14 shows the depths at which codas from an untagged whale were recorded by the tag. This figure has a similar form to Figure 13, indicating that focal sperm whales tend to produce codas when they hear them from other animals and that other animals respond to codas produced by the focal whale.
Figures 15-18 show the average number of codas produced by tagged and untagged whales during foraging dive descents (Figure 15), ascents (Figure 16), inter-dive intervals (Figure 17), and surface intervals (Figure 18). Although codas were produced and heard during all phases of the dive cycle, by far the most codas were produced during surface intervals. However animals tend to spend less of their day in the surface behavioral mode than in foraging dives, and so the low number of codas produced in each foraging dive still represent a significant portion of the total coda count. Codas were rarely produced during inter-dive intervals, i.e., between foraging dives.
Codas have previously been described as being produced primarily by animals tightly aggregated at the surface and during surface intervals. The data presented here demonstrate that codas are produced by animals during the descent and ascent portions of foraging dives as well, and are even produced at considerable depth (>500 m in the Mediterranean). This suggests that codas may be used generally by animals to maintain contact at all times, not just when at the surface.
The specific pattern of clicks in a coda has long been thought to indicate group allegiance or correspond to geographic location. Table 6 lists the numbers of distinct coda types recorded by tags in the North Atlantic. Although a wide variety of codas were heard, a majority of codas were of types 1 to 6. Nine, eight, and two click codas were common to two or more of the tag recordings, while all other codas types were only heard on a single tag recording. Tagged and untagged whales on the same tag recording seem to produce similar types of codas but whales tagged on adjacent days in close geographic proximity such as 206c and 207a do not seem to use similar coda types. This may reflect a diverse population in the North Atlantic or broad repertoire of codas. Work is continuing to compare coda usage between the three study sites.
Wayne Hoggard, Walter Zimmer, Debi Palka, Matt Grund, Alex Shorter, Kira Barton, Tom Hurst, Dan Englehaupt, crew and science party of the R/V Delaware.
A paper describing the coda results is currently in preparation by S. Watwood.
Publications and presentations drawing on this work:
Miller P.J.O., Johnson M., Tyack P.L., "Sperm whale behaviour is consistent with use of rapid echolocation click buzzes “creaks” in prey capture", Proc. Royal Soc, in press.
Tyack P.L., Johnson M., Madsen P.T., "Echolocation in wild toothed whales", 147th meeting Ac. Soc. Am., NY, May, 2004.
Miller P.J.O., Johnson M.P., Tyack P.L., Terray E.A., "Swimming gaits, passive drag, and buoyancy of diving sperm whales (Physeter macrocephalus)", J Exp Biol., 207(Pt
11):1953-1967. May, 2004.
Miller, P.J.O., Johnson, M., Tyack, P.L., Terray E.A., "Swimming gaits, passive drag, and buoyancy of diving sperm whales (Physeter Macrocephalus)", European Research on Cetaceans 18th, Sweden, 2004.
Madsen, P.T., Johnson, M., Tyack, P., "Biomechanics and dynamics of the sperm whale sound generator with implications for foraging", European Research on Cetaceans 18th, Sweden, 2004.