AEI Special Report: 2006 International Whaling Commission Noise Research - At each annual meeting of the International Whaling Commission, the Scientific Committee sponsors a summary of recent research entitled the State of the Cetacean Environment Report (SOCER), which includes a section on noise. This year, the Committee also held a pre-meeting workshop on the noise impacts of seismic surveys. Our Special Report provides a quick overview of recent research findings presented in both of these publications, as well as links to the full texts. [GO THERE]
Sperm Whale Dive Patterns Suggest Long-range Echolocation
Watwood, Miller, Johnson, Madsen, Tyack. Deep-diving foraging behaviour of sperm whales (Physeter macrocephalus). Journal of Animal Ecology 2006. 75, 814-825.
This study used acoustic tags to track and listen to sperm whales during dives. The researchers compared dive and vocalization patterns in three distinct populations of sperm whales in different parts of the world: the Atlantic Ocean, Gulf of Mexico, and Ligurian Sea. During their descent, whales spent an average of 64% of the time emitting echolocation clicks, suggesting they are devoting their descent to the search for prey. As they approach prey, the emit a buzzing sound, a more detailed echolocation signal. They found that dive and click/buzz patterns are consistent throughout the world's temperate and sub-tropical oceans (this study did not include high latitude populations). One interesting conclusion they reached was that sperm whale evolutionary success (relatively unchanged for 10 million years) is largely based on the ability to successfully echolocate during their descent, locating patches of prey from a significant distance (300-500m). They made no comments about whether ambient noise might hinder such long-range echolocation, but it may deserve consideration and study. Most dives last 40-50 minutes and range from 400 to 1200 meters at their deepest point (most commonly bottoming out at 600-900m). It may be that at depths, there is little propagation of noise that would interfere with the relatively high frequencies of echolocation clicks; higher frequencies do not generally travel much beyond a few hundred meters before becoming inaudible.
Elephants Respond to Seismic Stimuli
C. E. O’Connell-Rodwell, J. D. Wood, T. C. Rodwell, S. Puria, S. R. Partan, R. Keefe, D. Shriver, B. T. Arnason and L. A. Hart. Wild elephant (Loxodonta africana) breeding herds respond to artificially transmitted seismic stimuli. Behavioral Ecology and Sociobiology, 59:6, 842-850. April 2006.
Seismic communication in elephants takes place using infrasonic (low-frequency) sound transmitted through the ground. This study played seismic components of elephant alarm calls, and measured the behavioral reaction of elephants at a water hole. The researchers made sure that there were no airborne component of the sounds that might cue the animals. Elephants responded to the alarm calls as might be expected, by grouping closer together and by spending less time at the waterhole. The overall response rates were less than when alarm calls are received as airborne sound; researchers suspect that the seismic-only delivery of the sounds indicated that the threat was relatively distant. The study was not designed to see if elephants could distinguish meaning from the seismic signal (ie, no non-alarm seismic calls were used), so there is also the chance that the lesser reaction was related to not being sure what the call was communicating (ie they responded to the existance of a seismic elephant call, but not specifically defensively). The mechanism by which elephants perceive seismic calls is not yet known, though researchers suspect bone conduction via the toes; field studies have shown that elephants can detect seismic at distances of up to 2km, and models suggest possible perception at up to 16km in favorable soil conditions.
Right Whale Calls Changing in Industrialized Habitats
Parks, Clark, Tyack. Acoustic communication in the north atlantic right whale (Eubaleana glacialis) and potential impacts of noise. Presented at Ocean Science 2006 conference, January 2006.
Noting that the north atlantic right whale vocal repertoire is becoming better understood (sounds are used for making long-range contact, formation of social groupings, and reproductive advertisement), and that the whales live in a highly industrialized habitat, this study investigated changes in the whales' calls over time that may be in response to rising noise levels. On short time scales (minutes), both the fundamental and peak frequency of calls increase in the presence of elevated noise levels. On longer time scales (decades), the minimum and maximum frequency of a key whale call, the "upcall", have increased between the late 1950s and 2004; this increasing frequency has been gradually noted over decades. The North Atlantic Right whale upcalls are at a significantly higher frequency than the southern right whales' calls, which may be a result of differing ambient noise conditions in their environment. These results are significant, as they present evidence for a long-term, chronic behavioral change in the North Atlantic right whale calling behavior that may be a result of increased levels of anthropogenic noise.
Discomfort Zone Suggested as Alternative to TTS
Two recent studies undertaken as part of an environmental assessment of a new underwater communications system have introduced the concept of a "Discomfort Zone" as an alternative to estimates of Temporary Threshold Shifts (TTS), for scientists and regulators assessing the biological impacts of exposure to human sounds. TTS is a temporary hearing loss, generally meaning that quiet sounds are more difficult to hear. To prevent grounding of ships and collisions between ships in shallow coastal waters, an underwater data collection and communication network is currently under development: Acoustic Communication network for Monitoring of underwater Environment in coastal areas (ACME). Marine mammals might be affected by ACME sounds since they use sounds of similar frequencies (around 12 kHz) for communication, orientation, and prey location. If marine mammals tend to avoid the vicinity of the transmitters, they may be kept away from ecologically important areas by ACME sounds. A team of researchers from the Netherlands and the UK suggest that this new behavioral criterion is a more appropriate threshold of minimal allowable disturbance than the physiological threshold of TTS, because "if animals are deterred by sounds from ecologically important areas to less favourable areas, this might effect the population size." Such a shift of emphasis is especially relevant for chronic noise sources, such as the proposed communication network, or even shipping noise, which could be presumed to cause long-term or recurring avoidance of the resulting discomfort zones.
Harbour Seal Acoustic Discomfort Zone
Kastelein, van der Heul, Verboom, Triesscheijn, Jennings. The influence of underwater data transmission sounds on the displacement behaviour of captive harbour seals (Phoca vitulina).Marine Environmental Research 61 (2006) 19–39.
This study, using captive animals, was designed to determine the received sound levels at which harbour seals showed avoidance behavior, or what the researchers termed the "acoustic discomfort threshold." For all four test sounds, seals avoided zones where the sounds were louder than 107dB (SPL). These results are in an "ecologically neutral" area; that is, the seals could respond to simple discomfort; it is possible that in the wild, seals may tolerate higher levels, in order to get food, escape predators, or stay with a pup. The researchers suggest that "source levels can be selected that have an acceptable effect on harbour seals in particular areas" and recommend that "the source level of the communication system should be adapted to each area (taking into account the width of a sea arm, the local sound propagation, and the importance of an area to the affected species). The discomfort zone should not coincide with ecologically important areas (for instance resting, breeding, suckling, and feeding areas), or routes between these areas. In practice, their models suggest that the radius of the discomfort zone would range from 20m (if the source level of the ACME system is 130dB re 1Pa at 1m), to 200m (source 150dB), 2km (source 170dB), or 6.3km (source 180dB).
Harbour Porpoise Acoustic Discomfort Zone
Kastelein, Verboom, Muijsers, Jennings, van der Heul. The influence of acoustic transmissions for underwater data transmission on the behaviour of harbour porpoises (Phocoena phocoena) in a floating pen. Marine Environmental Research 59 (2005) 287–307.
This study measured the change in location in a pool of two harbor porpoises exposed to three different ACME test sounds. Both dolphins moved away from the sound, though one moved farther than the other. Within seconds after the test sounds stopped, they resumed normal behavior, generally moving quickly back to the end of the pen where the sound source had been. While the animals clearly moved away from the test sound, there was a significant difference in the amount of displacement caused by the various test sounds (mean discomfort zone ranged from 23m to 18m). This study, while suggestive, is limited by the fact that only two dolphins were tested, as well as by to other key factors: source levels were relatively low, so that the discomfort zone would be small enough to be measured in a relatively small pool, and animals were not exposed to test sounds for long periods, which might have revealed the potential for habituation. A key finding was that the porpoises were much more sensitive to some of the proposed ACME sounds than to others. Low bit-rate, chirp-like sounds, with clear on-off switching, were more disturbing than high bit-rate, more random sounds.
