Orcas Avoid Mid-frequency Sonar Signals, but not LFAS; Herring Unaffected
Kvadsheim, Benders, Miller, Doksaeter, Knudsen, Tyack, Nordlund, Lam, Samarra, Kleivane, Godo. Herring (slid), killer whales (spekknogger) and sonar - the 3S-2006 cruise report with preliminary results. Norwegian Defence Research Establishment (FFI). 30 April 2007
This paper reports preliminary results from an ambitious multi-national Controlled Exposure Experiment using acoustic D-tags, which allow researchers to record received sound levels while charting dive patterns. Six orcas were tagged, with 17 hours of data collected, with one animal exposed to LFAS signals, two to mid-frequency active sonar signals, and one used as a control, fewer samples than hoped. The whale exposed to LFAS signal did not change its behavior, nor did its companions. However, the group exposed to mid-frequency sonar signals ceased feeding and moved rapidly away; in addition, they exhibited an unusual dive pattern, diving roughly twice as deep (over 60m) as normal (20-45m), including a highly unusual reversal of their ascent (coming up to 15m from the surface, then retreating again to 60m). [Ed. note, not part of the report narrative, based on observation of included diagrams: Four other dives during the 35-minute sonar transmission were within the normal range of depth (the deep dive was the third of five dives during sonar transmission), with three longer than normal rest periods at the surface during the hour after sonar transmission ceased.] Received levels did not exceed 150dB re 1uPa. Looking at longer-term responses, while the experimental use of sonar in the herring trials did not seem to deter orcas from the general area, by contrast, no orcas were seen during three days of a planned Navy exercise in the area that included mid-frequency sonar use. The herring trials used bottom-mounted sensors to chart the mean depth of a school of herring as a sonar vessels passed nearby. Herring at shallow depths (25-50m) tended to show a minor downward reaction as the sonar source ship passed overhead, while herring located deeper, or in less dense schools, showed no detectable reaction; no horizontal avoidance was seen. While herring hearing curves suggest they should be able to clearly hear LFAS signals, but not mid-frequency signals, the responses were the same for all signals (including ship-only, no sonar), suggesting that the herring may have been responding to the sound of the ship, rather than the sonar signal; such reactions to ships have been seen for many fish species. A related trial using orca echolocation signals on the herring showed more of a response, suggesting that the herring could distinguish between the mid-frequency sonar and the orca sounds, but the three trials all produced slightly different response patterns, suggesting the need for further study.

Review of Possible Ways that Increasing Ocean Noise May Affect Marine Mammals
Peter L. Tyack. Implications for marine mammals of large-scale changes in the marine acoustic environment. Journal of Mammalogy, 89(3): 549-558, 2008. [DOWNLOAD PAPER(pdf)]
In this wide-ranging literature review, Peter Tyack of Woods Hole Oceanographic Institute sketches the history of research into the effects of noise on marine life, with some references as well to effects noted on terrestrial creatures. He begins by noting that while acute disturbance of individuals attracts the most attention, the likely more profound effects of chronic disturbance on population vitality (success in foraging and mating) are much harder to discern. Several examples are presented of studies that documented both temporary and long-term abandonment of key habitat when loud noise was present (including grey whales abandoning a birthing lagoon for several years, then returning when the salt production facility was abandoned, and dolphins moving away from foraging habitat when shipping traffic is heavy).

Next, Tyack turns to a detailed examination of the question of whether global shipping may be dramatically decreasing the area within which whales can hear each other's calls, beginning with the thought that the unintentional consequences of increased shipping noise may be creating unexpected problems analogous to those created by the introduction of industrial-waste gasses into the atmosphere, which went unnoticed for decades. Following on models created in the 1970s, updated to take into account the hundred-fold increase in shipping noise since then, he notes that "the increase in ambient noise from shipping seems to have reduced the detectable range of low frequency whale calls from many hundreds of kilometers in the prepropeller ocean down to tens of kilometers in many settings today." (For example, the finback whale range shrank from at least 400km in the pre-engine ocean to 90km in the 1960s, down to 32km today.) He notes that, as populations of great whales fall, the separation between them may increase, with these increases in shipping noise compounding the challenge of finding mates or sharing information about active feeding grounds. However, he then goes on to point out that there is, so far, no clear evidence that the great whales do indeed communicate over long distances; clear responses to the calls of other whales have been seen only at ranges of 10km or less; the fact that a human acoustic sensor can detect a signal at 400km does not necessarily mean that the whales themselves rely on hearing signals at such distances. He suggests that acoustic tags may help to clarify whether distant, faint signals from conspecifics (whales of the same species) do in fact trigger any discernable reaction (calling in response, or moving toward the distant whale).

While noting that it may be impossible to design scientifically valid studies to uncover the possible cost of "lost opportunities" when communication is drowned out by shipping noise, an indirect way to get at this question is within reach of researchers: if animals alter their calls in noisy conditions, we can infer that the noise is disrupting their normal communication channels. And indeed, Tyack notes a long list of studies that show such changes, such as beluga whales and manatees increasing the volume of their calls in noisy conditions, and an apparently dramatic increase in the frequency (pitch) of right whale calls in sections of the ocean where low-frequency shipping noise is more intense. While noting that these and other studies "suggest that vessel noise clearly does interfere with communication in marine mammals," Tyack also notes that we do not know how costly these adaptations are, or what noise level would preclude such compensation. Also, he asks, "When does noise so degrade the usefulness of a habitat that animals leave? Can this level be predicted by the compensation behavior?" As of yet, these are unanswered, and difficult to answer, questions.

Finally, Tyack turns to research that show clear disturbance reactions to ocean noise, including killer whales staying 4km away from acoustic harassment signals near fish farms, dolphin numbers dropping to 8% of normal within 3.5 km of similar noise-makers on other fish farms (with those small numbers implying that the avoidance distance was far greater). He notes that the degree of displacement or behavioral response is not necessarily a direct indicator of the severity of impact, suggesting that "if an animal is in bad enough condition that the risk of altering behavior is high, then it may be less likely to show a disturbance response." For example, hungry animals will linger in a feeding area the longest. He also notes that some responses to noise may be caused by noise sources that resemble a predator's call (as in recent modeling Tyack has done that suggests beaked whale decompression sickness may result from a long series of near-surface dives as the whales flee sonar signals that they mistake for orca calls). He cites some compelling studies on terrestrial animals showing that repeated disturbance exacts high costs in reproductive success and overall health (including a study of geese that showed that when undisturbed, geese increased their body mass and had a 46% breeding success, whereas in nearby areas where farmers scared them off their fields, they did not gain mass and had a breeding success of only 17%).

To conclude, Tyack suggests that there are several lines of research that have so far received little attention, which could help to move key understanding of noise impacts forward, including: focusing on the most vulnerable animals as subject of study into the effects of disturbance, further study of the possibility that predator responses underlay key behavioral impacts (including fleeing, increased vigilance, and avoiding habitats), and following up on the recent theory of allostasis (behavioral changes that allow an animal to maintain equilibrium in the face of external environmental changes or stressors) as a way of understanding the costs and benefits of changing behavior in the face of noise.

Marine Mammal Commission Report on Population Viability and Budgetary Priorities for Recovery of Engangered Marine Mammals
The Biological Viability of the Most Endangered Marine Mammals and the Cost-effectiveness of Protection Programs. A Report to Congress from teh Marine Mammal Commission. February 2008. [DOWNLOAD REPORT (pdf)]
This 400+ page report is the culmination of a multi-year initiative by the MMC. It includes about 60 pages of summation, followed by several lenghty appendixes, the most substantial being a 160-page species-by-species assessment of endangered, threatened, and depleted marine mammals, focusing on historic and current populations, and the status of protection programs for each, and a 30-page report on the population viability of each species; two other sections address Right whale recovery efforts, as this species is a major focus in the eastern Atlantic. Among the goals of the report is to make recommendations as to how best to prioritize population recovery efforts, within the context of limited funding. The report notes, for example, that some species have received relatively high levels of attention via directed funding (e.g., western Sterallar sea lions), while others have not received enough funding to prevent or even fully understand their ongoing declines (e.g., Cook Inlet beluga whales). Its key recommendation is that a coherent national strategy be developed, centered on a dynamic and adaptable approach that includes both a separate funding stream for research and management for marine mammal population recovery, and a strategy to prioritize recovery attention basedon objective criteria including risk of extinction, expected conservation benefits, competing conservation needs, based on a structured and transparent risk/benefit analysis. One striking element to the MMC report is the consistant attention paid to noise as a key factor in species stress, decline, and recovery.

Extensive Survey Finds Humpbacks Respond Minimally to Airgun Noise
Caroline Weir. Overt Responses of Humpback Whales (Megaptera novaeangliae), Sperm Whales (Physeter macrocephalus), and Atlantic Spotted Dolphins (Stellena frontalis) to Seismic Exploration off Angola. Aquatic Mammals 2008, 34 (1), 71-83.
During ten months of seismic surveys off the Angola coast, 2769 hours of marine mammal observations were made from a survey vessel, seeking to determine whether marine mammals avoided the airgun noise. This study did not examine subtler responses, such as dive patterns or call rates, but simply tracked sighting rates and distances. The total number of marine mammal sightings was rather small, given the long timeframe (66 humpbacks, 124 sperm whales, 17 dolphins); the author does not offer any hints as to whether populations are simply low in that area, or whether observations were limited for any other reason (weather, single observer, high seas, etc.). Airguns were active roughly half the time, providing a balanced set of data to look at. The mean distance at which all species were seen was greater when airguns were active than when they were silent, though only the dolphins showed a statistically significant difference. The closest approach of humpbacks averaged 3000m with guns off and 2700m with guns on, with sperm whale results virtually identical; dolphins, by contrast, came much closer during guns-off, 209m, than when guns were on, 1080m. Perhaps unexpectedly, more whales were seen at virtually each distance charted (from 1km to 6km) when the airguns were on--while this could indicate a lack of avoidance behavior, it is also possible that it was caused by the whales staying at or near the surface while airguns were active, a "vertical avoidance" of higher sound levels at depth (near the surface, the airgun noise is reduced by destructive interference as sound bounces off the surface). Counter to expectations that the large whales would be more sensitive to the predominantly low-frequency airgun noise, the dolphins were much more dramatically affected. All nine times that dolphins approached the ship occurred only in airguns-off periods, and on one occasion, an approaching group of dolphins clearly veered away as the airguns ramped up. While the dolphins clearly avoided an area near the ship, there was no evidence that the seismic survey activity displaced any species from the region; sperm whale sightings increased over the course of the survey.

Some Sperm Whales React to Aircraft Overflights
Smultea, Mobley, Fertl, Fulling. An unusual reaction and other observatoins of sperm whales near fixed-wing aircraft. Gulf and Caribbean Research Vol 20, 75-80, 2008.
Reports of sperm whale reactions to airplanes and helicopters have been nearly all opportunistic observations, with the few published reports or studies offering conflicting views. During this population-monitoring study, careful records were kept of any visible behavioral reactions, as part of the NMFS permit conditions. While the majority of whales encountered seemed to exhibit no obvious reaction (none of the groups that were over 360m responded in ways obvious from the air), a significant subset of groups that were approached within 360 m (3 of the 8 groups) did indeed respond with sudden dives as the plane first appeared, and a fourth group took up group formations the researchers interpreted as agitation, distress, and/or defense. In the context of this population survey, such disturbance was transient and likely insignificant in terms of population health. However, the researchers note that "repeated or prolonged exposure to aircraft overflights have the potential to result in significant disturbance of biological functions, especially in important nursery, breeding or feeding areas." They suggest that such cumulative effects could be possible in areas frequented by military training exercises, ecotourism flights (e.g. off Hawaii or New Zealand), and helicopter flights servicing oil and gas installations (which are projected to account for 25,000 to 55,000 flights per year in the northern Gulf of Mexico, centered on the Mississippi Delta area, a high-use area for sperm whales, particularly females and calves, and are likely equally significant in the North Sea and, increasingly, in the South Pacific and West Africa). The researchers stress the need for further study including, among other things, individual variability of sensitivity to noise (i.e., is a subset of the population likely to be consistently more "skittish" and therefore more impacted by repeated noise intrusions?) and the use of D-Tags to record received sound levels as well as more detailed behavioral response data (including call rates, dive patterns, respiration patterns) without relying on the noise intrusion itself as the observation platform, which limits the duration of observation and does not provide crucial information on behavior before, during, and after the noise intrusion.

Autonomous Gliders Provide New Platform for Acoustic Research
Moore, Howe, Stafford, Boyd. Including Whale Call Detection in Standard Ocean Measurements: Applications of Acoustic Seagliders. Marine Technology Society Journal. Winter 2007/2008, Vol 41, Number 4, p 53-57.
Reports on a 2006 trial in which broadband (5Hz to 30kHz) recorders were installed on three Seagliders off Monterey Bay. Blue whale calls were detected on all but two of 76 dives, and humpbacks were detected on 20% of dives. Clicks and whistles similar to those made by dolphins and small whales were also detected, though not the focus of the study. As the researchers note, "The potential to include whale call detection in the suite of standard oceanographic measures is unprecedented and provides a foundation for mobile sampling strategies at scales that better match the vertical and horizontal movement of the whales themselves."

Workshop Report: Encouraging Establishment of Noise-Free Zones in and Around Marine Protected Areas
Agardy, Aguilar, Canadas, Engel, Frantzis, Hatch, Hoyt, Kashner, LaBrecque, Martin, Notarbartolo di Sciara, Pavan, Servidio, Smith, Want, Weilgart, Wintle, Wright. 2007. A Global Scientific Workshop on Spatio-Temporal Management of Noise. Report of the Scientific Workshop. 44 pages. [DOWNLOAD(pdf)]
In June 2007, a workshop was held in the Canary Islands to consider the potentials for extending the management principles used in Marine Protected Areas to provide some protection from anthropogenic noise. Fundamental to the purpose and effectiveness of MPAs are "spatio-temporal restrictions" (STRs) of specific human activities: for example, excluding fishing, from a specific area (spatial restriction), or sometimes at times of special biological importance, such as spawning (temporal restriction). Few of today's MPAs are large enough to provide protection from "elevated levels of ensonification:" buffers of tens of kilometers would be necessary for protection from mid-frequency sound, and a hundred or more kilometers from low-frequency sound. Of today's 350 MPAs that include some cetacean habitat, 64 are large enough to provide some mid-frequency protection, 20 are large enough to provide at least some low-frequency protection (e.g. shipping), and only the 6 largest are probably sufficient to protect from shipping noise. (of course, shipping is not generally excluded from MPAs: this is merely a hint at the scale of noise STRs that would be useful.) The Workshop report includes several key sections:

• Descriptions of some existing attempts to provide STRs focused on noise: In 2003, Brazil established a large buffer zone around a small existing MPA, to exclude the sounds of seismic survey airguns from entering the MPA (the buffer was withdrawn by a court due to jurisdictional issues; attempts are underway to re-establish it). In the Canary Islands, a 50 nautical mile buffer zone has been established around the islands, in which active sonar is not allowed (there have been some subsequent strandings that raise questions whether this is large enough a buffer).
• Recommendations for MPA managers, centered on a framework for making management decisions regarding possible noise-related STRs.
• Recommendation that noise-producers provide more information, and longer lead times prior to operations near MPAs, to allow for analysis of effects of proposed noise. A far-reaching element of this is a call for use of "detectability curves" to reflect how easy it is to find various species of whales, and to insure that more effort is made to find hard-to-detect whales, rather than assuming that they are not present if none are found using standard observational techniques.
• Recommended measures that could reduce the noise impacts of the primary noise producing activities.
• Suggested MPAs or proposed MPAs where noise-oriented STRs could be introduced, as case studies for future MPA managment protocols. These include the PELAGOS Sancturay in the northwestern Mediterranean, off France, Italy, and Monaco, the Alborian Sea/Strait of Gibraltar, the Bay of Bengal, and East Asian waters off Japan, China, and the Philippines.

Ocean Fish Vary Widely in Startle Response to Noise
Kastelein, van der Heul, Verboom, Jennings, van der Veen, de Haan. Startle resposne of captive North Sea fish species to underwater tones between 0.1 and 64kHz. Marine Environmental Research 65 (2008) 369-377.
This study exposed eight marine fish species to pure tones ranging from 100Hz to 64kHz. The tests took place in specially designed quiet tanks; species were chosen in part due to their economic importance to fisheries. Some species did not respond to the sound at all, even at the highest dB levels that could be produced, while others exhibited very clear startle responses to a relatively narrow range of frequencies (generally 100-700Hz), at received levels of about 100dB (re 1uPa, rms) for the lowest frequencies, with the startle threshold increasing to the range of 160dB as frequency increased to 700Hz. Only one species responded to higher frequencies than this: Horse mackeral responses extended up to 2kHz. The species that did not startle at all were Atlantic cod, Pollack, Common eel, and Atlantic herring. Horse mackeral startled to the widest range of frequencies, with Sea bass also quite responsive; Thicklip mullet and Pout both startled to a narrower range of frequencies. Interestingly, for fish that have established audiograms, it appears that the startle response does not begin until the noise is 10-30dB above the hearing threshold; and, again, some fish showed no startle even at levels up to 45dB above their presumed hearing threshold. The researchers note that these results on captive fish to pure tones can not be reliably extraploated to wild fish in varied contexts or to more complicated sounds, but suggest that the extreme variability seen here is an important consideration in more natural situations as well. They suggest futher study using "sounds more similar to anthropogenic noise, to more complicated sounds, such as sweeps, and to the actual broad-band noise of, for instance, wind turbines and shipping..."

Quiet Reserch Vessels Still Scare Fish; May Be Pressure Waves
Sand, Karlsen, Knudsen. Coment on "Silent research vessels are not quiet" [J. Acoust. Soc. Am. 21, EL145-EL150]
Recent efforts to increase the accuracy of fish population surveys by employing specially-designed quiet research vessels that would not scare fish away with their approach were confounded by a study that indicated that a new quiet vessel actually scared the fish more easily. The commenters in this letter to the editor suggest that this may be due to the sensitivity of many fish species to pressure waves (or, "infrasonic particle acceleration") created by ship hulls. Thus design of research vessels may need to look beyond noise emission, and consider hull shapes. The vessel that was quiet yet disruptive had a large displacement volume; the commenters here suggest that minimal water displacement, such as hovercraft or foil type vessels may reduce the disruptive particle acceleration.

Harbor porpoise deterred by 50kHz tone
Kastelein, Verboom, Jennings, de Haan. Behavioral avoidance threshold level of a harbor porpoise (Phocoena phocoena) for a continuous 50kHz pure tone. JASA, 123(4), 1858-1861.
This simple study using one captive porpoise was aimed at determining whether pure tones in a frequency range not typically used by (or audible to) fish, seals, or other non-target species could be used to deter harbor porpoises from fish farms and gillnets. The ultrasonic, 50kHz pure tone being used is also less subject to masking by low- and mid-frequency-rich ambient noise. When presented with the 50kHz tone at a source level of 122dB (re 1uPa, rms), the porpoise swam away to a distance where the received level was 107dB; its respiration rate did not increase, indicating that it was relatively comfortable with the sound, and the avoidance behavior. It did not move to more distant areas of the pool where the sound level was lower, down to 98dB, or to nearby areas where levels were 101dB. During the three week study period, including 66 trials of 15 min with at least an hour between tests, no habituation was observed; when the signal was activated, the animal moved from its usual small swimming area (where the received level was averaged 113dB when the test signal was on), to an area of the floating pen where the signal was 107db. The researchers note that this single-animal test needs to be expanded to include more animals, to assure that individual hearing sensitivity, age, or habits of this porpose did not distort the results. (Ed. note: the area the animal chose to move to was closely adjacent to its preferred swimming location in one end of the pool; there may be a chance that this "site fidelity" affected how far it felt comfortable moving from the sound, and with less attachment to a specific location, it may have chosen to move further away. If so, this would suggest that even when strongly preferring a given location, the signal would be an effective deterrent, which could be important in areas where both humans and popoises like to fish.)

Construction Noise in Arctic Waters Travels 3-10km
Greene, Blackwell, McLennan. Sounds and vibrations in the frozen Beaufort Sea during gravel island construction. Journal of the Acoustic Society of America, February 2008, 123(2), p.687-695
Recodings made during construction of a man-made island, 5km offshore in 12km of water, reveal that the noises of ice-augering, pumping, backhoe trenching the seafloor, and pile driving can be heard for several kilomters underwater. Sound measurements were made above the ice (in-air) and underwater; vibrations in the ice were also measured. Airborne sounds disipated to background ambient levels at less than 3km, while underwater sound reached median background levels at just over 7km, and in-ice vibrations reached natural levels by 10km.

Toothed Whale Hearing Senstivities Can Be Turned Up and Down
Supin, Nachtigall, Breese. Hearing sensitivity during target presence and absene while a whale echolocates. J. Acoust. Soc. Am. 123 (1), January 2008, 534-541
This very interesting paper, digging deeper into a topic that had emerged in previous studies of toothed whale hearing, reveals that a pilot whale could apparently "turn up" its hearing sensitivity, so that it could listen for fainter (more distant) sounds when echolocation clicks did not reveal nearby echoes. The research used a captive whale, outfitted with suction-mounted EEG electrodes to measure evoked potentials as it echolocated; half the time, a target fish was nearby, and half the time there was no nearby fish. When no fish was present, hearing sensitivity was 20dB higher (ie it could hear sounds 20dB more faint).

Note: Following are some highlights of the 2007 Research Summaries; see archive pages linked above for more entries

Initial Cruise Report From First Controlled Exposure Studies of Beaked Whales
Ian Boyd, Diane Claridge, Christopher Clark, Brandon Southall, Peter Tyack. Behavioral Response Study-2007, Cruise Report, Phase 1
A summary of the project, and the preliminary cruise report are available: [WEBSITE]
Good article in Woods Hole magazine, Oceanus, on the research: [READ ARTICLE]
During August and September, 2007, the first controlled exposure experiments aimed at learning more about the ways that beaked and pilot whales respond to exposure to mid-frequency active sonar took place in the Bahamas. For the past decade or more, much emphasis has been placed on discovering what sound levels cause TTS (temporary threshold shifts, or short-term hearing impairment), with the thought that these levels could serve as a benchmark of exposure levels that we should be concerned about; however, it appears that in some cases, beaked whales that ended up stranding were exposed to much lower sound levels. Hence, the need to learn more about how they change their dive patterns and other behaviors in response to moderate sound exposure. D-tags, which have been successfully used in studies of sperm whales for several years, provide an opportunity to safely measure received sound levels and dive patterns simultaneously. The tags are applied with a long pole when the whales are at the surface, remain attached via suction cups, and fall off within 10 or 15 hours. The researchers noted that, in the absence of a clear sense of when and why some beaked whales are affected to such a strong degree that they beach and die, the result has been a highly precautionary and sometimes arbitrary approaches to management of sound, leading to debates between interested parties that have at times been difficult and ultimately unproductive. In planning for these experiments, the researchers worked with a wide range of parties, including environmental NGOs; while some NGOs had strong reservations about controlled exposure studies, the researchers note that "a constructive spirit of dialogue contributed to the success of the study." Goals of this study: to establish protocols for tagging and careful controlled exposures, to discern exposure parameters that cause a behavioral response (change in behavior), and to compare any responses to sonar signals and orca sounds, to begin to explore whether they respond to sonar as a possible predator. Ten animals were successfully tagged; 6 Blainsvilles beaked whales and 4 pilot whales. Seven provided control/baseline measurements, and 3 tagged animals were exposed to playbacks of MFA and/or orca sounds (1 beaked, 2 pilot). The researchers provide rather detailed descriptions of the responses of the one beaked whale that was tagged during controlled exposure; of course, with only one sample, and few controls, all results are very tentative.

Extended Near-surface Dives May Be Cause of Beaked Whale Bends
Walter, M.X. Simmer, Peter L. Tyack. Repetitive shallow dives pose decompression risk in deep-diving beaked whales. Marine Mammal Science, Volume 23 Issue 4 Page 888-925, October 2007.
ScienceNow summary of paper: [WEBSITE]
It is apparent that beaked whales are especially sensitive to mid-frequency sonar, but the reasons have remained elusive. This study explores a new idea about how the whales' dive patterns may be disrupted enough to cause decompression sickness (DCS, ie "the bends"). Some have suspected that exposure to sonar may cause the whales to surface more quickly than usual, but since the whales' lungs are collapsed in dives deeper than 70m (thus preventing nitrogen from entering the bloodstream and infiltrating into tissues where it could cause damage), it is not readily apparent how faster surfacing would cause DCS. Instead, this study looks at the "recovery" period observed in beaked whales, during which they make a series of near-surface dives before embarking on a new deep foraging dive. The researchers modeled the possible physiological effects of having this recovery period extended longer than usual. The team incorporated known physiological data into a model that charts how the bubble size might increase in the circulatory system, brain, muscles, and fat tissues when a whale dives repeatedly to between 30 and 80 meters for as long as 3 hours. The team's model predicts that if the whales' lungs do not collapse during a long series of shallow dives, the increased pressure can cause nitrogen bubbles to diffuse into tissues, increasing the risk of bubble formation on ascent. Such behavior may result if the whales perceive sonar transmissions as a predator: repeated dives travelling horizontally to escape the percieved predator could put the animals at risk. When fleeing an orca (their primary predator), such avoidance would like be short duration, and not dangerous; however, if the sonar transmissions continued to be audible for long periods of time, the whales might continue the avoidance dives to the point where they begin to sustain injury. This could also explain the relatively unusual appearance of beaked whales close enought to shore to end up beaching: they might be chased far from their normal habitat by continuing sonar sounds (ed. note: it also begs the question of whether many other animals are similarly injured, but happened to be fleeing in other directions). The team concludes that limiting the duration of sonar testing may prevent the animals from diving in these harmful patterns.
Related Paper: Analysis of Beaked Whale Dive Patterns With Consideration of Proposed Behavioral Risks in Response to Mid-Frequency Sonar
Tyack, Johnson, Soto, Sturlese, Madsen. Extreme diving if beaked whales. Journal of Experimental Biology 209, 4238-4253 (2006) [READ PAPER ONLINE]
This detailed report examines 44 dive sequences by 10 individual beaked whales. Deep foraging dives, during which the whales attempt to eat about 30 prey fish, last 45 minutes to an hour; between deep dives, they perform a series of dives closer to the surface. It appears that the surface dives become progressively shallower over the course of the hour to hour and a half spent between deep dives. The authors examine several proposed changes in dive behavior or possible physiological responses to observed dive patterns, and conclude that the evidence does not clearly support most of the proposals, noting that "aspects of the diving behavior of beaked whales remain enigmatic." They propose the theory explored in the physiological modeling paper above: that extending or altering the near-surface dive behavior could place the animals at risk for decompression sickness, triggering gas and fat embolic syndrome and stranding deaths.

Low Frequency Active Sonar Shows Less Impact on Fish than Airguns
Popper, Halvorsen, Kane, Miller, Smith, Song, Stein, Wysocki. The effects of high-intensity, low-frequency active sonar on rainbow trout. J. Acoust. Soc. Am. 122 1 , July 2007. p. 623-635.
This study extended a previous line of research that had measured physiological impacts of seismic survey air guns on fish kept confined in a cage and exposed to the noise. This time, the research team exposed trout (which share hearing mechanisms with salmon, which are of special concern due to their endangered status) to sounds produced by low-frequency active sonar. LFA sonar uses frequencies (100-500Hz) that many fish can detect, often the range of most sensitive hearing. Fish were tested for hearing sensitivity using Auditory Brainstem Response (ABR), and some were sacrificed to check for physiological damage, including swim bladder or ear hair damage. Results indicate that fish had reduced hearing sensitivity after exposure to LFA sonar, ranging from 17-25dB at particular frequencies (i.e., sounds needed to be that much louder in order to be heard), and that the effects lasted at least 48 hours (the longest followup the study included). However, the researchers note that there was quite a lot of variability in results, with some study groups showing little shift in hearing thresholds even with longer exposure to the LFA sounds, and some frequencies of hearing being little affected; also, the fish, being captive in a cage, were exposed to constant high sound levels that are unlikely in the wild, making this a probable worst-case scenario (the levels these fish were exposed to would occur only within 100m of the sonar transmission, which would be on a moving vessel). Unlike some earlier pile-driving and explosives studies, the fish exposed to LFA sounds did not show any acute tissue or organ damage. And, unlike earlier airgun studies, there was no apparent damage to ear hair cells; such injury would likely cause a permanent reduction in hearing sensitivity. The fish did respond to the onset of the sound with a rapid burst of swimming; this will be examined in another paper.

Boat Traffic Noise High Enough in Intracoastal Waterways to Raise Concerns About Hearing Damage and Making; Dolphins Seem to Avoid Weekends
Haviland-Howell, Frankel, Powel, Bocconcelli, Herman, Sayigh. Recreational boating traffic: A chronic source of anthropogenic noise in Wilmington, North Carolina Intracoastal Waterway. J. Acoust. Soc. Am. 122 (1), July 2007, p.151-160.
This study analyzed recordings of ocean noise during the summer season (June 21-September 1) in a 100m-wide intracoastal waterway off North Carolina. The mean received sound levels (measured as RMS re 1uPa, at frequencies averaged in steps over 0-37.5kHz) ranged from 109dB at 6am to 118dB in early afternoon and back down to 111dB by 10pm. Not surprisingly, weekends and holidays were 1-3dB louder than weekdays. The frequency spectrum shows that low frequencies (below 1kHz) dominate, with significant energy remaining up to 5kHz, and lesser but still perceptible noise up to the 37.5kHz limit of the study. Dolphin observations showed a clear reduction in numbers of dolphins observed on weekends and holidays, relative to weekdays; less than half as many dolphins were observed on weekends. Noise levels in the range of 5-25kHz, the primary range of dolphin social whistles, was of particular concern. The researchers note that "mean hourly RLs exceeded 116 dB nearly every day surveyed, indicating bottlenose dolphins in the ICW near Wilmington, North Carolina could be at risk for noise exposure on a daily basis. High mean RLs were often recorded over consecutive hours, making high sound levels the rule in this area during the summer, not the exception." Further, they note that since bottlenose dolphins feed mainly on soniferous fishes (fish that make noise), and that fish vocalizations are primarily below 1kHz, the range most dominated by boat sounds, dolphins may well find it more difficult to hear and find prey.

Current Marine Mammal Population Monitoring Effort Is Very Unlikely to Detect Even Precipitous Declines
Barbara L. Taylor, Melissa Martinez, Tim Gerrodette, Jay Barlow, Yvana N. Hrovat. Lessons from monitoring trends in abundance of marine mammals. Marine Mammal Science, 23(1): 157–175 (January 2007)
Marine mammals are notoriously hard to count, since they spend so much of their time underwater. Scientists, policy makers, and industrial and military planners all need to have accurate assessment of populations and population trends. However, many populations are not surveyed often enough or comprehensively enough to really know how many animals there are. Using statistical analysis, the researchers looked at a hypothetical situation in which populations were declining 50% over a 15 year period (the rate at which a stock can be legally classified as "depleted"). The percentage of precipitous declines that would not be detected as declines by current survey techniques and frequency was 72% for large whales, 90% for beaked whales, and 78% for dolphins/porpoises, 5% for pinnipeds on land, 100% for pinnipeds on ice, and 55% for polar bears/sea otters (based on a one-tailed t-test, ? = 0.05; this number measures the statistical significance of the results, or in lay terms, how confident we can be in the results--more on this key factor below). "Fundamentally, we cannot reliably detect even precipitous declines in most whale, dolphin, porpoise, and ice-hauling pinniped populations with present levels of investment in surveys and current survey technology and design," the researchers stressed. They recommended several alternatives to improve performance, including (to list a few) more diligent focus on indicator species, increase in survey frequency, and most fundamentally, a change in the "decision criteria." This last suggestion involves a shift in the balance of risk between over-protection and under-protection: the current standard of statistical significance of ? = 0.05 means that we will over-protect (perceive a decline where none actually exists) only 5% of the time; meanwhile, this standard, as suggested by the results above, leads us to MISS a decline up to 50-90% of the time. Softening our standard of significance to ? = 0.2 would detect a decline 80% of the time that one existed, while also over-protect 20% of the time (equal over and under). They also suggested possible changes to the math used in analyzing trends, development of better models, and designing surveys to more specifically detect trends than absolute abundance (though noted the drawback that, especially during declines, it is common for distributional shifts to occur. In many cases, for animals that range widely, repeated survey cannot be sure that they are observing the same animals/population; thus, researchers suggest that changing the decision criterion is a "more reliable" solution.

Pingers Used to Lower Dolphin By-Catch May Be Partially Effective
Leeney, Ruth H. et al. “Effects of pingers on the behaviour of bottlenose dolphins.” Journal of the Marine Biological Association of the United Kingdom 87 (2007): 129-133.
Pingers have been tested in the past few years for their usefulness in the mitigation of cetacean by-catch by fishing trawlers. In this study, Leeney et al. have conducted the first tests of this equipment on wild bottlenose dolphins. The study took place in the Shannon Estuary off the west coast of Ireland. Both constant pingers (CPs) and responsive pingers (RPs) were tested, the former making a sound every 5-20 seconds and the latter activating only when it senses dolphin clicks at close range. T-PODs, underwater recording submersibles, were moored both to the sea floor and to ships to record the dolphins’ vocal response to the pingers. Corresponding pingers were moved daily to prevent habituation of local dolphin populations to the sound. From the immobile locations, T-PODs recorded notably fewer clicks around active CPs than inactive, indicating avoidance behavior. The discrepancy was lower for RPs, which should be expected, as these only activate well within audial range. From the boats, both pingers had mixed effects. Sometimes dolphins would actively evade the sounds, and sometimes they would seem unaffected. It is unknown whether a pinger malfunction may have caused these differing reactions. The authors wish to emphasize that their results only apply to bottlenose dolphins, significantly different results having been found in previous studies on harbor porpoises.

Changes in Cetacean Abundance During Seismic Surveys in Brazil: Possible Long-term Monitoring Approach?
Parenti, JP de Araujo, ME de Araujo. Diversity of cetaceans as a tool in monitoring environmental impacts of seismic surveys. Biota Neotrop. Jan/Apr 2007 vol. 7, no.1
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In this study, Brazilian researchers analyzed existing data on cetacean abundance (as monitored by the Brazilian government and reported to the IWC, and as monitored by seismic survey vessels), on seismic surveys (from Brazilian oil and gas agencies), and on oceanographic parameters; the period analyzed was from 1999 to 2004. The results suggest a decrease in the diversity of species in the face of an increase in the number of seismic surveys during the years 2000 and 2001, even though there was no significant change in oceanographic patterns in this period, and that a relationship exists between diversity of cetaceans and intensity of seismic surveys between 1999 and 2004. Most of the differences in diversity were caused by fewer dolphin species being observed. While more detailed and ongoing data collection (including more species and a broader array of other possible causes for changes in species diversity) will be needed to evaluate this seeming connection, the results suggest that species diversity may be a useful indicator of the long-term impacts of seismic surveys on cetaceans.