(2008). MARINE MAMMAL NOISE-EXPOSURE CRITERIA: INITIAL SCIENTIFIC RECOMMENDATIONS. Bioacoustics: Vol. 17, No. 1-3, pp. 273-275.

Marine mammal noise-exposure criteria: initial scientific recommendations

1
Since the last thorough review of the effects of anthropogenic noise on cetaceans in 1995, a substantial number of research reports has been published and our ability to document response(s), or the lack thereof, has improved. While rigorous measurement of responses remains important, there is an increased need to interpret observed actions in the context of population-level consequences and acceptable exposure levels. There has been little change in the sources of noise, with the notable addition of noise from wind farms and novel acoustic deterrent and harassment devices (ADDs/AHDs). Overall, the noise sources of primary concern are ships, seismic exploration, sonars of all types and some AHDs.

2
Responses to noise fall into three main categories: behavioural, acoustic and physiological. We reviewed reports of the first two exhaustively, reviewing all peer-reviewed literature since 1995 with exceptions only for emerging subjects. Furthermore, we fully review only those studies for which received sound characteristics (amplitude and frequency) are reported, because interpreting what elicits responses or lack of responses is impossible without this exposure information. Behavioural responses include changes in surfacing, diving and heading patterns. Acoustic responses include changes in type or timing of vocalizations relative to the noise source. For physiological responses we address the issues of auditory threshold shifts and ‘stress’, albeit in a more limited capacity; a thorough review of physiological consequences is beyond the scope of this paper.

3
Overall, we found significant progress in the documentation of responses of cetaceans to various noise sources. However, we are concerned about the lack of investigation into the potential effects of prevalent noise sources such as commercial sonars, depth finders and fisheries acoustics gear. Furthermore, we were surprised at the number of experiments that failed to report any information about the sound exposure experienced by their experimental subjects. Conducting experiments with cetaceans is challenging and opportunities are limited, so use of the latter should be maximized and include rigorous measurements and or modelling of exposure.

Responses of cetaceans to anthropogenic noise

Sound-and-orientation recording tags (DTAGs) were used to study 10 beaked whales of two poorly known species, Ziphius cavirostris (Zc) and Mesoplodon densirostris (Md). Acoustic behaviour in the deep foraging dives performed by both species (Zc: 28 dives by seven individuals; Md: 16 dives by three individuals) shows that they hunt by echolocation in deep water between 222 and 1885 m, attempting to capture about 30 prey/dive. This food source is so deep that the average foraging dives were deeper (Zc: 1070 m; Md: 835 m) and longer (Zc: 58 min; Md: 47 min) than reported for any other air-breathing species. A series of shallower dives, containing no indications of foraging, followed most deep foraging dives. The average interval between deep foraging dives was 63 min for Zc and 92 min for Md. This long an interval may be required for beaked whales to recover from an oxygen debt accrued in the deep foraging dives, which last about twice the estimated aerobic dive limit. Recent reports of gas emboli in beaked whales stranded during naval sonar exercises have led to the hypothesis that their deep-diving may make them especially vulnerable to decompression. Using current models of breath-hold diving, we infer that their natural diving behaviour is inconsistent with known problems of acute nitrogen supersaturation and embolism. If the assumptions of these models are correct for beaked whales, then possible decompression problems are more likely to result from an abnormal behavioural response to sonar.

https://www.whoi.edu/fileserver.do?id=58303&pt=10&p=40212

Extreme diving of beaked whales

The purpose of this study was to develop a unified model capable of explaining the mechanisms of interaction of ultrasound and biological tissue at both the diagnostic nonthermal, noncavitational ( 100 mW·cm−2) spatial peak temporal average intensity levels. The cellular-level model (termed “bilayer sonophore”) combines the physics of bubble dynamics with cell biomechanics to determine the dynamic behavior of the two lipid bilayer membrane leaflets. The existence of such a unified model could potentially pave the way to a number of controlled ultrasound-assisted applications, including CNS modulation and blood–brain barrier permeabilization. The model predicts that the cellular membrane is intrinsically capable of absorbing mechanical energy from the ultrasound field and transforming it into expansions and contractions of the intramembrane space. It further predicts that the maximum area strain is proportional to the acoustic pressure amplitude and inversely proportional to the square root of the frequency () and is intensified by proximity to free surfaces, the presence of nearby microbubbles in free medium, and the flexibility of the surrounding tissue. Model predictions were experimentally supported using transmission electron microscopy (TEM) of multilayered live-cell goldfish epidermis exposed in vivo to continuous wave (CW) ultrasound at cavitational (1 MHz) and noncavitational (3 MHz) conditions. Our results support the hypothesis that ultrasonically induced bilayer membrane motion, which does not require preexistence of air voids in the tissue, may account for a variety of bioeffects and could elucidate mechanisms of ultrasound interaction with biological tissue that are currently not fully understood.

https://www.pnas.org/content/pnas/108/8/3258.full.pdf

Intramembrane cavitation as a unifying mechanism for ultrasound-induced bioeffects.

Beaked whales (Cetacea: Ziphiidea) of the genera Ziphius and Mesoplodon are so difficult to study that they are mostly known from strandings. How these elusive toothed whales use and react to sound...

/pdf/beaked-whales-echolocate-on-prey-1mcil97hti.pdf

Beaked whales echolocate on prey

Was sonar responsible for a spate of whale deaths after an Atlantic military exercise? There are spatial and temporal links between some mass strandings of cetaceans — predominantly beaked whales — and the deployment of military sonar1,2,3. Here we present evidence of acute and chronic tissue damage in stranded cetaceans that results from the formation in vivo of gas bubbles, challenging the view that these mammals do not suffer decompression sickness. The incidence of such cases during a naval sonar exercise indicates that acoustic factors could be important in the aetiology of bubble-related disease and may call for further environmental regulation of such activity.

Gas-bubble lesions in stranded cetaceans

Jepson et al. reply — We did not, as Piantadosi and Thalmann suggest1, present our findings as conclusive evidence of decompression sickness (DCS). We stated neither that DCS occurs naturally in cetaceans, nor that exposure to active sonar increases its occurrence2. However, we restate that there is now a generally accepted link between some beaked-whale strandings and sonar use, and that lesions in some cetaceans demonstrate that in vivo bubble formation (embolus) can occur and persist.

Pathology: Whales, sonar and decompression sickness (reply)

A number of peculiar postmortem findings were observed in the cetaceans under study. Ten beaked whales were found stranded in the Canary Islands shortly after a military naval exercise occurred nearby. This interesting paper suggests that gas bubble formation, possibly in response to either rapid decompression (‘‘decompression sickness,’’ or DCS equivalent?) or exposure of nitrogen-supersaturated tissues to sound waves 2 was the likely cause of death.3 The authors report that intravascular gas bubbles and fat emboli, presumably sonar induced, were found in ‘‘vital organs’’ without further specifying what these organs were. Were the heart and brain involved, as it would be reasonable to believe? And, if so, why not consider also the possibility that one or more large-sized gas bubbles may have caused, at least in some animals, sudden heart failure by means of ‘‘pure’’ mechanical compression, either on the myocardial vagal network or on nuclei in the brain from which vagal nerve fibers originate? Apart from their bacteriologic status, no other data regarding either the age or the preexisting health of the whales are provided, nor are the tissue levels of highly lipophilic persistent organochlorine pollutants (POPs), such as polychlorinated biphenyls (PCBs), 1 reported. We would like to suggest that gas bubble formation within the subcutaneous adipose tissue and widespread vascular embolization of fat material caused sudden spikes in the blood and tissue levels of PCBs or related xenobiotics. A similar pathogenetic mechanism could also have been involved in the cases of three delphinids and one beaked whale found stranded in the UK between 1992 and 2003. 3 The same authors report that these animals had gas-filled cystic cavities in their livers and other parenchymatous organs. The liver is another site for the accumulation of PCBs in cetaceans. 5 Apart from their immunosuppressive activity, 8 PCBs are known to be endocrine disrupters that have been associated with morphologic changes in several hormone-producing glands, such as the adrenal and thyroid glands. These effects have been clearly

E. Degollada

Papers

Gas-bubble lesions in stranded cetaceans

Pathology: Whales, sonar and decompression sickness (reply)

Editor: Sonars, Gas Bubbles, and Cetacean Deaths