Megan F. McKenna

Underwater radiated noise from modern commercial ships.

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1 μPa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1 μPa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments.

A synthesis of two decades of research documenting the effects of noise on wildlife

Global increases in environmental noise levels – arising from expansion of human populations, transportation networks, and resource extraction – have catalysed a recent surge of research into the effects of noise on wildlife. Synthesising a coherent understanding of the biological consequences of noise from this literature is challenging. Taxonomic groups vary in auditory capabilities. A wide range of noise sources and exposure levels occur, and many kinds of biological responses have been observed, ranging from individual behaviours to changes in ecological communities. Also, noise is one of several environmental effects generated by human activities, so researchers must contend with potentially confounding explanations for biological responses. Nonetheless, it is clear that noise presents diverse threats to species and ecosystems and salient patterns are emerging to help inform future natural resource‐management decisions. We conducted a systematic and standardised review of the scientific literature published from 1990 to 2013 on the effects of anthropogenic noise on wildlife, including both terrestrial and aquatic studies. Research to date has concentrated predominantly on European and North American species that rely on vocal communication, with approximately two‐thirds of the data set focussing on songbirds and marine mammals. The majority of studies documented effects from noise, including altered vocal behaviour to mitigate masking, reduced abundance in noisy habitats, changes in vigilance and foraging behaviour, and impacts on individual fitness and the structure of ecological communities. This literature survey shows that terrestrial wildlife responses begin at noise levels of approximately 40 dBA, and 20% of papers documented impacts below 50 dBA. Our analysis highlights the utility of existing scientific information concerning the effects of anthropogenic noise on wildlife for predicting potential outcomes of noise exposure and implementing meaningful mitigation measures. Future research directions that would support more comprehensive predictions regarding the magnitude and severity of noise impacts include: broadening taxonomic and geographical scope, exploring interacting stressors, conducting larger‐scale studies, testing mitigation approaches, standardising reporting of acoustic metrics, and assessing the biological response to noise‐source removal or mitigation. The broad volume of existing information concerning the effects of anthropogenic noise on wildlife offers a valuable resource to assist scientists, industry, and natural‐resource managers in predicting potential outcomes of noise exposure.

Anatomic geometry of sound transmission and reception in Cuvier's beaked whale (Ziphius cavirostris).

This study uses remote imaging technology to quantify, compare, and contrast the cephalic anatomy between a neonate female and a young adult male Cuviers beaked whale. Primary results reveal details of anatomic geometry with implications for acoustic function and diving. Specifically, we describe the juxtaposition of the large pterygoid sinuses, a fibrous venous plexus, and a lipid-rich pathway that connects the acoustic environment to the bony ear complex. We surmise that the large pterygoid air sinuses are essential adaptations for maintaining acoustic isolation and auditory acuity of the ears at depth. In the adult male, an acoustic waveguide lined with pachyosteosclerotic bones is apparently part of a novel transmission pathway for outgoing biosonar signals. Substitution of dense tissue boundaries where we normally find air sacs in delphinoids appears to be a recurring theme in deep-diving beaked whales and sperm whales. The anatomic configuration of the adult male Ziphius forehead resembles an upside-down sperm whale nose and may be its functional equivalent, but the homologous relationships between forehead structures are equivocal.

Assessing the Risk of Ships Striking Large Whales in Marine Spatial Planning

Marine spatial planning provides a comprehensive framework for managing multiple uses of the marine environment and has the potential to minimize environmental impacts and reduce conflicts among users. Spatially explicit assessments of the risks to key marine species from human activities are a requirement of marine spatial planning. We assessed the risk of ships striking humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and fin (Balaenoptera physalus) whales in alternative shipping routes derived from patterns of shipping traffic off Southern California (U.S.A.). Specifically, we developed whale-habitat models and assumed ship-strike risk for the alternative shipping routes was proportional to the number of whales predicted by the models to occur within each route. This definition of risk assumes all ships travel within a single route. We also calculated risk assuming ships travel via multiple routes. We estimated the potential for conflict between shipping and other uses (military training and fishing) due to overlap with the routes. We also estimated the overlap between shipping routes and protected areas. The route with the lowest risk for humpback whales had the highest risk for fin whales and vice versa. Risk to both species may be ameliorated by creating a new route south of the northern Channel Islands and spreading traffic between this new route and the existing route in the Santa Barbara Channel. Creating a longer route may reduce the overlap between shipping and other uses by concentrating shipping traffic. Blue whales are distributed more evenly across our study area than humpback and fin whales; thus, risk could not be ameliorated by concentrating shipping traffic in any of the routes we considered. Reducing ship-strike risk for blue whales may be necessary because our estimate of the potential number of strikes suggests that they are likely to exceed allowable levels of anthropogenic impacts established under U.S. laws.

Integrative Approaches to the Study of Baleen Whale Diving Behavior, Feeding Performance, and Foraging Ecology

For many marine organisms, especially large whales that cannot be studied in laboratory settings, our ability to obtain basic behavioral and physiological data is limited, because these organisms occupy offshore habitats and spend a majority of their time underwater. A class of multisensor, suction-cup-attached archival tags has revolutionized the study of large baleen whales, particularly with respect to the predatory strategies used by these gigantic bulk filter feeders to exploit abundant oceanic resources. By integrating these data with those from other disciplines, researchers have uncovered a diverse and extraordinary set of underwater behaviors, ranging from acrobatic diving maneuvers to extreme feeding events during which whales engulf volumes of prey-laden water that are much larger than their own body. This research framework not only improves our knowledge of the individual performance and behavior of these keystone predators but also informs our ability to understand the dynamics of complex marine ecosystems.

Cuvier's beaked whale (Ziphius cavirostris) head tissues:physical properties and CT imaging

SUMMARY Tissue physical properties from a Cuviers beaked whale (Ziphius cavirostris) neonate head are reported and compared with computed tomography (CT) X-ray imaging. Physical properties measured include longitudinal sound velocity, density, elastic modulus and hysteresis. Tissues were classified by type as follows: mandibular acoustic fat, mandibular blubber, forehead acoustic fat (melon), forehead blubber, muscle and connective tissue. Results show that each class of tissues has unique, co-varying physical properties. The mandibular acoustic fats had minimal values for sound speed (1350±10.6 m s–1) and mass density (890±23 kg m–3). These values increased through mandibular blubber (1376±13 m s–1, 919±13 kg m–3), melon (1382±23 m s–1, 937±17 kg m–3), forehead blubber (1401±7.8 m s–1, 935±25 kg m–3) and muscle (1517±46.8 m s–1, 993±58 kg m–3). Connective tissue had the greatest mean sound speed and density (1628±48.7 m s–1, 1087±41 kg m–3). The melon formed a low-density, low-sound-speed core, supporting its function as a sound focusing organ. Hounsfield unit (HU) values from CT X-ray imaging are correlated with density and sound speed values, allowing HU values to be used to predict these physical properties. Blubber and connective tissues have a higher elastic modulus than acoustic fats and melon, suggesting more collagen structure in blubber and connective tissues. Blubber tissue elastic modulus is nonlinear with varying stress, becoming more incompressible as stress is increased. These data provide important physical properties required to construct models of the sound generation and reception mechanisms in Ziphius cavirostris heads, as well as models of their interaction with anthropogenic sound.

Acoustic radiation from the head of echolocating harbor porpoises(Phocoena phocoena)

SUMMARY An experiment was conducted to investigate the sound pressure patterns on the melon of odontocetes by using four broadband hydrophones embedded in suction cups to measure echolocation signals on the surface of the forehead of two harbor porpoises (Phocoena phocoena). It has long been hypothesized that the special lipids found in the melon of odontocetes, and not in any other mammals, focus sounds produced in the nasal region that then propagate through the melon, producing a beam that is directional in both the horizontal and vertical planes. The results of our measurements supported the melon-focusing hypothesis, with the maximum click amplitude, representing the axis of the echolocation beam, located approximately 5.6-6.1 cm from the edge of the animals upper lip along the midline of the melon. The focusing is not sharp but is sufficient to produce a transmission beam of about 16°. Click amplitude dropped off rapidly at locations away from the location of site of maximum amplitude. Based on comparisons of forehead anatomy from similar sized porpoises, the beam axis coincided with a pathway extending from the phonic lips through the axis of the low-density/low sound velocity lipid core of the melon. The significant interaction between click number and hydrophone position suggests that the echolocation signals can take slightly different pathways through the melon, probably as a result of how the signals are launched by the production mechanism and the position of the acoustically reflective air sacs.

A quieting ocean: Unintended consequence of a fluctuating economy

Simultaneous long-term monitoring of underwater sound and ship traffic provided an opportunity to study how low-frequency noise correlated with ocean-based commercial shipping trends. Between 2007 and 2010 changes in regional shipping off southern California occurred as a consequence of economic and regulatory events. Underwater average noise levels measured before and during these events showed a net reduction of 12 dB. Statistical models revealed that a reduction of 1 ship transit per day resulted in 1 dB decrease in average noise. This synthesis of maritime traffic statistics with ocean noise monitoring provides an important step in understanding the magnitude and potential effects of chronic noise in marine habitats.

Evaluation of postmortem changes in tissue structure in the bottlenose dolphin (Tursiops truncatus)

Postmortem changes in geometry, density, and sound speed within organs and tissues (melon, bone, blubber, and mandibular fat) of the dolphin head were evaluated using computed tomography (CT) scans of live and postmortem bottlenose dolphins (Tursiops truncatus). Specimens were classified into three different treatment groups: live, recently dead, and frozen followed by thawing. Organs and tissues in similar anatomical regions of the head were compared in CT scans of the specimens to identify postmortem changes in morphology. In addition, comparisons of Hounsfield units in the CT scans were used to evaluate postmortem changes in the density of melon, bone, blubber, and mandibular fat. Sound speed measurements from melon, blubber, connective tissue, and muscle were collected from fresh and frozen samples in the same specimen to evaluate effects due to freezing and thawing process on sound speed measurements. Similar results in tissue and organ geometry, density, and sound speed measurements suggested that postmortem material is a reliable approximation for live melon, bone, blubber, muscle, connective tissue, and mandibular fat. These results have implications for examining viscoelastic properties and the accuracy of simulating sound transmission in postmortem material. Anat Rec, 290:1023–1032, 2007.

Response of Commercial Ships to a Voluntary Speed Reduction Measure: Are Voluntary Strategies Adequate for Mitigating Ship-Strike Risk?

Collisions between ships and whales are an increasing concern for endangered large whale species. After an unusually high number of blue whales (Balaenoptera musculus) were fatally struck in 2007 off the coast of southern California, federal agencies implemented a voluntary conservation program to reduce the likelihood of ship-strikes in the region. This initiative involved seasonal advisory broadcasts requesting vessel operators to voluntarily slow to 10 knots or less when transiting a 75 nm stretch of designated shipping lanes. We monitored ship adherence with those speed advisories using Automatic Identification System data. Daily average speed of cargo and tanker ships and the average speed of individual ship transits before, during, and after the notices were statistically analyzed for changes related to the notices. Whereas a small number of individual ships (1%) traveled significantly slower during the requested periods, speeds were not at or below the recommended 10 knots, nor were daily average speeds reduced during the notices. Voluntary conservation measures are established in a variety of contexts, and may be preferable to regulatory action; in this case, a request to make voluntary changes appeared largely ineffective. Reducing collision risks for whales in this area will require consideration of the various factors that likely explain the lack of adherence when developing an alternative strategy.