Linda Weilgart

The impacts of anthropogenic ocean noise on cetaceans and implications for management

Ocean noise pollution is of special concern for cetaceans, as they are highly dependent on sound as their principal sense. Sound travels very efficiently underwater, so the potential area impacted can be thousands of square kilometres or more. The principal anthropogenic noise sources are underwater explosions (nuclear and otherwise), shipping, seismic exploration by mainly the oil and gas industries, and naval sonar operations. Strandings and mortalities of especially beaked whales (family Ziphiidae) have in many cases been conclusively linked to noise events such as naval maneuvers involving tactical sonars or seismic surveys, though other cetacean species may also be involved. The mechanisms behind this mortality are still unknown, but are most likely related to gas and fat emboli at least partially mediated by a behavioral response, such as a change in diving pattern. Estimated received sound levels in these events are typically not high enough to cause hearing damage, implying that the auditory syste...

Group-specific dialects and geographical variation in coda repertoire in South Pacific sperm whales

Abstract Codas, which are patterned series of clicks, were recorded from female and immature sperm whales (Physeter macrocephalus) in a number of locations around the South Pacific Ocean and in the Caribbean Sea. Using K-means cluster analysis, 3,644 codas were categorized based on the number of clicks and their patterning. There were 30 resulting types of coda. The numbers of codas of the different types recorded were used to construct repertoires for each recording session, day, group of whales, place, area, and ocean. Strong group-specific dialects, which seem to persist over periods of years, were apparent, overlaid on weaker geographical variation. Significant differences in repertoire were found between the Caribbean and the Pacific Ocean. Sperm whales now join killer whales (Orcinus orca) as the only cetacean species in which dialects (differences in vocal repertoire among neighboring, potentially interacting groups) have been found.

Vocalizations of the North Atlantic pilot whale (Globicephala melas) as related to behavioral contexts

SummaryVocalizations of free-ranging North Atlantic pilot whales were studied in different behavioral contexts to gain insight into the function and biological significance of different sound types. Simple whistles (with no frequency inflections) were heard more frequently when whales were “milling,” a restful behavior type. During “surface active” behavior, energetic, often coordinated activity probably representing feeding, many sound types, especially complex whistles (with more frequency inflections) and pulsed sounds, occurred with greater frequency than when this behavior was absent. Greater numbers of most whistle types were produced when whales were spread over a larger area and when more subgroups were present. Thus, in pilot whales, there is a significant relationship between their sounds and their behavior, with vocalizations possibly serving to maintain contact and coordinate movements of the herd.

Click rates from sperm whales

The rate of production of clicks by groups of (mainly female) sperm whales off the Galapagos Islands was dependent on two principal factors: the number of whales present and the behavioral state of the group. When the whales were in their principal (occupying about 80% of their time) behavioral state, diving deep for prolonged periods and usually being seen at the surface singly or in pairs, each whale made trains of clicks with an interclick interval of about 0.5 s about 70% of the time. About 10% of the time, the groups remained at or near the surface, with individual members forming clusters containing greater than five individuals, and being generally silent. Group behavior was sometimes intermediate between these extremes, with some whales silent at the surface in medium‐sized clusters, and others clicking at depth. Click rate can be used as an indicator of the behavior of sperm whales, the size of a group, and/or the number of groups present. In our studies, groups associated often, and more frequen...

Allochthonous Drift from Backwaters to the Main Channel of the Mississippi River

Drift in Pool 9 of the Upper Mississippi River was sampled using paired nets suspended at 0.6 m and 2.7 m depths. Diel periodicity in numbers, differences in depth distribution, and differences between sampling months were noted for the drift. Drift coming through large side channels, draining backwater habitats, had mean numbers 10 times larger than that in the main channel of the Mississippi River. This allochthonous drift was largely in transport at night and reflected the backwater area drained and, in part, the benthic communities of backwater lakes. The pulsed inputs of allochthonous drift have been largely ignored and may influence the main stem of a large river ecosystem.

The Need for Precaution in the Regulation and Management of Undersea Noise

Undersea noise has been highlighted as one of the human-caused impacts on cetaceans particularly worthy of precautionary management. The reason for this is primarily that cetaceans are very difficult to study in the wild, spending most of their time underwater. As such, there is a huge dearth of knowledge on the impacts of environmental degradation on them, particularly on the long-term health of their populations. Underwater noise is especially problematic, because the potential spatial scale of impact can be huge, as sound travels very efficiently underwater. These same large potential scales of impact make the study of such impacts even more difficult. How does one begin to assess the environmental damage that may be occurring over 3.9 million sq. km. of ocean—the area over which the U.S. Navy’s Low Frequency Active Sonar can be heard at 120 dB, a level shown to produce avoidance in some marine mammals and fish? And how does one attempt to relate the sometimes subtle and short-term changes in whale behavior observable at the surface to a population impact? Links between short-term effects and long-term population consequences cannot usually be made. This is because some reactions may be subtle or not even detectable (e.g., changes in rates of miscarriage or mate finding), yet still be severe in their implications. Conversely, some short-term effects may be detectable (e.g., changes in dive pattern), yet do not necessarily constitute a long-term impact on the population. Population impacts are the most important ones as these can threaten the health and welfare of cetacean populations, yet these impacts are particularly elusive to determine for cetaceans. This is because population estimates for the vast majority of cetacean species are presently too imprecise

A modelling comparison between received sound levels produced by a marine Vibroseis array and those from an airgun array for some typical seismic survey scenarios

Marine Vibroseis (MV) may provide a marine seismic sound source that has less environmental impact than conventional airguns. Modelled sound levels from a realistic MV array and airgun array with similar downward energy at frequencies <100Hz were compared under three scenarios: shallow, deep, and slope. Changing the layout of the MV arrays higher frequency sources reduced sound exposure levels (SELs) by 4dB. At 100m range this MV was 20dB lower in peak-to-peak sound pressure level vs. the airgun array, decreasing to 12dB lower at 5km, the maximum modelled range for peak levels. SELs were less clear-cut, but for both shallow and deep water, MV produced 8dB lower SELs than the airguns at 100km range because of MVs reduced bandwidth. Overall, MV produced lower broadband SELs, especially at long range, and lower peak pressure, especially at short range, than airguns.

Science and the management of underwater noise: Information gaps and polluter power

To regulate underwater noise rationally and efficiently, we need to know its impact on population and community biology. This link can rarely be studied directly because of logistics and the spatial and temporal scales of ecological processes. There are two principal approaches: correlational studies of noise levels with population events or measures; and experiments in which the response variables (usually short‐term behavioral measures) are poor proxies for the population and ecosystem parameters about which we are concerned. Experimental studies also have costs. These may include the introduction of additional noise, delay of substantive regulation, and, when polluters are major funders, perceived gagging or biasing of knowledgeable scientists. This is a particular problem with underwater noise because the U.S. Navy (a major noise polluter) and allied organizations fund so much acoustic research. Consequently (a) managers must recognize that underwater noise is dangerous but its most important conseque...