Jonathan Gordon

A Review of the Effects of Seismic Surveys on Marine Mammals

This review highlights significant gaps in our knowledge of the effects of seismic air gun noise on marine mammals. Although the characteristics of the selsmic signal at different ranges and depths and at higher frequencies are poorly understood, and there are often insufficient data to identify the appropriate acoustic propagation models to apply in particular conditions, these uncertainties are modest compared with those associated with biological factors. Potential biological effects of air gun wilsnlwlu<kiphysical/physiological effects, behavioral disruption, and indirect effects associated with altered prey availability. Physical/physiological effects could include hearing threshold shifts and auditory damage as well as non-auditory disruption, and can be directly caused by sound exposure or the result of behavioral charges in response to sounds, e.g. recent observations suggesting that exposure to loud noise may result in decompression sickness. Direct information on the extent to which seismic pulses could damage hearing are difficult to obtain and as a consequence the impacts on hearing remain poorly known. Behavioral data have been collected for a few species in a limited range of conditions. Responses, including startle and fright, avoidance, and changes in behavior and vocalization patterns, have been observed in baleen whales, odontocetes, and pinnipeds and in some case these have occurred at ranges of tens or hundreds of kilometers. However, behavioral observations are typically variable, some findings are contradictory, and the biological significance of these effects has not been measured. Where feeding, orientation, hazard avoidance, migration or social behavior are altered, it is possible that populations could be adversely affected. There may also be serious long-term consequences due to chronic exposure, and sound could affect marine mammals indirectly by changing the accessibility of their prey species. A precautionary approach to management and regulation must be recommended. While such large degrees of uncertalnty remain, this may result in restrictions to operational practices but these could be relaxed if key uncertainties are clarified by appropriate research.

PAMGUARD: SEMIAUTOMATED, OPEN SOURCE SOFTWARE FOR REAL-TIME ACOUSTIC DETECTION AND LOCALISATION OF CETACEANS

PAMGUARD is open‐source, platform‐independent software to address the needs of developers and users of Passive Acoustic Monitoring (PAM) systems. For the PAM operator—marine mammal biologist, manager, or mitigator—PAMGUARD provides a flexible and easy‐to‐use suite of detection, localization, data management, and display modules. These provide a standard interface across different platforms with the flexibility to allow multiple detectors to be added, removed, and configured according to the species of interest and the hardware configuration on a particular project. For developers of PAM systems, an Application Programming Interface (API) has been developed which contains standard classes for the efficient handling of many types of data, interfaces to acquisition hardware and to databases, and a GUI framework for data display. PAMGUARD replicates and exceeds the capabilities of earlier real time monitoring programs such as the IFAW Logger Suite and Ishmael. Ongoing developments include improved real‐time l...

A REVIEW OF FREQUENCY AND TIME PARAMETERS OF CETACEAN TONAL CALLS

ABSTRACT Properties of the tonal calls of cetaceans are summarised and compared at the species level. Statistics are presented relating to start, end, minimum, maximum and centre frequencies, duration and number of inflections, together with information about recordings (location, number encounters/groups, length of recordings). Evidence of a linear relation between body-size and wavelength is given for odontocetes (R2 between 0.68 and 0.93, depending on frequency variable and least-squares method) but the relationship does not appear to fit well for mysticetes (R2 = 0.64). Results of preliminary investigations into acoustic discrimination of species by multivariate methods are also presented: a simple classifier for 10 species based on results derived from the literature gave a correct classification rate of 28% when tested with independent data. Some methodological recommendations for future descriptive work on cetacean acoustics are made.

FACTORS AFFECTING THE RESPONSES OF MARINE MAMMALS TO ACOUSTIC DISTURBANCE

The issues surrounding marine mammals and noise cannot be managed effectively without an understanding of the effects of that noise on individual mammals and their populations. In the spring of 2003 the National Research Council released Ocean Nolse and Marine Mammals, a report that reviewed sources of ocean noise (natural and anthropogenic), the effects of noise on marine mammals, patterns and long-term trends in ocean noise, and included recommendations intended to improve understanding of the sources and impacts of anthropogenic marine noise. This paper provides a brief summary of observed effects of ocean noise on marine mammals and the factors that can change the response of the animai to the noise exposure. It introduces the reader to short- and long-term behavior changes that have been observed in marine mammals in response to ocean noise, and discusses future directions for marine mammal research.

Individually distinctive acoustic features in sperm whale codas

Social animals may develop behavioural strategies that are based on individualized relationships among members. In these cases, there might be selection pressures for the development of identity signals and mechanisms that allow discrimination and recognition of particular individuals. Female sperm whales, Physeter macrocephalus, live in long-term, stable social units. Differential interactions among unit members suggest the need for an individual discrimination system. Sperm whales produce stereotyped series of click sounds called codas, which are thought to be used for communication. Although codas were initially proposed as individual signatures, later studies did not support this hypothesis. Using linear discriminant functions and Mantel tests, we tested variation within coda types as a means for individual identification, using recordings where codas were assigned to individual whales. While most coda types showed no indication of individual-specific information, individual differences that were robust to variation among recording days were found in the 5 Regular coda type. Differences in individual-specific information between coda types suggest that different coda types may have distinct functions.

Controlled exposure experiments to determine the effects of noise on marine mammals

Controlled exposure experiments or CEEs are an important technique for determining the responses of animals to signals that are not part of their own communicative repertoire. CEEs are useful for establishing the relationship between acoustic dosage and behavioral response, a critical element of risk assessment, similar to dose:response studies for exposure to chemicals. CEEs share some properties with playback experiments; the main difference between playbacks and CEEs is that CEEs involve the careful titration of acoustic exposure to the point where specific responses are observed. Most CEEs are applied research designed to answer questions related to wildlife conservation. The utility and power of CEEs lies in providing a sensitive measure of causal relationships between behavioral responses and particular stimuli. We review design features and experimental methods for CEEs, limiting our scope for this paper to studying the effects of underwater noise on wild marine mammals.

Automatic detection and classification of odontocete whistles.

Methods for the fully automatic detection and species classification of odontocete whistles are described. The detector applies a number of noise cancellation techniques to a spectrogram of sound data and then searches for connected regions of data which rise above a pre-determined threshold. When tested on a dataset of recordings which had been carefully annotated by a human operator, the detector was able to detect (recall) 79.6% of human identified sounds that had a signal-to-noise ratio above 10 dB, with 88% of the detections being valid. A significant problem with automatic detectors is that they tend to partially detect whistles or break whistles into several parts. A classifier has been developed specifically to work with fragmented whistle detections. By accumulating statistics over many whistle fragments, correct classification rates of over 94% have been achieved for four species. The success rate is, however, heavily dependent on the number of species included in the classifier mix, with the mean correct classification rate dropping to 58.5% when 12 species were included.

Sound and Cetaceans

“Of all forms of radiation known, sound travels through the sea the best. In the turbid, saline water of the sea, both light and radio waves are attenuated to a far greater degree than that from the mechanical energy known as sound.”

Tracking Technologies for Quantifying Marine Mammal Interactions with Tidal Turbines: Pitfalls and Possibilities

Currently, there is great uncertainty surrounding the environmental impacts of tidal turbines on marine mammals; one major concern derives from the potential for physical injury through direct contact with the moving structures of turbines. Collecting data to quantify these risks is challenging and methods for measuring movements underwater and interactions with turbines are limited. However, potential tools include a small number of cutting-edge technologies that are being used increasingly for research and monitoring; these include animal-borne telemetry, and active and passive acoustic tracking. Recent developments in these technologies are described along with their means of application in measuring fine-scale movements and avoidance or evasion responses by marine mammals around turbines. From a risk-characterization perspective, each technique can provide information to inform risk assessments or help parametrize collision risk models; however, each has its associated benefits and drawbacks and it is clear that, in isolation, none of them can provide all the data needed to address the problem. The three approaches appear highly complementary, with the strengths of one complementing the weaknesses in others; the solution to characterizing the risks posed by tidal turbines is likely to be a combination of such techniques.

Acoustic Techniques for Studying Cetaceans

In Chapter 4, we saw that sound propagates extremely efficiently through the sea and we explored some of the consequences of this for cetaceans. We showed that the dominant sensory modality for cetaceans is acoustic and that most cetaceans are highly vocal animals. This means that acoustic methods can often be very effective means for studying cetaceans. Studies of acoustic behaviour require a variety of specialised acoustic techniques. We will briefly review some of these here, highlighting some of the particular problems of working on cetacean acoustics and giving examples of solutions. In addition, largely because sound travels so well underwater, acoustic methods are often the most effective and efficient means of addressing questions about cetaceans which are not primarily acoustic in nature: assessing population distribution, abundance and movements for example.