cetaceans

For one year, starting on September 5th 1994, the behaviour of a captive new-born bottlenose dolphin Tursiops truncatus and its mother was monitored through both video and acoustic recordings. The main objective of such research was to study the behavioural evolution of the two during the first year of the calf's life. Attention was focused on acoustic behaviour and its use in relation to the contexts. In order to be able to discover any possible correlation, the acoustic signals were analysed with a Pc-based DSP Workstation developed at the University of Pavia, and the resulting real-time spectrographic analyses were superimposed on the live video recordings.

Within the frame of European Nature Conservation Year 1995, the Italian Navy set up a cooperative research program with universities and other institutions to give logistic support and to apply its technologies to the study and protection of the marine environment. The project includes a research program on cetacean acoustics, mainly dealing with the sperm whale Physeter macrocephalus, to unveil and monitor its seasonal movements and behaviour. The Italian Navy surface vessels crews have been trained to visually recognize them in order to complete sighting schedules. Besides, personnel working on submarines and maritime patrol aircraft have been trained in identifying biological sounds recorded during ASW (Anti-submarine Warfare) operations. ASW techniques proved to be successful in finding and recording cetaceans. Unclassified sound recordings made independently by the Navy, with surface vessels, submarines and sonobuoys, have been provided to the Cetacean Sound Library of the Centro Interdisciplinare di Bioacustica e Ricerche Ambientali. The research continued in 1996 mainly with the collection of recordings from sonobuoys deployed while performing ASW patrolling activities. To date, several valuable recordings have been collected from elusive species like the sperm whale and pilot whale. Several recordings of sperm whale codas typical of the Mediterranean Sea (/// / pattern) have been collected, including new "short'' codas with the same distinctive pattern. Whenever possible, species identification of vocalizing animals was made by comparing sounds with those available in the Cetacean Sound Library.

The problems of reducing small cetacean bycatch in fishing nets are many and complex, and acoustic solutions need to be tailored to suit individual species and net types. Active deterrent devices or alarms have recently been shown to be beneficial in reducing the bycatch of harbour porpoises Phocoena phocoena in some carefully monitored trials in North American sink-gillnet fisheries (Kraus et al. 1995). The methodology employed to date is still at an early stage of development; typical devices generate simple 10 kHz tonal pulses from small battery powered packages distributed at intervals along the fishing net. The long term effectiveness of this approach has already been questioned, as small cetaceans are known to habituate quite quickly to novel stimuli. A more sophisticated approach, now at the trials stage, uses higher frequency, wideband signals which have been determined to be more aversive to this species (Goodson et a1. above). To minimise habituation effects over time, such 'beacon alarm' signals need only be transmitted occasionally if the acoustic activity of an approaching echolocating animal can also be detected and used to trigger the device into a transponder type of operation. Such a device has now been designed at Loughborough University and implemented using digital micro-controller technology. As this circuitry is programmable almost any complex waveform can be generated to suit specific applications. The use of a digital micro-controller permits a number of additional features to be implemented in software without a significant increase in the overall component count and, despite the sophistication, the cost per device remains acceptably low. It may be argued that a silent animal could remain at risk. However, in the context of bottom set nets (sink-gillnets) this should not apply, as the harbour porpoise swimming close to the bottom in deep water is there to forage for prey and hence actively employing its echolocation sense. This interactive approach reduces spurious acoustic emissions which waste battery energy and, as most responses are triggered by the approach of an animal at risk of colliding with the net, the deterrent effect is expected to be longer lasting. The alarm response ceases quickly once the animal turns away. Provided that these devices are spaced apart along the net within detection range of each other, additional benefit is obtained if they also respond to a neighbour's alarm signal as this will result in a 'ripple-fire' of activity along the net. This linking of emissions provides better orientation information than can be given by simple randomly timed pingers. lnteractive devices are also intended for application to large pelagic trawls, where the delineation of the net's boundary by such a ripple-fire transmission is expected to give a clearer indication of the extent of the hazard to an animal which may have followed fish into the net. Since triggering can also be stimulated by a ship's echosounder, these devices should make the location and recovery of lost nets a relatively simple exercise.

In the search for an efficient acoustic method of reducing the bycatch of porpoises in bottom-set gillnets, the effects of presenting sounds at different frequencies and waveforms have been examined using a rehabilitated, ex- stranded, harbour porpoise as the subject in a 20 x 30 m floating net cage experiment. The animal was available for this study during the last phase of a planned programme of re-adjustment prior to its release. Low level sounds (SL<130 do re l µPa at 1m) were presented underwater using a purpose-built digital signal synthesiser with three types of output: narrow band tones; wide band frequency sweeps; and click burst sequences which replicated porpoise echolocation signal characteristics. These signals, derived from pre-programmed data stored in EPROM, could be clocked out at different frequencies by binary division of a master clock. This method produces signals with identical waveforms in a series of octave frequency steps when divided down from the 140 kHz maximum frequency. The signals were introduced into the water using four simple piezo 'bender' transducers spaced apart at 3 metre intervals starting at a corner of the net cage and extending along the longer 30 m side. Surfacing positions were subsequently extracted from the video camera images which recorded an overhead view of the pool. The animal's behaviour was studied in 20 minute periods, i.e. prior to, during and after exposure to a sound signal, and the results obtained demonstrate that certain signals caused marked and rapid movement of the animal to parts of the pool away from the transducers whereas other sounds had little or no obvious effect. Surprisingly, this animal's choice of position did not always favour the furthest corner from the transducers. However, a careful analysis of the acoustic sound pressure field shows that the complex pattern of sound caused by the four interacting sources produced nulls which the animal was apparently well able to sense and exploit. This paper demonstrates the complexity of the sound pressure level variations that must be taken into account when working in shallow water conditions, especially where constructive and destructive interference can occur between multiple sound sources and with reflecting surfaces.

The Pacific Marine Environmental Laboratory (PMEL) of the United States' National Oceanic and Atmospheric Administration (NOAA) has been monitoring and archiving sound recordings from the U. S. Navy's underwater hydrophone arrays since 1991. These data contain many marine mammal calls, including those made by blue whales Balaenoptera musculus. The call of the blue whale in the northeast Pacific is often sufficiently loud to be detected on more than one array. Matched filtering techniques can expand detection capabilities to additional arrays, allowing blue whale calls to be localized even when they are far from the arrays. In this manner, PMEL has identified regions where blue whales occur seasonally well offshore of the west coast of the U.S. In order to monitor areas of the world's oceans not covered by fixed hydrophone arrays, PMEL has developed autonomous moored hydrophones that have been used to record acoustic energy from both underwater seismic activity as well as that from whale calls. Each mooring package consists of an anchor, an acoustic release, line, hydrophone and data recorder, and a flotation package. The hydrophones are designed to be moored in the SOFAR channel; the titanium case containing the data recorder can withstand pressure to at least 1000 m below sea level. Currently each hydrophone can store up to 2.8 Gb of data; only the sampling frequency and battery life (up to 8 months, depending on sampling frequency) limit the duration of the experiment. The hydrophones are designed to be deployed as an array of independent instruments whose geometry can be determined by the needs of the experimenter in order to localize acoustic sources of interest. Deployment and recovery of each instrument takes as little as one hour depending upon the platform used. An array of six of these hydrophones was deployed in the NE Pacific in September 1995. One of the goals of this experiment was to compare and "ground truth'' locations of calling blue whales from the U.S. Navy's SOSUS data with those detected on the autonomous hydrophones. During the seven day experiment no blue whales were seen in the area, but two blue whales were detected and then tracked acoustically on the hydrophone array. One of these animals was detected on all three available SOSUS arrays. The locations of the blue whale from the two methods are comparable although the location accuracy is more precise on the local array.

Studies on captive bottlenosed dolphins Tursiops truncatus us have shown that they produce individually specific calls named signature whistles and that these whistles are sometimes imitated by other group members. It has been hyphothesised that signature whistles play an important role in individual recognition and that bottlenosed dolphins use imitation of signature whistles to initiate social interaction with specific group members. However, information on the individual, context-related usage of vocalizations in wild dolphins is still scarce, mainly because of the inaccessibility of the marine environment and the lack of observable correlates to sound production in these animals. In this study a hydrophone array was employed in a 500 m wide, natural channel to investigate the vocal behaviour of free-ranging bottlenosed dolphins in relation to spatial distance between individuals and their surface activities. The position of a vocalizing animal was calculated by comparing differences in times of arrival of the sound at different hydrophones of the array. Video recordings from the shore provided additional information on surface behaviour and position of all the animals present. First results showed that whistle interactions with non- matching whistle types as well as signature whistle imitation, occur frequently between individuals in the wild. This project was funded by a DAAD-Doktorandenstipendium aus Mitteln des zweiten Hochschulsbnderprogramms.

Whales living within seismically active regions are subject to intense disturbances
from strong sounds produced by earthquakes that can kill or injure individuals.
Nishimura & Clark (1993) relate the possible effects of underwater earthquake noise
levels in marine mammals, adducing that T-phase source signal level (10- to 30- Hz
range) can exceed 200 dB re: 1 µPa at 1 m, for a magnitude 4-5 earthquake, sounds
audible to fin whales which produce low frequency sounds of 16-20/25-44 Hz over
0.5-1s, typically of 183 dB re: 1 µPa at 1 m. Here we present the response of a fin
whale to a 5.5 Richter scale earthquake that took place on 22 February 2005, in
the Gulf of California. The whale covered 13 km in 26 min (mean speed = 30.2 km/
h). We deduce that the sound heard by this whale might have triggered the costly
energy expenditure of high speed swimming as a seismic-escape response. These
observations support the hypothesis of Richardson et al. (1995) that cetaceans may
flee from loud sounds before they are injured, when exposed to noise in excess of 140
dB re: 1 µPa 1 m.

This paper presents a framework effort to allow the experimentation of various devices in order to automatically record, detect and classify marine mammal vocalizations in the open sea. Some tools for the protection of Killer Whales and other cetaceans are founded in the analysis of their recorded vocalizations. With this framework we are able to test every part under controlled conditions before open sea experiments. Some of these devices have been designed to localize and track open sea populations in order to facilitate data collection for conservation management.
At this moment the framework consists of the basic necessary instruments and IT resources for continuously multichannel recording of vocalizations from four specimens of Killer Whale. The enormous raw data stream forces the implementation of a data reduction strategy. As a result, the present research is focused in the development of techniques for this purpose that will allow the automatic classification of events and obtain statistical data. Complementarily, our research goals are also focused on the design of prototypes for source localization using time tags of events on multiple channels for continuous real time logging of behaviour and position of specimens. This paper presents some preliminary results of automatically detected calls.