- Project Leader: Dr Per Berggren
- Sponsors: Xiamen-Newcastle Joint Strategic Partnership Fund
- Partners: Professor Yu Zhang (Xiamen University, China)
Marine bioacoustics is an emerging inter-disciplinary research field combining marine acoustics, marine biology, bionics and informatics that has shown important applications in underwater bio-sonar technology, signal processing and marine animal communication. Dolphins and other toothed whales (odontocetes) possess a highly sophisticated bio-sonar system which plays an important role in their navigation, prey detection, predator avoidance and communication.
The basic structures involved in the odontocete sound production (e.g. phonic lips, cranial air sacs and the melon) have been described from research of the harbour porpoise (Phocoena phocoena). However, few other species have been studied and the hypotheses regarding sound production and dolphin sonar still need experimental support to fully understand the structures involved and their respective function when producing the different sounds and frequencies. In addition, human generated noise from offshore construction (e.g. pile driving and drilling), wind and current generators, naval sonar, shipping and other anthropogenic activities have increased in the past decades and represent threats that may have both individual and population level effects on sound producing marine mammals. Therefore, studies investigating how odontocete bio-sonar may be affected by environmental and anthropogenic factors are important for future conservation and management efforts to safeguard marine mammals and in particular cetacean populations.
The objective of this joint research collaboration between Newcastle University and Xiamen University is to make significant impact in both basic and applied science of dolphin bio-sonar mechanisms in relation to anthropogenic and environmental effects.
The collaboration includes four projects:
1) Biomedical imaging (CT/MRI) to document acoustic characteristics of sound production tissues in dolphins
The Indo-Pacific humpback dolphin from Xiamen coastal waters and the white-beaked dolphin from Northumberland coastal waters will be used as study species based on dead specimens retrieved from stranding's and fisheries bycatch. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scanning will be conducted on a selection of dolphin heads to generate 3-D images and to determine properties of the tissues and organs involved in sound production. Using CT imaging, internal structures of the study specimens will be reconstructed from multiple projections formed by scanning thin cross sections of the heads with a narrow x-ray beam (Fig.1). The following sub-projects will be investigated:
- Three dimensional digital image visualization of the sound production and sound receiving structures (phonic lips, air sacs, connective tissues, melon and mandibular fat) of Indo-Pacific humpback and white-beaked dolphins.
- Comparison of the acoustic properties of the digitized sound production and sound receiving structures of Indo-Pacific humpback and white-beaked dolphins.
2) Physical properties of the tissues involved in dolphin sound production and sound reception
Sound velocity measurements of the dolphins’ forehead tissues will be performed using an ultrasound velometer. This requires knowledge of the tissues’ densities which will be estimated from CT scanning combined with mass and volume measurements. Based on the experiments the physical properties, sound velocity and density, of the dolphins’ sound production and receiving tissues will be explored as follows:
- Measurement and comparison of the sound velocity distribution in the sound production and sound receiving tissues in the heads of the Indo-Pacific humpback and white-beaked dolphin.
- Investigation of the correlation between density and HU in the Indo-Pacific humpback and white-beaked dolphin.
3) Model the ultrasound beam formation and echolocation of dolphin bio-sonar by using finite element simulations
The CT and MRI data will be used in computer simulations to further the understanding of the bio-sonar of odontocete cetaceans. Using scanned data, geometry models of the dolphins’ heads will be constructed and full-wave finite element simulations will be applied to numerically solve the acoustic fields in the head models. Following sub-projects will be investigated:
- The function of the melon in focusing the ultrasound beam in the Indo-Pacific humpback dolphin and the white-beaked dolphin.
- The effect of the rostrum morphology on reflecting the dolphin ultrasound beam.
- The effect of external noise on the beam pattern of dolphins’ ultrasound beams.
4) Anthropogenic noise impact on dolphin sound production and acoustic behaviour
Sound files of echolocating wild Indo-Pacific humpback dolphins in coastal waters off Xiamen and white-beaked dolphins off the Northumberland coast, UK, will be collected using autonomous sound recorders (SoundTrap, www.oceaninstrumnets.co.nz). These recorders have a very wide frequency range and very high sampling rate making them ideal to simultaneously record high frequency dolphin echolocation signals and lower frequency noise sound from anthropogenic activities. The anthropogenic activities that may generate noise at the deployment sites will be monitored by conducting visual ship surveys. By linking these data to the sound recordings it will be possible to evaluate what anthropogenic activity that has generated the recorded noise. The surveys will be conducted using the Xiamen and Newcastle University research vessels in the respective study areas.
The following sub-projects will be investigated:
- Description of echolocation sound profiles of Indo-Pacific humpback dolphin in Xiamen coastal waters and white-beaked dolphins off the Northumberland coast, UK.
- Description of noise generated from anthropogenic activities at the recording sites. Comparison of the dolphin echolocation signals in relation to different types and levels of anthropogenic noise.