Marine mammals and echolocation

Toothed whales and dolphins, or odontocetes as they are referred to commonly, use echolocation as a method of sensing the environment around them. Fundamentally, echolocation involves the production of sonar clicks. These clicks are reflected off objects within the environment and the returning echo is received and analysed by the animal. Echolocation can be used for exploration, communication, navigation and prey capture.

The characteristics of echolocation clicks vary with species, behaviour and habitat. For example, harbour porpoises (Phocoena phocoena) emit high-frequency, narrow-band echolocation clicks, whilst deep diving species such as sperm whales (Physeter macrocephalus) emit mid frequency click trains. It has been hypothesised that lower frequency sound, which travels greater distances, allows the animals to explore further afield. By recording, then analysing the characteristics of click trains, it is possible to make inferences about marine mammal behaviour. For example, similar to bats, feeding marine mammals appear to have specific click trains when locating, tracking and catching prey.

Bottlenose dolphins (Tursiops truncatus) in Western Australia. © OSC 2011.

Bottlenose dolphins (Tursiops truncatus) in Western Australia. © OSC 2011.

Echolocation click detectors

Echolocation click detectors, such as analogue T-PODs (www.t-pod.co.uk) and digital C-PODs (www.c-podclickdetector.com), are examples of static Passive Acoustic Monitoring (PAM) equipment (www.passiveacousticmonitoringsystem.co.uk). Once deployed, T-PODs and C-PODs can remain in situ for months at a time recording echolocation click data continuously. This makes them ideal for diel (24-hour) studies, and for studying species that are particularly difficult to monitor visually in the wild.

Echolocation click detectors like the C-POD comprise an omni-directional hydrophone, a processor and a logging system. Once the C-POD has been retrieved, data including time, duration, frequency, bandwidth and click intensity, can be uploaded from the removable memory card. Specialised analysis software can then be used to examine the data by a suitable qualified and experienced marine scientist.

Echolocation click detectors have been used extensively in acoustic research of marine mammals. Past applications have included presence and absence studies, habitat use, behaviour and abundance. Echolocation click detectors have also been used during offshore construction activities to assess changes in habitat use throughout the different stages of operation. Ocean Science Consulting Ltd (OSC) has used both T-PODs and C-PODs to conduct research on harbour porpoises in the North Sea. By deploying T-PODs and C-PODs around offshore platforms and in open water, OSC have found that harbour porpoises appear to be abundant around offshore oil and gas rigs and platforms, possibly using them as feeding grounds. Data also show that distinct diel patterns were evident in the data, with differences in the number and type of click trains, indicating potentially that harbour porpoises are feeding more at night. Please refer to www.osc.co.uk to see a full list of our publications along with links to PDFs.

Ocean Science Consulting

Since its foundation in 2004, OSC has been providing a comprehensive range of high quality services to the offshore oil, gas and renewable industries. Along with Marine Mammal Observer (www.marinemammalobserver.co.uk) and Passive Acoustic Monitoring (www.passiveacousticmonitoring.co.uk) services, OSC are able to cater for all your echolocation click detector needs. In addition to supplying all equipment, OSC can offer expert advice for all stages of the project from conception and feasibility through to delivery. Please refer to our main website www.osc.co.uk for a full list of the services we offer.

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