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.
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.