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Beaked whales are small, deep-diving whales that have been among the most mysterious of all cetaceans, as they are rarely found close to coasts, spend up to an hour at a time underwater and are hard to study. Recently they have attracted a lot of attention as it has become clear that they die during naval exercises using submarine-hunting sonars. The attachment of D-TAG (digital tag) sound and movement monitors - a very demanding task, although causing minimal disturbance to the animals - has produced a wealth of information on these species and has shown that they do frequently dive to depths beyond 1000 metres and seek their prey using sonar. D-TAG studies of Cuvier’s beaked whales showed that they do not generally use their sonar above a depth of 400 metres and that the clicks are highly suitable for the POD click detection hardware, being relatively long and narrowband. Blainville's beaked whale (Mesoplodon densirostris)
To make passive acoustic monitoring of these animals possible, a deepwater housing for the POD electronics and a low frequency transducer have been constructed and tested satisfactorily to a depth of 2000 metres. The system has given clear detections of beaked whales in the course of brief test deployments. These deployments showed that, at 750-800 metres, the acoustic environment was favourable and the trains detected corresponded well with established measures of click duration and inter-click intervals. Deployment, especially for longer term studies, is a key issue because of the water depth. These PODs are suitable for Environmental Investigation Assessments of sonars on beaked whales. Sowerby's beaked whale (Mesoplodon bidens)
There is little or no information on the sounds made by this, and other, beaked whales.
The chart below shows click trains logged at 800 metres in waters used by Cuvier’s beaked whales and Blainville’s beaked whales.
In this chart, the vertical height of the coloured lines represents the duration of a click, with the position on the X-axis showing the time of the start of each click. The dashed vertical lines mark transitions in the T-POD hardware configuration and this is why the clicks appear to get longer after the second dashed line. For more information on these species, please visit the Convention of Migratory Species web site.
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