Visual vs. Acoustic Monitoring of Cetaceans

Cetaceans, particularly diminutive species like the harbour porpoise (Phocoena phocoena), are notoriously difficult to observe and study in the wild, and ascertaining patterns in terms of habitat usage and behaviour, is problematic using visual methods only, mainly due to weather and daylight constraints. The T-POD and C-POD are static (surface or sub-surface moored), autonomous (unmanned), Passive Acoustic Monitoring (PAM) systems (, also known as echolocation click detectors, which can log cetacean activity 24 hours per day for months at a time, with fewer environmental limitations cf. visual observation methods; therefore, this technology can offer a more cost-effective solution for surveys.

C-POD Functionality

The C-POD is the digital successor to the T-POD (, but in summary, this technology comprises a hydrophone, processor, memory, and analysis software. Once deployed, the hydrophone detects echolocation clicks from cetaceans and other sources, characteristics of which are logged and stored, ready for downloading onto a PC equipped with the associated programme. The software identifies potential cetacean echolocation click trains, and then, through the use of a complex algorithm, classifies trains into “quality” categories, depending on the likelihood that the click train was produced by a cetacean. Click trains classified as “high” almost certainly originate from cetaceans, and with decreasing order of certainty, subsequent click trains are categorised as “moderate”, “low”, and “doubtful”. In the latest versions of C-POD software, “species” filters include “Narrow-Band High Frequency” (aka “NBHF”), “other cetaceans”, and “fixed rate/boat sonar”. From these data, habitat usage and behaviour can be assessed and inferred by investigating different click parameters and activity indicators. More complex analyses methods can be performed by Ocean Science Consulting Ltd (OSC), as per the company’s peer-reviewed research available at

Mooring configuration for a T-POD and C-POD acoustic survey of cetaceans during a nearby drilling operation. Source: © OSC 2009.

Mooring configuration for a T-POD and C-POD acoustic survey of cetaceans during a nearby drilling operation. © OSC 2009.

C-POD Applications

The C-POD click detector can be used for a wide range of other projects including, marine mammal population trend studies, Environmental Impact Assessments (EIAs), bycatch studies, and Before-After Control Impact (BACI) studies (often used to assess the effects of wind farm or turbine construction and operation on marine mammals). The C-POD can be used to detect and study a variety of odontocete (toothed whale) species, ranging from the smallest porpoises to the grand beaked whales.

OSC’s Track Record

Ocean Science Consulting has custom-developed a number of mooring configurations to cope with the harshest environments, ranging from offshore oil and gas installations to fishing grounds that are, on average, trawled no less than 14 times per year. Significantly, the scientists at Ocean Science Consulting have been using this technology since 2004, and yet they have never lost a single T-POD or C-POD, which is testament to the team’s project design, preparation, attention to detail, and determination for success.

For information on all the services offered by Ocean Science Consulting please see the main website at

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