Making Noise on Porpoise

This article was first published in University of Exeter’s Life Magazine in July 2015.

Studying cetaceans using static acoustic monitoring and applying the results to conservation science.

It isn’t easy to study cetaceans in their natural environment. As we can’t survive underwater, our options were limited to making brief dives, which provide useful data, but are restricted in how long you can collect data for, or using surface surveys.

Over the last decade, a technique known as Static Acoustic Monitoring (SAM) has become an increasingly popular tool to study cetaceans. It enables the study of their long-term ecology and distribution, using hydrophones to detect echolocation clicks. The hydrophones are secured using moorings, and collect data over periods of months at a time. One widely used SAM instruments is the C-POD, developed by the University of Exeter’s Nick Tregenza.

In my third year at Penryn Campus, my research focused on dolphins and porpoises off the Cornish coast and their distribution in time and space. Data were collected using C-PODs by my supervisor, Dr. Matthew Witt, and spanned numerous sites, and several years. The data were easy to work with and I concluded that SAM is a good technique for studying cetaceans; however, as with most things, there are both advantages and disadvantages to its use.

So what’s good about static acoustic monitoring? One of the main advantages is that instead of using human observation, we can deploy hydrophones at multiple locations for long periods, and by using an instrument to do the job for us removes the variation that inevitably creeps in if more than one person collects data.

The hydrophones can do things we just can’t. They can sit in the mid-water column for months on end, ‘listening’ and collecting data 24 hours a day, 7 days a week. Humans cannot possibly do this, and as surface surveys usually rely on visual sightings, night-time monitoring is impossible. Visual surveys can only monitor the surface layer of the ocean, whereas the hydrophone can collect data from underwater, in areas of the ocean we can’t see down to. Hydrophones can collect data in all weathers, too – you’d be hard-pressed to find many people willing to stand on a boat in howling wind and lashing rain trying to record the presence of cetaceans!

There are limitations, however. The instruments and hydrophones used are being continuously developed and improved; there have been several versions. There are documented differences in sensitivity between versions, and sensitivity may drift over time. This will affect how much data are collected and whether or not the data are directly comparable.

The instruments do not come cheap, either – the C-POD alone costs £2970, before you consider labour and maintenance costs.

The hydrophone may be lost during rough weather, if it is damaged or becomes detached, or it may be damaged by ocean traffic. In such cases, the data is lost and time and money wasted. Theft may also occur. Hydrophones are attached to a buoy which floats on the surface, allowing it to be retrieved – this may attract attention. In these cases, again all data, time and money are lost.

So what can we do with data from static acoustic monitoring? SAM opens up a whole new realm in which to gather data which wasn’t accessible before, and is proving ever more relevant. What we do in the oceans has a serious impact on species living there. Cetaceans are particularly vulnerable as they depend on noise for almost everything, and most of our oceanic activity e.g. shipping and renewable energy production produces lots of noise, the installation of wind turbines being a prime example. Knowing where they are and when enables more effective management of human activity. In the example of wind turbines, this may allow us to limit the noisier, more damaging activities to times when cetaceans are not so active in an area.

One of the main applications of such data is in damage limitation, however if used in the right way, SAM can also be good for studying the ecology of echolocating species and learning more about how these often enigmatic creatures of the deep live.

Whilst there may be issues and problems associated with using this technology, it is a useful technique to study and monitor cetacean activity, and as the technology develops and becomes more reliable, and more studies are done, we will get a clearer picture of what goes on underwater.

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