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Measuring Mantas

By Guy Stevens, 9th November 2011

Following the 60 Minute Australia shoot Dr. Mark Meekan was kind enough to leave with us the stereo cameras he had brought to help us get accurate measurements of our manta rays so we could gather even more data. Armed with an in depth briefing on how to use the cameras, what precisely we needed to film, how to charge the cameras, change the cards, download the data as well as (most importantly) what NOT to touch, Mark left us with the rather cumbersome device and went happily back to Australia 31kgs of baggage lighter!

Now, the first hurdle when using these cameras is moving them around. The two video cameras and their housings are fixed in a frame to ensure they film precisely what we need them to in order to get accurate measurements. The frame however, is over a meter wide and manoeuvring the cameras to and from the boat, in and out of the water and even in the water has taken a little practice and figuring out!

After a couple of trials however, we are very comfortable with our new addition to the team and we’ve been able to gather some very valuable data with almost 7 hours of footage already gathered of many of our regular mantas that we see on an annual basis. The last couple of weeks have proved to be some of the best for sightings that we have had all season, with up to 150 mantas being seen in a single feeding event.

The reason for this improvement in sightings is a return to the more usual weather for this time of the year, higher wind speeds and more unsettled conditions which boost productivity and therefore the manta’s planktonic food resulting in a lot of our core population of mantas putting in last minute appearances for the 2011 season.

Many thanks to Mark for the loan of the cameras! Hopefully, repeating this experiment over the next few years will really help to provide us with some very accurate data on size and growth rates of mantas here in the Maldives.

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