Manta Rays of Brazil

Latest update May 30, 2019 Started on March 31, 2019
sea

We study the movement and behavior of giant manta rays in relation to environmental factors in Brazil. Working together with Andrielli Medeiros and her team we try to understand why manta rays show breaching behavior in an estuary habitat.

March 31, 2019
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In The Field

While searching for manta rays and studying their breaching behavior Andrielli and her team started using thermal imaging cameras. It is very difficult to catch the exact moment when the manta rays are breaching and the team has been spending countless hours on the boat watching the water to be able to catch that moment with the thermal camera. These cameras, by rendering infrared radiations as visible light, allow us to see areas of heat. We have been sitting on the top of the boat for many hours and I liked to play around with the camera, watching the thermal images of dolphins swimming by or birds flying by. Andrielli has a big library of such images on breaching events already that we will start to analyze and will keep you posted about what we find.

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In addition to exploring the waters with the Trident ROV, we also use a hydrophone to record the sounds underwater. While waiting to see manta ray breaching from the top of the boat we also listen to the sounds and record the breaching when it happens. On this day we spent many hours on the top of the boat waiting. The type of hydrophone we are using is perfect for detection and recording of very loud signals, as well as listening and recording of more quiet sounds like cetaceans, whale watching operations. Since these hydrophones are used primarily for cetacean research, it works perfectly, as we can hear the sound of the dolphins in the area almost continuously. Andrielli showed me how to use the device and I really enjoy listening to the dolphins communicating around the boat and in the further distance, while also making some recordings. To keep me focused during hours and hours long of observation I even got a Brazilian pancake from Andrielli that she made, filled with Nutella and bananas and we successfully recorded a manta ray breaching around 200 feet away from us!

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Our first day on the field with the Trident ROV turned out to be pretty exciting! We tested it in the Paranagua estuary on a calm, perfect day. We went out with the boat early morning with Andrielli`s team and anchored at a location where we expected to see manta rays breaching based on her previous observations. While we were waiting for the changing tides I set up the ROV and tested it in open water for the first time. Unfortunately, the visibility was not too good on that day so the underwater video was not very helpful, but we could see manta rays breaching from the top of the boat. I also experienced some of the limitations, since I only had the 25m tether. The longer tether would have been much more useful to get further away from the boat and being able to monitor a larger area. Next time I will return with the longer tether for sure. I also found out that the weights intended to be used in the sea to keep neutral buoyancy were not necessary here since the water was rather brackish and the weights just made the ROV sink fast and more difficult to maneuver. All together we had a great day on the water and I learned a couple valuable lessons on how to improve using the ROV for the next time.

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Preparation

We are so excited to report that we are ready to test the Trident ROV on the field for the first time! Today I arrived at Pontal do Parana, at the Southern part of Brazil to meet my friends and collagues, Andrielli and Bianca. The trip was not without complications. I flew out from Rio de Janeiro, where all flights were either cancelled or delayed due to heavy rains in the last 24 hours. Finally, after an hour delay I could fly to Sao Paulo, but missed my connection to Curitiba. In the last minute the airline could put me on a flight that almost finished boarding already and I finally made it to Curitiba where my friends were waiting for me. After 2 hours drive we arrived at the small town, Pontal do Sul and started preparing for the exciting day tomorrow. We are going to try to find giant manta rays tomorrow in the Paranagua estuary and document their behavior!

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Expedition Background

The giant manta rays are often described as “oceanic”, however there have been several reports that described these animals in estuary habitats. At the Paranagua Estuary complex, in Brazil, manta rays have been observed breaching quite often at certain part of the year, but it is currently unknown what causes this behavior. Andrielli Medeiros and her team from the Universidade Federal do Paraná started studying these animals in the area years ago trying to find out what environmental factors might be influencing this behavior. The estuary is dynamic, where the conditions are changing, therefore providing a great opportunity to study how biotic and abiotic factors effects manta ray behavior. With the help of the Trident ROV we hope to find answer to these questions by exploring the underwater habitat, collecting environmental data and hopefully by recording some interesting manta ray behavior.

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