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Caught in the net - protect the whale sharks of Mafia Island

Mafia Island, Kilindoni, Tanzania

Caught in the net - protect the whale sharks of Mafia Island

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Mafia Island's endangered whale sharks need protection. A novel telemetry study investigates whale shark behaviour as never before. The use of Multi-Sensor Camera Tags will reveal the sharks' daily behaviour to design adequate conservation measures.

R. Kellner-Stoll from KELLNER & STOLL - STIFTUNG FÜR KLIMA UND UMWELTWrite a message

The name Mafia Island derives from the Swahili phrase ‘mahali pa afya’ which means ‘a healthy dwelling-place’. And that’s exactly what it is. Mafia Island off Tanzania is an important refuge for a huge variety of marine species. One of these species is the majestic whale shark that can reach up to 20 meters in length. The whale shark is the biggest fish on earth and yet it mostly consumes small plankton. To sustain their feeding needs whale sharks move seasonally to the tropical coastal regions with high density of plankton.

Mafia Island is a worldwide phenomenon because there whale sharks can be found year round. Hence the gentle giants, that we know so little about, can be observed and researched over an extended period of time on Mafia Island. Local fish and whale sharks both feed on plankton which creates conflicts with local fishermen. Often times whale sharks collide with boats or get caught in nets which can lead to serious injuries. We can use Mafia Island as an example of how conflicts develop between men and animals in shared spaces. 

So why is it important to further research whale sharks? The whale shark’s status on the IUCN Red List of Threatened Species has changed from “Vulnerable” to “Endangered” at the beginning of 2016. There are many things we do not know about these sharks yet, for example which behavioural patterns they exhibit and for how long they feed in surface waters, when they are especially at risk. To better protect them, we need to find out more about how they spend their lives. 

To gain more knowledge about the juvenile whale sharks of Mafia Island, Jens Paulsen with a M.Sc. of the University of Bremen is planning a novel study in cooperation with the Marine Megafauna Foundation. He wants to identify and quantify the different behaviours whale sharks exhibit at this aggregation site. To do this, he plans to put the rough equivalent of an iPhone on the sharks’ backs. In the science world, these iPhones are known as Multi-Sensor Data Logger or behavioural tags. These highly specialized sensors can record huge amounts of fine-scale movement data of whale sharks. Additionally, the tags have a video camera integrated, so we can get a shark’s view of its travels through the ocean. Jens attaches the tag on the 1st dorsal fin of the whale shark and the tag automatically falls off after a predetermined time. After Jens retrieves the tags, he will be able to follow the sharks’ behaviour directly from their point of view. The retrieval rate of the tags will be optimized by use of a modified drone. Finally a method for taking blood samples of the sharks will be developed. This will give us access to highly valuable data regarding the energetics and the health of the whale sharks. Results will be transferred into a computer model to determine the spatial use and behaviours of the whale sharks of Mafia Island. Findings will be of significant value to define conservation measures for whale sharks here and globally. 

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