Whale Sharks A Plenty in Mafia

We were lucky to meet Matt Potenski who came from Mafia Island to visit us during the expedition. He has sent the following report and pictures showing the work he has done in Mafia. Rachel our scientist from the WCS gave him some receivers and tags to put out so that we can all work together. It is a very exciting start for Mafia as you will read below!! Many thanks for the info Matt – at least we now know where all the sharks are!!!

EAWST Blog – Cooperation with Tanzania

     To all the EAWST friends, greetings from Tanzania.  My name is Matthew D Potenski, and I run a research program on whale sharks in Mafia Island, Tanzania.  Over the last few years, some data has been collected to suggest that whale sharks may use areas of both Kenya and Tanzania.  This year I had the pleasure to come up to Kenya to meet with members of the EAWST and head out into the field with Dr. Rachel Graham.  Upon discussion with both Dr. Graham and the EAWST, we were able to look at some data and agree to collaborate on projects in the future.  In that vein, I have just completed my season of field research at Mafia, and have a number of interesting things to report.

Last year I made observations of a tagged shark off Mafia Island.  This is not remarkable as I tag the sharks there, but this shark had a tag that was not like the ones I put out.  After some effort, I was able to remove enough algae from the tag to decipher a number.  The tag read K001, and I rightly guessed that the tag’s origin was in Kenya.  I contacted members of the EAWST and they confirmed that it was a tag they put out.   In the past few months, I have re-sighted this shark numerous times.  At the last count, I have encountered this shark six times over a span of three weeks.  All the sightings have been made in the waters immediately to the west of Mafia Island.  Shark K001 was seen on January 27th and 29th, and February 1st, 2nd, 9th, and 23rd.  The identification of this shark was confirmed by spot-pattern analysis.  Please see below for a spot ID picture taken of shark K001 on January 27th.


I am also happy to report that in cooperation with the EAWST and Dr. Graham, I have been able to deploy automated telemetry equipment at Mafia Island.


This means that Tanzania has joined with Madagascar, Mozambique, and Kenya in forming acoustic arrays for whale shark detection.  On March 20th-22nd I managed to deploy the eight transmitters I received from Dr. Graham.  Seven male sharks ranging from 3-6.5 meters and one 5m female were fitted with a Vemco V16 acoustic transmitter.


On the 23rd, a small team helped me deploy two Vemco VR2W acoustic receivers.  This involved diving on scuba and pounding iron bars into the sand.  We then attached the units both to the bars and to 150 kg cement blocks as a preventative measure.  There is some net fishing in the area where these receivers are located and the cement block should be heavy enough to keep the units from being pulled up in a net.


The important point is that the deployment of this equipment is completely reciprocal with transmitters and receivers deployed by the EAWST.  This automated telemetry equipment may give further insights into the actual amount of migration by whale sharks between Kenya and Tanzania.  Sharks tagged with transmitters in one location can be detected by receivers in another location.  The actual residence time or amount of time a whale shark spends in a location with each receiver will be measured.  This means that data on both local movements and migrations between receiver arrays can be collected.  The receivers will spend several months in the water before they are retrieved and their data downloaded.  I know I am very excited to see what data we will be able to get with this technology, and I look forward to comparing data with the EAWST so that we can get a more accurate picture of the behavioral patterns of whale sharks in East Africa.

Special thanks to Volker, Nimu, and all the volunteers at the EAWST and to Dr. Rachel Graham of the Wildlife Conservation Society for their friendship and support.   I look forward to more whale sharks in both Kenya and Tanzania in 2010.

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