As some of you will recall, last January I satellite tagged three manatees in eastern Senegal as part of a multi-agency group that rescued them from tributaries where they were trapped behind dams (See posting from 1/31/09). We released the manatees back into the Senegal River and they have been tracked since then by my colleagues at CBD-Habitat (the Spanish NGO that bought the tags) and Oceanium Dakar (Senegalese NGO).
In early April both the red and blue tagged manatees were in the Senegal River within several kilometers of each other. They were staying in the same area, likely feeding. Then, very suddenly, the red tag gave an accurate location in the village of Bababe, several kilometers inland from the river. The blue tag stopped transmitting it's location a day or two later. Oceanium Dakar sent two biologists to Bababe (a 10 hour bus trip) to recover the red tag, and when they arrived they found fishermen in the village had not only it, but the belt that goes around the manatee's tail as well. The fishermen said the manatee's tag had gotten entangled in their nets, the manatee had broken free and left the tagging gear. Infact, this is exactly what the tagging gear is designed to do- break off the manatee if it becomes entangled- because obviously we don't want the gear to cause the manatee any injury or to drown. The tag had fishing net wrapped tightly around the antenna (in the center of the photo below, courtesy of Kader Diagne).
After finding the red tag, the biologists used a radio tracking receiver to try to locate the blue tag on the river. It was later found in another village near Bababe and also had gotten caught in fishing nets. (Photo courtesy of Kader Diagne)
A fisherman shows where a manatee ripped a hole in his net. (Photo courtesy of Kader Diagne)
So while it's a disappointing that the tags came off, it's encouraging to know the safety mechanisms worked, and the travel data gained during the 3 months they were tagging is very valuable. This is the first time this technology has ever been used for West African manatees, so we're learning alot, both about the manatees and how the tags function in this part of the world.
Meanwhile, the yellow tagged manatee (the female) is still out there! She has made multiple movements up and down the Senegal River (shown in the map below by different colored tracks, courtesy of CBD-Habitat), and twice has come within 17 miles of crossing into Mali.
Now that 6 months have passed, the battery in the GPS unit in her tag is dying, but the tag can still be located by the VHF signal. So hopefully she can be relocated and the tag recovered. Even if we don't find her, the equipment is designed with bolts that corrode, so it will fall off. There is alot of data to be analyzed (tags also tell us things like water temperature and how much the manatee moves between each satellite fix, so we can tell if they are resting or traveling). I'm looking forward to continued collaboration with folks in Senegal to learn about their manatees!