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First age determination study for the West African manatee

By Lucy Keith Diagne, 28th March 2012

One attribute that manatees share with sharks is their ability to replace their teeth throughout life. Manatee teeth move forward along their jaw as the older ones in front of them wear down and fall out (think of a conveyor belt from the back of the jaw to the front). Because of this, teeth are not able to be used to determine the age of a manatee, so instead ear bones are used. Lucy Keith Diagne’s West African manatee project, in collaboration with colleague Katie Brill, is conducting the first age determination analysis of West African manatees using ear bones from carcasses. The technique (which requires slicing a very thin section of ear bone with a diamond saw and counting the rings, just like in a tree) has been used for Florida manatees for many years, but this is the first time this analysis has ever been conducted for West African manatees. We have recently aged the first 16 West African manatee ear bones from samples collected from four countries: Gabon, Ghana, Senegal, and Mali. The ages ranged from 12 to 39 years old (any age over 20 is considered old for a wild manatee!) and this information will be used along with genetic samples and stable isotope analyses (which are used to study manatee diet) collected from the same individuals to give us a picture of the lives of manatees in different populations. Age data also will be used to look at the impact of hunting on manatee populations throughout Africa. For example, 3 of 4 ear bones from Ghana were from young manatees that had not reached sexual maturity before they were killed, raising concerns that the population in this area is being hunted to extinction faster than they can reproduce. This study is ongoing and we plan to continue collection and analysis in order to obtain samples from throughout the range of the species.

Ear bone photo age answer= 16 years old

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