2,500 ring tailed lemurs in captivity ?! and only 75 black blue-eyed lemurs ?!
Well, as noted that's merely 2500 in accredited zoos which reported their figures back to the authors of the book (a rather long list which, incidentally, includes the aforementioned Christoph Schwitzer) with many more - perhaps twice as many - in captivity elsewhere!
I find it really quite scary actually this evident scarcity of some species kept ex-situ.
Indeed - as noted many of the species mentioned are now absent entirely from captivity, or nearly so. There are a few success stories however - for instance the number of Microcebus lehilahytsara in Europe is now somewhere in the region of 140 individuals, thanks in large part to the massive breeding colony at Zurich, which is free-roaming in the Masoala house.