Peter Hammond's book: 'Slavery, Terrorism, and Islam' had a lot of information on this topic.
The gist of it was that many more black Africans were taken off to be slaves - but probably around 90% died during the transportation, and the males were castrated. The women slaves had their offspring murdered (by their 'pro-choice' slave owners).
The link below: is from one of his talks on this subject: .
Slavery, What You've never been told