This is one of those magical questions to which there are two very different answers. A few dozen of them are actually registered, but our estimates are in the multiples of thousands because a number of dual citizens—likewise for the United States and the U.K. as these are the three largest diasporas in the world—go back to their country of origin to volunteer and work for, really, a pittance for the new, emerging government, or with local NGOs, or local civil society organizations. Many of them have gone back to start businesses or to open private hospitals and schools. They don't register with us, so we don't know the fulsome answer to your question.
On May 31st, 2018. See this statement in context.