What the colony is
The giant tortoises on Changuu, the island off Stone Town sold as Prison Island, are Aldabra giant tortoises kept in a fenced compound. They are a managed captive population, not a wild one and not a native one, and a great deal of excursion copy describes them as though they were neither.
That is the single most useful correction this page can make. Nothing here is being encountered in its own habitat. What is on offer is a well-established captive colony with an unusually well-recorded history, which is interesting for different reasons.
How they got there
Four Aldabra tortoises were sent as a gift from the British Governor of Seychelles in 1919. Every tortoise on the island descends from them.
One caution on the detail. Zanzibar’s own antiquities-era material names General Lloyd Mathews as the recipient of that 1919 gift. Mathews died of malaria in October 1901, so he cannot have received it. The date and the donor are well attested; the recipient in that sentence is not, and it is repeated widely because it comes from an official source.
The numbers, which are the real story
The colony’s history is a collapse and a rescue, and it is worth setting out because the tortoises are usually presented as a charming curiosity rather than as something that nearly disappeared.
From the four founders the population reached roughly 200 by 1955. It was down to about 100 by 1988, to 50 by 1990, and to seven animals by 1996. The cause is documented: people were taking them to sell abroad as pets or for meat.
Eighty hatchlings were imported in 1996 and forty of them disappeared. A secure compound was then built by the Zanzibar government with the World Society for the Protection of Animals, and by 2000 the island held 17 adults, 50 juveniles and 90 hatchlings. A semi-official count put it at around 100 animals in the period from roughly 2009 to 2012.
After that, nothing. No authority publishes a current figure, and the counts quoted on the island and in excursion listings — a hundred and something, two hundred and something, an animal of a precisely stated great age — have no published source behind them. Treat any number you are given on the day as an estimate offered in good faith rather than as a record.
Seeing them
The enclosure is a few minutes’ walk from the landing and is part of every Changuu half day out of Stone Town, alongside the ruins, the short forest walk and the snorkelling. Feeding is normally part of the visit.
Worth carrying, given the history above: these are long-lived animals in a small fenced space that exists because the free-ranging population was stolen almost to nothing within living memory. Handling and climbing on them is not a trivial matter whatever is permitted on the day. The conservation tours guide covers how to think about visits of this kind, and the sandbank and island hopping guide covers the trip they sit inside.
Common questions about the tortoises
Are they wild?
No. They are a captive colony in a fenced compound, and they are not native to Zanzibar. All of them descend from four Aldabra giant tortoises given by the British Governor of Seychelles in 1919.
How many are there?
No authority publishes a current figure. The last semi-official count, around 2009 to 2012, was about 100. Numbers quoted on the island have no published source.
Why were there only seven left?
Theft. From about 200 in 1955 the population fell to roughly 100 by 1988, 50 by 1990 and seven by 1996, as animals were taken for sale abroad as pets or for meat. Eighty hatchlings were imported in 1996 and forty of those vanished too, after which a secure compound was built.
Is this the same trip as Prison Island?
Yes. The enclosure is on Changuu, and the island’s history as a prison that never held prisoners and a quarantine station that did is covered on its own page.