this post was submitted on 31 May 2024
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If it's not clear, they were found when demolishing an old tuatara enclosure.
Also I found this interesting:
50,000 on one island in the Marlborough Sounds?
For a moment there I was thinking maybe people in Invercargill always have to check potential demo sites for tuatara before they proceed!
Me reading headline "omg there are a lot more tuatara down that way than I realized"
I had the same first impression! But unfortunately if you check the distribution map on the side of the wikipedia page, they basically only live on islands.
There's also this snippet:
Since Zealandia is a fenced reserve (that has a specific tuatara enclosure within that reserve), it seems they are not very common on the mainland at all.
To elaborate however, although Zealandia has a fenced "scientific" enclosure for Tuatara near the front, there's a separate group of them running wild around the rest of the sanctuary (though still inside the main fence). There's a particular track up near the back of the fence with artificial burrows where they're encouraged to hang out. You can often encounter them in the tracks near there, but it's also completely possible to meet them effectively living wild anywhere else within the fence, and also not entirely uncommon.
But yeah they basically don't live on the mainland outside fenced sanctuaries at all any more. Rats interfered too much that they were effectively gone from the mainland from some time after Maori arrival.
Ah I didn't realise they were all through! I haven't spent a lot of time there, we'll probably go more when the kids are older.
I coincidentally went to a talk about it tonight where it was noted they're getting so populous that there's a new suspected risk of tuatara burrowing under the fence and letting something bad in.
The fence is due to be replaced within the next decade, and apparently they have tentative plans for an adjusted design to prevent this from happening.
I guess it's a good problem to have.
Amazing that the tuatara burrowing is more of an issue than rabbits burrowing!
I just came across this document detailing the design of the fence, and was surprised to see it's not very deep at all!
I had expected a deep fence going down a metre or so underground, instead it seems they went out - with a mesh buried 10-20cm that comes out from the fence so that digging animals are overtop of the mesh when they think to dig, and can't dig through it. It makes sense now that burrowing tuatara could let animals in, as it would be much easier for an animal to dig out than for one to dig in.
Yes. What they found for rabbits, back in the day whilst figuring out how to design it, was that they'd always go right up to the fence and then try to dig. If they hit metal then they'd move sideways rather than backwards, so the skirt goes about 40cm outwards and that prevents all the rabbit incursions.
At the time I don't think they ever imagined the need to design for tuatara burrowing outwards, but probably good that it's only starting to become a question at about the time they've been planning for the fence to be replaced anyway. It'll be interesting to see if and how this affects all the other fenced sanctuaries that have sprung up later.
Another bonus of replacing the fence is that they'll be able to change the mesh, as the original one didn't have small enough holes to prevent baby mice getting through. I'm not sure how the mice inside will be properly eradicated after that's done. The original eradication was (I think) a brodifacoum drop which would no longer be practical unless everything important was somehow cleared out from inside the fence first.
Yeah I saw the mention of baby mice getting through. I'd guess having a fence that keeps them out is the first step, then they could probably reduce numbers with trapping, which may be able to wipe them out eventually. Not sure if there is an issue with say tuatara crawling into mouse traps?