Day 3 – March focus on Norfolk Island’s reef

Today, on day 3 of my March focus, I wanted to feature one of my favourite animals inside our lagoon – the giant (the size of a small beach ball) mollusc that goes by the scientific name Tonna melanostoma, or the black-mouthed tun. When I took the first photographs of this live animal and posted them on iNaturalist, I had no idea that there were no other – as in none, zip, nada – images of it in the public domain; just a couple of photographs of a broken shell housed in the Auckland Museum.

I'll just repeat that because it is important: there were no other photographs of the live animal anywhere in the world available in the public domain.

Back in the late 1990s I used to see these guys quite regularly, or at least the tops of the shells poking out of the sand during daylight hours (they are generally nocturnal). These days it is quite an exciting event to see one. Just over a year ago, we went through a period when we (as in, other snorkellers and myself) saw a few dead, empty shells. Now, although I can’t be certain, judging by the photographs I have taken over time, I think we are down to just a couple of live individuals of the black-mouthed tun.

There are two other species of Tonna – the tankervillii and perdix. Again, these are rarely seen in our lagoons today.

I have written a couple of blog posts about the black-mouthed tun, including a co-written a scientific paper published in the Royal Belgian Conchology Society's publication Gloria Maris. You can find these, here:

• Citizen science in action on Norfolk Island

• The black-mouthed tun snail – diary of an egg mass