Wednesday, 16 July 2008

Snail round-up in the Northern Territory

Years ago, when I was working on snails in central Australia, I devised a cunning plan to make collecting easier.

The problem with studying snails in the desert is they bury themselves deep in crevices or beneath piles of sandstone and fig leaves to avoid desiccation. A few species even live in the sand beneath spinifex hummocks. Locating the little buggers is one thing. Getting them out is another.

So I reckoned that the best way of collecting was to make them come to you. What brings them to the surface? Why, rain, of course. And how do you make it rain in a desert? Easy. You call in a firefighting helicopter to drop a bucket of water onto a suitable site and then you wait for a couple of hours and then gather the harvest.

As you can imagine, this plan never came to fruition because … well … the effects of the beer wore off and I calculated the damage that a tonne of water would do to a small and fragile area of sandstone and spinifex. It wasn’t a terrible idea but it wasn’t exactly a good one either. Still, you can’t have everything.

And now the Northern Territory’s Department of Natural Resources, Environment and the Yartz (NRETA) are combining gastropods and helicopters (but not water) in a study of endangered snails in the Top End. The work is concentrating on the Victoria River District (VRD).

Four of the Territory’s six most endangered land snails occur in the VRD, which sprawls across the NT – WA border from Katherine to the Kimberley. These species — Mesodontrachia fitzroyana, M. desmonda, Ordtrachia australis and O. septentrionalis — occupy restricted ranges. Very restricted ranges. Not that there's anything unusual about that with Australian camaenids*. Most of the central Australian species have such narrow distributions that the entire population could fit on the head of a pin without interfering with the angelic barn dance. But many of those centralian species are also safe and snug in protected areas. In the VRD, there's a problem when restricted ranges encounter threatening processes ...

Three species are associated with limestone. (M. desmonda is the odd one out, preferring to hang around near sandstone outcrops.) Because limestone is not at all abundant in tropical Australia, suitable habitat is patchy at best. So here we have endemics that are limited to certain parts of their restricted ranges. Add to that the pressures of grazing in the VRD, with associated soil compaction and changes in vegetation, and periodic burning and it's not looking good for the snails.

Anecdotal evidence suggests that the VRD species are declining. Presumably NRETA's study will look at whether that is the case or is an artefact of collecting patterns or is a little from column A and a little from column B. Whatever the conclusion about populations, the program will likely pile up the data on species that are poorly known from areas that are underexplored. And that's a Good Thing.

I quite like the idea of buzzing around the Top End in a helicopter but I'm not so envious of the hard work involved in snailing in the Dry. Maybe they should consider my water-bombing plan ...

... if they don't mind flat snails.


* Did I mention these interesting snails all belong to Camaenidae? No? How very unlike me.


Denis Wilson said...

It seems like a research project right up your alley.
Can they not be persuaded to take a hitch-hiker along? Or are you actually involved? Hope so.

Snail said...

I'm not involved, Denis, but I'm definitely going to stick my nose in. Sounds like a lot of fun!


Do these deserts get dew at night? If yes, that may bring the snails out towards the morning for a few hours.

Snail said...

That's a good question, Aydin. I'm not sure. I'll see what I can find.

Snail said...

Just had a quick look at the Met Bureau's site for the NT and today's dew point for Alice Springs is -1.9C, so I don't think there'll be any snails out tonight! Will keep looking.