The great Northern Ruahines snail hunt

Department of Conservation —  21/06/2018 — 4 Comments

Anthony Behrens shares his experience hunting down and photographing Powelliphanta marchanti snails in the Northern Ruahines…

Powelliphanta snail comes out of its shell. Photo: Anthony Behrens.

Powelliphanta snail comes out of its shell

I already had concerns about this job – how DOES one photograph a snail hunt? And then the email arrived:

“Currently the long-range forecast shows rain Tuesday and cold with snow Wednesday and temperatures down to -2C. This is not ideal…

Please ensure you have plenty of warm clothes for this work. Snail monitoring at 1300m altitude in May is cold work!

There is not much physical activity on a 10m x 10m plot so hence the need for clothing!!

Cheers,
Nobby”

It appeared that one photographs a snail hunt in the Northern Ruahines in May with a great deal of discomfort.

The mission

A week later, four DOC staff and I were flown into Ruahine Corner Hut. The goal was to locate ten GPS’d plots situated in nearby forest and the flat tussock lands, then count the Powelliphanta marchanti snails – alive and dead – within.

Powelliphanta snail hunters Ruahine Corner Hut. Photo: Anthony Behrens.

Powelliphanta snail hunters Ruahine Corner Hut

The greater northern Ruahine Ranges had been treated with a Battle for Our Birds 1080 drop six months earlier and the survey was assessing how well the operation had achieved the desired outcomes.

As we sat in the hut before going out to the first plot, Nobby, the only one of the five of us who’d hunted gastropods before, explained search methods and the forensic process. He referred to a folder, thick with results from previous expeditions on the same plots, and autopsy drawings – yes drawings – of empty and unpalatable shells.

Planning the hunt. Photo: Anthony Behrens.

Planning the hunt

An empty snail shell, like the body at a murder scene, gives up a few clues that will identify the killer.

• Possums hold and tear into the snail shells to get at the contents. Being uncivilised brutes, possums leave a gaping hole and untidy mess.

• Rats are smaller and their destruction is less boorish, but no less fatal. Little fingers and large, sharp buck-teeth leave pretty obvious clues.

• Thrushes are pretty untidy killers but this isn’t because they’re impolite… it’s just that they don’t have hands. The bird’s beak, nearby stones or roots are used to smash the shell, often exposing its spiral insides.

• Wild pigs crush the shell in their mouths, extract the meat, and spit out a flattened and shattered disc of semi-connected fragments. There’s not much protein at 1300 metres above sea level, so fleshy snails must be quite sort-after by these large animals.

Native birds would have once dined on the juicy little critters, but not so much now that they’re on the invaders’ menu too.

Finding the plots. Photo: Anthony Behrens.

Finding the plots

The hunt

A GPS guided us to the first plot, where the team set about finding the small and overgrown pegs that marked its boundaries. Nobby spelt out a few more hints on technique (no gloves!) then he, Sue, Morgan and Heemi, set out on their hands and knees across the first of four 5m x 5m quadrats to find their elusive prey.

I watched on in awe.

Marking a plot. Photo: Anthony Behrens.

Marking a plot

Powelliphanta like the chilly gloom of the forest floor, so probing hands were soon bright pink with the cold, yet it was surprising to see how sensitive the hunters’ numb fingers could be.

Nether-regions of Crown Ferns were prodded gently. Holes were delicately poked. Tree roots were lightly caressed. Over the few hours that I followed the search, two clutches of about a dozen jellyish slug eggs were found hidden deep in dank, moss-covered crevices.

Nobby directs operations at a snail plot. Photo: Anthony Behrens.

Nobby directs operations at a snail plot

None of the eggs got broken, although the ranger that located the giant green slug (the producer of the brood?), did let out an audible squeal of revulsion when he or she fingered the monster. I was passed the offending alien for a photograph and am embarrassed to report that a shiver of revulsion swept through me too.

I’ll man up next time.

Hands and knees plot searching. Photo: Anthony Behrens.

Hands and knees plot searching

As hours passed, and fingers got colder, snails large and small, shattered and whole, were handed over to Nobby for measuring and sorting. Live snails were placed safely behind the search party where they were originally found, while the remains of crushed snails were bagged for later analysis.

Measuring Powelliphanta snail. Photo: Anthony Behrens.

Measuring Powelliphanta snail

I said snails were placed safely behind the search party – this may imply that the environment remains intact after each search. No. While nothing was uprooted, a 70-90kg DOC ranger on his/her hands and knees isn’t a delicate thing on a forest floor. A certain amount of non-snail flattening is unavoidable.

Perhaps a trained snail dog – a chihuahua/german pointer cross – would be good.

Map and plot marker. Photo: Anthony Behrens.

Map and plot marker

What was found?

Since the recent drop there had been good signs that the 1080 had done its job in the area.

High numbers of juvenile whio in the nearby Mangatera River was evidence that stoats had been hit for a six. In normal years, unprotected whio pairs lose 90% of their fledglings, yet the 2018 autumn count, that was also part of Battle for Our Birds monitoring, found 12 young birds on a 10km stretch of the river. A very healthy total.

Rodent tracking tunnels had been put out before and after the 1080 drop and activity had gone from slightly more than 10% pre-drop on the rat index to 0% post-drop.

As a result, we hoped for a big haul of Powelliphanta marchanti over the five day search. Competition to find The Trophy Snail was fierce. (The largest found was a 56.2 mm shell)

Powelliphanta marchanti snail. Photo: Anthony Behrens.

Powelliphanta marchanti snail

A surprise finding

At the conclusion of the first plot count, there was no sign of rat or stoat predation, yet it was clear pigs had developed a taste for Powelliphanta. Pigs aren’t much of a problem in the southern Ruahine Ranges, but they seem to be making their presence felt at the north western end

Pig damage in search plot. Photo: Anthony Behrens.

Pig damage in search plot

As the week went on, pig predation proved to be a problem in many of the other plots too. Evidence of rat and stoats within the area that received pest control was nil – so the 1080 operation had worked as it was meant to, and the area’s birds will be safer from rats and possum for a while.

But this year’s increase in pig numbers has presented a new problem to solve.

Finding a Powelliphanta marchanti snail. Photo: Anthony Behrens.

Finding a Powelliphanta marchanti snail

Pigs developing a taste for snails isn’t good for a species that’s almost unique to the area. To make matters worse increasing numbers of rooting pigs will also be competing for the snail’s favourite diet of worms.

The Northern Ruahine kiwi population might not be too pleased about the pigs either.

Wild pigs are known to dig out and kill kiwi in their burrows and to destroy kiwi eggs. Untrained and uncontrolled hunter’s dogs can also be lethal to kiwi.

What about that snow?

The Ruahine Ranges are known for their unpredictable weather. Forecasting a hunting, tramping or monitoring trip in the area can be a bit like reading tea leaves in a dishwasher. It was cold worming around the forest floor at 1300 metres, but the snow never came and blue sky made the occasional appearance. In the end I even got some great photos.

Ruahine Corner, with its plateau of tussock and great swathes of pāhautea (mountain cedar) is a beautiful and quite unique area.

I’d recommend it as a place to crawl about almost any day.

Returning to Ruahine Corner Hut. Photo: Anthony Behrens.

Returning to Ruahine Corner Hut

Powelliphanta marchanti video

© Anthony Behrens

4 responses to The great Northern Ruahines snail hunt

  1. 
    Cherie Pagan 11/07/2018 at 8:36 am

    Really enjoyed this article and film. Learnt a lot. Thanks

  2. 

    Pigs have been rooting up Kauri snails and spreading Kauri Dieback for years, more control please

  3. 
    John Geboers 06/07/2018 at 11:14 am

    Smart work team , employ some pig hunters .Little by little wins the war.

  4. 
    Phil Battley 21/06/2018 at 12:10 pm

    This is science reporting at its best!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s