Tracking shows lift in rare snail numbers
If you want to see one of New Zealand’s rare Powelliphanta snails, your best chance is near Harwoods Hole in the Canaan Downs.
Radio tracking of the rare Powelliphanta hochstetteri in the Abel Tasman National Park revealed the population is even larger than previously estimated.
In a first, the carnivorous snails have been tracked at night. Snail researcher Dr Brian Lloyd radiotracked 10of the P. hochstetteri, day and night, for 41 days.
Lloyd and Dr Ruth Bollongino attached tiny radio transmitters to the snails near Canaan Downs, in the upper reaches of the Abel Tasman, to investigate their behaviour and activity.
Lloyd said it was uncommon for the snails to move during the daytime, but it was not known how far they travelled overnight.
‘‘By tracking them at night I was able to show they didn’t move long distances, they basically just went from one resting daytime spot to another.’’
On average, the snails travelled 1.3 metres a night, although one travelled almost three times that distance in a single night, covering 3.8 metres.
‘‘I was expecting the snails would travel in random directions, but they actually tend to move in a straight line with a slight leftward bias.
None went back to the same spot, which indicates they are not territorial and don’t seem to have a home base,’’ Lloyd said.
He said they typically moved when it was wet, and the tempera- ture was above 8 degrees Celsius.
Snails were usually only active for one or two nights during warm, moist conditions and then remained inactive for longer periods.
The survey used the mark and recapture method - tagging the snails found in a 70 square metre plot over five consecutive nights.
Lloyd said that information enabled them to calculate there were about 550 snails per hectare in the area near Canaan Downs and would help improve the accuracy of future population estimates.
As part of the survey, 200 snails were tagged, including the critically endangered Rhytida oconnori. Monitoring would be repeated to survey population changes over time.
The R. oconnori snail is found at only two sites in New Zealand, in the Abel Tasman and at Parapara Peak in Golden Bay.
The survey was undertaken as part of Project Janszoon’s work to restore the ecology of the Abel Tasman National Park.