Between 2011 and 2014 a trial was conducted as part of the Poutiri Ao ō Tāne project, a restoration project located at the Maungaharuru-Tutira catchment, 60 km north of Napier.
This trial sought to compare the efficacy of run-through tunnel traps and standard single-entry trap boxes for ship rats, stoats and ferrets.
The Poutiri Ao ō Tāne trapping trial ran from December 2011 to March 2014.
600 traps were placed at 100 m spacings, in lines approximately 1 km apart over a total area of approximately 6,000 ha of mixed pasture and forest fragments.
All boxes contained a single DOC250 stainless steel kill trap, designed to catch stoats, rats, hedgehogs and ferrets.
Specially constructed run-through tunnel traps with an entry hole at each end of the box, and standard single-entry trap boxes with an entry hole at one end and mesh covering the other were placed along trap lines in groups of four, with each ‘group’ containing two of each architecture type, randomly placed to minimise experimental bias.
The trial was designed to control stoats and ferrets, but not ship rats. The traps were not placed at high enough density to significantly impact on rat populations, but the catch data can still be used to assess the relative effectiveness of the two trap types.
Various lures were tested during the trial period, in a way that did not impact on the comparative assessment of the two architecture types.
Poutiri Ao ō Tāne 2011-14 captures by species and trap type
Of 401 rats caught during the trial, 242 (60%) were caught in the tunnel architecture compared with 159 (40%) in the standard boxes; in other words, the tunnel traps caught approximately 50% more ship rats than the single-entry boxes.
The sample size was large enough to conclude that run-through tunnel boxes are significantly better than standard single-entry boxes (Fisher exact test over total of 17000 checks, p < 0.0001) for catching ship rats.
Unfortunately, the difference between the number of stoats and ferrets caught were insufficient to be statistically significant.
Based on the results of this work, ZIP decided to deploy a tunnel architecture trap for rats and stoats as part of the ‘virtual barrier’ at Bottle Rock Peninsula. The ‘TUN200’ trap boxes used at Bottle Rock contain a further enhancement: double-set DOC200s to maximise capture compared with single-set traps. We estimate that this enhancement has led to an additional increase in efficiency of approximately 20%.
ZIP is currently developing a productionised version of the TUN200, to be known as the 'ZIP200'.
The DOC200 trap is the larger and more forceful of two DOC-developed traps for the control of rats, stoats and hedgehogs (the smaller of the two being the DOC150).
ZIP uses the ‘excessive force’ of the DOC200 in our virtual barrier, to remove rats and stoats, because the success of the Remove and Protect approach relies on us catching every last individual. A partial strike or escape could result in a wary animal that is unlikely to enter another trap.