GCN Bottle Traps
Floating Bottle Traps
Barry Wright of Dryad Ecology has had many issues about setting bottle traps around pond margins by wading in, potentially getting stuck and disturbing the mud. This means that, if you set the traps shortly before dusk you are then doing your torch survey before the sediment settles and will adversely affect the penetration of your torch and hence the accuracy of your data. Also, there is a risk of entering a pond margin that you could tread on a newt. The Dryad Ecology solution is to use a floating bottle trap tethered to the shore (see the photo below). This also means they can be 'launched' beyond any fringe of vegetation and into water that is potentially too deep for wellies or even waders.
Also, the normal method of rigidly attaching bottle traps to canes runs the risk of overnight rain causing the water level to rise, put the trap under water and remove the air bubble that keeps the newts alive until released, especially if a hole is left at the back of the bottle to allow air into the trap. But even without an air hole and relying on a captive air bubble inside the bottle, the bottle can turn as the water level rises and the air may escape.
The Dryad design has an air hole at the highest point at the back of the bottle. The three floatation tanks have been tested and they will keep the air hole above water with 100gms of 'newts' inside them, equivalent to 10 mature adult GCNs.
The advantages of the Dryad Ecology approach are:
No sediment disturbance,
No crushed or drowned newts and
Traps can be put beyond fringing vegetation.
Traps can be set in concrete-lined ponds and butyl pond lined ponds are not punctured.
The other Dryad Ecology innovation used for bottle trap survey is the use of meat-baited traps that maximise the possibilities of detecting newts reliably in low population ponds.
Having read papers about using baited traps to increase the possibility of detecting and recording more accurate numbers of GCNs in ponds Dryad Ecology tried a an experiment at a site we surveyed. We set 18 traps using three treatments:
No bait (control)
Dried beef (re-hydrated in the water)
These were alternated around the pond. Out of the six traps from each treatment the controls had two GCNs, the ones with worms had three and the beef had 11. This included one trap with five large females in a beef baited trap. Previously, using un-baited traps at this pond recorded generally low numbers and with no consistency or pattern of which traps were successful. This contrasted with the larger numbers regularly seen during torch searches on the previous evening.
The experiment has confirmed that baiting increases the numbers detected and improves the accuracy of the data collected to provide to Natural England as a population estimate. This also increases the confidence that a negative result is a true negative and not just a consequence of newts not finding an un-baited trap.