RAUK - Archived Forum - Please help - GCN

Caleb,

Thank-you for the reply.

I have, so far, contacted great number of organisations, but with limited success. I have obtained some specific data - GCN's in ditches 2 m wide, ponds no more than 50 cm deep (population of approximately 300) and one pond that had GCN's prior to the stocking of carp by an angling club. The latter was some time ago, but it shows that even so called benign species, stocked in sufficient numbers, can have a disastrous effect

Tom 

Tom,

I know that odonates can be wiped out by carp due them uprooting aquatic plants encouraging blooms of planktonic algae, which eventually lower oxygen content making the pond unviable. Could it be a similar process affecting GCN?

Gemma,

I suppose itÆs a possibility, it all depends on the level of stocking thatÆs undertaken. I know that surface area is a key factor in determining a sustainable population. Perhaps consideration should be given to the effects of biological oxygen demand (BOD) due to the eventual dacay of algae blooms brought on by disturbing silt deposits.

I really donÆt know if carp actively prey on newt larvae or if itÆs because there is an insufficient alternative for them to feed on. 

Carp are opportunistic feeders but definitely omnivorous.  They feed avidly on snails, slugs and worms in addition to vegetation while anglers create high protein mixes to tempt them.  However they hunt mainly by smell, or whatever you wish to call the sense using their tendrils.  I would imagine that an inactive newt would be happily consumed, but one that chose to swim away would get away.  Evolution therefore dictates that the carp would become predators of sickly and dying newts rather than active ones, but a high stocking level of carp could easily change this feeding behaviour to hunting by sight and chasing, which would eradicate the newts in short order. 

A succesful fishing fly has been developed to catch rainbow trout based on the GCN!

Tom,

The process of deoxygenation is also promoted by shading of oxygenating plants by the algea. I wonder how much of an affect this would have on the GCN larvae as opposed to direct predation of adults by carp. I suppose, as ever it's a mixture of factors specific to each pond.

I think it's quite interesting to see just how GCNs can survive and breed in very poor conditions. I have surveyed a number of ponds this year that have been way off the mark of the the 'text-book' GCN pond even with bits of engine and asbestos in them. Some eutrophic and some with good fish populations esp. Stickleback.

GCNs appear to be quite hardy little critters and it would seem that they can cope with quite 'harsh' and varied conditions especially in the metapopulation scenario.

I read a paper recently on the ability of Carp to increase the villi on the lung walls in order to make better use when obtaining oxygen from poor water quality  (environmental pressure response). Does anyone know if this happens with other water-based animals, particularly amphibians.

Brett.

Caleb,

It depends on how you define 'breeding success'. There were adult male and female animals, eggs, then larvae. But to estimate breeding success would be difficult from the single season survey. They were obviously reproducing.

One pond in particular was within proximity (50m or so) of a pristine pond that was every bit a breeding pond. It was this pond that had asbestos, rusty metal etc... with reproducing animals that was drawn to my attention.

Another one recently surveyed was of similar poor quality and had been deemed, from desk-top surveyors, to be unlikely to contain GCN's however first visit and a quick netting revealed the presence of GCN larvae. Now this pond again was linked by a network of waterways, but had recently been separated due to its ephemeral qualities.

I have also seen reproductive success in ponds containing fish such as stickleback. I am therefore often wary to committing myself to say that it is likely or unlikely to contain GCNs when fish are present. It really depends on the rest of the habitat suitability and waterbody connectivity.

It just goes to show you need to be out in the field to see these thingsà nature never really follows the text book..! :o)

Brett.