Monday, 21 April 2014

Mass Extinction of Gateshead Dragonflies !

I've just uncovered some interesting though quite disturbing news regarding Gateshead's Dragonflies.
I came across a report from a field study made by legendary entomologist Harry Eales, who (among other things) carries out surveys on behalf of Northumbria Water into the state of insect life (Particularly butterflies and dragonflies) at their Sewage Treatment Works throughout the northeast.

In 2011 he surveyed the Lamesley Reedbeds (part of Birtley STW) for the third time to chart progress after similar surveys in 2006 and 2008.
This is one site I have never visited in the summer for dragonflies as viewing the area is poor due to height of the reeds and there is no easy access (without permission) to the lagoons.

So it was interesting to read that monthly visits in 2006 and 2008 (April-October) gave the following list of species present :

Large Red damsel
Common Blue damsel
Blue-tailed damsel 
Emerald damsel
Azure damsel
Common Darter
Ruddy Darter  (These were all confirmed as breeding species and present in large numbers, increasing on the latter survey)

Southern Hawker
Migrant Hawker
Emperor Dragonfly (recorded in small numbers as non-breeding visitors)

Red-Veined darter
Yellow-Winged darter (rare migrants recorded during the influx of 2006 which is interesting as 'til now I'd only known about those recorded at Kibblesworth)

So things were looking good for the dragonfly population at this relatively new site, until the next survey year of  2011.
This time around, 2 visits per month were made during May to September and the following species were recorded:








No, I haven't forgotten to put in the list, there were actually no Odonata recorded at the site during the whole of 2011, as some kind of mass extinction event had wiped them out. :-O

How could it happen on such a vast site? Well the culprit, according to Harry's findings, is the Big Freeze winter of 2010/11, when three months of freezing temperatures killed off all aquatic larvae (not just dragonflies) here, as (due to the nature of the site) the water is little more than a foot deep throughout, which during a normal winter is fine for survival, but the prolonged winter of 2010/11 was more akin to a mini Ice-Age, and unfortunately the whole of dragonfly-kind was wiped out by the freezing cold.

Amazing but true, and goes to show the delicate balance of nature. Numbers will recover eventually, as dragonflies are great colonisers but no doubt many other sites throughout the country will have suffered similar extinctions.

In fact it just so happens that a site I visited just yesterday with the Birdman at Derwent Reservoir Nature Reserve suffered a similar fate.
Surveys in 2004 and 2007 had found Large Red, Common Blue and Emerald damsels, and Common and Black Darter to be breeding here in good numbers, but these ponds were mostly very shallow and were getting choked with vegetation, and once again it was found that the Big Freeze of 2010/11 wiped out all breeding species.
In 2011 the ponds were excavated again to deeper levels so hopefully they will soon once again hold good populations of those dragons found before, as it is not far from Hunter House Pond on the south shore, which holds good numbers of all the species seen in previous surveys and is apparently the only pond deep enough around the reservoir to avoid freezing during the harsh winter.

Ice Age on a small scale, if it ever occurred to you what effect it might have on dragonfly populations, well now you know :-(




 



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