… my on-going survey .
The story so far.
This farm’s irrigation lake, a lake of about 2 hectares, used to swarm with libellules (dragonflies and damselflies). I have recorded 18 species here, though a couple were admittedly most likely fly-throughs It was, though,a very thriving population with many breeding species and some in very large numbers. Swarms of various types of blue-striped damselflies (Coenagrionidae) used to be able to be seen ovipositing on the lake’s floating vegetation. Dragonflies rarely swarm but there were certainly large numbers of Red-veined Darters (Sympetrum fonscolombii) and Broad Scarlets/Scarlet Darters (Crocothemis eryhtaea) present. Also well represented were the ubiquitous Black-tailed Skimmers (Orthetrum cancellatum) and the slightly less ubiquitous White-tailed Skimmers (Orthetrum albistylum).
A few years ago, enter the Grass Carps and the ornamental-but-otherwise-useless Koi Carp intensively reared by a fish farmer with his own agenda and who, we suspect, “advised” farmer Luc about the lake’s ecology. The ecology certainly changed. The erstwhile abundant bird life disappeared completely as did the vegetation [Grass Carp – there’s a clue in the name]. The Libellule population also crashed. Several species disappeared altogether and those that remained appeared to be hanging on by their wing tips; no more swarms, just species represented by a few individuals, their populations now counted in single digits.
Last year we saw no evidence of the ornamental-but-otherwise-useless Koi Carp, though there were still many schools of fish of varying sizes to be seen cruising about. Also visible were a few huge leviathans which may well be the vegetation-eating Grass Carp. Farmer Luc visited us in England last year and he seemed to realize that the ecology of his lake had been changed for the worse. I think he wants to redress the balance.
What of this year?
This year, we see (again) no evidence of any ornamental-but-otherwise-useless Koi Carp, just the floating feeding device lashed in a quiet corner of the lake unused. There are still very many fish of varying sizes, though perhaps less than last year, which would be a move in the right direction. We’ve been told by Marcel, farmer senior, that a Cormorant took up residence for quite a while and was doing its best to reduce the fish population. Now, however, other than an occasional visit by a passing Mallard, there is no sign of any birdlife on the lake. Neither, still, can I see any evidence of floating vegetation, the vegetation that is so necessary for damselfly oviposition. The story remains much the same as last year but with possibly less fish.
Thus far I have again logged 10 species of Odonata but all in very low numbers. The one species that does seem to be doing quite well is the Western Clubtail (Gomphus pulchellus), which we’ve seen probably approaching double digits. Of one of the previously most numerous dragonfly species, the Red-veined Darter (Sympetrum fonscolombii), a normally very successful species with a reproduction cycle of less than a year, I have seen so far just one example. The Broad Scarlet/Scarlet Darter (Crocothemis erythraea), also previously very numerous, looks as if it has disappeared altogether. I noticed this last year but wondered if we were ahead of the flight season. This year I know that’s not the case because other lakes nearby are supporting good numbers of them already.
I’m happier to note that the delightful Tree Frogs, missing last year, have this year returned to the trees and hedgerows lining the campsite pitches. Their demise could well have been down to a severe winter with considerable snow fall a couple of years ago. Also, though we have still seen no sign of any tadpoles, we have have had an allmost nightly chorus of water frogs croaking in the lake and come eye to eye with a small froglet in the grass just beyond Guillaume. So, I imagine the water frogs are managing to breed and that some spawn is surviving the appetites of the still large fish population.
The lake, though, remains a somewhat sad sight, given the rich diversity of life that used to thrive here. At least no further damage is being done but, alas, significant damage has already been done. What is needed is some vegetation, not only for the Odonata but also for water birds – dabbling ducks need something to dabble for, after all. I’m wondering if what is needed is a good handful of predatory fish. Some Perch would make short work of the shoals of smaller fish and maybe a Pike or two would deal with the larger buggers. Then perhaps we’d get some vegetation back in the lake.
Dream on, Franco. I imagine nature will eventually strike a more natural balance once again; I’m just impatient. 😉