Monday, 15 April 2013

Sunday, 21 December 2008

Zander a real life experience.

Dr Ronald Campbell, Biologist, the Tweed Foundation

The portrayal below gives a graphic account of a project undertaken by Dr Campbell in which the dangers of inappropriate introduction are vividly described in a reply to the club about suspected Zander in the loch.

Almost the first thing I did in this job, when I started in 1990, was to follow up a report of Zander in St. Mary’s. As it happened, my previous job was in the Fisheries College of the University of the Mediterranean, in Turkey, working on a collapsed Zander fishery. I was therefore able to create picture posters of Zander asking if people had seen them and pass them around. There was no response.
It’s interesting that these rumours persist. The best explanation is, of course, just mis-identification, though someone might have put a few in (or some Ruffe?) that then died out – ( a lucky escape for us all). I would have thought that Zander would have become obvious by now if they had established. Zander introductions have been controlled for some time now, under the Wildlife and Countryside Act, where they are actually listed as a “dangerous animals”, as you rightly point out.

The loch I worked on in Turkey, Egirdir Golu, had Zander introduced to it in 1955, to “make use” of the indigenous fish species, 11 in number, some of which only existed in that loch. To begin with, it went very well and there were no less than 4 local fish factories producing frozen fillets for export to Central Europe - Zander is a superb eating fish. However, by the time I got there in 1988, the fishery had collapsed as there were just not enough fish of around 1kg being caught. Masses of small Zander, and the occasional very large ones were. What I found on investigation was that the Zander had run out of “forage fish” to feed on and the population had become almost entirely cannibalistic, feeding on their own young. As the water got up to 25 C in summer and there were masses of shrimp, the young-of-the-year Zander could grow to 24cms by the end of their first year, becoming too big for Zander less than 50cms to eat. Although Zander are naturally purely piscivorous from around 10cms in length, the Zander in Egirdir Golu were still having to turn to shrimp for at least part of the year until they got over 50cms in length. Even so, that meant them eating young Zander of half their length or just over – some would be netted with the tails of young Zander sticking out of their mouths, while the head in the stomach was more or less fully digested.
Two of the local species had survived, Common Carp and a fish called Vimba vimba (like a Whitefish to look at) – but I never found them in the Zander, nor any of the introduced Mosquito Fish (Gambusia). Why this should have been, I could not work out, except that Zander don’t feed in weedy areas, where Mosquito Fish live. It shows, however, just how devastating Zander can be. I did suspect that the lack of weed in Egirdir Golu might have made the native fish species unusually susceptible to Zander as it deprived them of refuges. The lack of weed was, I reckoned, due to the unusual chemical composition of the water, Magnesium was commoner than Calcium, and “flocculated” into small particles which were stirred up by the wind (which could blow for days, from the cold Anatolian Plateau down to the warm Mediterranean and the max depth was only 16m) and turned all the 500 km2 bright lime-green, an extraordinary sight. The shading of these particles would have minimized weed growth.

There you have it from the horse’s mouth so to speak, please destroy
any fish you suspect are Zander and give them to the loch keeper.

From the Archives

Taken from a committee meeting 04/1969 – It was noted that a busload of anglers were noted spinning all around the loch, it later turned out none of the anglers had permits. It was also agreed to increase the cost of bait/spinning day tickets to 12/6 which is approximately 62.5p.

Unfortunately the problem of illegal anglers is still with us but steps have now been taken to minimise this.

Merry Christmas to all our readers!

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