Probably at least once a week I wander down to the park after the hours of darkness and take a torch with me to shine into the lake and the various pools. I almost invariably see lots of small roach, and occasionally, the large (up to 30lb or so) common carp that inhabit the lake. I also occasionally see eels. I did see some tench last summer, but nothing since. I haven't seen a pike for ages, nor have I ever seen the one example of the wels (European catfish) which anglers tell me is in the lake and probably weighs in excess of 50lb now.
Eels, or so we were told in our primary school days, use the gulf stream to travel between their breeding grounds in the Sargasso sea and Europe/Africa/wherever they happen to turn up. However, reading a little around the subject, it seems that no-one has ever witnessed eels breeding in the Sargasso sea, or anywhere else for that matter.
It has crossed my mind for quite a while that it's a very odd trait for a species: why restrict yourself to one specific area of the world to breed? Other migratory species - most of which fly quite fast, which the eel manifestly doesn't - breed at either end of their migratory journey, and that makes a lot of sense. Why would an eel, or even two eels - not take advantage of any odd nook or cranny for a bit of hanky-panky as long as all other conditions remained satisfactory?
I had a hunt around the internet for anything that anyone might have written about eels, and there are indeed a few academic papers. Most of these, sadly, are behind paywalls and my interest, at this stage, doesn't extend to paying good money for something obscure which may well not answer my question. It seems that the panmixia hypothesis is documented in a 1925 paper from one J. Schmidt, and a 1977 book "The Eel" by F. W. Tesch.
However, the paper that interested me, and seems to undermine the panmixia hypothesis, is from 2001 by Thierry Wirth and Louis Bernatchez. Their research suggests that, from the different testing locations that they used, that if there were a single breeding population, there would be no genetic differences between eels caught anywhere east of the Atlantic. However:
Analysis of seven microsatellite loci among 13 samples from the north Atlantic, the Baltic Sea and the Mediterranean Sea basins reveals that there is global genetic differentiation. Moreover, pairwise Cavalli-Sforza and Edwards' chord distances correlate significantly with coastal geographical distance. This pattern of genetic structure implies non-random mating and restricted gene flow among eels from different sampled locations, which therefore refute the hypothesis of panmixia. Consequently, the reproductive biology of European eel must be reconsidered.
Which is jolly interesting.
Does anyone else ever meet any eels on their perambulations?
PS Tesch's book can be had from Amazon, a snip at £207 for a new one.
