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Lumpo31
275737.  Tue Feb 12, 2008 12:58 am Reply with quote

I had heard of it, but hadn't heard any details. I had a vague idea that they all start off in the Sargasso Sea or thereabouts, but nobody knows how they get from there to say, the UK.

Lisa

 
dr.bob
275753.  Tue Feb 12, 2008 4:13 am Reply with quote

I'm a bit confused by this idea of landlocked eels. Given that nearly all waterways eventually join up with the sea, how do eels become landlocked?

 
Spinoza
275788.  Tue Feb 12, 2008 5:35 am Reply with quote

Fishing is the nation's most popular pastime (more people go fishing every week than go to football matches). I imagine that anglers and naturalists will on the whole be familiar with the eel's reputation, but during my hunt for the truth yesterdayI was struck by the observation that although the story is widely repeated in academic books by "respectable" authors, it appears much more rarely in books written by and for anglers.

 
Spinoza
275789.  Tue Feb 12, 2008 5:36 am Reply with quote

Since I don't have much to do at the moment, I'm off today to make some further investigations.

 
Spinoza
275794.  Tue Feb 12, 2008 5:42 am Reply with quote

dr.bob wrote:
I'm a bit confused by this idea of landlocked eels. Given that nearly all waterways eventually join up with the sea, how do eels become landlocked?


You might as well ask how fish end up in ponds. Stories range from becoming stranded after floods, geomorphological accidents, eggs being carried on birds' feet, fish being transported by humans to enhance food and fishing opportunities, and so on.

 
Spinoza
276082.  Tue Feb 12, 2008 10:55 am Reply with quote

Wot,am I the only one who's interested in this problem? Oh,well. After another half a day's investigation into the matter, I'm now coming round to Anguilla's point of view that reliable evidence on tghe matter of eels moving over land is difficult to find, and probably non-existent. I concentrated today on looking through the memoirs of river-keepers and the like, and found one lengthy discussion which is definitely sceptical. I also found several more reference books which repeat the myth without any supporting evidence, and a couple of countrymen's accounts which are definitely unreliable.

My only hope now is to find some account of some ancient eel-festival centred around feasting on terrestrial eels, but don't hold your breath. Anyway this might do little more than to shed some light on the origins, rather than the truth, of the tale. May I suggest a round of applause for Anguilla, for doing what this forum is supposed to do? I now have to figure out how far I may have been responsible over the years for perpetuating General Ignorance!

 
Jenny
276496.  Tue Feb 12, 2008 9:54 pm Reply with quote

Cheers for all who tear down the barriers of General Ignorance!

 
dr.bob
276781.  Wed Feb 13, 2008 11:19 am Reply with quote

You might be interested in a new BBC series called World on the Move. From the press release:

Quote:
Special tagging devices will enable the tracking of individual creatures throughout their migrations.

Animals to be tracked during the series include an osprey travelling from west Africa to Scotland; leatherback turtles; Alaskan bar-tailed godwits flying 8,000 miles non-stop; black-browed albatrosses; and eels swimming from British rivers to the Sargasso Sea.

 
Spinoza
276789.  Wed Feb 13, 2008 11:31 am Reply with quote

Interesting......there seems to be some doubt about whether they actually ever get there, or whether European eels are in fact the offspring of the American species Anguilla rostrata.

 
Anguilla
276874.  Wed Feb 13, 2008 1:16 pm Reply with quote

It is often stated that stagnant watercourses become seeded with fish eggs carried on the feet of water birds. I have no idea how frequently this might occur; rarely, I suspect, but we do know that eel eggs cannot possibly be transported this way because eels do not breed in freshwater. We know too that eels can be found regularly but decreasingly so, in ponds and lakes many miles from the nearest river, so how then did they get there?

This part of the mystery is rather simple to explain and Spinoza touched on it earlier. Think back to the floods of 2007 that occurred in the south west and north of the country. Miles and miles of countryside were flooded for weeks when the rivers burst their banks. During such times, floodwater joins forces with the many lakes and ponds, reservoirs and gravel pits etc to become one massive sheet of water. Fish from the rivers, move over the flooded land. Once the water levels return to normal, some fish species of all types including eels find themselves stranded; not on dry land but in a pond or lake. Some species will survive and flourish; others will not adapt and so perish. (Barbel (Barbus barbus) are thought to breed only in running water). The reverse process is thought to be how species like goldfish and koi carp entered our waterways from garden ponds which became flooded, though it is apparent that anglers too carry out illegal and legal stocking of alien species.

Invertebrates too are known to have escaped into our rivers from holding ponds that have been flooded. In the case of the recently introduced American Red Signal Crayfish, the result has been devastating. This pest carries a fungus which our indigenous White Clawed Crayfish has no natural resistance to. Red Signals are also bigger and pugnacious and tend to bully our crays. As a result, the White Clawed Crayfish population has plummeted and they are now threatened throughout much of their range. It is true to say that anglers and commercial crayfish fishermen have illegally stocked both rivers and stagnant waters with Red Signals. Due to whatever means alien crays are now present throughout many of the waterways of England in plague proportions.

You may not remember many times of flood if you havenít been affected by them, but they do occur most years at some place somewhere throughout much of the low lying country.
Since the last war too, many of our smaller rivers have been diverted to prevent towns and villages flooding or they have dried up due to water abstraction. Many acres of land has been drained and re-claimed for construction or agricultural purposes, and of course anti-flooding schemes such as the Thames Barrier are an effective measure against flooding and as a result, also a measure against natural fish distribution. These defunct waterways may have been the highways on which the resident eel population swam to reach many lakes and ponds. Some rivers have been filled in and built over and Londonís River Fleet is a good example. The rivers may be gone but some lakes survive perhaps even with an aging eel population. Eels can live for a very long time. The longest recorded captive eel lived for 84 years and they may even reach greater ages so it may not be surprising that we could be identifying eels that entered a lake via a river that no longer exists.

There are a number of other perhaps less likely but certainly feasible routes by which baby eels (elvers or glass eels) could reach stagnant water and this, despite what I have written about adult eels, may well include terrestrial travel. But that is not the debate here. Here we are more interested in whether or not adult eels from stagnant watercourses travel overland on their journey back to the Sargasso.

 
Spinoza
276912.  Wed Feb 13, 2008 3:07 pm Reply with quote

I'm with Anguilla on this one, evidence for elvers travelling over (wet) land is much more reliable than for adults migrating in the opposite direction. I also have an interesting snippet concerning diseases of crayfish.

Some years ago, a former student of mine who now works for the Environment Agency told me that a major contribution to the spread of crayfish diseases was, the Environment Agency had concluded, their own operatives. They have been going around the country for years monitoring the spread of the disease. Eventually they noticed that new disease outbreaks tended to occur some time after a location had been visited by one of their monitoring teams. They would no doubt like to keep this quiet, and have started to sterilise their sampling gear between trips to the rivers.

Anglers are major suspects in the spread of fishes nowadays.

 
dr.bob
277086.  Thu Feb 14, 2008 4:28 am Reply with quote

Anguilla wrote:
We know too that eels can be found regularly but decreasingly so, in ponds and lakes many miles from the nearest river, so how then did they get there?


I'm a little bothered by your use of the word "lakes" here, though this is probably just a semantic issue.

When I hear the word "lake", I think of things like windermere or loch ness. Such bodies of water are far from being dissociated from rivers.

Your description of stagnant ponds created by receding flood waters also bothers me. Surely, without a regular supply of water to top it up, such ponds will simply dry out and therefore will be unable to support any life long-term.

I admit my knowledge in this area is scant, so I'd be interested to be told where I'm going wrong here.

 
Anguilla
277202.  Thu Feb 14, 2008 7:02 am Reply with quote

If you get a garden spade and start digging a hole, you may eventually find water depending on the topography of where you live. If you do find water that will be because you have entered the saturated zone or water table. This is an area below ground that is permenantly wet but the depth will vary depending on seasonal variations. If a big enough hole is dug in a saturated zone it will naturally fill with water and remain so, there being nowhere for the water to run to. Natural lakes and ponds formed because there were "natural" depresssions in the ground that extend below the saturated zone. We may return to this phenomena when we look at the means by which baby eels can find their way into inland waterways.

Small holes are usually called ponds, but large holes, whether natural or not are called lakes, or meres or lochs, or loughs depending on where you live.


Last edited by Anguilla on Thu Feb 14, 2008 12:08 pm; edited 1 time in total

 
Hummingbird
277220.  Thu Feb 14, 2008 7:30 am Reply with quote

Dagnamit. I thought this was a thread about the splendid MR E and his pop combo.

I now know more about eels than I wanted to.

 
slade
316191.  Mon Apr 14, 2008 4:55 pm Reply with quote

I've just been watching a repeat of QI's "electricity" episode, which claims some (unidentified) people would catch electric eels by sending horses into the water first.

The idea was that the eels would exhaust their electrical charge on the horses, leaving them safe to catch. It was said that the horses would sometimes have heart attacks as a result of this. Some would die.

Assuming all that's true, isn't it rather a self-defeating tactic? I mean, how many eels do you have to catch to make it financially worthwhile losing even a single horse?

 

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