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Anguilla
270025.  Sun Feb 03, 2008 5:07 am Reply with quote

Take it from me, eels do not come up on land to eat peas and beans. I have no idea where such a thought originated (it's a new one on me!) but it should be consigned immediately to the midden alongside other such ridiculous historic notions that eels erupted from the hooves of horses!

There is still so much we don't know about the eel and there was much more interesting and alarming factual information that you could have included. For example, the world wide population of Anguilla anguilla, (our european eel) has recently crashed. Numbers now are estimated to be at only 1% of what they were twenty years ago. The reasons are not fully understood, but early speculation blames everything from overfishing to an alien parasite that invades the swim bladder causing it to remain full of gas and thus preventing the eel from descending to the depths in order to spawn. Again all speculation since we still know virtually nothing about eels or their spawning habits. What we do know is that the eel is now severly threatened and is in danger of going extinct.

Eels, it is confidently and repeatedly stated, migrate over dry land but..., has anyone here ever seen an adult eel out on dry land? (not one recently caught).

Anguilla.

 
braintrustkid
273660.  Fri Feb 08, 2008 2:39 pm Reply with quote

It seems there is some scientific evidence that eels do indeed come out on land (not sure about the peas and beans aspect...)

From an article in the Journal of Experimental Biology

Quote:
In addition to snakes, several diverse species of elongate fish
are also known to make transitory excursions into the terrestrial
environment (Gordon and Olson, 1995). Anguillid eels are a
good example, being known to move across land under a
variety of circumstances (Gray, 1968; Lindsey, 1978; Tesch,
1977).


The references about anguillid eels quoted are:

Gray, J. (1968). Animal Locomotion. New York: W. W. Norton &
Co. Inc.

Lindsey, C. C. (1978). Form, function and the locomotory habits infish. In Fish Physiology, vol. VII (ed. W. S. Hoar and D. J. Randall), pp. 1Ė100. New York: Academic Press.

Tesch, F. W. (1977). The Eel: Biology and Management of Anguillid
Eels. London: Chapman & Hall.

 
Spinoza
274089.  Sat Feb 09, 2008 11:00 am Reply with quote

Eels, and a surprising number of other fish, do venture onto land, th0ough not to eat peas and beans. It seems that these adventurous fish do attract tall tales. One example of this is the Indian species Anabas, the so-called climbing perch, which was atf one time widely believed to actually climb trees.

It certainly does go walkabout on a regular basis, but its alleged arboreal habit seems to have arisen in an account in a letter home from a diplomat or army officer in the nineteenth century, who recounted that he found one of these fish in the fork of a tree during an excursion into the Indian countryside. How it really got there is anybody's guess, I suppose it got stranded there during a severe flood.

Anabas normally lives in slow-flowing rivers and hot, stagnant pools, which frequently have very low levels of dissolved oxygen in them. When the fish finds the level of dissolved oxygen in the water distressingly low, it crawls out of the water and breathes air, and crawls about looking for a better bit of water. Obviously this fish has a number of adaptations which allow it to do this, but there are quite a number of fish, particularly in Asia, Africa and South America which are effectively air-breathers. It seems that living in swamps and murky waters requires fish to develop abilities and modifications which also allow them to survive for surprisingly long periods on land. Maybe, millions of years ago, such fish found there were some advantages to going walkabout, for example the complete absence of predators, and so terrestrial vertebratge animals evolved.

 
Anguilla
274414.  Sun Feb 10, 2008 6:02 am Reply with quote

Braintrustkid refers to work that has been undertaken by scientists who have measured the muscle activity of eels when placed on dry land. The insulting inference of this work is that eels do indeed spend considerable time out of water. Had the same scientists carried out a similar study on the muscles of a domestic cat that has been thrown into a raging flooded river they would also come up with some interesting data, none of which could positively conclude that cats spend a considerable amount of time swimming across raging rivers. Obviously, neither exercise can prove conclusively that mature eels migrate overland or that cats frequently swim across raging rivers. We know enough about domestic cats though to be fairly certain that if we spot one in a river, someone somewhere will dive in to save it, or at the very least, call the fire brigade! We would also rightly conclude that the cat should not be in the water! Cats and water donít mix! We still know next to nothing about migrating eels.

Spinoza on the other hand cites examples of other species of fish which are Ďknowní to come out on dry land. Yes thank you Spinoza. We are all aware of these species of fish and of course the lung fish species, some of which evolved into the earliest amphibians. We know all about these because we see them in their natural habitats: sometimes in, sometimes out of water. Can anyone NOT draw a mudskipper?

The question remains; Has anyone positively identified a mature eel out on dry land and apparently migrating to the sea. (Not one that has been recently caught and filmed for the benefit of a television documentary). My hypothesis is that eels may on occasion leave a landlocked watercourse. This may be because the water in which they are living has dried up, become polluted or is devoid of food for example. I believe this may be an exceedingly rare event. I believe too that only eels that have lived out their entire lives in coastal waters or rivers connecting to the sea retain a desire to spawn. It is therefore only these eels that migrate back to the Sargasso. Landlocked eels (Eels that inhabit lakes and ponds) remain in freshwater until they die. They simply have no urge to spawn. If this were not so, surely, we would spot them slithering through the grass or hiding under logs. Itís pretty hard not to see a three foot long eel. Surely too, night predators like foxes, badgers and otters would seek them out and eat them. Herons, will be stalking the grass alongside lakes and ponds. There would simply be more evidence

According to the Environment Agency, catches of eels for export have declined due to the falling population. However, a peak year for export came in 1996 when 600 tonnes of eels were caught. Since the traps are set in rivers, it can be safely assumed that the catches should include eels from all water courses, including of course, those from lakes and ponds. Lets assume then that only 10% of the eels came from landlocked sources. (I have no idea what the landlocked population might be, but 10% is given for this exercise) That's still 60 tonnes of eels that someone somewhere should have spotted. How many more would have perished along the way? Probably more than half would not have made it. So that means there would be at the very least, 120 tonnes of eels slithering along the grass and roads of Britain sometime during the autumn migration. How many were reported? None!


Last edited by Anguilla on Wed Feb 13, 2008 1:37 pm; edited 1 time in total

 
Spinoza
274522.  Sun Feb 10, 2008 10:58 am Reply with quote

OK, Anguilla, despite a lifetime of hanging about on river banks and similar places, I've never actually seen an eel out of water of its own volitiuon,nor have I met anyone who has. But I still believe that eels do go walkabout, but I agree with you that this would only occur under pretty rare circumstances. I'm also not surprised that it's hard to find reliable witnesses to such events. For whatever reasons, eels are far less common than they used to be, and most of us nowadays live in urban environments. Eels are primarily nocturnal, and even a 3-foot specimen (unlikely) wandering through dense vegetation in the countryside at night would not be conspicuous, even if it had an audience.

In my line of business we frequently have to go to considerqble lengths to distinguish hard fact from mere gopssip and purely anecdotal evidence is usually dismissed out of hand. To accept anecdotal evidence, the anecdote has at least to be very common, scientifically plausible and supported by other evidence. I think the eel going walkabout does pass this test, but if you're going to demand eye-witness testimony from a reliable source, then I agree it's a tricky one. I don't have access to all my possible sources of information at the moment, but a quick check through what I do have to hand was quite interesting, if inconclusive.

T. Bagenal, author of the authoritative Observer's Book of Freshwater Fishes, simply states that "Eels undoubtedly sometimes leave water and cross land from one piece of water to another". He was a serious scientist, brought up as I was in the strict English school of ecology, and my reading of this is that if he is prepared to make such a statement it's because he thinks it falls into the category of "things which are so well-established and widely-known that they don't need a supporting reference in a short book for the general reader". Disappointing, you might say, if it doesn't make you even more cross.

So then, since this is an old tale, I went for a historical perspective. To 1653, in fact, and Izaak Walton's "Compleat Angler". He clearly refers to the fact that poor people at that time would dig eels out of the earth for food: " In Lancashire, fishes were digged out of the earth with spades, where no water was near to the place".

Even the idea that eels are catadromous, i.e. migrate from frewsh water in Europe to the Caribbean to breed, only dates from the late 19th century and was not fully accepted until the mid-20th century. I guess thaqt proves there is indeed probably still a lot we don't know about eels, and I'll go out tomorrow and find you chapter and verse about the walkabouts.

 
Jenny
274608.  Sun Feb 10, 2008 2:21 pm Reply with quote

Anguilla wrote:
Can anyone NOT draw a mudskipper?


<raises hand>

 
Anguilla
274702.  Sun Feb 10, 2008 4:19 pm Reply with quote

Spinoza, You say, ĎTo accept anecdotal evidence, the anecdote has at least to be very common, scientifically plausible and supported by other evidence.í

So, letís take the ostrich as an example of what you are talking about.

a) It is commonly believed that an ostrich buries itís head in the sand.

b) It is scientifically plausible

c) There is no supporting evidence.

Now for the eel.

a) It is commonly believed that mature eels travel over land during their migration

b) It is scientifically plausible

c) There is no supporting evidence.

Are you prepared to accept as undeniable fact that ostriches bury their heads in the sand?

 
Spinoza
274773.  Sun Feb 10, 2008 6:27 pm Reply with quote

Of course not. But doesn't everybody know that the ostrich story is apocryphal? However, I take your point.

But I don't think the eel's terrestrial excursions have anything to do with reproductive migration, more probably they are triggered by extreme cold or some factor such as overcrowding or shortage of food. Other species of catadromous fish have land-locked populations, but nobody supposes that sticklebacks are driven by reproductive frenzy to venture onto land.

I'll still go out researching tomorrow to see if I can find something to satisfy you. Meanwhile if you want to know why we don't see such things nowadays, try top imagine that eels were £20 notes, that 95% of the population lived in the country and not in towns, and that we were all so hungry we were always on the lookout for some nice wild animal to eat.

 
Anguilla
275116.  Mon Feb 11, 2008 8:18 am Reply with quote

Spinoza,

It's not hard to imagine that each truffle is a £20 note. They are apparently very rare and rather difficult to find unless you have a pig or some sixth sense. Nevertheless, country folk (and some restruanteers nowdays) have been digging them up for centuries. No doubt the secrets of finding a few truffles is handed down through the generations and some people go out each week with a degree of expectation on finding one or two. Somewhere, someone will have written general information on where to look and what to do with one. As far as I know, and i'm sure you will correct me if i'm wrong, no reliable information is available on how to catch terrestrial eels. We all just assume that they exist. Why? I'm not sure we can accept Isaac Walton's story as fuctual. The Complete Angler was written several hundred years ago and who knows what he was talking about? Leeches? Lampreys? Worms maybe?


Last edited by Anguilla on Wed Feb 13, 2008 1:34 pm; edited 1 time in total

 
Spinoza
275151.  Mon Feb 11, 2008 8:40 am Reply with quote

I'm just on my way out to find some information you might accept, but for now let's examine the reliability of Izaak Walton. Obviously one can't accept his account of the matter as in any way equivalent to modern, scientific observations. Nevertheless he distinguishes between eels, lampreys and worms. I rate his observations as valid natural history observed at a time very different from our own. His book is in no way polemical, he has no reason to lie or embellish the facts, and he lived at a time when the majority of people were more inrterested in the habits of animals than they are today, because wild animals were an important source of food for the majority of people.

Where he is dead wrong is on the matter of eels' reproduction. He points out that no-one had ever seen eels spawning. If he were like you he would therefore conclude that eels didn't reproduce at all, but instead he goes on at some length about the ways eels might reproduce without spawning. Obviously he comes up with some pretty absurd suggestions, at you might expect from a 17th-century author. At that time it was widely believed, for example, that flies were born out of rotting meat and mice out of dirty linen baskets. Here we must of course part from Walton.

He also is confused about the relationship between eels' terrestrial ventures and their reproductive habits,which as I ssaid before are probably not connected at all. He does cite some interesting, but not entirely reliable, examples which suggest that the eel comes out of water in response to extreme cold.

Anyway, I'm off to hunt for some evidence you can accept.

 
Anguilla
275537.  Mon Feb 11, 2008 4:33 pm Reply with quote

Spinoza,
If science and therefore knowledge is to advance we must not be afraid to question and if necessary, drop our commonly held beliefs in the light of modern research and evidence. Science, of course, is a system of continuous advancement and our knowledge will increase as new facts emerge. It is true that throughout history, much which was once accepted as fact has been discredited once the subject is given serious study. Darwin famously introduced the world to natural selection which in turn completely reversed conventional thinking regarding our own family tree, and of course that of every other species. Iím sure that the earlier naturalists such as Isaac Walton and even Pliny did not set out to mislead. They simply observed a behaviour and recorded their understanding or interpretation of it. Some of their observations were right. Others completely and hopelessly wrong.

You are mistaken when you suggest that my belief is that eels do not spawn at all. Of course eels spawn. Iím just not convinced that landlocked eels spawn. I have been looking for the evidence that suggests otherwise for several years. Most books on the subject simply repeat what every other book states. But I can find no serious authenticated study which has tracked migrating eels overland from landlocked waters. (There are studies which trace the eel underwater) I have searched through scientific papers and I have corresponded with a number of eel farmers both here and overseas who have filled me in on a lot of interesting behavioural patterns that their eels display in the holding tanks. Only one told me that he has caught a number of adult eels at the bottom of a meadow close to the holding tanks. What does this prove? Were these eels seeking a better environment, or where they migrating? Arguably too, a holding tank might be considered to be a river, since they are normally fed by flowing water from an adjacent river. It may therefore be unsurprising that eels raised in such holding tanks, (under artificial conditions), retain the urge to migrate. Good luck with your search.

 
Spinoza
275606.  Mon Feb 11, 2008 5:37 pm Reply with quote

I have to report that my search was not successful. I was, however, confined to a crap library in a very crap university. Nevertheless I have to admit to being a bit surprised at what I found. You are right, on the question of eels moving over land there are statements to be found in any number of respected monographs, but a distinct shortage of first-hand observations. Many authors simply state it as a fact, but a few use quite extravagant language, which seems quite unjustified. I am chastened.

Of course, I know very well that academic authors are often guilty of simply repeating whatever someone has already written. After a couple of generations the repetition becomes accepted fact. There are some notorious examples which are now known, and probably a larger number which aren't. Alternatively, academic authors may look around at what "information" is available from cognate, but typically less well-refereed sources (I'm thinking of the literature on natural history in this case), and inadvertently perpetuate myths.

So, eels can undoubtedly get about on land, but it isn't clear that they do actually choose to do so. I won't give up the search just yet, as I couldn't lay my hands today on one or two sources that I had in mind, or which came up during my preliminary search. I didn't mean to imply, by the way, that I thought you believed eels don't spawn, just that you could conclude that on the basis that nobody ever saw it. In actual fact, though it's scarcely relevantr now, Izaak Walton noted that eels were in possession of all the external apparatus necessary for spawning, which in his eyes only added to the mystery; and in the late 19th century, somebody had the patience to keep eels for up to 20 years and to dissect them to establish that they did develop mature male and female gonads.

Incidentally I dfid come across quite a few examples of landlocked catadromous species evolving into species (or sub-species) which are wholly freshwater. Not too surprising, really.

 
Flash
275642.  Mon Feb 11, 2008 6:31 pm Reply with quote

Well this has all been most edifying and informative.

Anguilla, as you're not a long-established poster I ought to introduce myself as someone who's involved in the production of the TV show. I'm trying to figure out if this topic can be exploited in the upcoming series (F for Fish) because it does seem to me to have scope. I have to confess that I had not previously encountered this idea that eels migrate overland, but as I understand it your position is that this is widely assumed to be the case in all the literature, but actually there's no good evidence for it that you can find. I don't know how many people are following this thread, but can I just take a straw poll? How many of you had heard this idea before you read this thread? IE, if this is a myth is it one that's worth busting, or will people just look at us blankly?

 
samivel
275684.  Mon Feb 11, 2008 7:30 pm Reply with quote

I'd heard of the idea of eels travelling over dry land, but I often get blank stares, so maybe I'm in the minority.

 
Jenny
275701.  Mon Feb 11, 2008 8:44 pm Reply with quote

I hadn't heard of this before.

 

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