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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?

 
dr.bob
316348.  Tue Apr 15, 2008 4:18 am Reply with quote

Depends if the horse is yours, or if you're driving a pack of wild horses into the water. Even if the horse is yours, it may be at the end of its useful life and destined for the glue factory.

Or perhaps the financial viability of the tactic rather depends on how many horses actually died in this endeavour. "Some" is a rather vague number.

 
Flash
316379.  Tue Apr 15, 2008 5:34 am Reply with quote

It's true enough, slade (and we'll try to hide the hurt we're feeling that you doubted it); this is an account given by the Prussian explorer Humboldt.
Quote:
To catch the gymnoti with nets is very difficult, on account of the extreme agility of the fish, which bury themselves in the mud. We would not employ the barbasco, that is to say, the roots of the Piscidea erithyrna, the Jacquinia armillaris, and some species of phyllanthus, which thrown into the pool, intoxicate or benumb the eels. These methods have the effect of enfeebling the gymnoti. The Indians therefore told us that they would "fish with horses," (embarbascar con caballos.* (* Meaning to excite the fish by horses.)) We found it difficult to form an idea of this extraordinary manner of fishing; but we soon saw our guides return from the savannah, which they had been scouring for wild horses and mules. They brought about thirty with them, which they forced to enter the pool.

The extraordinary noise caused by the horses' hoofs, makes the fish issue from the mud, and excites them to the attack. These yellowish and livid eels, resembling large aquatic serpents, swim on the surface of the water, and crowd under the bellies of the horses and mules. A contest between animals of so different an organization presents a very striking spectacle. The Indians, provided with harpoons and long slender reeds, surround the pool closely; and some climb up the trees, the branches of which extend horizontally over the surface of the water. By their wild cries, and the length of their reeds, they prevent the horses from running away and reaching the bank of the pool. The eels, stunned by the noise, defend themselves by the repeated discharge of their electric batteries. For a long interval they seem likely to prove victorious. Several horses sink beneath the violence of the invisible strokes which they receive from all sides, in organs the most essential to life; and stunned by the force and frequency of the shocks, they disappear under the water. Others, panting, with mane erect, and haggard eyes expressing anguish and dismay, raise themselves, and endeavour to flee from the storm by which they are overtaken. They are driven back by the Indians into the middle of the water; but a small number succeed in eluding the active vigilance of the fishermen. These regain the shore, stumbling at every step, and stretch themselves on the sand, exhausted with fatigue, and with limbs benumbed by the electric shocks of the gymnoti.

In less than five minutes two of our horses were drowned. The eel being five feet long, and pressing itself against the belly of the horses, makes a discharge along the whole extent of its electric organ. It attacks at once the heart, the intestines, and the caeliac fold of the abdominal nerves. It is natural that the effect felt by the horses should be more powerful than that produced upon man by the touch of the same fish at only one of his extremities. The horses are probably not killed, but only stunned. They are drowned from the impossibility of rising amid the prolonged struggle between the other horses and the eels.

We had little doubt that the fishing would terminate by killing successively all the animals engaged; but by degrees the impetuosity of this unequal combat diminished, and the wearied gymnoti dispersed. They require a long rest, and abundant nourishment, to repair the galvanic force which they have lost.* (* The Indians assured us that when the horses are made to run two days successively into the same pool, none are killed the second day. See, on the fishing for gymnoti Views of Nature Bohn's edition page 18.) The mules and horses appear less frightened; their manes are no longer bristled, and their eyes express less dread. The gymnoti approach timidly the edge of the marsh, where they are taken by means of small harpoons fastened to long cords. When the cords are very dry the Indians feel no shock in raising the fish into the air. In a few minutes we had five large eels, most of which were but slightly wounded. Some others were taken, by the same means, towards evening.


A. von Humboldt, A. Bonpland - Travels to the Equinoctial Regions of America, 2
http://explorion.net/a.von-humboldt-equinoctial-regions-america-2/page-62.html

 
Sadurian Mike
317229.  Tue Apr 15, 2008 8:44 pm Reply with quote

[Boney M]"Ooooh, those Prussians..."[/Boney M]

 
ticklishtrout
397841.  Tue Aug 26, 2008 9:27 am Reply with quote

Just reading your post on eels and migration across land.
I was actually searching this fact to see if I could find any locations in NZ where I might be able to observe and possibly film the event. As yet, I still some more searching to do. From what I have read here and also been lead to believe, I would agree that it is probably the behaviour of landlocked eels, though I have been told by old timers of this event, and in one particular location, there is no landlocked water to mention. The creek was a small tributary (big enough for 4-5 pound trout to spawn in), which flowed into a slightly bigger stream (too small to canoe down), which then fed into a very large lake of several kilometres. I wonder if during the migration the small stream was running very low and that on a dewey night, shear numbers forced some out onto the banks and then across the grass into the stream (His house was maybe 20m from both streams and he had seen them in large numbers across his front lawn).

In other areas, I could imagine a small pond on a farm which has over time become isolated through land modification (ie excavation activities), though with eels left living in the ponds coming to maturity several years later and having no option.

One thing I have observed with eels during night fishing on the mouth of the Buller River in NZ during December, is eels coming out of the lake and up the pebbled foreshore (at least a couple of meters) to steal freshly killed brown trout. This is a very common occurrence and I now hang the trout, once gutted, up in the manuka trees to prevent this happening.

And now onto cats. Several years ago (2004), I was trout fishing near Mt Cook on the Tasman River (or part thereof) above where it flows into lake Pukaki. Approximately 150-200metres off upstream we watched a wild cat (apparently oblivious of us....and well out of danger from us), run across the braided river gravels and then straight into the river and across on what was a very swift and turbulent head of the run/corner of the river (we are talking to swift and deep for your average person to contemplate crossing at this point and a width of approximately 8-10m). The water at this point would have been in excess of 1.2- 1.5m deep. On reaching the other side, it went straight up the bank and carried onward on its very direct route. Wild introduced cats are a real problem in the McKenzie basin and other parts of NZ. This was the first time I had seen what appeared to be a completely normal and every day river crossing for a cat (tabby).

Lastly, a mate and I set off fishing one day from his house and wandered down the drive way to the 6mile creek. One of his pet cats Ruby followed us. We got to the creek and continued across the very bony run, yet deep enough to wet our shoes in up to shin deep water. The width of the stream was approximately 6-8m wide We were both astounded when we looked back to see the pet cat meowing and coming forth across the stream with us. At a pinch the cat could probably have touched the bottom most of the way, but it was intent on coming with us and it was a fun sight to see. On reaching the bank it was completely wet, yet unphased. This particular cat was a large tortoise shell.

Just to stimulate some debate, my grandfather once told me he watched a rabbit swim across a pond (in the UK)??

 

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