As a member of the NAC i fish for and have studied eels i thought i would start a thread on this species instead of hi jacking other threads....sorry about that. A few of you have had a few questions of late and i thought it best to simply start a thread here....so i will start with some basic info on the eel and its decline.

The European Eel Anguilla anguilla starts life in the Sargasso Sea where it drifts on oceanic currents before reaching European shores up to 4 years later. From here, as Elvers, they migrate into our River systems where they spend up to 50 years, feeding and growing before returning back to the Sargasso to spawn.
This long lifecycle along with some natural and anthropogenic influence makes the species susceptible to possible extinction. It is already thought that the species has declined by approximately 99% since the 1980’s. This is alarming and has raised the question as to whether Eel stocks are sustainable.

The decline of the species has been reported since the 1940’s in Northern Europe and since the 1980’s in the rest of the continental range. Scientists from Indicang (pan European Eel research group) have demonstrated that Eel stocks are in decline and in some regions, mainly in the North of its distribution area, the situation is critical. Some restocking programmes (Northern Ireland, Baltic Sea and Italian lagoons) have succeeded in sustaining local fisheries but the decline continues where stocking has not been carried out. So what are the causes of this dramatic decline?
There are two major stages of the lifecycle which affect the decline in stocks
• Elver Recruitment
• Spawner escapement
Both are linked, it is thought that a reduction in spawning stock, caused by declining Eel stocks may be sufficient to cause a recruitment collapse as in 1980. There is evidence that the decline in recruitment was preceded by a decline in Eel landings approximately 2-3 decades earlier, as the time lag roughly corresponded to the generation period for faster growing stocks. Therefore, initial stock decline could not be caused by reduced recruitment but could be a potential cause of reduced recruitment.
Causes.

Recruitment Decline
• Over Exploitation
• Changes in oceanographical conditions, possibly linked to climate change
• Reduction in accessible freshwater habitat
• Pollution
• Parasitism
Stock Decline
• Over Exploitation
• Loss of good yellow Eel habitat, loss of wetlands, pollution, over abstraction.
• Barriers to migration, physical - weirs etc and water quality and quantity.
• Reduction in Elver stocking in waters beyond normal migration range.
Climate Change
Recent papers suggest marine events such as a Northward shift in the North wall of the Gulf Stream have caused Leptocephali to follow longer routes exposing them to less favourable conditions and food availability.
Parasites
The nematode Anguillicola crassus was spread to Eel stocks in Europe from the Japanese Eel imports in the 1980’s. This affects the swim bladder and may cause serious physiological effects and affect the normal migration patterns.
Habitat Loss and barriers
Many scientists attribute the decline to loss of habitat and accessibility. The amount of available habitat is thought to have been reduced by at least 50% during the last century. The habitat area currently available is estimated to be approximately 87 000 Km2. Habitat loss is caused by dams, drainage, and reduced water quality.
Sub lethal poisoning
Due to the high fat content Eels are susceptible to storage of many contaminants namely brominated flame retardants. These can affect gonad development and impair the spawning ability.
Over Exploitation
Although the above factors are serious and attributed to the decline they are not sufficient to explain the extent and timings of the decline in recruitment.
When arriving Eels are super abundant and freshwater mortality is density dependant then the effects of recruitment variation (due to Elver fishing) on the number of older Eels is negligible. At some point reduced recruitment through fishing will reduce stock and it is thought this point has already been reached. A total of 25 - 30 000t of Eels are exploited every year due to demand for food and even as bait for other species. Elver fisheries account for 800 - 900t per year or 2.7% which equates to 2.4 billion Elvers which is sufficient to restock the whole of Europe at a rate of 0.1kg per hectare.
Eels are not bred in captivity; aquaculture relies on the collection of seed Eels (Elvers) which are then grown on. This means that the species is unsustainable as ALL Eels sold in restaurants, shops and bait suppliers have been taken from the wild initially.
The European Eel is currently deemed the most at risk vertebrate in the country and is currently on the IUCN Red list.

Is there anything available on eel growth rates Chris? Having grown up in an area where none of the rivers, at the time, contained fish, let alone eels, I have been pleasantly surprised to catch the odd eel in the revitalised streams nearby. I hear they are slow growing, and so an age/weight table would get me somewhat closer to when they first started to colonise locally. How old, for instance would a 3 pound eel be?

i heard they are very slow growing as well,and was told by a bloke in devon when i lived down there that an eel of say 15 to 18 inches in length could be 20 years old.

Growth rates in eels are not very straight forward to be honest as there a number of factors to consider, temperature, prey species, head shape etc. A very broad guide but by no means definite is to say 10 years to every 1lb in weight. But it would be dependant on the some or all of the factors mentioned. It is important to note also that weight is not really a good variable to base growth on, for example an eel living in a rich, commercial lake rammed with prey fish is going to pile the weight on much quicker than an eel living in a highland glacial loch with low productivity. An eel caught in a net in the highlands weighed 7lb 4 oz after studying the otoliths it was found to be 84 years old. I will now try and explain growth/age/feeding etc as best i can as they are all linked.

The eel is unusual as it has two phases in its life cycle, the oceanic phase and the continental (freshwater) phase. In the European eel the oceanic "larval" stage is approximately 2-4 years. Because the procedure in reading larval otoliths is unreliable age is usually taken from the glass eel stage. Ageing eels is done by removing the otoliths, splitting and burning them and then counting the rings ( i wont go into the exact technique here)
The otoliths from eels kept in ponds gave a very accurate indication of the years passed.
By recapturing marked eels it was possible to confirm the slow growth made on eels along the German coast. These showed that at a length of between 40 and 50 cm eels grow 2-3cm per year. Eels between 78 and 87cm captured in lake Ontario indicated an annual increase of 3.1cm. This was how it was decided that otoliths were a reliable method of assessing age. Scales are present on eels but only a few are formed in small patches and usually at around 4 or 5 years old so these were deemed unreliable as a method.

Total body length is used as a measure of growth as weight varies with nutritional conditions.

Differences in growth between males and females

The majority of eels that come from overpopulated areas and which show slow growth rates during their first years of freshwater life tend to develop into males, therefore it is likely that males will show a slower growth rate than females. This has been confirmed by a number of investigations, from the age of four onwards females are as much as 10cm longer in all regions of Europe and Japan. So the only way to establish this is to back calculate the length attained at an earlier age. So it was found that until eels are at least 20cm long males are undifferentially externally. Eels from North coastal regions are about 3 years old when they reach this length. The lengths of European Silver eels recorded over a period of several years from different waterways have been combined and show that the average length of male eelsis between 35 and 41cm. In European feamle silver eels range from 54 -61cm. It is also important to note that the average length can vary from year to year, although this is only slight and could be due to a population increase after intensive restocking. This occured in a lake in Denmark, at the same time there was an increase in the proportion of males which may confirm the view on the dependance of sexual differentiation on population density.

Head width and growth

Data on feeding habits have shown that organisms eaten by broadheaded ( BH)individuals differ from those eaten by narrowheaded ( NH). In general BH eels eat animals that are larger and more difficult to capture, these exhibit larger, more powerful jaws. It is therefore likely that there will be a difference in growth rate. The results of a study where the age of BH/NH was determined show that BH had a much higher growth rate than NH. The length advantage in BH increases from 5cm after 6 years to 10cm in eels aged 8-10 years. Another study showed a greater increase - 2-4 cm for every 10cm increase in length. These differences however are only relative as they occurred within a given population. Eels from Heligoland serve as examples of extreme BH, head width was equal to 36% of total head length or 1:21 in total body length. The latter ratio is 1:40 in NH. In Heligoland good growth rates are only seen in eels which are less than 30cm long after which they do not grow as well as other eel populations.

During my studies in the far NW Highlands i noticed that the majority of eels were broadheaded, all were taken on fish baits, i used two rods, one worm one fish every session. In some cases eels also showed the extreme broadheadedness where the jaw width exceeded the jaw length. In instance a 700mm eel regurgitated a 360mm narrow head. This got me thinking, do some eels where prey is limited ( the water in question only contained natural trout populations and was largely unproductive, the only influx of prey would come from eels/elvers) exhibit a more cannibalistic habit, this may explain the extreme BH here. But thats another story.

Differences in growth due to environmental factors

The main factors influencing growth rates in all members of a population are population density, temperature and the amount of food available per unit of area. Observations from two rivers in Wales ( the Ffraw and the Rhyd-hir)show how population density can influence growth. In the first river, female eels in particular showed a much better growth rate, until their 8th year than eels from the second river. The difference in length of eels the same age was as much as 4cm. After the ninth and in eels over 45cm this difference had disappeared. The data showed that the river with slow growth had a population density of 4 eels per square metre whereas the river with faster growth had a density of 1 eel per square metre.
Where large eels are concerned growth rate is not adversely affected even in high density areas, this is due to the fact that individuals feed differently and males over 40cm leave for spawning, this results in a sharp decrease in competition for food. In addition the proportion of females decreases at higher densities, since females made up 50% of the eel population in the river with good growth rate but only 10% in the river with slow growth then competition in eels over 40cm was reduced in the latter. Competition in the good river would have been intense amongst the females which then became members of a population which had in effect been reduced by half.

There is much more on this subject but you get the idea, we at the NAC have been trying to devise a scale for weights like the Mona scale for pike but it is very difficult, we find that differences in the eels length, girth, weights vary so much from water to water, some water they are short and fat others are long and lean. Waters with crayfish tend to produce big eels. We have found that also waters with big eels tend to have less crays, where waters have low numbers of eels then crays are abundant, i mentioned this to various biologists up north and a few projects have begun in the hope it may eradicate crays from waters up there.

Think that will do for now but keep the questions coming...

Havent read the article but In the January edition of Coarse Angling Today, Dan Williams, Assistant Editor of Pike and Predator Magazine, writes a guest editorial about the decline of the eel, and how a foreign parasite has damaged eel stocks. He then writes : “Some things evolve and some things become extinct, that's just a fact of life. We can possibly help to improve future eel stocks, but do we need to ? Why not let nature take its course, which may see that parasite evolve and the eel become extinct ? Why spend money in this day and age on something that may only help a few anglers ? Future generations just may not have the eel to catch so they will have to focus on another species. Just like we watch meerkats at the zoo instead of panda's......”

Believe me its not the parasite thats a major issue, and in truth the parasite was introduced from Japanese eel stocks during the import/export process so when it boils down to it man/humans are again to blame so its not a natural extinction.

I find this article disgusting.

Is there a temperature below which Eels will not feed. I ask because during the recent (very brief) period of warmer water on the Severn (8.4 oc) luncheon meat baits were coming back with distinct bites taken out of them. Someone suggested it could be Eels doing this ??

The magical figure when eels feed confidently is said to be 10 degrees C, however that is not set in stone. I have caught at 4 degrees and 7 degrees and i reckon the majority of eels i caught in the glacial lochs in Scotland in waters over 100ft deep were feeding in lower temperatures. So yes they probably were eels, had the temperature been much lower in the period previous??? as a sudden rise could trigger feeding.

A few NAC members do target eels all year round and although sport is slow eels have been caught at lower temperatures, thing to remember is they will require less food as metabolisms slow ( same as other fish) and eels are known to feed and then fast so the window of opportunity lessens even more.

Hope this helps

should also add that as bite marks were find they were probably bootlaces as small eels tend to take small chunks off a bait as opposed to swallowing, resulting in shredded baits and constant tapping although sometimes bites wont register.

You should also consider other species being possibly responsible for the bite marks, including crayfish of course.

As regards that article, it would be interesting to read all of it. My reaction to the extract is one of disbelief. Eels are far more important that just one more species that anglers seek. They have been part of the UK fauna for a long long time, and if money can help ensure their continued survival then let it be spent. It may not be fluffy like the panda, but it is equally important, and I would like to see its continued presence in our waters. How the parasite came to be here is irrelevant...apart from being one more example of man's major errors in his mis-manipulation of the natural world.
Anglers seeking eels is trivial indeed compared to having such a unique and fascinating creature in our lakes and rivers. An astonishing fish that would be a loss to us all, not just to fishermen.
A bloody silly, adolescent, ill-considered article.

Thanks for the quick reply. The temperature had risen 2.5 oc over 2 days from just below 6 oc. The bite marks were quite small i.e < 1cm and we experienced a lot of small pulls so I suspect your bootlace theory is correct.