Massive elver run in the Severn

[Worms]

I've been doing a number of aquatic surveys over the last three years near the Severn estuary...no shortage of eels or elvers that I can see...'though I must be wrong...as there are also only 100 cod left in the North Sea...

[Phone]

Worms,

 

EEW - not carp?! How many eel hides does it take to make a pair of boots?

 

What sex are most eels?

 

Phone

[Guest twofoottwitch]

eelers,

 

I'll once again show my ignorance. What do elvers eat?

 

Phone

More of what eats elvers, it's a long way from the Saragoso Sea to the Severn, these tiny things finally make the Severn here only to be scooped up by licensed netters who sell them on for as much as £200 a kilo.

I imagine all the coarse fish in the system will be gorging themselves silly, fantastic news though that they are back in large numbers.

[Leon Roskilly]

What sex are most eels?

 

As well as salinity, temperature and diet, sex determination is also dependent on population density.

 

Lots of elvers and they mostly become males, few elvers and they mostly become females.

 

(On the UK west coast mostly males, in the East 'shadow' mostly larger females. But they don't develop reproductive organs until the effort of a long swim back to the breeding grounds releases the hormones that bring about the changes)

 

One of the concerns of falling elver numbers is that we end up with a population of nearly all female eels that can;t find breeding partners back on the spawning grounds..

 

 

http://www.mendeley.com/catalog/long-term-study-population-characteristics-downstream-migrations-european-eel-anguilla-anguilla-l-ef/

[RelaxGod]

I had no idea they were eaten that small, seems like a waste to me.

[Dales]

Leon, what you posted about different areas having predominantly eels of one sex or the other is very interesting. However I don't see how that can effect the breeding chances of the species. I always assumed maybe wrongly that they would meet up with other groups of fish maybe from all over the world and so by the time they reached the spawning grounds they would be breeding with other populations of eels.

[Dales]

If there is a problem with eel populations surely the best solution would be to allow elvers to run and restock our waterways. Surely even stoping harvesting for 1 season would have a positive effect. The current solution to protect eel stocks is nothing short of complete bonkers.

[Leon Roskilly]

Leon, what you posted about different areas having predominantly eels of one sex or the other is very interesting. However I don't see how that can effect the breeding chances of the species. I always assumed maybe wrongly that they would meet up with other groups of fish maybe from all over the world and so by the time they reached the spawning grounds they would be breeding with other populations of eels.

 

 

Although the American eels, similar to European eels) are thought to spawn in the same area as the European eels, they tend to spawn at a different time (possibly because they have a shorter journey and have done their thing by the time the European eels start arriving).

 

From a common ancestor, American and European eels have evolved into different species.

 

http://news.softpedia.com/news/Eels-the-Oddest-Migration-for-Sex-73420.shtml

 

 

Two groups of eels formed from the ancestral species, Anguilla ancestralis: the 17 modern species from Indo-Pacific basin and 2 from Atlantic.

 

All eels kept the same lifestyle: bred in marine warm sea waters at 400 m (1,330 ft) depths and grew in freshwater.

 

The Anguilla atlantidis bred in the Sargasso Sea, in the young Atlantic Ocean, which was much smaller than today.

 

The young reached by drifting Europe or North America, and this way resulted the North American (Anguilla rostrata) and European (Anguilla anguilla) eels, which differ only through the number of vertebrae (115 in the European species, 107 for the American species).

 

The expansion of the Atlantic Ocean increased the distance, so the European eel had to make to Sargasso Sea to breed.

 

Other regional populations of eels of different species breed in other areas, so there is no mixing.

 

In any case, it's not just a UK problem, eels around the world are suffering the same decline. :-(

[Leon Roskilly]

If there is a problem with eel populations surely the best solution would be to allow elvers to run and restock our waterways. Surely even stoping harvesting for 1 season would have a positive effect. The current solution to protect eel stocks is nothing short of complete bonkers.

 

Elvers suffer huge natural mortality, with very few becoming breeding eels.

 

Under present regulations a proportion of elvers harvested have to be sent to fish-farms where they are fed and allowed to grow without predation before being used to restock waters with live adult eels.

 

And a proportion of the adults will 'escape' back to the sea, calculated to be larger than if nature had been allowed to take its course and no commercial exploitation of elvers/restocked eels had taken place.

 

So, commercial exploitation can strangely result in more eels making their way back to sea to breed!

[Phone]

Leon,

 

Didn't I read once that human hormones (etc) were interfering with natural sexing of eels? Eels aren't sexed when they are born - they choose which sex to be in freshwater. Everything I've just said is a question.

 

Here's a good "thingy" on eels.

 

http://www.sustainableeelgroup.com/wp-content/uploads/2012/10/A-Eel-Facts-Myths-Poster+Refs-18July11.pdf

 

Phone