Kingston University Biodiversity Action Group

18-10-2013 : ZSL Eel forum

On Friday 18th October our Middle Mill eel trap monitors joined volunteers from other trap sites around London at London Zoo for their annual Eel Forum to discuss this season's results and plans for the future.

Joe Pecorelli thanks all volunteers for their work this season

ZSL project lead, Joe Pecorelli, said the summer of 2013 had been good for the European eel, commenting the increased elver numbers at our Hogsmill trap since habitat improvement works at the Clattern bridge in August was a particularly encouraging sign.

This Citizen Science project is providing otherwise unavailable data to conservation organisations which enables prioritisation of investment in conservation measures, he said. Without volunteers like ours from KU and local residents getting their waders on and spreading the word, the plight this species is facing would only be known to a limited few. This kind of project works wonders for raising the profile of 'uncuddly' species like the European eel and wider conservation issues such as river habitat quality.

The programme has expanded from 3 sites in 2011 to 11 sites in 2013 all monitored by volunteer teams, and provides a valuable insight into the migration of the European eel in the Thames catchment. Joe explained that now is a good time to pause and reflect on the findings, with particular analysis of zero and low count sites. A review of active monitoring sites will be conducted and new ones at the River Ash, Teddington Lock and River Mole will be added to the scheme. With such intriguingly low numbers, monitoring at the Hogsmill trap will continue at Middle Mill, with a view to increasing check sites upstream as habitat improvement work is undertaken.

Joe spreads the love for eels!
In the jovial spirit of the project, this year Joe presented awards to three teams for their work this season. Receiving limited edition 'I love eels' mugs were:

  • Merton Abbey Mills for the finest excuse for having to stop monitoring as a moorhen took up residence nesting on the trap!
  • River Crane for a victory for hope over experience as the team have never seen an eel in the three years they have been involved!
  • Bow Locks for the most enthusiastic email circulated to all volunteers upon discovering an eel in their trap!
Perhaps next year, our Hogsmill team will be the lucky recipients, we shall see.

Following Joe's upbeat roundup and emphatic thanks to all eel monitoring volunteers, the Environment Agency's Darryl Clifton-Dey spoke about installing eel passes to overcome barriers on rivers, and Andy Thomas from the Wild Trout Trust described the importance of good quality habitat in urban rivers.

Darryl illustrated the common problem with eel passes fitted onto gauging weirs.
Some 3000 weirs in the South east of England are huge barriers to eel migration, Darryl claimed. They are suffering density dependent mortality - too many eels become trapped in one area because they can't reach more suitable habitat. Therefore eels die as the area cannot support them all.

Darryl emphasised that not all weirs need to be removed straight away to improve things, just critical sites downstream which will enhance habitat access for the eels. He listed the numerous barriers to migration including gauging weirs, flood gates and culverts which are all hard for eels to navigate, especially as eels are not good swimmers (despite their ability to swim the 2000miles from the Sargasso sea strangely!).

The European eel (Anguilla anguilla) prefers to crawl in damp conditions, rather than battle against a strong flow. It needs to be able to find the entrance to an eel pass easily and it must exit into suitable low-flow habitat too. Darryl commented that although eel passes are increasingly being installed, not all are working due to a lack of understanding of these basic needs. Fixing a pass to a gauging weir for example, is tricky as the Environment Agency needs to ensure unobstructed passage of flow over the sharp metal plate in order to measure river flow. A pass must have a trickle of flow for it to allow eel movement, but also mustn't inhibit the edge of the weir and skew calculations. That said, Darryl claimed research has proven that eel tiles can be bolted on in some cases with minimal interference with the gauging weir calculations.

Andy Thomas highlighted the advantage of volunteer work parties to improve river habitat 
In addition to eel passes, attendees heard more about habitat improvement from Andy Thomas of the Wild Trout Trust. "The shape of the channel let's down the ecology of urban rivers" he remarked. In order to counter this for maximum benefit, making the habitat as diverse as possible will encourage the right conditions for a variety of species, including trout and eels. Andy referred to the Habitat Bottleneck model while describing the habitat needs of trout, but explained that this need for different habitats at different stages of development equally related to other species too.

He underlined the benefits of using large woody debris (large tree sections) in rivers to create pools, shelter and act as fly egg-laying stations. Coarse woody debris (brash) too can encourage sediment accumulation, serve as a natural flow deflector and again provide shelter for fish from predators. Management of trees and vegetation on the riverbanks can also play an important role by affecting the amount of light reaching various sections of the river. Coppicing, for example, must be maintained on a cyclical regime to ensure the benefits of more light are also maintained.

After a tasty lunch and networking opportunity, ZSL staff kindly gave a tour of the seahorse breeding facility at the Zoo, as a thank you to all volunteers. 

Excited eel monitoring volunteers enter the Aquarium for a sneaky-peak behind the scenes!
We were invited behind the scenes to observe the breeding tanks for two european species - the short snouted and the long snouted seahorse (Hippocampus hippocampus and Hippocampus guttulatus respectively) - both notoriously difficult to breed in captivity. Success in the last five years has in part been due to modelling conditions more accurately on real-life habitats such as that in Studland Bay. Tall but small tanks enable the spiralling breeding ritual to take place uninhibited for the monogamous pairs. The seahorse fry are spun in small circular tanks to mimic real currents and avoid collision with the tank side. They have achieved a 30% survival rate in captivity - much higher than the estimated 1% in real life.

A poor swimmer against currents, the Seahorse clings on to vegetation in its tank
So the Eel Forum 2013 ended in the Aquarium with delighted volunteers seeing first hand how ZSL is helping boost populations of endangered species, after a morning of fascinating data, facts and inspirational advice. Hopefully this will secure their interest in volunteering at our eel monitoring trap next year. Have you been inspired too?


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