European eels are critically endangered, largely due to human activities. One of the major problems they face is swimming upstream through managed watercourses. Guglielmo Sonnino Sorisio is one of the researchers investigating a solution to this problem: eel tiles.
Guglielmo: https://profiles.cardiff.ac.uk/research-staff/sonninosorisiog
Produced in collaboration with Simon Clark, https://www.simonoxfphys.com
This is a European eel it’s found all over Europe and it’s critically endangered with populations declining more than 95% since 1980 one of the reasons the species is so endangered is because of its complex life cycle from birth they are transported by Oceanic currents from the saraso sea to the
Coasts of Europe and North Africa here they enter freshwater using the ties to help them swim upstream because of their poor swimming performance after a while they turn into elvers about 9 cm long and up and darken color it is essential for them to get Upstream to be able to
Grow large enough over a number of years to mature into silver eels and undertake a migration back Downstream to the Sea and back to the saraso one of the reasons for the huge decline in numbers is the amount of barriers that we place in rivers that eels need to overcome to
Complete their migration an example of such a barrier is a culvert elts can restrict the flow and increase the flow velocity by virtue of having very smooth walls and bed compared to a natural River the problem is that elvers have trouble swimming fast enough to get Upstream of these culverts some fail to
Pass these barriers and other become over tired so they need to rest near the Culvert where they are more vulnerable to predation a low cost solution to this issue is yel tiles they simply bolt onto the bed of the Culvert they’re made out of plastic and they comprise of a base
And two densities of cylindrical protrusions but can they help heels get upstream and if they can how do they do it this has been focus of part of my PhD they mount to the side of the channel because that is where eels prefer to swim to simulate this I use The Flume at
Cardiff University School of Engineering with the same tiles that are planned to be used in rivers then simulated flow conditions which may occur in a river the tiles also act to create a severe reduction in flow velocity within the protrusions and also manag to reduce velocity above and besides the tiles an
Inflection Point can be noticed on the graph level with the top of the protrusions that shows the two different layers of flow this can allow the fish to navigate the cver much more easily in theory but in practice things are more complicated at the interface between the
Slow moving flow within the tiles and the higher velocity flow around them is a layer of high Shear this can create an instability called The Calvin hell puls instability this instability can manifest itself as a series of vortices which can destabilize fish in reality we can see
That the vortices do not form in our case but the instability causes an upward and downward shedding in the vertical plane and a side to side illation in the horizontal plane but this can still be enough to impact a swimming fish to better understand how the eels use the tiles I analyzed the
Kinematics without the tiles the eels swim very fast symmetrically but use a lot of energy when swimming near the tile they take full advantage of the slower Flow by tucking themselves into the slowest part of the flow and swimming a as symmetrically but when they swam above the tile they were slow
And swam with reduced amplitude suggesting the turbulence above the tile could be affecting them this is further supported by this graph showing how many tail beats per second they needed to swim in each area essentially showing us swimming efficiency we can see they needed more tail beats to go faster in
Turbulent areas but they still needed to swim faster in the open Channel through all the pros and cons of the tiles they were able to help the eels get Upstream more often and more easily which is good news but more evidence is needed on their effect on different species and
Their ability to reconnect habitats culverts are unfortunately only one of many challenges facing eel populations climate change the spread of the aasis parasite chemical pollution and other barriers and rivers all threaten the species but by solving as many of these problems as we can we can help prevent populations from further reducing and
Hopefully restore them to healthier numbers seemingly small devices and changes like yield tiles and other yield passes all contribute and must all work together to help do this I would like to thank the whole team at Cardiff University and especially my supervisors Professor Joe cable and Dr Katherine
Wilson I would also like to thank uh Andy Don and the environment agency for making this work possible