WHEN conservationists released 16,500 tiny eels into two Suffolk reedbeds this spring the fascinating fish was given a lifeline to help it avoid slip-sliding into East Anglian oblivion.
Catastrophic crashes have been recorded for the eel across Britain and Europe, and East Anglia’s population is among those that have plummeted in recent years. That’s obviously bad news for the eel – and it’s also bad news for the bittern, the rare, iconic reedbed bird that is more than partial to eels as prey.
But now a partnership involving the Environment Agency, the Suffolk Wildlife Trust and the RSPB is giving the eel a better chance of survival and helping the bittern continue its own rise back from the brink of local extinction.
The eel’s life cycle involves a truly jaw-dropping epic of migration from and to the Sargasso Sea – a “sea without shores” more than 4,000 miles from British waters way out in the Atlantic, the only known spawning grounds of the entire European population. The partnership, however, has given the eels a helping hand – transporting tiny “shoelace-like” young eels from the River Severn in Gloucestershire by train and car to the Suffolk Wildlife Trust’s Hen Reedbeds near Southwold and the RSPB’s Minsmere reserve near Westleton. The aim, quite literally, is to put them on the road to recovery.
The local eel populations had reached such a perilous low that re-stocking is now seen as a vital step, and one that will also benefit the bittern.
Alan Miller, the trust’s north-east sites manager, is hoping to re-stock the Hen area regularly, but will need to find funds to cover the costs.
“When we established the reedbeds I was keen for everything to evolve naturally, building up populations of fish and everything else in the natural way,” he said. “There seemed to be plenty of fish, we saw many shoals and the nearby heronry and the number of little grebes we had seemed to prove that there were plenty .
“But the bitterns at the Hen were feeding on roach, which they are not usually said to do so commonly elsewhere, so after a while I was keen to find out more about the fish populations.”
The Environment Agency’s fisheries department helped by electrofishing to study the populations. It was found there were very few rudd, the majority of fish were roach with a few tench. The eel population was low, as it is throughout East Anglia.
“It was decided to re-stock, at first, with 10,500 young glass eels from the River Severn,” said Mr Miller. “They were put on a train from Gloucester to Peterborough, in polystyrene boxes packed with ice and water then brought over in a car with its air conditioning on full blast all the way to keep them cool.
“Eels are amazing creatures with a fascinating life cycle. It’s incredible to think that these glass eels can be in salt water in the Severn and within eight hours they can be in fresh water in our reedbed over this side of the country.”
Mr Miller hopes the re-stocking will prove to be the first phase of a long-term project, with repeat releases to give a wide age range of eels. “Some of them could be in the reedbed for about 20 years or so before they start their incredible return journey to the Sargasso Sea spawning area. Each re-stocking costs about £3,000 so we will be casting around for funds locally,” he said.
“The project will be good for the eel population and good for bitterns. At present there area two bittern nests and three booming males, although the site is capable of holding three nests, so to have a diverse, healthy fish population is extremely important.”
At Minsmere, 6,000 glass eels were released into the reserve’s reedbeds as part of the same project – following on from releases in 2008 that totalled about 8,000.
In the past Minsmere’s eel recruitment may have been stifled by the old-fashioned design of the sluice entering the sea and other barriers within the drainage network. The RSPB has worked to improve the wetland infrastructure to make it more accessible to eels and other fish species. Eel ladders have been installed in the past and, together with the Environment Agency, the RSPB hopes to install a new one when the reserve’s North Marsh sluice is redesigned in the coming year.
The recent re-stocking at both sites was carried out by Environment Agency fisheries scientist Andy Hindes who said the eel’s serious population crash had been widespread in Britain and Europe.
“It has got to a stage where now all member states of the EU have to draw up eel plans and implement them,” he said. “We have to facilitate the passage of eels past potential barriers to their migration and look at eel population dynamics because they are not particularly well understood.”
The re-stocking involved tiny 3in glass eels that arrived in British waters after having been hatched in the Sargasso as much smaller “leaf-like” creatures that drift with the currents. They became bigger as they approach Britain and many, predominately females, used to migrate further on to East Anglia but the numbers doing so were now very small, he said.
It was not only new physical obstacles to migration that was causing the problem. Changes in Atlantic currents were thought to be responsible too, and the eels had been dogged by parasites in their swim bladder which created difficulties when the adults came to migrate to the Sargasso. When they reach the Continental Shelf the adults usually dive deep but, because of the parasite problem, they were now unable to regulate the depth at which they swam.
The River Severn population seemed to be holding up, however, and so was the source of the re-stocking schemes. “We are navigating overland for them, if you like, by taking them to sites that are identified as being suitable, such as the Hen and Minsmere,” said Mr Hindes.
“It may seem strange that we are taking them to places where they can be preyed upon by bitterns.
“However, the bitterns will not take anything like the whole number we release and, at the Hen for example, others may well navigate further up the River Wang while some will stay in the Wang and Wolsey marshes which make up the Hen Reedbeds until they mature at 15 or 20 years and are ready for migration out to sea and back to the Sargasso.
“It has been a pleasure and a privilege to work with the Suffolk teams. They are so enthusiastic and professional. It has been fantastic to be involved in the advice and research and then to complete it with the releases.
“Hopefully we will be able to work at other such sites – eel sanctuaries if you like – with the RSPB and the Suffolk Wildlife Trust,” said Mr Hindes.
“Transporting the glass eels by car was a bit chilly. You have to keep them at below 10C because that is less stressful for them so the air conditioning really was on full blast – but it certainly has been worth it.”