Scientists have been knee deep in the Thames since April, waiting for the eel migration to begin. Every year, young eels slither up the lower Thames estuary in black wriggling margins and a team from the Zoological Society of London (ZSL) try to catch them. Sloshing around in plastic cisterns, the eels are counted, weighed and measured before being released back into river to continue their journey upstream.
So far this year less than 30 eels have been caught. The weather hasn’t helped. One of the triggers of eel migrations is temperature and this spring/summer have been particularly cold. But even if a sudden spike of warmth brings a pulse of eels along the banks, the conservationists would be worried.
“The eel is at a historical all time low. So even if we see a slight increase, we’re pleased but still massively concerned about the species,” said Dr Matthew Gollock, a biologist with ZSL. Scientists believe the number of eels reaching freshwater has declined by up to 95% over the last 30 years across Europe.
Low supplies means that the old East End staple of jellied eels is getting harder to find. “They’ve been over-fished for a long time and have been threatening to disappear completely for the last couple of years but they haven’t. We’re still getting supplies of them but they are constantly going up in price and when we enquire as to why it’s a case of they are in very short supply” says Geoffrey Manze, owner of the oldest pie and mash shop in London.
Demand for eels is not the same as it used to be either. In his grandfather’s time the shop used to sell hundreds of portions a day, now that number is reduced to only a handful. “There’s no profits in eels but it is something that’s part of a pie and and mash shop. It wouldn’t be the same place without them.”
Overfishing is only one of the reasons believed to be behind the decline. Increasing barriers to upstream migration, freshwater habitat loss, pollution, changes to the oceanic currents and a parasite are all thought to be contributing to their decline. The eels migrate across huge swathes of international waters and what can be done in the UK to protect the species is limited.
It’s thought that the eels spawn in the Sargasso Sea and that the larvae float back on the ocean currents to continental shores and enter rivers across Europe to migrate upstream. It can take up to 20 years of maturing in freshwater habitats before the eels are ready to make the 6,500km trip back to the Sargasso, where they spawn once and then die.
Their huge migration is proof of the eel’s hardiness. It was one of the first species to return to London after the River Thames was declared biologically dead in the 1960s, even though the river remained heavily polluted. “I think that when a lot of people first see an eel, they think it’s like a snake and that it is horrible… but I think people grow from being slightly disgusted by it to being zealous about it when they realise what an amazing animal it actually is,” says Dr Gollock.
Enthusiasm for the eel’s toughness is infectious and groups of volunteers are now helping with the eel monitoring. With extra help from Londoners, there are plans to expand the scheme to look at the adult eel as it makes its one way trip to the sea. “Hopefully we’ll get some idea of numbers so we can start to build a wider picture which we can feed into management strategies” says Rebecca Short, programme coordinator for marine and freshwater conservation at ZSL.
Scientists think the eel is tough enough to stumble on in low numbers without help but for an animal that resists so much and comes so far, it’s a risk that conservationists and many Londoners are unwilling to take.
© Camila Ruz 2012