Really good news as elver population grows

THIS year, the number of elvers swimming up UK rivers and waterways was 20 times the norm of recent decades. This is good news.

Already, 660,000 Severn elvers have been donated for re-stocking English rivers, and this figure will rise. UK rivers will be healthily stocked with eels for the next six to 10 years. Elvers need to be taken out of the Severn and relocated because flood barriers are so effective they would be unable to reach other streams and tributaries and would perish. Eel-depleted rivers in Sweden, Denmark, Holland, Germany, Latvia and Lithuania also receive elvers from the Severn.

Over the past few years, a general increase in elvers reaching Ireland has been recorded in index sites on the west and east coasts, along with witness accounts of elver migration on the Bandon, Boyne, Corrib, Erriff and Burrishoole Rivers.

Populations of the European eel (Anguilla anguilla) began to crash in the 1970s. By 2010, the numbers of elvers arriving in freshwater habitats in Europe had fallen by 95%. By Oct 2011 the species was classified on the All-Ireland Red Data List as Critically Endangered, our most threatened native fish species.

The fishing of the tiny glass eels that arrive from the Atlantic annually, along with environmental pollution and other human impacts, have all contributed to a significant decline in eel numbers over the last quarter century. Glass eels are considered a high-premium delicacy in Asia, and tens of tons are shipped there each year. Similarly, for some restaurants and supermarket chains in the UK, eels are meals, and an increase in numbers will simply mean more eels on the menu.

Food tastes in Britain and Ireland have become more exotic and in the UK there has been a surge in demand for jellied eels, once considered to be a salty goo appealing only to Cockneys and East Enders. Now, Tesco sells them in 300 outlets and sales have increased by 35% over the last two years.

Many eels on the market were raised in farms; however the industry is still totally dependant on wild-caught juveniles (ie glass eel) caught during their migration up estuaries along the Atlantic coast. The majority of these will never return to the Sargasso Sea, which may or may not be their exclusive breeding ground. Why the sudden surge in elvers has occurred is not understood. Much of the European eel’s life-cycle remains a mystery. Popular belief has it that our eels breed in a great ball of Sargassum seaweed drifting in the Caribbean. Some eel species spend their entire lives slithering through that seaweed forest but the tiny, leaf-shaped larvae of the European eel drift away and are carried 5,000km by the Gulf Stream currents to our rivers.

Larval European eels have been found in the Sargasso Sea — but no adult European or American eel, or its eggs, has ever been found there.

A major initiative to track adult eels’ journey back to their breeding ground was undertaken by the 2008 to 2012 EU and national government-funded EELIAD project (European Eels in the Atlantic: Assessment of Their Decline). The pan-European quest to find the breeding ground had begun in 2006, led by the Danish Fisheries Institute.

The first task of the participating Irish biologist, Dr Paddy Gargan, was to find 22 eels big enough to carry the tags, valued at €4,000 and the size of a small flashlight, across the Atlantic against strong, adverse currents.

The requirement was for eels over one metre long. Females were more likely to fit the bill than males, having a maximum recorded length of 133 cm (4.4 feet) and weight of 6.6kg. Between 2008 and 2012, the project attached 500 tags to eels leaving European rivers, monitoring the direction and depths at which they swam. The tags, programmed to come adrift, floated to the surface and relayed information to a satellite. Migration was mapped to beyond the Azores, some 3,000km, and for a duration of six months.

It is good news that the EU has recently proposed a plan to reduce the current harvest levels for all life stages and to improve the access and quality of freshwater habitats. The objective is to ensure that 35% of glass eel catches are reserved for restocking of EU waterways, this to rise to 60% in 2013.

More in this section