independent

Saturday 24 August 2019

Endangered eel population in serious decline

JIM HURLEY

IN THE latest Red List produced by the National Parks and Wildlife Service, the status of the European Eel in our waterways is rated as 'critically endangered'. The Eel is not the most handsome of creatures and is one of those species that is either loved or hated. Its population size has suffered a sudden and very serious decline in recent years not just in Ireland but throughout Europe. Why numbers of the once common fish have declined so rapidly is poorly understood.

It is known that mature adult Eels leave our waterways each autumn and head out into the Atlantic Ocean to go somewhere to breed. Where exactly they go to have their young is not clear. Most of the migrating fish are too small to carry the very sophisticated but large satellite tags needed to track their movements. Only an estimated one in a thousand fish is big and bulky enough to carry these tags that are designed to pop off, float to the surface and transmit their information to satellites to be relayed home to researches sitting in their offices.

Eel eggs would pinpoint breeding sites but they have never been found. However, very young Eels have been caught in the Sargasso Sea near the Gulf of Mexico so it assumed that the adults must breed there or thereabouts.

Wherever they breed, the number or juvenile Eels returning from the breeding grounds to Ireland has declined dramatically. The decline is so great that it is classified by fishery scientists as "outside safe biological limits". Continued commercial fishing for Eel became unsustainable and in 2009 the fishery was closed with a review of the commercial fishing ban promised in 2012. Those Eels that do return to our waterways can be long-lived; some exceptional individuals are known to live to over fifty years of age.

So, where have all the Eels gone? The number returning from the ocean is now less than seven percent of the pre-1980s averages. The reason for the decline is unclear but suggested possible causes include climate change and shift in ocean currents, overfishing, habitat loss in the freshwater range, mortality in hydropower plants, disease and parasites, and chemical contamination affecting reproductive ability.

Whatever the reasons turn out to be, only time will tell if the 'critically endangered' European Eel makes a comeback in our waterways.

The Red List referred to above is available online at http://www.npws.ie/publications/redlists/RL5.

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