Mysterious lives of conger eels

THE other day I got a chance to talk to a marine biologist who’s an expert on conger eels.

They’re a very interesting fish so I was keen to learn more about them. I was particularly interested because last July a diver swimming 25 metres below the surface of Killary Harbour was subjected to what appears to have been an unprovoked attack from a large conger which severely damaged his face and came close to costing him his life.

All large congers around the Irish coast are females and they are the largest eels in the world, capable of growing to at least 2.2 metres in length and 60kg in weight. Males never exceed more than a couple of kilos. The Killary attack, which received some lurid publicity in the media and on the internet was, according to the expert I spoke to, completely out of character.

Congers are predators but they are virtually blind, hunting by smell, usually at night. During the day they tend to hole up in a rock crevice and doze. The biologist knew of quite a few of these dens and frequently dived on them. He got acquainted with the congers that lived in them and became intimate enough to give them a friendly scratch under the chin. He said they were gentle, shy creatures and if you met one in open water it would just swim quietly away from you.

This was very different to the preconceptions I had from talking to other divers, commercial fishermen and sea anglers.

They live on rocky shores around our coasts, and also on offshore wrecks and reefs, preferring water 20 to 30 metres deep. At the end of 10 or 12 years they undergo strange physical changes, particularly the female eels. They swell up as their reproductive organs enlarge enormously, their skeletons start to dissolve, their teeth fall out and they stop eating.

They then swim out into the mid-Atlantic, meeting up with other congers from all over Europe at a spot near the Azores. There they mate and die. The baby eels then make their way thousands of kilometres back to Ireland to start the whole cycle over again.

How this odd life cycle first developed and what evolutionary advantage it offers the eels is a mystery. And the fact that they are a shy and non-aggressive species, according to someone who knew what he was talking about, came as a surprise to me. We have a tendency to demonise other species, persecute them and then discover that we were wrong all along. A century ago eagles were branded as vermin and exterminated in this country. Now we’re expending a lot of effort and money trying to re-introduce them.