The Croneen Story - The Tale of a Genetically Unique Trout

By Dr Fran Igoe

Native trout heritage on the Shannon

Over the last two years the Shannon Regional Fisheries Board has been reassessing the importance of our native brown trout heritage in the Shannon catchment. Recent developments in fisheries management and advances in genetics indicate that we must be more careful how we manage our wild trout populations to avoid problems associated with inbreeding and lowering genetic fitness.

Until recently it was believed that the trout in the Shannon catchment were all the one, i.e, the same variety of brown trout. It was not generally thought that we had genetically distinct stocks as has been shown for Lough Mask or Lough Melvin. However this view has changed as the ShRFB has investigated this matter more thoroughly and consulted with local angling clubs and interests. Below is a general account of one of our better known trout varieties, the Croneen.

The study of the Croneen trout was initiated by the ShRFB with the direct assistance of the Little Brosna and Camcor Fishing Club. This study has grown to involve the expertise of both Marine Institute and Queens University. This collaborative exercise could be called catchment management at a scientific level.

 So what is a Croneen trout?  The Croneen is a fresh water migratory brown trout which spawns in the Little Brosna and Camcor and migrates to Lough Derg to feed.  Other populations are known from other rivers draining the Lough Derg catchment but these have undergone a decline due to habitat degradation (poor water quality, drainage etc).This silver torpedo-shaped trout can gain weights of over 4lb and is very popular with anglers. The presence of the Croneen has been known by local people in the Birr area and many anglers throughout the country for some time. However it is the recent study in the genetics of the fish that has grabbed people’s interest.

ON SATURDAY 7^TH DECEMBER 2002,  Mr Tom Parlon TD, Minister of State at the Department of Finance with special responsibility of the Office of Public Works, launched a public information board on Croneen trout. 

The Minister, in welcoming this initiative by the Birr anglers, stressed the importance of maintaining the biodiversity of the region.  This can be achieved through increased public awareness and appreciation of our local heritage.  It is hoped that today’s project will lead to a greater public participation in conserving our environment and encourage the people of Birr and its surrounds to take pride in their locality.

The event which took place in Birr on Saturday at Camcor Park was attended by over seventy people from all ages (4 months to 81 years of age). Such a good turn out of all ages on a freezing cold Saturday afternoon shows just how important the local community views the Croneen trout. A talk on the Croneen in the Country Arms Hotel was given immediately afterwards by Dr Fran Igoe of the Shannon Regional Fisheries Board.

It’s all in the genes: The Croneen trout – How Unique are they ?

What every body is asking about concerns the recent study on the genetics of the fish? However before discussing the genetics we must realise that current scientific thinking at the highest level is reassessing the traditional notion of all our trout belonging to one single species, the brown trout. Indeed advances in genetics and DNA techniques show that trout such as the Gillaroo, Sonaghan and the ferocious predator the ferox trout are indeed distinct species. This point is very important from a conservation and a heritage point of view not to mention a management point of view. Additionally it has been shown that many of our lake trout populations in particular belong to races or “conservation units” that must be protected as they have evolved and adapted to suit the conditions to the lake and river sometime after (and in some cases before) the last Ice Age, 13,000 years ago. The facts that they ‘home’ to their place of birth on the river ensure that they do not mix. This is why we must be very careful when we interfere with rivers and their trout.

The Croneen has been shown to be very unique and one of the most distinct forms in Ireland.

“Current microsatellite (sophisticated genetic analysis technique) data show that the Croneen were incorporated in a study of the phylogenetic (family tree looking at genetic characters) relationships of trout from a wide number of Irish lakes and they were found to be among the most highly differentiated (i.e., very unique) and therefore deserving of considerable conservation efforts. Of that there is no doubt.” Niall McKeown, Queens University Belfast.

Queens University under the stewardship of Prof. Andy Ferguson, are continuing the study of the Croneen using what is known a mitochondrial DNA. This DNA is only inherited along the maternal line. The plan is to relate the Croneen with samples taken from other lakes, from Lough Melvin, to Lough Mask to the Killarney Lakes.  What is coming out so far is very interesting. It appears that Irelands native fish fauna is much more diverse and interesting that previously thought. This should change how we see our fish heritage and how we manage them. Even that insignificant little stream outside your door could actually be more important than you think. In a way Ireland has been fortunate in that it has escaped most of the environmental destruction experienced by our European neighbours, and many of our native trout populations are relatively intact. The Croneen is a good example of this. Mr. Niall Mc Keown commended the local anglers for the extremely high quality of the samples and full credit should go to Mr John Smith and his friends

Where did the word Croneen originate?

An interesting aspect to the Croneen story is the origin of the name. We have searched widely to try and get an explanation on the origin of the name of the fish. One line of enquiries suggests that the name come from the Irish, Cronín, meaning the little brown or yellow one. Indeed we contacted Dr. Michael Kennedy, formerly of the Inland Fisheries Trust and he said that they had assumed it had something to do with the colour of the fish. This may indeed refer to the fish in spawning condition, which would be a dull brown. However during the main run the fish are definitely silver. So is this really the origin. Maybe the fish were only accessible to the local Gaelic speakers over their spawning beds. This is quite probable, as other fish such as salmon were often taken in this manner. However another likely explanation is that the Croneen was infact named after a person. Croneen is infact the Gaelic version of Cronin. The name Croneen was very common in parts of Cork and there was even a place called Croneenstown. However its association with Birr appears to be remote. 

Biological Analyses.

A summary of the more important biological findings may interest the readers. Scientific investigations by the Shannon Regional Fisheries Board and the Marine Institute on the Croneen over the past two years show the following results. The local anglers collected over 90 specimen samples, which includes a donation of  20 rod caught fish from the Camcor River itself.

The majority of fish analysed in 2002 were 3+ and 4+ years old i.e fish in their 4^th and 5^th year of growth. Most spend 2 years in the river and then migrate down to the lake. Growth is initially very fast, but then slows down as the fish mature. Maturity occurs in the third year. Some fish sampled were almost 6 years old, it is likely that a few may reach a greater age.

Examination of the parasites was interesting. Only two species were found, one a nematode (parasitic roundworm) and the other a cestode (tapeworm). The prevalence of the cestode was greatest suggesting that the fish were feeding on this parasites intermediate host, called copepods. These small plankton live in the lake water feeding on small algae or phytoplankton. From this we can deduce that it is probable that the fish are mostly pelagic (like mackerel at sea) they feed on small crustaceans (water fleas etc.).

The fecundity of the average fish ranged from about 300 to 500 eggs per female in the fish examined.

 Where do we go from here ? 

The Croneen as a unique species has significant heritage, glacial and recreational value and therefore requires rigorous protection. The work undertaken by the Little Brosna and Camcor Fishing club in collaboration with the Shannon Regional Fisheries Board should be continued to help us develop a clearer picture of the Croneen and to employ the necessary conservation measures to protect the species and their habitat over the coming years.  

The Shannon Regional Fisheries Board run periodic environmental and fisheries awareness workshops and field trips. Over 2003 we will announce these on our website and local papers for those who wish to attend. 

The Shannon Regional Fisheries Board has collected tissue samples from the other major lakes on the Shannon including Loughs Ennell, Rea, Owel and Allen, with the assistance of the Lough Ree Angling Club and the Central Fisheries Board. 

For further information contact Assistant Fisheries Inspector Ms Lorraine O’Donnell Shannon Regional Fisheries Board Tel: 061 300238 or Mr Brian Mc Manus, Angling Section Tel 061 21777.

Email info@shannon-fishery-board.ie

Links: Use the drop down menu to access our links on Catchment Management Projects and other fisheries projects undertaken by the Board

Migration Route of the Croneen - click map

Catchment Management