A Pioneering Study of the Genetic Makeup of Brown Trout stocks in the Suir Catchment.

Press Release February 3rd, 2012

Inland Fisheries Ireland (IFI), with the assistance of the Office of Public Works, population geneticists from University College Dublin and Irelands trout anglers have commenced a study of the genetic makeup of trout stocks in Ireland’s larger riverine catchments. The first two catchments to be examined were the Suir and Boyne in 2011 and the results are now available.

Scientists refer to this type of study as a “micro-satellite DNA analysis”. In layman’s terms this means that a chemical analysis of scale samples from the fish can reveal their genetic makeup - a similar process to that used by police forces worldwide to identify criminals.

In the case of the Suir, trout stock samples of young fish from all of the major tributary sub catchments were examined genetically. The analysis showed that, in genetic terms, the young trout from these different rivers were discrete –i.e. young fish from the Drish were genetically different to those in the Anner, or the Tar, or any other tributary.

The next stage in the process was to examine samples of adult fish from the main stem of the Suir itself and to relate these back to the tributary “genetic types”. At this point IFI sought the assistance of the angling club members along the Suir from Templemore downstream to Carrick-on-Suir. Anglers were requested to take a few scales from any fish they caught ,place them in an envelope and record the date of capture, capture location and the length of the fish on the individual envelope. Many of the fish scaled were returned alive by the anglers once these details were collected. The enthusiasm of the anglers was key to the success of this project. They collected hundreds of scale samples from trout right along the Suir from Loughmoe almost downstream to Carrick-on-Suir which were subsequently analysed genetically.

The results are quite amazing and of very significant value to IFI in managing the Suir which is Ireland’s premier riverine brown trout fishery. A brief summary of the findings are as follows;

There are seven different families of trout in the catchment (Figure 1).Although some families live in more than one tributary a more detailed analysis allowed one to distinguish the fish from individual tributaries.
There is no discrete stock of trout which are born and subsequently spend their entire life in the main stem apart from one family which are born in the headwaters north of Thurles. Apart from this group all of the adult trout caught by anglers in the main stem could be traced to one of the tributary stocks. In other words some fish born in tributaries migrate to the main stem, live there until adulthood, subsequently returning to their tributary of origin to spawn.
The contribution of fish from individual tributaries to the main stem stock is very variable and bears no relationship to the size of the individual sub catchment (Figure 2). For example fish from the Nier River make up 22.5% of the main stem adult stock. In contrast no fish from the Anner or Ara rivers were found in the main stem sample even though we know that both of these rivers support large trout stocks. These fish are staying at home!!
The movement of young trout, after leaving a particular tributary and entering the main stem, is quite extraordinary. Two examples are provided (Figures 3 and 4). They illustrate that an angler fishing in Holycross, Golden, Cahir or Clonmel is actually catching fish which were born in streams as far apart as Borrisleigh, Twomileborris, Clogheen or Ballymacarbry! These data also show that young trout entering the Suir are just as likely to travel upstream or downstream.
The results show clearly that the trout fishery in the Suir is one large complex fishery reliant on contributions from many of its tributaries.

Contribution of tributaries to main stem stock

Locations of Multeen trout caught by anglers

Locations of River Nire trout caught by anglers

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Media Enquiries:

Suzanne Campion
Head of Business Development
Inland Fisheries Ireland
Anglesea Street,
Clonmel, Co. Tipperary.
Tel: 052 6180055 Fax: 052 6123971
Email: suzanne.campion@fisheriesireland.ie Website: www.fisheriesireland.ie

Notes to Editor

Inland Fisheries Ireland is a statutory body operating under the aegis of the Department of Communications, Energy and Natural Resources and was established under the Fisheries Act on 1st July 2010. Its principal function is the protection and conservation of the inland fisheries resource. IFI will promote, support, facilitate and advise the Minister on, the conservation, protection, management, development and improvement of inland fisheries, including sea angling and develop and advise the Minister on policy and national strategies relating to inland fisheries and sea angling.