A Pioneering Study of the Genetic Makeup of Brown Trout stocks in the Boyne 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 Boyne, trout 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 Stonyford were genetically different to those in the Skane, the Knightsbrook, or any other tributary.

The next stage in the process was to examine samples of adult fish from the main stem of the Boyne 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 Boyne. 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 Boyne from Inchamore Bridge near the Hill of Down downstream to Broadboyne Bridge, a point half way between Navan and Slane. These samples were subsequently analysed genetically.

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

There are five 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. Two different families were identified in one sub catchment (Kells Blackwater).
There is no discrete stock of trout which are born and subsequently spend their entire life in the main stem. 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 trout born in three tributaries in the middle reaches of the catchment (Stonyford, Trimblestown and Knightsbrook) made up 63% of the main stem stock. In contrast the trout in the Kinnegad, Monga, Deel and Kells Blackwater make little or no contribution to the main stem population. These fish are staying at home!!
The movement of young trout, after leaving a particular tributary and entering the main stem, is quite extraordinary (Figures 3).They illustrate that an angler fishing in the Boyne is actually catching fish which were born in streams as far apart as Longwood, Clonmellon, Kilmessan or Moynalty. These data also show that young trout entering the Boyne are just as likely to travel upstream or downstream.
The trout stock in the Mattock is very different to all other populations in the system and, in genetic terms, seems to be an isolated stock. This suggests that they are a sea trout population functioning independently to the rest of the trout stock in the catchment.
The results show clearly that the brown trout fishery in the Boyne main stem is one large complex fishery reliant totally on contributions from many of its tributaries.
In management terms these data will help in pinpointing the less productive parts of the catchment which would benefit from enhancement programmes.

5 trout groups in the Boyen, 2 in the Kells Blackwater

Contribution of tributary trout stocks to the main stem

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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.