Catchment News

The Lough Derg Native Fish Biodiversity Project: unlocking our hidden underwater biodiversity through a locally led large scale citizen science project

Ireland’s freshwater fish fauna represent some the most unique aspects of our native biodiversity. Unlike some of our other “native species” there is no issue with regard to how they arrived to Ireland towards the end of the last Ice Age some 20,000 years ago. It is even possible that some fish species may have survived the last cold period nearby in glacial refugia further south. Either way once the ice retreated, anadromous or sea run populations of salmonid species such as Brown trout, Atlantic salmon and their distant cousins Arctic char colonised Ireland, in waves, from different areas of Europe; lineages which are still represented in many populations in Ireland today. In addition, further genetic differentiation occurred as salmonids generally head home to their natal streams – so over time genetic traits that conferred a survival advantage to specific populations became fixed.

Today the genetic biodiversity of Irish native salmonids is high and some forms are even unique to Ireland. It was in this context and amid concern for Lough Derg as a fishery and its declining trout population that the Lough Derg Native Fish Biodiversity Project was initiated.

The project commenced in 2006, and has been a collaboration between Lough Derg Angling Federation and its constituent 13 local angling clubs, the Irish Char Conservation Group, Inland Fisheries Ireland Limerick (formerly Southern Regional Fisheries Board), ESB, Lough Derg Sub Aqua Club, Lough Derg Science Group, Queens University, University of Waterloo, Canada and North Tipperary County Council. The project was originally coordinated by the Shannon Regional Fisheries Board and subsequently managed by the Irish Char Conservation Group.

Community Citizen Science

The project is a great example of a large scale community led project involving citizen science in an effort to get quality information that can be used to support good planning and management. In addition the information is interesting in its own right and shines an extra light on what is part of our unique natural and cultural heritage.

The project was initiated by the anglers, who wanted to find out more about the fish in the lough, and they had a number of specific queries. For example anglers wanted to know if the different “types” of trout that they had been catching, which looked different from each other, meant anything from a taxonomic point of view. In other words are there different species of trout in the lough?

Lough Derg species of trout, whitefish and pollan

Could it be possible that there might even be different species of trout within the lake like the trout in Lough Melvin, which has three distinct species? A number of other issues arose, such as do the Gillaroo trout still exist in the lake? The Gillaroo is an unusual species of trout which has deep red spots. They feed primarily on snails and other invertebrates with hard shells, giving their stomachs the appearance of a gizzard. They are only known from a few other lakes in Ireland. It is documented that back in the 1700s, the Bishop of Killaloe dined on the gizzard of the Gillaroo trout, and that it was one of his favourite dishes.

Another form of trout known as the Croneen trout, which spawns in the Camcor and Little

Derg, with these adults then migrating back up the Shannon to these rivers in a catchment area around Birr, Co. Offally. The Croneen is an unusual trout in that it looks and behaves like a sea trout but never goes to sea.

Other questions that the anglers and other stakeholders wanted answers to included did the unique Irish whitefish (probably an endemic species to this country) known as the freshwater pollan still occur within the lake? The lough once supported a commercial fishery for this species but they had not been recorded for a number of years. Anglers also wanted to know more about a landlocked form of parasitic lamprey that attached itself to trout. What species was it, and was it damaging the trout fishery?

Collecting and surveying

The anglers were given specific tasks to do. These included the collection of fish tissue for genetic analysis, the taking of fish scales for aging purposes, photographs for morphometric and meristic analysis and collection of macroinvertebrate and plankton samples to be processed for stable isotope analysis. Notices were put in the local press and signage placed around the lake and in local shops to encourage visiting anglers and non-club affiliated anglers to participate. The anglers also carried out additional fish surveys which allowed a comparison between current fish stocks with historic figures available prior to the construction of Ardnacrusha Dam at the outflow of Lough Derg. Funding was accessed through a range of sources.

IFI and ESB collected juvenile fish samples from all of the streams flowing in to the lough where the trout spawn, in addition to the Camcor and Little Brosna Rivers where the Croneen trout spawn. The Lough Derg Subaqua Club divers took benthic samples and Lough Derg Science Group also took plankton samples and provided identification of macroinvertebrate samples. The project recorded the first record of the invasive crustacean species Gammarus tigrinus which was found in large densities at depth within the lough (perch have been feeding heavily on them!). The EPA funded the trout genetics element of the programme. The University of Waterloo carried out the stable isotope analysis. Funding was acquired for a number of project actions including the placement of a fish counter on the Nenagh River. This is the 1st and only fish counter counting migrating freshwater trout in Ireland.

A massive effort was undertaken by all involved. 1969 lake trout samples were recorded. The fish survey found that:

• Pollan exist within the Lough, albeit a very small population – only 1.5% compared to 1920 figures.
• Regrettably, no record of Gillaroo trout has been established and it appears that this trout “species” is extinct within the lough.
• The lamprey that are feeding on trout are in fact juvenile sea lamprey which are feeding off fish opportunistically as they migrate downstream to the sea.

The project established that the juvenile sea lamprey also attack other fish species including roach and bream. It is likely that these lamprey are the progeny of a few adult lamprey that had escaped through the Dam at Ardnacrusha. Subsequent work using eDNA (analysis carried out by UCD) collected by the project, established the presence of sea lamprey in a number of tributaries flowing into Lough Derg, suggesting that these may be the location of the sea lamprey spawning grounds. This is a significant result as heretofore it was unknown where they might spawn and the data tallies with anecdotal information collected by the project.

The trout genetics are currently being reported on and form a significant body of work which will be published in the scientific literature and will change how the management of the lake trout is conducted in the catchment. Initial results do suggest that the trout within Lough Derg are genetically diverse and require appropriate management strategies to reflect this fact.

The project is ongoing and information generated to date is the result of the participation of many individuals and organisations (both state and nongovernmental), in the spirit of collaboration and genuine interest in the conservation of the native fish biodiversity in the lough.

Fran Igoe, voluntary scientific advisor to the Lough Derg Native Fish Biodiversity Project for almost 10 years.