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Coregonus autumnalis pollan Thompson
Pollan is a glacial relict of an Alaskan-Siberian whitefish species and is not found anywhere in Western Europe outside of Ireland. It is a good example of the importance of correct taxonomy in determining conservation importance. For most of the twentieth century, pollan was regarded as one or other of two coregonid species found in Britain. However, molecular studies in the 1970s showed conclusively that it was C. autumnalis, but that there were sufficient differences to regard it as a distinct subspecies C. a. pollan. In a recent revision, Kottelat has suggested that it should be designated as a full species C. pollan rather than a subspecies, which would make it an endemic Irish species. Further work is required to validate this proposal. Irrespective of its exact classification, pollan is one of the most unique elements of the Irish fauna. Pollan entered the Shannon system as a migratory fish at the end of the last Ice Age, some 14,000 years ago, and from there it spread to Loughs Erne and Neagh, all of which were interconnected in the period of glacial retreat. As the sea temperature and salinity increased, pollan lost its migratory habit and became restricted to freshwater. However, pollan have been found in the Erne estuary at Ballyshannon and downstream of Coleraine on the Lower River Bann. Since Neagh, Erne and Shannon (Ree and Derg) stocks have been isolated for over 10,000 years, undoubtedly genetic differences have evolved among them as a result of adaptation to local conditions and by genetic drift. There is also some evidence of distinct populations within Lough Neagh, presumably maintained as a result of natal homing to separate spawning areas.
Pollan is a silvery trout-shaped fish, with a dark greeny-blue back. Superficially, it resembles a herring but is easily recognised due to the presence of the diagnostic salmonid adipose fin, a small fleshy dorsal fin just in front of the tail.
Pollan spawn in December and January in shallow rocky areas of the loughs where wave action provides good oxygenation for the developing eggs. The young fish feed on animal plankton and on larger invertebrates as they grow older. $Mysis relicta$, a glacial relict crustacean, is an important food source in Lough Neagh, as are the abundant larvae of chironomid midges. Spawning takes place from about three years of age and individuals can generally live for about five years, although a seven-year-old has been recorded from Lower Lough Erne.
There are no similar freshwater species present in Ireland but two related whitefish species are found in Scotland, Cumbria, and Wales, although several populations of these have become extinct in recent decades.
How to see this species
Lough Neagh pollan are fished for commercially and can be seen as fishermen land their catches at various quays around the lough. They can be bought in some fish markets and shops during the fishing season (March to October). Pollan sometimes move down the Lower River Bann and they have been caught by anglers downstream of Coleraine.
Although still common in Lough Neagh, pollan is no longer found in Upper Lough Erne and has become very rare in Lower Lough Erne since the 1970s. It was abundant in Lough Erne in the early part of the twentieth century where it formed the subject of a substantial commercial fishery. Exploitation of Lough Neagh pollan is controlled by Fisheries Legislation, enforced by the Fisheries Conservancy Board Northern Ireland.
Why is this species a priority in Northern Ireland?
Pollan is not found anywhere else in Western Europe outside Ireland
Threats/Causes of decline
Pollan require water with a good level of oxygen and so eutrophication, due to nutrient enrichment, and climatic warming are major threats, especially in the deeper lakes where oxygenation due to wind-mixing is reduced. The other major threat is increase of non-native species such as pike, roach and zebra mussel, which have been linked to the decline in Lower Lough Erne, possibly as a result of predation and decline in zooplankton availability. The recent introduction of zebra mussel into Lough Neagh presents a serious threat to pollan in this lough.
Conservation of this species
An all-Ireland Species Action Plan was published in 2005. There is also a UK Species Action Plan which was published in 1995.
What you can do
Support the restoration of Northern Ireland lakes to high water quality status. Help prevent the further spread of zebra mussels within Lough Neagh.
Text written by:
Professor Andrew Ferguson