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Sea lamprey in Irish RiversThe return of adult Sea Lampreys to spawn in Irish rivers is an annual event. Adults begin entering fresh water as early as April but chiefly during late May and early June. These eel-like fish can be up to 90cms long and mottled brown in colour on their upper side. They are characterised by having a sucker-like mouth instead of jaws. On return to freshwater they begin to construct large redds or spawning nests in shallow, fast-flowing stony sections of channel, known as riffles. The lamprey move cobbles and small stones to excavate a bowl-like structure. Up to several adults at a time may be seen moving stones with their sucker mouths or using their tails to disperse finer sediments. In addition, individuals may often be seen in fast flowing water attached to rocks with their sucker. Spawning occurs throughout June, with the adult fish dying immediately afterwards. The redds are large structures, over 1 metre wide and up to 50 cm deep. Where a lot of spawning is taking place, redds may be excavated side-by-side and wide sections of channel are used. The redds can be distinguished by their size and by the mound of freshly-turned cobble and gravel on the downstream side of the hole. This fresh gravel will be much lighter in colour than the surrounding undisturbed bed material. Sea lamprey like to travel long distances upriver to spawn. However, man-made structures such as weirs and dams can prevent upstream migration of returning Sea Lampreys, and aggregations of these fish may often be noted at the bases of these barriers. Thus, sea lamprey are regularly seen downstream of the weirs at Annacotty (R. Mulkear), in Ennis (R. Fergus), Clonmel (R. Suir).
While Sea Lamprey are well-known from sections of some rivers, such as the Ridge Pool on the Moy and the Galway fishery on the Corrib, less is known of their presence in other parts of Ireland, particularly in the South, South-East and East of the country. Knowledge regarding their return to other rivers throughout Ireland is poor and in urgent need of updating. We are anxious to collect information on the distribution of Sea Lamprey spawning rivers and you may be able to help! The easiest place to look is from a bridge, where you have a good view up- and downstream of the channel. If the channel has a good stone bed and little instream weed, watch out for signs of redds and of Sea Lamprey in them. Things to watch for are:
What to do: If you see Sea Lamprey or signs of their presence in a river near you please contact us. We would appreciate information regarding:
Contacts:Email:
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Video of sea lampreys building redds
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Predation by Otters at this time is commonplace, with Sea Lamprey remnants visible along river banks and at bridges and weirs. Carcasses of spent fish may also be noted on the river bed or floating downstream.