Author: Ruairí Ó Conchúir, project manager, MulkearLIFE MulkearLIFE is a five year, partnership-based project working on the restoration of the Mulkear River catchment, which forms part of the Lower Shannon Special Area of Conservation (SAC). It is one of the most important integrated catchment management projects in Ireland and a flagship EU co-funded LIFE Nature project with a €1.75 million budget. Inland Fisheries Ireland is the lead partner, working with the Office of Public Works (OPW) and Limerick City and County Council, with additional funding from the National Parks and Wildlife Service. The main objective is to restore, through in-stream rehabilitation works, degraded habitats along stretches of the Mulkear River and its main tributaries – the Newport, Bilboa, Dead, Clare-Annagh and Killeengarriff rivers. While the key target species are Atlantic salmon, sea lamprey and otter, the project actions benefit a wide range of other fish species, invertebrates, birds and mammals by creating habitat complexity, thereby greatly enhancing the overall biodiversity of the region.
[caption id="attachment_18121" align="aligncenter" width="821"] Sea lamprey passing the Annacotty weir - Mulkear River[/caption]
Degradation and loss of instream habitat, due to river drainage works dating back to 1874, has had a negative impact on the project’s target species. Drainage schemes, both recent and historic, have prevented rivers from recovering to a more natural state. Consequently, MulkearLIFE has implemented various habitat rehabilitation techniques to mimic natural conditions and create habitat complexity. Techniques including the installation of rubble mats, random boulders, paired deflectors and vortex stone weirs all help to break-up uniform habitat. Rubble mats, for example, are a useful feature when introduced to rivers that have been subject to past drainage work. They essentially mimic natural riffle areas, which were present pre-drainage. The construction of a rubble mat on the river bed reduces the cross-sectional area of the river, thereby increasing flow velocities at low summer flows. On the Mulkear River, individual mats have utilised up to 250 tonne of rock per mat, using rock which is generally 15 to 25cm in diameter and creating an interlocking top cobble layer. This results in important ecological changes on this top layer. The faster-flowing area on top of the rubble bed is quickly colonised by aquatic vegetation. In addition, a considerable variety of invertebrates favour such conditions and will colonise the rubble mat in significant numbers. This level of colonisation happens very rapidly (within months). More importantly, the fast-flowing nature of the water over the rubble mat provides exceptional habitat for young salmon and trout and, with invertebrate colonisation having taken place, provides such fish with ample food supplies.