River Roe and Tributaries ASSI

The area is of special scientific interest because of the physical features of the river and its associated riverine flora and fauna. The River Roe and Tributaries ASSI includes the River Roe and its tributaries the Curly River, the Gelvin River, the Bovevagh River (and its tributary the Altahullion Burn), the Wood Burn, the Owenbeg River (and its tributary the Clogherna Burn), the Owenrigh River, the Black Burn (and its tributary the Currawable Burn) and the Owenalena River.
In total, the area encompasses approximately 87km of watercourse and is notable for the physical diversity and naturalness of the banks and channels, especially in the upper reaches, and the richness and naturalness of its plant and animal communities, in particular the population of Atlantic salmon, which is of international importance and in the extent of upland oakwood present.

Atlantic salmon are widely distributed in the north Atlantic Ocean. Within Europe, the species ranges from Portugal in the south to Sweden and Finland in the north. However, numbers are declining and the salmon population of the United Kingdom comprises a significant proportion of the total European stock. Although the species is still widespread in the UK, being found in several hundred rivers many of which have adult runs in excess of 1000, the latest estimates of the UK spawning population are approximately 50% down on the ten-year average.

It is estimated that the number of returning salmon entering the river system included within the ASSI is in excess of 4,000, which is 8% of the Northern Ireland spawning population and making the River Roe and Tributaries one of the most important salmon rivers in the British Isles.
Recent micro-satellite DNA analysis of stocks within the Foyle area (Booth, 2003) has provided evidence for population differentiation within the River Roe catchment. The main run of fish occurs during the summer months with significant numbers also entering in the autumn. The River Roe and its tributaries are among the most productive rivers within the Foyle area while the typical timing of spawning is later than most other rivers within the Foyle area, typically occurring from mid/late December to the end of January. The River Roe also has a considerable run of migratory sea trout.

The fish community reflects the extent and diversity of the river system. As well as salmonids, which include brown trout and Atlantic salmon, the fast-flowing waters support stone loach, minnow, eel and 3-spined stickleback. Sea Lamprey are also known to migrate into the lower reaches of the River Roe, where the flow is less dynamic, to spawn. Downstream sections also contain euryhaline (fish that can survive both in freshwater  and seawater) and marine species such as flounder.

Such an abundant fish resource attracts predators, with otter signs, in the form of spraints, found along the whole length of the River Roe and its main tributaries but occuring most frequently in the upper reaches of these watercourses.

The area is also important as a river habitat. In their upper catchments, the tributaries are all fast-flowing spate rivers with dynamic flow regimes, characterised by sequences of riffle ( a shallower area with faster flowing water and larger sediments) and run ( an intermediate category between pool and riffle) with occasional cascades, water falls and deep pools.
Although the banks along some stretches have been modified, the channel is natural and composed of mixed substrate of boulder, cobble, gravel and pebble with scattered sections of bedrock and sandy deposits. Cobble side and point bars are occasional features. At the upper end of the River Roe and along its tributaries, the aquatic flora reflects the highly acidic character of the water, with mosses such as river feather-moss, claw brook-moss and yellow fringe-moss and St Winifrid's moss and the liverwort star-headed liverwort occurring on stabilised boulders and rocks.
In the middle reach the channel vegetation is characterised by greater water-moss while in lower reaches of the River Roe where the flow is less dynamic the bryophyte community is generally replaced by beds of stream water-crowfoot in the channel and reed canary-grass along the banks.

The river channel of the River Roe and its tributaries has a tree fringe along a large proportion of its length. Occasionally this fringe widens out up the valley sides to form discreet woodland blocks. In total there is more than 138ha of fragmented woodland within the site. Marginal woodland is very important to the river and its wildlife. It helps to stabilise the river bank and regulate the local climate, while submerged roots create a refuge for fish. Many of the insects and other invertebrates associated with the woodland provide food for fish.

The main woodland blocks are predominantly upland oak wood which is acidic in nature. It can have a mixed canopy comprised of Sessile oak, downy birch, hazel, ash, alder and willows, in addition to introduced species such as beech and sycamore. Shrubs include hawthorn, holly and rowan. The ground cover is very variable. Grasses are dominant where grazing is heavy. Where the wood is less disturbed, species include wood-sorrel, herb Robert, pignut, common dog-violet and great wood-rush growing with taller ferns and thickets of bramble. In some locations where the conditions are particularly acidic bilberry forms a low field layer over a moss carpet.

Site Related Documents

Site map (.PDF 1.3Mb), Citation document (.PDF 171Kb) and Views about Management document (.PDF 70Kb).