The River Usk
rises in the acidic uplands of the Carmarthen Fans but as it winds
its way southwards, it collects more basic water and this is reflected in
the diversity of the flora and fauna of the valley. Such is its importance
that the River Usk is designated a Site of Special Scientific Interest (SSSI)
The river hosts a number of fish species including the chub, dace, roach
and the bullhead but is best known as a trout and salmon river. The sea
trout also enters the river to spawn, though in smaller numbers than the
salmon.
Other migratory fish are the twaite and very rare allis shads which migrate
up the river to spawn in the spring. Once abundant in western Europe, these
two species are becoming scarcer but are both represented in the rivers
Usk and Wye. Two species of those primitive eel-like fishes, the lampreys,
also come into the river to spawn. These are the river and sea lampreys.
There is also a small resident species, the brook lamprey. In all three
fish the jaws are replaced by suckers, which enable them to become attached
to other fish from which they suck their sustenance.
Some decades ago the otter was nearing extinction in Britain but the Usk
Valley was a focus of its survival. This beautiful mammal is now distributed
throughout the length of the river. Less fortunate is the gentle water vole
which is now exceedingly scarce, mainly due to the depredations of the North
American mink which, although only one tenth of the weight of the otter,
has caused immeasurable damage to the wildlife of Britain. There is, however,
still a thriving population of this vole below Brecon.
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