The Dales main rivers are important spawning (breeding) sites for Salmon, Brown/Sea Trout and Grayling. Females of all these species deposit their eggs in gravel in running water where they are fertilised by the males. To develop properly, the eggs need clear, unpolluted, well-oxygenated, cool water and making sure these conditions are available in at least some stretches of river is a key requirement to maintain populations. See the page ‘Upper Wharfe Restoration Project’ for a description of some of the work that is going on in the Dales to create, restore and maintain river habitats in good condition for spawning fish and other aquatic life.
Salmon spend most of their lives in the sea but when ready to breed, swim up rivers to find suitable spawning grounds. After spawning the adult fish return to the sea. Many die during migration, but a few may make the arduous journey to breed three or, exceptionally, four times, but not necessarily to the same river each time.
Brown Trout and Sea Trout are actually one and the same species (Brown/Sea Trout). Sea Trout look very similar to Salmon and, like Salmon, they live off the coast and ascend rivers to breed. Brown Trout stay in the rivers in which they were born and can be found also in lakes.
Eels migrate similarly to Salmon or Sea Trout except in reverse: They spawn in the Sargasso Sea in the western Atlantic and then make an epic journey as youngsters (‘elvers’) to the rivers where they live most of their lives as adults.
Lampreys are eel-like creatures lacking jaws but having mouths formed into a sucking disc that they use to latch onto and suck blood from other fish. Like sharks they are boneless and possess skeletons made of cartilage. Two species, the Sea Lamprey and the River Lamprey migrate to sea and return to rivers to breed, while a third, the Brook Lamprey, lives all its life in freshwater. All three Lamprey species can be found in the River Eden in the Dales.
Two small fish that live under stones in rivers and streams in the Dales are the Bullhead and the Stone Loach. Shoals of Minnows may be seen swimming in shallow water but these too seek refuge under stones when threatened.
Three-spined Sticklebacks are small fish that may be found in clear ponds and lakes.
Brown Trout are non-migratory but are thought to be members of the same species as the migratory sea trout. It is widespread throughout the British Isles and is an indicator of relatively clean water but their populations are currently declining. In the national Species and Habitats Review 2007, Brown trout/sea trout was added to the UK list of priority species for biodiversity action. The colouration of brown trout varies depending on the prevailing conditions. For example, it is said that brown trout in acidic moorland tarns are dark-coloured, whereas brown trout in alkaline rivers in limestone country can be crimson with black spots.
Furthermore, a brown trout in a deep pool can often be dark and is capable of lightening its own colouration in a matter of minutes if it moves into the clear shallows. However, generally adult fish are brownish with numerous black and rusty red spots on their upper sides. In the UK this species tends to develop to 30cm long.
Brown trout are present in most rivers and streams in the Yorkshire Dales National Park. National Park staff and Dales Volunteers have assisted a PhD student who was studying brown trout populations in the Ure catchment with Durham University. The Rivers Trusts are carrying out numerous practical measures to benefit river catchments.
The bullhead, also known as Miller’s thumb is present but not common in most of England and Wales. At a European scale this species is comparatively rare which makes the UK population of European significance.
The bullhead is a small bottom-dwelling fish that inhabits rivers, streams and stony lakes, with fast-flowing, clear, shallow water with a hard substrate. They are also said to be found in the headwaters of upland streams. The bullhead is a short-lived species (3-4 years), which matures early and spawns several batches of eggs each year between February and June. It feeds on small invertebrate species such as freshwater shrimps, mayfly nymphs and caddis larvae.
Nationally the population is thought to be declining due to the lowering of the water table and changes in drainage due to agricultural and forestry pressures. Due to the European significance of the UK population the bullhead is listed in Annex II of the EC Habitats Directive 92/43/EEC, which has been translated into UK legislation and is known as the Habitat Regulations of 1994.
In the Yorkshire Dales National Park, rivers in which the bullhead has been formally recorded include the Wharfe, the Ribble, the Dee (Dentdale), the Clough River (Garsdale), the Swale and the Ure catchment. In 2007 bullhead was found frequently in the Ure catchment as part of a PhD project based at Durham University. The Rivers Trusts are carrying out numerous practical measures to benefit river catchments.
The Yorkshire Dales Biodiversity Forum is organising a Rivers conference in November 2013 and the Catchment Sensitive Farming project also has significant benefits for river species.