In the fourth of a series of articles, Thames21 Catchment Partnership Development Officer Will Oliver explains why he is in search of brown trout in the River Roding
The brown trout is a species of fish native to UK rivers. Unlike some other native fish species which have wider tolerance levels, brown trout are ‘picky’ when it comes to exactly where they call home.
In general, they will only be found in rivers that have clean, unpolluted water with a range of high-quality habitats. The riverbed must also have areas of loose gravels free from fine sediment for the trout to spawn in. Some brown trout, for reasons still not fully understood, migrate out of rivers and into the sea to feed, before returning to rivers to spawn later in their lives (in a life cycle similar to that of a salmon). Known as sea trout, these fish require a river channel to be free of barriers, such as weirs and dams, to complete their migration. For these reasons, brown trout require the entire river system to be healthy and functioning as close to its natural state as possible.
On the face of it, it may therefore seem misjudged to mention the River Roding in the same sentence as brown trout. The Roding has suffered degradation throughout the 20th and early 21st centuries and has been affected by sediment pollution from the intensively-farmed upper catchment, as well as pollution from road run-off, wastewater and combined sewer overflows in the more urban stretches. Sections of the river have also been dredged through history, removing the gravels that brown trout depend on for spawning.
However, it’s highly likely the Roding would have once held good numbers of brown trout and there are still some areas in the upper Roding where the habitat and water quality remains good enough to potentially support some small, relic populations of the species. Additionally, compared with many of the other major tributaries of the Thames, the Roding has the fewest barriers to fish migration.
It therefore seems possible that trout could still exist in isolated populations within the Roding. If this is true, then work to improve the habitats and water quality of the Roding could encourage these populations to expand. If this is not the case, and pressures on the Roding have caused trout populations to undergo localised extinctions, then it is possible that by improving spawning habitats and making barriers to migration passable, sea trout – which are known to be present in the Thames Estuary – could be encouraged to return to the river to spawn. Generally improving the water quality and health of our rivers will, in turn, attract a greater variety of wildlife and plants.
If you have seen or caught brown trout in the Roding or any of its tributaries, then we would love to hear from you.
For more information on the Thames21 project and to get in touch, email email@example.com