Life Isn’t Going too Swimmingly For Fish on the Ouse…
On Monday 2nd June, we met at Vuggles Farm to discuss fish species diversity along the river Ouse. Fish populations across the Ouse are struggling due to several factors which include hard engineering throughout the river reducing river connectivity, a reduction in quantity and variety of natural habitat available to fish and, invasive species entering the river. As a result, the ecological status of every waterbody in the Ouse fails on fish populations. The group was joined by the Ouse and Adurs Rivers Trust (OART), who took us on a tour of two local sites where they planned to undertake projects to encourage fish populations in the Ouse.
The first site was a remnant meander which had been cut off from the main river channel during the canalization of the river Ouse. This activity had created a pond habitat within the meander with no river flow running through it. As a result, it was now being negatively impacted by a species known as parrot feather. Parrot feather is commonly bought from garden centres to be used in garden ponds. The species benefits from low/no flow environments and can easily escape into the natural system and take over a habitat. Though OART have attempted to control the spread of Parrot Feather throughout the habitat, even the smallest remnants of the plant can recover and dominate once again.
One of the solutions to the problems in the meander would be to reconnect the meander to the main river channel. This would allow flow to once again pass through the meander and reduce the abundance of parrot feather. The nature of meanders themselves also offer great habitat for fish. The differing levels of sediment build up created microclimates and different flow rates suitable for different fish activity. Restoring the meander is just one of many habitat interventions OART have encouraged to benefit fish. Another is the creation of areas of woody debris and shaded areas of river. Shade offers respite to all fish during hot days. Fish don’t survive very well over temperatures above 19 degrees, so it’s important this variety of habitats can be offered. Debris allows smaller growing fish to shelter from predators, especially due to the growing damage invasive coy carp, that escape from angling lakes and ponds, is doing to the river. The carp are also having a wider effect on riverine species due to their wide-ranging diet and have been known to eat water vole in large numbers.
Next, we walked down to our second site to look at a weir structure. These structures reduce river connectivity as fish are unable to move upstream. Many weirs are required to be built with mitigations in place such as ladders where fish can jump up each step to reach the next level of the river. However, these are often broken or unintuitively designed against natural behaviour that fish would follow. At this site, OART were proposing to divert the Ouse flow through a remnant lock structure. This is because the weir itself is considered a heritage asset which cannot be removed. OART emphasised the importance of approaching river restoration with a landscape scale approach. Removing a single weir structure could dry up areas of river upstream due to other engineering structures and therefore a joined up approach needs to be adopted to benefit the whole river system.
Finally, we also discussed the benefit that species re-introduction could have on the Ouse and the current changes to licenses for beaver release. OART stressed the positives and negatives to the re-introduction of beaver in the Ouse. The main impact of beaver on fish was the reduction of river connectivity due to beaver dams. Despite this, beaver dams are generally recognised to be much more porous in nature than hard engineered structures. In addition, beavers don’t naturally dam in water that is deep enough for them to feel safe and as a result, understanding the landscape into which beavers are being released will be essential to a successful re-introduction.
A huge thank you to OART who took the time to come out and speak to the group.