BIG FISH LEAVE SMALL POND

British Waterways is relocating over half a tonne of fish from the side ponds of the famous Caen Hill Flight of Locks on the historic Kennet & Avon Canal, near Devizes, to improve conditions for aquatic wildlife including dragonflies.

The relocation follows a successful trial project in 2009, which saw a tonne of fish, including large tench, carp, bream, roach, perch and pike removed from the ponds.

The significant numbers of boats that move through the locks at Caen Hill stirs up silt and so do, perhaps surprisingly, large fish feeding on the bottom of the ponds. This stirring of the silt causes the growth of algae due to the subsequent release of nutrients in the water. Over recent years, the water in the side ponds has, therefore, become less suitable for invertebrates such as dragonflies and damselflies, as well as scarce aquatic plants that rely on clear-water environments. By removing the large fish a more natural balance will be created in the ponds, as there will be reduced excessive predation from these larger fish on the younger and smaller fish and other invertebrates.

British Waterways’ ecologist, Oda Dijksterhuis said:

“In 2009 we removed the first batch of big fish from the ponds and installed silt screen curtains. The results of this habitat management work have been fantastic with aquatic plants, such as the rare potamogetons and hornworts returning to the ponds that we haven’t had in the waterway for years. In addition to these plants we have seen an increase in dragon and damselfly populations, the ponds are now teeming with diverse dragonfly larvae and other invertebrates such as the water scorpion.

“The fish relocations happening this week will help to improve the habitat of the other ponds on the flight, so hopefully we’ll see more plants and invertebrates appear in the coming months around all of Caen Hill’s ponds.”

British Waterways has employed a specialist fisheries team to co-ordinate the relocation of the fish, and initial works have suggested that there will be many large pike relocated from the ponds.

Many of the fish will be relocated along the Kennet & Avon Canal, where local anglers will be able to fish for them, and a proportion will go to Toddbrook Reservoir in the Peak District which needs restocking following works at the site.

The Caen Hill side ponds were originally designed 200 years ago as ‘holding tanks’ to store the water needed to operate this extraordinary flight of locks, due to the steepness of the terrain. Together, these side ponds represent one of the largest stretches of open water in this part of Wiltshire and are a great wildlife habitat for species including grass snakes, various birds and water voles.

Once the water in the side ponds has been drained down to a level of about two feet, a the fisheries experts will use 100m seine nets to trap fish before wading in to scoop up the largest. The fish will be carefully transferred into aerated tanks before being transported to their new home.

John Ellis, fisheries manager for British Waterways, says: "We take great care of the fish throughout every part of the process and local anglers will welcome the release of some of these larger fish into the canal."