Tuesday, March 29, 2011

No place for big fish in small pond

British Waterways is relocating over half a tonne of fish from the side ponds of the Caen Hill Flight of locks on Devizes Flight of the Kennet & Avon Canal to improve conditions for wildlife. 

A pike removed from Caen Hill.
This relocation follows a successful trial project in 2009 when a tonne of fish that included large tench, carp, bream, roach, perch and pike were removed from the ponds.

The large number of boats that move through the Caen Hill locks stirs up silt and, surprisingly, so do large fish feeding on the bottom of the ponds. This stirring of the silt releases nutrients into the water and causes the growth of algae and makes the side-ponds less suitable for invertebrates such as dragonflies and damselflies — as well as rare aquatic plants that need clear-water to thrive.

And by removing the large fish a more natural balance is created in the ponds because there are fewer predators to feed on the younger and smaller fish and invertebrates.

Carp removed from Caen Hill. 
BW 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."

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

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