It is an early Thursday morning and I am on the banks of The Bure in Norfolk. Three Environment Agency staff are sweeping across a windy stretch of river; two with electro-fishing rods, another pushing a boat behind them. Sometimes they sing (despite their waders the water is cold and spirits need to be kept high) and every few seconds a quick flick of a hand net transfers a momentarily knocked out fish into a bucket on the boat - these fish will be passed to us and on the bank we will weigh, measure and ‘gut-flush’ certain fish before all are returned to the river alive and well.
I am with Murray Thompson, a PhD student at the Natural History Museum studying the effect of woody debris on life in rivers. He tells me that last year; they only pulled 31 trout out of this particular stretch of river compared to 56 this year, a sign that in the Bure, trout are prospering from the presence of trees. Also included in the haul were: 11 stone loach, 3 three-spined stickleback, 1 roach and, rather wonderfully, 1 eel. Murray wants to find out whether recreating natural tree-fall in rivers creates better environments for the various levels of life in a river, something that ultimately benefits top predators like the trout.
Many of the rivers he works on have been straightened and had any woody debris removed. All of the rivers are fished and although potential hook snags like fallen trees are an obstacle for fishermen, Murray hopes that by showing that mixed and complex environments ultimately benefit the fish, those who own the rivers (and the rites to fish on them) will be more inclined to leave rivers in a more natural state.
‘Gut-flushing’ a trout
It is important to know what the fish in a river are eating and to do this without killing them we ‘gut-flushed’ a few of each species sampled:
After being measured and weighed the fish to be gut-flushed are placed in a bucket of river water to which we add a few drops of sedative. In just a few minutes the fish are subdued at which point they can be ‘gut-flushed’. River water is gently pumped into the stomach of the fish and the contents of the stomach are regurgitated. These stomach contents are then collected in carefully labeled test tubes to be brought back to the museum and analyzed in the lab. The 'gut-flushed' fish is then placed in a bucket with aerated river water and after just a few minutes will be fit for release back into the river.
This process is repeated at various sites along the river; some have natural pieces of woody debris - namely fallen trees not yet removed, some have nothing and some are sites to which Murray has carefully added woody debris or fallen trees. This process is also repeated in another 4 rivers in an attempt to find common trends within the vast array of ecological variability encountered across the country. The results from these different sites will hopefully provide Murray with evidence for the effectiveness of ‘Re-wilding Britain’s rivers’.
Thanks to National Trust Head Warden Dave Brady for devising the restorations, Murray Thompson, Charlie Hanison, Jon Clarke, Tom Howard, and Nick Beardmore from the Environment Agency.