SPRING NOTES – AUNE CONSERVATION ASSOCIATION
Life in the Devon Avon continues much as normal although recreational activity in the estuary has been severely curtailed during ‘Lockdown’. Unfortunately, our social gathering in the form of the Tidal Road clean-up planned for the end of April was another casualty of the coronavirus pandemic and advice on social distancing, etc. Our Spring AGM will probably suffer the same fate.
As for normality, this is the time of year when as salmon begin to mature, they adapt for life in salt water in an intermediary stage known as smolts. This process marks the beginning of their first migration from their home river to the ocean. Anadromous fish, like salmon, that move from fresh to salt water and back again over the course of their lives, must be able to change their physiology – the way their bodies work. In a process called smoltification, salmon adapt to the changes salt water causes to their bodies. In fresh water, the salmon’s body is saltier than the water in which it swims. To work properly, the body needs salt so it tries to keep the salt in. Some escapes, but the salmon gets enough from the food it eats to make up for the loss. In the ocean, the water is saltier than the salmon’s body needs to be, so it must try to keep the salt out and the water in. When salmon swim in the ocean, the salt water draws water out of the fish’s cells. Salmon adapt by drinking seawater to replace the water their cells lose. They excrete the excess salt through their gills and urine. As the smolts prepare for ocean life, their appearance also changes, from the dark colours of the fry to the silvery colour of adult salmon. This helps them hide in the light conditions of the surface waters of the open ocean, where there is no dark shade from overhanging trees. While approximately 30 fry from a redd of 2000 to 2500 eggs grow into smolts, less than four survive to become adults.
We are now approximately midway through the smolt migration season, locally, but a big problem in the Devon Avon (Aune) is the potential shortage of water to enable these migrations to occur. The Aune is a spate river meaning that it is rain-fed, short and fast flowing so the run-off time is quicker; water levels rise and fall relatively quickly, especially upstream. The water level recorded at the gauging station near Didworthy usually ranges between 0-1.40m; early on 3rd May it was 0.37m. In contrast, downstream at Loddiswell (usual range from 0.25m -1.80m); the level was 0.26m and falling. The Avon dam exacerbates the problem of seasonal water shortages although, as part of the original agreement when the dam was built in the 1950s, an ecological ‘bank’ or ‘freshet’ of water should be released in times of drought. Some years ago, we managed to negotiate with the Environment Agency (EA) and Southwest Water (SWW) to make sure these water releases actually happened – for the first time since the dam was built. Unfortunately, owing to retirements and headcount reductions in both organisations, the agreement details seemed to become ‘forgotten’ despite my best attempts to familiarise replacement staff with the arrangements. Happily, following yet more staff reassignments and the appointment of a new, better informed, EA fisheries officer to cover our region, I have just been notified that because April was a very dry month – although it is raining as I write – the overspill from the dam has been very small of late. Therefore, a ‘freshet’ of water will be arranged with SWW. Hopefully, more smolts will make their way to the sea as a result and will eventually come back to our river as adult fish.
Stuart Watts – May 2020