Fishy health checks in Shropshire

Our fish monitoring programme is now in full swing and our people have been undertaking lots of electric fishing surveys. On Wednesday 18th June we surveyed the River Onny near Onibury in Shropshire.

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Using electric current we surveyed 100m of the River Onny and caught:

127 juvenile Salmon

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18 Brown Trout

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3 Grayling

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2 large eels

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We measured all the fish and removed 3 scales from each salmon and trout in order for them to aged by our Brampton Laboratory.

This is a fantastic result! We counted salmon redds (nests) on this same stretch in October and November last year and saw salmon spawning, redds and dead kelts (fish that have died from exhaustion after spawning).

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The large numbers we caught shows the river in a great health and that not all the redds got washed away by the winter floods.

Staff from the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) joined us and took 30 salmon parr away to check if they have a parasite, Gyrodactylus salaris.

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It is a category one notifiable disease. The parasite has decimated rivers in Norway and CEFAS check each catchment in the UK every 5 years. Luckily no parasites have been found in our rivers to date.

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Spawning salmon spotting in Shropshire

The River Onny is an important river for migratory Salmon, with numerous fish running the river to get to suitable spawning ground in the upper reaches.

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To spawn salmon cut redds, which are shallow excavations in gravel beds, and lay their eggs at the tail end of the redds where the fertilised eggs can grow into alevins in the relative sanctuary of the deep gravel beds.

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The simplest way to determine the amount of salmon that have run the river to spawn is to count the amount of redds that are cut over a set area and time period. This gives us a good idea of how strong the salmon run has been in any one year and therefore how this will relate to year class strength within the existing population.

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On the stretch of the River Onny, from Stokesay to Onibury, that we surveyed last week 10 salmon redds were seen as well as a pair of salmon guarding a recently cut redd. Four dead cock fish and one dead hen fish were seen. This is all part of the natural life cycle as not all salmon make it back downstream due to exhaustion.

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