Salmon spawning on Dorchester’s Mill Stream

Salmon have given the ultimate seal of approval to Dorchester’s recently enhanced Mill Stream, as they returned to the River Frome for the annual winter spawning.

This month’s survey of salmon ‘redds’ or nest sites found they had more than doubled in the 450m stretch where work was carried out last summer by Dorset Wildlife Trust.

Annual surveys of the Frome had previously found only three redds in one part of the Mill Stream, a man-made tributary whose unnaturally wide, straight-sided channel and silt-laden gravel bed had not been suitable for the fish to make their characteristic gravel nests.  Last summer, low level shelves (or berms) were used to narrow the wide sections, allowing the river to create cleaner gravels, pools and shallow riffles to accommodate spawning adults, and hiding places for the growing juvenile fish.  

Sarah Williams, Dorset Wild Rivers Officer at Dorset Wildlife Trust said, “This is fantastic news for the local fish populations; although the salmon redds are easier to spot, there is a good number of brown trout spawning sites too. Due to low water levels this winter, large fish are easier to see and you should be able to spot the salmon ‘redds’, which are about 2  metres wide and 4 to 6  metres long, but it is important that people don’t wade into the river as this could damage the eggs.  Salmon and trout cannot be caught in the winter months and this is to allow them to breed.”

The adult salmon return to the Frome from their feeding grounds in the North Sea and as far away as Greenland, finally reaching their home river between November and early January after an epic journey without feeding.  They then have to make their way upstream and find clean gravels where the female can lay the eggs, fertilised by the male and then cover them with a protective mound of gravel.  The eggs will hatch in the spring.

The Dorchester Mill Stream Enhancement Scheme, a Dorset Wild Rivers project, is supported by SITA Trust’s Enriching Nature Programme through the Landfill Communities Fund and also by the Environment Agency, The Big Lottery Fund, the Wild Trout Trust and many charitable trusts.    Dorset Wild Rivers is supported by Wessex Water and The Dorset Area of Outstanding Natural Beauty.

For more information visit www.dorsetwildlifetrust.org.uk/dorsetwildrivers or ring 01305 264620.