The River Wye has seen a decline in the number of salmon

The aim of the measures is to reduce by about 20% the rate at which salmon stocks are falling.

The by-laws, introduced after pressure from the Environment Agency, will cause a delay to the start of the fishing season.

The measures also ban entirely the practice of fishing for salmon with worm, prawn or shrimp.

Anglers will additionally be restricted to the method of spinning for salmon during a certain part of the year.

Mandatory release

The agency hopes that the by-laws will work alongside other measures designed to increase salmon numbers, including work to improve access and rehabilitate rearing areas along the upper Wye.

Anglers are being urged to release the fish they catch

The measures mean that the start of the salmon season has been moved back from 26 January to 3 March and that anglers must release any salmon they catch before 16 June.

Peter Gough, the Environment Agency's area environment manager for the Wye, said: "These by-laws are the latest in a series of legal and voluntary measures to protect Wye salmon.

"They are vital for the future of the stock, and complement other initiatives under way on the river."

Patrick Darling, spokesman for the Wye Salmon Fisheries Owners Association, said: "We welcome measures such as these that will result in more fish surviving to spawn.

"The Wye stock is currently at a very low level and, in addition to by-law control, we urge anglers to exercise further restraint through voluntary catch and release of all fish."

The new measures became law on 1 September and will expire on 31 December 2008.