Anglers in Scotland are being urged to put back all the salmon they catch in a bid to conserve stocks.
The Association of Salmon Fishery Boards (ASFB) said numbers were down on almost all of the major rivers.
At present more than 70% of salmon caught are released back into the water but the group said there was a "strong case" to make it 100%.
ASFB managing director Andrew Wallace said he hoped it would only be a "temporary setback" for fishing.
Salmon fishing is estimated to be worth millions of pounds to economies across Scotland.
However, this year's run of spring fish is one of the weakest for several years.
ASFB Chairman Hugh Campbell Adamson said it was the cause of serious concern.
He urged anglers to show "maximum restraint" over the next two months so that as many fish as possible had the opportunity to spawn later in the year.
The ASFB has also written to the Salmon Net Fishing Association of Scotland asking its members not to start fishing until the end of June.
Mr Wallace said that after several years of small improvements in spring runs and catches it was "most disappointing" to have reached this point.
"It suggests that the recovery is fragile and hence the need for special measures to be adopted immediately," he said.
"There can be little doubt that marine survival of this year's spring salmon has been particularly poor.
"In addition to spring salmon, sea trout numbers are also in significant decline and any exploitation by both anglers and netsmen should be minimised."
Mr Wallace appealed to everyone fishing Scotland's rivers to back the move.
"This will only be possible with the help of anglers and netsmen who we hope will support these voluntary but nevertheless important measures," he said.
"We will also be looking at conservation measures that may be required in the autumn when spring fish reappear in catches."
The action has been supported by Nick Yonge, clerk to the River Tweed Commission.
He has written to all beats along the river urging them to "spare as many spring caught fish as possible".