Cod stocks in the North Sea have plummeted to critical levels, according to the latest scientific advice.
The assessment by the International Council for the Exploration of the Sea (Ices) says cod is being "harvested unsustainably".
It has recommended a 63% reduction to the available catch to just 10,457 tonnes and follows a 47% cut last year.
Conservation charity Open Seas has described the assessment as a "crying sea of shame".
A discard ban is being partly blamed which increases the amount of cod fishermen can catch but forces them to land it.
Until the change, around 20% of fish caught was thrown back into the sea dead.
Some groups suggest the practice of discarding has continued, meaning even more fish are being caught.
Significant pressures have also come from climate change.
Bertie Armstrong, chief executive of the Scottish Fishermen's Federation (SFF), said: "There's no escaping the fact that this unexpected downturn in the cod stock will be damaging for our fleet.
"However, we have proved before and we will prove again that through a series of responsible, practicable measures to be agreed with government fisheries managers we can overcome the challenge, albeit that this time as we understand it climate change is a very significant factor.
"The fishing industry has a long and noble tradition of adapting to the ever-shifting dynamics of the natural world, and while it won't be easy, we will do what is necessary to help restore the stock."
The advice will now be the subject of negotiations between the coastal nations which border the North Sea.
It will likely result in a reduction to the Total Allowable Catch (TAC) for 2020 but it will not necessarily be as strict as the advice suggests.
Some conservationists are even suggesting that emergency measures should be introduced this year.
A Scottish government spokesperson said: "The scientific advice on certain species is challenging, as we expected it to be. This is particularly restrictive for our North Sea and West Coast cod fishermen.
"As ever, the focus of the Scottish government has been to find a balance between protecting industry from the introduction of restrictive measures, whilst taking a responsible and scientific approach to protecting our precious marine life.
"By doing so we create a sustainable environment for the fishing industry in the long run.
"And it is the responsibility of all the nations who fish these waters to respond collectively."
Cod stocks collapsed in 2006 after a long period of decline which began in the 1970s.
A cod recovery plan was agreed which saw numbers beginning to recover and in 2017 it received a "blue tick" from the Marine Stewardship Council (MSC).
The certification meant cod could be eaten "with a clear conscience".
But stock levels have since fallen rapidly.
Erin Priddle, MSC programme director for UK and Ireland, said: "While we understand that the outcome of today's advice is disappointing for the sector, we look forward to industry introducing a suite of measures to secure the long term sustainability of this iconic and ecologically important stock.
"Protecting North Sea cod for this and future generations must be a key priority for all involved."
Nick Underdown, from Open Seas, said: "We need a long-term fix for this, not empty reassurances by the big fishing lobby that the problem will go away.
"The problem is not just overfishing, trawling the seabed close to shore destroys nursery grounds for fish, and indiscriminately catches young cod before they can mature.
"We need to protect spawning habitat urgently, remove damaging bottom trawling from inshore seas, and end the wasteful bycatch of juvenile fish.
"Until our politicians have the courage to do this, our fishing industry will keep lurching from crisis to crisis."
Helen McLachlan, fisheries programme manager at conservation organisation WWF, said: "Cod play a crucial role in maintaining healthy oceans.
"This is a real crisis for our seas and fixing it will require an emergency response from governments."