Catch quotas are tradeable among fishing companies, creating a capital resource worth a total of about $5 billion that has been used as collateral for investments.

Boats would be given bigger catch quotas in return, with supporters of the scheme arguing that the numbers of fish taken overall would still be less than at present.

Due to concerns about overfishing, catch quotas were repeatedly reduced in the 1980s and 1990s.

However, recruitment of the stock fell to a low level in 2006 and has been weak ever since, causing declining spawning stock and eventually triggering strong reductions in catch quotas.