MADRID (BLOOMBERG) - Plummeting global demand for fish and seafood as a result of the coronavirus crisis is likely to create an effect similar to the halt of commercial fishing during World Wars I and II, when the idling of fleets led to the rebound of fish stocks.
The closure of restaurants and hotels, the main buyers of fish and seafood, together with the difficulties of maintaining social distancing among crews at sea have caused hundreds of fishing vessels to be tied up at ports around the world.
Marine scientist have already started investigating the effects this will have on marine life.
"Studies after the first and second world wars showed a spectacular recovery," said Mr Carlos Duarte, a research chair at the Red Sea Research Centre in Saudi Arabia. "We are hoping that this unintended closed season between February and June or July will accelerate the recovery of fish stocks and allow us to reach conservation objectives faster."
The Covid-19 outbreak has decimated the restaurant trade and wreaked havoc with food supply chains.
Demand and prices have collapsed in Asia, home to some of the world's largest seafood and fish markets.
In Spain, which has the largest fleet in the European Union, half of the ships are staying at port.
The EU enacted emergency measures last month to allow member states to give financial aid to help the fishing and aquaculture industries through what it called a "dramatic slump" in demand for seafood.
The downtown adds to uncertainty for EU members such as Spain and France over future access to British waters as a result of Brexit.
The marine environment can only benefit from the reduced pressure on stocks, however.
While evidence of a recovery in marine life is still anecdotal, increases in the presence of mammals such as killer whales, dolphins and seals have been recorded in areas where they hadn't been seen in decades, said Mr Duarte, who is part of a consortium of scientists in Britain, Canada, Spain and Saudi Arabia compiling data.
"The noise and the activity on the water have diminished," he said. "These animals have a culture that is passed through generations and the young ones are probably feeling curious about areas that were part of their territory decades ago."
Signs that marine life is recovering include reports of turtles nesting in now-abandoned beaches in Brazil, he said.
The same phenomenon could happen in the Mediterranean coast later this year when breeding season arrives.
As well as the Mediterranean, the lockdowns are likely to help marine species in the Atlantic, which breed between April and June.
In Spain, where fishermen are allowed to work during the lockdown because they're considered essential workers, the sector is struggling, said Mr Javier Garat, secretary general of industry group Cepesca.
Small boats going back to port at the end of each day are now selling what they catch at "reasonable" prices in local markets after prices initially halved, he said.
The seafood sector in the country's north is completely halted, while Spanish trawlermen involved in fisheries off western Africa are freezing everything they catch as they wait for restaurants to reopen and demand to pick up.
Long distance fishermen catching cod, shark or swordfish in the northern Atlantic or the Indian ocean face great uncertainties.
They work on shifts of up to four months, some of which have been extended, but the solution is not permanent.
"These crews are unloading the fish without stepping on the docks -right now they're probably one of the safest places in the world," Mr Garat said. "But this can't go on forever, eventually they'll have to rest and flying replacement crews to places as far as Seychelles is almost impossible right now."
To be sure, the recovery of diversity and fish numbers is a slow process and the experience in marine protected areas shows a full recovery can take as much as two decades, said Prof Nick Graham at Lancaster University in Britain, co-author of a study analysing fish populations in over 1,800 tropical coral reefs in 41 countries.
The study, led by Prof Joshua Cinner at the James Cook University in Australia, classified the reefs according to their fish stocks, the biodiversity and the state of the ecosystem.
Only 5 per cent of reefs analysed were in the top "A" category, all of them in remote locations with little human pressure, showing the importance of marine reserves and fishing restrictions to help reefs in lower categories recover.
"The most direct impact on fish is fishing," said Prof Graham. "Where there's more people, it tends to be more fishing pressure to meet the demands of larger human population, and if a reef is less fished then more fish will survive."