VATICAN CITY (Reuters) – Pope Francis paid tribute on Wednesday to hundreds of thousands of seafarers stuck on ships due to the coronavirus pandemic, a situation the United Nations has said poses a risk to the safe operation of the world’s merchant fleet.

In a special video message for sea workers, Francis said the work of maritime personnel and fishermen had been made even more important during the pandemic because it was providing the world with food and other primary needs.

He said they had been hit particularly hard by the ripple effects of the pandemic.

“In these past months, your lives and your work have seen significant changes; you have had to make, and are continuing to make, many sacrifices,” Francis said.

“Long periods spent aboard ships without being able to disembark, separation from families, friends and native countries, fear of infection…All these things are a heavy burden to bear, now more than ever.”

About 90% of world trade is transported by sea and continued complications with changing over ship crews due to restrictions against the coronavirus in some jurisdictions is still affecting supply chains despite a widespread easing of lockdowns.

On Tuesday, Kitack Lim, Secretary-General of the U.N.’s International Maritime Organization, said some seafarers had been marooned at sea for 15 months, well over the 11-month maximum laid out in a maritime labour convention, and a situation he described as a “humanitarian crisis”.

In his message, the pope thanked them for the hardships they are enduring. “I would like to say something to all of you. Know that you are not alone and that you are not forgotten,” he said.

The International Transport Workers’ Federation (ITF), which represents seafarers, told them on Monday that it was no longer acceptable to force crews to work.