Hundreds of grey seal pups are dying on the shores of the Baltic Sea in Estonia and Latvia as the Nordic coastline faced the first winter without ice in decades, researchers said.

Grey seals need ice - which helps them keep a distance from predators like wolves or foxes - in order to breed pups during the winter.

Without it, they have been forced onto islets they would not normally inhabit, causing overcrowding, disrupting the breeding season and reducing the survival rate of newborns.

"There were some islands that were white, all covered with seal pups ... We haven't seen such a picture before," researcher Mart Jussi, who has studied seals for the last 30 years, said. He said some of the larger islands were so over-populated that he estimated the mortality rate among seal pups there would be at least 50 percent. That high rate was in part because pups lose their mothers more easily and so don't get enough food. Around 3,000 seal pups are born each year on the Baltic Sea coast. "Most of the pups are going to die right now," Jussi added.

This spring the problem is compounded by the coronavirus, which is keeping researchers away from the seals, as Estonia has halted travel between the mainland and its islands.

Agnese Balandina, a specialist working with Latvia's nature conservation agency, said the coronavirus outbreak combined with the warm weather had driven Latvians to the country's beaches, increasing the likelihood of contact between people and seals.

The agency has set up warning signs on Latvian beaches asking people to keep a distance of at least 50 metres (164 feet), but some people ignored the advice and ventured closer to take photographs of seal pups on their phones at Jurmala near Riga.

Balandina, who with a colleague caught an injured seal pup at Jurmala, said the agency had received 200 calls about lone seal pups on Latvia's beaches over the previous weekend.

Unless the pups are injured or in danger the agency prefers not to intervene - and even those that are rescued and sent for rehabilitation in Riga's zoo or in other facilities around the country may not survive.

Meteorological agencies in both Estonia and Latvia said on their websites at the beginning of March that the winter of 2019-2020 was much warmer than usual.

The Estonian Weather Service said the average air temperature over winter was 2.5 degrees Celsius (36.5 Fahrenheit) rather than the historical average of -3.3 Celsius (26.5 Fahrenheit) - the warmest since 1961.

Latvia's Environment, Geology and Meteorology Centre said it was the warmest winter since records began in 1924.