Endangered right whales are dying at unusually high rates in the Atlantic Ocean off Canada and the northern United States, sparking an investigation by authorities in both countries, officials said Friday.
Thirteen of the massive, bus-sized marine mammals have been found dead this year, a large number considering the entire population numbers just 450-500, said experts at the National Oceanic and Atmospheric Administration (NOAA).
Typically, 3.8 right whales per year are found dead in Canadian and US waters combined.
David Gouveia, protected Species Monitoring Program branch chief at NOAA Fisheries Greater Atlantic Region, described the deaths as "significant" and said an immediate response is needed.
"The North Atlantic right whale recovery is fragile and one of most difficult conservation challenges," he told reporters on a conference call.
"Every factor influencing their ability to survive is significant."
Getting entangled in fishing nets or colliding with ships are considered the most likely causes of the whale deaths, but experts are awaiting the results of necropsies to determine the reasons and to suggest solutions.
NOAA has declared an "unusual mortality event," or UME, kicking off an investigation and making funds available for the probe.
"The first reported stranding in this event was on June 7, 2017 and was a dead North Atlantic right whale reported floating to the west of Prince Edward Island in the Gulf of St Lawrence, Canada," said a NOAA statement.
Ten of the whales have been found in Canada and two in US waters.
Prior to the announcement of the UME, a North Atlantic right whale calf was found dead in April 2017 in Cape Cod Bay, bringing the year-to-date total to 13.
Four right whales were found entangled in nets in Canada, and two of them were successfully disentangled and appear to have escaped with their lives.
One of the whales in the US was a severely decomposed carcass that washed up in Martha's Vineyard, and the other was 160 miles (258 kilometers) offshore but NOAA was unable to retrieve the carcass for further study.
Experts hope to know more from the necropsy results in the next few weeks.