Federal researchers are sharpening their focus on the recent deaths of endangered North Atlantic right whales.
The animals are among the rarest marine mammals in the world, with only about 500 still living.
At least 13 right whales have been found dead this year off the coasts of New England and Canada, prompting the National Oceanic and Atmospheric Administration to declare the deaths an "unusual mortality event" and to launch an investigation.
Representatives from NOAA Fisheries and from Fisheries and Oceans Canada planned to provide more details Friday on the investigation into the cause of the deaths. Authorities and conservationists have said some of the whales died due to ship strikes or fishing gear entanglement.
Conservationists say the right whale population is too small to survive a year of poor reproduction and heavy mortality. According to Charles "Stormy" Mayo, a senior scientist at the Center for Coastal Studies in Provincetown, Massachusetts, only a few baby right whales were born this year.
Biologist Regina Asmutis-Silvia of Whale and Dolphin Conservation calls the number of deaths "unprecedented." She and other conservationists have said right whales haven't suffered such high mortality since the whaling era, when their populations were decimated.
Hunting right whales became illegal 80 years ago. This year, 10 of the dead whales were found off of Canada's coast and three off the coast of Massachusetts.
The whales migrant north every summer to feed. Scott Kraus, who heads the New England Aquarium's right whale research program, has said it's possible the whales are more vulnerable to hazards because they are traveling more due to changes in the availability of food.