Federal officials plan to provide more details on their investigation into the recent deaths of endangered North Atlantic right whales.

The whales are among the rarest marine mammals in the world. Only about 500 right whales exist.

At least 13 right whales were found dead this year off New England and Canada. Authorities and conservationists say some of the whales died due to ship strikes or fishing gear entanglement.

The National Oceanic and Atmospheric Administration has declared the deaths an "unusual mortality event" and is launching the investigation.

Representatives from NOAA Fisheries and from Fisheries and Oceans Canada plan to provide more details Friday.