PORTLAND, Maine (AP) — Marine authorities in the U.S. and Canada said Friday they will marshal resources to try to find out what's behind a string of deaths of endangered North Atlantic right whales.

The animals are among the rarest marine mammals in the world, with only about 500 still living. The countries will collaborate on a report that could help craft future regulations that protect the vulnerable whales, representatives said.

Representatives of the National Oceanic and Atmospheric Administration and Fisheries and Oceans Canada both said ship strikes and entanglement in fishing gear hav...