The study, published Tuesday by the Woods Hole Oceanographic Institution and the University of Massachusetts, warns the giant mammals could be facing extinction.
Researchers say this is the first time anyone has identified a decline in the population. Until now scientists have claimed that the whale's numbers were growing, but slowly.
The study shows that in the early 1980s about two per cent of the whale population was dying each year. Now about seven per cent, or 18 whales die each year.
Researchers estimate there now about 300 North Atlantic right whales left. Only about 12 whales are born each year and females usually produce every five years.
The report authors say increased fishing along the coast is contributing to the higher death rate. Right whales are slow moving and tend to feed closer to shore than other types of whales. This makes running into a fishing boat or being tangled by fishing gear more likely.
Groups in the United States and Canada are beginning to work to protect the right whales. On Apr. 1 the U.S. will pass legislation to ban certain kinds of fishing gear and to restrict fishing in some areas where whales are often found.
In Nova Scotia biologists are launching a whale emergency network with a phone hotline to warn ships of the whales' movements.
The North Atlantic right whales were heavily hunted in the late 19th century because of their size and slow speed. The population has been slow to recover due to the whale's natural behavior and slow reproductive rate.