In a series called Deep Trouble, CBC News explores the perils facing the endangered North Atlantic right whale.

Three North Atlantic right whales are now entangled in the southern waters of the Gulf of St. Lawrence, according to the Department of Fisheries and Oceans, after two more were spotted on Thursday.

One was seen by officials in a Transport Canada plane east of Quebec's Gaspé Peninsula. It appeared to have rope trailing from both sides of its head down its body. It has not yet been identified, the DFO said in a statement.

The second whale was spotted by a researcher east of Miscou, N.B. It appeared to be trailing a line of rope from underneath its body. Officials said they believe the animal, known as No. 4423, was previously entangled in U.S. waters in April.

The third whale, No. 4440, was spotted on June 29, by the coast guard and DFO, east of Miscou. It had rope around its tail stock and appeared to be dragging something heavy.

That whale was spotted again, still entangled, on Tuesday.

Surveillance underway

All three whales were spotted in areas already closed to fishing, officials said. Certain zones of the St. Lawrence have been closed to fishing to lower the risk of whale entanglement.

"Aerial and at-sea surveillance is underway in an effort to monitor these particular whales and get a better sense of their entanglements," the department said.

The department also said it's considering options for attaching tracking buoys to the ropes on the whales if it is safe to do so. It also said attempts at disentanglement will only be considered if they can be done safely.

Six North Atlantic right whales have died in eastern Canadian waters since early June. There are only about 400 of the endangered whales left in the world.