The population of endangered North Atlantic right whales is under threat due to entanglement in fishing gear and a resulting drop in birth rates, according to a study published by the journal Frontiers in Marine Science.

A North Atlantic right whale that a team of state and federal biologists assisted in disentangling on Dec. 30, 2010, off the coast of Daytona, Florida.Florida Fish and Wildlife Conservation Commission

Even though North Atlantic rightwhales numbers have modestly increased from 295 individuals in 1992 to 500 individuals in 2015, the rate of baby right whales born annually have dropped by nearly 40 percent since 2010, the study states.

Due to these low calving rates, the study implies that the whale's already-precarious population faces a grim future.

"Our review of the recent science suggests that fishing gear entanglements are increasing in number and severity, and that this source of injury and mortalities may be overwhelming recovery efforts," the authors warn.

A 2015 draft marine mammal stock assessment for right whales from the National Marine Fisheries Service (NMFS) reported that between 2009 and 2013, an average of 4.3 right whales were killed by human activities each year—nearly all attributable to entanglement in fishing gear.

A whale tangled in fishing gear such a ropes and nets can suffer and ultimately die from a painful death. The International Whaling Commission Entanglement states on its website that entanglement can lead to drowning, laceration, infection and starvation. According to a report cited by the organization, an estimated 308,000 whales and dolphins die each year due to entanglement in fishing gear.

Even whales that survive entanglement can suffer from long-term negative physical and reproductive effects, Scott Kraus, a scientist with the New England Aquarium in Boston and study author, described to the Associated Press.

"They are carrying heavy gear around, and they can't move as fast or they can't feed as effectively," he said. "And it looks like it affects their ability to reproduce because it means they can't put on enough fat to have a baby."

The research found that entanglements have surpassed ship strikes as the number one killer of right whales in recent years. From 1970 to 2009, 44 percent of right whale deaths were due to ship strikes and 35 percent due to entanglements. But from 2010 to 2015, 15 percent of deaths were due to vessel strikes and 85 percent due to entanglements.

Right whale deaths from vessel strikes have declined thanks to governmental regulations that lowered ship speed limits near right whale habitats in 2008. But on the flip side, "despite a nearly 20-year U.S. federal effort to reduce accidental kills of whales in fishing gear, sub-lethal and lethal entanglement rates have increased, and there is no evidence that current fishing regulations have been effective at reducing mortality," the study states.

"As of 2015, 83 percent of all right whales display scars or carry ropes indicative of past entanglements," the study says.

As CBC News noted from the study, growth in offshore fishing and the introduction of of heavier offshore fishing gear and increased movement of existing whale populations has led to ever-grislier injuries from entanglement.

"As they encounter stronger ropes and heavier gear, the damage to the animals is more severe and lasts longer," Kraus told CBC News. "It's like if you break a leg, it takes you weeks or months to recover."

Researchers are currently working on ways to reduce entanglement. Science Daily reported that aquarium scientists Amy Knowlton and Tim Werner are working on developing fishing ropes that can more readily break when whales become enmeshed in them.

The authors of the current report stress that right whales "are not yet a conservation success story" and "need immediate and significant management intervention to reduce mortalities and injuries from fishing gear."

"Managers need a better understanding about the causes of reduced calving rates before this species can be considered on the road to recovery," the authors conclude. "Failure to act on this new information will lead to further declines in this population's number and increase its vulnerability to extinction."

North Atlantic right whales, identifiable by their distinctive white spots on its head, have had a long history with human exploitation, especially during the whaling industry era, the World Wildlife Fund states. Whaling for this species became illegal in the 1930s as the population neared extinction. The whales are also under threat due to climate change and warming oceans that affect their food sources.