- [Narrator] A great whale, virtually free from predators, (whale snorting) and yet, in 10 years, 30% of the population has disappeared.

Not a single adult has known to have died of natural causes in more than a decade.

Maria Harvey is an entanglement responder with the Center for Coastal Studies in Provincetown, Massachusetts.

- Going in, what we knew was there was rope coming out of the mouth, two trailing lines with a possible twist.

- [Narrator] Entanglements that involve a whale's mouth can interfere with feeding.

If the rope becomes wrapped around a fin or tail, it will tighten over time.

- And a whale is essentially moving 24 hours a day, seven days a week.

And so over time, that rope can saw certainly through skin, through blubber, through muscle, and even into bone.

- [Narrator] Scott Landry leads the center's entanglement response, part of a network of seven teams situated between Florida and New Brunswick that record about 36 entanglements in the North Atlantic each year.

- Essentially what I was trying to do is making sure that we weren't running over any of her entangling lines but also keeping the people on the bow as close to her as possible so that they could throw the grappling hook into her entanglement.

(whale snorting) - [Person] Good.

- [Maria] Oftentimes, we will add flotation to keep them at the surface.

- [Person] Put it through.

(dramatic music) - [Maria] And that's called kegging, the exact same thing that the whalers used to do.

- [Scott] Now, once that buoy was affixed to her entanglement, her behavior changed entirely.

- [Maria] And unfortunately, when an animal is entangled, they will try and bolt away from you.

It could just go in any direction, totally erratic.

(dramatic music) - It's pretty rough what we do.

They're just out in the wild living their lives and then we're harassing them the best we can to sort of improve and give them a better chance of life.

- [Person] I see it.

- [Narrator] From 2017 to 2022, scientists have documented 34 North Atlantic right whale deaths and 20 injuries expected to cause death between Florida and the Gulf of St. Lawrence.

Among the cases where the cause was known, 13 of the deaths or serious injuries resulted from vessel strikes and 27 from entanglement.

- The real culprit in this is rope.

It is not a particular target species, it's not a country.

It is rope in the places where these animals have to live.

At this point, it makes it very difficult for a right whale or almost any whale to move through their environments without becoming entangled.

- [Person] Yep.

(whale snorting) (rope clanging) (rope splashing) - [Scott] And any measure that would reduce the amount of rope would benefit whales.

I'm talking about reducing rope, not reducing fishing.

- I got it, I got it, I got it.

- Our goal was to just cut the rope sort of shorter and sort of see if she can then shed it on her own.

What I'm hoping to see the next time someone sees her is that there's no rope left at all.

- [Narrator] Rescuers removed more than 100 feet of trailing line from Snow Cone.