- [Narrator] You might be wondering what this angler is doing.

He's attaching what's called a descending device to a scamp grouper, which is a deep water dwelling fish.

The fish is suffering from barotrauma.

More on that in a moment.

That device will save the grouper's life.

Now, watch what happens to the fish and the descending device.

Fish that live in deep water are essentially incapacitated when they are brought to the surface.

Descending devices slowly return the fish to deeper water and release them.

Watch this fish recover and swim away.

The device is brought back to the boat.

It's part of a unique effort to save an important fishery.

- [Tom] Another little grouper.

- [David] Yep.

- [Tom] That's another little scamp.

- [Narrator] Here's the challenge in fishing for deep water dwelling fish.

- [Tom] Oh!

- [David] So the way barotrauma works is fish are at really deep depths, and their swim bladder, which is filled with gas, is compressed.

When they're pulled to the surface, that swim bladder expands, because there's a reduce in pressure.

- [Narrator] If that sounds just like the bends, the condition that affects scuba divers when they come to the surface too fast without decompressing, you're right.

- [David] A lot of times when you pull them to the surface, that swim bladder expands so much that they can't swim off on their own, because they're bloated.

You'll see things like the stomach protruding from the mouth, or eyes bulging, and they'll just float off at the surface.

But these devices with the proper weight can get the fish back to depth really quickly, and allow that bladder to recompress, and allow them to swim off pretty easily.

[gentle music] - The ocean, it's a huge open place, and it still seems to be the sort of frontier that we don't completely understand.

- [Narrator] Captain Tom Roller is working with other charter boat captains to adopt the use of descending devices.

- [Tom] It feels like the right thing to do.

People say it's easier just to throw the fish back.

I would disagree with that statement.

I think it's harder to go fishing, and see the impact of your own actions, to see yourself take a fish that, for whatever reason, you don't wanna keep, you can't keep, 'cause the season's closed, and have to throw it back in not as good a condition as it could be.

- You're good.

- You want anybody fishing in the back?

- You can fish wherever.

Just like from here up, just from console up.

That way I can see we can de-hook stuff better.

- The first time I used a good descending device, I could not believe how cool it was.

It felt like I was actually doing the right thing when I was bottom fishing for the first time.

Not to say that bottom fishing is bad, it's just the nature of this style of fishing is you're going to have discards.

And for the first time I felt like I could really do something really effective and really easy.

- [Narrator] Until now, those fish would be tossed away, left to float on the surface and die.

The descending device slowly takes the fish down into deeper water and releases it at a specific depth.

- [David] The regulation is that you have to have a descending device readily available on a vessel when fishing for snapper grouper species in the South Atlantic.

The way these devices work, this device in particular, there's several depth settings you can set it to and it's pressure triggered.

And so this particular one is a, it has a 50 foot depth, a hundred foot and 150 feet.

And so if I caught the fish in a hundred feet, I want to set it to a hundred feet and then you'll actually kind of clip this onto the fish's mouth and then literally just drop the fish over the side of the rail of the boat and then send it down.

And then once it gets to that a hundred foot depth, this device will just pop right back open.

The fish will just swim right back off and you'll just reel it up to do it again.

- [Narrator] Keep watching.

The fish is approaching the depth set on the descending device.

A little closer and there it's released and it swims away.

Marine scientists say their research shows fish recover quickly when descending devices are used.

- Or big grunts, right?

That's a good one right there.

- [Narrator] And that's important to preserving an iconic and valuable fishery.

- The snapper grouper complex is comprised of probably 55 different species, different snappers, different groupers.

It's a bottom fish fishery.

It's very important to both recreational anglers and commercial harvesters.

And it's also a favorite of consumers.

- Yeah, that's a big trigger.

You check this bad boy out.

That is a nice one right there, man.

- [Narrator] But the data shows the fishery may be in trouble.

- [Kyle] Some of the stocks of these species are doing very well.

Some of them are increasing and others are not doing very well.

Some are are decreasing.

And yeah, one concerning trend that we've seen over the past couple of decades is in the grouper species and the sea basses and porgies that they've had a decrease.

And we think that it is due to poor recruitment or not producing enough baby fish over time.

And we're not sure why that's occurring.

We're doing research into why that may be, whether it's environmentally driven or fishery driven or ecologically driven.

- [Narrator] And because this is a multi-species fishery in which anglers target a lot of different species using the same techniques, nobody knows what fish will be pulled up from the bottom.

That puts all species at risk for barotrauma.

- For the the red snapper fishery, the stock assessments estimate that overfishing has been occurring and the primary source of overfishing in this case is discard mortality.

And so this is a key example of how using descender devices can help mitigate overfishing by reducing discard mortality.

- [Narrator] Which is why scientists and fisheries manager believe descending devices are an easy way to help preserve a valuable resource.

- It's not only important for fishermen to use descending devices and use their best fishing practices, but it's just as important for them to tell us when they're doing that.

That helps us to get a better understanding of a release fishes chance of survival.

And that helps us to take that into account when making management decisions in the future.

- We have to worry about the future.

We have to worry about the availability and abundance of fish.

And unfortunately, I can sit here and tell you stories about many fisheries that I've lost in my lifetime.

And I mean, I'm 42 and are already talking about the way things used to be.

That's not a good thing.

So we have to worry about all these species.

We have to take care of everything.

And if we take care of the fish that we're allowed to harvest, hopefully that will give us longer seasons, more availability in the future.

I mean it and all of us.

It takes our part in which to do that.