UNC-TV Science: Most Fun Study Ever

UNC-TV Science: March 14, 2014
Black Sea Bass and the Most Fun Study Ever

I’m going to get a little meta for a second. In the course of keeping up this blog, I go through a great deal of research. I’ve posted stories about everything from supernovas to genetic engineering to brain imaging. Every study is more interesting than the last but I’ll admit that after enough images of space based on light we can’t see, assays on lab benches and brain scans, I crave something that takes the scientific method out to play for a while.

That’s why I was so happy when I stumbled on what may be the most fun study I’ve ever seen. Imagine three NC State University researchers, a local fisherman, a boatload of scuba and fishing gear, and one simple mission: catch as many black sea bass as possible. It’s going to be a party.

By now you’re probably wondering what makes this research and not a fishing trip. The answer to that question lies in the fish: the black sea bass. Black sea bass are a hugely popular fish, both for commercial and recreational fishers in the southeastern United States, and in an effort to make the keep the black sea bass fishery sustainable, federal and state governments have imposed limits on how many and what size bass are okay to catch and keep.

It’s simple catch-and-release fishing. If the fish is too small, you let it go. In fact, according to an NOAA study in 2009, 89.7% of the 2.72 million black sea bass caught by recreational fishermen were released.

But biologically, catch and release presents a bit of a problem for ray-finned fish like the black sea bass. They have an internal organ called a swim bladder or fish maw that helps the fish control its buoyancy. It looks like one of those balloon animal balloons with a cinch in the middle to make two compartments. It’s filled with gas and at a depth of 29–34 meters, where the black sea bass live, pressure compresses the swim bladder. But as the fish are brought to the surface, the pressure plummets and the fish bladder expands, forcing the fish’s organs to move and even pushing the fish’s stomach into its mouth.

This is called barotrauma, and for many years, people assumed that barotrauma would ultimately kill a fish, a big problem for a sustainable fishery.

So as part of a larger study, NC State researchers Paul Ruderhausen, Jeffery Buckel and Joe Hightower decided to examine how often fish with barotrauma survived the catch-and-release process.

Here’s the fun part. They went out into Onslow Bay with fisherman Tom Burgess and caught thousands of black sea bass. Not only did they use the deep water traps that commercial fishermen use, but also old fashioned hook-and-line (both with electric reels and manual).

They tagged the fish they caught and lumped them into four categories: (1) fish that came up unharmed and swam back down (2) fish with barotrauma that swam back down (3) fish that had been hurt by hooks that swam back down (4) fish that remained at the surface.

Next, they went back out and fished even more, trying to recapture the fish they had tagged to see how many from each group remained.

And if lots of fishing wasn’t fun enough, they did one last comparison between categories on fish that they caught and released at the surface and ones that they didn’t bring up, to get a baseline of how catch-and-release affects survival rates regardless of barotrauma.

So how do you tag and track a fish without bringing it to the surface? The researchers trapped the fish at the bottom of the ocean and used SCUBA gear to dive down and tag them. They tagged 296 fish this way.

The results are actually a bit surprising. You might expect that a fish with its stomach pushed into its mouth wouldn’t generally live to tell his fish friends about it. But the data showed that the barotrauma fish survived 90.1% as often as the unharmed ones they brought to the surface. That’s compared to 36% for the fish with severe hook damage and 16% for the ones that just floated at the top.

As a whole process, catch-and-release did a pretty good job preserving the fish it was meant to. The caught-and-released fish survived about 87% as often as the ones they tagged with the SCUBA gear. The researchers also found that all three methods they used to catch fish yielded similar bass survival rates (around 80%). Manual hook-and-line fishing was marginally more harmful, which the researchers say is most likely due to increases in hook damage.

The study was published online in Canadian Journal of Fisheries and Aquatic Sciences.

- Daniel Lane

Daniel Lane covers science, medicine and the environment as a reporter/writer. He is currently pursuing a master's degree in medical and science journalism at UNC - Chapel Hill.