Saving Black Sea Bass

Black sea bass is a valuable North Carolina seafood, but degrading coastal nurseries threaten the population.

MOREHEAD CITY — The black sea bass provides a valuable commercial and recreational fishery for North Carolina. Ian Kroll is part of it.

“They’re a good fish to eat and besides that, they’re pretty easy to catch,” Kroll says as he puts a piece of squid onto his hook. “Usually you drop a line with a squid or shrimp on it and they come right up.”

At least he’s hoping it’s that easy.

“Black sea bass always live in areas closely associated with the bottom,” Kroll explains. That’s why he’s mastered the technique of dropping his line all the way down to the bottom and then pulling it up just a bit. “They are really drawn to oyster reefs and pilings like this. They also like concrete structures like jetties and basically anything that can give them some protection from predators.”

Sure enough, after a few minutes of slowly bobbing the pole and the line up and down, Kroll yells.

“Gotcha,” Kroll exclaims before frantically reeling in his line. But in this case, the black sea bass and the end of the line isn’t meant for dinner. It’s for research.

“What I’m looking at is how habitats support an adult population,” explains Kroll, on the way back to the lab at the University of North Carolina Institute of Marine Sciences in Morehead City. The pier he was fishing on is part of the Institute.

“Black sea bass are really important to the economy, so we want to know how we can produce more of them, or at least produce them at a level we need them,” says Kroll. “So to figure out how to do that, we need to look at their juvenile or young stage.”

Black sea bass spawn in the ocean but then the larvae drift and swim into the estuaries where they find food and shelter. It’s a good place to grow up. They stay through the spring and summer but then return to the ocean in the fall. 

However fishermen and scientists have been finding young black sea bass offshore and those fish are finding shelter in sunken ships, artificial reefs and even natural reefs. So Kroll is looking at two different habitats, in-shore, estuarine habitats and then offshore habitats, trying to determine what habitats convey more benefits to the fish so they can mature and carry on the population. For example, if a fish finds a particular habitat, like an estuary, that offers more protection and more food allowing them to grow quicker and mature faster it will affect the fate of the fish and ultimately the population.

The same can be said of an offshore reef. If that habitat allows the fish to grow better it will affect the fate of the fish and eventually the population.

It’s an intriguing question. However it is a difficult question to study and answer because fish aren’t easy to track. They are hard to see and follow. In addition, the ocean is large. But it turns out fish have a kind of flight data record built into them. It’s called an otolith. It’s a kind of ear bone.

“The use of otoliths in this type of research is relatively new, but it provides a fantastic research tool because otoliths grow like a tree with rings, which means you can determine the age of an individual,” explains F. Joel Fodrie, Assistant Professor of Oceanography at the UNC Institute of Marine Sciences. “In addition, based upon the chemistry of the otolith, you can tell if the fish grew up in fresher water or saltier water, or water to the north or the south, so we have an individualized record of the fish movement through space and time.”

The otolith bone structure is extremely delicate. The tiny bone sits just behind the brain. And once it’s removed, if you look closely you can see, and count, the rings. Those rings tell the precise age of the fish. By analyzing the bone chemistry, researchers can tell where the fish has lived. By collecting otoliths from juvenile black sea bass in estuaries and adults offshore, researchers hope to build an atlas of black sea bass populations.

“This research is going to tell us where these fish grew up and that gets to the question of which habitat is providing the large amount of stock that we see offshore as well as which habitat is more successful at getting the fish past the juvenile stage and into adult stage,” explains Kroll as he places a delicate otolith onto a tray.

That knowledge should help guide habitat protection, because it will give scientists and fisheries management officials a good idea at which habitat is most important to the species. That’s an important part of preserving the $1.4 million black sea bass fishery.

“The whole discovery of otoliths, what they mean and what they tell us about the fish and the population as a whole is incredible,” says Kroll, as he uses tweezers to hold an otolith up to the light in his lab, allowing a clear view of the rings in the bone structure. “It lets us learn so much more about what is going on in the ocean. For example, if you look at this fish on the lab table, I can tell you its size and maybe its sex. But if I look at the otolith I can tell you its age precisely and I can tell you where it has been and perhaps we can look at migration patterns.”

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