Local Researcher Aims To Bolster Black Sea Bass Fishery

Jul 14, 2015

Credit UNC Institute of Marine Sciences

Black sea bass are making a comeback in North Carolina after the species was overfished a decade ago.  We visit the Institute of Marine Sciences in Morehead City where they’re using ear bones from hundreds of black sea bass to learn which habitats along our coast best support the fishery. 

The commercial fishing industry is an economic engine for the state. $369 million of economic impact was generated by commercial fishing in 2013, according to the Department of Marine Fisheries.  One of the many species caught off the coast is black sea bass.  You may have had it at a fancy restaurant coated in herb butter and served with a wedge of lemon.  Also known as blackfish or old humpback, black sea bass grow to 24 inches and 6 pounds, and they can be found in inshore and offshore waters.  At the University of North Carolina’s Institute of Marine Sciences in Morehead City, graduate student Ian Kroll is involved in research with black sea bass and what types of habitat are best suited for the fish.

“If we can find out what habitats produce the best quality fish and maybe the quickest amount of time, there kind of leads to that impetus to conserve these habitats.”

The black sea bass fishery was identified as overfished in 2005.  But in the last decade, their numbers have bounced back, due to more stringent regulatory standards.

“In 2014, commercially, there was over 500,000 lbs of black sea bass, and that equals about $1.4 million going to the economy.  And, just looking at it on the South Atlantic scale, that’s over half the black sea bass caught in the South Atlantic comes from North Carolina.”

Credit UNC Institute of Marine Sciences

Black sea bass are also an important fishery for recreational anglers, with 135,000 pounds caught last year. 

Ian received a three year fellowship from NOAA Fisheries and NC Sea Grant to conduct his study.  At one point, it was believed that black sea bass grew up in the estuarine waters and eventually moved offshore as adults.  But researchers have found juveniles at sea.  Ian is studying what types of ecosystems along our coast are most productive for supporting black sea bass, and how their environment affects their growth rate and sexual maturation.

To conduct his research, Ian is extracting something called an odolith, or an “earbone” from black sea bass.  Odoliths are hard, calcium carbonate structures located behind the brain of a fish.  Not only do they help a fish with orientation, balance and sound detection, it works a lot like a flight data recorder.

“I’m looking at the growth rings, these growth bands during the juvenile or the younger stage of their life to try to see how quickly they grew up, and we can look at that by seeing how far the growth bands are apart.”

Credit UNC Institute of Marine Sciences

It’s similar to counting the number of rings on the crosscut of a tree.  You can tell the age and what type of environmental conditions the fish experienced by examining the odolith under a microscope.  In order to conduct his research, Ian needs samples.  So, I’ve come to the Institute of Marine Sciences to help him out.

“So we’ve got a couple of hook and lines that we’re using, we’re just hooking them with squid from the local bait shop.”

Ian sets down the fishing rods, a bucket of water and the bait on the North Carolina Division of Marine Fisheries dock in Morehead City.  It’s about 10 o’clock, so it’s not too hot out.  The tide is starting to come in which, I’m told should improve our chances of catching black sea bass.  

IK: “We see that the juveniles really like structured habitats to hang around.  So piers work really well, jetties, they like to hide out around there.  Maybe hide from some predators as the tide moves in.”

JB: “So we don’t want to cast very far out, we want to stay close to the dock?”  

IK: “we want to stay close to the dock. It gets a little risky for your hook, it might get caught on something.  But that’s where we like to find them”

Credit UNC Institute of Marine Sciences

We drop our lines in the water.  Ian didn’t have to wait long before he felt a tug at the other end of the line.

IK: “Alright, so the line just hit the bottom.  They seem to be biting pretty well today.”

JB: “Uh oh, got one already!”

Less than 15 seconds and fish was hooked.

IK: “oh.  Pinfish.”

Not what we’re looking for today.  Just as Ian throws it back, I start reeling in a black sea bass.

IK: “I’m going to let him calm down a second, otherwise I’ll get poked.”

Black sea bass are black when their adults.  But my fish is a dusky brown color, about six inches long.  It wouldn’t make much of a meal, but Ian says it’s the perfect size for his research, so I put him in the bucket.

Credit UNC Institute of Marine Sciences

In about an hour, we caught a half dozen black sea bass.  Ian grabs the bucket and carries it to the wet lab at the Institute of Marine Sciences.  The dark room has plastic pipes running along the ceiling, pumping water from Bogue Sound into glass aquariums. One by one, Ian gently places each fish into a tank.

“You can see, they start draining their color when they get nervous, or traumatized.  The first thing they like to do is hang out near the fake reefs I created for them because it’s what they know. That’s the structure, it equals safety for them.”

The aquarium will hold the fish until Ian is ready to extract the fish’s odolith.  In addition information about age and growth rates, the ear bone will also yield information as to where the fish was born- whether in estuarine waters or offshore.

 “As the bones grow, they incorporate the amount of trace metals like magnesium or barium that’s available in the water.  And they incorporate into the actual structure.  So we can go in later and try to get out that signature and determine what type of environment they grew up in.”

Areas along the coast have different chemical signatures due to changing salinity and water temperatures.  For example, the coast of Wilmington is not the same as the waters of the Pamlico Sound.  Ian says they have a machine that can detect these subtle chemical differences in their clean lab.  I follow him through a series of hallways and doors.

Credit UNC Institute of Marine Sciences

“So, we’re now in the clean lab.  We’re pretty cautious about dust and external contaminants in here because the machine we use to extract it is very sensitive.  And often times, we’re looking at levels in the nanomolars.  So really, really, really small amounts of these chemicals.”

Ian puts on latex gloves and a lab coat.  So far, he’s collected about 750 odoliths over the past six years. He hopes to create a “catalog” of chemical signatures.

“If I catch a fish that’s five years old, we can assume it’s growing up, it’s 2015 now, in 2010.  So if I can go back and I have a record, of signatures from 2010, it will make it a lot easier to identify where it came from.”

Ian plans to conclude his fishing trips at the end of this summer.  In addition to learning more about the species, Ian hopes to identify areas along the North Carolina coast that are productive black sea bass habitats so that these areas may be protected.  He says his findings could be applied to other fish species who grow up inshore and move to the ocean, such as snapper and grouper, which are also important fisheries to the State.