Behind a barricade, crowds gather to see an animal typically only seen offshore. Blue marlin, fish that can be as long as a car, are weighed at Big Rock Landing in Morehead City, NC. The excitement builds as spectators hold their breath waiting to hear the weight and learn if it puts the angler in the running to win one of the multi-million dollar awards for the heaviest blue marlin caught.

But what happens after the thrill of the weigh-in, after the photos are taken, after the champagne is popped for the lucky winners? Behind the glitz of the tournament, parties, and awards, researchers at NC State Center for Marine Sciences and Technology (CMAST) have a unique opportunity to sample these highly migratory pelagic fish. The remoteness of blue marlin habitat and the substantial costs associated with offshore sampling, including vessel operation and specialized fishing equipment, make it difficult to obtain samples of this species. Additionally, since most recreational catches of these fish are catch and release, they are rarely brought to the docks.

CMAST’s 24-year partnership with the Big Rock Tournament provides a unique opportunity for a relatively large sample size of blue marlin within the same time of year and same area of the ocean from year to year. These samples have been taken from these fish and sent to labs studying billfish across the country at Stanford University, Texas A&M University and NOAA Southeast Fisheries Science Center.

When the fish leaves the weigh-in station the work begins. CMAST graduate students back the work truck right up to the fish hanging at the weigh station, and with help, secure it in the bed of the truck.

“I’ve been doing this for six years, and this was the first fish that was so large, its tail was actually scraping the road because it was hanging so far over the tailgate,” said recent Ph.D. graduate Johnna Brooks of the 919 lb winning fish.

Not only did Brooks complete her Ph.D. at CMAST, but she also grew up down the road from it. Her family is from nearby Harkers Island, so she has been familiar with the Big Rock tournament even before being involved in the behind-the-scenes research. Her brother, Captain Cameron Guthrie, has been fishing in the tournament since the early 2000s. And this year, Cameron was the captain of the Marlin Fever, the boat which caught the winning marlin.

The researchers then drive the few miles to CMAST and pull up to waiting staff and students, where it is all hands on deck. Literally. It took seven people to pull this recording-winning marlin off the truck and onto the grass where they will sample the day’s marlin catches.

Fish Printing

When graduate student Bethany Wager and Brooks brought the record-breaking fish back to the lab, there was something special to be done before sampling. Fish prints. Brooks is not only a proud sister and researcher, but also an artist. She knew she wanted to capture the emotion of seeing this tournament winning fish, and the best way to do that is by fish printing, or gyotaku.

“We’ll always have the pictures of the fish, but being able to walk up and see the size of the fish like this is something you can’t take away,” says Brooks. “It’s so cool to be able to preserve it this way after all our dissections and sampling and the fish is no longer here, it’s still here in some capacity.”

With multiple drop-cloths, a cup of paint, some brushes, and many hands, Brooks printed the massive marlin onto the cloth. Later, she went in and did some touch-ups to end up with the finished product.

The Sampling

Sampling the fish caught at Big Rock is done by students and faculty based at CMAST in NC State’s Department of Applied Ecology and the College of Veterinary Medicine.

Applied Ecology

For the past five years, Ryan Tharp has led the Big Rock sampling team as a graduate student in the Buckel Lab, but after graduating with his Ph.D. he passed the torch to Ph.D. candidate and labmate Bethany Wager. Wager, Tharp and Brooks sampled each blue marlin that came to the Big Rock weigh-in station.

Samples are taken of the stomach contents, intestines, muscle tissue, skin, liver, intestines, skin, blood, eye lenses, and the whole eye of each marlin. Later, they remove the otoliths, which are bony structures in the fish’s ear, with yearly rings similar to tree’s rings. Otiliths can be sectioned to count the rings that indicate how old that fish was when it was caught.

They also take samples of the fish’s gonads, which are always ovaries, since all of the fish brought back from the Big Rock tournament are female marlin. We know this because male blue marlin only reach about 350 pounds and the tournament minimum is 400 pounds, which is why we only see females at the dock. After sampling, some of the samples are packed up and shipped to scientists in California, Texas, and Florida to conduct research on these billfish.

Meanwhile, back at the docks, Professor Jeff Buckel, Research Scholar Paul Rudershausen, and Jeffrey Merrell, perform all the sampling of the game fish brought in. For each wahoo, yellowfin tuna, and dolphinfish, they sample the stomach contents to see what the fish has been eating.

Veterinary Medicine

In addition to the Applied Ecology faculty and students involvement, NC State’s College of Veterinary Medicine has a team assisting in sampling during the tournament. This year they sampled 112 fish.

Their research focuses on game fish, specifically the dolphinfish, wahoo, yellowfin tuna, as well as blue marlin. The sampling efforts are led by Professor Greg Lewbart, and Sydney MacDonald, third-year veterinary medicine student. Together with a team of veterinary students, they collect blood samples from the sinus venosus (a chamber of the heart), ocular samples (vitreous and aqueous fluid) and organ samples (spleen and liver). From this initial research, these veterinary students and faculty are hoping to see how biomarkers, such as sodium, potassium, and glucose levels, change after a fish is deceased.

To compare postmortem blood samples taken from the tournament fish, the veterinary team also collects samples from live gamefish during offshore summer fishing trips. The team takes many of the blood samples to the lab where they centrifuge the blood to isolate the plasma. They may be the first veterinary researchers to compare fish blood changes over time (pre-mortem and post-mortem).

This research will be used to validate the use of blood chemistry values from deceased fish in a tournament setting. They will determine which values can be used from sample collection and which cannot be used to assess overall health of the species. Additionally, they bank the samples for future research. Collected plasma can be used for PFAS assays, also known as forever chemicals. Additionally, red blood cells may be used for DNA/RNA research.

The two ocular fluids the students collect are termed aqueous and vitreous. They hope to gain more insight on both the difference in values between these as well as compare these values to the plasma samples. Eyes are an immune privileged area, meaning they limit inflammatory immune responses. With that knowledge, the veterinary team suspects ocular fluid values may change more slowly than blood samples in a deceased fish.

Currently, the team has two years of organ samples and hope to run the samples in the lab soon. The data from these samples will be used to conduct research on heavy metals in these fish.

With plans to continue their sampling efforts during the tournament in the coming years, there will be a growing dataset for veterinary students and faculty to learn more about and track the health of these fish. The tournament partnership with CMAST is instrumental to building baseline health data, and as MacDonald highlights, “we are giving scientific value to every fish brought into the docks!”

What is the strangest thing you’ve found when sampling a Blue Marlin?

The resounding answer from the sampling team was a bill from a billfish that was found inside the winning marlin’s head. It must have had a liking for eating billfish, because it also had two more in its stomach! The vets at CMAST took a portable x-ray machine to see how the bill lodged in the head, and then they removed it to estimate that the bill had been in the marlin’s head for about two months. The vets could tell that the wound was healing and noted how it’s amazing these animals can heal themselves without a doctor!

It looks like two bills because the bone structure of a bill is two bones that go out and then fuse together. That fusing of the bones separated when it was stuck inside the head of the marlin. Researchers don’t yet know the species of the billfish but since there was still tissue on the bone of the bill, they are hoping to do some genetic testing to determine the species.

Other notable items found in past blue marlin’s stomachs are bullet and frigate mackerel, dolphinfish, papered nautilus, a wahoo and not in the stomach, but still a fun surprise this year was a small remora stuck to the underside of the marlin!

Why don’t we eat these fish?

These fish are large apex predators, meaning they are at the top of the food chain. A phenomenon called bioaccumulation causes mercury to build up in their tissues that can make it unsafe for humans. With recent technology however, researchers are now able to distinguish between the different types of mercury that are inside the muscle tissue rather than only looking at the total mercury concentration. There are two primary types: methylmercury and inorganic mercury. Methylmercury is toxic to humans, but inorganic mercury is typically not toxic in small amounts. Looking at blue marlin muscle collected from 1975 to 2021, the Buckel Lab found that these fish actually have higher concentrations of inorganic mercury, not methyl mercury, which is not what is typically observed in fish. Additionally, the lab found high protective values of selenium concentrations in the fish, which is thought to provide a buffer against the toxicity of methylmercury. Their findings suggest that interpretations of the toxic effects of eating blue marlin should be made with caution. Federal consumption advisories could be revisited with more studies on selenium concentrations potential to offset mercury toxicity in seafood products.

However, the most relevant reason these fish are not consumed in the context of the tournament is simply a practical one. Many of the fish brought back to the dock weigh more than 400 pounds, far too large to fit in the insulated fish boxes found on most boats. As a result, they remain on deck during the hours-long trip back to shore, often exposed to high temperatures. Without proper chilling, the meat can spoil, making the fish unsuitable for consumption.

The Power of Partnership

CMAST is incredibly grateful for its longstanding support and partnership with the Big Rock Tournament. This collaboration provides invaluable opportunities to connect with the fishing community, access fish species that are otherwise difficult to sample, and maintain a continuous dataset spanning more than two decades. Together, these efforts have significantly advanced our understanding of pelagic fish populations and fisheries along the North Carolina coast.

“The Big Rock Tournament has become much more than just a fishing competition. This event and its organizers make for a vital scientific partnership for us,” said CMAST Director, Dave Eggleston. “The willingness of anglers, tournament organizers and the community to work alongside our researchers has allowed us to build a unique, long-term dataset that simply would not exist otherwise. That collaboration has led to meaningful discoveries, benefitting fisheries science today and will continue to inform conservation and management for years to come.”

To learn more about the research made possible through the Big Rock Tournament partnership, we’ve included below a list of the peer-reviewed publications that have used data collected from tournament fish samples.

The Data in Action: Featured Publications

• Feeding Ecology of Blue Marlins, Dolphinfish, Yellowfin Tuna, and Wahoos from the North Atlantic Ocean and Comparisons with Other Oceans
• Computed Tomographic Assessment of Hooking-Related Injuries in Recreationally Angled Blue Marlin
• Total mercury, methylmercury, and selenium concentrations in blue marlin Makaira nigricans from a long-term dataset in the western north Atlantic
• Short-term variability but long-term consistency in diets of dolphinfish Coryphaena hippurus in the western North Atlantic
• Omnidirectional sonar increases catch efficiency in a pelagic sportfishing tournament
• Temporal changes in lengths of Dolphinfish revealed by sampling at sportfishing tournaments in the southeastern United States
• Age, growth, and reproduction of dolphinfish (Coryphaena hippurus) caught off the coast of North Carolina