Spring 2023

Hook, Line & Science

Where Dolphinfish Roam, What Fish Remains Tell Us, and Where Red Drum Go When They Escape

March 28, 2023 Scott Baker and Sara Mirabilio 7-min. read

The award-winning series curated by Scott Baker and Sara Mirabilio, fisheries specialists with North Carolina Sea Grant

Where Do Dolphin Fish Roam?

As part of the world’s largest fish tagging program, anglers up and down the East Coast have played a key role in tracking the species’ movements — and you can help, too.

Dolphinfish, also known as “dorado” or “mahi mahi” (Coryphaena hippurus), is a relatively easy sportfish to catch. The short-lived species grows fast and is popular among anglers and seafood consumers alike. In fact, in 2021, anglers landed 1.9 million pounds of dolphinfish in North Carolina, the most on the East Coast with the exception of Florida, where anglers landed 3.9 million pounds.

Despite the fish’s popularity, its management is challenging due to insufficient data to support a traditional stock assessment. This is especially problematic considering the increasing popularity of dolphinfish among anglers in the South Atlantic, Gulf of Mexico, and the Caribbean since the 1990s, as well as recent research that suggests that the relative abundance of dolphinfish in the Atlantic Ocean has been declining.

Scientists and fishers have been collaborating to learn more about dolphinfish to better understand the drivers of the population and health of the species. Since 2002, the Dolphinfish Research Program has utilized a flotilla of anglers to capture, tag, and recapture dolphinfish using both traditional and satellite tags. It is the world’s largest fish tagging program.

What did they study?

From 2002 to 2017, the Dolphinfish Research Program distributed over 37,000 tags to 1,313 captains and more than 3,285 fishing mates from around the world. Collectively, these participants took part in tagging and releasing 23,232 dolphinfish, with the majority of fish releases (87%) occurring along the East Coast.

Wessley Merten, of Beyond Our Shores Foundation, and his colleagues analyzed the data to identify participation rates, trends, recapture rates, and movement patterns. The analysis identified gaps in the data and also provided important information — including findings specific to North Carolina and the East Coast.

What did they find?

During the study period, 571 dolphinfish were recaptured. Most fish were tagged off Florida (68%), followed on the East Coast by Georgia/South Carolina (14%), North Carolina (3%), and the remaining coastal states from Virginia north to Maine (1%). Anglers in the Bahamas/Caribbean contributed 13% of tagged fish.

On average, dolphinfish moved northward along the East Coast, from Florida to the Mid-Atlantic Bight, in 44 days. The fastest straight-line movement from Florida to North Carolina was 7 days.

Most tagged fish were 18 to 22 inches in fork length. Most recaptures (71%) occurred within 40 days of tagging.

What else did they find?

Tag recapture data suggests that the Antilles Current (a surface current that meets the Florida Current before joining the Gulf Stream Current) could be a major supply route for South Atlantic dolphinfish fisheries. Enhanced tagging efforts might assist with documenting specific migration routes that dolphinfish take in the South Atlantic.

So What?

The contributions of anglers, particularly those that recaptured dolphinfish, allowed scientists to document expanded movement patterns.

Programs like this one are especially important because financial resources for fisheries management in the Southeast are limited. By combining the interests of anglers and researchers, everyone benefits.

You can sign up for a tagging kit, view a map of the tagging and location data that anglers provided, see who tagged the most fish, and learn more about the project at dolphintagging.com.

by Scott Baker, marine fisheries specialist, North Carolina Sea Grant.

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Are Fish Remains a Historical Indicator of Household Status?

A new study reveals how wealth and slavery affected the diversity and type of fish that Charleston residents consumed between 1710 and 1900.

Charleston, South Carolina, has had a prolific angler scene dating all the way back to 1670. There are many anecdotal accounts of its diversity and richness, with indications that White-European households of the time purchased non-local and expensive catches.

African slaves historically dominated the fishery industry until 1860, after which African workers remained on the docks and continued to control the buying and selling of fish outside of the traditional fish markets of the time.

Comparing historical records of fish market sales and anecdotal tales with zooarchaeological remains can help paint a picture of what wealthy households ate compared to lower income households. This research also helps shed light on how Black men and women impacted the fish economy of Charleston at the time.

What did they study?

Each household in Charleston from the 18th to 20th centuries was responsible for disposing of its own food waste, which meant many homeowners and laborers used their own lands for disposal. Elizabeth J. Reitz, of the Georgia Museum of Natural History, and her team identified 55 land plots that they separated into lower, moderate, or upper status households (based on historical records) and studied the zooarchaeological remains of fish in each land plot. They also looked at fish remains at fish market sites.

Specifically, archeologists looked at the diversity and number of fish present in each plot of land from 1710 to 1900. They then compared these numbers and types of fish to historical records of fish market sales to draw connections between households and the fish they bought.

What did they find?

Archeologists discovered a total of 62 fish species present in these land plots, 11 of which make up over half of the Charleston fish remains and which are still common catches along the Carolinas’ coasts. They identified two types of sea catfishes (hardhead catfish and gafftopsail catfish), and black sea basses (locally known as blackfishes) — along with five drum species, the most abundant of which were seatrouts, Atlantic croakers, black drums, and red drums.

Sea catfishes are the dominant fish in all the groups examined, despite the fact that modern anglers consider these fish inedible or even poisonous.

Comparing samples from the sites of lower, modest, and upper status households and samples from fish market sites showed that upper status groups had a higher diversity and number of fish between 1750-1820 compared to modest and lower status households and samples from market sites. Upper and modest households had roughly the same diversity and number for all other periods but were both consistently higher than the lower status and market site groups.

This suggests households with higher incomes purchased a greater number and variety of fish than those with lower incomes.

Samples from fish market sites had the fewest remains, which scientists speculate could be due to consumers bringing home whole fish and disposing of the remains themselves.

Although upper and modest status households consumed larger numbers of fish in greater diversity, the cost of the fish they consumed was relatively low. This could be due to wealthier households employing a larger staff that needed to be fed more cheaply.

What else did they find?

The amount of fish present in these land plots was disproportionately higher than the number of fish reported sold at fish markets. This suggests that laborers purchased fish for their households through formal and informal methods.

Informal fish sales were a key part of the Charleston fish scene during this time period. A majority of household chefs and other workers were African and most likely purchased fish informally from African fishers.

by Alexa Cortes, science communicator at North Carolina Sea Grant.

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Where Do Red Drum Hide?

A 2022 South Carolina study finds that where red drums go to escape depends on whether they are hatchery-raised.

Research Need

Did you know that red drum are the state saltwater fish of North Carolina, due to their popularity as a sportfish?

Red drum are also extremely popular with South Carolina anglers. In the 1980s, South Carolina red drum populations began to decline, a concern for anglers and fish biologists alike.

In response to these declines, managers began spawning red drum in hatcheries to supplement wild populations and create more angling opportunities. Biologists release the juvenile fish when they are about 2 inches long into estuarine oyster reefs, mudflats, and vegetated marshes.

The South Carolina red drum stocking program has been active since the late 1980s and releases as many as 1 million juveniles a year into coastal waters. Now, scientists want to know what happens to the fish after release.

We cannot assume that hatchery-reared fish behave in the same way as wild fish, so studying how fish move, select habitat, and react to predators after release is essential to conservation efforts.

In fall of 2022, scientists in South Carolina evaluated how hatchery-reared red drum juveniles select between oyster reef beds and marsh grass communities. They also observed if behavior changed in the presence of a predator.

What did they study?

To observe and better understand juvenile red drum behavior, Bruce W. Pfirrmann, of Baruch Marine Field Laboratory, and his team created mesocosms — artificial structures that simulate a natural area. The mesocosms in this case were aquariums, the size of an average 10-gallon fish tank. Creating these mesocosms is important for behavior research, since it is difficult to observe fish in the open water.

The researchers manipulated the water chemistry, temperature, and material at the bottom of the tank to match wild conditions. They placed oyster shells on one half of each mesocosm and planted marsh grass on the other, and the fish could easily move to either side. The scientists then placed the juvenile fish into the center of the tank and monitored where the fish swam.

They also ran trials with a blue crab in each mesocosm to test if the presence of a predator changed which side of the tank the fish swam to. Blue crabs represent one of the many predators that juvenile red drum face.

What did they find?

After running multiple trials, scientists observed that hatchery-reared juvenile red drum were three times more likely to hang out in the oyster shell than in the marsh grass. The fish also swam to the oyster reef side of the tank when there was a blue crab in the aquarium.

In previous studies, wild-caught red drum selected marsh grass when a predator was introduced. This raises the question of whether fish gain skills for avoiding predators from maturing in the wild.

In other words, are there survival benefits to growing up in the wild that hatchery-raised fish miss out on?

What’s next?

Understanding fish habitat selection after release will help managers plan the best locations for stocking, which will maximize the survival of stocked fish each year.

Research on habitat selection is also important to anglers. If the red drum stick around in oyster reefs until maturity, these results could be good news for the anglers who fish there.

by Hanne Parks, science communicator at North Carolina Sea Grant.

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