Summer 2023

Hook, Line & Science

Will you find more big fish during the day or night?

June 2, 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

What Fish Can We Expect to See at the East Coast’s Offshore Wind Farms?

Oysters provide important structural habitat along coastlines. Anglers who fish in inlets know the surrounding water in the estuaries is usually murky or turbid, which makes it quite challenging for researchers to assess which marine creatures are swimming past, living in, or stopping by oyster reefs.

Current methods to evaluate oyster reefs typically require direct capture, which is often destructive and sometimes lethal. Scientists at North Inlet–Winyah Bay National Estuarine Research Reserve and the University of South Carolina’s Baruch Marine Field Laboratory wanted to determine if acoustic imaging sonar could sample the numbers and size of swimming organisms, but in a way that was not harmful to the organisms and that did not require the substantial time delay for processing that usually follows field sampling.

What did they study?

Researchers placed high-frequency sonar imaging devices in 10 fringing intertidal oyster reefs in Georgetown County, South Carolina. The scientists used high-frequency sonar to reduce the risk of harming the aquatic life they were studying.

Their objective was to collect estimates of the numbers and size of fish swimming past the reefs. Because they were using sonar imaging, they could collect information day and night.

What did they find?

In total, they counted over 4,500 fish during the daytime and over 1,900 at night. The number of fish per site ranged from seven to 800.

Results of the sampling showed that there was a higher number of small fish in the reefs during the day, but the average fish size was smaller at night. That said, there also were several instances where a few very large fish were detected at night but not during the day.

One limitation of the study is that the sonar images are not detailed enough for scientists to reliably determine the fish species. However, pairing the sonar imaging with the regular catch data can be useful for evaluating the overall numbers of fish in an estuarine habitat under murky or dark conditions.

What’s next?

Sonar could be useful for comparing different types or ages of restored artificial reefs, as well as to compare communities on different reef types. Researchers also could use repeated deployments of sonar to check habitat use across annual, seasonal, or tidal stages.

by Christine Ryan, Hook, Line & Science Communication Fellow

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Will the Big Fish Have Enough to Eat?

A new model shows that in some cases the amount of available forage fish won’t meet the needs of predator fish.

The smaller fish in our sounds and coastal ocean, known as forage fish, provide food for nearly all commercial and recreationally important fish species, as well as sea birds, marine mammals, and more.

To have healthy fish populations for larger predator fish, fishery managers need to ensure there’s plenty of small fish to eat. But this is easier said than done. Scientists are working to better account for the role forage fish play in the marine ecosystem. What type of management approach would ensure that important predators have enough to eat?

What did they study?

A research team from NC State’s Center for Marine Sciences and Technology and East Carolina Univeristy’s Department of Biology chose Pamlico Sound, North Carolina, to develop a fish-focused, multispecies model of “who eats who” and what factors might influence this. Pamlico Sound and its tributaries serve as critical nursery habitat for numerous species and support several economically important recreational (e.g., spotted seatrout and red drum) and commercial (e.g., blue crabs and shrimp) fisheries.

The team included data about the diets of larger predator fish that eat smaller fish, commercial and angler catches, and estimates of other variables, such as levels of consumption overall by predator fish. They also evaluated the extent to which predator fish and fishing fleets target the same forage fish.

What did they find?

Researchers were able to estimate total predator demand for forage fish and identified important species, including the top fish predators in
Pamlico Sound.

Predators removed the majority of forage fish, consuming over 62,000 tons of fish annually in Pamlico Sound. Atlantic menhaden, anchovy, spot, and Atlantic croaker were the top forage fish in Pamlico Sound and comprised over 80% of the total amount of fish that predators consumed.

Bluefish and longnose gar consumed the most fish. In fact, these two plentiful species consumed more prey fish than the fishing fleet removed. As fish populations fluctuate, other predator fish, such as southern flounder or weakfish, could replace bluefish and longnose gar as the top consumers of fish in Pamlico Sound.

Fishing fleets removed over 6,300 tons of fish annually in Pamlico Sound, and forage fish accounted for 61.2% of it, specifically. Because predator fish also consumed Atlantic croaker and spot in high quantities, these two species have the largest combined removal from the waterbody.

Anything Else?

The scientists determined that, in some cases, the forage base is insufficient, but in others, sufficient, to support increased predator demand. Under one scenario, predation and harvest did too much damage to the population of spot for it to remain sustainable. However, the production of shrimp and blue crab, according to the model, remained sustainable even with increases in predatory consumption.

So What?

The model directly addresses management questions that are not possible to address with a single-species approach. It illustrates that tradeoffs between fisheries for forage fish and predator fish should be considered when assessing and managing fisheries in Pamlico Sound.

The scientists recommend tracking managed predator fish (weakfish, southern flounder, summer flounder, red drum, and striped bass) over time and regularly comparing their numbers to the populations of important forage species (spot and Atlantic croaker).

They do note that their model focused on predator-prey interactions only. Environmental stressors, such as low dissolved oxygen events in Pamlico Sound, also have the potential to impact forage fish.

by Sara Mirabilio

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Are East Coast Anglers Catching Tunas, Sharks, and Billfishes Farther North?

Trends from a longstanding recreational survey can help anglers, tournaments, and communities plan for changing fisheries.

Highly migratory species like tunas, sharks, and billfishes are prized by offshore anglers and charter fishing operations. In many communities along the East Coast, fishing for these species is centered around tournaments that, by necessity, are located near the populations of these species and that take place at a time of year when they are most available.

Offshore anglers are skilled at utilizing environmental data to locate the fish, often referring to personal catch histories, changes in sea surface temperatures, and insight from other fishers. But as a more consistent resource, NOAA conducts an annual survey each year that helps us manage these fisheries.

The NOAA Large Pelagics Survey is a specialty survey that spans Maine to Virginia and focuses on the highly migratory species that anglers target from June to October. This survey exists because highly migratory species — unlike nearshore species like flounder, drum, and trout — are considered “rare-event,” and are much less likely to be encountered. We know that the warming ocean is forcing some species to shift northward, meaning anglers should also be catching highly migratory species farther to the north. Looking at the most recent 18-years of recreational catch data is one way to verify this.

What did they study?

NOAA scientists utilized dockside interview data from the Large Pelagics Survey from 2002 to 2019 to see when and where anglers reportedly caught 12 highly migratory species. Coupled with detailed public records of sea-surface temperature, the team could then use models to determine shifts in captures in relation to latitude, time of year, and water temperature.

The scientists focused on species of interest to anglers: albacore tuna, bigeye tuna, skip-jack tuna, yellowfin tuna, bluefin tuna (both small and large, coded as different target species), blue shark, shortfin mako shark, Atlantic common thresher shark, Atlantic blue marlin, swordfish, and white marlin.

What did they find?

Scientists looked at more than 96,000 dockside interviews in the dataset, some from highly migratory species tournaments.

Since the earliest year of the study period (2002), the analyses indicate that highly migratory species catch locations have shifted north. Further, many are being captured earlier in the year. These shifts are strongly linked to increasing sea surface temperature.

For example, northerly shifts in capture over the time series ranged from about 0.5 nautical-miles per year for blue marlin to about 5 nautical- miles per year for small bluefin tuna. And for every ~2° F increase in sea surface temperature, species shifted northwards a minimum of 1.5 nautical-miles (large bluefin tuna) to 22 nautical-miles (blue shark).

Anything Else?

The most frequently encountered species in the survey were yellowfin tuna (14,326), small bluefin tuna (8,177), and white marlin (7,786).

So What?

The NOAA Large Pelagics Survey was designed to monitor the catch of bluefin tuna during the primary fishing season off the coast of the Northeast U.S., but reanalysis of the data available clearly suggests that the survey provides insight on many Highly Migratory Species important to anglers and communities along the entire East Coast).

by Scott Baker

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Read more from the award-winning series at HookLineScience.com.