Scientist at the Pier

From Bayside to Oceanside
November 23, 2016
A Fellow Goes Fishing
November 23, 2016

In Gloucester Point, Virginia, a wooden, T-shaped public fishing pier juts into the York River, six miles from where the waterway meets Chesapeake Bay. To the pier’s right, the Coleman drawbridge connects rural Gloucester Point to Yorktown, a destination for seekers of colonial-era charm. To the pier’s left, the Virginia Institute of Marine Science’s brick buildings sit up on a hill, only a few minutes away by foot.

At 3 a.m. on a Wednesday, you’d expect the pier to be dark, empty, and quiet. None of these things are true. The night is bright and loud. Bridge lamps spill orange light onto the river, and fifteen anglers stand and sit in the shine of the pier’s stadium lights, their fishing poles leaning against railings. They yell and laugh as if it’s a house party. Then a big, white truck with the Virginia Institute of Marine Science (VIMS) logo pulls into the parking lot.

Cindy Marin Martinez, a VIMS graduate student, jumps from the driver’s side door. It’s June, but she wears a fleece jacket, jeans, and rubber boots to keep out the night’s chill. Her hair is long and thick and black, already escaping from a hastily made braid. But she doesn’t seem to care, as she wheels a wagon holding a large net from the truck  to the pier—she’s here to catch larval fish. Nights like these usually involve a lot of waiting, but Martinez tries to make the most of her time.

“Some nights I watch the moon,” she says. “Sometimes there are fireworks across the river.” The fireworks are from Williamsburg’s Busch Gardens, a theme park 15 miles away. An avid angler herself, Martinez occasionally brings her own pole, rigs her net so that she doesn’t have to hold it, and casts a line, joining the nighttime anglers around her.

These nights at the pier tie into Martinez’s work as a Virginia Sea Grant graduate research fellow. She wants to find out how environmental conditions, like water temperature and salinity, affect the abundance of larval fishes in the York River—the one and only source of adult fishes. Without larval fishes, no anglers would be at the pier tonight.

A fish is “larval” from the moment it hatches until it becomes a juvenile, which is defined by the presence of fins and scales. Larval fishes are transparent and range from four- to thirty-millimeters long. They look more like miniscule shards of glass than fish. While some are miniatures of their adult form, many species look nothing like their future selves.

That is, if they live long enough. Although the larval stage for most species is only several weeks, this is when a fish is most likely to die. The water is a dangerous place if you are tiny and terrible at swimming. Larval fishes primarily rely on tides and currents for transportation. When a predator, which includes almost everything in the water larger than a larval fish, confronts them, there’s no escape.

Martinez is studying five species that support important commercial and recreational fisheries: Atlantic menhaden, Atlantic croaker, spot, summer flounder, and American eel. Some people may recognize summer flounder from their dinner plate, or the American eel for its historic role as staple food of Native Americans and early colonists of the Chesapeake Bay region. But these other, less familiar fish are equally as valuable—like the Atlantic menhaden.

Menhaden has a serious underbite and comically large mouth. The National Oceanic and Atmospheric Administration describes it as “unfit for human food consumption due to its small size and high oil content.” Yet this fish supports the largest commercial fishery in the Chesapeake Bay, and the second largest fishery in the United States because it is chock-full of omega-3 fatty acids—essential fats that humans and many other animals must acquire through diet. Fisheries grind menhaden into fishmeal and oil, which are ideal ingredients for pet food, livestock and aquaculture feed, and dietary supplements.

"If there’s a lot of freshwater input one year, it may kill off croaker larvae."

Though commercial fisheries also harvest Atlantic croaker and spot from Chesapeake Bay, these species are better known for their popularity among recreational anglers. Both species make a croak-like call, but only the croaker is named for the noise it makes. Spot is named for a black dot next to its gill opening.

Of all these species, only American eels are considered overfished. Populations of the others remain strong. For now. But climate change is altering environmental conditions in ways that could be detrimental to certain species. If Martinez can identify what conditions affect the abundance of specific species, she might be able to provide fishery managers insight into how to keep fish populations at healthy levels despite looming environmental changes.

Eric Hilton, an associate professor at VIMS who is Martinez’s research mentor, gave a hypothetical example of how fishery managers could use her research.

“Say we find that discharge of freshwater from the Susquehanna [River, into the Chesapeake Bay] negatively affects croaker larvae,” he poses. “If there’s a lot of freshwater input one year, it may kill off croaker larvae. And then in two to three years when those larvae croaker are at catchable size, there would be a decrease in numbers.” If there are fewer adult croaker, fishery managers need to impose stricter fishing limits to allow this species to recover from a bad larval year.

Martinez started studying larval fishes in her home country, El Salvador. There, she learned about the fishes that live in the warm waters of the Pacific Ocean. She moved to the United States to attend graduate school at VIMS.

“I came here, and had to learn all the fishes in the Atlantic,” she says. “At first, it was a hard task. But at the same time I loved learning about all the different fishes.” In addition to acclimating to a new country, new waters and new species, she also had to join her lab’s demanding, long-term larval fish sampling effort.

The Larval Fish Monitoring Program began in 2007 with funds from Virginia Sea Grant. Every week for the past nine years, VIMS scientists have sampled larval fishes from the York River at the Gloucester Point pier. Tonight, Martinez is the scientist at the pier.

She must work under the cover of darkness. Larval fishes, which can sense if it’s day or night, stay a few meters below the river’s surface during the day to avoid predators. At night, when there are probably fewer predators laying in wait and more food is available, do larval fishes dare ride the currents that pull them to the water’s surface.

Martinez also must sample during the arrival of high tide. Tonight, high tide was scheduled for just after 3 a.m. Around 3:15, Martinez stands on the pier, peering into the river, which looks swampy green under the lights. “You’ll know when high tide is running, because there are all these bubbles on the surface moving up-river,” she explains, as she points at a swathe of light froth on the river surface. “That’s not enough bubbles.”

On nights when the high tide runs, Martinez throws a net shaped like an ice cream cone with holes smaller than one millimeter in the water. The flow of high tide rushes through, causing the net to billow the way a windsock inflates with wind. She holds the net underwater for 30 minutes; every submersion is called a “tow.” The incoming tide carries larval fishes into the net. The number of larvae per tow varies by season, topping out at 100 per tow in the summer months. Back in the lab, Martinez sorts and identifies the caught fishes on weekends, when the campus is near vacant and she can blare her stereo. Under the microscope, she counts the number of each species, and records their scientific names—Micropogonias undulatus (Altantic croaker), Brevoortia tyrannus (Atlantic menhaden), Leiostomus xanthurus (spot), Anguilla rostrata (American eel), Paralichthys dentatus (summer flounder)—in a composition notebook, her pencil marks adding to nine years of data.

A typical night of sampling is three tows. Often, while she’s waiting, one of the fishermen will come over to ask Martinez what she’s doing, which she loves. She will explain what VIMS’s Larval Fish Monitoring Program is, and how she’s using data from that program to see how environmental conditions could affect what fish are available for the fishermen to catch at that very same pier.

Tonight, no anglers approach Martinez. At 4 a.m. she calls off the sampling, but still drops the net in the water. It sags limply, lacking the push of the tide. She’ll have to come out tomorrow night for the next high tide, but seems unperturbed.

“I’m happy doing what I do.”

By Chris Patrick, science writer
"I came here, and had to learn all the fishes in the Atlantic."
Of all these species, only American eels are considered overfished. Populations of the others remain strong.