My guides that day, oceanographer Jamison Gove and fish biologist Jonathan Whitney of the National Oceanic and Atmospheric Administration in Honolulu, are nearly three years into a research project that aims to make sense of this chaotic scene. The larval stage is the “black box” of fisheries science: Fertilized eggs go in, and young fish come out—but what happens inside remains sketchy. The larval fish are so small and fragile they’re exceedingly difficult to study. The overwhelming majority will never become adults. Yet fish populations around the world, and the animals that eat them, depend on just how many larval fish make it, and in what condition.

What Gove and Whitney have found lately—and what David Liittschwager’s photographs of their water samples document—is that fish and wholesome fish food are not the only things collecting in the slicks off Hawaii. Microplastics, tiny shreds of human trash, are there as well, and in such abundance that larval fish are eating them in their first days of life.

“The most critical moment is that first feeding,” Whitney says. “If they get a piece of plastic, that could be it. A single thread in the stomach of a larval fish is potentially a killer.”

Plastic waste, mostly from rivers or careless dumping on land, washes into the oceans at an average rate of about nine million tons a year, according to a 2015 study by Jenna Jambeck of the University of Georgia. The visible trash, along with heartbreaking images of its impact on everything from turtles to birds to whales, has generated a public outcry. But sunlight, wind, and waves eventually break down ocean plastic to bits that are barely visible. One of the biggest unknowns—and concerns—is the effect that these microplastics, smaller than a fifth of an inch, might be having on fish.

Fish provide critical protein to nearly three billion people and countless seabirds and other marine animals. But fish stocks worldwide have fallen by half since 1970, surveys show. Populations of the largest predatory fish, such as tuna, have fallen even more. The decline is largely because of overfishing, but pollution and waters warmed and acidified by climate change are having a growing impact.

As long ago as the early 1970s, scientists were finding plastic pellets—the material used to manufacture plastic goods—in the stomachs of fish caught off New England and Great Britain. More recent studies have documented the presence of even smaller microplastic particles in a growing array of adult fish. Larval fish have been studied much less but are likely to be more vulnerable to microplastics, as they are to everything else. “Any stressor will likely have more of an impact on early life stages than later life stages,” says Susanne Brander, a toxicologist at Oregon State University who is studying how plastics might affect the growth of fish.

Most ocean fish are terrible parents. A few species guard their eggs on the seafloor; others protect them inside their mouths. But most fish release thousands or even millions of eggs and sperm into the wide ocean and never see their offspring. When eggs hatch a day or two later, the newborn fish are on their own.

Newborn fish look misshapen, heads oversize, tails barely formed. They have to eat like crazy to grow into their body. Whereas human babies develop in the shelter of the uterus, fish mainly develop after they emerge into an unforgiving world.

Predators or starvation will get most of them. “That’s why fish spawn so many eggs,” says Su Sponaugle, an Oregon State University marine ecologist who specializes in the early life stages of fish. “They have to hedge their bets.”

The larval phase is treacherous every step of the way—starting with the need for the larvae to find food, which they do in a surface slick. Surface slicks form mostly in coastal regions around the world, wherever currents, tides, or subsurface waves cause water to converge and concentrate the organic gunk that floats in it. Slicks can be seen by satellite as long, squiggly ribbons that run parallel to coasts.

Some larval fish swim to slicks, some drift, as do eggs not yet hatched. Predators converge on slicks too. If a baby fish manages to avoid being eaten and to find enough food, it will be about two inches long when it heads back to its permanent habitat—a reef, say. The right current will transport it there, the wrong one out to sea.

“If you miss an island, good luck with that. If there’s no reef, you cannot complete your life cycle,” Sponaugle says. Life for newborn fish was a crapshoot even before they met our plastic trash.

Off Hawaii, a single eight-minute tow of the NOAA team’s net yields a plethora of living organisms and plastic.

Pushed into a surface slick by converging currents, they’re separated in the lab by a technician with tweezers. A computer program counts the plastic pieces and measures each one; the technician uses a microscope to identify the creatures.