Students Cast Nets for Tiniest Billfish

Six miles off shore, where the waters of the Atlantic turn deep blue and the city skyline fades to haze, they cast their net. The quarry: billfish.

“Good,” says Colin Schmitz as the 20-foot-long cone of fine mesh trails out from the boat’s stern like an unfurling cloud. “Looks good,” agrees Stacy Luthy, and she turns to signal the captain, who kicks the boat into gear. For five miles they drag the net along the surface.

Over the years, tens of thousands of trophy hunters have come here to the Gulf Stream in pursuit of billfish: the spectacular sailfish, the magnificent blue marlin or a swordfish that can weigh as much as 1,300 pounds.

Not far away, off the coast of Cuba on the other side of the Stream, is where Ernest Hemingway’s fictional Santiago valiantly battled his great fish in “The Old Man and the Sea.” “But, thank God, they are not as intelligent as we who kill them,” muses the Old Man on the second day of his epic struggle with the marlin, “although they are more noble and more able.”

Now, in the face of increasing commercial pressure, the billfish is not able to sustain its populations and is declining in all the world’s oceans. The International Commission for the Conservation of Atlantic Tunas has listed billfish as “fully exploited,” and two environmental groups, SeaWeb and the Natural Resources Defense Council, have called for a boycott on eating swordfish in particular.

The National Marine Fisheries Service recently proposed a long-range billfish management plan that includes reducing the number caught, increasing the legal minimum size for sailfish and marlin and establishing a federal bag limit of one billfish per vessel per trip.

Billfish are among the largest and most prized creatures on Earth, yet much about them remains a mystery. Sport and commercial fisheries know how to catch them, but scientists have few clues to their life cycle. “You almost never see a billfish from 1 to 3 feet, for example,” said Tom Capo of the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. “How fast do they grow, what do they eat and where do they travel?”

Those are just some of the questions that Capo and other researchers--including graduate students Luthy, 23, and Schmitz, 22--were pondering on a 24-hour trip to the Gulf Stream. Backed by $500,000 in grants, the university is just getting started on a three- to five-year project designed to provide clues to management and preservation of the threatened species.

But unlike commercial fishermen or trophy hunters, the researchers are not fishing for monsters. Rather, they are seining the top few inches of the Gulf Stream spawning grounds for larval and juvenile billfish, some so small that with the naked eye they are hard to distinguish from seaweed. Yet specimens of 3 inches or more are easily seen as perfect miniatures of their wall-mounted elders: the prolonged, spear-like bill of the upper jaw, the flamboyant dorsal fin, the sleek, torpedo-like body.

If catching an 8-foot sailfish is tough, then netting a 2-incher is even tougher. And keeping it alive has proved to be tougher still.

In a pilot study two years ago, UM scientists scooped up 291 baby billfish, proving that the north-bound Gulf Stream transports enough larval and juvenile fish to support a more thorough investigation. But many of the fish died of stress before they could be moved to the lab, and all were dead within three days.

On this trip, Capo hoped to relax the frenetic captives by pumping extra oxygen into their holding buckets. And at first it seemed effective. Working through the night with shrimp-dipping nets, Luthy and Schmitz scooped up three baby sailfish that were drawn to a light hung in the water off the boat’s stern.

“They’re doing well,” Capo exulted when the diving and darting of the tiny fish seemed to slow during the voyage back to shore and on the trip to the laboratory. But within three days, all were dead. “We are collecting some data . . . “ said biologist Jerry Ault. “But the first year in the life of a billfish remains quite an enigma. We know they undergo explosive growth, from larval stage up to 4 feet.

“But what about after that? And we don’t know much about their food regime, which must change almost by the day.”

There is no other marine research institution in the world better positioned to conduct field work on billfish than the University of Miami, with its Key Biscayne lab just four miles from the Gulf Stream. And there are years of work ahead.

“Sports fishermen know where the big ones are, and they just put a line out and wait until they catch one,” said Nasseer Idrisi, one of the project scientists. “But we are more like detectives, defining and solving problems. These eggs are tossed out into wide-open ocean, and we have no clue as to where they go when the eggs hatch or their behavior.

“It’s an extreme challenge. And from start to end, all of it is thrilling.”