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Miami Marine Scientists Study Endangered Billfish Populations Off Florida's Coast

November 1, 1999
University Of Miami
During the past two decades, the numbers of immense silvery billfish sailing through Florida's aqua blue waters have been steadily declining due to over-fishing. The billfish's popularity, however, has become a serious liability.

KEY BISCAYNE, FL -- During the past two decades, the numbers of immense silvery billfish sailing through Florida's aqua blue waters have been steadily declining due to over-fishing. The species, which include sailfish, blue marlin, white marlin, spearfish and swordfish, are some of the state's most popular catches among both commercial fishermen and sport fishing enthusiasts.

The billfish's popularity, however, has become a serious liability. Growing to hundreds or even thousands of pounds in size, the billfish are now listed by the International Commission for the Conservation of Atlantic Tunas as being "fully exploited," meaning they can no longer be caught in great numbers without sustainably damaging their populations. Florida's multi-billion dollar a year sports and commercial fishing industries are perplexed about what to do to increase the species' dwindling numbers because so little is known about billfish -- particularly their early life stages and habitat.

To help learn more about the mysterious billfish, scientists from the University of Miami Rosenstiel School of Marine and Atmospheric Science are conducting an on-going research project to study the early life history of the species which spawn in the warm Gulf Stream running along the coast of South Florida. Funded with a half a million dollars in grants, the UM project will investigate the collection, transportation and rearing of larval and juvenile billfish.

As part of the study, the marine scientists hope to learn a great deal more about the "baby" billfish in the wild -- such as what they eat, how fast they grow and where they travel as well as what water quality, temperature and salinitylevels they need to thrive. The researchers from the Rosenstiel School will use this benchmark study to provide knowledge for the future management and preservation of the threatened species.

Three years ago, as part of an initial pilot study, UM scientists were able to collect billfish larvae and keep them alive in their lab for several days. This was the first time in history that researchers were able to study the 1/8 of an inch-long larvae up close in captivity. As a result of the initial study, the UM team realized that they needed more information on how the larvae live in their natural environment before being able to replicate those conditions in the lab. The findings of the study were reported in the journal Bulletin of Marine Science in 1997.

The new study, which was launched two months ago, involves week-long research expeditions in the Gulf Stream aboard UM's 67-foot research vessel Calanus. The scientists capture billfish larvae and eggs with plankton nets and keep the specimens alive in the shipboard laboratory for as long as possible. The researchers are able to observe the larvae and conduct experiments to determine ideal lab conditions for keeping the billfish larvae alive in captivity.

"During our pilot study, we transported the fish back to our shore labs," says Tom Capo, hatchery manager for UM's Rosenstiel School of Marine and Atmospheric Science. "This time we want to solve the problems at sea, in conditions that are as natural as possible."

During the 12-month period of the pilot project, investigators made several important advancements. On 21 research cruises, 291 baby billfish were captured, proving that the Gulf Stream off Miami transports enough larval and juvenile fish to support the prolonged study.

"Many of these fish survived the trip back to the hatchery and several survived for up to three days while feeding on laboratory-cultured food. We consider this a great success because we accomplished this with just 12 months of work and minimal support," says Capo. "We proved that we can reliably collect and transport larval and juvenile billfish back to our facilities. It's only a matter of time and effort until we can extend the survival time of billfish in captivity. My ultimate goal is to learn enough about these fish to someday have them swimming around year-round in our tanks."

During two recent exploratory trips to the Gulf Stream, Capo and his team captured 35 sailfish larvae and what appears to be one swordfish larva. If the latter find proves true, it would be the first time the UM billfish research team has captured the larva of a swordfish, a species that has nearly disappeared from Florida's Atlantic coast.

According to Capo, Rosenstiel School scientists will concentrate their efforts on better understanding the environmental and physical requirements needed by billfish during their early life stages.

"Our current data on the life history of these species is, for the most part, fishery-based having been acquired through the study of large animals contributed by sport and commercial fishermen," says Don de Sylva, a veteran billfish researcher at UM's Rosenstiel School. "Very little is known about their early life history, from the egg through the larval and juvenile stages. During the past 25 years there have been several attempts at collecting small fish but they have never been successfully kept in captivity. Our work at the University of Miami is designed to fill the gaps in our knowledge and to chart new territory."

The Rosenstiel School's state-of-the-art Experimental Fish Hatchery is located on the edge of Biscayne Bay on Virginia Key near Miami, only seven miles from the Gulf Stream. "The facility's close proximity to the western edge of the Florida current and the Straits of Florida gives us fast, easy access to the best locations for catching adult, juvenile and larval billfish. We can reach this habitat with a boat within minutes and with minimal stress and mortality for the fish," says Capo, who oversees the hatchery.

The Rosenstiel School is currently conducting a $20 million fund-raising drive to establish a Center for Sustainable Fisheries that will provide a multi-disciplinary approach to enhancing the stocks of a variety of fish species, such as snapper and seatrout.

"Our plan is to greatly expand the capabilities and scope of the hatchery through the Center for Sustainable Fisheries and draw on the knowledge and skills of resource managers, marine biologists, oceanographers and marine policy experts," says marine biologist Pat Walsh, scientific director of the UM center. A specialist in fish physiology, Walsh brings a biotechnology approach to the studies, looking at ways to maximize fish growth within the constraints of hatchery conditions.

Some of the key scientists working on the sustainable fisheries projects include Capo, Walsh and biologist Jerry Ault. Each of the UM researchers work directly with the hatchery fish, conducting experiments and determining their physical needs, life cycles and other factors effecting survival, growth and development. Ault, who specializes in mathematical and computer modeling of fish stock dynamics, is helping to determine space needs for raising the optimal number of fish at the most cost-effective level. Michael Schmale, a marine pathologist, is working to alleviate the various diseases that can affect hatchery fish.

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EDITOR'S NOTE: More information on the billfish research can be found by contacting the University of Miami's Rosenstiel School of Marine & Atmospheric Sciences at (305) 361-4000 and by visiting their website at

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University Of Miami. "Miami Marine Scientists Study Endangered Billfish Populations Off Florida's Coast." ScienceDaily. ScienceDaily, 1 November 1999. <>.
University Of Miami. (1999, November 1). Miami Marine Scientists Study Endangered Billfish Populations Off Florida's Coast. ScienceDaily. Retrieved April 29, 2017 from
University Of Miami. "Miami Marine Scientists Study Endangered Billfish Populations Off Florida's Coast." ScienceDaily. (accessed April 29, 2017).