Scientists seek answers to open-ocean aquaculture unknowns

By: Becca Burton

MIAMI -- A school of juvenile mahi-mahi swims around in a circular tank at University of Miami’s Rosenstiel School of Marine and Atmospheric  Science on Key Biscayne.

In an adjacent tank, a group of wild cobia, caught the same morning in Biscayne Bay, snatches the chunks of baitfish being thrown to them at meal time.  They are rather thin compared to the cobia raised on site.

A graduate student carefully takes water samples, records data and prepares fish feed.

Daniel Benetti (second from left) and Ron Hoenig (third from left) and two graduate students are working the University of Miami Rosenstiel School of Marine and Atmospheric Science's experimental hatchery to solve some of the knowledge gaps of marine aquaculture. Credit: Florida Sea Grant

These are some of the sights in the experimental hatchery of Florida Sea Grant researcher Daniel Benetti, professor and director of aquaculture at the University of Miami.

Benetti is currently assessing the environmental impacts of open-ocean aquaculture on the marine ecosystem with $225,755 in funding from a special National Sea Grant aquaculture research initiative.

He and his team are working closely with Open Blue Sea Farms, a U.S. corporation that commercially farms cobia. Although the company is using U.S. technology, the 50-yard- wide offshore pens are submersed in the waters off Panama due hurdles in the permitting process.

The U.S. is now finalizing NOAA’s Gulf Aquaculture Plan which would allow between 5 and 20 fish farms to set up shop in the federal waters of the Gulf of Mexico, producing up to 64 million pounds of native Gulf species.

Benetti said part of the reason the plan has not been finalized is due to the uncertainty associated with environmental impacts of caged fish.  The nutrients in the waste they discharge pose less of a threat in the open ocean than in coastal estuaries, he said, but farming on a large enough scale could alter various food webs.

Excess nutrient levels can cause dead zones, harmful algal blooms and fish kills. But Benetti said it is possible that in open-ocean aquaculture facilities, nutrients dilute enough to not have any detectable impact.

A school of hatchery-raised juvenile mahi-mahi swim along in one of the tanks at the hatchery, which serves as a research facility. Scientists use the lab to address knowledge gaps in aquaculture. Credit: Florida Sea Grant

To conduct the study, Benetti and his team have been taking water samples near the Open Blue Sea Farms facility. Using that data, they will create a model developed to mimic the West Florida Shelf. Based on the impacts shown in the model, the team hopes to inform best management practices for open-ocean aquaculture in the Gulf of Mexico.

This research is on track for completion by the end of August. Benetti said the preliminary results are promising.

“The results have shown over and over that the environmental impacts are negligent, if at all,” he said. “In fact there has been no significant or cumulative impact.”

Benetti added that the scale of the Open Blue operation adds to the reliability of the environmental assessment.

“They already have 17 large cages, so it’s big. It’s not like two or three cages that we used to use to measure environmental impact in the past,” Benetti said.

“We would be able to apply the results of these models to the Gulf and assist in getting the legislation and the permitting process in place so that we could do it in the US.”