Preliminary results of a new study at Buck Island suggest a tightly focused lionfish removal program may be able to preserve local fisheries from this voracious, exotic Asian predator that has spread explosively throughout the region.
For the last year, the National Park Service, Oregon State University, Reef Environmental Education Foundation and the University of the Virgin Islands have been working with dive volunteers to study different approaches to suppressing the lionfish population. The last of the data is being collected this week and scientists working on the study shared the preliminary results with the CRABBS diving club Tuesday.
While lionfish have been in Florida for two decades, it was not until 2004 that one was spotted in the reefs of the Bahamas, said Lad Akins, director of operations for REEF. Now the invasive species is found from the coast of North Carolina to the cost of Paraguay and throughout the Caribbean. It has been found in all types of environments, from coastal mangroves to 1,000 feet deep. And in areas like the Bahamas where lionfish have spread unchecked, "you see up to a 95 percent reduction in fish biomass," Akins said.
With the fish so widespread, and at depths unreachable by divers, eradication is not going to happen, so the study instead will look at what sort and how much suppression it will take, and at what cost, to preserve local fish stocks, he said.
Oregon State University conservation research fellow Stephanie Green said researchers collected data on lionfish population density’s relationship to what proportion of the local fish communities are eaten to home in on specific sites to target for lionfish removal. They carefully measured and laid out study sites in different depths and types of undersea terrain around Buck Island off St. Croix, she said.
Volunteer divers came out every two months and removed lionfish from the selected sites and they tracked the efficiency and cost of culling lionfish below target levels, Green said.
One part of the puzzle is how many lionfish need to be present before local fish populations begin to plummet, Green said, showing a graph of data from a number of sites indicating that any more than two or three lionfish presages a sharp drop in local fish. How often they have to be removed to keep the numbers at a manageable level is another part of the study.
On some sites, they removed every lionfish and "as soon as we stopped, three months later, the numbers were right up to where they were before we removed any lionfish," Green said. But in other locations, periodic sweeps kept the numbers down low enough.
They will be crunching the data over the summer and should have some final results over the summer, Green said. Ultimately they hope to fill in the missing variables in a formula to identify "the threshold density above which lionfish start to cause problems and things start to get bad," Green said.
"Can we use that as a target for control? I think so. If we can keep lionfish below this sweet spot we can, I think, maintain populations" of local fishes, she said. They will know more once they analyze all the data, she said.
UVI biologist Bernard Castillo shared findings about the numbers, weights, sizes and diets of the lionfish removed from around Buck Island. V.I. lionfish averaged 253 mm in length, weighing an average of 275 grams. The largest one caught weighed 584 grams.
An array of other fish and sea animals were found in the lionfish’s stomachs. The top three items in the stomachs were shrimp, damselfish and wrasse, which are the same top three items found in another study, but other areas show other contents, so it appears they "go for what is available," Castillo said.
Lionfish are a local vector for the foodborne illness ciguatera and 12 percent of the lionfish tested exceeded the FDA limit for the toxin, he said.
Green will give more details of the study and possible approaches to suppressing lionfish Thursday at 1 p.m. on the St. Croix campus of UVI in Building EVC-401 (the main theater).