A decline in prey like shrimp and crabs is not the main cause of the drop in bonefish populations in Florida Bay, according to a one-year study conducted by Audubon Florida and funded by the nonprofit Bonefish Tarpon Trust.
The study by researchers Pete Frezza, Shawn Liston, Jerry Lorenz and Michelle Robinson suggests other factors — the diversion and quality of freshwater delivered to Florida Bay; toxins in bottom sediments; pollutants from farms and yards; increased boating pressure; mercury contamination; and ocean acidification — might share the blame for the decline of a sport fish that pumps $427 million annually into the Florida Keys economy.
“While a decrease in prey may likely have been part of the cause of the decline since the 1980s [and perhaps even earlier], prey abundance alone does not appear to explain the dramatic decline in Florida Bay bonefish that has occurred in recent years [since 2006],” the authors wrote.
The researchers recommend implementing marine-protected areas for bonefish such as pole/troll and catch-and-release-only zones in Everglades National Park and the Florida Keys National Marine Sanctuary. They endorse Everglades restoration initiatives, such as bridging the Tamiami Trail and completing the second phase of the C-111 project to improve the quality and quantity of freshwater flowing into Florida Bay.
The study — conducted in 2012 — compared flats in the Lower Keys, Upper Keys and Biscayne Bay to see if creatures bonefish eat — such as blue crabs, pink shrimp, toadfish and others — were less abundant than in the 1980s and ’90s when initial research by other scientists was conducted. The Audubon researchers measured sea grass cover and collected prey at each site.
They found that Sawyer Key in the Lower Keys had more prey and more bonefish while the Upper Keys had fewer prey and fewer bones. But when they compared the numbers with those from the earlier studies, they found no real decline in prey at those sites.
“It certainly wasn’t a smoking gun,” Aaron Adams, operations director at Bonefish Tarpon Trust, said. “I guess I was a little bit surprised at the lack of difference between the current prey abundance and in the 1980s and ’90s. It just means we have to step back and look at other possibilities.”
Adams said the Trust is looking into conducting further research, such as “what if there’s something in the water that’s interfering with bonefish’s ability to reproduce.” He suggested examining bottom sediments for contaminants and sampling the fish themselves to see if they are absorbing harmful toxins. Future projects might include trying to raise bonefish in captivity then restocking them.
“Once we can figure out the causes, we can begin work on restoring the bonefish population,” he said.