Fighting lionfish

Armed with spears, divers skewer lionfish and present them bloodied and half-dead to Caribbean reef sharks. The idea is to give the sharks a taste for the beautiful but destructive fish, thus halting their rampant expansion.

But when the blood spills out, swirling red in the crystal clear water, the sharks get a little too hungry, pushing up against the divers. While the sharks seem to be able to stomach the venomous lionfish, the divers decide to end the novel experiment after one week.

"The sharks would get very excited, which would cause a risk to divers," says Giacomo Palavicini, executive director at the Roatan Marine Park (RMP), who organized the experiment in 2010 off the coast of Roatan, a Honduran island in the Caribbean.

Roatan has been battling the maroon-colored animal for the past six years. Despite its unique appearance, with white stripes and fan-like pectoral fins, the lionfish is unwelcome due to its voracious appetite for fish, crabs, and other bottom feeders that are essential to keeping the Mesoamerican barrier reef system healthy.

Other parts of the Caribbean and the west Atlantic have been dealing with the ravenous invasive species, native to Indo-Pacific waters, since the 1980s.

While the short-lived hand-feeding experiment might seem extreme, it's just one sign of how bad the lionfish invasion had become. And it marked the beginning of a wider effort on Roatan to train people, and animals, to halt their encroachment.

The battle with the fish is also symbolic of a greater struggle to sustain biodiversity in Roatan, which requires keeping the island's shores and waters clean, says Palavicini.

Shooting coconuts

The RMP educates locals on the environmental and economic impact of the lionfish invasion, and has trained more than 1,500 people in how to kill them sustainably - not an insignificant number for an island of about 100,000 people.

Working with government authorities, the nonprofit insures that hunters are properly trained with spears so as not to damage other marine life while hunting. During training, participants practice spearing coconuts hidden in the water. If divers miss their targets and hit the surrounding reef more than once, they don't get their lionfish-hunting license.

The efforts seem to be having an impact.

"Lionfish are no longer just floating around the reef like the early years. It is harder to find them because they have been shot at repeatedly," said Nicolas Bach, RMP director of communications and marine infrastructure. "They now learn to hide from us or flee when they hear the sound of bubbles."

Divers say they've noticed lionfish are hiding during the day and reverting to their natural behavior of feeding at night, indicating the fish may be fearful of possible predators. A recent study also showed that in the waters off the Sandy Bay-West End area of the island, where culling activity is particularly high, lionfish numbers are down dramatically, and native fish populations are more abundant.

If you can't beat 'em, eat 'em

Roatan's initial experiment to curtail lionfish by training sharks wasn't exactly a failure, adds Palavicini. What it demonstrated to him and his team was that marine life would be willing, over time, to chow down on an unfamiliar, invasive species.

While some culled lionfish are left for the current to deal with, in other cases they are fed to groupers, snapper or triggerfish. Some islanders have recently reported sightings of grouper eating the spindly interlopers.

But Bach says training local species to prey on the invader is the not necessarily the best option, as it can make the would-be predators more aggressive. It's also dangerous for the trainers, as the shark experiment showed.

A 2013 study published in PLOS ONE found that a form of sustained culling similar to the spearing practised by RMP is probably the ideal way to control lionfish populations. They could also be fished to eat, says the study.

But so far Roatans, fearful of the lionfish's venomous spines, are reluctant to eat them, says Palavicini. Still, the creature is safe to eat if prepared properly, and the RMP holds barbecues for tourists interested in trying the fish's buttery meat.

Focusing on water quality

Roatan's largely untouched crystal-like aquamarine waters and colorful coral reefs, teeming with more than 500 species of fish, are a big draw for tourists. But sustaining the biodiversity that attracts people to the island in the first place takes more than culling lionfish.

Protecting seagrass and mangroves - the first line of defense against water pollution thanks to their cleansing properties - is essential, as is preventing sewage from spilling into the ocean.

Bay Islands Conservation Association, for instance, works with German development bank KfW to do just that by improving the sanitation system for the homes of low-income families on Roatan.

Conservation groups have also been training locals and businesses in sustainable tourism best practices.

"We're at the right time on the island to stop the degradation of the reef," says Palavicini. "The community has to take responsibility to be part of the solution at every level."