Lionfish: The Caribbean Endgame

I'm sure you know by now that lionfish, which were introduced sometime in the 80s to the southern Atlantic and Caribbean (probably by aquarists who found the fish too big for their tanks), are an extraordinary threat to scores of native species throughout that region. At the Diving Equipment & Marketing Association's convention in November, Lad Akins, head of research nonprofit REEF, noted that lionfish in their natural habitat Indo-Pacific reach about 12 inches in length. But thanks to their prolific hunting in the new habitat they're invading, they are now reaching 20 inches in length, with a lifespan of eight to 10 years.

By tagging the fish, scientists have found that lionfish tend to hang out in one area; 90 percent of the tagged fish stuck around their environs. While that means spearfishers might keep a marine park fairly clear of them, large populations have been found at 200 feet, and a few have been found as deep as 1,000 feet. So spearfishing won't make a dent in their population, and because they are not inclined to take bait, line-fishing is of no help. There are at least 90,000 lionfish in Florida waters (the first sighting was in 1985), and because a female produces as many as two million fertilized eggs a year, we have a Malthusian nightmare.

Divers at many Caribbean resorts have been issued spearguns with the request, "Shoot the lionfish and feed the fish." That soon will become taboo, because sharks, morays and all the other fish being fed are associating the humans with food, and that is not going well. For example, David L Maislen (Arroyo Grande, CA) who was on Belize's Turneffe Island in December, writes, "The eels have been fed so often that they are all out free swimming. I was taking a picture of a lobster in a hole and a large green moray swam right between my legs into the hole. Triggerfish, groupers and the morays follow divers to feed on lionfish that are killed." So training agencies and resorts will soon have new rules: If you are going to spear a lionfish, you will have to take it with you.

And while lionfish are tasty, humans will never eat enough to reduce the population, nor will any species below the surface help out. In the Caribbean, there seem to be no reports of any fish attacking and eating a lionfish on its own. In the Indo-Pacific, coronetfish occasionally eat lionfish, and Undercurrent's John Bantin observed frogfish eating lionfish in the Red Sea, but those specific species do not exist in our waters. In fact, put a lionfish in a tank with hungry groupers and the groupers will ignore them

According to Akins, scientists have found as many as 64 juvenile fish in a lionfish's belly, and more than 30 species have been discovered in dissected lionfish. One had 21 juvenile drums. They are particularly prolific at picking off fish that eat algae, especially juvenile parrotfish. At one Bahamas reef, lionfish had reduced the biomass by up to 95 percent in just two years. Even if their food supply runs low, they are superb survivors. For three months, researchers fed nothing to lionfish they kept in a tank. None died.

People have speculated that while the preyed-upon Caribbean reef fish are naïve about this new predator, once they move through a few generations, they'll begin to recognize the lionfish as a predator and slip away. Darwinian theory at its best, right? Unfortunately, a new study seems to put that to rest. Researchers at the James Cook University in Queensland, Australia have found that a lionfish's success lies in the power of camouflage -- they are virtually undetectable by small fish. "For over a decade, scientists have tried to understand how these predators can wreak such havoc on their invaded ecosystem," lead researcher Mark McCormick told the press. Now, McCormick and his team have a clue. They observed that lionfish are undetectable by prey, as if they were ghosts able to feed on anything without being discovered. One likely possibility: a chemical camouflage, where the lionfish gives off a scent that labels it as non-threatening.

"We tested the response of small prey fish to three different predators, one of them the lionfish," says James Cook University scientist Oona Lönnstedt. "Surprisingly, the common prey fish - juvenile chromis -- were unable to learn that lionfish represented a threat, which was very different to their response to two other fish predators. Lionfish were able to sneak up on their prey and capture every single one, while the other predators had much lower feeding success." This ability to bypass a very well-studied learning mechanism commonly used by prey to learn new risks is a first, and has in part led to the astounding success of lionfish in the Caribbean. Without any natural enemies in their new system and no problem catching food, the lionfish are practically unstoppable. ( The study is available online at www.plosone.org )

Yet some control may be possible. A recent study in the journal Ecological Applications by scientists using computer models and 18 months of field tests reports that reducing lionfish in a specific area by 75 to 95 percent will allow a rapid recovery of native fish biomass in the area, and it may aid larger ecosystem recovery as well. At 24 coral reefs near Eleuthera Island in the Bahamas, researchers removed the necessary amount of lionfish to reach this threshold, then monitored recovery of the ecosystem. On reefs where lionfish were kept below threshold densities, native prey fish, like Nassau grouper and yellowtail snapper, increased by 50 to 70 percent in 18 months. Where no intervention was made, native species continued to decline and disappear. Stephanie Green, a marine ecologist at Oregon State University and lead author on the study, says, "It shows that by creating safe havens -- small pockets of reef where lionfish numbers are kept low -- we can help native species recover. And we don't have to catch every lionfish to do it."

The problem, of course, is this is a labor-intensive strategy that depends on legions of divers catching lionfish, probably now and forever. Green noted that in specific areas, the first 75 percent of the fish are easier to catch, but after that, it is diminishing returns. Many divers spend about 30 percent of their time trying to get those last few individuals. "That time is better spent moving to a new site and starting over," she says. She hopes that conservationists, fishermen and divers will band together to create a few pockets of almost-lionfish-free zones, where native reef dwellers such as parrotfish, grouper and snapper can be replenished.

The ultimate problem is that Caribbean and Atlantic reefs cover an enormous amount of territory, and the lionfish, tragically, have settled into them. It's impossible to imagine that, without significant economic incentives, there will be never be enough divers to keep more than a few marine parks in heavily populated areas relatively free of lionfish.

-- Ben Davison