At first, the appearance of Pacific lionfish in the waters of the Caribbean was met with pleasure by legions of divers and underwater photographers. There is an exotic beauty about lionfish; with their canopy of plume-like dorsal spines they look like ancient Asian warriors on the march. The excitement diminished somewhat for me when I knelt on one in the dark. One of its glorious dorsal spines went through my wetsuit with the ease of a hypodermic needle. The pain was instant, considerable and shocking. End of enchantment. Start of more caution, especially when night diving on their turf.
Delight with the lionfishes’ arrival in the Caribbean soon turned to dismay. It became apparent these picturesque beauties multiply with the facility of rodents and are apex predators in the world of small reef fishes they inhabit. More ominous still, lionfish have no natural enemies to balance their destructive appetites. Without some way of checking their proliferation, marine scientists fear a critical assault on the balance of the reef food chain.
When lionfish were found in Roatan, Honduras, the first remedial actions were taken by divemasters who speared and killed the invaders. Lionfish are docile, nonevasive and easily shot. I accompanied several tours in which hunters strung the foes onto their spears like shish kebab, brought the catch back to the boat and let the guests try the enemy as hors d’oeuvres. Soon the Roatan Marine Park began issuing divers licenses to spear the invasive fish. Nonetheless, the population continued to increase. Only a small percentage of Roatan’s waters are visited by divers, and the destructive invaders are entrenched all across the island’s reefs.
Sergio Tritto, an innovative Roatan dive professional, had an idea for a more effective counterattack. For weeks he had been spearing and killing the lionfish that appeared in the area where he conducted shark-feeding dives. When it occurred to him the sharks might be interested in his kills, he experimented by releasing the dead animals in the open water, retreating and watching. To his delight — and surprise — his predatory friends gobbled up the prey, toxic spines and all. With that, he expanded the experiment by just wounding the prey and releasing it alive. He hardly had time to move aside before the sharks swooped in to take the struggling creatures.
The sharks very quickly learned to associate lionfish-hunting divers with a free meal. Within weeks of initiating this remarkable partnership, the combined efforts of divemasters and their finned allies had made Tritto’s reef area virtually free of lionfish. But Tritto’s goal is much more ambitious: He hopes to teach sharks to prey upon healthy lionfish. “[The sharks] can help us keep this animal under control,” he says. And help is certainly needed. Tritto continues, “We believe the very survival of the ecosystem in the Caribbean depends on our capacity to control the lionfish.” Although it is too early to know whether Tritto’s dream will be realized, it is encouraging to see divers fighting for the marine environment and seeking creative solutions to the challenges the reefs face.
Lionfish Population Control
By Lad Adkins
Whether we like it or not, we are in the midst of what may be the worst biological disaster ever to face the western Atlantic, Caribbean and Gulf of Mexico. The lionfish invasion has been highlighted as one of the top-15 emerging threats to global biodiversity, discussed at length in international scientific conferences, featured in countless high-profile media pieces and become the bane of commercial fishermen in the region. Researchers predict dire consequences if the invasion continues unabated, but what can be done?
As divers encounter lionfish face to face, we have the rare combination of opportunity and responsibility to address the invasion firsthand. Throughout the region, programs are being implemented to organize and encourage lionfish removal through regular dive outings, monthly contests and single-day derby events. The good news is these efforts appear to be having significant success in minimizing lionfish populations at these targeted sites. The bad news: Due to scuba depth limitations and the scarcity and cost of human resources, divers can’t possibly cover the entirety of lionfish habitat in the region. Lionfish are being found in every marine habitat from inches-deep mangrove shorelines down to more than 1,000 feet (observed from a submersible) and in a range from North Carolina to South America and west to Central America and the Gulf of Mexico. This vast seascape is just too large for humans to cover.
Enter fish feeding. In many locations throughout the region, well-meaning divers and dive professionals are not only collecting lionfish using spears and nets, but some are now offering up their catch to marine predators. The hope is that after tasting lionfish these predators will turn to consuming them as a regular menu item, thus controlling populations even in depths and areas where divers do not venture. However, a quick look at lionfish biology and behavior casts uncertainty on this hope.
Lionfish have formidable defenses in the form of 18 venomous, needle-sharp spines across their backs and undersides. These spines are typically angled in the direction of potential threats (divers or predators), and healthy, aware lionfish can prove quite a challenge for predators. These defenses evolved over many thousands of years as a truly effective way to avoid predation. It is unlikely predators would risk injury or death to oust lionfish from well-chosen hideouts simply because they’ve been conditioned to accept dead or incapacitated lionfish. At this time the body of evidence does not support predation by native predators, even where they have been conditioned. There are shark-feeding sites in the Bahamas that still have some of the largest lionfish populations in the world even though the sharks are fed lionfish (spines removed) on a regular basis as part of the feeding attraction. There are other parts of the Caribbean where lionfish still fill the reefs even though grouper eagerly await handouts from divers. Conditioned predators may become nuisances or even hazards to divers.
For now, diver removal of lionfish is the only truly effective method of population control. There are numerous ongoing research projects seeking additional solutions, including studies in the tropical Pacific to determine how population density is controlled in the lionfishes’ native range. Let’s hope this research reveals additional methods of control.
© Alert Diver — Q2 Spring 2012