Lionfish are one of my favorite animals (I study them, after all). They’re stunningly beautiful. Of course, they’re also a devastating invasive species. Though they’ve only been in the Atlantic Ocean for some 15 years or so, they’ve taken over reefs, eating everything in their path. They’ve been found to reduce the recruitment of native fish by 79% on average, and are occurring in densities 8 times higher than in their native range. To say they’re bad is an understatement. The damage is so severe that they were listed as one of the top 15 threats to global biodiversity in 2010.
There’s little hope that the reefs will adjust to their newest members on their own. Lionfish are armed with an array of venomous spines, and aren’t known to have natural predators even in their native range. They spawn year round, producing millions of eggs each time. Estimates place the founding population in the Atlantic below 10 individuals; now, you can find that many on a single head of coral in the Bahamas. Though they’ve been invasive for less than two decades, the lionfish are already having ecosystem-level effects. The local reefs simply don’t have time to figure things out for themselves.
So it’s up to us to combat this invasion. Already, areas with high infestation rates like the Bahamas have launched a full-on assault. The goal: kill them. Every one of them. Period. So-called ‘lionfish derbies’ can round up thousands in an afternoon, and local communities have begun trying to eat the lionfish out of their reefs by promoting them as a delicacy. But the big question is, is such a plan going to work?
That’s what Andrew Barbour and his colleagues from the University of Florida decided to investigate. To do so, they took fisheries management math and turned it around. Normally, fisheries ask the question “how much can we catch sustainably?”, with the goal being to maximize the catch at each size of fish without causing a collapse. Instead, Barbour and his team wanted to know how much we’d have to catch to cause a collapse. In other words, how many lionfish do we have to take to overfish them?
Of course, not everything is known about the lionfish populations in the Atlantic, so the team simulated many fisheries scenarios to come up with a minimum catch needed to collapse the lionfish fishery. Depending on the natural mortality rate, they found that we need to fish 35% – 65% of the population. Given estimates of density, they estimate that we need to remove 157 – 293 lionfish per hectare per year. If we just count the 52,000 km2 of coral reefs in Caribbean Sea, that translates to somewhere between 800 million and 1.5 billion lionfish annually. That’s a LOT of lionfish.
Even more sobering, though, is that when they estimated how long it would take the population to rebound if fishing pressure decreased, the scientists found that the lionfish could recover in as little as 6 years. So not only do we need to catch upwards of 50% of the lionfish out there, but we can’t stop. We can’t just fish them out and then relax. We have to constantly keep the pressure on the population, or they’ll come right back.
In the end, the authors conclude that intense, sustained fishing activity would be required to even have a shot, and that even that is unlikely to succeed in managing lionfish populations “it cannot be assumed,” the authors write, “that any level of lionfish removal will be beneficial to native aquatic communities.”
Attempts to do so might even backfire. By killing larger lionfish, for example, the authors caution that we may serve as a selective pressure towards a higher density of smaller sized lionfish which would eat more juvenile native fishes.
We like to think that if we just came up with the right strategy, we can solve problems like the lionfish invasion. That we, as the smart, capable being that we are, are able to overcome any obstacle and take on the role of caretaker of our natural world. Sure, we might make mistakes, like introducing the lionfish to the Atlantic, but we can fix them, too! Right?! But results such as these show that we’re not as powerful as we think. There may be absolutely nothing we can do now that the lionfish have invaded, except to watch the massacre and see what survives.
Barbour, A., Allen, M., Frazer, T., & Sherman, K. (2011). Evaluating the Potential Efficacy of Invasive Lionfish (Pterois volitans) Removals PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019666