Are Lionfish Really That Harmful to the Marine Environment?

In this edition of Ask a Marine Biologist, Dr. David Shiffman answers a question about invasive species.

Question: Are lionfish as harmful to the marine environment as we’ve been told? And if so, how can we get rid of them? – Dave G., Florida

Answer: I don’t know what you’ve been told, but the lionfish invasion is ecologically disastrous. And while we don’t have a great way to get rid of them, derbies help.

First of all, let’s define “invasive species.” According to the U.S. National Park Service, a “non-native species” is one that is found outside of its historic, natural range, but is not necessarily established in its new home and is not necessarily causing any kind of ecological disruption there. One fascinating recent marine example of this is the presence of whitetip reef sharks, native to the Indo-Pacific, off the coast of Brazil. It’s pretty crazy that they’re there, but they don’t seem to be founding a new population; it’s just a few individuals that aren’t causing much trouble (yet). An invasive species is a particularly nasty subset of the category of non-native species—these organisms have established themselves in their new home outside of their natural range, and are causing ecological disruption there. It’s no accident that lionfish are frequently a textbook example of invasive species since they were introduced in the Caribbean in the 1990s, they have been causing all kinds of harm.

Lionfish are voracious predators, both outcompeting native coral reef fishes for prey and also directly eating juvenile native reef fishes. They’re actually eating so many native fish that scientists studying invasive lionfish found an unusual tissue in them—it turns out that many Caribbean lionfish are obese. According to the nonprofit Reef Environmental Education Foundation, lionfish can eat more than 70 species of native fish and invertebrates, including individuals up to half the size of the lionfish, and can eat 460,000 fish per acre per year—which has reduced native fish populations on some reefs by up to 90 percent. Because they have no predators in their native range (yes, some groupers and sharks sometimes eat them, but not nearly enough to control their populations), they are found in super high abundance in the Caribbean—sometimes up to 200 fish per acre! In some ecosystems, about half of the total predator biomass is now lionfish, remarkable for a species that just wasn’t there 30 years ago. Oh, and they reach reproductive maturity in under a year, and one female can spawn over 2 million eggs in a single year.

So, lionfish are indeed an ecological problem. What can we do about them? One of the most popular strategies is lionfish derbies, such as those run by the aforementioned REEF. The goal of a derby is to get a lot of volunteers together to target one reef and kill (by spearfishing) as many lionfish as possible in a day, which in recent years is often a few thousand lionfish. These derbies also serve to provide scientific samples to researchers, and to train people in safe and effective lionfish removal so they can continue killing and removing lionfish that they encounter anytime they’re out on the water.
These derbies do not (and cannot) remove all the lionfish out there—there are just too many of them, and their habitat extends well into depths that divers can’t reach. However, derbies (and regular removal by divers trained in safely catching lionfish) help, and should be continued. They’re the only thing keeping numbers in check in some cases, and they do successfully remove a significant number of adult lionfish from a small area.

Some people have suggested that we make an industrial-scale fishery to remove lionfish from the Caribbean and Atlantic. I think we’re probably a long way from having a commercial fishery for these animals, at least one of any significant scale, but they do taste pretty good, and some Florida restaurants have them on the menu.

In summary, lionfish are indeed a major ecological problem, and we don’t have a way to get rid of them completely, but lionfish derbies are a great way for the dive community to help keep their numbers in check.

Ask a Marine Biologist is a biweekly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at WhySharksMatter@gmail.com with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.