The Lionfish Enigma: Atlantic Threat But Not Pacific

invasive red lionfish
An enigma and an explosion. A juvenile Pterois volitans photographed in the Caribbean, where it shouldn’t be. 

LIONFISHES HAVE BEEN AROUND IN THE INDO/PACIFIC FOR EONS, yet almost all talk about them focuses on their presence in the Atlantic and Caribbean. Google “lionfish” and you’ll find a zillion articles on them as an invasive threat in the Atlantic basin for each one about them in their native habitat.

Okay. That’s a bit of hyperbole, but the idea is good. There’s an enormous disparity in Atlantic and Pacific lionfish articles. Almost all of them emphasize the fishes’ role as Atlantic basin invaders and their array of venomous spines, exotic appearance and voracious appetite.

The reason for such attention in the Western Hemisphere: As invasive predators, the unhindered ability these fish, mostly Pacific red lionfish (Pterois volitans), to feast on native species make them a threat to the stability of reef life throughout the Atlantic/Caribbean basin. They eat almost anything, often from fishes like wahoo, jacks and groupers to crustaceans like lobsters and crabs and critters like octopuses and squids. Often, they slurp up juveniles, degrading native populations in their early stages.

Pterois volitans
A red lionfish (P. volitans) was photographed on the Great barrier Reef, where it belongs.

WHAT HUNTS LIONFISH IN THE PACIFIC?

The question is, why are they a threat in the Atlantic/Caribbean but not in the Pacific? The most commonly accepted answer is that, as invaders, they lack natural predators in the Atlantic.

But what preys on these fish in the Indo/Pacific? Their predators there appear to be an assortment of fishes that feast on sea life in general: sharks, groupers, eels, frogfish (frogfish?), maybe snappers.

But as the website Lionfish Hunting puts it, “Unfortunately, because lionfish are “NOT” a problem in their native range, not much study has been done on them prior to lionfish becoming an invasive species in the Atlantic.”

INVASIVE LIONFISH FACTS

  • There are 12 species of lionfish worldwide. They’re members of Family Scorpaenidae, which makes them relatives of scorpionfishes.
  • Red lionfishes (P. volitans), make up some 93 percent the invaders in western Atlantic waters.
  • As exotic fishes with dramatic red, white and black banded patterns and extensive “manes” of 18 venomous spines, they are popular in the aquarium trade.
  • As aggressive predators, they have a habit of taking out other fishes with which they may share aquariums.
  • Which may account for the fact that they appear to have been introduced into the Atlantic off the east coast of Florida in the 1980s by someone, it’s surmised, releasing them from a home aquarium. They were detected in the Atlantic as early as 1985.
  • In the absence of natural predators, Pterois volitans invaders have spread throughout the massive ocean range encompassing Bermuda, the Bahamas, the Caribbean, the Gulf of Mexico and South America.
  • A second species, the common lionfish (P. miles, also referred to as the “firefish”) apparently made its way through the Suez Canal into the Mediterranean and is currently found around the islands of Cypress and Malta. P. miles also makes up the other seven percent of lionfishes found in the Atlantic range.
Pterois miles
Most Pterois invaders are Pacific red lionfishes (P. volitans) but a second species, P. miles (sometimes called the “firefish), has sneaked through the Suez Canal into the Mediterranean. And some into the Atlantic basin.

WHY AREN’T THEY PREYED ON MORE?

So why does Pterois volitans get a pass in the Atlantic basin? The answer is far from clear. Perhaps they (still) are so foreign to marine life in those oceans that they tend to be ignored and left alone.

Occasionally, an article pops up in the media that a grouper has been observed eating one, or an eel has been found with a lionfish in its belly. But the frequency of this behavior is not considered significant enough to be a solution.

TRAINING PREDATORS – FOR WHAT?

Certainly, at many Caribbean/Bahamas resorts, lions that are speared by divemasters and offered to a grouper or an eel or a shark (shark!) are enthusiastically devoured.

The argument for their doing this is that they’re training the groupers, eels and sharks in question to seek out lions as prey. Also, it entertains the groups of vacationing divers they are leading.

But a lot of people think this is a bad idea. They see it as really training the groupers and their pals to expect lionfish handouts from human divers, sometimes aggressively. The eels that rushed at my group in Belize on one dive turned away once they saw we didn’t have any in hand, but it was an unsettling moment. Also, I didn’t get good photos.

grouper eating lionfish
This grouper eagerly accepted a speared lion from a divemaster in Belize. The hope is to give native fishes a taste for hunting down lionfishes. But it may just be training them to look for handouts from divers.

DO THE VENOMOUS SPINES DETER PREDATORS?

 Considering the amount of attention given to P. volitans’ stinging spines, one might picture them as repelling any grouper or eel that tries to chomp down. But the coatings on the spines are venomous, not poisonous. They have to be injected into a cut or abrasion in the body’s skin, caused, of course, by a spine.

That’s different from a poisonous toxin, which has to be ingested. Consuming a venomous substance is not a toxic process. At least, presumably as long as that grouper avoids getting jabbed, it can take the stuff in internally, spines and all, without  harm.

As for humans, the stings still hurt like crazy, but it’s rare for the sting to be life-or-limb threatening (excluding complications like infection or anaphylactic shock).

DON’T LIONFISHES USE THEIR SPINES TO ATTACK PREY?

One might picture the evil lionfishes sneaking up and stinging their prey into an easy meal, but no. Actually, they use their spines as defensive weapons, not for hunting.

There are suggestions that they sometimes hunt together, and that they use the spines to herd prey into a corner. But the showy spines are basically defensive.

HOW DO LIONFISHES HUNT?

Turns out they’re sneaky little devils in another way: Researchers studying P. volitans) found they often utilize a technique of blowing jets of water toward their prey to confuse or distract it and cause it to turn to face the predator – and present an easier target.

Other fish species have long been know to blow water to, say, clear sand in the hunt for worms or crustaceans. But P. volitans is the only species known to direct water jets against other prey fish.

The technique offers the predator two advantages. It may overwhelm the prey fishes’ lateral lines, masking detection of vibration signals associated with their strikes. And they may cause the prey to turn to face them, enabling an easier, faster head-first capture.

Pterois volitans
Often, they’re spotted solo but sometimes they hang out together – and sometimes cooperate in hunting. 

MORE LIONFISH FACTS:

  • Reputedly, P. volitans can eat things bigger than their mouths and their stomachs can expand 30-fold.
  • A study found that on reefs they infest, the density of their prey declines an average of 65 percent. Sometime much more. Another study found six different species of prey in a single lionfish stomach.
  • When you encounter a lionfish during a day dive, they are likely to seem inactive, almost suspended dormant in the water column. They are believed generally to do their hunting at night.
  • If native marine life doesn’t recognize lionfishes as dangerous predators, the invaders themselves often don’t seem to recognize divers carrying spears as dangers to them. They often seem indifferent to a diver’s presence…
  • ….unless they’ve been hunted in the past and escaped. In that case, they may know to seek shelter in a hole or crevice.
  • And, efforts to get rid of them is overmatched by their ability to produce new fishes. They become capable of reproducing within their first year, can live for 15 years, spawn as frequently as every four days year-round and produce more than two million eggs each year.
hunting lionfish
A divemaster returns with a batch in Belize.

SOME GOOD NEWS

Lionfish Derbies have become commonplace throughout their Atlantic range, removing thousands of the invaders from their places of residence. And in some sites visiting divers may well take up the challenge of spearfishing lionfishes (it’s often legal even when other spearfishing is prohibited). Anecdotally, sightings of Pterois volitans have become rare at some resorts I’ve been to, presumably because the dive population has done a good job of their removal.

lionfish as food
Dishes like these lionfish fingers are delicious, and one solution to the lionfish abundance is to turn them into a regular food fish.

SOME BAD NEWS

The bad news is that populations of Pterois volitans apparently have learned to hang out in the depths, below most divers’ safety limits, putting them out of reach for spearfishing.

MORE GOOD NEWS

But – the good news about that is that a company called Robots in Service of the Environment (RISE) has developed a remotely operated vehicle call the Guardian LF 1 that can pursue and scoop up lionfish at depths as deep as 700 feet. Designed to be operated from the surface by non-techies, it’s invented by the folks who created the company iRobot. It’s sort of a Roomba for the Reef. and, it’s intended to be affordable for resorts to purchase and use.

invasive
The Guardian LF1 zeroes in on its targets.

Ralph Fuller, Editor

PRINCIPAL SOURCES: Pacific Red Lionfish, Florida Museum, University of Florida;  Lionfish Fact: The 10 Most Common Lionfish Myths Busted!, What Easts Lionfish?, Lionfish Hunting; Why are lionfish a growing problem in the Atlantic Ocean?, The Lionfish Invasion, Some Lionfish Biology, NOAA; Lionfish, Encyclopedia Britannica; Top Five Myths About Lionfish, Red Lionfish, National Geographic; Lionfish Crash Course, REEF – Reef Environmental Education Foundation; Robots in Service of the Environment; Pterois, Wikipedia.org; Lionfish vs. moray eel, no contest, Florida Today.

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