FGCU scientists study invasive lionfish, endangered smalltooth sawfish in research projects
A pair of scientists at Florida Gulf Coast University are studying a pair of fish species that swim on opposite ends of Florida’s ichthyological spectrum.
On one end, lionfish are beautiful and all-too-plentiful non-natives that people wish would just go away; on the other end, smalltooth sawfish are weird-looking and endangered natives that people wish we had more of.
Emma DeRoy, a graduate student at the University of Windsor in Ontario, Canada, is observing live lionfish at FGCU’s Vester Marine Field Station in Bonita Springs to understand the species’ feeding behavior – lionfish are a major threat to any marine environment they invade because they eat vast quantities of juvenile native fishes, including economically important species such as snappers and groupers.
Hidetoshi Urakawa, an associate professor in FGCU’s Department of Marine and Ecological Sciences, is part of a team that is using molecular ecology approaches to determine the diet of smalltooth sawfish and how the species uses its habitats in Southwest Florida – smalltooth sawfish were listed as endangered under the Endangered Species Act in 2003; the species’ current population is 5 percent of its historic size.
With lakes St. Clair and Erie the closest large water bodies to Windsor, DeRoy became interested in lionfish through undergraduate course work and wrote a research paper on the species. When the time came for her to do her master’s thesis, she decided to study lionfish in Southwest Florida, where one of her biggest challenges was the summer heat – the average high temperature in Windsor during July is 82 degrees, and the average low is 62, compared to Southwest Florida’s average July highs and lows of 92 and 75.
“Lionfish are a model invasive species,” said DeRoy, who has been living and working at Vester since April. “They’re generalist feeders. They have a wide range of physiological tolerances. A lot of research has been done on invasive freshwater and terrestrial invasive species but not on marine invasive species. I’m trying to use feeding behavior to understand the impacts of lionfish, and that could be translated to other invasive species.”
Natives of the Indo-Pacific, lionfish were first reported off Florida in 1985, probably the result of aquarium releases. Since then, lionfish, which have few known natural predators and reproduce at an alarming rate (females can spawn every four days and produce 2 million eggs a year), have spread in huge, voracious numbers throughout the Western Atlantic, including the Gulf of Mexico.
For her study, DeRoy needs live lionfish, so field station manager Bob Wasno and a rotating team of divers have been capturing them in 90 to 100 feet of water at the Captiva Blue Hole, 30 miles off Redfish Pass.
Capture protocol, devised by Wasno and DeRoy, is simple: Lionfish don’t spook when approached by divers, so the lionfish team just swim up to them and catch them between two short-handled nets. Then the lionfish are put into a cage (designed by Wasno) on the sea floor and slowly brought to the surface.
Back at Vester, DeRoy observes, among other things, lionfish attack distance (the distance the fish travels to catch its prey), which “adds another dimension to understanding feeding ecology.”
Such information could lead to further research about feeding and prey-capture techniques of other invasive species.
DeRoy is also looking at how lionfish density (the number of lionfish in a given area) affects feeding dynamics.
“Are lionfish better hunters in groups?” she said. “Some studies have suggested that lionfish hunt cooperatively, but when you get a higher density of predators, sometimes they compete for prey, so that each predator ends up with fewer prey items when hunting in groups. So, with lionfish, does cooperative hunting increase consumption?”
To test the effects of density in feeding, DeRoy will put different numbers of lionfish in a tank and feed them specific numbers of prey items (small fish and shrimp).
“Invasion biologists have done a lot of research on the impacts of invasive species,” DeRoy said. “But we still don’t really understand the scope of their impacts because the impacts are often subtle, they change over the invaded range, or they’re delayed, which makes them difficult to quantify and predict. This is especially the case with marine invaders.”
Student Taylor Hancock, left, and Associate Professor Hidetoshi Urakawa analyze the DNA sequence data of fish eaten by sawfish, while student Carissa Flaherty prepares a specialized gel used to visualize DNA samples.DeRoy’s research, which is being funded by the Natural Sciences and Engineering Research Council of Canada, can fill in some of the gaps concerning impacts of invasive marine species.
“Better understanding their impacts is key in mitigating their threat and developing appropriate management strategies,” DeRoy said.
Smalltooth sawfish were once common in Florida and ranged from Texas to North Carolina, with sightings as far north as New York. Today, smalltooth sawfish are restricted primarily to Southwest Florida from Charlotte Harbor to the Keys.
Fishing pressure was the primary cause of the species’ collapse. Recreational fishermen caught sawfish and cut off the saws as souvenirs; commercial fishermen didn’t target sawfish, but many sawfish were killed when they became entangled in commercial nets. Fishing pressure is still a concern along with habitat loss.
Florida Fish and Wildlife Conservation Commission (FWC) sawfish researcher and FGCU adjunct professor Gregg Poulakis was the lead author of a new sawfish paper published in Endangered Species Research, titled “Sympatric elasmobranchs and fecal samples provide insight into the trophic ecology of the smalltooth sawfish.” This work was done with Urakawa as a member of a broad collaboration team. The project also included researchers from Florida State University, Stony Brook University in Stony Brook, N.Y., and, coincidently, the University of Windsor, Ontario, Canada, and was funded by the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service.
“This was a multi-disciplinary approach,” Urakawa said. “All the researchers had different skills. We had different kinds of researchers working together.”
Urakawa’s part of the project was, with the help of two FGCU students, Taylor Hancock and Carissa Flaherty, to determine what sawfish eat and how they use their local habitat (the Charlotte Harbor system, including the Caloosahatchee, Peace and other rivers). Aside from anecdotes and some supporting data that sawfish feed on schooling fishes and crustaceans, little was known about the species’ diet.
One of the methods the team used was to look at stable isotopes (atoms that have more or fewer neutrons than protons) in sawfish fin tissue samples supplied by Poulakis. Different prey species contain specific amounts of carbon and nitrogen isotopes, which become stored in the tissue of the predator as it grows, so researchers can indirectly determine what a predator has been eating by analyzing the isotopes that have been incorporated into the tissue samples.
Researchers have been using stable isotopes in dietary studies since the late 1970s, but Urakawa combined new molecular tools to study feeding ecology of sawfish: high throughput DNA sequencing and environmental DNA (eDNA), which is DNA released by an organism into the environment. Sources of eDNA include feces, mucous, and shed skin.
“On TV, you see FBI agents going around a crime scene with a piece of tape, picking up skin cells and hair for DNA analysis,” Urakawa said. “We’re doing the same thing in the marine environment. You can get eDNA from the water, soil, and sediments. You filter the water or take a tablespoon of sediments, extract the DNA, and identify what kind of animals have been there.”
Urakawa used feces from sawfish caught by Poulakis and his team – simply put, DNA from what sawfish eat can be found in sawfish feces.
“When they catch sawfish, the sawfish sometimes poo in the boat,” Urakawa said. “Gregg has been collecting sawfish poop for a decade. He has a most precise collection, and I had the good fortune to be able to work with it.”
“High throughput DNA sequencing is kind of a miracle. You can identify what an animal is eating without killing it or using a stomach pump. You can’t kill sawfish because they’re protected by law. Also, trying to pump a sawfish’s stomach would be dangerous. The poop method is the best method for sawfish.”
Fish also leave eDNA in the water and sediments of their habitat, and Urakawa is using eDNA to detect the presence or absence of sawfish and to track sawfish movements in area waters.
“It’s a very powerful method,” Urakawa said. “You could apply this method to Florida panthers, which are cryptic and difficult to find. You bring soil samples from an area to the lab, and the eDNA would show evidence that a panther existed there.”
Researchers could also use eDNA to track unwanted non-native species such as lionfish and pythons, Urakawa said.
“Environmental DNA is cutting-edge technology,” he said. “This was the first feeding ecology study performed for sharks and rays using a high-throughput DNA sequencing. FGCU is taking the lead, but it’s only possible with the cooperation of FWC. We’re in a good position now.”
Among the team’s findings is that sawfish, which are shark-like rays, eat bony fish and elasmobranchs (fishes with cartilaginous skeletons such as sharks and rays) throughout life and that sawfish are born in the Caloosahatchee and other rivers and live in those rivers for up to three years; also part of the study, bull sharks are born in the same rivers but move out during their first year.
For the next projects, the team will use eDNA to determine whether or not smalltooth sawfish inhabit the Indian River Lagoon and Tampa Bay, which historically contained smalltooth sawfish, and will continue looking at the sawfish diet in Southwest Florida.
Ultimately, this work will help assess the recovery of sawfish populations.
“Students prefer to work with iconic marine creatures like manatees, sharks, and sea turtles, but marine ecosystems are more than that,” he said. “People are always attracted by visible creatures, but most creatures in the sea are invisible and they play fundamental roles in the ocean as well as many physical and chemical processes.”
How to…kill, clean and cook a lionfish
Beware the venomous spines when cleaning
Old joke: How do porcupines mate? Very carefully.
The same could be said about killing, cleaning and cooking lionfish.
You see, lionfish, which are very tasty, have 18 venomous spines that can inflict an excruciating wound, so you need to handle the fish very carefully. The killing part can be done by scuba divers and snorkelers, and the weapon of choice is usually a pole spear with three or more prongs.
Shooting lionfish is easy because, unlike grouper and snapper, they don’t spook when approached by humans. Maybe they think nobody’s going to mess with them and their spines.
You really need to start being careful once you’ve speared your lionfish because that’s when you start dealing with the fish close-up.
You can’t just put lionfish on a stringer, as you would other species, because the spines of a lionfish on a stringer will stick you. So, an essential tool for lionfishermen is a lionfish containment unit (or LCU), of which there are two main types (you can find these at your local dive shop or online):
- A PVC tube closed at one end with a funnel at the other. All you do is jam the end of your spear, with the lionfish on it, into the funnel end; when you pull the spear out, the fish stays in the LCU.
- Puncture-proof bags, which come in various designs and have different mechanisms for getting the lionfish off the spear.
When you get back to shore with your LCU full of lionfish, you need to fillet them – very carefully.
The important thing to know is the location of the 18 venomous spines: 13 in the dorsal fin, three in the anal fin and two in the pelvic fin, and those spines can sting you long after the fish is dead.
Some people cut the spines off with a knife or pair of scissors; others just work around them. If you decide to cut them off, make sure you get all 18.
Whether you remove the spines or not, filleting lionfish is like filleting any other fish. Of course, you can cook the fish whole and avoid the whole filleting process.
If you don’t dive or snorkel or just don’t want to kill your own lionfish, Florida’s 26 Whole Foods stores sell whole lionfish, and if you don’t want to mess with cleaning the fish, a store fishmonger will do it for you.
As for cooking your lionfish, here’s what Chef James Fraser, an instructor in FGCU’s School of Resort & Hospitality Management, wrote in an email for this story:
“Because lionfish is delicate and not very meaty, in the sense that there’s a lot of bone and spine, I like to fillet the fish, batter and deep fry!! And of course, that leaves many options for the type of batter, i.e., beer-batter, tempura batter, or various breadings, and can be paired with many types of sauces, like aioli, sweet chili sauce, honey mustard – whatever matches the theme of your meal.
“For those who shy from fried foods, a nice blackening seasoning, or just salt and pepper, sautéed with a small amount of oil or sprayed with a light coating of oil of choice and broiled in a preheated oven. I love fish tacos with a squeeze of lime, spiced mayo and fresh cabbage slaw.”
Lionfish also need to be cooked very carefully: The worst thing you can do to a tasty fish is overcook it.