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Tethered Lunch: How conditioning native predators can help control invasive species.



Article:  Diller, J. L., et al. (2014). “Coping with the lionfish invasion: Evidence that naïve, native predators can learn to help.” Journal of Experimental Marine Biology and Ecology 455(0): 45-49.

DOI: 10.1016/j.jembe.2014.02.014


Our world is a well-connected world. We can communicate on a global scale and we can travel from continent to continent with ease. But this connection comes with an ecological cost. Species are being transported from place to place with much higher frequency and are reaching places that would not have been possible a few centuries ago. Invasive species continue to be a hot topic in biology: zebra mussels are taking over the Great Lakes and dense plots of kudzu are blooming in the American southeast.

Fig 1: The spread of the invasive lionfish in the Atlantic. Red indicates invaded areas.

Fig 1: The spread of the invasive lionfish in the Atlantic. Red indicates invaded areas.

What is an invasive species?  First, an invasive species is one that is introduced from somewhere else. This could be aided by human activity or it can be natural, but invasive species are not native to the habitat they are introduced to. Second, invasive species are nuisances, causing trouble for native species by depleting resources and taking up space. Not all introduced species are invasive, meaning they may not last in their new environment or they don’t cause trouble. Invasive species typically share similar traits. They are hearty and can survive different environmental conditions; they reach maturity rapidly and can reproduce quickly. Invasive species are often aided by what is called the “enemy release hypothesis,” an ecological concept describing the lack of natural predators of invasive species.

In the 1980’s, lionfish were first discovered in the Atlantic. This species is well known as an aquarium fish and is native to the Indo-Pacific. Shortly after it’s discovery, lionfish populations exploded, moving into the Caribbean and up the eastern coast of the US (Fig 1). Lionfish fit the bill as an invasive species and populations seem to benefit from the lack of predation. Despite the presence of native predators, like sharks and grouper, nothing seems to be eating the lionfish! Lionfish are now found in densities of 400-650 fish per hectare. That would be like having a 1-acre lawn covered by about 160-260 fish. Lionfish are wreaking havoc on coastal ecosystems; they can eat up to 4% of their body weight each day and are eating fish important to maintaining coral reefs.

Humans have stepped in and started to cull coastal habitats looking to remove lionfish. In doing so they noticed something interesting. If dead lionfish were left in the water native predators would actually eat them. So could these predators be conditioned to go after live lionfish?

Fig 2: "What is this? Do we eat this?"

Fig 2: Shark A: “What is this? Do we eat this?”                          Shark B: “I’ve never seen it before, it doesn’t look like food.”

The Study:

Researchers from the University of Florida set out to investigate whether or not they could condition native predators to start eating live lionfish. 132 lionfish were hand-collected off of Little Cayman Island, anesthetized, and then measured. Researchers used lines and hooks (noting no major impacts to the fish) to tether lionfish to a lead weight. Tethered lionfish were then brought to 3 different habitats: heavily culled reefs (often fished for lionfish), rarely culled reefs, and seagrass meadows and left to sit overnight exposed to large natural predators, just like the goat in Jurassic Park. Researchers returned to the locations the next day to count remaining lionfish and had video surveillance at several sites to document the predatory species eating the lionfish.

It was found that nurse sharks and Nassau grouper were consuming the lionfish. In heavily culled reefs, the predation rate was the highest. No less than 80% of the lionfish were eaten. This is most likely due to predators having potentially eaten dead lionfish previously. Predation rate was the lowest in the seagrass meadows; this was predicted by the researchers due to lower predator abundance. Predation ranged from 20% – 60%. The size of the individual fish played a significant role in the seagrass meadow and the rarely culled reefs where smaller fish were not consumed as frequently as larger fish (Fig 3).

Fig 3: These graphs show the proportion of tethered lionfish that were eaten. Graph A shows that the time of year makes no difference in predation but the size of the fish does. Graph B shows the three different habitats and how fish of different sizes were consumed.

Fig 3: These graphs show the proportion of tethered lionfish that were eaten. Graph A shows that the time of year makes no difference in predation but the size of the fish does. Graph B shows the three different habitats and how fish of different sizes were consumed.


Invasive species are detrimental to ecosystems and the lionfish is no exception. Despite efforts by humans, these fish continue to thrive in the western Atlantic. If large predatory fish could recognize lionfish as a viable source of food, this may enact a biological control, keeping lionfish populations in check. Predators don’t seem so quick to bite, but this research has shown that in a number of habitats, predatory fish will eat live lionfish (Fig 4). It appears that conditioning is possible and we will soon have a hand in dealing with invasive lionfish. This may prove helpful in other ecosystems where invasive species are taking over. Biological controls represent a natural way of dealing with invasive species and are also much cheaper!

Fig 4: "This isn't so bad, I could get used to this!"

Fig 4: “This isn’t so bad, I could get used to this!”



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