Are Lionfish Hunts Making It Harder to Kill Them?

Given the Caribbean and Atlantic invasion by the Indo-Pacific lionfish, dive operators generally consider it a good idea to huntdown and kill this serious predator to preserve indigenous creatures. However, what if those repeated hunts are actually influencing lionfish behavior, making the species harder to find and kill off? Research published in the online journal PLOS One in April suggests just that.

esearchers at Simon Fraser University in British Columbia compared how lionfish act if they lived in an area where spear-based culling had occurred to lionfish living in areas where no such hunts had taken place. The 16 coral reef patches were all in the Bahamas. On eight of those patches, divers had been culling the lionfish with three-prong pole spears every three or six months for two years. On culled reefs, a lower proportion of the fish were active during the day, and they hid themselves much more carefully as well. The investigators assigned a "hiding score" to the fish based on certain behaviors; half of the lionfish on culled reefs achieved the highest such score, compared to only 19 percent of those on the unculled reefs. This suggests, of course, that if a lionfish survives a cull, it becomes more likely to survive the next one as well. It is, in a sense, a very rapid form of natural selection.

Of course, any animal hunted by humans presumably might alter its behavior to avoid being killed. However, this study does have implications for how to control invasives. Culls sometimes set goals of a certain percentage of the species, but if we intentionally leave 30 percent of an animal, it may make it that much harder to get back to 30 percent the next time we give it a shot. This also backs up those invasive species-control programs that aim for total annihilation. For example, the leader of an attempt to kill off the invasive brown rat in the sub-Antarctic Island of South Georgia said last year that "killing 99.999 percent is a failure. If we don't get every last one, we may as well not have gone there in the first place."

With the lionfish, this study just adds fuel to the idea that aiming for eradication is likely the best approach. In one Bahamas study from 2012, an increase in lionfish abundance coincided with a 65 percent drop in the total biomass of the 42 types of fish that it eats. It is likely not possible to completely eradicate the invasive lionfish from the Atlantic at this point, but plans for individual culls may have to consider marine life's ability to adapt in order to keep this problem fish's population down.

"What Doesn't Kill You Makes You Wary? Effect of Repeated Culling on the Behavior of an Invasive Predator," by IM Cote, ES Darling, L Malpica-Cruz et al; PLOS One, 9 (4) e94248. DOI: 10.1371/journal.pone.0094248