Invasive species poses massive ecological threat
Ninety-feet below the surface with a mile of blue oblivion below, I approach her slowly as she stalks her prey. She hypnotizes a small snapper with her crimson mane, but I send my spear through her head before she can strike. I slip her into a bag full of lionfish as I ascend, and begin to make my way back to the lab.
Native to the Indian and Pacific oceans, lionfish are new to the Caribbean. They are a popular and beautiful fish for home aquariums, but multiple releases of this invasive species has led to a massive ecological threat. These superb predators threaten snapper, grouper, and other tropical fisheries by consuming their juveniles and competing for prey. To combat this threat to native fisheries, local communities have initiated massive lionfish spear fishing events. Part of my research involves assisting these hunts and documenting lionfish impacts on native fish, but I’m more interested in what’s in their heads than their stomachs.
Inside a fish’s head there are three pairs of calcium carbonate bones called “otoliths” used for sound detection, balance, and orientation. As a fish grows, calcium carbonate crystals are added to its otoliths, with the rate of otolith growth closely matching that of the fish. Fish growth is seasonal—faster in summer and slower in winter. This difference in growth rate is marked by the formation of varying colored rings on the otolith. During slow growth winters, minerals accumulate and form dark rings; during fast growth summers, mineral deposition is spread over a larger area, resulting in clear rings. By counting these annual rings, we can determine a fish’s age and growth rate.
My research is focused on aging hundreds of lionfish to learn about the biology of this invasion. In general, otolith aging is a vital tool for fisheries scientists and managers. Understanding how old a fish is and how fast or slow it grows is of paramount importance to harvest regulations. If a fish takes years to get to a reproductive size—like a tarpon, orange roughy, or ‘Chilean sea bass’—harvesting that species could be dangerous due to a slow rate of population recovery. If the species is fast growing—like a mahi-mahi—you can harvest fish in high numbers without fear of crashing their population.
Unfortunately, lionfish appear to be fast growing, meaning they can reproduce as quickly as we can kill them. Fortunately, lionfish are delicious (although anecdotal reports of ciguatera have been circulated) and their venomous spines do not affect the quality of the meat. So the next time you are in Florida or the Caribbean, grab a speargun and join a lionfish hunt. It may not compare to landing a bonefish or permit on fly, but if you skip the flats on a cloudy or windy day to go play underwater whack-a-mole, you’ll be rewarded with a great, environmentally friendly dinner.