Aliens from Below: Studying Deep-Reef Invasive Lionfish


By: Sarah Yerrace
Previous Assistant Dive Safety Manager at Mississippi Aquarium, Gulfport MS from 2021 to 2022
Master’s Student at the School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA

We typically think of coral reefs as shallow water ecosystems. However, reefs do not stop at the recreational diving limit− they extend deeper into the ocean. These deep reefs are understudied compared to their shallow water counterparts due to the increase of time and resources required to conduct research below 130ft. In 2011, the Smithsonian started an initiative called “Deep Reef Observation Project” (DROP) to target this knowledge gap. The objectives are to document and observe the biodiversity changes from the surface down to 1,000 ft. The University of Washington joined this effort in 2017. Biodiversity sampling from DROP has led to the description of dozens of new species in a relatively small sampling area. During this project, lionfish were discovered as deep as 800 ft. off the coast of Curacao and down to 1,000 ft. in Roatan. At these depths, lionfish have been observed eating rare, undescribed, or endemic species. 

Lionfish are heavily studied as a prolific invasive species. But like our knowledge of reefs, our understanding of how lionfish impact local ecosystems is biased to the top 100 ft. of the ocean, a fraction of their range and distribution. My master’s thesis is focused on exploring and comparing the biology of red lionfish (Pterois volitans) above and below 130 ft. in the Caribbean. I use SCUBA to collect lionfish above 130 ft. and a manned submersible (the Curasub from Substation Curacao; Substation Curacao) to collect lionfish down to the limits of their depth distribution around Curacao. To better understand lionfish biology, I will be using DNA to identify prey species from gut contents, body condition analysis using length to weight ratio, and gonads to look at male to female ratio and reproductive capacity. Understanding these basic questions will help inform conservation efforts for native species and management of lionfish in the Western Atlantic.

Specimens were collected off the southern coast of Curacao, around the Substation, during four collection trips in the spring and winter of 2019 and 2022. Four scientists from the University of Washington and Smithsonian Institution go into the field at a time. Two individuals conduct SCUBA dives at dawn and dusk, during peak lionfish hunting times, while two individuals go into the submersible to hunt lionfish below diving limits. Submersible dives are usually around five hours in duration but can be longer. Collecting lionfish on SCUBA was relatively straightforward. Lionfish are very patient and will wait for the diver to line up a perfect shot. However, collecting lionfish with a submersible presents new challenges. The submersible, the Curasub, already had hydraulic arms used for research, but the sub was further modified with a reloadable spear. The challenge was to spear the lionfish, anesthetize the fish, remove the fish from the spear, scoop the fish into a basket with a trap door, and finally reload the spear. On more than one occasion, a technical difficulty would leave us without the ability to reload or a broken spear. Where on the body the lionfish was speared was recorded with detail as well as depth information so back on the surface, we could differentiate each lionfish (i.e., individual with shot below soft dorsal fin on the left side from 380 ft, individual with right ventral shot behind pectoral fin from 540ft, etc). Exploring the depths provided several unique experiences in addition to lionfish hunting. On one occasion, the sub was visited by a burrfish that we were very surprised to see so deep. On another occasion, we came across a discarded barrel with a small opening. Curiosity got the best of the on-board scientists, and we couldn’t help but to spray anesthetic into the opening to see what would come out. Eventually an eel slithered out, to everyone’s delight. PBS Nova featured this research as a part of an hour-long special covering lionfish in the Caribbean. 

I recently received the DNA sequences from the guts of collected lionfish back from the sequencing company. I will spend the summer identifying and analyzing the sequences. I anticipate submitting my thesis mid-2024.

Video of Lionfish eating undescribed species:

Video of spearing lionfish with a submarine:

Video of Burrfish:

Link to PBS NOVA documentary:  

Read more about DROP here: