In our Research Highlights blog series, we debut newly published fisheries research by our women of fisheries colleagues. If you have research you would like to highlight and share with our readers, submit a nomination form here!
This Month’s Research Highlight:
Torres-Molinari, A., A.C. Engman, K. Pacifici, C.A. Dolloff, B.J.E. Myers, and T.J. Kwak. 2023. Patterns in longitudinal distribution of American Eel (Anguilla rostrata) population characteristics in rivers of Puerto Rico. Fisheries Management and Ecology 00, 1–12.
The American Eel Anguilla rostrata is a fascinating species with a large geographic range stretching from Greenland to northern South America – and amazingly, these fish are all part of a single, interbreeding stock. After spawning in the Sargasso Sea, the clear leaf-like larvae are transported by oceanic currents to coastal areas throughout this range. They then transform into juvenile eels, some destined to stay in the marine waters while others travel into estuarine and freshwater systems. Where they go and how long they stay there can vary from individual to individual and from location to location, but when conditions are right, they will undergo their final transition into mature silver eels. It is then they must make the arduous journey back to the Sargasso Sea to spawn – a journey that can span thousands of kilometers – all for a single chance to further their species.
Unfortunately, they sometimes get a bad rap due to their snake-like appearance and the copious amounts of slime they produce (ever try to hold one and you’ll know!). However, they are, and have historically been, an important source of food and bait for sportfishing and are an integral part of aquatic food webs. Despite being the subject of many studies, albeit in a limited portion of their range, there is so much we still don’t know about them.
That brings us to this month’s research highlight set in the Caribbean, specifically Puerto Rico, where Ámbar Torres-Molinari and her term set out in search of the American Eel Anguilla rostrata. “From a personal standpoint,” Ámbar notes, “I really enjoy working with fish species that are undermined and often times are the ones with the most intriguing life history strategies.”
With Puerto Rico’s extensive river systems comprising more than 8,000 km in all and its proximity to the Sargasso Sea, it offers an ideal opportunity to learn about the American Eel in a tropical region. Little is known about the density, size, and sex distribution of American Eel in tropical rivers, so this study can help fill information gaps that are important for the proper management and conservation of the species.
In their study, Ámbar and her team sampled five river basins during both the dry and wet seasons. Eels were collected by backpack electrofishing at different reaches of the river ranging from the river mouth up to 10 to 17 kilometers upstream. Their work revealed that eel density decreased as they went upstream and upstream populations contained larger female eels – a finding that supports what others have reported in temperate regions.
This work contributes to the knowledge base for American Eel, which continue to face threats throughout its range such as overfishing, infection of an exotic swimbladder parasite, and habitat degradation. Puerto Rico is no different. Ámbar notes that “Although, to my knowledge, there isn’t a recorded fishery for the species in the island, the American Eel faces in-stream barriers, threats from urbanization as the island has densely populated areas, climate change, invasive species, among many others.” In fact, she and her team found reduced size in the highly urbanized Piedras River and absence of eels above a natural in-stream barrier in the Sabana River, which provides evidence for these kinds of impacts. There is some good news, however, and that is the exotic swimbladder parasite has yet to be observed in any Puerto Rican eels. Future work is planned to examine additional eels for this and other parasites to learn more about the health status of eels on the island.
Wrapping up this eely adventure in Ámbar’s words, “Upstream environments in Puerto Rico serve as optimal places for the development of large and female American Eel which is a key finding to understand the importance of river connectivity and the impacts of dams and other in-stream barriers on this and other migratory freshwater fish species. It may also indicate that Puerto Rico could significantly contribute to the spawning population in the Sargasso Sea because of how close the island is to those locations.”
(Photo Credit: Ámbar Torres-Molinari)
American Eel may be mysterious and at times misunderstood, but this is a story of hope. In learning more about these understudied populations, we can better inform efforts in the future to protect and conserve this species – not just in the tropics, but all throughout its expansive native range.
The full manuscript can be found or downloaded here:
doi.org/10.1111/fme.12645 (open access)
I’ve learned that networking and building meaningful connections with other professionals in this discipline is extremely important. This is how you learn new things.
Ámbar Torres-Molinari (Photo Credit: Thomas J. Kwak)
I’ve learned to be patient with myself as I learn new things throughout this career. I didn’t grow up fishing, so there are many new experiences that I’ve gained along the way and ones that I have yet to learn. We never stop learning something new each day when working with fish, their conservation, and management.
I was blessed enough to be part of a great group of fishery biologists at NC State University. My advisor, Thomas J. Kwak, his students, post-doc, and faculty had a big impact in my development as a scientist and professional. I found this opportunity to join them through working various tech jobs and just reaching out routinely to offer my help.
Please know that it is never too late to pursue the career you want and take some time off to do internships or tech jobs to know where you most enjoy to work. There will be challenging times that come, but never give up and remember to enjoy every step of the way!