Addressing invasive fish management through organized spearfishing
Caleb Blanton, a 2019 wildlife and fisheries sciences graduate, planned on going to medical school, but quickly realized—the ocean was calling.
At the time, Blanton worked as an undergraduate teaching assistant in the microbiology lab at the Texas A&M College of Veterinary Medicine and Biomedical Sciences. Some of his coworkers referred him to the Applied Biodiversity Science Conservation Scholars, ABSCS Program, and a few potential faculty members who could help him, which led Blanton to Joshuah Perkin, Ph.D.
“The program gave me the funds and the ability to work with a PI to do my own research, as well as participate in a summer research program of my choosing,” Blanton said. “Dr. Perkin was kind enough to agree to help me with my spring research and I got the opportunity to work with Dr. Joel Llopiz at the Woods Hole Oceanographic Institute in the summer of 2019.
While Blanton’s spring research didn’t get him to the ocean, it did allow him to engage in hands-on aquatic research. Blanton said he learned of the growing problem of invasive suckermouth armored catfish, SAC, in the San Marcos River from conversations with Kirk Winemiller, Ph.D. and approached Dr. Perkin with some ideas on how to address them.
“There was not much research being done on that particular population and Perkin already had some experience in that region,” Blanton said.
Applying a new technique for stock assessment
The pair decided to investigate management of the species further, by looking into how spearfishing might contribute to population control.
“The intent of the research was to determine the effects of the local bi-annual spearfishing competition, as well as the contracted spearfishing, on the population size of the SAC in the San Marcos River,” Blanton stated.
Perkin is an assistant professor in the Department of Ecology and Conservation Biology. He leads research in the Riverscape Ecology Lab and served as Blanton’s primary mentor on the study.
“The Edwards Aquifer Authority began collecting data on the numbers and sizes of SAC removed by spearfishing from the San Marcos River in 2014, but the data had not been formally analyzed.” Perkin stated, “It was excellent timing for Caleb to be interested in assessing the effects of removal just as a new analysis method was developed by marine fishery scientists.”
To achieve this goal, the research team set three objectives for their study. The first was to review the global distribution of the species to document the spread of invasion and identify areas where their assessments might be applied. Additionally, the team set out to assess removal patterns in spearfishing tournaments from 2015-2018.
The most involved, however, was their final objective—which aimed to use a newly developed statistical model to assess changes in the length-frequency of SAC harvested from the San Marcos from spearfishing over a four-year period.
This method, called the length-based Bayesian biomass estimation method, or LBB, uses the number of speared suckermouth armored catfish and the length of the fish that is caught and applies several fisheries equations to produce a graph.
“This graph can tell us what the exploited biomass is overall, relative to what the biomass is without spearfishing,” Blanton said. “In turn, we can use this data to determine if our spearfishing efforts are working to reduce or maintain the population.”
Blanton said using the LBB method was effective, as they were able to obtain records and data regarding SAC removal per day over the years, from Nick Menchaca, with Atlas Environmental, who organized the spearfishing competitions.
“Results revealed spearfishing control efforts increases mortality 1.5-1.75-times beyond natural background mortality, and that biomass was 20-30% of what it would be without control,” the pair state in their most recent article.
Perkin said that this study contributes needed data regarding the efficacy of the SAC removal program.
“Invasive species control programs require clear goals and evidence of advancement toward said goals to justify continued funding,” Perkin said. “This study provides managers with decision-support tools for developing formal program goals.”
Perkin stated that another benefit is that the time series results provide a way to assess progress toward program goals.
Laying foundations for the future
Blanton and Perkin said their study represents the application of a new fisheries stock assessment tool to the problem of invasive fish management and posit that the length-based Bayesian biomass estimation method can be applied to other invasive species control programs.
“The Blanton et al. study provides estimates of removal efficiency based on state-of-the-art modelling,” Perkin said. “Our next challenge is to validate these estimates using independent methods.
Perkin said their next project involves developing experiments that address the mechanism of reduced biomass. Perkin said the follow-up study will provide a clearer view of how spearfishing removal compares to natural mortality.
This study also laid the groundwork for other research with suckermouth armored catfish management in the San Marcos River. Perkin and undergraduate researcher Allison Hay were featured talking about that research in the July 2020 newsletter produced by the Edwards Aquifer Habitat Conservation Plan.
Blanton said this undergraduate research experience allowed him to network, collect and analyze data and gave him the opportunity to present research and become familiar with the journal submission process. All of these things, Blanton said provided him with a foundation to be successful in the future.
Blanton is currently living in New York, working to achieve his career goals.
“I was very lucky to have the opportunity to participate in this program early on,” Blanton said. “Getting hands-on research experience as an undergraduate student gave me valuable insight and gave me a starting point for my goals in marine science.”