Project abstract
Scalloped hammerhead sharks (Sphyrna lewini) are important predators in tropical marine ecosystems worldwide but are highly vulnerable to overfishing. In Panama, Sphyrna lewini is the most common shark caught in artisanal fisheries, with a high proportion of the catch being neonates and juveniles. This threat has serious implications for the sustainability of its populations, motivating management efforts. To set effective sustainable harvesting targets, additional information is needed about S. lewini age and growth rates, especially during its early life stages when it is particularly vulnerable to capture by fisheries. Additionally, understanding how environmental conditions influence the development of these sharks is essential for designing management strategies tailored to the characteristics of each region.
On the Pacific coast of Panama, key nursery habitat for S. lewini intersects with artisanal fisheries grounds in areas with different oceanographic conditions. This setting provides a natural experiment for studying the growth and development of S. lewini as well as how these demographic properties are shaped by local oceanographic processes. The Gulf of Panama is characterized by seasonal upwelling, which increases nutrients and productivity in the gulf. In contrast, the Gulf of Chiriquí experiences weaker upwelling, producing warmer and more stable conditions. We are using this system to test how S. lewini demographics are shaped by their environment; namely, do sharks growing up in a higher productivity environment achieve larger sizes at equivalent ages and have higher fitness than their counterparts in a more stable environment?
To address this question, our project aims to compare growth estimates of juvenile S. lewini between the Gulf of Panama and the Gulf of Chiriquí to explore how these contrasting environments affect their population demographics. Vertebral samples collected from S. lewini bycatch in each gulf will be used to determine their size at birth and subsequent growth, leveraging growth bands revealed through thin-sectioning of the vertebral centra. The project will also quantify variation in growth-band formation to determine how consistent this process is within individuals and incorporate this variability into analyses of growth and fitness. Together, these data could help inform regional population assessments and improve our understanding of this species’ vulnerability to fishing pressure across gulfs in the Panamanian Pacific.
Skills required
The intern will work with fishermen to obtain shark bycatch specimens as well as sample vertebrae, teeth, and tissues in the laboratory. They will also be responsible for preparing shark vertebral samples for analysis using transmitted light microscopes, photographing the vertebrae, recording data in Excel, and performing statistical analyses.
Minimum qualifications: previous experience dissecting sharks and conducting shark vertebral analysis; experience with microscopy; knowledge of statistical methods and experience in programming languages such as R; ability to work independently and as part of a team with individuals from diverse backgrounds; and commitment to science communication and public outreach.
Mentor name: Aaron O’Dea
Link to lab page: https://odealab.com/
Co-mentor(s): Erin Dillon
Location of internship: Naos Marine Laboratory
