A new study finds that alarmingly large levels of 12 heavy metals, including mercury, exist in the muscle tissues of reef and tiger sharks sampled throughout The Bahamas. Discovered by research crew Beneath the Waves, the new findings carry important implications for human health in the Greater Caribbean region, where humans occasionally consume sharks.
Over the last hundred years, human activity has caused a large increase in metals and metalloids entering the marine environment, posing potential risks to biodiversity and food security. Beneath the Waves evaluated muscle tissues of 36 individual sharks from six species. The research team provides the first account of metal concentrations in sharks sampled in The Bahamas. The Bahamas are a relatively pristine marine ecosystem where sharks live peacefully in a large marine protected area. Humans rarely consume sharks in The Bahamas.
Sharks are apex predators. They naturally bioaccumulate toxins in their bodies from eating other species of fish. The impacts of heavy metals on shark health remain unknown. However, the concentrations of metals present in the study exceed levels considered toxic for human consumption. The study also finds that reef sharks, the more resident species, have higher mercury levels than tiger sharks. According to the study, reef sharks’ mercury levels increased as they matured and grew larger.
“Understanding how sharks are affected by humans is critical for ongoing conservation efforts of these ecologically and economically important species,” says Dr. Oliver Shipley, the study’s lead author, Research Associate at Beneath the Waves, and postdoctoral researcher at The University of New Mexico. “Working in areas such as The Bahamas where shark abundance is relatively stable and healthy due to effective long-term protection, is important for us to be able to establish these baseline studies. If the levels are high in The Bahamas, imagine what they could be in other parts of the world where sustainability and environmental conservation are not a priority.”
Researchers identify the need for future studies to understand how these metals enter the marine food web. However, the human health risks of ingesting heavy metals by consuming Caribbean shark species are clear.
“Shark fisheries are not very prevalent in most of the Greater Caribbean region, but eating sharks can be culturally important to some nations,” says study co-author Dr. Austin Gallagher, Chief Scientist at Beneath the Waves and co-founder of The Caribbean Shark Coalition. “Yet with a strong demand for shark products worldwide, this is another piece of evidence to steer people away from consuming sharks,” he adds.
“Humans and oceans are intricately connected, and this work highlights the notion that science can and should guide decisions that improve ocean and human health.”- Dr. Austin Gallagher.
To download an open-access PDF of the full research paper, please visit: www.nature.com/articles/s41598-020-79973-w
Shipley ON, Lee CS, Fisher NS, Sternlicht JK, Kattan S, Staaterman ER, Hammerschlag N, Gallagher AJ (2021) Metal concentrations in coastal sharks from The Bahamas with a focus on the Caribbean Reef shark. Scientific Reports
Founded in 2013, Beneath the Waves is an ocean NGO using cutting-edge science to advance scientific discovery and catalyze ocean policy, focusing on threatened species and marine protected areas. www.beneaththewaves.org