Worldwide, shark meat has been consumed since the fourth century, especially in Asian countries. Seafood has numerous health benefits due to their exceptional nutritional properties (high-quality proteins, vitamins, essential omega-3 fatty acids). Unfortunately, anthropogenic environmental impacts (industry, agriculture, mining) significantly increase the amount of heavy metals found in seafood to potentially toxic concentrations. Heavy metal accumulation (e.g. mercury, arsenic, copper, selenium, lead, and cadmium) is a critical parameter for establishing food safety because of the multiple harmful effects they have on our bodies.
Shark meat has a higher risk of bioaccumulation of environmental toxins than other fish species. And researchers from Beneath the Waves (BTW) have documented and revealed alarmingly high levels of 12 heavy metals, including mercury, in the muscle tissues of large reef and tiger sharks sampled throughout The Bahamas. A total of 36 individual sharks from six species were evaluated, spanning two regions/study areas, with a focus on the Caribbean reef shark (Carcharhinus perezi).
“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.”
The new study is the first assessment of metal and metalloid concentrations in the muscle tissue of coastal sharks from The Bahamas. Published in Scientific Reports, it carries significant implications for human health in the Greater Caribbean region, since sharks are occasionally consumed here. The high and variable concentrations of metals in the muscle tissue of the coastal sharks in this region exceeded concentrations considered toxic for human consumption. “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. “With [such] a strong demand for shark products worldwide, this is another piece of evidence to steer people away from consuming sharks.”
The study also found that reef sharks, the more resident species, had higher mercury levels than tiger sharks, and that reef sharks’ mercury levels increased as they matured and grew larger. But why? One explanation is that the larger sharks have a piscivorous diet, feeding predominantly larger coral reef-associated fishes (such as grouper, snapper, and barracuda), which exhibit high metal concentrations here. While the impacts these high metal concentrations have on shark health are unknown, the human health risks of ingesting heavy metals by consuming Caribbean sharks species are clear. “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,” adds Gallagher.
Beneath the Waves hopes that there are future studies to understand the pathways for how these metals ultimately enter into the marine food web. And since shark meat is being consumed globally, the team hopes that detailed consumption guidelines keep different shark species in mind. As a non-profit research institute dedicated to promoting ocean health, BTW is bound to be part of the movement to have a more sustainable relationship with our seafood.
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