By RASHAD ROLLE

Tribune Senior Reporter

rrolle@tribunemedia.net

ALARMINGLY high levels of 12 heavy metals, including mercury, have been found in the muscle tissues of large reef and tiger sharks in The Bahamas.

Researchers from the non-profit organisation Beneath the Waves (BTW) say the discovery has important implications for human health insofar as sharks are consumed by people.

“Over the last century, human activities have rapidly accelerated the influx of metals and metalloid entering the marine environment, posing potential risks to biodiversity and food security,” BTW said in a press statement yesterday.

“Evaluating muscle tissue of 36 individual sharks from six species, the results from this study provide the first amount of metal concentrations in sharks sampled in The Bahamas, a relatively pristine marine ecosystem where sharks live risk-free in large marine protected areas. Sharks are not commonly consumed by humans in The Bahamas.

“As apex predators, sharks naturally bioaccumulate toxins in their bodies from eating other species of fish. While the impacts of shark health remain unknown, the concentrations of metals quantified as present in the study were determined to exceed the levels that are considered toxic for human consumption. 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.”

Dr Oliver Shipley, the study’s lead author, said understanding how humans affect sharks is critical for conservation efforts.

“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 said while the human risks of ingesting heavy metals by consuming Caribbean shark species are clear, more studies are needed to “understand the pathways for how these metals ultimately enter into the marine food web.”

Jamie Fitzgerald, the general operations manager for BTW, said smaller fish species more commonly eaten in The Bahamas are also known to have mercury and other metals. However, she said their study focused only on the tissues of sharks.

In 2011, The Bahamas banned shark fishing and prohibited the sale, import and export of shark products.