I have previously blogged about the how the demand for shark fin soup poses a large threat to shark populations. However, newly published research has found high concentrations of toxins linked to human neurodegenerative diseases in the fins and muscles of 10 species of sharks.
In the study, fins and muscle tissue samples were collected from 10 shark species found in the Atlantic and Pacific Oceans for concentrations of two toxins—mercury and β-N-methylamino-L-alanine (BMAA). BMAA is produced by some cyanobacteria or blue green algae. Recent studies have linked BMAA to neurodegenerative diseases such as Alzheimer’s disease, dimentia, and amyotrophic lateral sclerosis (ALS).
Shark products including shark fins are widely consumed in Asia and globally in Asian communities, as a delicacy. Shark meat is consumed in many communities or used as fertilizer and shark cartilage is used in dietary supplements. The demand for these products are driving overfishing of many shark populations worldwide. About 16 percent of the world’s shark species are now threatened with extinction.
The study detected concentrations of mercury and BMAA in the fins and muscles of all 10 shark species evaluated at levels that may pose a threat to human health. While both mercury and BMAA by themselves pose a human health risk, together they may also have synergistic toxic impacts. Therefore, restricting consumption of shark parts can have positive health benefits for consumers and also for shark conservation by reducing the demand and subsequent exploitation of sharks.
Mercury is an element, which has been introduced into the aquatic environment, primarily due to human activity such as coal fire burning. Most of the mercury in the environment comes from atmospheric deposition from distant mercury polluting sources. BMAA concentrations in cyanobacteria are increasing due to changes in the climate and human activity that impacts coastal waters. For example, nutrient pollution into the water can cause massive cyanobacterial algae blooms producing BMAA. Organisms in the water are exposed to these toxins or consume them and in both cases these organisms are consumed by larger organisms and the toxins biomagnify up the food web.
While it remains unknown how widespread these two toxins are in sharks globally, high mercury concentrations in sharks is pretty well established due its ability to biomangify up the food web and BMAA has been detected from all shark species analyzed to date from multiple ocean basins. However, given the cyanobacterial source, BMAA is likely to be more common and at higher concentrations in sharks from areas that are exposed to frequent algal blooms, such as areas with high nutrient pollution from land.
Eating foods with BMAA and mercury doesn’t mean that the consumer will develop a neurodegenerative disease. Similar to smoking cigarettes, health risks depend on repeated exposure, toxin levels, as well as the baseline health and genetic predisposition of the consumer.
It is unclear if BMAA and mercury in the tissues of sharks pose a threat to shark health or if they have developed some mechanism to cope with the toxins. However, the study authors suggest that restricting shark consumption could have positive health benefits for humans and also aid in shark conservation efforts.
The study, titled “Cyanobacterial Neurotoxin BMAA and Mercury in Sharks,” was published in the journal Toxins.
Check out this infographic on the hidden harm of shark finning