Understanding Mercury in the Marine Food Web
Mercury is a naturally occurring element, but industrial activity, particularly the burning of coal, has increased its presence in the environment. Once in aquatic ecosystems, microorganisms convert elemental mercury into methylmercury, a highly toxic form that is absorbed by marine life.
This process is particularly concerning due to biomagnification, where mercury becomes more concentrated as it moves up the food chain. This means smaller organisms have low levels, but as they are eaten by larger predators, the mercury accumulates and becomes more concentrated in the tissues of animals higher on the food chain, such as sharks. Critically, methylmercury binds to the protein in fish muscle tissue, so it cannot be removed through cooking, freezing, or other preparation methods.
Gummy Shark Mercury Levels: A Closer Look
When considering the question, "Is gummy shark high in mercury?", it's important to look at specific data. Research from 1971 on commercially caught sharks in Victoria, Australia, found notable differences between species. While school sharks had a mean mercury level of 0.90 ppm, gummy sharks (Mustelus antarcticus) had a significantly lower mean of 0.37 ppm.
Several factors contribute to this difference:
- Size and Age: As with other predatory fish, mercury concentration in gummy sharks varies with size and age, with larger, older individuals accumulating more over time.
- Growth Rate and Lifespan: Gummy sharks are a relatively small, fast-growing species with a shorter lifespan compared to some of the larger, apex predator sharks. This reduces the timeframe for mercury bioaccumulation.
- Diet: Gummy sharks are primarily bottom-dwellers that feed on crustaceans and cephalopods, lower on the food chain than large piscivorous sharks.
Gummy Shark vs. Other Fish: A Mercury Comparison
The best way to contextualize the mercury levels in gummy shark is to compare them with other commonly consumed seafood. The table below uses data from the U.S. FDA/EPA to provide a reference, with gummy shark data included based on the historical Australian study.
| Fish Type | Mercury Level (PPM) | Health Advice (FDA/EPA/FSANZ) | Typical Size/Lifespan |
|---|---|---|---|
| Shark (General) | 0.98 (average) | Avoid | Large, long-lived predator |
| Gummy Shark (1971 data) | 0.37 (mean) | Limit/Moderate Consumption | Smaller, faster-growing species |
| Swordfish | 1.0 (average) | Avoid | Large, long-lived predator |
| Tuna (Bigeye) | 0.69 (average) | Avoid | Large, long-lived predator |
| Salmon (Fresh/Frozen) | 0.022 (average) | Best Choice | Small/medium size, lower on food chain |
| Sardines | 0.013 (average) | Best Choice | Small size, low on food chain |
Recommended Consumption Guidelines
For most people, the nutritional benefits of including seafood in their diet outweigh the risks associated with mercury. However, some populations are more vulnerable and require specific advice.
- Pregnant or breastfeeding women and young children: The developing nervous system of an unborn baby or young child is especially sensitive to the effects of methylmercury. Health authorities often advise these groups to severely limit or completely avoid high-mercury species. For flake (gummy shark), some Australian guidelines recommend no more than one serve per fortnight for pregnant women.
- The general population: For healthy adults, moderate consumption is less of a concern. Many guidelines suggest limiting consumption of high-mercury fish to no more than one serving per week.
How to Make Safer Seafood Choices
To minimize your mercury exposure while still enjoying the nutritional benefits of fish, consider these tips:
- Choose Lower-Mercury Fish: Opt for species like salmon, sardines, trout, and cod, which are lower on the food chain and typically contain less mercury.
- Diversify Your Choices: Instead of eating the same type of fish repeatedly, vary your selections to avoid a high intake of mercury from a single source.
- Check Local Advisories: If you consume locally caught fish, check advisories from local health or environmental agencies, as mercury levels can vary significantly by location.
- Eat Smaller Fish: As a general rule, choosing smaller, younger fish can help reduce mercury exposure, as they have had less time to accumulate the metal.
- Consider Certified Seafood: Look for seafood with certifications from reputable organizations like the Marine Stewardship Council (MSC), which can provide assurance of sustainable sourcing, though it is not a guarantee of low mercury.
Conclusion
While the stereotype of all sharks having high mercury is true for many larger species, the situation with gummy shark is more nuanced. As a smaller, faster-growing species, its mercury levels are generally lower than those of larger predatory sharks. However, it is not mercury-free, and consumption guidelines should be followed, especially for vulnerable populations like pregnant women and young children. By practicing moderation and choosing a variety of seafood, you can enjoy the nutritional benefits of fish while managing your mercury intake effectively. For the most current and specific guidance, always consult resources like the FDA's Advice about Eating Fish.
