Sustainability and Public Health

by Ashley Greenley

It’s a tough job being a responsible consumer in this day of the information era, especially when the news that spills out of every media outlet never quite seems to be consistent in its messaging. Take seafood consumption – there couldn’t be a more confusing platform for health-conscious consumers: seafood is healthy because its rich in Omega 3s; seafood consumption is risky due to high mercury levels in fish, bluefin tuna from Japan is radioactive but not at levels of concern for human consumption, etc. etc.  Paralleling the health considerations for seafood are the environmental issues, which stand to equally overwhelm consumers with reports of overfishing (75% of the worlds fisheries are overfished!!!), incredibly high bycatch rates in fisheries, concerns about aquaculture (should we eat farmed seafood or not?!), fraudulent seafood labeling (that tuna in your sushi restaurant is likely escolar!!), and the list continues indefinitely…

Fortunately, seafood consumers have been given a break. Amidst the maddening mix of health and environmental concerns, the final take home message appears to be one in the same: healthy seafood can also be sustainable seafood.

This past week, a new study from Arizona State University scientifically demonstrated that sustainable seafood items are also consistently safer for human consumption. The study compared sustainability data from seafood ranking programs (MBA Seafood Watch and Blue Ocean Institute) and fisheries datasets, against two indices of human health: omega 3 content (representing health benefits in seafood) and mercury levels (denoting health risks in seafood). Interestingly, there was no difference in Omega 3 health benefits among seafood categorized in the various sustainability rankings, but there was a significant increase in health risks from mercury exposure as seafood rankings moved from green (sustainable) to red (unsustainable) (see graph below). The authors explain their findings by noting patterns in mercury accumulation in fishes. Namely, fishes that are higher in the food chain, such as top predators like tunas, sharks, and swordfish, tend to accumulate high levels of mercury in their tissues and are also, given their long life spans, more susceptible to overfishing. 

The authors conclude that seafood consumers striving to minimize their mercury exposure will also be purchasing seafood that tends to be more sustainable.  Right? Well, yes… to some extent.

One key consideration overlooked in the study is the pattern of seafood consumption in the United States. According the National Marine Fisheries Service, approximately 90% of seafood consumed domestically is comprised of 10 species (see table below), of which the majority has low associated mercury risk. For the top fishes consumed, tuna (if its canned albacore) and Atlantic cod were recognized in the study for having high mercury content as well as environmental concerns for sustainability. Yet do the patterns of human health risk and sustainability hold for the other most consumed species?  Unfortunately, at the cost of simplicity, the answer depends on a few factors.

Salmon, for example, are the third most popular seafood item in the United States and also have relatively low mercury content. However, the sustainability rating for salmon greatly depends on the source; wild salmon from Alaska is sustainable, but the Monterey Bay Aquarium currently ranks all farmed salmon as unsustainable. Similar complexities arise for other frequently consumed fish. Farmed tilapia, for example, can be either ranked green, yellow, or red depending on whether the farm in located in the United States, Central/South America, or Asia.

What about shellfish and other invertebrates? Fortunately, the majority of invertebrates consumed for seafood have low risk associated with mercury, although other toxins may be a concern. Yet, like all seafood, the environmental impacts from harvesting invertebrates depend on many factors such as catch methods, species resilience to fishing pressure, effectiveness of management, etc.

In conclusion, there is no simple metric that will serve as definitive guide to sustainability. In the present study, the authors provide evidence that consumers, by avoiding fish high in mercury, also avoid eating long-lived species that are vulnerable to overfishing. While this can serve as a general rule of thumb, multiple criteria need to be considered if a consumer wants seafood that is healthy AND sustainable. The good news is that many resources, such as the Monterey Bay Aquarium’s Seafood Watch guides, can help consumers sort throughout the masses of information to make responsible seafood purchases. Additionally, we at FishWise are working hard with major retailers to ensure sustainable options are available and labeled on supermarket shelves- so that ultimately, consumers won’t have to work quite so hard to do the right thing.  

Figure from Gerber et al. 2012.  Black bars indicate health benefits of seafood (Omega 3 content) and gray bars show health risks (Mercury concentration).  Green, Yellow, and Red are sustainability ratings based on the Monterey Bay Aquarium Seafood Watch.