Behind the Colors: How Our Scientists Calculate Your Seafood Watch Ratings

You are standing at the fish counter, scanning the rows of shimmering fillets and iced shellfish. You see a small green sticker or a mention of a "Best Choice" rating. For many, that simple color-coded system is the final word in a sustainable purchase. But have you ever wondered what actually happens before that sticker is applied? How do we determine if a North Atlantic swordfish is a better choice than a Pacific one, or if farmed shrimp from Southeast Asia meets our environmental standards?

Behind every Green, Yellow, and Red recommendation lies a mountain of data and months of intensive investigation. Our team of marine biologists and researchers acts as ocean detectives, piecing together evidence from across the globe to ensure the seafood on your plate supports a healthy ocean. This process is built on a foundation of scientific rigor, impartiality, and transparency, designed to ensure that the ocean flourishes and people thrive.

At the Monterey Bay Aquarium, we believe that providing you with a simple recommendation requires navigating immense complexity. In this article, we pull back the curtain on the six core stages of our scientific process, revealing how we calculate the ratings that guide the global sustainable seafood movement.

1. The Foundation: Setting the "Gold Standard" for Sustainability

Before a single fish is ever rated, we must first define what "sustainable" actually means. We do not look at seafood in isolation; instead, we take an "ecosystem-based" approach. This means our standards aren't just about whether there are enough fish left to catch next year. We ask a much bigger question: does this fishing or farming operation allow the entire marine environment to remain healthy and resilient?

Our three foundational standards—for fisheries, salmon fisheries, and aquaculture—serve as our North Star. These documents are developed in collaboration with global experts and reflect a conservation ethic that prioritizes the well-being of coastal ecosystems and the people who depend on them. We evaluate every operation against three main pillars: environmental protection, social responsibility, and economic viability.

The "Gold Standard" ensures that our recommendations account for the big-picture health of the ocean, not just individual species counts. By setting these high bars, we provide a consistent benchmark that can be applied to everything from a small-scale blue mussel harvest in Maine to massive industrial tuna fleets in the mid-Pacific. This consistency is what allows businesses and consumers to trust that a "Green" rating truly represents the pinnacle of environmental performance.

2. Wild vs. Farmed: Two Distinct Detective Stories

Not all seafood is created equal, and neither are the risks associated with producing it. One of the first steps in our assessment process is determining which "playbook" to use. Our scientists utilize different standards depending on whether the seafood is wild-caught or raised through aquaculture (farming). Each path requires a different set of questions and a unique investigative focus.

For wild-caught fisheries, the story is one of extraction. We examine how taking a species out of the water affects the wild population and the surrounding habitat. For aquaculture, the story is one of introduction. We look at what is being put into the water—such as feed, chemicals, and waste—and how those inputs impact the local environment.

Using distinct standards for wild and farmed seafood allows our scientists to address the specific environmental risks unique to each production method. While a wild fishery might be penalized for accidental bycatch of sea turtles, an aquaculture farm would be scrutinized for the amount of wild fish used in its feed. This specialized approach ensures that no matter how your seafood was produced, we are looking at the right data points to measure its true impact.

3. The Wild Audit: Assessing Impact, Bycatch, and Management

When our researchers dive into a wild fishery assessment—such as our recent draft report on the Blue Mussel (Mytilus edulis) in the Northwest Atlantic—they follow a strict four-criterion framework. This is where the detective work becomes highly technical, involving the analysis of "Productivity-Susceptibility" and fishing mortality rates.

• Criterion 1: Abundance and Fishing Mortality. We ask: Is the population healthy? Our scientists look at biomass levels to ensure the species isn't being overfished. For the Blue Mussel, this involves looking at populations across Maine, Massachusetts, and New York.
• Criterion 2: Impacts on Other Species (Bycatch). This is a critical factor. We investigate if the fishing gear—whether it’s a hand dredge or a longline—accidentally catches "non-target" species like sharks, seabirds, or marine mammals.
• Criterion 3: Management Effectiveness. We evaluate the rules in place. Is there a management strategy that actually prevents overfishing? We look for evidence of enforcement and scientific monitoring.
• Criterion 4: Habitat and Ecosystem Impacts. Does the gear damage the seafloor? A hand-harvested mussel has a very different impact than a heavy bottom dredge that might scrape away sensitive coral or seagrass beds.

The Wild Audit ensures that a fishery is managed with a long-term view that protects both the target species and the broader marine community. By scoring these four criteria, we can identify exactly where a fishery is succeeding and where it needs to improve to reach a sustainable level.

4. The Aquaculture Audit: Feed, Chemicals, and Clean Water

Farming seafood presents a different set of challenges. Under our Aquaculture Standard V4, we shift our focus to the "footprint" of the farm itself. We look at the efficiency of the operation and its potential to pollute the surrounding waters. Three factors are particularly vital in this calculation:

• Effluent and Waste Management. We calculate the "waste discharged per ton of fish." If a farm releases too much nitrogen or phosphorus into the water, it can cause harmful algal blooms. We look at both farm-level impacts and the cumulative effect of many farms in one area.
• Chemical Use. We scrutinize the use of antibiotics and pesticides. Overuse of these chemicals can lead to resistant bacteria or harm local wildlife that isn't part of the farm.
• The Feed Criterion. This is perhaps the most complex part of the aquaculture audit. We calculate the "wild fish use" and "net protein gain." We want to ensure that we aren't using three pounds of wild-caught fish just to produce one pound of farmed salmon.

The Aquaculture Audit prioritizes resource efficiency and environmental containment to ensure that farming doesn't come at the expense of local water quality. Our scientists also look at "Habitat Conversion," ensuring that sensitive areas like mangrove forests aren't being destroyed to make room for ponds.

5. The Peer Review Gauntlet

Our ratings are never decided in a vacuum. To maintain the highest level of scientific integrity, every assessment must pass through a rigorous, multi-step review process. This is the "gauntlet" that ensures our data is accurate and our conclusions are impartial. Once a Seafood Watch author completes a draft report, it is sent to external peer reviewers who are experts in that specific field.

We rely on the expertise of scientists like Dr. Larry Crowder from the Center for Ocean Solutions and aquaculture specialists like Peter Bridson. These experts provide a critical check on our work, challenging our assumptions and ensuring our methodology holds water. Furthermore, we maintain transparency by opening our draft assessments—like the 2025 Blue Mussel report—to public comment. This allows industry members, other NGOs, and the public to provide additional data or feedback.

The Peer Review Gauntlet guarantees that Seafood Watch recommendations are based on the best available science and are free from industry or political bias. This transparent process is why our ratings are trusted by major retailers and world-class chefs alike. We don't just ask you to take our word for it; we show our work.

6. The Final Verdict: Translating Math into "Traffic Lights"

After months of research and review, all the data points are synthesized into a final numerical score. This math is what triggers the familiar "traffic light" recommendations that you see on our app or in stores.

• Green (Best Choice): These species are the "valedictorians" of the ocean. They are well-managed, have healthy populations, and are caught or farmed in ways that cause little to no harm to the environment.
• Yellow (Good Alternative): There is usually one significant concern—perhaps a lack of data, moderate bycatch, or a management plan that isn't quite perfect. They are okay to buy, but there is room for improvement.
• Red (Avoid): These fisheries or farms have critical conservation concerns. This could mean the species is overfished, the gear is destroying habitat, or the management is non-existent.

The final rating is a bridge between complex marine biology and your everyday purchasing decisions. It takes hundreds of pages of scientific analysis and condenses them into a simple, actionable guide. When you choose a Green-rated fish, you are directly supporting the fishers and farmers who are doing things the right way.

Make Your Choice Count

Science is a powerful tool, but its true impact only happens when it leads to action. Now that you know the rigor, the peer reviews, and the detective work that goes into every Seafood Watch rating, you have the power to influence the future of the ocean with every meal.

By choosing sustainable seafood, you are sending a clear signal to the market that ocean health matters. You are supporting the work of the Monterey Bay Aquarium and the thousands of scientists, fishers, and advocates working to keep our blue planet thriving.

Your Next Step:
Download the Seafood Watch app today. It puts the power of our scientific research right in your pocket, making it easy to check ratings at the grocery store or your favorite restaurant. Together, we can turn the tide toward a more sustainable future.