The science of sustainable seafood, explained

New paper explains the role of seafood in sustainable diets

Everything you eat costs the planet something. Land for crops and livestock, inputs to grow them, and energy for everything else. Reducing humanity’s dietary footprint will be the toughest conservation challenge of the 21st century. Electricity and transportation will eventually be 100% renewable, but there is no way to replace food—it will always have costs. The challenge will be feeding Earth’s growing population while minimizing the impacts.

On this site, we have chronicled this feeding-the-world challenge over the past few years while covering the science and math of how seafood fits in to it all. Now a new paper has taken an exciting novel approach to the food/conservation dichotomy. While most research has measured environmental impact per unit of  protein or calorie, Koehn et al. 2022, The role of seafood in sustainable diets out last week in IOP Science (open access), measures environmental impact against nutrition, i.e.—how impactful is a food compared to the nutrients it provides? It’s the first paper to quantify and compare environmental impacts to nutrition, a broader and more complete look vs simply calorie or protein.

Comparing the nutrition to impact ratio of various land-based foods is fairly straightforward, especially with meats—there are only a few species of livestock raised for human consumption. Seafood is different: There are hundreds of different species humans eat, all with different nutrient profiles and impacts. Koehn et al. 2022 helps determine which types of seafood can be incorporated into a low-impact diet.

How do you measure the environmental impact of food?

The most comprehensive studies of food (or any product) are called life cycle assessments (LCAs). LCAs seek to track a product’s resource-use from beginning to end-user. For food, this often means the study of a complex supply chain: everything from inputs to energy use to processing to packaging to food waste. Often, the impacts are standardized into CO2 equivalents to measure climate change impact, though other environmental impacts can be quantified, like SO2 to measure air pollution impacts, or PO4 to measure water pollution potential from runoff.

In 2018, Poore and Nemecek compiled an LCA database that standardized a global discussion of food and its impacts, e.g. Our World in Data uses Poore and Nemecek’s database as the basis for their Environmental Impacts of Food Production visualization. More recently, the Lancet reported on a “planetary health” diet meant to balance environmental impact with fulfilling nutrition requirements. The Lancet diet concludes that a mostly plant-based diet with some seafood and poultry is best, however neither the Lancet, nor Poore and Nemecek examine seafood beyond broad “fish” and “crustacean” categories.

Just a week after Poore and Nemecek’s LCA database was published, Hilborn et al. 2018 published a similar database of seafood LCAs. Now, Koehn et al. 2022 builds on that work to see how different kinds of seafood can fit into a healthy-for-the-planet type diet.

Koehn et al. 2022 compiled LCAs of various seafoods to measure greenhouse gas emissions as its main metric of environmental impact. However, researchers needed to figure out a way to score nutritiousness, or the density of nutrients in a food. They came up with a nutrient richness index by relying on a standardized nutrient group that scores a food on how nutritious it is. They ended up with 12 nutrients:

Macronutrients

  • Protein
  • Fiber

Vitamins

  • Vitamin A
  • Thiamine
  • Riboflavin
  • Folate

Minerals

  • Zinc
  • Magnesium
  • Potassium
  • Calcium
  • Iron

Special category

  • Omega 3s DHA + EPA

Here is figure 1 from the paper showing nutrient richness for all food. You can think of this as a ranking of healthy foods.

Graph showing nutrient richness scores for several types of food.
Figure 1 from Koehn et al. 2022. Composite nutrient richness index scores averaged across 12 nutrients as determined by % of daily requirements in a 100g serving. Colors correspond to food type.

The next challenge was to figure out a way to compare nutrition to greenhouse gas emissions. They decided on a ratio of nutrition to GHG, with ratios “calculated as both impacts per nutrient richness composite index and per individual nutrients.”

Here are the results for impact per nutrition; note the GHG impacts are on a logarithmic scale.

Figure 2 from koehn et al. 2022 - nutrition to greenhouse gas emissions graph
Figure 2 from Koehn et al. 2022. Greenhouse gas emissions relative to composite nutrient richness across major food groups. The grey horizontal line indicates the median for all observations across the food groups (2725.10 g GHG emissions required to meet the nutrient requirement across 12 nutrients).

Sustainable seafood as nutrition

Lead author Zach Koehn said, “Diversity is important when considering how we can meet nutritional needs while limiting GHG emissions. For aquatic foods, some have emissions that are as low per nutrient richness as plants, while others have emissions as high as beef.”

Small pelagics (sardines & anchovies), big pelagics (tuna & billfish) and farmed seafood like carps, bivalves, and salmon were found to be lower impact than other animal-sourced food. Nearly all the seafood products studied were lower than pork, lamb, and beef except for shrimp and crustaceans like lobster and crab.

It’s also worth noting that the Koehn et al. 2022 analysis was completed before two recent LCA studies of Alaska pollock and salmon could be included. Those studies suggest pollock and salmon are low-impact options as well.

Wild-caught shrimp and crustaceans require a lot of fuel to catch and aren’t as nutritious as other kinds of seafood. Shrimp are generally caught via bottom trawl or dredge—it takes much more power to drag a net through mud and sand than through water. For crab and lobsters, the extra fuel use is thought to be due to excessive starting and stopping the engines to set and collect traps.

Farmed shrimp GHG emissions mostly come from land-use change. Unfortunately, in many tropical countries, mangroves have been cleared to make way for shrimp ponds.

The authors presented the best and worst terrestrial and aquatic foods on a per-nutrient basis in the figure below.  

Figure 3 from Koehn et al. 2022. GHG emission impacts needed to meet daily requirements for individual nutrient richness across the best and worst terrestrial (roots and beef) and aquatic (small pelagics, prawn) food groups.

Seafood, in all its diversity, deserves a place at the table when discussing healthy diets for the planet. With more refined data on the impacts of different seafood species, policy-makers and advocacy organizations can shape policies and campaigns to shift diets away from beef, lamb, pork, and shrimp, to lower-impact proteins like poultry and most other seafoods.

Planning for our future requires a food system that produces enough to address malnutrition for growing populations while minimizing its global and regional environmental impacts.

The results make clear that not all seafood is equal with respect to their environmental impacts and nutrient richness. Diversity with respect to species groups and production systems should be further recognized in future research and decision-making on the selection of food production systems that minimize environmental impacts and maximize contributions to food security and nutrition outcomes.

Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW.

Share this story:

Share
Tweet
Pin
Post
Email
Link

Subscribe to our newsletter:

Read more:

Leave a Reply

Ray Hilborn's every-so-often newsletter

The best way to keep up with our stories.