Featured Image Caption: Reducing the fuel usage of fishing fleets would be a major step in decreasing the greenhouse gas emissions from catching wild fish. (Credit: milivigerova, via Pixabay.)
Source Article: Gephart, J. A., Henriksson, P. J. G., Parker, R. W. R., Shepon, A., Gorospe, K. D., Bergman, K., Eshel, G., Golden, C. D., Halpern, B. S., Hornborg, S., Jonell, M., Metian, M., Mifflin, K., Newton, R., Tyedmers, P., Zhang, W., Ziegler, F., & Troell, M. (2021). Environmental performance of blue foods. Nature, 597(7876), 360–365. https://doi.org/10.1038/s41586-021-03889-2
Food and Environmental Impacts
Everyone has to eat, but the environmental impacts of food production have many scientists searching for ways to reduce our footprint. Globally, food production is responsible for over a quarter of all greenhouse gas emissions, three-quarters of the world’s water use, and the use of half of the planet’s ice-free land. “Blue foods”, including fish and other aquatic foods, have been identified as one way we could reduce some of these environmental pressures.
An international team of scientists, led by Jessica Gephart, Patrik Henriksson, Robert Parker, and Alon Shepon, hoped to assess the impact of a wide array of blue food groups. They drew on studies that reported data representing over 1,690 farms and 1,000 fishery records to compare the effects of raising or catching different species.
Rankings, Winners, and Runners-up
The final report looked at 23 species categories ranging from seaweeds to shrimp to salmon, and included both wild-caught and farmed species. The scientists began by considering how raising or catching species from each group impacted land use, freshwater use, greenhouse gas emissions, and the release of nitrogen and phosphorus.
Several species stood out for their low impact. Wild-caught trout and salmon used the least land and water, and farmed seaweeds and bivalves (shellfish such as oysters and clams) had the lowest greenhouse gas emissions. Most aquatic food production releases nitrogen and phosphorus through the breakdown of fish waste and the use of fertilizer, but seaweed, bivalves, and some silver and bighead carp actually removed more of these elements from the environment than they generated. This is important because excess nutrients in water may promote excessive plant growth that lowers oxygen levels through a process called eutrophication. In contrast, farmed silver and bighead carps had the highest water use due to high evaporation rates. Milkfish, shrimp, and silver and bighead carp used a large amount of land because they require large ponds, and the categories of farmed “miscellaneous diadromous fish” (fish that spend part of their lives in saltwater and part in freshwater) and miscellaneous marine fish used large amounts of water to produce their feed.
The researchers found key differences between farmed and caught species. For instance, greenhouse gas emissions from fed aquaculture (farming that requires feed, typically fish farming) were primarily from producing feed, while greenhouse gas emissions from catching wild species were mostly from vehicle fuel use. Predictably, catching wild fish did not use much land or freshwater, and also produced low amounts of nitrogen and phosphorus.
Beyond the impacts already described, there are less common, though still important, ways of comparing the environmental impacts of foods. For example, both farming and catching fish could promote disease spread, introduce invasive species, or physically disturb the seafloor. Catching fish and other aquatic food appears to be the better choice when considering nitrogen, phosphorus, water, and land use impacts, but this can still have other effects that may dramatically change ecosystems. Targeting certain species for fishing may decrease their populations and change the frequency of certain sizes or ages. This frequency change may impact predators which primarily eat a certain size of prey, or further reduce the population if many reproductive-age individuals are caught. Additionally, catching wild species risks catching non-targeted species (known as by-catch), including larger animals such as dolphins and turtles. These animals often suffer injuries or die, which is especially harmful to endangered species.
Towards a Sustainable Future
The researchers identified several ‘performance gaps’ in the current fishing and farming systems, which could be addressed to reduce the environmental impact of aquatic foods. For instance, changing the compositions of farmed fish feed to use deforestation-free crops may reduce greenhouse gas emissions. Other feed options could include fishery by-products and novel feeds like algal, microorganism, and insect meals, although the impacts of these choices have not been fully explored. The study team also identified alteration of the feed conversion ratio as a way to reduce emissions, land use, and water consumption. The feed conversion ratio compares the amount of feed given to the fish with the output fish weight as a way to measure how efficiently the feed is converted into fish for human consumption. With improving feed technologies, this ratio may improve.
Reducing fuel use is a primary opportunity for reducing fishing emissions. This could be done by transitioning fishing fleets to use low-fuel gears or new technologies, such as electric, hydrogen fuel, and sail-assisted boats. Alternatively, increasing the overall populations and sizes of wild fish would reduce fuel use, as fleets would not have to travel as far to catch as much.
Overall, there is no type of aquatic food that is clearly the ‘best’ for the environment, but keeping the benefits and drawbacks of each in mind is an important step in reducing our overall footprint. With improving technology and greater awareness of our options, we can continue our progress towards more sustainable food.