Wild-caught tuna is unique from the other commodities studied, because the growing stage is not applicable, so the processing and distribution stages become the area of focus. Transport of wild-caught tuna products is particularly important. In 2018, about 51% of global tuna products were transported through Asia, and about 58% of global tuna products were transported frozen. The extent to which tuna is globally transported, particularly with the use of refrigeration, contributes heavily to the fuel use intensity and emissions associated with tuna products.
The emissions associated with wild-caught tuna vary based on fishing, transportation, and processing methods, as well as by fishery size and location. Across all methods, greenhouse gas emissions appear directly correlated to acidification and eutrophication potential, as all three emissions arise largely from fuel use during processing and transport. Greenhouse gas emissions were specifically evaluated across fishing methods, and it was found that purse seine fleets have low emissions and fuel use intensity. Purse seining is the most widely used fishing method, but these fleets are unable to catch large, higher quality tuna. This shortcoming allows longline fisheries and other fishing methods, which have higher greenhouse gas emissions, to persist.
Table 1. An overview of the relationships found between environmental indicators for tuna production. Data from Avadà et al. (2015), Hillborn et al. (2018), Hospido et al. (2006), Hospido & Tyedmers (2005), Minami et al. (2004).
Generally, efforts to ameliorate the environmental impacts of the tuna industry should focus on reducing fuel use. Data collection in this field should continue, as many extant environmental impact assessments of tuna lack data on acidification and eutrophication potential, and tend to focus solely on GHG emissions. Further study of the environmental impacts of the tuna industry is critical to produce more nuanced evaluations of the diverse characteristics of tuna products. Within the tuna industry, markets like canned tuna versus sushi-grade fish demand different fishing and processing methods, and should be evaluated distinctly.