Fishery Carbon Footprint Calculator

Fishing emissions are dominated by one term. The diesel factor of 3.17 kg CO2 per litre follows from stoichiometry rather than convention: marine gas oil has a density near 0.84 kg per litre and is roughly 86 percent carbon by mass, and each carbon atom leaves as a CO2 molecule 3.67 times heavier than itself. Because fuel is 60 to 90 percent of a vessel's operational footprint, the decisive variable is fuel use intensity in litres per kilogram landed, set almost entirely by gear type. Purse seining on dense pelagic schools runs around 0.05 to 0.2 L per kg, pelagic longlining 0.5 to 2, and bottom trawling 1 to 5 because towing gear through sediment converts most engine power into drag. Expressed as carbon intensity, small pelagics land below 1 kg CO2 per kg of fish while trawled shrimp and lobster exceed 5 and sometimes 10, against the 4 to 5 kg typical of poultry. The boundary drawn here is the voyage plus processing, so several material sources are excluded. Refrigerant leakage is often the largest omission, since HFC-404A and HFC-134a have global warming potentials in the low thousands and a leaking system can add more warming than the fuel used to run it. Vessel construction, gear, port infrastructure and distribution are also outside the boundary; air-freighted fresh fish alone can add 5 to 10 kg CO2 per kg, while container shipping adds under 0.3. Seabed carbon disturbed by trawling is likewise excluded, and the grid factor of 0.5 kg CO2 per kWh is a global-average placeholder, well above the French figure and below coal-heavy grids.

Fuel efficiency became a fisheries research topic after the oil shocks of 1973 and 1979, when the FAO and national institutes began publishing work on vessel and gear energy use in response to sudden operating cost pressure. Environmental framing came later, with the spread of life cycle assessment methods standardised by ISO 14040 and 14044 from 1997 onward, which gave analysts a consistent way to allocate emissions per kilogram of product across capture, processing and distribution. The global picture was first quantified by Peter Tyedmers, Reg Watson and Daniel Pauly, who estimated in Ambio in 2005 that the world's fishing fleets burned roughly 50 billion litres of fuel a year, about 1.2 percent of global oil consumption, and emitted on the order of 130 million tonnes of CO2. Robert Parker and colleagues updated this in Nature Climate Change in 2018, putting fisheries emissions near 179 million tonnes of CO2 equivalent in 2011 and showing an increase of about 28 percent since 1990 driven largely by growth in fuel-hungry crustacean fisheries even as landings stagnated. A 2021 Nature paper led by Enric Sala argued that bottom trawling disturbs sediment carbon on a scale comparable to aviation, a claim other researchers have contested over how much disturbed carbon actually reaches the atmosphere, and the question remains open.