Reply to Ziegler et al. "Adding perspectives to: Global trends in carbon dioxide (CO2) emissions from fuel combustion in marine fisheries from 1950-2016" and addressing concerns of using fishing effort to predict carbon dioxide emissions

There are currently two separate approaches for estimating global CO2 emissions from marine fishing. One approach uses catch-based fuel use intensity (FUI) estimates for well-studied areas/fisheries to estimate FUI in data poor regions. The second approach, effort-based FUI, uses reconstructed fishing effort data to estimate fuel use based on vessel size and fishing times. Both methods utilize assumptions which are inherently uncertain; the advantages and disadvantages of each method are discussed. The two approaches are found to be complementary to one another, not contradictory, and global estimates of CO2 emissions from marine fishing should be based on a combination of both approaches, depending on the data locally available.