Understanding and reducing the greenhouse gas emissions of bottom trawl fisheries is of importance, as it directly impacts efforts to mitigate climate change and promotes sustainable fishing practices. As a considerable part of global landings is fished using demersal trawls and vessel renewal is often mentioned as an important mitigation measure. This study compares the greenhouse gas emissions of older and newer trawlers in the Icelandic fleet, using Life Cycle Assessment methodology with the functional unit “1 kg of demersally trawled fish at landing”. The global warming potential (kg CO2-eq) from older Icelandic bottom trawlers was assessed and compared to the newer ones, where older vessels were in some cases being decommissioned. A total of 11 trawlers were assessed, providing a cross section of the Icelandic bottom trawler fleet, with respect to age, size, catch composition and onboard operations. The results show that freezer trawling was more energy-intensive compared to trawlers landing their catches chilled/superchilled. Fleet renewal alone does not explain the reduction in fuel use and greenhouse gas emissions in the Icelandic bottom trawl fleet between 2012 and 2022, highlighting the need for a comprehensive approach considering multiple factors such as catch composition, fishing ground, and vessel characteristics, which explained 87% of the emissions. Catching indicated increased fuel consumption compared to steaming. The greenhouse gas emissions allocated to each demersal fish species ranged on average from 0.5 to 1.0 kg CO2-eq/kg of the weight of demersal fish landed, and from 1.4 to 2.7 kg CO2-eq/kg of the edible part of demersal fish landed (mass allocation), where redfish stood out as having the highest emissions.