Energy savings in Mediterranean demersal trawl fisheries: full and model scale comparison of experimental and conventional gears on drag and fuel consumption

Abstract

Reducing fuel consumption, hydrodynamic drag and seabed impact without compromising catch performance and size selectivity remains a key challenge for demersal trawl fisheries. This study presents a comparison of demersal trawl configurations designed to reduce energy demand and improve the environmental performance of a Mediterranean bottom trawl fishery. The analysis focused on two configurations of the four-panel otter trawl design known as the "Americana": a traditional commercial configuration and a newly optimised experimental design developed through targeted modifications in mesh size distribution, netting material and belly geometry. The two gears were first evaluated through flume-tank trials using 1:10 scale models. These tests showed that the experimental trawl achieved a wider horizontal geometry and substantially lower towing load than the traditional design, supporting the expected reduction in drag associated with the decrease in twine surface area and projected resistance. Full-scale sea trials were then conducted in the central Adriatic Sea, Italy, under comparable operational conditions. A total of 19 comparative hauls were carried out, alternating between the traditional and experimental configurations. Fuel consumption, vessel speed, towing loads at the winch and wing-ends, net geometry and GPS data were collected using a harmonised instrumentation system. Catch data were also recorded to assess changes in fishing performance, catch composition and size-dependent catch efficiency. A dedicated lift test was used to derive a vessel-specific speed–fuel consumption model and to partition total fuel use during towing into vessel-related and gear-related components. Compared with the traditional gear, the experimental trawl showed greater horizontal net spread and markedly reduced vertical opening. These changes resulted in a 26.7% reduction in hydrodynamic drag and a 15% decrease in fuel consumption during towing. When fuel use was partitioned, gear-related fuel demand showed an even larger relative reduction of 29.7%. Total catch rates did not differ significantly between gear configurations. Catch comparison analyses indicated species-specific responses, with higher catch efficiency for pelagic and semi-pelagic species and reduced retention of smaller individuals for some demersal species. Overall, the results demonstrate that targeted trawl modifications can improve energy efficiency and potentially reduce seabed interaction while maintaining commercially acceptable catch performance.