CASELEM

Context

The implementation of the Landing Obligation within the framework of the Common Fisheries Policy has increased the need to improve the selectivity of bottom trawling, particularly in fisheries where certain low-quota species may compromise the economic viability of the fleet.

Trials on commercial vessels allow selective devices to be validated under real conditions; however, their high cost limits the experimental scope. Therefore, the use of the oceanographic vessel Emma Bardán enables the testing and adjustment of innovative configurations—including new codends and semi-pelagic doors—in a controlled environment close to commercial operations.

In 2025, the project expanded its scope by incorporating the evaluation of gear impact on the seabed and the analysis of fuel consumption, thus integrating objectives of selectivity, environmental sustainability, and energy efficiency. The innovative element introduced was the use of semi-pelagic trawl doors, known as “flying doors”, which, by operating off the seabed, have the potential to reduce both seabed impact and fuel consumption during trawling. In 2026, further progress continues along this line, moving towards semi-pelagic doors to achieve even greater reductions in impact and fuel consumption.

Objectives

The overall objective is to contribute to the adaptation of the trawl fleet to European regulations related to the Landing Obligation through an experimental campaign aimed at improving the selectivity of bottom trawling, while also evaluating the reduction of seabed impact.

Specific objectives

• To design and manufacture innovative selective devices adapted to the challenges of bottom trawling in ICES area 8abd, with the aim of reducing unwanted catches of TAC-regulated species.
• To qualitatively and quantitatively assess the effect of different codend configurations on gear selectivity.
• To analyse selectivity with particular focus on hake (Merluccius merluccius) and megrim (Lepidorhombus spp.), species subject to de minimis exemptions whose continuity requires further technical advances.
• To also consider other TAC-regulated species subject to the Landing Obligation: horse mackerel (Trachurus trachurus), mackerel (Scomber scombrus), blue whiting (Micromesistius poutassou) and boarfish (Capros aper).
• To evaluate the impact of “flying doors” compared to traditional bottom trawl doors.
• To analyse fuel consumption patterns associated with the use of semi-pelagic doors versus conventional ones.
• To conduct direct observation through underwater imaging of species behaviour in response to selective devices.

Expected Results and Impact

The CASELEM project will generate technical and scientific evidence to:

• Improve bottom trawl selectivity, reducing unwanted catches and facilitating compliance with the Landing Obligation.
• Support the continuation of de minimis exemptions through new experimental data focused on hake and megrim.
• Reduce physical impact on the seabed, through the operational validation of semi-pelagic and pelagic doors.
• Optimise energy efficiency, by assessing the potential reduction in fuel consumption and, consequently, carbon footprint.
• Carry out a comparative analysis of catches between flying doors and bottom trawl doors.
• Advance towards more integrated fisheries management, through detailed characterisation of captured biodiversity.

Overall, the results will help strengthen the scientific basis for regulatory decision-making, support technological innovation in the fleet, and improve the balance between marine ecosystem conservation and the economic viability of the fishing sector.

Final Report

Study on Selectivity and Semi-Pelagic Doors in the Bottom Trawl Fleet of the Bay of Biscay – 2025

Video

Funding