Context
The implementation of the Landing Obligation under the Common Fisheries Policy has increased the need to improve bottom trawl selectivity, particularly in fisheries where certain low-quota species may jeopardize the economic viability of the fleet.
Trials carried out on commercial vessels allow selective devices to be validated under real fishing conditions; however, their high cost limits the experimental scope. For this reason, the use of the research vessel Emma Bardán makes it possible to test and fine-tune innovative configurations — including new codends and semi-pelagic trawl doors — in a controlled environment closely aligned with commercial operations.
In 2025, the project expands its scope by incorporating the assessment of gear impact on the seabed and the analysis of fuel consumption, thereby integrating objectives related to selectivity, environmental sustainability, and energy efficiency.
Objectives
The overall objective is to support the adaptation of the trawl fleet to European regulations concerning the Landing Obligation through an experimental campaign aimed at improving bottom trawl selectivity, while also evaluating the reduction of seabed impact.
Specific objectives
- To design and manufacture innovative selective devices tailored to the challenges of bottom trawling in ICES division 8abd, with the aim of reducing unwanted catches of TAC-regulated species.
- To qualitatively and quantitatively assess the effect of different codend configurations (T90, T45 or square mesh, T0, and control) on gear selectivity.
- To analyse selectivity with particular focus on European hake (Merluccius merluccius) and megrim (Lepidorhombus spp.), species subject to de minimis exemptions whose continuation requires further technical advancements.
- To consider other TAC-regulated species subject to the Landing Obligation: horse mackerel (Trachurus trachurus), Atlantic mackerel (Scomber scombrus), blue whiting (Micromesistius poutassou), and boarfish (Capros aper).
- To assess the impact of semi-pelagic 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 imagery of species behaviour in response to selective devices.
- To comprehensively characterise all catches (fish and invertebrates) from the 2025 hauls, incorporating a biodiversity and integrated fisheries management approach.
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 European hake and megrim.
- Reduce physical impact on the seabed through the operational validation of semi-pelagic doors and net modifications.
- Optimise energy efficiency by assessing the potential for fuel consumption reduction and, consequently, carbon footprint mitigation.
- 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 within the fleet, and improve the balance between marine ecosystem conservation and the economic viability of the fisheries sector.
Final Report
Study on Selectivity and Semi-Pelagic Doors in the Bottom Trawl Fleet of the Bay of Biscay – 2025
Video
Funding
Ministry of Agriculture, Fisheries and Food; General Secretariat for Fisheries; Directorate-General for Sustainable Fisheries; Deputy Directorate-General for Fisheries Research and Data Collection
