EU/UK joint request regarding mixed fisheries science

This service provides an overview of exploration into the science underpinning the annually produced mixed‑fisheries considerations.

Sensitivity to fleet and métier structure

Analyses in the Celtic Sea and North Sea found little sensitivity in the resulting overall catches to the fleet and métier structure. This was primarily due to the assumption of a fixed share of effort between métiers within a fleet and the lack of fleet-specific discard information. However, disaggregation of the current fleet–métier structure would bring other benefits such as enabling spatial information to be incorporated through métier definitions to explore alternative assumptions of fleet dynamics and to facilitate linkages with external groups (i.e. economic impact assessments of mixed‑fisheries scenarios).

Uncertainty and sensitivity to model assumptions

Analyses on the uncertainty in, and sensitivity to, input parameters were conducted for the Celtic Sea and Bay of Biscay mixed-fisheries models. The methodologies developed could be incorporated into the existing mixed‑fisheries framework and would provide useful information on risk. A retrospective examination of the North Sea model found that the current model assumption used (status quo values) for fleet quota shares and métier effort shares and catchabilities outperformed several alternative assumptions. The analyses on sensitivity and uncertainty highlighted the need for more disaggregated discard information (by vessel length category or by geographic region) as well as the requirement for high-quality data to properly condition highly influential parameters such as catchabilities and, to a lesser extent, the effort share between métiers.