Publication | Statement Assessing seafloor sensitivity for the Belgian Fishing grounds: comparison of two approaches
The Belgian Sea fishery focuses on bottom trawling for sole, plaice, and shrimp. However, concerns about the ecological impact of bottom trawling have arisen due to its link to reduced benthic biomass, diversity, and alteration of faunal community traits (Hiddink et al., 2019). Consequently, EU conservation policies, such as the Marine Strategy Framework Directive (MSFD), emphasize the evaluation and management of seafloor ecosystems. The UK is no longer bound to these EU policies and has established their own approach to improve the health of their waters trough the Environment Act 2021. To achieve its targets, the country will implement stronger management measures for seafloor health, with a primary focus on Marine Protected Area’s (MPAs). Since Belgium's fishing fleet predominantly uses mobile bottom contacting gear impacting the seabed, assessing seabed ecosystems is crucial. Benthic indicators have been developed to evaluate trawling impacts, categorized into risk and state indicators. This report section compares the sensitivity outcomes of two commonly used risk indicators, namely the OSPAR BH3 (UK approach) and ICES FBIT indicator, across Belgian bottom trawling regions. The goal is to enhance our understanding of seafloor conditions and aid policymaking and fishing practices that promote Good Environmental Status in EU waters and healthy sea-bottom ecosystems in UK waters.
We compared the sensitivity outcomes of two benthic risk indicators (BH3 & FBIT) to investigate: 1) if both indicators evaluate the same habitat as sensitive/least sensitive in each assessment region (similar outcomes) ; 2) if both methods are comparable (i.e., if there is there a correlation between them) and 3) if habitat classification influences indicator outcomes as both indicators make use of a different habitat map to calculate their sensitivity. These questions are relevant for defining sea-bottom sensitivity, as these indicators are used to manage fishery impacts (E.g. excluding fishery in sensitive areas) and delineate MPAs (E.g. sensitive habitats to be protected).
ICES FBIT and OSPAR BH3 benthic sensitivity data for the Greater North Sea and Irish and Celtic Sea regions were obtained from the ICES GitHub repository and OSPAR QSR 2023, respectively. To ensure comparability, the FBIT shapefiles were aligned to fit the OSPAR regions. A merged dataset was created on the OSPAR regional reporting level, which include FBIT outcomes, abrasion sensitivity scores (OSPAR sensitivity), and both EUNIS level 3 and MSFD broad habitat type (BHT) classifications for each grid cell.
Mean sensitivity was compared across the five major habitats (km2) in each region for both MSFD and EUNIS classifications, with ranking used to assess sensitivity similarities between both indicators. Additionally, a boxplot and jitter plot analysis were conducted at the grid cell level to examine indicator correlation and habitat classification influence. This approach enhances our understanding of benthic habitat sensitivity to fishing pressures across regions and habitat types.
Our analysis revealed inconsistencies between BH3 and FBIT indicators, as median longevity (FBIT indicator) did not consistently correlate with BH3 sensitivity classes across regions and habitat classifications. These discrepancies were further underscored by differences in mean sensitivity outcomes, particularly in identifying the most and least sensitive habitats within a region. This misalignment reflects methodological differences, suggesting that each indicator prioritizes different aspects of ecosystem responses. These findings support the use of multiple indicators to capture diverse ecosystem dynamics. However, discrepancies in sensitivity outcomes also highlight the influence of habitat classifications, as variations in habitat data resolution between indicators may contribute to these differences.
Overall, our research offers valuable insights into bottom trawling impact assessment, aiding in understanding benthic habitat sensitivity. This work lays the basis for our follow-up study, Benthis Nationaal 2, where we aim to develop a more balanced approach to bottom disturbance impact assessments by comparing and integration a broader set of indictors. The goal is to create a sensitivity map, based on these integrated indicators, to support Belgian fisheries management strategies while aligning with EU and Uk policies on seafloor protection measures. Additionally, this map will be made available onboard Belgian fishing vessels via the VISTOOLS platform, providing fishers with a practical tool to address bottom disturbance issues effectively and realistically in their daily operations.