Who fishes, what is caught and how? A characterization of candidate ecoregions of the International Commission for the Conservation of Atlantic Tunas to support the implementation of the Ecosystem Approach to Fisheries Management

[ES] La transición hacia un Enfoque Ecosistémico para la Gestión Pesquera (EEGP) ha llevado a la ICCAT a proponer ecorregiones candidatas como nuevas unidades espaciales. Este estudio aborda la necesidad de validar empíricamente estos límites mediante el análisis de su adecuación a la realidad operativa de las flotas pesqueras. Utilizando las bases de datos oficiales de la ICCAT, esta investigación transforma un marco teórico en una herramienta funcional, proporcionando una base científica para la implementación práctica del EEGP en el Atlántico. El objetivo principal es evaluar la validez de tres ecorregiones candidatas: Atlántico Norte (NAE), Atlántico Tropical (TAE) y Atlántico Sur (SAE), mediante un análisis comparativo de flotas y especies objetivo. El estudio aborda tres preguntas de investigación: ¿Quién pesca? (Caracterización de la flota): Identificación de las flotas principales, los estados del pabellón y los patrones espacio-temporales. ¿Qué se captura? (Composición de la captura): Evaluación de si la producción biológica justifica las divisiones espaciales actuales. ¿Cómo? (Artes de pesca): Examen de las artes y estrategias empleadas por las flotas principales. Metodología: -Delimitación espacial: Los datos se filtran y se asignan a la NAE, la TAE y la SAE mediante técnicas de unión espacial basadas en las coordenadas geográficas de la Tarea 2. -Integración de datos y herramientas: Mediante RStudio, el estudio integra las bases de datos de la Tarea 1 de ICCAT (captura nominal), la Tarea 2 (captura/esfuerzo georreferenciado) y la CCSBT (para el atún rojo del sur) para garantizar una visión completa de las especies altamente migratorias.

• Clasificación de la flota: Indicadores específicos categorizan las flotas en flotas regionales (limitadas a una ecorregión) y flotas interregionales (que abarcan múltiples límites).
• Análisis histórico: La caracterización se realiza utilizando fuentes personalizadas: Tarea 1 para flotas regionales (suponiendo que la actividad total corresponde a la ecorregión) y Tarea 2 (CATDIS) para flotas interregionales, para atribuir con precisión las capturas a unidades espaciales. El análisis desagrega las capturas por especie, arte y origen, lo que garantiza una atribución clara de la fuente de datos para proporcionar una validación sólida del marco espacial propuesto.

[EN] The International Commission for the Conservation of Atlantic Tunas (ICCAT) is progressing in the development of integrated, ecosystem-based tools and advisory products to support the implementation of the Ecosystem Approach to Fisheries Management (EAFM). Within the ICCAT Convention Area, a spatial framework consisting of five candidate ecoregions has been proposed with the primary objective of developing such integrated tools and advisory products that integrate ecosystem and fisheries information to complement existing single-species fisheries assessments and management advice. However, prior to their application in research, management, and resource planning, it is essential to assess the validity of these candidate ICCAT ecoregions. This thesis contributes to this evaluation by examining whether the proposed ICCAT ecoregions constitute coherent, meaningful, and operationally relevant spatial units for the development of integrated, ecosystem-based tools such as ecosystem models and advisory products such as Ecosystem Fisheries Overviews (EFOs). To test whether EFOs can be meaningfully developed at the ecoregional scale, the study focuses on three ecoregions - North Atlantic (NAE), Tropical Atlantic (TAE), and South Atlantic (SAE) - and applies a methodological framework structured around three core questions central to the EAFM: who fishes within each ecoregion, what is fished, and how fishing activities are conducted. The extent to which each ecoregion exhibits an internally coherent and distinct fishing system is used as the primary criterion for evaluating its suitability as a spatial unit for developing EAFM tools such as ecosystem models or advisory products such as EFOs.
To operationalise this framework, publicly available ICCAT fisheries statistics were used, including Task 1 nominal catch data and Task 2 CATDIS raised catches, covering the period from 1950 to 2023. A set of indicators were applied to identify core fleets, defined as those accounting for the majority of catches and fishing activity within each ecoregion, and to characterise their long term catch composition. Fleets were further classified as Regional Fleets or Across-Regions Fleets based on their degree of spatial fidelity and operational restriction to individual ecoregions. The results reveal pronounced spatial structuring of fishing activities across the three ecoregions. Distinct combinations of core fleets, dominant fishing gears, and target species are consistently associated with the proposed ecoregional boundaries. Regional fleets dominate fishing activity in the North Atlantic and Tropical Atlantic ecoregions, exhibiting strong spatial fidelity, whereas Across-Regions fleets—predominantly long-distance industrial longliners—play a more prominent role in the South Atlantic, reflecting its function as a shared fishing domain for highly mobile fleets targeting different species in each ecoregion. Importantly, this spatial connectivity is structured and fleet-specific rather than random and therefore reinforces rather than undermines the analytical coherence of the ecoregional framework. Despite limitations related to incomplete spatial resolution and taxonomic coverage of the ICCAT fisheries statistics, particularly for small tunas and sharks, the methodological approach applied in this study enables a robust characterization of fishing systems at the ecoregional scale. By integrating historical catch information with fleet-based spatial analyses, the study provides an integrated snapshot of who fishes, what is fished, and how fishing is conducted within each ecoregion, even in the absence of fully georeferenced data. Overall, the findings demonstrate that ICCAT candidate ecoregions capture coherent fishing systems and represent a scientifically defensible and operationally relevant intermediate scale which bridges individual stock assessments and basin-wide analyses. As such, ecoregions are well suited to support the development of ecosystem-based tools such as ecosystem models and advisory products, such as Ecosystem Fishery Overviews (EFOs), which complement existing stock-based advice and contribute to more integrated and ecosystem-aware fisheries management within ICCAT.