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The stock concept plays a pivotal role in fisheries assessment and management. Stocks are defined according to biological, geographical, economic or socio-political factors. The General Fisheries Commission for the Mediterranean (GFCM) has established thirty management geographical sub-areas (GSAs) based on political and statistical considerations rather than biological or economic factors. Here, we present our view on the main biological and ecological aspects that should be considered for delineating different management units in the Mediterranean. We focus on the Balearic Islands (GSA05) as a case study highlighting its specificities compared to the adjacent coast of the Iberian Peninsula (GSA06), but the approach could be generalized to the problem of identifying stock boundaries in other areas. The work is based on published information from different marine disciplines such as geomorphology, ecology and fisheries, combined with the analysis of new data coming from official fishery statistics and scientific surveys. This approach avoids the important drawbacks (inconclusive results, high costs) of other time-consuming techniques used in stock identification, such as genetics. According to the information presented, we conclude that GSA05 should be maintained as an individualized area for assessment and management purposes in the western Mediterranean. ; El concepto de stock juega un papel clave en la evaluación y gestión de pesquerías. Los stocks se definen en base a factores biológicos, geográficos, económicos o socio-políticos. La Comisión General de Pesca para el Mediterráneo (CGPM) ha establecido treinta subáreas geográficas de gestión (GSAs) basándose más en consideraciones políticas y estadísticas que en factores biológicos o económicos. En este trabajo presentamos nuestro punto de vista sobre los principales aspectos que deberían considerarse para definir diferentes unidades de gestión en el Mediterráneo. Aunque nos hemos centrado en las Islas Baleares (GSA05) como caso de estudio, resaltando sus especificidades en relación a las costas adyacentes de la Península Ibérica (GSA06), el enfoque podría generalizarse al problema de la identificación de stocks en otras áreas. El trabajo combina el uso de información publicada de diferentes disciplinas marinas como la geomorfología, ecología y pesquerías, con el análisis de datos inéditos procedentes de estadísticas pesqueras oficiales y campañas científicas. El enfoque que presentamos evita importantes inconvenientes (resultados no concluyentes, elevados costes) de otras técnicas más complejas y laboriosas utilizadas en la identificación de stocks como la genética. En base a la información presentada, concluimos que la GSA05 debería mantenerse como un área individualizada para la evaluación y gestión en el Mediterráneo Occidental.

The Mediterranean Sea is one of the world's hotspots for marine bio-invasions. Most invasions are first documented based on an initial record of occasional adult captures. However, reports of larval stages could indicate that there is an adult population that is reproducing and therefore well established in the area. The spread of the oriental shrimp, Palaemon macrodactylus, from its native estuarine waters of southeast Asia to new regions worldwide is well documented. We report the first record of this species in the Mediterranean based on the presence of its larval stages in plankton samples. Decapod larvae were collected in five offshore plankton surveys performed off the Balearic Islands (western Mediterranean), and zoeae III and VI of the oriental shrimp were found among them. Taking into account the duration of the successive developmental stages, and the hydrodynamic characteristics of the study area, these larvae were most probably spawned by adult populations not yet documented. The larvae were found in marine waters despite the fact that adults usually inhabit brackish waters. Our study is a good example of how plankton studies can help to detect larval stages of invasive species before the adult populations are detected. ; The research was carried out within the framework of the projects BALEARES (CTM 2009-07944 MAR) and IDEADOS (CTM2008-04489-C03-01), funded by the Spanish Plan R+D+i. Torres acknowledges pre-doctoral FPI Fellowship support from the Regional Government of the Balearic Islands, selected as part of an operational program co- financed by the Fondo Social Europeo. ; Peer Reviewed

Publicación online disponible en: http://www.icm.csic.es/scimar/index.php ; [EN] Data obtained over a period of twenty years from 214 bottom trawls, towed on a single warp at depths between 402 and 1993 m in the western Mediterranean (Algerian and Balearic basins) and eastern North Atlantic (Rockall Trough and Porcupine Seabight), allowed a standardised comparison of density, biomass composition and size-related structure for both the whole fish fauna and for the most common species found within the deep-sea fish assemblages. All four areas are characterised by distinctly different and well-documented oceanographic conditions, biogeographical affinities and fishing exploitation. The results showed clear differences between the Atlantic and the Mediterranean deep-sea fish fauna, not only in density, species richness and composition, but also in the structure of the biomass that constitutes these assemblages. These differences are discussed in relation to environmental conditions and fishing pattern, which have determined the adaptive responses of both individual species and the whole ecosystem. ; [ES] Los datos obtenidos a partir de 214 pescas de arrastre de fondo con un sólo cable, realizadas a lo largo de un período de veinte años en el Mediterráneo occidental (cuencas argelina y balear) y Atlántico nor-oriental (Rockall Trough y Porcupine Seabight), entre 402 y 1993 m de profundidad, han permitido una comparación estandarizada de la densidad y de la composición y estructura de tamaños de la biomasa, tanto del conjunto de la ictiofauna como de las principales especies comunes en estas comunidades ícticas de gran profundidad. Estas cuatro áreas se caracterizan por diferencias, ampliamente documentadas, en sus condiciones oceanográficas, afinidades bio-geográficas y de explotación pesquera. Los resultados han mostrado claras diferencias entre la ictiofauna profunda atlántica y mediterránea, no sólo en términos de densidad, riqueza específica y composición, sino también en la estructura de la biomasa que compone estas comunidades. Estas diferencias se discuten en relación con las condiciones medio-ambientales y de explotación pesquera, las cuales han determinado las respuestas adaptativas, tanto de las especies individuales como del conjunto del ecosistema. ; Support for the analysis of the Atlantic data was obtained from the following European Commission projects: DGXIV Study Contract (92-10) "Biological parameters of deep-water fish species", MAST2-CT920033 and FAIR CT-95-655 "Developing deepwater fisheries: data for their assessment and for understanding their interaction with and impact on a fragile environment". This latter project also supported the studies in the Algerian basin, while those in the Balearic basin were funded by the Spanish research programs BATIMAR (PAC86-008/ID821) and ZONAP (PB90-0166). The analysis of the data and the preparation of the paper was funded by a Spanish Government Studies License and a bursary from the Scottish Association for Marine Science. ; Peer reviewed

Marine resources stewardships are progressively becoming more receptive to an effective incorporation of both ecosystem and environmental complexities into the analytical frameworks of fisheries assessment. Understanding and predicting marine fish production for spatially and demographically complex populations in changing environmental conditions is however still a difficult task. Indeed, fisheries assessment is mostly based on deterministic models that lack realistic parameterizations of the intricate biological and physical processes shaping recruitment, a cornerstone in population dynamics. We use here a large metapopulation of a harvested fish, the European hake (Merluccius merluccius), managed across transnational boundaries in the northwestern Mediterranean, to model fish recruitment dynamics in terms of physics‐dependent drivers related to dispersal and survival. The connectivity among nearby subpopulations is evaluated by simulating multi‐annual Lagrangian indices of larval retention, imports, and self‐recruitment. Along with a proxy of the regional hydroclimate influencing early life stages survival, we then statistically determine the relative contribution of dispersal and hydroclimate for recruitment across contiguous management units. We show that inter‐annual variability of recruitment is well reproduced by hydroclimatic influences and synthetic connectivity estimates. Self‐recruitment (i.e., the ratio of retained locally produced larvae to the total number of incoming larvae) is the most powerful metric as it integrates the roles of retained local recruits and immigrants from surrounding subpopulations and is able to capture circulation patterns affecting recruitment at the scale of management units. We also reveal that the climatic impact on recruitment is spatially structured at regional scale due to contrasting biophysical processes not related to dispersal. Self‐recruitment calculated for each management unit explains between 19% and 32.9% of the variance of recruitment variability, that is much larger than the one explained by spawning stock biomass alone, supporting an increase of consideration of connectivity processes into stocks assessment. By acknowledging the structural and ecological complexity of marine populations, this study provides the scientific basis to link spatial management and temporal assessment within large marine metapopulations. Our results suggest that fisheries management could be improved by combining information of physical oceanography (from observing systems and operational models), opening new opportunities such as the development of short‐term projections and dynamic spatial management. ; M. Hidalgo acknowledges support of two contracts funded by the Spanish national program "Ramon y Cajal" (RYC‐2015‐18646) and by the regional government of the Balearic Islands, the later co‐funded by the European Social Fund 2014‐2020. V. Rossi acknowledges support of a post‐doctoral 'Juan de la Cierva Incorporacion' fellowship (IJCI‐2014‐22343) provided by the Spanish MICINN and a networking grant through the HYDROGENCONNECT project funded by the French program MISTRALS ENVI‐Med. E. Ser‐Giacomi thanks French program "Investissements d'Avenir" (ANR‐10‐LABX‐54 MEMOLIFE and ANR‐11‐IDEX‐0001‐02 PSL Research University). This work was also supported by the Spanish National projects LAOP (CTM2015‐66407‐P) P. Monroy and E. Hernandez‐Garcia and CLIFISH (CTM2015‐66400‐C3‐1‐R) and to M. Hidalgo, B. Guijarro, and E. Massuti (AEI/FEDER, EU). P. Reglero and M. Hidalgo acknowledge funding of the H2020 PANDORA project (Nr. 773713). ; Peer reviewed

International audience ; Independence of science and best available science are fundamental pillars of the UN-FAO code of conduct 41 for responsible fisheries and are also applied to the European Union (EU) Common Fishery Policy (CFP), 42 with the overarching objective being the sustainable exploitation of the fisheries resources. CFP is 43 developed by DG MARE, the department of the European Commission responsible for EU policy on 44 maritime affairs and fisheries, which has the Scientific, Technical and Economic Committee for Fisheries 45 (STECF) as consultant body. In the Mediterranean and Black Sea, the General Fisheries Commission for the 46 Mediterranean (FAO-GFCM), with its own Scientific Advisory Committee on Fisheries (GFCM-SAC), plays a 47 critical role in fisheries governance, having the authority to adopt binding recommendations for fisheries 48 conservation and management. During the last years, advice on the status of the main stocks in the 49 Mediterranean and Black Sea has been provided both by GFCM-SAC and EU-STECF, often without a clear 50coordination and a lack of shared rules and practices. This has led in the past to: i) duplications of the 51 advice on the status of the stocks thus adding confusion in the management process and, ii) a continuous 52 managers' interference in the scientific process by DG MARE officials hindering its transparency and 53 independence. Thus, it is imperative that this stalemate is rapidly resolved and that the free role of science 54 in Mediterranean fisheries assessment and management is urgently restored to assure the sustainable 55 exploitation of Mediterranean marine resources in the future.

International audience ; Independence of science and best available science are fundamental pillars of the UN-FAO code of conduct 41 for responsible fisheries and are also applied to the European Union (EU) Common Fishery Policy (CFP), 42 with the overarching objective being the sustainable exploitation of the fisheries resources. CFP is 43 developed by DG MARE, the department of the European Commission responsible for EU policy on 44 maritime affairs and fisheries, which has the Scientific, Technical and Economic Committee for Fisheries 45 (STECF) as consultant body. In the Mediterranean and Black Sea, the General Fisheries Commission for the 46 Mediterranean (FAO-GFCM), with its own Scientific Advisory Committee on Fisheries (GFCM-SAC), plays a 47 critical role in fisheries governance, having the authority to adopt binding recommendations for fisheries 48 conservation and management. During the last years, advice on the status of the main stocks in the 49 Mediterranean and Black Sea has been provided both by GFCM-SAC and EU-STECF, often without a clear 50coordination and a lack of shared rules and practices. This has led in the past to: i) duplications of the 51 advice on the status of the stocks thus adding confusion in the management process and, ii) a continuous 52 managers' interference in the scientific process by DG MARE officials hindering its transparency and 53 independence. Thus, it is imperative that this stalemate is rapidly resolved and that the free role of science 54 in Mediterranean fisheries assessment and management is urgently restored to assure the sustainable 55 exploitation of Mediterranean marine resources in the future.

International audience ; Independence of science and best available science are fundamental pillars of the UN-FAO code of conduct 41 for responsible fisheries and are also applied to the European Union (EU) Common Fishery Policy (CFP), 42 with the overarching objective being the sustainable exploitation of the fisheries resources. CFP is 43 developed by DG MARE, the department of the European Commission responsible for EU policy on 44 maritime affairs and fisheries, which has the Scientific, Technical and Economic Committee for Fisheries 45 (STECF) as consultant body. In the Mediterranean and Black Sea, the General Fisheries Commission for the 46 Mediterranean (FAO-GFCM), with its own Scientific Advisory Committee on Fisheries (GFCM-SAC), plays a 47 critical role in fisheries governance, having the authority to adopt binding recommendations for fisheries 48 conservation and management. During the last years, advice on the status of the main stocks in the 49 Mediterranean and Black Sea has been provided both by GFCM-SAC and EU-STECF, often without a clear 50coordination and a lack of shared rules and practices. This has led in the past to: i) duplications of the 51 advice on the status of the stocks thus adding confusion in the management process and, ii) a continuous 52 managers' interference in the scientific process by DG MARE officials hindering its transparency and 53 independence. Thus, it is imperative that this stalemate is rapidly resolved and that the free role of science 54 in Mediterranean fisheries assessment and management is urgently restored to assure the sustainable 55 exploitation of Mediterranean marine resources in the future.

International audience Independence of science and best available science are fundamental pillars of the UN-FAO code of conduct 41 for responsible fisheries and are also applied to the European Union (EU) Common Fishery Policy (CFP), 42 with the overarching objective being the sustainable exploitation of the fisheries resources. CFP is 43 developed by DG MARE, the department of the European Commission responsible for EU policy on 44 maritime affairs and fisheries, which has the Scientific, Technical and Economic Committee for Fisheries 45 (STECF) as consultant body. In the Mediterranean and Black Sea, the General Fisheries Commission for the 46 Mediterranean (FAO-GFCM), with its own Scientific Advisory Committee on Fisheries (GFCM-SAC), plays a 47 critical role in fisheries governance, having the authority to adopt binding recommendations for fisheries 48 conservation and management. During the last years, advice on the status of the main stocks in the 49 Mediterranean and Black Sea has been provided both by GFCM-SAC and EU-STECF, often without a clear 50coordination and a lack of shared rules and practices. This has led in the past to: i) duplications of the 51 advice on the status of the stocks thus adding confusion in the management process and, ii) a continuous 52 managers' interference in the scientific process by DG MARE officials hindering its transparency and 53 independence. Thus, it is imperative that this stalemate is rapidly resolved and that the free role of science 54 in Mediterranean fisheries assessment and management is urgently restored to assure the sustainable 55 exploitation of Mediterranean marine resources in the future.