International audienc

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The study of small pelagic fish by hydroacoustic methods in the Mediterranean Sea began in the Adriatic in the 1950’s. Since 2009, internationally coordinated, extensive, regular surveys have been conducted in the framework of the MEDIAS - Mediterranean International Acoustic Surveys – action, under the EU Data Collection Framework, to provide inputs for the management of small pelagics, particularly European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus). The surveys cover EU Mediterranean waters and monitor the distribution and abundance of small pelagic species using a common protocol. The hydroacoustic surveys, historically conducted by each Country separately, have since been standardized and harmonized. This is a review of the evolution of the surveys from the beginning up to the present and discusses the future prospects. It reports the historical time series of anchovy, sardine and other small pelagics in different areas and describes the spatial and temporal distribution of small pelagic species in decadal maps of the major areas of their distribution in the European Mediterranean Sea. Furthermore, it discusses the use of MEDIAS data for stock assessment purposes, the collection of auxiliary information for an ecosystem-based management approach, the need for further standardization and future challenges.

Summary:Anchovy is a commercial species that supports large fisheries in the Mediterranean Sea. In addition, anchovy is an essential element of the pelagic food web, playing a considerable role in connecting the lower and upper trophic levels. Comparisons made regarding length frequency distribution, demographic structure, growth during the first year inferred from otoliths, and the condition factor of anchovy inhabiting the Spanish Mediterranean Sea (General Fisheries Commission for the Mediterranean management units, GSA06-Ebro Delta and 01-Alboran Sea), based on five-year data, clearly showed significant growth differences between areas and evidenced the existence of two independent anchovy stocks in the Spanish Mediterranean Sea. The anchovies inhabiting the Alboran Sea had higher growth than the anchovies inhabiting the Ebro Delta for the same age (one year old). The dramatic decline of the Alboran Sea anchovy could be related to the current management legislation in the Spanish Mediterranean Sea, based mainly on a common minimum catch size (9 cm), which should be revised given that sustainable anchovy exploitation is crucial for the pelagic food web equilibrium.Keywords: anchovy growth; length-frequency distribution; otolith first radius; anchovy stocks; condition factor; fisheries management; Spanish Mediterranean Sea. Otolitos de anchoa (Engraulis encrasicolus) revelan diferencias de crecimiento entre dos áreas del Mediterráneo españolResumen: La anchoa es una especie de interés comercial sometida a gran explotación pesquera en el mar Mediterráneo. Asimismo, esta especie es un elemento esencial de la cadena trófica pelágica dado que actúa como nexo entre los niveles más altos y más bajos de ésta. En este trabajo se han llevado a cabo comparaciones, basadas en un conjunto de datos de 5 años, entre las distribuciones de frecuencias de tallas; la estructura demográfica; el crecimiento durante el primer año, inferido empleando otolitos y el factor de condición de individuos de anchoa recogidos en el Mediterráneo español (unidades de gestión de la General Fisheries Commission for the Mediterranean, GSA06-Delta del Ebro y GSA01-Mar de Alborán), mostrando diferencias significativas entre áreas y evidenciando la existencia de dos stocks de anchoa independientes en el Mediterráneo español. Las anchoas procedentes del mar de Alborán presentaron un mayor crecimiento que aquellas procedentes del Delta de Ebro para la misma edad (1 año). La dramática disminución de la población de anchoa del mar de Alborán podría estar relacionada con la aplicación de una única legislación para todo el Mediterráneo español basada, principalmente, en una misma talla de primera captura (9 cm), que debería ser revisada puesto que la explotación sostenible de la anchoa es de crucial importancia para el equilibrio de la cadena trófica pelágica.Palabras clave: crecimiento de anchoa; distribución de frecuencias de tallas; primer radio del otolito; stocks de anchoa; factor de condición; gestión de pesquerías; mar Mediterráneo español.

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Data on Sardinella aurita (round sardinella) and Sprattus sprattus (European sprat) in the Mediterranean Sea are limited due to their scarce commercial interest, at least in European countries. Yet, these two small pelagic fish, sitting at opposite ends of the thermal range, could be interesting sentinel species to monitor the effects of climate change in the basin. Using the Mediterranean International Acoustic Surveys (MEDIAS) – the most extensive source of information on these species – we analyzed their biomass in several geographical subareas of the central and western Mediterranean Sea in relation to satellite-derived environmental parameters. Our findings highlight that the S. aurita biomass responded to temperature, salinity, chlorophyll concentration and sea level anomaly, depending on the GSA examined, whereas the S. sprattus biomass correlated significantly with salinity in GSA 6, with salinity and chlorophyll concentration in GSA 7, and with sea level anomaly in GSA 17. These data widen our knowledge of the factors that contribute to the ecology of these species. Further studies of their spatial distribution and of their interactions with other small pelagic species, predators and prey are needed to depict a more comprehensive scenario.

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