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Maturity is one of the most important biological parameters used in stock assessment programmes. Indeed, the macroscopic stage of gonadal development is an essential feature in estimating the maturity ogive and spawning stock biomass. It is also useful for determining the spawning season of a species and for monitoring long-term changes in the spawning cycle as well as for many other research needs related to the biology of fish. Despite the efforts made during the last few decades to standardize maturity stage data among all the researchers, marine biologists continue without a manageable and unique maturity scale to describe the reproductive development of fish gonads. For these reasons, the objectives of this article are 1) to investigate the biological parameters of five selected key species (Mullus barbatus, Galeus melastomus, Etmopterus spinax, Aristeus antennatus, Loligo vulgaris) with different reproductive strategies following the macroscopic maturity scales based on the same univocal criteria adopted in the MEDITS programme and described in this work; and 2) to compare them among some Mediterranean geographical sub-areas (GSAs) involved in the programme. Neither spawning periods nor size at first maturity (SFM50) for the studied species showed particular differences in the investigated GSAs., La madurez es uno de los parámetros biológicos más relevantes utilizados en los programas de evaluación de stock. De hecho, la etapa macroscópica del desarrollo gonadal es una característica esencial en la estimación de la madurez de la biomasa de la ojiva y del desove. También es útil para determinar la temporada de desove de una especie y para monitorear los cambios a largo plazo en el ciclo de desove, así como para muchas otras necesidades de investigación relacionadas con la biología de los peces. A pesar de los esfuerzos realizados durante las últimas décadas para estandarizar los datos de las etapas de madurez entre todos los investigadores, los biólogos marinos continúan sin una escala de madurez única y manejable para describir el desarrollo reproductivo de las gónadas de peces. Por estas razones, el objetivo de este artículo es 1) investigar los parámetros biológicos de 5 especies clave seleccionadas (Mullus barbatus, Galeus melastomus, Etmopterus spinax, Aristeus antennatus, Loligo vulgaris) con diferentes estrategias reproductivas siguiendo las escalas de madurez macroscópica basadas en criterios iguales y unívocos adoptados en el programa MEDITS y descritos en este trabajo y 2) para compararlos entre algunas sub-áreas geográficas del Mediterráneo (GSAs) involucradas en el programa. Tanto los períodos de desove como el tamaño en la primera madurez (SFM50) para las especies estudiadas no han mostrado diferencias particulares en las GSA investigadas.

The present study describes for the first time the spatial distribution of five macrourid species throughout the Mediterranean Sea and analyses depth, geographical and time-related trends regarding their abundance, biomass and mean fish weight. The data were collected as part of the MEDITS annual bottom trawl survey carried out by several European Mediterranean countries from 1994 to 2015, using the same standardized gear and sampling protocol. The most represented species in terms of abundance and biomass was Coelorinchus caelorhincus. The bathymetric trend was different for each species. The shallowest occurring species was C. caelorhincus, followed by Hymenocephalus italicus and Nezumia sclerorhynchus, while Nezumia aequalis and Trachyrincus scabrus were the deepest. Overall, the mean weight of all the species increased with depth. C. caelorhincus and H. italicus occurred in the entire study area: the first species showed relatively high catches in most areas, while the second was more abundant in the central and easternmost areas. N. aequalis and T. scabrus were mainly reported in the western basin, and N. sclerorhynchus in the central-eastern areas of the Mediterranean. An increasing inter-annual trend in abundance was only detected for C. caelorhincus and N. sclerorhynchus, while variable fluctuations were observed in the other species., El presente estudio describe por primera vez la distribución espacial de cinco especies de macrúridos a lo largo del Mediterráneo en su vertiente europea, analizando las tendencias batimétricas, geográficas y temporales de la abundancia, la biomasa y el peso medio de las especies. Los datos utilizados provienen de las campañas de arrastre de fondo anuales, MEDITS, desde 1994 a 2015, llevadas a cabo por los países mediterráneos europeos utilizando un arte de arrastre y un protocolo de muestreo estandarizado. La especie más representativa en términos de abundancia y biomasa fue Coelorinchus caelorhincus. Las tendencias batimétricas fueron variables según la especie. La más costera fue C. caelorhincus seguida de Hymenocephalus italicus y Nezumia sclerorhynchus mientras que Nezumia aequalis y Trachyrincus scabrus son las que se localizaron a mayor profundidad. En general, el peso medio de las especies se incrementó con la profundidad. Geográficamente, C. caelorhincus e H. italicus se encontraron distribuidas a lo largo de toda el área de estudio: la primera mostró capturas relativamente elevadas en la mayoría de las áreas mientras que la segunda fue más abundante en las zonas central y oriental. N. aequalis y T. scabrus se capturaron fundamentalmente en la cuenca occidental mientras que N. sclerorhychus en las áreas centro-este del Mediterráneo. Únicamente se detectó incremento interanual en C. caelorhincus y N. sclerorhynchus, mientras que en el resto de las especies no se registó incremento ni descenso sino fluctuaciones interanuales.

Thanks to the availability of the MEDITS survey data, a standardized picture of the occurrence and abundance of demersal Chondrichthyes in the northern Mediterranean has been obtained. During the spring-summer period between 2012 and 2015, 41 Chondrichthyes, including 18 sharks (5 orders and 11 families), 22 batoids (3 orders and 4 families) and 1 chimaera, were detected from several geographical sub-areas (GSAs) established by the General Fisheries Commission for the Mediterranean. Batoids had a preferential distribution on the continental shelf (10-200 m depth), while shark species were more frequent on the slope (200-800 m depth). Only three species, the Carcharhiniformes Galeus melastomus and Scyliorhinus canicula and the Torpediniformes Torpedo marmorata were caught in all GSAs studied. On the continental shelf, the Rajidae family was the most abundant, being represented in primis by Raja clavata and then by R. miraletus, R. polystigma and R. asterias. The slope was characterized by the prevalence of G. melastomus in all GSAs, followed by S. canicula, E. spinax and Squalus blainville. Areas under higher fishing pressure, such as the Adriatic Sea and the Spanish coast (with the exception of the Balearic Islands), show a low abundance of chondrichthyans, but other areas with a high level of fishing pressure, such as southwestern Sicily, show a high abundance, suggesting that other environmental drivers work together with fishing pressure to shape their distribution. Results of generalized additive models highlighted that depth is one of the most important environmental drivers influencing the distribution of both batoid and shark species, although temperature also showed a significant influence on their distribution. The approach explored in this work shows the possibility of producing maps modelling the distribution of demersal chondrichthyans in the Mediterranean that are useful for the management and conservation of these species at a regional scale. However, because of the vulnerability of these species to fishing exploitation, fishing pressure should be further incorporated in these models in addition to these environmental drivers., Gracias a la disponibilidad de los datos de campañas de pesca experimental MEDITS, se ha realizado una imagen estandarizada de la presencia y abundancia de Chondrichthyes demersales en el norte del Mediterráneo. Durante el período primavera-verano entre 2012 y 2015, se detectaron 41 Chondrichthyes, incluidos 18 tiburones (5 órdenes y 11 familias), 22 batoides (3 órdenes y 4 familias) y 1 quimera, de varias Subáreas Geográficas (GSA) establecidas por la Comisión General de Pesca para el Mediterráneo en la zona. Los batoides tuvieron una distribución preferencial en la plataforma continental (10-200 m de profundidad), mientras que las especies de tiburones fueron más frecuentes en la ladera (200-800 m de profundidad). Solo tres especies, Carcharhiniformes Galeus melastomus, Scyliorhinus canicula y Torpediniformes Torpedo marmorata fueron capturadas en todos los GSA estudiados. En la plataforma continental, la familia Rajidae fue la más abundante, representada en primer lugar por Raja clavata y luego por R. miraletus, R. polystigma y R. asterias. La pendiente se caracterizó por la prevalencia de G. melastomus en todos los GSA, seguido de S. canicula, E. spinax y Squalus blainville. Las áreas bajo mayor presión de pesca, como el Mar Adriático y la costa española (con la excepción de las Islas Baleares), registran una baja abundancia de condricthianos, pero otras áreas con un alto nivel de presión de pesca, como el suroeste de Sicilia, presentan una gran abundancia de estas especies. Sugiere que otros impulsores ambientales trabajen juntos con la presión pesquera para dar forma a su distribución. Los resultados de los modelos aditivos generalizados resaltaron que la profundidad es uno de los factores ambientales más importantes que influyen en la distribución de las especies de batoides y tiburones, aunque la temperatura también mostró una influencia significativa en su distribución. El enfoque explorado en este trabajo muestra la posibilidad de producir mapas que modelen la distribución de los condrictios demersales en el Mediterráneo, útiles para el manejo y la conservación de estas especies a escala regional. Sin embargo, teniendo en cuenta la vulnerabilidad de estas especies a la explotación pesquera, la presión pesquera debería incorporarse a estos modelos, además de estos factores ambientales.

Elasmobranchs constitute a target or bycatch of a wide variety of fishing techniques. Such anthropogenic pressure has brought to a drastic reduction of local populations across the Mediterranean Sea. Moreover, limited - data collection and species misidentif ication, among others, have led to a scarcity of historical data on species occurrence and abundance trends in several taxa. Such information is particularly valuable to study migration dynamics and behavior variations, as well as to reconstruct historical trends. To fill this data gap, the use of local ecological knowledge from professional fishermen can be considered as a valuable source of semi - quantitative information on several aspects of species ecology, abundance and behavioral aspects. Through a questionnaire survey, fishermen operating with diverse fishing gears such as bottom and pelagic trawlers, set nets and longlines were interviewed by trained researchers with the aid of photo - identification materials. A total of 211 interviews were collected across nine Mediterranean FAO - GSA sub - areas (9, 10, 11, 16, 17, 18, 19, 22, 28). Results covered a wide range of elasmobranch species with regard to coastal, pelagic and deep - sea environment. Interviewers indicated species that were abundant in the past, declined recently and showed size variation compared to past catches. Moreover, fishermen reported aggregation sightings/events, seasonal movements and species - specific fishing area. The present study constitutes a baseline regarding abundance and distribution of elasmobranch species in historical times and may represent a valuable tool for data deficient taxa. It also gives new insights on elasmobranchs behavioral and ecological aspects and highlights priority species and suitable geographic areas for conservation and behavioral studies.

The rapid expansion of fisheries and globalized trade are emerging as the principal drivers of coastal and ocean threat. Considering the important role of Chondrichthyes as predators at the top of food chain in marine ecosystems, knowledge on their biology remains scarce in the Mediterranean. In this regard, our objective is to give information on their spatial distribution, abundance and population structure. Data were collected for 25 demersal species, including batoid species, sharks and holocephalans from 1994 to 2013 during scientific bottom trawl surveys (MEDITS project) carried out around the Sardinian seas. The total frequency of occurrence (f%), the Biomass Index (BI, kg/km2), and the Density Index (DI, N/km2) were estimated for the continental shelf (10-200 m), slope (200-800 m), and overall (10-800 m) depth strata. Size trends were also calculated for the most abundant species considering all depth strata. The correlation among MEDITS figures (f%, BI, DI, size structure) and years were assessed by species computing the Pearson linear coefficient. From f% and abundance indexes investigation, only the small spotted catshark Scyliorhinus canicula and the thornback ray Raja clavata were ubiquitous in all strata investigated, instead, all the other species showed a preferential distribution for the shelf or the slope. In general, the temporal trends of BI and DI were stable or positive for both macro-strata, except for the longnose spurdog Squalus blainville which seemed to show a statistically significant decreasing trend. All analyzed species displayed temporal stable trends in size structure analysis, apart from Raja brachyura and Dipturus oxyrinchus that showed a statistically significant increase. Despite the time series analysis revealed stable or positive trends, it appears clear the need of urgent management measures to protect the demersal chondrichthyan species extending the monitoring over time and implementing the data collected by scientific and commercial trawl surveys.

Skates are often considered vulnerable to overfishing because of their peculiar life cycle characteristics rendering them susceptible to overexploitation. In this regard, life-history traits of a by-catch species, the long-nosed skate Dipturus oxyrinchus (Linnaeus, 1758) from Sardinian waters, were investigated. The age, growth and reproduction were studied using 706 specimens sampled during experimental and commercial hauls (depths 76-671 metres). Females (10.4-117.5 cm in total length, TL) attained larger sizes than males (14.5-99.5 cm TL). To evaluate the growth, a subsample of 130 individuals (76 females and 54 males) was employed. The age was estimated through the annuli counts on sectioned vertebral centra. A high ageing reproducibility and precision was obtained (Index of Average Percent Error=6.56; %CV=8.9). Four models were applied on length at age data: the von Bertalanffy (VBGF), the Exponential, the Gompertz and the Logistic functions. According to the Akaike’s Information Criterion, the Gompertz model (L∞=127.5±4.9 cm; k=0.14±0.009; inflection point=3.97 y-1±0.9) provided the best fitting curve, showing a higher growth rate and a lower L∞ than what obtained with the VBGF (L∞=144.4±11.5 cm; k=0.08±0.001; t0=-1.09±0.23). The oldest female and male were 17 (115.5 cm TL) and 15 years (96 cm TL), respectively. Lengths at maturity were 103.5 cm (14 years) for females and 91 cm (12.1 years) for males corresponding to 88 and 91.5% of the maximum observed length, respectively. The monthly evolution of maturity stages highlighted an extended reproductive cycle with spawning females and active males almost over the year, as confirmed by the Gonado-somatic Index. Ovarian fecundity reached a maximum of 26 yolked follicles. Given the relative abundance in Sardinian seas, we hope that these results will prove useful for the implementation of basic management measures in order to ensure the sustainability of catches of this species, particularly sensitive to fishing pressure, in the Mediterranean Sea.