Search

The Graham Bank (NW Sicily Channel, Central Mediterranean) is characterised by a complex seafloor morphology, where morphostructural highs, submarine plain, escarpments, and negative and positive relieves indicate a complex structural setting and the occurrence of seepage fluids. New high-resolution acoustic data (multibeam, Chirp profiles) and multi-channel profiles, allowed us to differentiate two main morphological sectors, and to identify several pockmarks and mounds linked to fluid escape phenomena. The eastern sector, corresponding to the volcanic edifices of the Graham Bank, is characterised by volcanic context with rough morphology, several mounds, focused seepage plumes and magmatic acoustic substrate, all related to the activity forming both the Graham Bank and the new volcanic cones here identified. The western sector displays a generally flat morphology dominated by Late Pleistocene-Holocene outer shelf deposits, where mounds and pockmarks with sub-circular and ellipsoidal shapes, V- to U-shaped in cross-section, are the prevailing features indicating the migration of fluids to the seafloor. These two areas are separated by a vertical deep fault forming a deeply incised channel with NW-SE direction. The latter is bordered by steep walls forming fault escarpments, which shed the eroded materials to the adjacent lower slope and deep-water zones. The overall morphostructural setting suggests a tectonic control in the morphological conformation of the seabed and in the distribution of both pockmarks and mounds. The aligned mounds have both NW-SE and NNW-SSE orientation, sometimes extending several hundred metres and forming hummocky surfaces. The aligned pockmarks are strictly comparable to the orientation of the faults related to the most recent tectonic activity. The good correlation between fluid escape structures and the main fault systems involving the kilometric sedimentary cover suggests that the degassing of fluids is rooted in depth revealing that extensional tectonics acts with very deep subvertical recent faults developing along and reactivating the Cenozoic (both Plio-Quaternary and Messinian) and Mesozoic tectonic systems., peer-reviewed

59 páginas, 8 anexos, The recorded maturity stage at the time of observation is an important biological parameter to be used in the calculation of maturity ogives (and therefore of Spawning Stock Biomass), for the definition of the spawning season of a species, for the moni-toring of long-term changes in the spawning cycle, and for many other research needs regarding the biology of species. Thus, maturity data are fundamental part of the stock assessment process and hence a vast effort is put on validating the macro-scopic inspection of gonads. In the last decade a series of workshops addressed the maturity staging of different species with the objective of developing common ma-turity scales, decreasing discrepancies between laboratories and validating maturity staging through microscopic evaluation. A total of 11 of those workshops on species-specific maturity staging were revised here. These workshops have analysed 20 teleosts, elasmobranchs as a whole subclass, three orders of cephalopods and four crustacean species. The WKMAT 2007, and later WKMSCWHS 2007, proposed a six point maturity scale for both males and fe-males that have been used as a reference in the different maturity workshops to de-velop and adopt a common scale between laboratories for each species. A notable effort has been made by all workshop participants to standardize the existing maturi-ty scales and accommodate the standard scale proposed. All workshops acknowl-edged the biological differences between the reference scale stages. All workshops proposed new scales that although were generally consistent with WKMAT scale, showed several differences. As a result, the four stage scale proposed in WKMAT has generally not adopted, partially because such scale does not allow reflecting specific particularities, useful for a number of species., To overcome this, we propose the use a single scale of 4+2 stages or divisions which is believed to be universal, that is, it can be used for the majority of species, although viviparous and hermaphrodites may need some adaptation. This 6 stage codes and names should be used for all species and both sexes without exception; species-specific particularities should be reflected creating subdivisions and never modifying the 6 main stages. Using this proposed coding system, particularities of species and stocks can be addressed by each workshop (subdivisions), without losing consistency and traceability (divisions). In this way the code number of the divisions or main stages has the same biological meaning across species and laboratories. Some poten-tial subdivisions are proposed as well, for its facultative use in some batch spawners an in viviparous species. The merging of different stages should be avoided and in-stead a combined code should be used. In this manner the consistency of stages defi-nition and codes is maintained across species. The definition of each stage needs to be linked to biological phases and incorporate into its description species-specific aspects relevant for an easy identification of each stage. The use of the terminology for maturity stages considers a general scheme of the reproduction that can be applied to all male and female elasmobranchs and tele-ost fishes, including hermaphrodites and livebearers. A full glossary of terminology was compiled. Training (of the observers) is the major issue for maturity staging, and it should be strengthen within the umbrella of ICES., When staging maturity macroscopically timing of the sampling is critical to obtain reliable results. To define this period it is important to know the timing of the repro-ductive cycle, as this is species specific. If maturity staging outside the optimal peri-ods is required, this should be based on histological information. However, we suggest that whole mounts preparations are useful to validate macroscopic staging of ovaries being particularly useful to separate between early developing and develop-ing specimens, immature and regressing/regenerating specimens, or even specimens that have just completed a spawning season from those have not yet entered sexual maturity. Nevertheless, it is recommended that the whole-mounts method is careful-ly calibrated before taken into practical use. The maturity Workshops should discuss the new and general scale in their respective WKs by e-mail to assess the correspondence with the agreed scale, and evaluate the uncertainties and the problems this new general scale may cause. At the same time, ICES should ensure an appropriate attendance and a required level of basic knowledge, both on maturity studies and on the species targeted by the Workshop. Beyond of experts in the matter, the participants should be trained people, this can be achieved by training courses in ICES. We have revised and updated the Guidelines for Workshops on Maturity Staging, and provided general recommendations for future workshops., We reviewed a total of 148 stocks of 53 species from 8 ecoregions from which ICES provides some type of advice. In 88 stocks (59%) maturity data are not used or are used improperly. This includes the use of time invariant maturity ogives when annu-al ogives can be available. In 39 stocks (26%) the assessment uses a proper maturity ogive, but over a limited time period. Finally in only 21 stocks 14% of the total ad-vised stocks the maturity ogive has been estimated on regular basis and in these cases they are used properly in the assessment. Therefore, lack of data and/or poor quality is the main causes of maturity not being used. However, there is a general lack of information in the reports on how the maturity data was collected, ogive estimated, quality control and other relevant information. There is a need to determine what maturity data are required for assessment purposes, including how phenomena such as skipping spawning should be included in assessments. In spite of the effort on collecting maturity data, almost in 100% of the cases sex-specific ogives are combined without analysing the impact of this. Expert groups should provide comprehensive reports on how the maturity data is used, and more specifically, at least: the method used to estimate maturity, in which sex and how a sex-specific maturity ogive is used in the assessment, source of data (survey, commercial sampling), the time of the year when the sampling was conduct-ed, and years of proper estimation. The impact on the assessment of combining sex-specific maturity ogives should be analysed.

Because the meagre (Argyrosomus regius) is not currently found around the Balearic Islands (western Mediterranean), the Balearic government is carrying out a restocking programme to recover its population. The success of this programme is critically dependent on improved knowledge of the meagre’s life cycle, and particularly its reproductive biology. Data on key reproductive parameters based on both reared and wild specimens are reported here. Histological examinations and gonadosomatic indices from 342 reared specimens demonstrated that 1) the potential reproductive season ranged from April to June and peaked in May, and 2) length at maturity (L50) was 49.3 cm for males and 57.2 cm for females, age at maturity (A50) was 2.7 years for males and 3.5 years for females, and weight at maturity (W50) was 1396 g for males and 1892 g for females. Histological examinations of 37 wild fish from Cádiz (SW Spain) demonstrated that the meagre has determinate fecundity. The annual potential fecundity of reared females ranged from 0.9 to 4.2 million oocytes, which is exponentially dependent upon female size., La corvina (Argyrosomus regius) actualmente no se encuentra en las Islas Baleares (Mediterráneo Occidental) y, por tanto, se están realizando esfuerzos para recuperar su población a través de un programa de repoblación que se está llevando a cabo por el Gobierno Balear. El éxito del programa de recuperación depende fundamentalmente de la mejora de los conocimientos del ciclo de vida de la corvina, y en particular de su biología reproductiva. Este estudio presenta datos sobre los principales parámetros reproductivos de la especie, basándose tanto en ejemplares criados en cautividad como salvajes. Los exámenes histológicos e índices gonadosomáticos de 342 especímenes criados en cautividad demostraron lo siguiente: 1) la potencial época de puesta se extendió de abril a junio y alcanzó su punto máximo en mayo, y 2) la talla de madurez (L50) fue de 49.3 cm para los machos y 57.2 cm para las hembras, la edad de madurez (A50) fue de 2.7 años para los machos y 3.5 años para las hembras, y el peso de madurez (W 50) fue de 1396 g para los machos y 1892 g para las hembras. Los exámenes histológicos de 37 peces salvajes procedentes de Cádiz (SO de España) demostraron que la corvina tiene fecundidad determinada. La fecundidad potencial anual de las hembras criadas en cautividad, la cual está exponencialmente relacionada con el tamaño de la hembra, osciló entre 0.9 y 4.2 millones de ovocitos.

5 páginas, 1 tabla, 1 figura

Acoustic surveys represent the standard methodology to assess the spatial distribution and abundance of pelagic organisms characterized by aggregative behaviour. The species identification of acoustically observed aggregations is usually performed by taking into account the biological sampling and according to expert-based knowledge. The precision of survey estimates, such as total abundance and spatial distribution, strongly depends on the efficiency of acoustic and biological sampling as well as on the species identification. In this context, the automatic identification of specific groups based on energetic and morphological features could improve the species identification process, allowing to improve the precision of survey estimates or to overcome problems related to biases in biological sampling. In the present study, we test the use of well-known unsupervised clustering methods focusing on two important krill species namely Euphausia superba and Euphausia crystallorophias. In order to obtain a reference classification, the observed echoes were first classified according to specific criteria based on two parameters accounting for the acoustic response at 38 kHz and 120kHz. Different clustering methods combined with three distance metrics were then tested working on a wider set of parameters, accounting for the depth of insonified aggregation as well as for energetic and morphological features. The clustering performances were then evaluated by comparing the reference classification to the one obtained by clustering. Obtained results showed that the k-means performs better than the considered hierarchical methods. Our findings also evidenced that working on a specific set of variables rather than on all available ones highly impact k-means performances.

The Svalbardsis one of the most intensively studied marine regions in the Artic; here the composition and distribution of marine assemblages are changing under the effect of global change, and marine communities are monitored in order to understand the long-term effects on marine biodiversity. In the present work, acoustic data collected in the Kongsfjorden using multi-beam technology was analyzed to develop a methodology for identifying and classifying 3D acoustic patterns related to fish aggregations. In particular, morphological, energetic and depth features were taken into account to develop a multi-variate classification procedure allowing to discriminate fish species. The results obtained from clustering suggest that from a mathematical point of view three distinct groups could be identified. The proposed approach, that allows to discriminate the acoustic patterns identified in the water column, seems promising for improving the monitoring programs of the marine resources, also in view of the ongoing climate changes.