Differences between demersal fisheries discards: high and low productivity zones of the Northwestern Mediterranean Sea

Publicado

Evaluación de la gamba rosada, Aristeus antennatus (Risso 1816), en el mar Balear

Directoras de la tesis doctoral: Dra. Demestre M. (Montserrat) y Dra. Moreno I. (Isabel)Resumen: La especie de crustáceo decápodo Aristeus antennatus, explotado en el talud superior de las Baleares se encuentra explotado desde hace más de 50 años por las flotas de arrastre que operan alrededor de las Islas. La biología de la especie aparece adaptada al medio en que vive, con una composición de las poblaciones similar en todas las zonas, dominada por las hembras y con un patrón de movilidad entre caladeros claramente relacionado con la reproducción y con los procesos de maduración y puesta en zonas concretas. La puesta parece producirse a profundidades superiores a las que se desarrolla la pesquería. El reclutamiento aparece preferentemente en las mismas zonas de puesta en verano y otoño. La condición fisiológica de las hembras disminuye durante la maduración ovárica con transferencia de soma al crecimiento de las gónadas. Las hembras presentan un patrón de movilidad relacionado con la reproducción. Los machos presentan un patrón de movilidad más reducido, el acoplamiento se produce en primavera y en todas las zonas en donde la especie vive. Se asocia el aumento y la disminución de la proporción de machos a los procesos de acoplamiento y a una mortalidad diferenciada relacionada tanto con su menor longevidad como con los procesos de acoplamiento. El estudio de crecimiento confirma un modelo de crecimiento aproximado de 1 mm mensual en los primeros años. Las hembras tienen una longevidad de hasta 7 años de vida y los machos 5. Las edades mejor representadas en las poblaciones explotadas corresponden a las edades 2, 3 y 4 para ambos sexos. El reclutamiento corresponde a la edad 1, y aparece en la pesquería con un año de desfase y pertenece a la puesta del año anterior. El éxito reproductivo reflejado en el reclutamiento aparece dependiente de la condición y de la estructura de tallas de las poblaciones de machos, y en menor medida también de las hembras. La disminución de la talla media, o de la condición fisiológica de los machos parece tener una mayor influencia en el potencial reproductor de la población. Del estudio histológico del ovario se deriva que la especie tiene una puesta sincrónica. La pesquería que tiene como objetivo la gamba rosada, se caracteriza por estar formada por embarcaciones de potencias similares. Las capturas presentan una composición de especies características del hábitat del talud superior, y están formadas, en una proporción de en torno al 40% por la gamba rosada. La especie no tiene descarte y el descarte global de la pesquería representa el 20% de la captura y está formado en un 97% por especies no comerciales. La estandarización del esfuerzo ha permitido establecer que los componentes anuales y estacionales son los que presentan una mayor contribución a la variabilidad de las capturas. La especie es altamente rentable, representando tan sólo el 10% de las capturas del arrastre y aportando el 40% de los beneficios de la pesquería de arrastre. El efecto de la variabilidad ambiental se refleja en la abundancia de la población y aparece relacionada con los índices climáticos que afectan al hemisferio norte y con las condiciones hidrográficas estacionales. La aplicación de modelos estructurales permite establecer el estado de explotación de la especie, diagnosticando y pronosticando el futuro de esta especie en su explotación. Los métodos aplicados han estimado el ajuste de los modelos a los datos y han estimado la incertidumbre de los modelos. Los diferentes tipos de modelos aplicados complementan sus resultados y han servido para validar la utilización de dichos modelos para esta especie. En relación a los modelos estructurales, los resultados han mostrado que su aplicabilidad es limitada y debe ser realizada para el conjunto de la población, teniendo en cuenta el crecimiento diferencial de los sexos. La especie se presenta con una moderada variabilidad en las estimaciones de reclutamiento, y con una situación del stock actual frente a la explotación, mejor a la estimada históricamente. Los modelos, tanto estructurales como de producción aplicados, requieren series de tiempo suficientemente largas (al menos 10 años) que permitan establecer tendencias para realizar un pronósticos adecuado. Los resultados obtenidos por dichos modelos, pronostican a largo plazo capturas similares a las obtenidas en la actualidad y recomiendan, dentro del "precautory approach", la reducción del esfuerzo en un 30% para asegurar que la especie se mantenga dentro de los límites de seguridad que garanticen su explotación en el tiempoAbstract: The species of the decapod crustacean Aristeus antennatus harvested in the upper slope of the Balearic Islands has been being exploded for more than 50 years by the trawl fleets that operate around the Islands. The biology of the species appears adapted to the environment in which it lives, with a similar population composition in all the areas, dominated by the females and with a pattern of mobility between fishing grounds clearly related to the reproduction and the processes of maturity and spawning in specific areas. The spawning seems to take place in deeper waters than the used by the adult population. The recruitment preferably appears in the same spawning area and takes place in summer and autumn. The physiological condition of the females drop during the ovarian maturation, with transference of soma to the gonad growth. The females display a pattern of mobility related to reproduction. The males display a reduced pattern of mobility, with mating taking place in spring in all the areas in which the species lives. The increase and the decrease of the male proportion in associated with the processes of mating and to a different mortality related to his shorter longevity and to the mating processes. The growth study confirms a model of approximated growth of 1 mm per month in the first years. The females have a longevity of up to 7 years and the males of 5, the ages better represented in the fishing populations are ages 2, 3 and 4 for both sexes. The recruitment corresponds to age 1 and appears with a year lag and comes from the spawning of the previous year. The reproductive success reflected in the recruitment, appears related to the condition and the demographic composition of the male populations and to a lesser extent, also of the female one. The decrease of the average size, and physiological condition of the males seems to have a greater influence in the reproductive potential of the population. The histological study of the ovary shows that the species has a synchronous spawning. The fleet that has the red shrimp as objective species is formed by boats of similar power. The captures present a composition of species characteristic of the habitat of the upper slope, and are formed, in average around 40% by red shrimp. The species does not have any discard while the global discarding of the fishery represents 20% of the capture and is formed in a 97% by noncommercial species. The standardization of the effort has allowed to establish that the annual and seasonal components are those that present a greater contribution to the variability of the captures. The species is highly profitable, representing only 10% of the captures of trawling and contributes in around 39% of the benefits of the trawl fishery. The effect of the environmental variability is reflected in the population abundance and appears related to the climatic indices that affect the North Hemisphere, as NAO climatic index, and with the seasonal hydrographical conditions. The application of structural models allows to establish the state of the species, diagnosing and predicting the future of this species. The new applied methods have considered the fitness and uncertainty of the models to the data. The different types of models applied complement their results and have been used to validate the final results. In relation to the structural models the results have shown that its applicability is limited and must be made for the set of the population, considering the different growth of both sexes. The species appears with a moderate variability in the recruitment estimations, with a situation of the present stock facing exploitation is better estimated than before. Applying structural models, as well as production models, require sufficient long series of time (at least 10 years) that allow to establish tendencies to make suitable predictions. The results obtained by these models, forecast long term captures similar to those obtained at the present time, and recommend, in order to maintain the species within the limit of security, that guarantees their harvesting during time, the reduction of the effort in a 30

First record of Gonostoma elongatum Günther, 1878 (Osteichthyes: Gonostomatidae) in the North - Western Mediterranean

The first record of Gonostoma elongatum Günther, 1878 (Osteichthyies: Gonostomatidae) in the North-Western Mediterranean (South West of Majorca lsland) is reported. lt is a deep mesopelagic fish, with a circumglobal distribution, tropical and subtropical. It occurs in the Atlantic, Pacific and Indo-Pacific between 500 to 1200 m. Morphometric and meristic characteristics are given.Hom dóna la primera cita de Gonostoma elongatum Günther, 1878 (Osteichthyies: Gonostomatidae) en la Mediterrània Nord Occidental (Sudoest de Mallorca). Es tracta d'una especie mesopelàgica d'aigües profundes de distribució circumglobal, tropical i sub tropical. Es troba al Atlàntic, Pacífic i Indo-Pacífic a profunditats d'entre 500 i 1200 m. Es donen les principals caracteristiques morfomètriquesPublicado

Biogeography of epibenthic crustaceans on the shelf and upper slope off the Iberian Peninsula Mediterranean coasts: implications for the establishment of natural management areas

Special Volume: Mediterranean marine demersal resources: the Medits international trawl survey (1994-1999)The patterns of occurrence and bathymetric distribution of epibenthic crustaceans on the continental shelf and upper slope down to a depth of 800 m are analysed based on data gathered during six demersal trawl surveys performed annually in spring along the Mediterranean coasts of the Iberian Peninsula (from the Straits of Gibraltar to Cape Creus) between 1994 and 1999. A total of 598 valid hauls has been studied providing a total of 108 species of decapods, two stomatopods, one euphausiid, one mysid and one isopod. The study area has been subdivided into seven sectors according to their geomorphological characteristics, and the patterns of occurrence and abundance by depth have been analysed separately for each of the sectors. Detailed data on bathymetric distribution are presented for each species. Two main biogeographical areas can be discerned along the study area, which can approximately be separated at Palos Cape: the Alborán Sea to the southwest, and the northwestern Mediterranean (Levantine and Catalan Seas) northwest of Palos Cape. The continental shelf in the Alborán Sea (the most western area of the Mediterranean) is extremely narrow whereas it is much wider in the northwestern Mediterranean. The influence of Atlantic waters entering the Mediterranean is particularly strong in the Alborán Sea which shows a particularly high species richness of Atlantic affinity. Within the context of the western Mediterranean Sea, the Alborán Sea region shows important faunistic characteristics such that it might be considered as a possible separate natural management area for demersal fisheriesVersión del editor1,006

Composition and distribution of the larval decapod community in the deep sea of the Western Mediterranean Sea Balearic Sub-basin

Mechanisms facilitating larvae transport from continental to more oceanic areas were investigated in the Balearic sub-basin (BSB), Western Mediterranean Sea. The abundance, distribution, and development stages of decapod larvae were recorded for a transect of 28 stations crossing the central eddy of the BSB. Zooplankton samples were taken to 1,800 m depth by horizontal and oblique 500-μm mesh size nets hauls towed near the benthic boundary (BBL) and in deep scattering layers (DSL). In total, 67 taxa belonging to Decapoda and one Stomatopoda were identified. Advanced development represented 75% of the individuals recorded. 75% of the species corresponded to adults of deep-sea species, 9% were sergestids (mesopelagic species), and the remaining 16% corresponded to shelf and coastal species. Cluster assemblages formed were related to the hydrological conditions, water masses dynamics, and geomorphologic structures mainly associated with nepheloid layers. Advanced and juvenile specimens of commercial species such as Parapenaeus longirostris, Geryon longipes, and Aristeus antennatus were found close to seafloor BBL. The influence of trophic ecology should be considered as the priority factor of larvae concentrations in deep.En prens

Condition and recruitment of Aristeus antennatus beyond fishing ground (to depths of 2200 m) in the Mediterranean: relationship with environmental factors

Depth relationships and seasonal trends in the biological condition and recruitment of the red shrimp Aristeus antennatus have been analyzed along down to 2300 m, over all the slope in the Balearic Basin (western Mediterranean). The analysis is based on a composite year (2008-2012 period) and identifies environmental causes of the trends. We found good reproductive and general biological condition of A. antennatus (Gonado-somatic index, GSI) at 800-1300 m in summer (June-July), depths below the fishing grounds. Mating and spawning were at depths below the more saline waters of the Levantine Intermediate water mass. Recruits Smallest juveniles (recruits, ca. 1 yr age) were exclusively distributed below 1000 m, associated with high near-bottom O2 concentration, low turbidity and high C/N in sediments implying favourable trophic conditions. A seasonal migratory pattern is suggested for females, which move shallower to the upper slope during periods of water-mass homogeneity (autumn-winter) to feed in canyons, increasing their energy reserves (hepatic gland weight, HSI). Females move downslope (800-1100 m) to spawn (high GSI) during periods of water mass stratification (late spring-summer). HSI of A. antennatus females decreased linearly with depth down the slope in February and in October-November, i.e., before and after the reproductive period. This nutritional condition of females in these periods is consistent with more consumption of benthic prey (ophiuroids, polychaetes, Calocaris macandreae) at the canyon heads (Cartes, 1994) in late autumn and winter. Our results confirm/suggest: i) how important it is to study the biology of deep-sea species over the whole depth range they inhabit and not only over fishing grounds, and ii) that changes in environmental conditions linked to the progressive warming of Mediterranean Deep Water (WMDW) with a parallel increase of salinity could provoke a decrease of O2 in water masses at below 1000 m, affecting A. antennatus recruitment and its life cycle, which is extensible to other deep-sea specie

Discards of the Western Mediterranean trawl fleets

We present a quantitative analysis of the composition (commercialized catch and corresponding discard) of trawl catches, in seven ports of the western Mediterranean. Discards are defined here as the fraction of the catch from the haul that is returned to the sea by the fishermen, because it does not have commercial value. A sampling programme on board commercial was performed from June 1995 to June 1996. The hauls were sampled for the collection of the total catch in weight, by species, for the commercial and discarded fractions separately. The factors of stratification considered were in all the ports, depth, with three strata, stratum A (350 m), to which factor for two types of gear in the Porto Santo Stefano or two classes of vessel power in Vilanova were added. The results obtained have allowed to characterize the commercial and discards fractions. The discarded biomass always constituted an important fraction of the total catch. However, the discard of species with high commercial interest was very low or nilPublicado

Some applications of the bootstrap in Spanish Discards Sampling Scheme

Herein we propose a nested boostrap scheme to explore di erent sources of variability in discard data. The proposed tool resamples on trips, hauls within trips and lengthclasess within hauls to include all sources of variability identified in the Spanish DCR sampling program scheme. Megrim (Lepidorhombus wiffiagonis) and Hake (Merluccius merluccius) discard data collected in 2008 from OTB-51 metier operating in ICES Division VI - VII, and Mediterranea DEF-Southern metier operating in the GSA 6S area were considered as case studies. Bootstrap Error and Coeficients of Variation associated to mean discards per trip were obtained and compared with asymptotic estimates. Furthermore, we use the bootstrap to quantify the contribution of the given sources of variability to global variability, and to assess simulated sampling scenarios differing each others in sampling effort. The last application of this method is for detecting outliers in 2008 sampled units (Trips). The good performance of the bootstrap method validates its use to obtain reliable error estimates in further regression and/or classiffication studies on discard data