Influence of upwelling conditions on feeding habits and trophic position of planktophagous fish

The effect of upwelling conditions on the trophic level of four planktofagous fish (Gadiculus argenteus, Capros aper and juveniles of Micromesistius poutassou and Merluccius merluccius) on the continental shelf off Northwestern Spain was assessed by coupling stomach content analyses and isotopic data. The study was performed during two consecutive years characterized by contrasting oceanographic conditions during the summer season; the first year (2012) had an intense and extended upwelling period, while the second (2013) had an intermittent and weak upwelling season. Sampling was carried out in autumn, after the summer upwelling, along a transect parallel to the coast on the continental shelf (130-180m depth), following the main upwelling gradient towards the Northeast. In addition to stomach content sampling and isotopic analyses of fish muscle, the isotopic signature of benthic detritus and sub- superficial phytoplankton were also indentified to characterize the basal isotopic level. We hypothesize that differences in isotopic ratios under these contrasting upwelling intensities possibly originate from both changes in the isotopic ratios of basal levels and shifts in the feeding habits of planktofagous species. Basal ratios of carbon and nitrogen in benthic detritus showed neither interannual variability nor relation with the upwelling gradient. However, particulate organic matter (POM) had significantly higher δ15N and δ13C during the first year. Isotopic signature of the four species was significantly different among years but followed different patterns, only related to POM basal levels in the case of C. aper. The ratio of 15N indicated that the four fish species considered had a trophic level of two, standing approximately 6 points over the basal levels and probably predating on consumer species. Stomach sampling evidenced that euphausiids constituted the majority of diet in G. gadiculus and juvenile M. merluccius and M.poutassou in both years. Euphausiid species would act then rather as consumers than predators, as a preliminary analysis of their isotopic signature confirmed (for the species Nyctiphanes couchii and Meganyctiphanes norvergica). While basal differences in isotopic ratios exist, our analyses suggest that shifts in feeding habits may have a major role in determining species isotopic positio

Evaluation and measurement of heliostat misalignment in solar power plant using vector model

Heliostat alignment evaluation is among the main issues in solar tower concentration plant operation and maintenance. This paper describes a novel method used to evaluate heliostat misalignment and its experimental verification. This method provides a different way of visualizing beam centroid pointing errors by generating the complete deviation curve for each axis. This, for example, would be useful for verifying a heliostat’s correct alignment by using a measurement performed out of the receiver target, using these traces to calculate its reflection’s expected location, given a known misalignment. This measurement could be performed during operation simply by including a reflective element in the heliostat and two detector arrays on the tower’s surface. This model has been tested for various types of misalignments of a heliostat at different hours, dates, and heliostat locations. The simulation results have been validated by using an experimental setup at a scale of 1:100

Spatio-temporal variability in the cannibalistic behaviour of European hake Merluccius merluccius: the influence of recruitment abundance and prey availability

Cannibalistic behaviour of European hake Merluccius merluccius was studied through the analysis of 49 836 gut contents belonging to individuals from 6 to 82 cm in total length (LT). Samples were collected every autumn between 1993 and 2009. The results showed that the consumption of conspecific individuals was consistent over space and time. The abundance, spatial distribution patterns and LT structure of M. merluccius recruits were the main variables involved in M. merluccius cannibalism. A geographical pattern was found since increasing cannibalism was observed in areas of recruit aggregations. The LT spectrum of recruits in autumn was also a key factor and dependent on the spawning period. When adults spawned from late spring to summer, an increasing cannibalism trend was found in autumn, due to the ideal size structure of the prey (M. merluccius recruits) for predators. Depth was also a significant variable, and a cannibal peak was detected at depths ranging between 50 and 200 m, coinciding with a spatial overlap of predator (pre-adults) and prey (recruits). The cannibalistic behaviour of M. merluccius began at c. 12 cm, although 75% were mid-sized individuals between 16 and 30 cm. Additionally, 90% of prey-hake were recruits <18⋅5 cm. Some biological and ecological aspects such as growth rate, spawning period, predation and competition interactions and the effect of some oceanographic events on M. merluccius cannibalism are also discussed.En prens

Food web functioning of the benthopelagic community in a deep-sea seamount based on diet and stable isotope analyses

14th Deep-Sea Biology Symposium (DSBS), 31 August 2015 - 04 September 2015, AveiroPeer Reviewe

Trophic mechanisms underlying bentho-demersal community recovery in the north-east Atlantic

En prens

Empleo de modelos de series temporales para la mejora de la calidad de las series históricas en pesquerías

Abstract: The so-called baca trawl fleet of the port of A Coruña working in the VIIIc ICES Division Area has been used since 1985 as the tuning fleet for the analytical assessment of the southern stock of hake Merluccius merluccius (L., 1758). The historical series of cpue dates from 1983 to 2000 with data missing from 1998. From January 1999, landings were estimated by means of monthly samplings in port. The predictions of the arima model fit the 1983-1997 series, and estimates of the transfer function model from the 1983-2000 series made it possible to complete the series, and to detect errors and possible changes in the orientation of the fleet. The comparison of the two models confirms the series’s stability over time, validating the estimates made in the last two years.Empleo de modelos de series temporales para la mejora de la calidad de las series históricas en pesquerías La flota de baca del puerto de A Coruña que opera en el área VIIIc del CIEM se usa desde 1985 como flota de calibración en la evaluación del stock sur de merluza Merluccius merluccius (L., 1758). Se dispone de una serie histórica mensual de cpue (1983-2000), excepto para 1998, año del que no se posee información. Desde enero de 1999 los desembarcos han sido estimados a partir de muestreos mensuales en lonja. Las predicciones efectuadas por el modelo arima ajustado a la serie 1983-1997 y las estimaciones del modelo de función de transferencia, considerando la serie 1983-2000, han permitido completar la serie, así como detectar errores o cambios en el comportamiento de la flota. La comparación de ambos modelos confirma la estabilidad de la serie, validando las estimaciones efectuadas en los dos últimos años.Instituto Español de Oceanografí