Institute Of Recherches Pour Le Developpement Ird
Institute Of Recherches Pour Le Developpement Ird
Jouffre D.,Montpellier University |
Borges M.D.F.,Institute Investigacao das Pescas e Do Mar IPIMAR INRB |
Bundy A.,Bedford Institute of Oceanography |
Coll M.,CSIC - Institute of Marine Sciences |
And 7 more authors.
ICES Journal of Marine Science | Year: 2010
Under the context of an ecosystem approach to fisheries (EAF), there is keen interest in providing insights into the evolution of exploited ecosystems using simple ecosystem indicators. Many nations have long-term scientific research surveys, originally driven by conventional approaches in fisheries assessment and management. The aim of this study is to address the practical concerns linked to current objectives of monitoring simple EAF indicators, using data from surveys that were not historically designed for the purpose. Based on the results of an expert survey designed to collect expert knowledge on research surveys from scientists working on different ecosystems worldwide, a list of challenges faced during indicator estimation is highlighted, along with associated concerns and constraints. The work provides additional information useful in the interpretation of the results obtained on the state and trends of ecosystems using EAF indicators by the IndiSeas WG. Further, the related discussion provides potential pathways that could be useful for future research and development aiming to improve the ecosystem indicator approach in the operational context of EAF. The question of the utility for EAF of using historical dataseries of scientific trawl series is also discussed. Such long-term series are concluded to be useful, that they are even inescapable (since the past cannot be resamplied), and that EAF therefore brings a supplementary reason for continuing such monitoring and to incorporate new insights in how research surveys may be conducted. © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.
Paramo J.,Leibniz Center for Tropical Marine Ecology |
Paramo J.,University of Magdalena |
Gerlotto F.,Institute Of Recherches Pour Le Developpement Ird |
Oyarzun C.,University of Concepción
Journal of Applied Ichthyology | Year: 2010
In fish resource assessment, it is very important to know about the behaviour and form of fish schools. This paper describes the three-dimensional (3D) morphology and internal structure of pelagic schools observed using vertical-scanning multibeam sonar. The acoustic data were collected in waters off Venezuela, Senegal, and Mexico. The data were used to derive metrics of school location, density, shape and internal structure from a total of 668 schools: 257 from Mexico, 343 from Venezuela and 68 from Senegal. In general, school shapes were amoeboid-like (e.g. spheres or ellipsoids) and not simply geometric. Also, the fish were patchily-distributed, forming both nuclei (groups) and vacuoles (empty spaces) within the schools. The results support the hypothesis of 'auto-organization of the fish inside schools', meaning that the distribution of fish within a school arises from the elementary reaction of the individuals. © 2010 Blackwell Verlag, Berlin.
Abril G.,University of Bordeaux 1 |
Abril G.,University of the State of Amazonas |
Commarieu M.-V.,University of Bordeaux 1 |
Commarieu M.-V.,University of Liège |
And 9 more authors.
Estuarine, Coastal and Shelf Science | Year: 2010
Estuarine turbidity maxima (ETMs) are sites of intense mineralisation of land-derived particulate organic matter (OM), which occurs under oxic/suboxic oscillating conditions owing to repetitive sedimentation and resuspension cycles at tidal and neap-spring time scales. To investigate the biogeochemical processes involved in OM mineralisation in ETMs, an experimental set up was developed to simulate in vitro oxic/anoxic oscillations in turbid waters and to follow the short timescale changes in oxygen, carbon, nitrogen, and manganese concentration and speciation. We present here the results of a 27-day experiment (three oxic periods and two anoxic periods) with an estuarine fluid mud from the Gironde estuary. Time courses of chemical species throughout the experiment evidenced the occurrence of four distinct characteristic periods with very different properties. Steady oxic conditions were characterised by oxygen consumption rates between 10 and 40 μmol L-1 h-1, dissolved inorganic carbon (DIC) production of 9-12 μmol L-1 h-1, very low NH4+ and Mn2+ concentrations, and constant NO3- production rates (0.4 - 0.7 μmol L-1 h-1) due to coupled ammonification and nitrification. The beginning of anoxic periods (24 h following oxic to anoxic switches) showed DIC production rates of 2.5-8.6 μmol L-1 h-1 and very fast NO3- consumption (5.6-6.3 μmol L-1 h-1) and NH4+ production (1.4-1.5 μmol L-1 h-1). The latter rates were positively correlated to NO3- concentration and were apparently caused by the predominance of denitrification and dissimilatory nitrate reduction to ammonia. Steady anoxic periods were characterised by constant and low NO3- concentrations and DIC and NH4+ productions of less than 1.3 and 0.1 μmol L-1 h-1, respectively. Mn2+ and CH4 were produced at constant rates (respectively 0.3 and 0.015 μmol L-1 h-1) throughout the whole anoxic periods and in the presence of nitrate. Finally, reoxidation periods (24-36 h following anoxic to oxic switches) showed rapid NH4+ and Mn2+ decreases to zero (1.6 and 0.8-2 μmol L-1 h-1, respectively) and very fast NO3- production (3 μmol L-1 h-1). This NO3- production, together with marked transient peaks of dissolved organic carbon a few hours after anoxic to oxic switches, suggested that particulate OM mineralisation was enhanced during these transient reoxidation periods. An analysis based on C and N mass balance suggested that redox oscillation on short time scales (day to week) enhanced OM mineralisation relative to both steady oxic and steady anoxic conditions, making ETMs efficient biogeochemical reactors for the mineralisation of refractory terrestrial OM at the land-sea interface. © 2010 Elsevier Ltd. All rights reserved.
Collinet J.,Institute Of Recherches Pour Le Developpement Ird |
Leprun J.-C.,Institute Of Recherches Pour Le Developpement Ird |
Asseline J.,Institute Of Recherches Pour Le Developpement Ird
Geomorphologie: Relief, Processus, Environnement | Year: 2013
Runoff and soil erosion analysis was developed with simulated rainfall on a representative soil transect from the south Sahelian to Guinean zones in West Africa (15° N to 05° N). Twenty-six sites were studied and are presented in the first section, with the runoff and erosion measurement protocols. The second part presents a data interpretation based on erodibility by rain, latitudinal distribution of the sites and the most efficient characteristics for soil hydrodynamic behaviour. This synthesis, based on a new treatment of experimental data obtained from 1975 to 1981, distinguishes the lower hydraulic conductivities of the Sahelian and Sudanese soils from the higher ones measured in the Guinean zone. These differences are attributed to the soil surface fabric resulting from the combined effects of rain energy and runoff flow that control soil hydraulic properties. These surface features are formed in all conditions, but they are more stable and perennial in the arid north with its sparse vegetative cover and low biological activity than in the humid south with its continuous vegetative cover, high biological activity and hence deeper water percolation and storage. Our experimental study is a dynamic valuation of cartographic documents useful for didactic, development purposes, but also for providing new information sources for distributed models and GIS.