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462 results on '"Louzao, M."'

27. Structure and functioning of the Bay of Biscay ecosystem: A trophic modelling approach

Author

Ministerio de Ciencia e Innovación (España), Eusko Jaurlaritza, Corrales, X., Preciado, Izaskun, Gascuel, D., Lopez de Gamiz-Zearra, A., Hernvann, P. Y., Mugerza, E., Louzao, M., Velasco, Francisco, Doray, M., López-López, Lucía, Carrera, Pabl, Cotano, U., Andonegi, E., Ministerio de Ciencia e Innovación (España), Eusko Jaurlaritza, Corrales, X., Preciado, Izaskun, Gascuel, D., Lopez de Gamiz-Zearra, A., Hernvann, P. Y., Mugerza, E., Louzao, M., Velasco, Francisco, Doray, M., López-López, Lucía, Carrera, Pabl, Cotano, U., and Andonegi, E.

Abstract

Characterizing the structure and functioning of marine ecosystems requires a deep understanding of the dynamics of its populations and the biotic interactions among them. To this end, we developed a mass-balanced food-web model of a regional sea in the Northeast Atlantic, the Bay of Biscay (BoB), considering one of the most important anthropogenic disturbance in the area, the fishing pressure. The food-web model was performed for the whole BoB region for the first time. The model represents the ecosystems in the early 2000s, encompassing 120433 km2 between 0 and 1000 m depth. The model was composed of 52 functional groups, ranging from primary producers to top predators, and considering both Spanish and French fishing fleets. Input data included biomass obtained locally from bottom trawl and acoustic surveys, data from stock assessment, official fishery statistics, published and unpublished data on stomach content analyses and the use of empirical equations to estimate consumption and production rates. Our results highlight the importance of the pelagic domain, since the main trophic flows are determined by the interaction between phytoplankton, zooplankton and forage fishes. The role of the detritivore pathway was also relevant due to the relatively high abundance of detritivores organisms and the large percentage of primary production flowing to the detritus. Forage fish have resulted to be a key compartment fostering the connectivity between the benthic and pelagic domains. Pelagic sharks, dolphins, anglerfish, large hake and large demersal fishes were identified as potential keystone functional groups in the BoB model. The results also showed an intense exploitation by fisheries in early 2000s. Different strategies between Spanish and French fleets were also found. French fleets were mainly focussed on low trophic level forage fish (e.g., sardine and anchovy) and had larger impacts on higher trophic levels, while Spanish fleets mostly focussed on higher trophic

Published
2022

29. Where, when and why: modelling the distribution and habitat of deep-diving cetaceans incorporating variables depicting the deep oceanic layers

Author

Auriane Virgili, Teillard, V., Dorémus, G., Dunn, T. E., Laran, S., Lewis, M., Carmen Louzao, M., Martinéz-Cedeira, J., Pettex, E., Ruiz, L., Saavedra, C., Canneyt, O., José Antonio Vázquez Bonales, Vincent Ridoux, Lacalle, Martine, La Rochelle Université (ULR), Aix Marseille Université (AMU), Joint Nature Conservation Committee, Marine Habitats Team, AZTI - Tecnalia, Coordinadora para o Estudo dos Mamiferos Mariños (CEMMA), CEMMA, Instituto Espanol de Oceanografia, and Instituto Español de Oceanografía

Subjects
diving, modelling, [SDE] Environmental Sciences, [SDE]Environmental Sciences, distribution, habitat, eddy kinetic energy
Abstract

The use of Species Distribution Models (SDMs) has increased considerably in recent decades, notably for conservation purposes. SDMs are used particularly to characterise and predict marine top predator distributions thanks to the use of surface dynamic environmental variables (easily accessible and available at various spatial and temporal scales) as proxies for prey distribution. For oceanic species that spend most of their time in depth waters like deep-diving cetaceans (here beaked whales and sperm whales), the use of surface variables may limit the ability to correctly infer their habitats through SDMs. We combine, static variables that characterise the topography of the bottom water and dynamic variables integrated over different depth classes that characterise the water column into Generalised Additive Models to model the distribution of deep-diving cetaceans in the Bay of Biscay and to identify which variables are the most important for each species. We obtained relationships with the environment that allow predicting the highest densities of beaked whales and sperm whales near the continental slope, near canyons and seamounts and in the abyssal plain of the Bay of Biscay. We also identified different responses between beaked whales, for which surface, subsurface and static variables were selected as the most important variables, and sperm whales. For the latter only surface and depth variables were selected, which could suggest differences in foraging strategies and in the prey targeted between these species. The continuous development of ocean models and the availability of depth variables, allows as we have shown, the improvement of the tools available for the planning of human activities, especially for species that would be closely linked to processes taking place in deep waters, such as top predators.

Published
2022

45. Seasonal changes in the diet and feeding behaviour of a top predator indicate a flexible response to deteriorating oceanographic conditions

Author

Xavier, J.C., Louzao, M., Thorpe, S.E., Ward, P., Hill, C., Roberts, D., Croxall, J.P., and Phillips, R.A.

Subjects
Albatrosses -- Behavior -- Food and nutrition, Biological sciences
Abstract

Shifts in the diet of top predators can be linked to changes in environmental conditions. In this study, we tested relationships between environmental variation and seasonal changes in diet of a top predator, the grey-headed albatross Thalassarche chrysostoma, breeding at Bird Island, South Georgia in an austral summer of 1999/2000. Oceanographic conditions in that year around South Georgia were abnormal (i.e. anomalously high sea surface temperature to a relative 19-year long-term mean). The diet of grey-headed albatrosses showed high seasonal variation, shifting from cephalopods (42.9 % by mass) in late February to Antarctic krill Euphausia superba (58.3 %) in late April, and grey-headed albatrosses breeding performance was low (16.8 %). This study shows these albatrosses did not manage to find sufficient alternative prey and highlight the risk to top predators if there is an increase in the frequency or severity of food shortages in Antarctic waters., Introduction Climate processes have a major impact on the structure and function of ecological systems (Stenseth et al. 2002). A wide range of studies has shown links between fluctuations in [...]

Published
2013
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