José Luis Varela
University of Cádiz
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Publication
Featured researches published by José Luis Varela.
PLOS ONE | 2013
Guillermo Aranda; Francisco J. Abascal; José Luis Varela; Antonio Medina
Spawning behaviour of Atlantic bluefin tuna (Thunnus thynnus) was investigated using electronic satellite tags deployed in the western Mediterranean spawning ground, around the Balearic Islands (years 2009-2011). All the fish were tagged underwater and released within schools. In general, the fish tagged in the same year/school displayed common migratory trends. Following extended residency around the Balearic Islands, most tagged tuna crossed the Strait of Gibraltar heading for the North Atlantic. Discrepancies between the migratory tracks reconstructed from this and previous electronic tagging studies suggest that the bluefin tuna Mediterranean population may comprise distinct units exhibiting differing migratory behaviours. The diving behaviour varied between oceanic regions throughout the migratory pathways, the shallowest distribution taking place in the spawning ground and the deepest at the Strait of Gibraltar. A unique diving pattern was found on the majority of nights while the fish stayed at the spawning ground; it consisted of frequent and brief oscillatory movements up and down through the mixed layer, resulting in thermal profiles characterized by oscillations about the thermocline. Such a pattern is believed to reflect recent courtship and spawning activity. Reproductive parameters inferred from the analysis of vertical profiles are consistent with those estimated in previous studies based on biological samples.
Marine Biodiversity Records | 2014
José Luis Varela; Enrique Rodríguez-Marín; Marta Ruiz; Antonio Medina
The diet of young Atlantic bluefin tuna ( Thunnus thynnus ) in the Bay of Biscay foraging ground was assessed using stomach-content analysis (SCA) and stable-isotope analysis coupled with isotope mixing model. Whereas SCA showed that the young tuna fed mainly on horse mackerel ( Trachurus trachurus ), the estimation of liver and muscle mixing model analyses indicated that northern krill ( Meganyctiphanes norvegica ) was the most important food resource. These contrasting observations are probably due to the different time scales spanned by the different methods. The present results suggest that young bluefin tuna prey at different trophic levels of the Bay of Biscay pelagic food web, thus behaving as an opportunist and generalist predator.
Marine Environmental Research | 2018
José Luis Varela; Elisa Rojo-Nieto; Joan Miquel Sorell; Antonio Medina
Stable isotope analysis (δ13C and δ15N from liver and muscle) was used to assess trophic relationships between Atlantic bluefin tuna (ABFT) (Thunnus thynnus) and striped dolphin (SC) (Stenella coeruleoalba) in the Strait of Gibraltar (SoG). δ15N values from ABFT muscle and liver tissues were significantly different from those of dolphin samples, but no for δ13C values. Diet estimation by MixSIAR models from muscle and liver revealed that ABFT fed mainly on squids (Todaropsis eblanae and Illex coindetii). The shrimp Pasiphaea sp. was estimated to be the most important prey-species in the diet of SC. Trophic positions estimated from muscle and liver isotopic data suggested that ABFT occupy a higher trophic level than SC. Estimations of isotopic niche, as measured by the standard ellipse area, indicated that ABFT show a broader trophic niche than SC; furthermore, SEAc did not show trophic overlap between both predators. The results of this study suggest that resource partitioning occurs between ABFT and SC in the SoG ecosystem.
Journal of Experimental Marine Biology and Ecology | 2011
José Luis Varela; Alex Larrañaga; Antonio Medina
Journal of Sea Research | 2013
José Luis Varela; Enrique Rodríguez-Marín; Antonio Medina
Aquaculture | 2012
José Luis Varela; F. de la Gándara; Aurelio Ortega; A. Medina
Aquaculture Research | 2016
A.J. Vizcaíno; Sara Isabel Mendes; José Luis Varela; Ignacio Ruiz-Jarabo; Rosa M. Rico; Félix L. Figueroa; Roberto Abdala; Miguel A. Moriñigo; Juan Miguel Mancera; F.J. Alarcón
Marine Ecology Progress Series | 2015
Antonio Medina; Nicolas Goñi; Haritz Arrizabalaga; José Luis Varela
Aquaculture Research | 2015
José Luis Varela; Aurelio Ortega; Fernando de la Gándara; Antonio Medina
Fisheries Research | 2018
José Luis Varela; Joan Miquel Sorell; David Macías; Nicolas Goñi; Haritz Arrizabalaga; Antonio Medina
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