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Lopez-Garcia J.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Navia A.F.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Mejia-Falla P.A.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Rubio E.A.,University of Valle
Journal of Fish Biology | Year: 2012

Sexual, ontogenic and temporal effects in the diet of Dasyatis longa were evaluated to determine feeding habits and trophic ecology. Numeric indices and the index of relative importance were applied to establish the feeding strategy of the species. Independence of the diet with respect to sex, dry or rainy season and size was evaluated with contingency tables, correspondence analysis and multivariate analysis (MANOVA). The trophic relationships of D. longa (by sex and size intervals) were determined using Levin's niche breadth index and the Pianka's diet overlap index and their significance was determined by null models. The trophic level for each size interval and the species was also calculated. Dasyatis longa showed a narrow niche breadth feeding mainly on shrimps and fishes and its diet was dependent on size, but not on sex or season. Juvenile individuals (class I) fed on shrimps, sub-adults (class II) on fishes and adults (class III) on stomatopods. Significant overlaps between size classes I and II and classes II and III were found. The trophic level shows D. longa to be a secondary or tertiary consumer. Due to considerable fishing pressures on shrimps, the principal prey of D. longa, it will be important to determine their ability to adapt to changes in prey populations. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles. Source


Mejia-Falla P.A.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Navia A.F.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Lozano R.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | Tobon-Lopez A.,Fundacion colombiana para la investigacion y conservacion de tiburones y rayas SQUALUS | And 4 more authors.
Revista de Biologia Tropical | Year: 2014

The ecotouristic approach to sharks and rays has developed rapidly in the last 20 years. We studied three species in Gorgona Island from 427 dives (2004-2011), including 866 photographs and videos. There was at least one sighting in 34.4% of the dives, and 25.0% of the photos and videos were useful for identification of individuals. T. obesus was seen in all months of the year, and its presence was correlated with depths of 20-30m (66.9%), sandy-rocky bottoms (79.8%), and western (61.2%) and south (52.9%) areas of the island. The southern area had groups of up to 9 individuals but abundance was not correlated with zone, depth, bottom type or temperature. R. typus and M. birostris were mainly seen at 28-33oC, in the north, where plankton was more abundant. We identified individually five whale sharks, 15 manta rays and 38 whitetip sharks, 9 of which (one ray and 8 whitetip sharks) were recaptured in different months and years. Most of recaptured whitetip sharks were alone (63.06%), resting (49.37%) and on the bottom (82.91%) in the same area of the photographic capture, suggesting a high philopatry of this species on the island; however, the recapture of three individuals in different zones indicate connectivity between of this species in the west, south and north zones. The Gorgona Island is an important area for breeding and growth of T. obesus, with presence of gravid females and births. It is also a seasonal passage area for R. typus and M. birostris, which occur most frequently between March and September, but do not form aggregations around the island. © 2014, Universidad de Costa Rica. All rights reserved. Source

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