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Isla de Margarita, Venezuela

Hernandez-Avila I.,University of the East Venezuela | Tagliafico A.,University of the East Venezuela | Rago N.,Oceanografia y pesca
Revista de Biologia Tropical | Year: 2013

Bivalve aggregations constitute a microhabitat for a wide variety of organisms in intertidal, subtidal and deep-water marine benthic habitats. Increase in density of bivalve beds could offer more crevices and substratum for the associated fauna, affecting community composition. Beds of the Atlantic Pearl Oyster (Pinctada imbricata) and the Turkey Wing (Arca zebra) of contrasting population densities were evaluated to determine the composition and structure of the associated macrofauna of three taxa (Crustacea Decapoda, Mollusca and Echinodermata). We evaluated plots of three levels of bed density in both species, the associated fauna were identified and counted. Other species were collected by qualitative samples. Univariate and multivariate descriptors were tested comparing the associated fauna between the beds of two species at three levels of density. In these beds a total of 104 species belonging to 58 families were recorded. Mithraculus forceps (Majidae), Crucibulum auricula (Calyptraeidae) and Ophiotrix angulata (Ophiothrichidae) were the most common species found in these assemblages. The medium and high-density bivalve beds exhibited greater species number, abundance, Shannon diversity, evenness, taxonomic diversity, and taxonomic distinctness of associated fauna, than low-density bivalve beds. Moreover, multivariate analysis detected different assemblages of associated fauna between beds with different densities. Additionally, similarities were found in the communities of macrofauna in both beds of P. imbricata and Arca zebra. Our results suggest that bivalve aggregations at Cubagua Island provide additional habitat for macrofauna living in other shallow habitats such as Thalassia beds, corals and rocky environments. Bed density, associated with topographic complexity, represents an important factor for the composition and complexity of the associated fauna. Source


There is limited biological information about the starfish Oreaster reticulatus and the nine-armed starfish Luidia senegalensis in Venezuelan waters. These species are currently considered threatened in many localities of the Caribbean, Brazil and Colombia. Therefore, the aim of this study was to describe their population density, size distribution and population structure in Cubagua Island. During 2008, 52 stations located around the island were evaluated using band transects of 50m2. Each organism was counted and measured (maximum radius), and its size was compared to the maturity length reported in the literature. The results for O. reticulatus include: 167.3ind./ha; 33% juveniles and 67% adults; average size of 10.7±5cm (range: 2.2-21cm); a wide distribution around the island, with higher densities in the Eastern and Southwest areas. The 50% of the specimens were found in seagrass beds, 25% in sand, 16% in areas covered by decomposed seaweeds, 9% in oyster beds and 1% coralline patches. The densities of O. reticulatus were higher than those reported in the Caribbean, Panama and Puerto Rico, but lower than Venezuelan National Parks: Mochima and Morrocoy; as well as in the Virgin Islands and Belize. For L. senegalensis we found an average density of 40ind./ha; 95% exceeded the reported size at maturity, with mean length of 12cm±3.5cm (range: 3.5-22.3cm); they were found only in 15% of the stations of which 92.5% were sandy bottoms and the other 7.5% oyster beds. The degree of aggregation of L. senegalensis was greater than O. reticulatus, with an estimated k of 0.06. However, it was not possible to compare the densities of L. senegalensis with any other study. For both species is recommended to carry out reproductive studies and to monitor their population densities to infer temporal variations. Source


Fishery and biology of Rhinobatos percellens (Rajiformes: Rhinobatidae) caught by the artisanal fishery at La Pared beach, Venezuela. R. percellens is incidentally caught in Venezuela by the artisanal fishery using bottom gillnets. This species was classified by the IUCN as being "near threatened", and there is poor knowledge about its biology and fishery in Venezuela. For this reason, we analyzed the specimens caught by the artisanal fleet in playa La Pared, once a week, from January to December 2007. We determined total length, sex and maturity for each captured specimen. A total of 210 specimens were analyzed, 159 females and 51 males. The 81% of all specimens caught were adults, but within this group 27% were pregnant. The average size of sexual maturity was found between 51 and 52cm for females and males, respectively. Adult females were found all year round, and pregnant females in seven of the months sampled; highest numbers were found between February-March and September. The analyzed females had a total of 96 embryos with a size range between 2 and 19cm, with a maximum fertility of four embryos per litter. February and June-July showed the maximum breeding time, and considering the broad range of embryos sizes and the frequency of pregnant females along the different months, allow us to believe that they reproduce throughout the year. Fishing regulation including minimum catch size in relation to maturity length and release of pregnant females in water is recommended. Source


Tagliafico A.,University of the East Venezuela | Tagliafico A.,Southern Cross University of Australia | Rago N.,Oceanografia y pesca | Barany M.,Venezuelan Institute for Scientific Research | And 2 more authors.
Revista de Biologia Tropical | Year: 2015

Rhizoprionodon lalandii is a small shark (< 1.5 m) classified as Data Deficient by IUCN; however, in Venezuelan coastal waters, it represents one of the most captured species, with daily landings in many areas of the country, being an important component of traditional dishes with high demand and with an increased economical value in local markets. Due to the lack of biological information, the present work studied some reproductive and feeding aspects, with the main objective to contribute with base-line information for necessary sustainable management of the fishery. Samples were taken in two landing ports and two local markets once a week between January 2006 and December 2007. Total length (Lt), sex and maturity were evaluated for a total of 656 individuals with an average length of 56 ± 9 cm of Lt. Additionally, 108 stomachs were taken for the diet analysis. Significant differences were found in the overall sex ratio, with 54 % females (F), and 46 % males (M), and also in the embryos (60 % F, 40 % M), 45 % of the individuals were below average maturity length and 22 % of the females were gravid. Females reach maturity length (53 cm) before males (57 cm). Maximum fecundity was 5 embryos, with a maximum total length of 30.1 cm. Reproductive patterns were not clear throughout the years; nonetheless, between November and February the birth season was intense, with the highest rates of pregnant females and embryos with most length. The species principally feeds on fishes and, in less scale, cephalopods. The calculated trophic level was 3.7. We strongly recommend to fix a minimum length of capture (> 57 cm de LT), ban the catches of pregnant females and the application of a banned season of at least four months per year, to preserve the economic benefits of this fishery. © 2015, Universidad de Costa Rica. All rights reserved. Source


Dasyatis guttata and D. americana are target species of some artisanal fisheries in Venezuela. Because there are directed fisheries for their catches and there have been few studies on its biology, both species are listed in the IUCN as Data Deficient. Therefore, the objectives of this research were to analyze the catches of the artisanal fishery in Margarita Island in order to provide reproductive data to contribute to the management of both species. For this reason, 3 fishing communities and 2 markets selling fish were sampled once a week, from January 2006 to December 2007. Disc width, sex and maturity were determined for each specimen captured. A total of 355 specimens of D. guttata showed that females (32-173 cm) were larger than males (28.6-113 cm), 35% of the catches were immature individuals, and although exists differences in the sex ratio there were no difference in the size at maturity (L50 to both sexes: 56 cm); nonetheless, all individuals were mature above 78 cm. A gravid female was observed in June 2007 with 5 embryos. For D. americana a total of 224 specimens were analyzed; 40% of these had not reached sexual maturity; females showed higher sizes (21.2-164 cm) than males (35-147 cm) and also a higher size at maturity (L50: females: 64 cm, males: 56 cm), but all specimens were mature above 70 cm. Differences in the sex ratio and gravid females were observed only for August 2006 and March 2007, with a highest fecundity of 5 embryos. We recommend setting minimum catch lengths and periods of closure of the fishery. Source

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