Alan Giraldo

Feeding ecology of elasmobranch fishes in coastal waters of the Colombian Eastern Tropical Pacific

BackgroundStomach contents of 131 specimens of five elasmobranch species (Mustelus lunulatus, Dasyatis longa, Rhinobatos leucorhynchus, Raja velezi and Zapteryx xyster) caught in the central fishing zone in the Pacific Ocean of Colombia were counted and weighed to describe feeding habits and dietary overlaps.ResultsTwenty-one prey items belonging to four major groups (stomatopods, decapods, mollusks and fish) were identified. Decapod crustaceans were the most abundant prey found in stomachs. The mantis shrimp Squilla panamensis was the main prey item in the diet of M. lunulatus; tiger shrimp Trachypenaeus sp. was the main prey item in the diet of Rhinobatos leucorhynchus and Raja velezi, and Penaeidae shrimp were the main prey items in the diet of Z. xyster. Furthermore, fish were important in the diet of Raja velezi, Z. xyster and D. longa. The greatest diet breadth corresponded to Z. xyster whereas M. lunulatus was the most specialized predator. Finally, four significant diet overlaps between the five species were found, attributable mainly to Squillidae, Penaeidae and Fish.ConclusionShrimps (Penaeidae and stomatopods) and benthic fishes were the most important food types in the diet of the elasmobranch species studied. Diet breadth and overlap were relatively low. Determination of food resource partitioning among the batoid species studied was not possible. However, we identified partitions in other niche axes (time of feeding activity and habitat utilization). It is possible to assume that diffuse competition could be exceeding the biunivocal competition among the studied species. Therefore, this assemblage would have a strong tendency to trophic guild formation.

Condiciones oceanográficas en isla Gorgona, Pacífico oriental tropical de Colombia

RESUMEN. La zona de influencia costera de isla Gorgona es un area marina protegida localizada en el Pacifico Oriental Tropical (POT) de Colombia. Aunque alberga uno de los arrecifes coralinos mas desarrollados del POT, la caracterizacion de las condiciones oceanograficas superficiales locales y su variabilidad temporal y espacial han sido escasamente abordadas. Para incrementar el conocimiento sobre la variabilidad de la temperatura y la salinidad en esta localidad se realizaron registros sistematicos de estas variables durante cuatro periodos (septiembre 2005, diciembre 2005, marzo 2006 y junio 2006), se instalaron sensores de registro continuo de temperatura a 15 m de profundidad en la zona oriental y occidental de la isla, y se realizo un monitoreo del patron local de circulacion superficial utili-zando un perfilador de corrientes (AWAK-ADCP) durante junio 2006 y febrero 2007. Se identificaron dos periodos contrastantes para las condiciones oceanograficas en la capa superficial (0-50 m) de la columna de agua: un periodo calido y de baja salinidad superficial entre mayo y diciembre (profundidad termoclina 47 m) y un periodo frio y salino entre enero y abril (profundidad termoclina 7,5 m). Se descarto la presencia de proceso local de surgencia y los resultados indicaron una fuerte influencia de procesos de mesoescala (surgencia en el Panama Bight) sobre la variabilidad temporal de las condiciones oceanograficas en la zona de estudio. En este mismo sentido se sugiere que la variabilidad espacial estaria mas asociada a procesos climaticos regionales (patron de precipitacion) y la cercania de la zona de estudio al complejo deltaico rio Patia - rio Sanquianga. Palabras clave: temperatura, salinidad, oceanografia, isla Gorgona, Colombia, Pacifico Oriental Tropical.

Sexual, ontogenetic, temporal and spatial effects on the diet of Urotrygon rogersi (Elasmobranchii:Myliobatiformes)

The food habits and trophic ecology of Urotrygon rogersi were analysed to ascertain sexual, ontogenetic, temporal and spatial effects on the diet. These effects were examined with contingency tables, simple correspondence analysis and MANOVA. The trophic relationships of the species were determined with Levins niche amplitude index and Piankas diet overlap index. Urotrygon rogersi is a predator of benthic organisms, especially shrimp and polychaetes. Analysis of sex and time showed no significant differences, but differences among class sizes were found. A strong trend towards diet specialization and a strong overlap between sexes and between class sizes were found. Finally, fishing activity on shrimps in the study area could force U. rogersi to change its trophic spectrum over time as an adaptation to the considerable reduction in its principal prey.

Notas biológicas de la raya ocelada Zapteryx xyster Jordan & Evermann, 1896 (Chondrichthyes: Rhinobatidae) en la zona central de pesca del Pacífico colombiano

The specific life history of rays from the family Rhinobatidae includes low fecundity, ovoviviparous repro- duction, and few progeny, making the species vulnerable to recruitment in fishing zones. In Colombia, Zapteryx xyster does not have any commercial value but is captured incidentally by small-scale and industrial fisheries in the Pacific. We studied the biological aspects of 55 Z. xyster specimens caught during shrimp prawn trawling in the central fishing zone of the Colombian Pacific between July and December 2001. Individuals were caught between 30 and 45 m depth, especially at night. Sizes ranged between 27 and 66 cm total length and the species presented isometric relationships for total length-weight (b = 2.85) and disc width-weight (b = 2.72). The studied specimens included all stages of gonad development, with state II predominating (40.7%). The diet of Z. xyster is based on six prey items; four of these are classified as principal. Shrimps from the family Penaeidae were the preferred prey.

Notas sobre la biología y dieta del toyo vieja (Mustelus lunulatus) en la zona central de pesca del Pacífico colombiano

Specimens of Mustelus lunulatus captured in the trawling fishery of a shrimp vessel in the central zone in the Pacific Ocean off Colombia were analyzed. The size, weight, growth pattern, sexual proportion, stages of maturity and diet were determined. The captured specimens were between 50 and 125 cm, the sexual proportion was 1:1, and the isometric-type length-weight relationship was described by WT = 0.005·LT 2.92 . In all, 13 food items were identified in the stomach content, with the stomatopods (Squilla panamensis and S. parva) being the dominant taxonomic group in number and weight.

Ictioplancton superficial de la cuenca del océano Pacífico colombiano (septiembre 2003)

RESUMEN. Se presentan los resultados del analisis taxonomico y ecologico del ictioplancton obtenido mediante arrastres superficiales en 23 estaciones de muestreo durante la campana oceanografica Pacifico XXXVIII ERFEN–XXXVI en la cuenca del Oceano Pacifico colombiano. Se identificaron estadios larvales de 19 especies pertenecientes a 18 familias, en su mayoria de interes para la pesca. Las familias mas abundantes fueron Photichthyidae (179 larvas·1000 m -3 ) y He-miramphidae (106 larvas·1000 m -3 ). Se determino la distribucion y abundancia de huevos mediante el analisis grafico de mapas de dispersion espacial. Destacaron por su frecuencia de ocurrencia y abundancia las larvas de Vinciguerria lucetia (Familia Photichthydae) con 112 larvas·1000 m -3 , Cetengraulis mysticetus (Familia Engraulidae) con 104 larvas·1000 m -3 , y Hyporhamphus sp. y Oxyporhamphus sp. (Familia Hemiramphidae) con 73 y 33 larvas·1000 m -3 respectivamente. Considerando las limitaciones del muestreo (hora, tipo de red y arrastre), es muy probable que los valores de abundancia de larvas fueron subestimados.Palabras clave: ictioplancton, huevos de peces, larvas de peces, Colombia, Oceano Pacifico.

Hipéridos (Crustacea: Amphipoda) en el sector norte del Pacífico oriental tropical colombiano

In order to analyze the composition, abundance, and diversity of hyperiid amphipods at Punta Cruces and Cabo Marzo, on the northern Pacific coast of Colombia...

Ichthyoplankton in the Nacional Natural Park Isla Gorgona (Pacific Ocean of Colombia) during September 2005

The taxonomy, spatial distribution, and abundance patterns of ichthyoplankton collected in September 2005 from the coastal zone of Gorgona Island National Natural Park in the Colombian Pacific Ocean were analyzed. The ichthyoplankton in the study area was collected with oblique tows using a minibongo net (30 cm; 250 μm mesh). The tows were made from variable depths depending on the stations but never exceeding 50 m. A sampling grid with 24 stations was used. Fish larvae abundance was between 69 and 16,837 larvae·1000 m -3 . Larval stages of 35 species belonging to 14 families were identified. Gobiidae (35%) and Sciaenidae (15%) were the most abundant and frequent families. Lythrypnus sp. (8,519 larvae·1000 m -3 ) and Sciaenidae spp. (6,553 larvae·1000 m -3 ) were the most abundant and frequent species. The analysis of larval spatial distribution suggested a tendency to aggregate towards the south of the study zone, approximately 5 km offshore. Significant differences were detected in the ichthyoplankton abundances between the eastern and the western zones of the study area (Mann-Whitney, p = 0.000062). However, no significant relationship was observed between ichthyoplankton abundance and average temperature (Spearman, R = -0.346), salinity (Spearman, R = 0.227), and water transparency (Spearman, R = 0.10).

How many trophic roles can elasmobranchs play in a marine tropical network

The aims of the present study were to identify the trophic roles of shark and batoid species in a tropical marine food web and to examine how ontogenetic dietary changes affect these roles. Elasmobranch species at different stages of maturity (juveniles and adults) are distributed at medium and high trophic levels (3.2–4.2), preying on numerous fish and invertebrates. Nine trophic groups comprising species at different stages of maturity were identified. Considering the maturity stages, elasmobranchs were found in five trophic groups and 37.5% of the regular equivalence nodes in the web. These species had roles as both predator and prey in four trophic levels of the web, participating in most of the roles identified, and are highly redundant in their functions as prey and mesopredators, but not in their role as top predators. The results of the present study suggest that elasmobranchs can be fundamental to the structure and function of marine food webs and highlight the need to include the effect of ontogenetic changes in the diet of these predators in future assessments of their ecological relevance.

Turtle ectoparasites from the Pacific coastal region of Colombia

This study provides an update on the ectoparasites (ticks and leeches) associated with Rhinoclemmys annulata and provides new accounts on the ectoparasites associated with R. nasuta, R. melanosterna andKinosternon leucostomum from the Pacific coast of Colombia. The presence ofAmblyomma sabanerae on R. nasuta and R. melanosterna provided two new host records for the tick species. Also, the documentation ofA. sabanerae from the Department of Valle del Cauca represents a new department record for the species in Colombia. Placobdella ringueleti was identified fromR. nasuta and K. leucostomum, which represents a new host record for the leech species, as well as a significant extension of the known range.