Andrés F. Navia

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.

Reproductive variables of Urotrygon rogersi (Batoidea: Urotrygonidae): a species with a triannual reproductive cycle in the eastern tropical Pacific Ocean.

Reproductive aspects of the round ray Urotrygon rogersi were studied based on 2005 specimens obtained in the artisanal shrimp fishery operating on the Colombian Pacific coast. Females reached greater maximum total length (L(T) ), disc width (W(D) ) and mass (M) (38·0 cm, 19·9 cm and 348 g) than males (32·5 cm, 17·0 cm and 165 g). Sex ratio of juveniles and adults was 1:1. Clasper length increased rapidly between 10·0 and 12·5 cm W(D) . The smallest mature male measured 10·5 cm W(D) and the largest immature individual 13·7 cm W(D) . Male first maturity was reached at 61·8% of maximum W(D) , and estimated W(D50) was between 11·5 and 11·8 cm. The smallest mature female measured 10·5 cm W(D) ; the size at first maturity was 52·8% of maximum W(D) , and estimated W(D50) was between 11·8 and 12·3 cm. Embryos were found in females ≥ 10·5 cm W(D) and maximum fecundity was three embryos per female (mode = 1) and varied with maternal size. Embryos were found in all months, but three birthing peaks per year were identified and a gestation period of 4-5 months estimated. Based on ovulation time, embryonic growth and parturition dates, a triannual reproductive cycle was inferred for this species, with overlapping ovarian and uterine cycles. These results suggest that U. rogersi has a reproductive strategy based on low fecundity, a rapid reproductive cycle (short ovulation and gestation time), three birth peaks per year and large embryos. This strategy probably allows U. rogersi to withstand the fishing pressure they are subject to on the Colombian Pacific coast. The results also suggest that the study area is an important nursery and reproductive area for this species.

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.

Feeding habits and trophic ecology of Dasyatis longa (Elasmobranchii: Myliobatiformes): sexual, temporal and ontogenetic effects.

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 Levins niche breadth index and the Piankas 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.

Changes to Marine Trophic Networks Caused by Fishing

Andres F. Navia1,2, Enric Cortes3, Ferenc Jordan4, Victor H. Cruz-Escalona2 and Paola A. Mejia-Falla1 1Fundacion Colombiana Para la Investigacion y Conservacion de Tiburones y Rayas SQUALUS 2Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional 3NOAA, National Marine Fisheries Service, Panama City Laboratory 4The Microsoft Research – University of Trento COSBI, Trento 1Colombia 2Mexico 3USA 4Italy

First record of morphological abnormality in embryos of Urotrygon rogersi (Jordan & Starks, 1895) (Myliobatiformes: Urotrygonidae) in the Tropical Eastern Pacific

Resumen en: This is the first report of morphological abnormalities in embryos of Rogers roundray Urotrygon rogersi in the Tropical Eastern Pacific. The embryos of ...

Biología de la raya guitarra Rhinobatos leucorhynchus (Günther, 1867) (Rajiformes: Rhinobatidae) en el Pacífico colombiano

The guitar ray Rhinobatos leucorhynchus is commonly caught as by-catch of industrial and artisanal shrimp trawling in the shallow waters of the Colombian Pacific. The biological aspects of this species were studied using 286 animals caught as by-catch between 2001 and 2007. The females were proportionally larger than males, although growth was similar (allometric) for both sexes. The embryos showed no significant differences by sex in either size or weight. The adult sex ratio was 2.4:1 (females-males), whereas in embryos this ratio was 1:1. 51.5% of males, 51.5% had developed, calcified claspers, and 56.5% of females were pregnant, carrying between 1 and 6 embryos of 3 to 19.5 cm, suggesting a size at birth of 19 to 19.5 cm TL. The median size at maturity for females was lower than that of males (48.48 cm and 51.18 cm TL, respectively), and the females had embryos starting at 44 cm TL. The feeding habits of this species showed 30 prey items, with shrimp from the Penaeidae family and especially Trachypenaeus sp. as main food. The diets of male and female guitar rays differed significantly, and the niche breadth indicated that this species has a specialist diet. The results of this study provide useful information for proposing management measures for R. leucorhynchus, a species that requires attention given its biological characteristics and its importance in terms of commerce and human consumption.

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.

Zoogeography of Elasmobranchs in the Colombian Pacific Ocean and Caribbean Sea

In order to investigate zoogeographical patterns of the marine elasmobranch species of Colombia, species richness of the Pacific and Caribbean and their subareas (Coastal Pacific, Oceanic Pacific, Coastal Caribbean, Oceanic Caribbean) was analyzed. The areas shared 10 families, 10 genera and 16 species of sharks, and eight families, three genera and four species of batoids. Carcharhinidae had the highest contribution to shark richness, whereas Rajidae and Urotrygonidae had the greatest contribution to batoid richness in the Caribbean and Pacific, respectively. Most elasmobranchs were associated with benthic and coastal habitats. The similarity analysis allowed the identification of five groups of families, which characterize the elasmobranch richness in both areas. Beta diversity indicated that most species turnover occurred between the Coastal Pacific and the two Caribbean subareas. The difference in species richness and composition between areas may be due to vicariant events such as the emergence of the Isthmus of Panama. It is unlikely that the Colombian elasmobranch diversity originated from a single colonization event. Local diversification/speciation, dispersal from the non-tropical regions of the Americas, a Pacific dispersion and an Atlantic dispersion are origin possibilities without any of them excluding the others.