Trophic ecology of common elasmobranchs exploited by artisanal shark fisheries off south-western Madagascar

Knowledge of the trophic ecology and interactions of marine top predators is fundamental for understanding community structure and dynamics as well as ecosystem function. We examined the feeding relationships of 4 heavily exploited elasmobranchs caught in coastal artisanal shark fisheries in south-western Madagascar in 2009 and 2010—Sphyrna lewini, Loxodon macrorhinus, Carcharhinus falciformis and Rhynchobatus djiddensis—using stable isotope (δ15N and δ13C) analysis. Relative trophic position (indicated by δ15N) and foraging location (indicated by δ13C) differed among species. Isotopic niche width was highly variable: more pelagic species, such as S. lewini and C. falciformis, had the broadest isotopic niches while the benthic R. djiddensis had the narrowest. A high percentage of niche overlap occurred between R. djiddensis and 2 of the species, C. falciformis (93.2%) and L. macrorhinus (73.2%), and to a lesser extent S. lewini (13.3%). Relative trophic position of S. lewini significantly increased with size, suggesting a dietary shift with age. Sex differences in δ15N values were observed in L. macrorhinus, suggesting intraspecific niche partitioning. Variation in stable isotope values among these 4 highly exploited elasmobranch species indicates trophic structuring, likely driven by differences in diet and habitat use as well as by size and sex. This study provides the first baseline information on the trophic ecology of elasmobranchs caught in artisanal fisheries from south-western Madagascar

Spatial ecology of Carcharias taurus in the northwestern Mid-Atlantic coastal ocean

The sand tiger shark Carcharias taurus is a highly migratory coastal species with declining populations worldwide. This species exhibits many behaviors that make coastal sharks difficult to manage, including aggregatory behavior, sexual segregation, and large-scale migrations through shallow coastal waters with many opportunities for human interactions. Sand tigers from the Western North Atlantic subpopulation are known to seasonally inhabit Delaware Bay and surrounding coastal waters. This region has been recommended as a habitat area of particular concern for the Western North Atlantic sand tiger population, and increased understanding of their movements and habitat requirements will facilitate management efforts. We developed models to predict sand tiger occupancy using spatially dynamic environmental predictors. Our models predicted sand tiger (juveniles, adult males, adult females, and all sharks combined) occurrences in 2 study regions, the Delaware Bay and the western Mid-Atlantic coastal ocean. Sea surface temperature, day of year, water depth, and remote sensing reflectance at 555 nm were the most important environmental predictors of occurrence, and correctly predicted 80-89% of sand tiger acoustic telemetry records in the 2 study regions. Our models predicted differences in the timing and location of occurrences among juveniles and adults, as well as areas where these life history stages overlap in the Mid-Atlantic coastal ocean. Our hope is that a daily forecast of sand tiger occurrence from our modeling efforts could be useful for conservation and management efforts in this important region, as well as for studying the spatial and behavioral ecology of this important top predator

Dietary overlap of carcharhinid sharks in the Gulf of Papua

Assessing the feeding patterns of sharks provides insight into ecological interactions. Three coastal sharks are common by-catch in the Gulf of Papua prawn fishery in Papua New Guinea. The diets of Carcharhinus coatesi (n = 122), Rhizoprionodon acutus (n = 83) and Rhizoprionodon taylori (n = 177) were assessed using stomach content analysis. Teleosts, crustaceans and molluscs were the main prey. Percentage frequency of occurrence (%FO) and percentage frequency by number (%N) were computed to describe dietary compositions. Non-metric multidimensional scaling and Morisita Index determined the level of feeding overlap. Rhizoprionodon taylori was a generalist feeder having the broadest diet, R. acutus was the most selective feeder, preying predominantly on teleosts and C. coatesi consumed the greatest proportion of crustaceans that increased with size. The pairwise ANOSIM tests showed significant difference in dietary compositions of R. acutus and R. taylori (P = 0.1%, R = 0.318) and R. acutus and C. coatesi (P = 0.1%, R = 0.589), which indicate potential resource partitioning. Further work should aim to adequately characterise diets, improve prey identification and investigate spatial and temporal resource use patterns. Understanding ecological processes informs ecosystem approaches fisheries management

Seasonal Movements and Habitat Use of Juvenile Smooth Hammerhead Sharks in the Western North Atlantic Ocean and Significance for Management

Upper trophic level predators dramatically impacted by fisheries include the large-bodied hammerhead sharks, which have become species of conservation concern worldwide. Implementing spatial management for conservation of hammerhead populations requires knowledge of temporal distribution patterns and habitat use, identification of essential habitat for protection, and quantification of interactions with human activities. There is little such information for the smooth hammerhead shark, Sphyrna zygaena. We used fin-mounted satellite tags to examine the movements and habitat use of juvenile smooth hammerheads, a demographic segment particularly threatened by exploitation. Six sharks were tagged off the US mid-Atlantic and tracked for 49–441 days (mean 187 ± 136 days). Sharks consistently showed area-restricted movements within a summer core area in waters of the New York Bight and a winter core area off Cape Hatteras, North Carolina, with directed movements between them in autumn. There was high overlap of shark winter core area use and the Mid-Atlantic Shark Area (MASA) – a 7 month per year, bottom-longline fishery closure – indicating that this area closure offers seasonal reduction in fishing pressure for this species. Based on timing of shark movements and the MASA closure, protection for juvenile smooth hammerheads may be increased by beginning the closure period 1 month earlier than currently scheduled. Generalized additive mixed models revealed that area-restricted movements of sharks in their summer and winter core areas coincided with high primary productivity, and elevated sea surface temperature. Consistency in use of summer and winter core areas suggests that the coastal waters of the New York Bight and Cape Hatteras, North Carolina could be considered for Essential Fish Habitat designation for this species. This study reveals the first high resolution movements and habitat use for smooth hammerheads in the western North Atlantic to inform management planning for this population

Seasonal Movements and Habitat Use of Juvenile Smooth Hammerhead Sharks in the Western North Atlantic Ocean and Significance for Management

Upper trophic level predators dramatically impacted by fisheries include the large-bodied hammerhead sharks, which have become species of conservation concern worldwide. Implementing spatial management for conservation of hammerhead populations requires knowledge of temporal distribution patterns and habitat use, identification of essential habitat for protection, and quantification of interactions with human activities. There is little such information for the smooth hammerhead shark, Sphyrna zygaena. We used fin-mounted satellite tags to examine the movements and habitat use of juvenile smooth hammerheads, a demographic segment particularly threatened by exploitation. Six sharks were tagged off the US mid-Atlantic and tracked for 49–441 days (mean 187 ± 136 days). Sharks consistently showed area-restricted movements within a summer core area in waters of the New York Bight and a winter core area off Cape Hatteras, North Carolina, with directed movements between them in autumn. There was high overlap of shark winter core area use and the Mid-Atlantic Shark Area (MASA) – a 7 month per year, bottom-longline fishery closure – indicating that this area closure offers seasonal reduction in fishing pressure for this species. Based on timing of shark movements and the MASA closure, protection for juvenile smooth hammerheads may be increased by beginning the closure period 1 month earlier than currently scheduled. Generalized additive mixed models revealed that area-restricted movements of sharks in their summer and winter core areas coincided with high primary productivity, and elevated sea surface temperature. Consistency in use of summer and winter core areas suggests that the coastal waters of the New York Bight and Cape Hatteras, North Carolina could be considered for Essential Fish Habitat designation for this species. This study reveals the first high resolution movements and habitat use for smooth hammerheads in the western North Atlantic to inform management planning for this population

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

<p>Abstract</p> <p>Background</p> <p>Stomach contents of 131 specimens of five elasmobranch species (<it>Mustelus lunulatus</it>, <it>Dasyatis longa</it>, <it>Rhinobatos leucorhynchus</it>, <it>Raja velezi </it>and <it>Zapteryx xyster</it>) caught in the central fishing zone in the Pacific Ocean of Colombia were counted and weighed to describe feeding habits and dietary overlaps.</p> <p>Results</p> <p>Twenty-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 <it>Squilla panamensis </it>was the main prey item in the diet of <it>M. lunulatus</it>; tiger shrimp <it>Trachypenaeus </it>sp. was the main prey item in the diet of <it>Rhinobatos leucorhynchus </it>and <it>Raja velezi</it>, and Penaeidae shrimp were the main prey items in the diet of <it>Z. xyster</it>. Furthermore, fish were important in the diet of <it>Raja velezi, Z. xyster </it>and <it>D. longa</it>. The greatest diet breadth corresponded to <it>Z. xyster </it>whereas <it>M. lunulatus </it>was the most specialized predator. Finally, four significant diet overlaps between the five species were found, attributable mainly to Squillidae, Penaeidae and Fish.</p> <p>Conclusion</p> <p>Shrimps (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.</p

Talla de madurez y relación peso-talla del tiburón de profundidad Etmopterus bigelowi (Squaliformes: Etmopteridae) capturado en el sudeste de Brasil

The blurred lantern shark Etmopterus bigelowi, a deep-water squaloid shark, is globally widespread in temperate and tropical waters, but there is little available information about its biology owing to its relative rarity of capture and taxonomic confusion with its sibling species Etmopterus pusillus. Specimens used in this study were collected from July to December 2004 as by-catch in the commercial deepwater trawl fishery targeting red shrimp Aristaeomorpha foliacea in the southwestern Atlantic. We examined 55 specimens (22 males and 33 females) ranging in total length (TL) from 31.5 to 73 cm and in total weight from 103 to 1600 g. Length-weight relationships were explored for each sex and significant differences were found in the slope coefficients of the male and female regressions. The size at maturity for each sex was evaluated fitting a logistic regression. Females matured at larger sizes than males, with estimated sizes at first maturity of 56.0 cm TL for females and 45.1 cm TL for males. The present study provides important preliminary information about E. bigelowi that can be incorporated in risk assessment and stock assessment models, essential for efficient management practices aimed at avoiding overexploitation of these vulnerable deep-sea sharks.El tiburón de profundidad Etmopterus bigelowi se distribuye globalmente en aguas templadas y tropicales; sin embargo, hay poca información disponible sobre su biología ya que raramente se captura y existe confusión taxonómica con su especie hermana Etmopterus pusillus. Los ejemplares utilizados en este trabajo se obtuvieron de julio a diciembre de 2004 como captura incidental de la pesca comercial de arrastre de aguas profundas dirigida al camarón rojo Aristaeomorpha foliacea en el Atlántico sudoccidental. Se examinaron 55 ejemplares (22 machos y 33 hembras) de 31.5 a 73 cm de longitud total (LT) y de 103 a 1600 g de peso total. Se analizó la relación peso-talla para ambos sexos, observándose diferencias significativas en las pendientes de las regresiones, tanto de hembras como de machos. La talla de madurez para cada sexo se evaluó ajustando una regresión logística. La talla de primera madurez de las hembras (56.0 cm LT) fue mayor que la de los machos (45.1 cm LT). El presente trabajo aporta información preliminar esencial sobre E. bigelowi que puede ser incorporada en modelos de evaluación de riesgo y evaluación de la población, cruciales para prácticas de gestión dirigidas a evitar la sobreexplotación de estos vulnerables tiburones de aguas profundas.info:eu-repo/semantics/publishedVersio