title: Population and individual foraging patterns of two hammerhead sharks using carbon and nitrogen stable isotopes.
abstract: BACKGROUND
  Individual foraging behavior is an important variable of predators commonly studied at the population level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods.
  
  
  METHODS
  We determined the isotopic composition (δ(13)C and δ(15)N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values.
  
  
  RESULTS
  There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ(15)N values of S. zygaena vertebrae, with lower values in the first group of samples.
  
  
  CONCLUSIONS
  Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology.
authors.affiliation: Universidad Laica Eloy Alfaro de Manabí, Departamento Central de Investigación, Vía San Mateo S/N, Manta, Manabí, Ecuador.|Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, P.O. Box 592, 23096, La Paz, Baja California Sur, México.
authors.forename: P
authors.initials: P
authors.lastname: Loor-Andrade
authors.affiliation: Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, P.O. Box 592, 23096, La Paz, Baja California Sur, México.
authors.forename: F
authors.initials: F
authors.lastname: Galván-Magaña
authors.affiliation: Centro Interdisciplinario de Ciencias Marinas, Av. IPN s/n, P.O. Box 592, 23096, La Paz, Baja California Sur, México.
authors.forename: F R
authors.initials: FR
authors.lastname: Elorriaga-Verplancken
authors.affiliation: Oficina de Generación del Conocimiento y la Información, Autoridad Nacional de Acuicultura y Pesca, Calle 40a No. 13-09, Piso 6., Bogotá, Colombia.
authors.forename: C
authors.initials: C
authors.lastname: Polo-Silva
authors.affiliation: Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de las Palmeras 4, 18100, Armilla, Granada, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Delgado-Huertas