Résumé
We quantified temporal changes in blood plasma delta C-13 and delta N-15 values collected from recaptured juvenile blacktip reef sharks (Carcharhinus melanopterus, n = 14) and sicklefin lemon sharks (Negaprion acutidens, n = 4) at liberty in Moorea, French Polynesia for 10-50 days, and juvenile bull sharks (Carcharhinus leucas,, n = 7) at liberty in the Florida Coastal Everglades for 34-127 days to investigate shifts in assimilated biomass from energy reserves and consumed biomass. Blacktip reef and bull sharks exhibited significant changes in plasma delta C-13 as they grew, with a mean Delta delta C-13/cm total length +/- SD of 0.41 parts per thousand/cm +/- 0.72 and-0.82 parts per thousand/cm +/- 0.67. While low sample sizes precluded statistical analyses, sicklefin lemon exhibited a change of 0.49 parts per thousand/cm +/- 0.77. Blacktip reef sharks and bull sharks also exhibited significant shifts in delta N-15 values - mean Delta delta N-15/cm TL +/- SD = -0.23 parts per thousand/cm +/- 0.59, and -0.24 parts per thousand/cm +/- 0.20; shifts in delta N-15 values for sicklefin lemon sharks averaged 0.19 parts per thousand/cm +/- 0.52. When data were normalized across species (accounting for species-specific difference in delta C-13 and delta N-15 ranges), no significant difference were found in the rate of delta N-15 change between bull and blacktip reef sharks, but mean changes in delta C-13/day among blacktip reef and sicklefin lemon sharks (similar to 1%/day) were twice as fast as bull sharks (similar to 0.5%/day). Comparisons between plasma and muscle isotope values in bull sharks yielded similar results to comparisons of plasma isotope values - rapid changes in delta C-13 and delta N-15. The magnitude and direction of changes in delta C-13 and delta N-15 values, however, were not uniform among individuals within each species, suggesting intraspecific variation in trophic interactions within the shark nurseries studied. Further studies quantifying shifts in energy pathways may contribute to elucidating the factors that shape foraging development in sharks and variation in trophic interactions within shark nurseries. (C) 2015 Elsevier B.V. All rights reserved.