Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.

Bird_etal_shark_trophic_geography Carbon isotope data compiled from muscle tissues of 5394 sharks from 114 species. Data provided include d13C values, latitude of capture, designation as shelf, slope or oceanic shark, length, depth of capture (where available), C/N ratios of muscle, and lipid extraction method if used. Also included are phytoplankton d13C data modelled from Magozzi et al 2016 (Ecosphere 8(5):e01763. 10.1002/ecs2.1763). Model data expressed as the median and standard deviation d13C value for the Longhurst Biogeographic province corresponding to the location of shark capture

Peer reviewed