Can biochemical tracers reveal ontogenetic trophic shift and individual prey selection in white sharks from Guadalupe Island, Northeast Pacific?
Photo Credit: © Juan Sharks
Can biochemical tracers reveal ontogenetic trophic shift and individual prey selection in white sharks from Guadalupe Island, Northeast Pacific?
Gaël Le Croizier | Mauricio Hoyos-Padilla | Felipe Amezcua-Martínez | Marc Aquino-Baleytó | Lucien Besnard | Fabienne Le Grand | François Le Loc’h | Margaux Mathieu-Resuge | Jean-Marie Munaron | Arthur Ory | Fany Sardenne | Gauthier Schaal | Anne Lorrain
Environmental Research 262 (2024); 119507
DOI: https://doi.org/10.1016/j.envres.2024.119507
Highlights
Stable isotope and fatty acid analyses in white sharks from Guadalupe Island
No significant influence of size on the biochemical composition of sharks
Fatty acids suggest that most sharks fed on pelagic prey and only a few on pinnipeds
Different trophic strategies may be driven by energetic and physiological needs
Abstract
Refining the role of apex predators in marine food webs is a necessary step in predicting the consequences of their global decline under the footprint of fishing activities. White sharks (Carcharodon carcharias) are vulnerable predators, performing large migrations and able to forage on a variety of prey in different habitats. In the Northeast Pacific, juvenile and adult white sharks are found seasonally at the same aggregation sites, such as Guadalupe Island off Mexico. While adults are thought to target local pinniped colonies, very few prey-predator interactions have been documented and the diet of juveniles in this area remains poorly understood. Here we used carbon/nitrogen stable isotopes and fatty acids to characterize the trophic ecology of white sharks at Guadalupe Island. In contrast to the ontogenetic trophic shift paradigm, we detected no influence of size on muscle stable isotope and fatty acid composition, revealing no significant dietary variation between juvenile and adult sharks. Stable isotopes did not allow definitive conclusions to be drawn regarding the diet of white sharks at Guadalupe Island, due to significant variability in the contribution of different potential prey depending on the trophic discrimination factors used. However, most sharks were rich in polyunsaturated fatty acids (such as long-chain omega 3), suggesting a local diet of mainly pelagic prey (potentially large fish or cephalopods). A few individuals appeared to show recent consumption of pinnipeds, with higher proportions of saturated and monounsaturated fatty acids. These individual differences in fatty acid composition could reflect an ecological trade-off between consumption of prey rich in fat (marine mammals) versusprey rich in polyunsaturated fatty acids (pelagic prey), respectively meeting the energetic and physiological needs of white sharks. Although ontogenetic trophic changes were not able to be discerned, our results thus provide new insights into the physiological drivers of predator-prey interactions, which can benefit the definition of conservation strategies in a changing ocean.
Keywords: Stable isotope, Fatty acids, Pelagic prey, White shark