Parasitic Copepods as Biochemical Tracers of Foraging Patterns and Dietary Shifts in Whale Sharks (Rhincodon typus Smith, 1828)

Understanding the diet of whale sharks (Rhincodon typus) is essential for the development of appropriate conservation strategies for the species. This study evaluated the use of the parasitic copepod (Pandarus rhincodonicus) as a proxy to infer short-term foraging habitats and trophic positions of whale shark hosts. To accomplish this, bulk stable carbon (d(13)C) and nitrogen (d(15)N) isotope compositions were analysed from 72 paired samples of whale shark skin (dermal) tissues and copepods collected across six years at the Ningaloo Reef aggregation site, Western Australia. This study found that d(15)N from parasites and whale shark hosts were strongly correlated. As turn-over times of the parasite and whale shark differ (months vs. years, respectively), the ability of copepods to predict d(15)N values indicates that the trophic positions of whale sharks remain consistent across these timeframes. Contrastingly, d(13)C in the parasite and host were weakly correlated, likely reflecting differences in the physiology and lifecycle of the copepod parasite compared to the host. Our results suggest d(15)N from parasitic copepods provides a reliable proxy of the trophic position of their whale shark hosts, but interpretation of d(13)C values as a proxy for the host will require future studies on the lifecycle of P. rhincodonicus.

Automated summary

Understanding the diet of whale sharks is crucial for conservation strategies, and this study suggests that parasitic copepods can be used as a proxy to infer the short-term foraging habitats and trophic positions of whale shark hosts. The study found a strong correlation between the nitrogen isotope compositions of the parasites and whale shark hosts, indicating consistent trophic positions over time. However, the carbon isotope compositions showed a weak correlation, suggesting differences in physiology and lifecycle between the copepod parasite and the host.