Tiny parasites that hitch a ride on the lips of whale sharks store enough dietary information to help scientists manage the species ongoing conservation
Researchers at The University of Western Australia and the Australian Institute of Marine Science (AIMS) tracked 72 whale sharks in WA’s Ningaloo Reef region over six years and found the ‘copepod’ parasite acts like a black box of stored information about the species’ diet and energy flow.
Observing what whale sharks eat can be challenging because the species is rare and often feeds at night or in very deep water, so researchers used a microchemistry (isotopes) approach to look at their diet.
Lead researcher Brendon Osorio, a recent graduate from UWA’s School of Biological Sciences, said carbon and nitrogen isotope compositions were analysed from both whale shark skin and the copepods, with nitrogen, in particular, showing a strong correlation.
“Our results suggest the nitrogen composition of parasitic copepods provides a reliable and accurate proxy of the whale sharks’ diet integrated over both time and space,” Mr Osorio said.
“Direct observation of whale sharks may only reveal part of their diet activity at any one point in time, whereas this biochemical analysis of host-specific parasites makes it possible to obtain more comprehensive insights into whale shark feeding at weekly and monthly time scales.
“Given that the nutrition provided in coastal aggregations is likely to be critical to individual growth and the demography of whale shark populations, understanding diet and foraging habitats within these sites is important for strategies to manage and conserve the populations.”
The largest filter-feeding fish in the world, the whale shark is currently listed as endangered under the International Union for Conservation and Nature’s Red List.
Adjunct Senior Research Fellow Dr Mark Meekan, from UWA’s Oceans Institute, said threats to the species’ existence included hunting, ship strike, pollution and climate change, which could impact the distribution of the plankton that whale sharks feed on.
“A better understanding of the life history and ecology of copepods is still required to fully understand the relationship between the whale shark host and its parasite, but the latest study had shown copepods to be an accurate and less invasive method of diet analysis than biopsies,” Dr Meekan said.