University of Western Australia: Large fish prefer using sharks for scraping

Research by marine biologists from The University of Western Australia has found sharks are the preferred scraping surface for large pelagic fishes, which could help improve their health.

National Geographic Pristine Seas Postdoctoral Research Fellow Dr Chris Thompson and Professor Jessica Meeuwig, from The University of Western Australia’s Marine Futures Lab and School of Biological Sciences, were authors of the study published in PLOS One.

“Parasites can negatively affect the fitness of their hosts by draining resources and diverting energy from growth, reproduction and other bodily functions,” Dr Thompson said.

“Pelagic fishes are hosts to a diverse array of parasites, however their environment provides few options for removal.”

The research spanned three ocean basins and recorded scraping interactions involving tuna, blue sharks and mako sharks as well as the first records of scraping within the same species.

“We found that scrapers preferred scraping their head, eyes, gill cover and lateral surfaces – areas where parasites are commonly found and where damage would likely have a substantial impact on fitness,” Professor Meeuwig said.

The scraper species varied in their scraping preferences with tuna scraping mostly on the tail end of sharks and occasionally members of the same species, while rainbow runner fish scraped in more varied locations on both sharks and other rainbow runners.

“Lengths of scrapers and scrapees were positively correlated and fish scraping on sharks were larger than those scraping on members of the same species, suggesting that risk of predation may be a limiting factor,” Dr Thompson said.

“The decline of shark populations in the world’s oceans and the reduction in mean size of many species may limit these interactions, eroding possible fitness benefits associated with this behaviour and consequently place more pressure on already highly targeted and vulnerable species.”