Sharks are the preferred scraping surface for large pelagic fishes: Possible implications for parasite removal and fitness in a changing ocean

Abstract

Mutualistic and commensal interactions can have significant positive impacts on animal fitness and survival. However, behavioural interactions between pelagic animals living in offshore oceanic environments are little studied. Parasites can negatively effect the fitness of their hosts by draining resources and diverting energy from growth, reproduction, and other bodily functions. Pelagic fishes are hosts to a diverse array of parasites, however their environment provides few options for removal. Here we provide records of scraping behaviour of several pelagic teleost species, a behaviour that is likely used for parasite removal. These records span three ocean basins and, to the best of our knowledge, include the first records of scraping interactions involving tunas, blue sharks, and mako sharks as well as the first records of intraspecific scraping. 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. Scraper species varied in their scraping preferences with tunas scraping mostly on the posterior caudal margins of sharks and occasionally conspecifics, while rainbow runner scraped in more varied locations on both sharks and conspecifics. Lengths of scrapers and scrapees were positively correlated and fish scraping on sharks were larger than those scraping on conspecifics, suggesting that risk of predation may be a limiting factor. We show that pelagic teleosts prefer to scrape on sharks rather than conspecifics or other teleosts and suggest that this behaviour may have a positive impact on teleost fitness by reducing parasite loads. The decline of shark populations in the global ocean and the reduction in mean size of many species may limit these interactions, eroding possible fitness benefits associated with this behaviour, and consequently placing more pressure on already highly targeted and vulnerable species.

Studying Chondrichthyans Using Baited Remote Underwater Video Systems: A Review

“…This type of BRUVS allows us to record a wide range of sharks, rays [14,24,26,48], and chimeras [47,74,79,93]. Mid-water and pelagic drifting BRUVS, although less used and with fewer records of Chondrichthyans, are useful to monitor pelagic species such as Sphyrna spp., Carcharhinus spp., Alopias pelagicus, Prionace glauca, Isurus oxyrinchus, Mobula birostris, Galeocerdo cuvier [22,25,30,40,58,68,70,71,83]. From the standard set-ups, there are some exceptions, such as drifting deep-water BRUVS used for the construction of species distribution models [35] and baited drumline cameras used to meet special study goals, such as asses the fishing efficacy of baited hooks [60].…”

“…The method's versatility has proven crucial for conservation efforts, providing essential insights into species diversity, distribution, and the impacts of marine protected areas, ultimately aiding in the development of informed management strategies [20]. To date, BRUVS have been successfully used to monitor sharks, rays, and chimeras worldwide [14,20,22,23]. However, despite the increasing prevalence of this technique in the literature, a comprehensive review of the potential of BRUVS in the study of cartilaginous fish is still lacking.…”

Remote seamounts are key conservation priorities for pelagic wildlife

“…Declines in pelagic wildlife weaken ecosystem functioning, drive biodiversity loss, and undermine food security and economic stability for many of the world's people.Remote regions of the ocean that remain less impacted by humans are refuges for mobile and heavily targeted species. These regions harbor wildlife assemblages with higher diversity, greater abundance, larger size, and increased biomass, and can yield valuable insights into ecological processes (Campbell et al, 2020;Juhel et al, 2019;Thompson & Meeuwig, 2022). Remote regions offer a glimpse of what the ocean was like prior to largescale anthropogenic impact, a source from which the rest of the ocean can be regenerated, and a benchmark for marine protected areas (MPAs) and fisheries management.…”