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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.

Bathymetric features such as islands and seamounts, as well as dynamic ocean features such as fronts often harbour rich marine communities. We deployed mid-water baited remote underwater video systems on three expeditions in Ascension Island’s Exclusive Economic Zone (EEZ), surveying the waters associated with six different bathymetric and dynamic ocean features: Ascension Island, two shallow seamounts (summits ≤ 101 m), one deeper seamount (summit > 250 m), apparent fronts, and haphazardly sampled open ocean areas. At Ascension Island, the pelagic assemblage consisted of a moderate proportion of predators and a diverse range of other taxa, including turtles, dolphins, and large non-piscivores. At the two shallow seamounts, sharks, tunas, billfish, and other large pelagic predators formed the vast majority of the assemblage, contributing > 99.9% of biomass and > 86% of abundance. At the deeper seamount, the pelagic community was comparatively depauperate, however the functional composition of its assemblage indicated some similarities to the shallow seamounts. Apparent fronts did not significantly differ from random offshore sites for metrics such as total abundance and taxonomic richness. However, they harboured assemblages with more abundant sharks, tunas, and large piscivores than random ocean open locations and these differences may be driven by certain front-associated species. Our results illustrate that pelagic assemblages vary markedly among different physical and oceanographic features and that seamounts appear particularly important for pelagic predators. The diversity and abundance of the assemblage, as well as the threatened status of many of the species observed, serve to highlight the conservation value of the Ascension Island EEZ. Our results also provide important baseline information of pelagic wildlife assemblages against which the performance of the recently implemented Ascension Island Marine Protected Area can be evaluated.

Tristan da Cunha Islands, an archipelago of four rocky volcanic islands situated in the South Atlantic Ocean and part of the United Kingdom Overseas Territories (UKOTs), present a rare example of a relatively unimpacted temperate marine ecosystem. We conducted the first quantitative surveys of nearshore kelp forests, offshore pelagic waters and deep sea habitats. Kelp forests had very low biodiversity and species richness, but high biomass and abundance of those species present. Spatial variation in assemblage structure for both nearshore fish and invertebrates/algae was greatest between the three northern islands and the southern island of Gough, where sea temperatures were on average 3-4o colder. Despite a lobster fishery that provides the bulk of the income to the Tristan islands, lobster abundance and biomass are comparable to or greater than many Marine Protected Areas in other parts of the world. Pelagic camera surveys documented a rich biodiversity offshore, including large numbers of juvenile blue sharks, Prionace glauca. Species richness and abundance in the deep sea is positively related to hard rocky substrate and biogenic habitats such as sea pens, crinoids, whip corals, and gorgonians were present at 40% of the deep camera deployments. We observed distinct differences in the deep fish community above and below ~750 m depth. Concurrent oceanographic sampling showed a discontinuity in temperature and salinity at this depth. While currently healthy, Tristan's marine ecosystem is not without potential threats: shipping traffic leading to wrecks and species introductions, pressure to increase fishing effort beyond sustainable levels and the impacts of climate change all could potentially increase in the coming years. The United Kingdom has committed to protection of marine environments across the UKOTs, including Tristan da Cunha and these results can be used to inform future management decisions as well as provide a baseline against which future monitoring can be based.

Marine fjords along the northern Labrador coast of Arctic Canada are influenced by freshwater, nutrients, and sediment inputs from ice fields and rivers. These ecosystems, further shaped by both Atlantic and Arctic water masses, are important habitats for fishes, marine mammals, seabirds, and marine invertebrates and are vital to the Labrador Inuit who have long depended on these areas for sustenance. Despite their ecological and socio-cultural importance, these marine ecosystems remain largely understudied. Here we conducted the first quantitative underwater scuba surveys, down to 12 m, of the nearshore marine ecology of Nachvak Fjord, which is surrounded by Torngat Mountains National Park located in Nunatsiavut, the Indigenous lands claim region of northeastern Canada. Our goal was to provide the Nunatsiavut Government with a baseline of the composition and environmental influences on the subtidal community in this isolated region as they work towards the creation of an Indigenous-led National Marine Conservation Area that includes Nachvak Fjord. We identified four major benthic habitat types: (1) boulders (2) rocks with sediment, (3) sediment with rocks, and (4) unconsolidated sediments, including sand, gravel, and cobble. Biogenic cover (e.g., kelp, coralline algae, and sediment) explained much of the variability in megabenthic invertebrate community structure. The kelp species Alaria esculenta, Saccharina latissima, and Laminaria solidungula dominated the boulder habitat outside of the fjord covering 35%, 13%, and 11% of the sea floor, respectively. In contrast, the middle and inner portions of the fjord were devoid of kelp and dominated by encrusting coralline algae. More diverse megabenthic invertebrate assemblages were detected within the fjord compared to the periphery. Fish assemblages were depauperate overall with the shorthorn sculpin, Myoxocephalus scorpius, and the Greenland cod, Gadus ogac, dominating total fish biomass contributing 64% and 30%, respectively. Understanding the composition and environmental influences within this fjord ecosystem not only contributes towards the protection of this ecological and culturally important region but serves as a baseline in a rapidly changing climatic region.

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.