Trophic resources and mercury exposure of two silvertip shark populations in the Northeast Pacific Ocean

Abstract

Worldwide shark populations have experienced rapid declines over the last decades, mainly due to overfishing. Marine protected areas (MPAs) have thus become an indispensable tool for the protection of these marine predators. Two recently-created MPAs in the Northeast Pacific Ocean, the Revillagigedo National Park and Clipperton atoll, are characterized by different trophic structures potentially influencing trophic niche and contaminant exposure for resident sharks in these two sites. In this context, we used carbon (δ13C) and nitrogen (δ15N) stable isotope analyzes as well as total mercury concentrations ([THg]) to assess the role of foraging site on the trophic niche and Hg levels of juvenile ST sharks Carcharhinus albimarginatus. Analyzing fin clip samples from both Revillagigedo and Clipperton, we found that shark δ15N varied spatially in relation to δ15N baselines, suggesting similar trophic position in both MPAs. Moreover, δ13C values indicated that ST sharks from Revillagigedo would feed on different food webs (i.e. both benthic and pelagic) while individuals from Clipperton would only rely on benthic food webs. These differences between MPAs led to a weak overlap of isotopic niche between the two populations, highlighting site residency for juvenile ST sharks. Within populations, [THg] was not correlated to trophic tracers (δ15N and δ13C) and was also similar between populations. This study revealed no influence of site or food web in [THg] and raises the question of the origin of Hg exposure for reef shark populations in the Northeast Pacific Ocean.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.

Mercury isotopes as tracers of ecology and metabolism in two sympatric shark species

“…Top predators using coastal ecosystems are known to feed on different food webs (Bird et al, 2018), inducing exposure to different sources and concentrations of contaminants (Le Croizier et al, 2016, 2019b. To characterize dietary resources, nitrogen and carbon stable isotopes (δ 15 N and δ 13 C) are traditionally used in ecotoxicological studies (Le Bourg et al, 2019;Le Croizier et al, 2020), reflecting respectively the trophic position (Pethybridge et al, 2018) and foraging habitat (Bird et al, 2018) of consumers. However, these tools show limitations, such as the variability of N and C isotopic fractionation during trophic transfers (Kim et al, 2012;Malpica-Cruz et al, 2012).…”

Total mercury and methylmercury (MeHg) in braised and crude Boletus edulis carpophores during various developmental stages

“…Thus, Hg in low concentrations is a notorious contaminant of both, vegetarian and nonvegetarian diets. Within nonvegetarian foods, it occurs at lowest levels in farmed livestock and at higher levels in game, but the highest focus is on its presence in fish and seafood (Le Croizier et al 2020 ; Nawrocka et al 2020 ; Petrova et al 2020 ). The exposure to Hg and its effects in human are largely linked to the occurrence of MeHg in the muscle tissues of marine fish and other seafood, where it is a major or almost the sole Hg compound (Brambilla et al 2013 ).…”