Concentrations and stable isotopes of mercury in sharks of the Galapagos Marine Reserve: Human health concerns and feeding patterns.

The human ingestion of mercury (Hg) from sea food is of big concern worldwide due to adverse health effects, and more specifically if shark consumption constitutes a regular part of the human diet. In this study, the total mercury (THg) concentration in muscle tissue were determined in six sympatric shark species found in a fishing vessel seized in the Galapagos Marine Reserve in 2017. The THg concentrations in shark muscle samples (n = 73) varied from 0.73 mg kg-1 in bigeye thresher sharks (Alopias superciliosus) to 8.29 mg kg-1 in silky sharks (Carcharhinus falciformis). A typical pattern of Hg bioaccumulation was observed for all shark species, with significant correlation between THg concentration and shark size for bigeye thresher sharks, pelagic thresher sharks (Alopias pelagicus) and silky sharks. Regarding human health concerns, the THg mean concentration exceeded the maximum weekly intake fish serving in all the studied species. Mass-Dependent Fractionation (MDF, δ202Hg values) and Mass-Independent Fractionation (MIF, Δ199Hg values) of Hg in whitetip sharks (Carcharhinus longimanus) and silky sharks, ranged from 0.70‰ to 1.08‰, and from 1.97‰ to 2.89‰, respectively. These high values suggest that both species are feeding in the epipelagic zone (i.e. upper 200 m of the water column). While, blue sharks (Prionace glauca), scalloped hammerhead sharks (Shyrna lewini) and thresher sharks were characterized by lower Δ199Hg and δ202Hg values, indicating that these species may focus their foraging behavior on prey of mesopelagic zone (i.e. between 200 and 1000 m depth). In conclusion, the determination of THg concentration provides straight-forward evidence of the human health risks associated with shark consumption, while mercury isotopic compositions constitute a powerful tool to trace the foraging strategies of these marine predators. CAPSULE: A double approach combining Hg concentrations with stable isotopes ratios allowed to assess ontogeny in common shark species in the area of the Galapagos Marine Reserve and the human health risks concern associated to their consumption.

International fisheries threaten globally endangered sharks in the Eastern Tropical Pacific Ocean: the case of the Fu Yuan Yu Leng 999 reefer vessel seized within the Galápagos Marine Reserve.

Shark fishing, driven by the fin trade, is the primary cause of global shark population declines. Here, we present a case study that exemplifies how industrial fisheries are likely depleting shark populations in the Eastern Tropical Pacific Ocean. In August 2017, the vessel Fu Yuan Yu Leng 999, of Chinese flag, was detained while crossing through the Galápagos Marine Reserve without authorization. This vessel contained 7639 sharks, representing one of the largest seizures recorded to date. Based on a sample of 929 individuals (12%), we found 12 shark species: 9 considered as Vulnerable or higher risk by the IUCN and 8 listed in CITES. Four species showed a higher proportion of immature than mature individuals, whereas size-distribution hints that at least some of the fishing ships associated with the operation may have been using purse-seine gear fishing equipment, which, for some species, goes against international conventions. Our data expose the magnitude of the threat that fishing industries and illegal trade represent to sharks in the Eastern Tropical Pacific Ocean.