Elevated accumulation of the toxic metal mercury in the Critically Endangered oceanic whitetip shark Carcharhinus longimanus from the northwestern Atlantic Ocean

Abstract

The oceanic whitetip shark Carcharhinus longimanus is a widely distributed large pelagic shark species once considered abundant in tropical and warm temperate waters, but recently listed as Critically Endangered by the IUCN due to drastic population declines associated with overfishing. In addition to risks posed to its populations due to overexploitation, oceanic whitetip sharks are also capable of accumulating elevated quantities of harmful environmental toxicants, placing them at special risk from anthropogenic pollution. Herein, we provide the first data on accumulation of the toxic, non-essential metal mercury (Hg) in northwest Atlantic (NWA) oceanic whitetip sharks, focusing on aggregations occurring at Cat Island, The Bahamas. Total Hg (THg) concentrations were measured in muscle of 26 oceanic whitetip sharks and compared with animal length and muscle δ15N to evaluate potential drivers of Hg accumulation. THg concentrations were also measured in fin and blood subcomponents (red blood cells and plasma) to determine their value as surrogates for assessing Hg burden. Muscle THg concentrations were among the highest ever reported for a shark species and correlated significantly with animal length, but not muscle δ15N. Fin, red blood cell, and plasma THg concentrations were significantly correlated with muscle THg. Fin THg content was best suited for use as a surrogate for estimating internal Hg burden because of its strong relationship with muscle THg levels, whereas blood THg levels may be better suited for characterizing recent Hg exposure. We conclude that Hg poses health risks to NWA oceanic whitetip sharks and human consumers of this species.

Consumption of shark products: The interface of sustainability, trade (mis)labelling, human health and human rights

“…There are other dimensions beyond biological sustainability that consumers are generally unaware of when choosing to consume or not consume a shark product. Most shark species are apex‐ or meso‐predators (Heupel et al, 2014) and frequent consumption of these species may disproportionately increase a consumer's exposure to many pollutants, including heavy metals, persistent organic pollutants and microplastics, which bioaccumulate and biomagnify through marine food webs (Gelsleichter et al, 2020; Tiktak et al, 2020). This can pose a serious risk to human health (Bosch et al, 2016a), particularly if consumers are unaware of what they are consuming due to product mislabelling (Biffi et al, 2020).…”

Analysis of Toxic Metals Found in Shark Fins Collected from a Global Trade Hub

“…Our results are comparable and within the range of other studies examining toxic metal concentrations in seafood throughout the world’s oceans and more specifically in sharks, ,,,, but it should be noted that each of these studies reported maximum values much higher than all of those we report here. Singapore has regulatory maximum limits for lead, cadmium, mercury, and arsenic in food products that are for sale.…”

Non-Lethal Sampling Supports Integrative Movement Research in Freshwater Fish

“…Non-lethal skin and muscle samples can provide a variety of metrics that are useful in spatial ecology projects. Historically, tissues derived from muscle, scale, and skin biopsies have been used in the quantification of accumulated environmental toxicants ( Aerts et al, 2015 ; Alves et al, 2016 ; Gelsleichter et al, 2020 ; Charette et al, 2021 ; Stahl et al, 2021 ), isotopic compositions ( Cunjak et al, 2005 ; Kim et al, 2012 ; Busst et al, 2015 ; Peterson et al, 2017 ; TinHan et al, 2018 ), pathogenic microbes ( Bowers et al, 2008 ; Elliott et al, 2015 ), DNA ( John Nelson et al, 2003 ; Dominik et al, 2010 ; Smith et al, 2018 ; Thorstensen et al, 2019 ), and physiological metrics such as hormonal levels and tissue energy contents ( Fagan et al, 2012 ; Olsen et al, 2013 ; Verkamp et al, 2021 ). Koi ( Cyprinus carpio ) mucus was assayed for 11-ketotestosterone ( Schultz et al, 2005 ), while mucus was also useful for stable isotopes analysis of rainbow trout diet ( Salmo gairdneri ) ( Church et al, 2009 ), and DNA in Nile tilapia ( Oreochromis niloticus ) ( Taslima et al, 2016 ).…”