Gaël Le Croizier
email: gael.lecroizier@hotmail.fr

Jeroen Sonke

Anne Lorrain

Marina Renedo

Mauricio Hoyos-Padilla

Omar Santana-Morales

Lauren Meyer

Charlie Huveneers

Paul Butcher

Felipe Amezcua-Martinez

Le Croizier Gaël

Sonke Jeroen

Lorrain Anne

Renedo Marina

Hoyos-Padilla Mauricio

Santana-Morales Omar

Meyer Lauren

Huveneers Charlie

Amezcua-Martinez Felipe

Foraging plasticity diversifies mercury exposure sources and bioaccumulation patterns in the world's largest predatory fish

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

The Anthropocene era has led to the global decline of shark populations, due to overfishing, bycatch, and other indirect threats including habitat loss and changes in prey availability [START_REF] Baum | Collapse and Conservation of Shark Populations in the Northwest Atlantic[END_REF][START_REF] Myers | Rapid Worldwide Depletion of Predatory Fish Communities[END_REF][START_REF] Ferretti | Shark Baselines and the Conservation Role of Remote Coral Reef Ecosystems[END_REF][START_REF] Dulvy | Overfishing Drives over One-Third of All Sharks and Rays toward a Global Extinction Crisis[END_REF] . Removing predators can result in trophic cascading effects impairing the structure and functioning of marine ecosystems [START_REF] Heithaus | Predicting Ecological Consequences of Marine Top Predator Declines[END_REF][START_REF] Ferretti | Patterns and Ecosystem Consequences of Shark Declines in the Ocean[END_REF][START_REF] Pimiento | Functional Diversity of Marine Megafauna in the Anthropocene[END_REF] . In this context, it has recently been suggested that the white shark (Carcharodon carcharias), the world's largest predatory fish, may become extinct during the 21 st century, along with its ecosystem role as apex predator 7 . Despite a global decline in abundance over the past half century, the different populations of white sharks do not follow the same trajectories [START_REF] Pacoureau | Half a Century of Global Decline in Oceanic Sharks and Rays[END_REF] . While some populations are considered stable, including in eastern Australasia [START_REF] Davenport | Effective Number of White Shark (Carcharodon Carcharias, Linnaeus) Breeders Is Stable over Four Successive Years in the Population Adjacent to Eastern Australia and New Zealand[END_REF] , a decrease in the abundance of white sharks has been observed in other regions, such as the Mediterranean sea [START_REF] Moro | Abundance and Distribution of the White Shark in the Mediterranean Sea[END_REF] .

White sharks are highly mobile, generalist predators with foraging plasticity encompassing a wide range of prey and habitats [START_REF] Huveneers | Future Research Directions on the "Elusive" White Shark[END_REF] . In the north-eastern Pacific (NEP), white sharks perform seasonal migrations from inshore seal colonies to offshore areas where they likely forage on deep mesopelagic prey [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF]13 . In Australian waters, white sharks are divided into two populations, namely the eastern Australasian (EA) and south-western Australasian (SWA) populations [START_REF] Blower | Population Genetics of Australian White Sharks Reveals Fine-Scale Spatial Structure, Transoceanic Dispersal Events and Low Effective Population Sizes[END_REF] . In the SWA population, although occasional offshore movements were observed, immature and adult sharks mainly occupy coastal waters on the continental shelf where they primarily target locally abundant pinnipeds [START_REF] Bradford | Evidence of Diverse Movement Strategies and Habitat Use by White Sharks, Carcharodon Carcharias, off Southern Australia[END_REF][START_REF] Bruce | Movements and Swimming Behaviour of White Sharks (Carcharodon Carcharias) in Australian Waters | Bycatch Management Information System (BMIS)[END_REF][START_REF] Meyer | The Impact of Wildlife Tourism on the Foraging Ecology and Nutritional Condition of an Apex Predator[END_REF] . Conversely, EA sharks show an ontogenetic (developmental) shift in habitat use, with immature sharks being mainly restricted to coastal waters [START_REF] Spaet | Spatiotemporal Distribution Patterns of Immature Australasian White Sharks ( Carcharodon Carcharias )[END_REF][START_REF] Bruce | Broad-Scale Movements of Juvenile White Sharks Carcharodon Carcharias in Eastern Australia from Acoustic and Satellite Telemetry[END_REF] and larger individuals performing wide-spread movements across ocean basins to New Zealand and tropical Pacific islands [START_REF] Duffy | Regional Population Connectivity, Oceanic Habitat, and Return Migration Revealed by Satellite Tagging of White Sharks, Carcharodon Carcharias, at New Zealand Aggregation Sites. Global perspectives on the biology and life history of the white shark[END_REF][START_REF] Bonfil | Large-Scale Tropical Movements and Diving Behavior of White Sharks Carcharodon Carcharias Tagged off New Zealand[END_REF] . As the east coast of Australia is devoid of primary seal colonies, coastal fish are the predominant prey for immature EA sharks [START_REF] Grainger | Diet Composition and Nutritional Niche Breadth Variability in Juvenile White Sharks (Carcharodon Carcharias)[END_REF] .

J o u r n a l P r e -p r o o f

Mercury (Hg) is a global pollutant of particular concern to human and wildlife health.

Mercury is emitted to the atmosphere from natural and anthropogenic sources and largely deposited to the ocean surface, where a fraction is converted to methylmercury (MeHg) by microorganisms [START_REF] Driscoll | Mercury as a Global Pollutant: Sources, Pathways, and Effects[END_REF] . Methylmercury is characterized by strong neurotoxicity, bioaccumulation in marine biota and unique biomagnification properties in food webs [START_REF] Kidd | Bioaccumulation and Biomagnification of Mercury through Food Webs[END_REF] . Due to their longevity and high trophic level, white sharks are among the marine species displaying the highest concentrations of Hg, assumed to be predominantly MeHg [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF][START_REF] Mckinney | Global versus Local Causes and Health Implications of High Mercury Concentrations in Sharks from the East Coast of South Africa[END_REF] . The impact of Hg exposure on shark neurophysiology is still poorly understood [START_REF] Ehnert-Russo | Mercury Accumulation and Effects in the Brain of the Atlantic Sharpnose Shark (Rhizoprionodon Terraenovae)[END_REF][START_REF] Rodrigues | Ecophysiological Effects of Mercury Bioaccumulation and Biochemical Stress in the Deep-Water Mesopredator Etmopterus Spinax (Elasmobranchii; Etmopteridae)[END_REF] and shark species could exhibit metabolic mechanisms allowing them to reduce toxicity, such as in vivo demethylation of MeHg 28 . However, the particularly high Hg concentrations found in white sharks likely induce deleterious effects (e.g. damage to the central nervous system, loss of neurons, sensory and motor deficits, oxidative stress) as observed in marine mammals and other shark species [START_REF] Rodrigues | Ecophysiological Effects of Mercury Bioaccumulation and Biochemical Stress in the Deep-Water Mesopredator Etmopterus Spinax (Elasmobranchii; Etmopteridae)[END_REF][START_REF] Krey | Assessment of Neurotoxic Effects of Mercury in Beluga Whales (Delphinapterus Leucas), Ringed Seals (Pusa Hispida), and Polar Bears (Ursus Maritimus) from the Canadian Arctic[END_REF][START_REF] López-Berenguer | A Critical Review about Neurotoxic Effects in Marine Mammals of Mercury and Other Trace Elements[END_REF] and represent an additional pressure on this vulnerable species.

In the context of global change, the future trend of Hg concentrations in marine predators remains uncertain. Empirical studies do not reach consensus, as a decrease [START_REF] Lee | Declining Mercury Concentrations in Bluefin Tuna Reflect Reduced Emissions to the North Atlantic Ocean[END_REF][START_REF] Bank | Rapid Temporal Decline of Mercury in Greenland Halibut (Reinhardtius Hippoglossoides)[END_REF] , stability [START_REF] Médieu | Stable Mercury Concentrations of Tropical Tuna in the South Western Pacific Ocean: An 18-Year Monitoring Study[END_REF][START_REF] Yurkowski | Contrasting Temporal Patterns of Mercury, Niche Dynamics, and Body Fat Indices of Polar Bears and Ringed Seals in a Melting Icescape[END_REF] or increase [START_REF] Drevnick | Increase in Mercury in Pacific Yellowfin Tuna[END_REF][START_REF] Dietz | Analysis of Narwhal Tusks Reveals Lifelong Feeding Ecology and Mercury Exposure[END_REF][START_REF] Vo | Temporal Increase in Organic Mercury in an Endangered Pelagic Seabird Assessed by Century-Old Museum Specimens[END_REF] in predator Hg content has been observed over the past decades, depending on the species and regions considered. Most model projections predict increased Hg levels in meso and top predators under different scenarios of seawater warming and dietary changes due to overfishing of prey stocks [START_REF] Schartup | Climate Change and Overfishing Increase Neurotoxicant in Marine Predators[END_REF][START_REF] Alava | Projected Amplification of Food Web Bioaccumulation of MeHg and PCBs under Climate Change in the Northeastern Pacific[END_REF][START_REF] Booth | Food Webs, and Marine Mammals: Implications of Diet and Climate Change for Human Health[END_REF] . However, current predictions ignore the foraging plasticity and wide range of ecological traits of apex predators such as white sharks. This could mask the heterogeneity in future contamination patterns within a single species, as individual foraging strategies have been shown to influence Hg exposure and ultimately Hg levels in mesopredators [START_REF] Peterson | Marine Foraging Ecology Influences Mercury Bioaccumulation in Deep-Diving Northern Elephant Seals[END_REF] . It is therefore essential J o u r n a l P r e -p r o o f to characterize and understand intraspecific variability in Hg exposure to better predict the effects of global change on predator contamination and marine ecosystem health.

In recent years, the measurement of the natural abundances of Hg stable isotopes has greatly improved knowledge on the sources of exposure, transfer pathways, and metabolism of Hg in marine consumers [START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF][START_REF] Renedo | Identification of Sources and Bioaccumulation Pathways of MeHg in Subantarctic Penguins: A Stable Isotopic Investigation[END_REF][START_REF] Li | Selenium and Stable Mercury Isotopes Provide New Insights into J o u r n a l P r e -p r o o f Mercury Toxicokinetics in Pilot Whales[END_REF] . Many abiotic (e.g. photoreduction, volatilization) [START_REF] Bergquist | Mass-Dependent and -Independent Fractionation of Hg Isotopes by Photoreduction in Aquatic Systems[END_REF][START_REF] Zheng | Mercury Isotope Fractionation during Volatilization of Hg( 0 ) from Solution into the Gas Phase[END_REF] and biotic processes (e.g. methylation, demethylation) 28,[START_REF] Perrot | Natural Hg Isotopic Composition of Different Hg Compounds in Mammal Tissues as a Proxy for in Vivo Breakdown of Toxic Methylmercury[END_REF][START_REF] Janssen | Fractionation of Mercury Stable Isotopes during Microbial Methylmercury Production by Iron-and Sulfate-Reducing Bacteria[END_REF] result in mass-dependent isotope fractionation (MDF, reported as δ 202 Hg), whereas massindependent fractionation of odd-mass number isotopes (odd-MIF, reported as Δ 199 Hg or Δ 201 Hg) has been primarily observed during aquatic photochemical reactions [START_REF] Bergquist | Mass-Dependent and -Independent Fractionation of Hg Isotopes by Photoreduction in Aquatic Systems[END_REF] . In addition, significant MIF of even-mass number isotopes (even-MIF, reported as Δ 200 Hg) is thought to occur via Hg photochemistry in the upper atmosphere [START_REF] Chen | Unusual Fractionation of Both Odd and Even Mercury Isotopes in Precipitation from Peterborough, ON, Canada[END_REF] . The analysis of Hg isotopes in marine biota therefore provides information about atmospheric Hg deposition pathways to the marine environment [START_REF] Jiskra | Mercury Stable Isotopes Constrain Atmospheric Sources to the Ocean[END_REF] , Hg methylation / demethylation processes in the water column and sediments [START_REF] Tsui | Review of Stable Mercury Isotopes in Ecology and Biogeochemistry[END_REF] , as well as on species biology and ecology, such as Hg metabolism and foraging habitat [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF][START_REF] Croizier | Mercury Isotopes as Tracers of Ecology and Metabolism in Two Sympatric Shark Species[END_REF] . Mercury isotopes have been successfully used to distinguish Hg exposure between sedentary, low trophic level marine fish populations [START_REF] Cransveld | Mercury Stable Isotopes Discriminate Different Populations of European Seabass and Trace Potential Hg Sources around Europe[END_REF][START_REF] Pinzone | Contamination Levels and Habitat Use Influence Hg Accumulation and Stable Isotope Ratios in the European Seabass Dicentrarchus Labrax[END_REF] . However, uncertainty remains regarding the possibility of applying this method to assess intraspecific variability in Hg exposure in highly mobile top predators such as white sharks.

To evaluate intraspecific variability in Hg contamination in marine apex predators, we tested the capability of Hg isotopes to identify differences in Hg exposure among three white shark populations (NEP, SWA, and EA) with contrasting ecology and large spatial scales. We discussed the potential links between Hg sources and the known ecological characteristics of these populations. We also sought to describe the dynamics of Hg bioaccumulation within each population. We hypothesized that Hg exposure and levels may vary between J o u r n a l P r e -p r o o f populations, making the assessment of Hg fate in marine predators under global change more complex than previously thought.

MATERIALS AND METHODS

Sample collection

-North-eastern Pacific population White sharks (n = 30) were sampled at Guadalupe Island (Mexico) between September and November in 2016, 2017 and 2018 (Figure 1). Free-swimming white sharks were attracted with bait near the research vessel. Muscle samples were taken using a biopsy probe targeting the tissue directly below the dorsal fin. After collection, samples were immediately transferred to a -20 °C freezer onboard the vessel.

-South-western Australasian population White shark samples (n = 40) were collected from January 2015 to July 2020 at the Neptune Islands Group Marine Park, South Australia (Figure 1), where free-swimming sharks were targeted opportunistically throughout the year during standard cage-diving operations.

Sharks were attracted to the cage-diving vessels using a combination of attractants. Biopsies were taken from diving cages or from the surface using a single 20-mm rubber speargun, with the end of the 1.3 m spear modified into a hollow 1 cm diameter stainless steel biopsy probe [START_REF] Meyer | Simple Biopsy Modification to Collect Muscle Samples from Free-Swimming Sharks[END_REF] , targeting the dorsal or upper flank musculature directly below the dorsal fin.

Biopsies were immediately frozen (-4 °C) and transported to the laboratory where white muscle tissue was dissected from the sub-dermal tissue and skin.

-Eastern Australasian population J o u r n a l P r e -p r o o f White sharks (n = 44) were sampled along the east coast of New South Wales, Australia (within a radius of ~30 km around the town of Ballina, Figure 1) between 2016 and 2020, using SMART drumlines as part of a bather protection research program [START_REF] Tate | The Effectiveness of Shark-Management-Alert-in-Real-Time (SMART) Drumlines as a Tool for Catching White Sharks, Carcharodon Carcharias , off Coastal New South Wales, Australia[END_REF][START_REF] Tate | The Acute Physiological Status of White Sharks (Carcharodon Carcharias) Exhibits Minimal Variation after Capture on SMART Drumlines[END_REF] . After capture, sharks were secured to the side of the vessel and a muscle sample was taken using an 0.8 cm sterile biopsy punch (Kai medical) targeting the tissue directly behind the dorsal fin. Tissue samples were immediately placed into a 5 ml screw cap vial on ice and transferred to a -4 °C freezer.

Individual sharks from all three populations (NEP, SWA, and EA) were sexed (based on clasper presence/absence), and total length was measured to the nearest 10 cm using visual size estimates (NEP and SWA) [START_REF] May | Eyes on the Size: Accuracy of Visual Length Estimates of White Sharks, Carcharodon Carcharias[END_REF] or to the nearest 1 cm using a certified tape (EA) [START_REF] Tate | The Effectiveness of Shark-Management-Alert-in-Real-Time (SMART) Drumlines as a Tool for Catching White Sharks, Carcharodon Carcharias , off Coastal New South Wales, Australia[END_REF][START_REF] Tate | The Acute Physiological Status of White Sharks (Carcharodon Carcharias) Exhibits Minimal Variation after Capture on SMART Drumlines[END_REF] .

Mercury concentration analysis

Once in the laboratory, muscle samples were lyophilized and homogenized using an electric grinder that was rinsed with alcohol between samples (Figure S1). Total Hg (THg) concentration was determined on aliquots (around 10 mg) of homogenized samples by combustion, gold trapping and atomic absorption spectrophotometry using a DMA80 analyzer (Milestone, USA). As THg is predominantly in the MeHg form in shark muscle 28,59-63 , THg was used as a proxy for MeHg concentration, in accordance with previous studies [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF][START_REF] Besnard | Foraging Depth Depicts Resource Partitioning and Contamination Level in a Pelagic Shark Assemblage: Insights from Mercury Stable Isotopes[END_REF] .

Total Hg concentrations in samples are expressed on a dry weight basis (ng•g -1 dw). Only one analysis was performed per sample, but the accuracy and reproducibility of the method were established using two freeze-dried certified biological material: a tuna fish flesh homogenate reference material (IAEA 436, IRMM) and a lobster hepatopancreas reference material (TORT 3, NRCC). The certified values for IAEA 436 (4.19 ± 0.36 μg•g -1 dw, n = 10) were reproduced (measured value: 4.33 ± 0.19 μg•g -1 dw) within the confidence limits. The J o u r n a l P r e -p r o o f certified values for TORT 3 (0.292 ± 0.022 μg•g -1 dw) were also reproduced (measured value: 0.286 ± 0.024 μg•g -1 dw, n = 10) within the confidence limits. The detection limit was 0.005 μg•g -1 dw.

Mercury isotope analysis

Aliquots of approximately 10 mg of dry muscle were left over night (~12 hours) at ambient room temperature in 3 mL of concentrated bi-distilled nitric acid (HNO 3 ). A volume of 1 mL of hydrogen peroxide (H 2 O 2 ) was added, and samples were digested on a hotplate for 6h at 100°C. A volume of 100 µL of BrCl was then added to ensure a full conversion of MeHg to inorganic Hg. The digest mixtures were finally diluted in inverse aqua regia (3 HNO S1). Measured isotope signatures as well as analytical reproducibility of standards (UM-Almadén, ETH-Fluka and ERM-BCR-464) were found to be in agreement with previously published values [START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF][START_REF] Masbou | Application of a Selective Extraction Method for Methylmercury Compound Specific Stable Isotope Analysis (MeHg-CSIA) in Biological Materials[END_REF][START_REF] Jiskra | Source Tracing of Natural Organic Matter Bound Mercury in Boreal Forest Runoff with Mercury Stable Isotopes[END_REF] (Table S1). Duplicate analysis was performed on a subset of 15 white shark tissues to assess the analytical uncertainty of δ 202 Hg (2SD = 0.12‰) and ∆ 199 Hg values (2SD = 0.10 ‰) in the samples.

Data analysis

For comparison of Hg isotope signatures among white shark populations, data were first checked for normality (Shapiro-Wilk tests) and homogeneity of variances (Bartlett tests). One-way analyses of variance (ANOVAs) were applied when these conditions were met, followed by Tukey's HSD tests. In the absence of homoscedasticity, Welch's ANOVAs with Games-Howell post-hoc tests were used. Linear regressions were used to assess relationships between different Hg isotope values, between Hg concentration and shark length, or between Hg isotope values and shark length. Analyses of covariance (ANCOVAs) were used to compare Hg accumulation rates between populations. Generalized linear models (GLMs) were used to evaluate the influence of population, shark length, gender, and Hg isotope values (Δ 200 Hg, Δ 199 Hg and δ 202 Hg) on Hg levels. Based on the analysis of the residuals, a Gaussian distribution and identity link function were used in the GLMs. The models were built using backward stepwise selection, ranked based on Akaïke's Information

RESULTS AND DISCUSSION

Atmospheric Hg deposition pathways

White shark Δ 200 Hg values were close to zero in all three populations (Table 1). The Δ 200 Hg signature has previously been used as a conservative tracer of atmospheric inorganic Hg deposition pathways [START_REF] Lepak | Factors Affecting Mercury Stable Isotopic Distribution in Piscivorous Fish of the Laurentian Great Lakes[END_REF][START_REF] Masbou | Hg-Stable Isotope Variations in Marine Top Predators of the Western Arctic Ocean[END_REF] . The deposited Hg subsequently becomes the substrate for MeHg production in marine environments. Δ 200 Hg mainly discriminates between dissolution of gaseous Hg(0) (slightly negative Δ 200 Hg of -0.05 ‰) and wet and dry deposition of inorganic Hg(II) through precipitation and dry deposition (positive Δ 200 Hg values of 0.14 ‰) [START_REF] Enrico | Atmospheric Mercury Transfer to Peat Bogs Dominated by Gaseous Elemental Mercury Dry Deposition[END_REF] . Terrestrial plants and soils have been shown to take up atmospheric Hg(0), and continental runoff by rivers to the oceans thus constitutes an additional Hg source with Δ 200 Hg similar to Hg(0) [START_REF] Obrist | Tundra Uptake of Atmospheric Elemental Mercury Drives Arctic Mercury Pollution[END_REF] . As coastal food webs receive Hg from all three sources, their Δ 200 Hg values are generally closer to the Hg(0) than the Hg(II) end-member [START_REF] Masbou | Hg-Stable Isotope Variations in Marine Top Predators of the Western Arctic Ocean[END_REF][START_REF] Meng | Mercury Isotope Variations within the Marine Food Web of Chinese Bohai Sea: Implications for Mercury Sources and Biogeochemical Cycling[END_REF] . Conversely, pelagic ecosystems show equal contributions of Hg(0) and Hg(II) deposition, resulting in Δ 200 Hg signatures around 0.05 ‰ [START_REF] Lepak | Factors Affecting Mercury Stable Isotopic Distribution in Piscivorous Fish of the Laurentian Great Lakes[END_REF][START_REF] Motta | Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios[END_REF] . Here, the mean Δ 200 Hg values of 0.06, 0.04, and 0.03 ‰ for NEP, EA and SWA populations respectively (Table 1) would thus reflect an equivalent contribution of Hg(0) and Hg(II) sources, characteristic of pelagic environments [START_REF] Jiskra | Mercury Stable Isotopes Constrain Atmospheric Sources to the Ocean[END_REF] . However, the NEP population displayed a significantly higher Δ 200 Hg than the SWA population (p < 0.05, Figure 2A that NEP white sharks were dietary exposed to mesopelagic MeHg [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] , which is mainly produced from Hg(II) supplied by precipitation and dry deposition in the subtropical Pacific [START_REF] Motta | Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios[END_REF] . Although Hg isotope signatures of prey have not yet been characterized for Australasian sharks, movement data showed that SWA sharks primarily occupy coastal waters [START_REF] Bradford | Evidence of Diverse Movement Strategies and Habitat Use by White Sharks, Carcharodon Carcharias, off Southern Australia[END_REF][START_REF] Bruce | Movements and Swimming Behaviour of White Sharks (Carcharodon Carcharias) in Australian Waters | Bycatch Management Information System (BMIS)[END_REF] (Table 1), which are believed to receive more Hg(0) inputs via continental runoff. The coastal affinity of SWA sharks, opposed to the pelagic foraging behavior of NEP sharks, could thus explain the variations in Δ 200 Hg observed between these populations (i.e. higher Δ 200 Hg in NEP sharks, Figure 2A).

A recent global analysis of marine Δ 200 Hg (including particulate Hg, sediments, and biota) showed the occurrence of a latitudinal isotopic gradient, with lower Δ 200 Hg values at high latitudes, indicating larger ocean Hg(0) uptake compared to intermediate and tropical areas [START_REF] Jiskra | Mercury Stable Isotopes Constrain Atmospheric Sources to the Ocean[END_REF] . However, this study reported similar Δ 200 Hg values at the latitudes corresponding to our sampling sites, i.e., around 30°N and 30°S (Figure 1). The variability in Δ 200 Hg observed in our study seems to be governed by differences in atmospheric Hg sources between coastal and offshore shark habitats, rather than by a latitudinal gradient in Δ 200 Hg at the global scale.

Marine MeHg sources

Mercury odd-MIF signatures in marine biota are not affected by trophic transfers or metabolic processes [START_REF] Perrot | Natural Hg Isotopic Composition of Different Hg Compounds in Mammal Tissues as a Proxy for in Vivo Breakdown of Toxic Methylmercury[END_REF][START_REF] Kwon | Absence of Fractionation of Mercury Isotopes during Trophic Transfer of Methylmercury to Freshwater Fish in Captivity[END_REF] and are specifically derived from the photodegradation of MeHg in seawater prior to food web biomagnification [START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF] . Although similar Δ 201 Hg/Δ 199 Hg ratios across regions suggest a common mechanism for MeHg photodegradation (Figure S2 and additional discussion), we found significant variations in Δ 199 Hg values between populations (p < 0.01, Figure 2B), indicating exposure to distinct MeHg pools that experienced different intensities J o u r n a l P r e -p r o o f of photodegradation. In the open ocean or near offshore islands, where marine organisms are mainly exposed to pelagic MeHg, fish species are characterized by Δ 199 Hg values generally higher than 1 ‰ 28,42,75 . Conversely, marine fishes exposed to MeHg produced in coastal sediments or turbid waters, where light penetration is limited, display significantly lower Δ 199 Hg values (typically lying between 0 and 1 ‰) [START_REF] Meng | Mercury Isotope Variations within the Marine Food Web of Chinese Bohai Sea: Implications for Mercury Sources and Biogeochemical Cycling[END_REF][START_REF] Senn | Stable Isotope (N, C, Hg) Study of Methylmercury Sources and Trophic Transfer in the Northern Gulf of Mexico[END_REF][START_REF] Perrot | Mercury Bioaccumulation in Tilefish from the Northeastern Gulf of Mexico 2 years after the Deepwater Horizon Oil Spill: Insights from Hg, C, N and S Stable Isotopes[END_REF] . In addition, as Hg photodegradation decreases with light attenuation in the water column, Δ 199 Hg values generally decrease with increasing foraging depth in marine fishes [START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF][START_REF] Croizier | Mercury Isotopes as Tracers of Ecology and Metabolism in Two Sympatric Shark Species[END_REF]75 . Δ 199 Hg values in a marine predator may thus reflect vertical or horizontal habitat use, or a combination of both, depending on the environment considered [START_REF] Sun | Distribution and Transformation of Mercury in Subtropical Wild-Caught Seafood from the Southern Taiwan Strait[END_REF] . As it was previously shown that NEP sharks are primarily exposed to deep and offshore MeHg [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] , and SWA and EA sharks occupy mainly coastal and shallow habitats [START_REF] Bradford | Evidence of Diverse Movement Strategies and Habitat Use by White Sharks, Carcharodon Carcharias, off Southern Australia[END_REF][START_REF] Bruce | Movements and Swimming Behaviour of White Sharks (Carcharodon Carcharias) in Australian Waters | Bycatch Management Information System (BMIS)[END_REF][START_REF] Spaet | Spatiotemporal Distribution Patterns of Immature Australasian White Sharks ( Carcharodon Carcharias )[END_REF][START_REF] Bruce | Broad-Scale Movements of Juvenile White Sharks Carcharodon Carcharias in Eastern Australia from Acoustic and Satellite Telemetry[END_REF] , Δ 199 Hg signatures were expected to differ between NEP and Australasian populations, as observed in our dataset (Figure 2B). Surprisingly, the NEP population showed a Δ 199 Hg of 1.54 ‰, which fell between the Δ 199 Hg of SWA and EA populations (1.69 and 1.25 ‰, respectively) (Table 1). Photochemical degradation of MeHg is known to vary globally, primarily related to water clarity and UV penetration depth [START_REF] Motta | Mercury Stable Isotopes in Flying Fish as a Monitor of Photochemical Degradation of Methylmercury in the Atlantic and Pacific Oceans[END_REF] . Differences in habitat characteristics and water clarity (based on Secchi depth; Table 1) therefore suggest variations in Δ 199 Hg baselines across distant regions, complicating direct comparison of NEP and Australasian populations. By focusing on spatially close populations, a gap in Δ 199 Hg values was also observed between SWA and EA sharks, despite an apparent similarity in vertical and horizontal habitat use for the size classes considered [START_REF] Bradford | Evidence of Diverse Movement Strategies and Habitat Use by White Sharks, Carcharodon Carcharias, off Southern Australia[END_REF][START_REF] Bruce | Movements and Swimming Behaviour of White Sharks (Carcharodon Carcharias) in Australian Waters | Bycatch Management Information System (BMIS)[END_REF][START_REF] Spaet | Spatiotemporal Distribution Patterns of Immature Australasian White Sharks ( Carcharodon Carcharias )[END_REF][START_REF] Bruce | Broad-Scale Movements of Juvenile White Sharks Carcharodon Carcharias in Eastern Australia from Acoustic and Satellite Telemetry[END_REF] , and in average water clarity in both regions [START_REF] He | Recent Changes of Global Ocean Transparency Observed by SeaWiFS[END_REF] (Table 1). However, when closely examining the fine-scale distribution in the water column, SWA sharks were observed to primarily occupy the upper 50 m 15 , while EA sharks were most abundant between 50 and 130 m depth [START_REF] Lee | Oceanographic Conditions Associated with White Shark (Carcharodon Carcharias) Habitat Use along Eastern Australia[END_REF] . As the MeHg photodegradation gradient is steep in shallow depths [START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF][START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] , this J o u r n a l P r e -p r o o f inconspicuous but significant difference in vertical habitat is consistent with the Δ 199 Hg variation observed between Australasian (SWA and EA) populations. This exemplifies the ability and sensitivity of the Δ 199 Hg tracer to capture slight variations in vertical habitat used by nearby predator populations.

Although many biotic and abiotic processes affect Hg MDF, hepatic MeHg demethylation has been identified as one of the major mechanisms leading to increased δ 202 Hg values in the muscle tissue of predators such as marine mammals [START_REF] Li | Selenium and Stable Mercury Isotopes Provide New Insights into J o u r n a l P r e -p r o o f Mercury Toxicokinetics in Pilot Whales[END_REF][START_REF] Perrot | Natural Hg Isotopic Composition of Different Hg Compounds in Mammal Tissues as a Proxy for in Vivo Breakdown of Toxic Methylmercury[END_REF] , seabirds [START_REF] Poulin | Isotope Fractionation from In Vivo Methylmercury Detoxification in Waterbirds[END_REF][START_REF] Renedo | Mercury Isotopes of Key Tissues Document Mercury Metabolic Processes in Seabirds[END_REF] , and more recently sharks 28,[START_REF] Besnard | Foraging Depth Depicts Resource Partitioning and Contamination Level in a Pelagic Shark Assemblage: Insights from Mercury Stable Isotopes[END_REF] . The preferential demethylation of light Hg isotopes in the liver increases δ 202 Hg in the remaining MeHg pool, with a fraction ultimately stored in muscle [START_REF] Perrot | Natural Hg Isotopic Composition of Different Hg Compounds in Mammal Tissues as a Proxy for in Vivo Breakdown of Toxic Methylmercury[END_REF][START_REF] Poulin | Isotope Fractionation from In Vivo Methylmercury Detoxification in Waterbirds[END_REF] . Here, we found high δ 202 Hg values (up to 1.43 ‰ in the SWA population; Table 1) and near zero Δ 199 Hg/δ 202 Hg slopes (Figure S3 and additional discussion) which may suggest substantial MeHg demethylation in white sharks, as previously established for other large species such as bull and tiger sharks [START_REF] Croizier | Mercury Isotopes as Tracers of Ecology and Metabolism in Two Sympatric Shark Species[END_REF] . Alternatively, it may result from the consumption of marine mammals, which can represent an important part of the white shark diet [START_REF] Grainger | Diet Composition and Nutritional Niche Breadth Variability in Juvenile White Sharks (Carcharodon Carcharias)[END_REF][START_REF] Hussey | Size-Based Analysis of Diet and Trophic Position of the White Shark (Carcharodon Carcharias) in South African Waters. Global Perspectives on the Biology and Life History of the White Shark[END_REF] and which also display elevated δ 202 Hg values due to MeHg demethylation [START_REF] Perrot | Natural Hg Isotopic Composition of Different Hg Compounds in Mammal Tissues as a Proxy for in Vivo Breakdown of Toxic Methylmercury[END_REF][START_REF] Bolea-Fernández | High-Precision Isotopic Analysis Sheds New Light on Mercury Metabolism in Long-Finned Pilot Whales (Globicephala Melas)[END_REF] . The higher δ 202 Hg found in SWA sharks compared to the NEP and EA populations (Figure 2) could thus be the result of either higher demethylation or more frequent consumption of marine mammals. In our study, SWA sharks had much higher Hg concentrations than NEP sharks (Table 1), which does not support the hypothesis of higher demethylation. However, the second hypothesis is supported by the modest contribution of mammals to Hg exposure of NEP sharks [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] and dietary intake of immature EA sharks [START_REF] Grainger | Diet Composition and Nutritional Niche Breadth Variability in Juvenile White Sharks (Carcharodon Carcharias)[END_REF] , while the SWA shark samples were collected near a large colony of pinnipeds (Neptune Islands Group Marine Park; Figure 1).

J o u r n a l P r e -p r o o f

Individual variability in Hg exposure

No variation in Hg isotope signatures related to gender or body length has been previously found in NEP sharks, suggesting a common Hg exposure at the population scale [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] .

Conversely, ontogenetic variability was observed here within the two Australasian populations. In the EA population, Δ 199 Hg was positively correlated with shark total length (Figure 3A). Previous studies of the EA white shark population have shown an ontogenetic increase in travelling behavior [START_REF] Lee | Oceanographic Conditions Associated with White Shark (Carcharodon Carcharias) Habitat Use along Eastern Australia[END_REF] , with coastal areas dominated by small immature individuals [START_REF] Spaet | Spatiotemporal Distribution Patterns of Immature Australasian White Sharks ( Carcharodon Carcharias )[END_REF][START_REF] Bruce | Broad-Scale Movements of Juvenile White Sharks Carcharodon Carcharias in Eastern Australia from Acoustic and Satellite Telemetry[END_REF][START_REF] Grainger | Diet Composition and Nutritional Niche Breadth Variability in Juvenile White Sharks (Carcharodon Carcharias)[END_REF][START_REF] Spaet | Environmental Conditions Are Poor Predictors of Immature White Shark Carcharodon Carcharias Occurrences on Coastal Beaches of Eastern Australia[END_REF] and large sharks more likely to undertake large-scale offshore migrations [START_REF] Duffy | Regional Population Connectivity, Oceanic Habitat, and Return Migration Revealed by Satellite Tagging of White Sharks, Carcharodon Carcharias, at New Zealand Aggregation Sites. Global perspectives on the biology and life history of the white shark[END_REF][START_REF] Bonfil | Large-Scale Tropical Movements and Diving Behavior of White Sharks Carcharodon Carcharias Tagged off New Zealand[END_REF][START_REF] Francis | Spatial and Temporal Habitat Use by White Sharks (Carcharodon Carcharias) at an Aggregation Site in Southern New Zealand[END_REF] . Such an increase in offshore dispersal would result in greater exposure to pelagic MeHg sources, typically characterized by higher Δ 199 Hg values 28,[START_REF] Blum | Methylmercury Production below the Mixed Layer in the North Pacific Ocean[END_REF]75 than MeHg produced in coastal habitats [START_REF] Meng | Mercury Isotope Variations within the Marine Food Web of Chinese Bohai Sea: Implications for Mercury Sources and Biogeochemical Cycling[END_REF][START_REF] Senn | Stable Isotope (N, C, Hg) Study of Methylmercury Sources and Trophic Transfer in the Northern Gulf of Mexico[END_REF][START_REF] Perrot | Mercury Bioaccumulation in Tilefish from the Northeastern Gulf of Mexico 2 years after the Deepwater Horizon Oil Spill: Insights from Hg, C, N and S Stable Isotopes[END_REF] , and would explain the ontogenetic variation in Δ 199 Hg found in EA sharks.

In SWA sharks, both δ 202 Hg and Δ 200 Hg were found to increase with size (Figure 3B, 3C). Mercury metabolism in sharks is supposed to increase δ 202 Hg values over time, through enhanced MeHg demethylation in older individuals [START_REF] Croizier | Mercury Isotopes as Tracers of Ecology and Metabolism in Two Sympatric Shark Species[END_REF] . In addition, white sharks are known to increase their consumption of marine mammals as they grow larger [START_REF] Hussey | Size-Based Analysis of Diet and Trophic Position of the White Shark (Carcharodon Carcharias) in South African Waters. Global Perspectives on the Biology and Life History of the White Shark[END_REF] , which may increase the uptake of MeHg with δ 202 Hg higher values [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] . It is therefore difficult to deconvolute the different mechanisms (Hg metabolism, change in prey) responsible for ontogenetic variations in the δ 202 Hg signature. However, as δ 202 Hg values did not increased with size in NEP and EA populations, changes in δ 202 Hg are unlikely to be caused by metabolism alone.

Considering that oceanic Δ 200 Hg baselines are generally slightly higher than coastal baselines [START_REF] Lepak | Factors Affecting Mercury Stable Isotopic Distribution in Piscivorous Fish of the Laurentian Great Lakes[END_REF][START_REF] Meng | Mercury Isotope Variations within the Marine Food Web of Chinese Bohai Sea: Implications for Mercury Sources and Biogeochemical Cycling[END_REF][START_REF] Motta | Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios[END_REF] , the higher Δ 200 Hg observed in large SWA sharks suggests an ontogenetic increase in offshore movements in this population. This is consistent with a recent tracking study documenting movements of large SWA sharks (> 4.5 m) off the continental shelf and J o u r n a l P r e -p r o o f suggesting that females may disperse further offshore than males [START_REF] Bradford | Evidence of Diverse Movement Strategies and Habitat Use by White Sharks, Carcharodon Carcharias, off Southern Australia[END_REF] . While we did not observe differences in Hg exposure between sexes, Δ 200 Hg values provide evidence for an ontogenetic change in foraging habitat in the SWA population.

Mercury bioaccumulation

Log-transformed THg concentrations were positively correlated with shark length (a proxy for age) in Australasian sharks (Figure 4) and the log(THg)/length slopes were similar in SWA and EA populations (ANCOVA, p > 0.05). These results indicate a comparable rate of Hg bioaccumulation in the two Australasian populations. Methylmercury bioaccumulation in fish muscle results from a high MeHg assimilation efficiency, strong binding to cysteine residues of proteins and low excretion rate [START_REF] Wang | Bioaccumulation Kinetics and Exposure Pathways of Inorganic Mercury and Methylmercury in a Marine Fish, the Sweetlips Plectorhinchus Gibbosus[END_REF][START_REF] Manceau | Demethylation of Methylmercury in Bird, Fish, and Earthworm[END_REF] . Moreover, MeHg stored in muscle comes from the residual blood MeHg exiting from the liver after in vivo demethylation. As MeHg is the dominant form of Hg in shark muscle [START_REF] Croizier | Mercury Isotopes as Tracers of Ecology and Metabolism in Two Sympatric Shark Species[END_REF][START_REF] Matulik | Bioaccumulation and Biomagnification of Mercury and Methylmercury in Four Sympatric Coastal Sharks in a Protected Subtropical Lagoon[END_REF][START_REF] De Carvalho | Assessment of Total and Organic Mercury Levels in Blue Sharks (Prionace Glauca) from the South and Southeastern Brazilian Coast[END_REF] , increased Hg concentration in the muscle of Australasian sharks may imply that trophic exposure to MeHg exceeds demethylation capacity. Our findings are consistent with a previous study which observed an increase in Hg concentration with size in juvenile EA individuals 90 . In contrast, no increase in Hg concentration with age was observed in NEP sharks (Figure 4), suggesting a balance between MeHg exposure and demethylation/excretion. Consequently, while Hg concentrations were similar in all three populations for smaller sharks (i.e., 11 and 12 ppm at 2.5 m total length for Australasian and NEP sharks, respectively), Australasian populations were three times more contaminated than the NEP population for larger sharks (e.g., 30 versus 10 ppm at 4.5 m total length for SWA and NEP sharks, respectively; Figure S4). Similar muscle Hg concentrations observed in young white sharks do not argue for variations in marine MeHg baselines across regions. However, the difference in Hg J o u r n a l P r e -p r o o f accumulation kinetics found between Australasian and NEP populations (Figure 4) could be related to different trophic strategies adopted by adult sharks. While δ 202 Hg values suggest a size-based increase in MeHg uptake from marine mammals consumption in SWA sharks (Figure 3B), the NEP population is thought to be primarily exposed to MeHg from mesopelagic prey with limited contribution from pinnipeds, regardless of size [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] . As predators, marine mammals generally display higher Hg content than mid-trophic mesopelagic species [START_REF] Kemper | A Review of Heavy Metal and Organochlorine Levels in Marine Mammals in Australia[END_REF][START_REF] Pethybridge | Lipid and Mercury Profiles of 61 Midtrophic Species Collected off South-eastern Australia[END_REF] . A greater proportion of mammals in the diet of adult SWA sharks could thus partly explain their higher δ 202 Hg values and Hg concentrations compared to the NEP population. This assumption is consistent with the outputs of generalized linear models used to predict Hg levels in white shark muscle. The top-ranked model (w i = 0.60) included δ 202 Hg, length and population, and δ 202 Hg was the best stand-alone predictor of Hg concentration, explaining 36% of Hg variation in shark muscle (Table S2). This result revealed that consumption of marine mammals (exhibiting high δ 202 Hg values [START_REF] Croizier | The Twilight Zone as a Major Foraging Habitat and Mercury Source for the Great White Shark[END_REF] ) could be a major driver of Hg levels in white sharks. In the future, this hypothesis can be verified by comparing the trophic level of adult sharks from the NEP and Australasian populations, but may require the use of amino acid nitrogen isotopic analysis to overcome spatial variations in isotopic baselines [START_REF] Ohkouchi | Advances in the Application of Amino Acid Nitrogen Isotopic Analysis in Ecological and Biogeochemical Studies[END_REF] .

CONCLUSION

Global change is expected to influence Hg contamination in marine biota, yet intraspecies differences in Hg exposure are rarely considered. Here, we applied for the first time the recent technique of Hg isotope analysis to characterize dietary Hg exposure across different populations of white sharks, the world's largest predatory fish. Our results revealed that the broad ecological spectrum of white sharks implies exposure to different sources of J o u r n a l P r e -p r o o f

3 : 1

 31 HCl, 20 vol.% MilliQ water) to reach a nominal Hg concentration of 1 ng•g -1 . Certified reference materials (ERM-BCR-464) and blanks were prepared in the same way as tissue samples. Mercury isotope composition was measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS, Thermo Finnigan Neptune Plus) with continuousflow cold vapor (CV) generation using Sn (II) reduction (CETAC HGX-200). Mercury isotope ratios are expressed in δ notation and reported in parts per thousand (‰) deviation from the NIST SRM 3133 standard, following sample-standard bracketing according to the following equation: δ XXX Hg (‰) = * ( XXX Hg/ 198 Hg) sample / ( XXX Hg/ 198 Hg) NIST 3133 ) -1 ] X 1000 where xxx represents the mass of each mercury isotope. δ 202 Hg represents Hg MDF, and ∆ notation is used to express Hg MIF by the following equation: ∆ xxx Hg (‰) = δ xxx Hg -(δ 202 Hg X a) where a = 0.2520, 0.5024 and 0.7520 for isotopes 199, 200 and 201, respectively. J o u r n a l P r e -p r o o f Total Hg in the diluted solutions was quantified by MC-ICP-MS using 202 Hg signals: mean recoveries of 98 ± 11% (n = 84) for samples and 96 ± 6 and dilution% (n = 12) for certified reference materials were found. Mercury levels in blanks were below the detection limit of 0.005 ng•g -1 . Reproducibility of Hg isotope measurements was assessed by analyzing UM-Almadén (n = 24), ETH-Fluka (n = 22) and the biological tissue procedural standard ERM-BCR-464 (n = 12) (Table

  J o u r n a l P r e -p r o o fCriteria adjusted for small sample sizes (AIC c ) and compared using ΔAIC c and Akaike weights (w i ). All statistical analyses were performed using the open source software R (4.1.1 version).

  ), with EA sharks showing intermediate values. Despite the small magnitude of even-MIF, Δ 200 Hg values revealed a greater contribution of Hg(II) inputs in the NEP population compared to SWA sharks. This hypothesis agrees with a previous study showing J o u r n a l P r e -p r o o f

  J o u r n a l P r e -p r o o f Hg among individuals, likely leading to the marked differences in Hg bioaccumulation patterns observed between populations. Given this large intraspecific variability, predicting Hg levels in marine predators under global change could be more complex than previously thought. Future modelling research should therefore focus on a widely distributed top predator model species and account for population variations in Hg exposure and concentration to improve projections of predator Hg levels at the global scale. ecosystems' (MERTOX, PI DP) for providing financial support for Hg isotope analysis. The project was funded in Mexico by Alianza WWF-TELCEL, The Annemberg Foundation, International Community Foundation, Fins Attached Marine Research and Conservation and Pfleger Institute of Environmental Research. Field work in Mexico was greatly facilitated through courtesies extended to us by personnel of the University of California, Davis, Centro Interdisciplinario de Ciencias Marinas (CICIMAR), Secretaría de Marina, Comisión de Areas naturals Protegidas (CONANP), Island Conservation (GECI), Horizon Charters, Islander Charters, Solmar V, Club Cantamar and local fishermen from Guadalupe Island. In Mexico, white shark samples were collected under permits from the Secretaría del Medio Ambiente y Recursos Naturales (SEMARNAT): OFICIO NUM.SGPA/DGVS/07052/16 in 2016, OFICIO J o u r n a l P r e -p r o o f NUM.SGPA/DGVS/06673/17 in 2017 and OFICIO NUM.SGPA/DGVS/004284/18 in 2018. Fieldwork in South Australia was possible thanks to the logistic support of the white shark cage-diving industry. We also thank the Save Our Seas Foundation, Holsworth Wildlife Research Endowment (HWRE2016R2098), Oceania Chondrichthyan Society and Passions of Paradise for providing funding to support sample collection. In South Australia, samples were collected in accordance with DEWNR permit #Q26292 and Flinders University Animal Ethics Committee approval #398 for South Australian samples. In New South Wales (NSW), samples were collected by the NSW DPI shark research team and SMART drumline contractors. NSW samples were collected under NSW DPI 'scientific' (Ref. P01/0059(A)), 'Marine Parks' (Ref. P16/0145-1.1) and 'Animal Care and Ethics' (ACEC Ref. 07/08) permits as part of the Shark Management Strategy. We also thank Jonathan Werry for his contribution to shark sampling in Eastern Australia. White shark samples were exported from Mexico under the CITES permit (number MX007) of the Universidad Nacional Autónoma de México and from Australia under the CITES permit (number AU089) of Flinders University. Samples were imported in France under the CITES permit (number FR75A) of the Muséum National d'Histoire Naturelle. We thank Laure Laffont and Jérôme Chmeleff for expert management of the OMP mercury and mass spectrometry facilities. J o u r n a l P r e -p r o o f

Figure 1 :

 1 Figure 1: Map of the spatial distribution of white sharks from the north-eastern Pacific (NEP), eastern Australasian (EA) and south-western Australasian (SWA) populations. Sample collection sites are figured (*).

Figure 2 :

 2 Figure 2: Raw data points, boxplots and data distribution of A) ∆ 200 Hg, B) ∆ 199 Hg and C) δ 202 Hg values in the muscle of different white shark populations: the north-eastern Pacific (NEP), eastern Australasian (EA) and south-western Australasian (SWA) populations. Different letters indicate significant differences between populations (ANOVAs; p < 0.05).

Figure 3 :

 3 Figure 3: Relationships between A) ∆ 199 Hg, B) δ 202 Hg and C) ∆ 200 Hg values and body length in the eastern Australasian (EA) and south-western Australasian (SWA) populations. Data fits a linear regression in A) R²=0.40, p<0.001; B) R²=0.49, p<0.001 and C) R²=0.26, p<0.01.

Figure 4 :

 4 Figure 4: Relationships between log-transformed Hg concentration and total length (m) in the muscle of different white shark populations: the north-eastern Pacific (NEP), eastern

Table 1 :

 1 Summary of Hg analyses (mean ± standard deviation) carried out in white shark muscle. Shark length is indicated as mean (range). Habitat characteristics are reported according to previous studies46,47,53,54 .

	Population	n	Total length (m)	Maturity stage	TH g (µg ٠g -1 )	δ 202 Hg (‰)	∆ 199 Hg (‰)	∆ 200 Hg (‰)	Vertica l habitat	Horizo ntal habita t	Sec chi dep th
					10.
	North-eastern Pacific (NEP) Eastern Australasian (EA) South-western Australasian (SWA) J o u r n a l P r e -p r o o f 3 0 3.1 (2.0-5.0) Juvenile to adult 58 ± 2.6 4 0.88 ± 0.25 1.54 ± 0.18 0.06 ± 0.03 Epi to mesop elagic 4 4 2.4 (1.6-3.5) Juvenile to subadult 10. 50 ± 5.5 1 0.92 ± 0.25 1.25 ± 0.19 0.04 ± 0.05 Epipela gic 4 0 3.2 (1.8-4.7) Juvenile to adult 18. 31 ± 8.0 8 1.43 ± 0.40 1.69 ± 0.19 0.03 ± 0.05 Epipela gic	Offsho re Contin ental shelf Contin ental shelf	50 30 30

Acknowledgments

Gaël Le Croizier was supported by a postdoctoral grant from the French National Research Institute for Sustainable Development (IRD) and the ISblue "Interdisciplinary graduate School for the blue planet" project (ANR-17-EURE-0015). We thank the French National Research Agency ANR-17-CE34-0010 project 'Unraveling the origin of methylMERcury TOXin in marine

Funding acquisition. Omar Santana-Morales: Investigation, Resources, Writing -Review & Editing, Funding acquisition. Lauren Meyer: Investigation, Resources, Writing -Review & Editing, Funding acquisition. Charlie Huveneers: Investigation, Resources, Writing -Review & Editing, Funding acquisition. Paul Butcher: Investigation, Resources, Writing -Review & Editing, Funding acquisition. Felipe Amezcua-Martinez: Writing -Review & Editing. David Point: Resources, Writing -Review & Editing, Supervision, Funding acquisition. J o u r n a l P r e -p r o o f

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: