Stewart Island Research Articles

The ethical dilemma of provisioning pelagic birds in exchange for a close encounter

ABSTRACTThe rapid expansion of wildlife tourism over recent decades has led to a growing concern about the potential negative impacts these viewing activities can have on targeted species. Marine wildlife tourism has been no exception, and many researchers have investigated the issues surrounding wildlife watching activities for various marine species. The majority of such studies have focussed on the potential negative effects on either the species in question, on visitor education, or on tourist satisfaction. Only recently have ethical dimensions been addressed, particularly the practice of provisioning wildlife during touristic encounters. This study explored the tourist experience of pelagic birdwatching tours in Kaikoura and on Stewart Island, New Zealand. Unprompted, qualitative comments from birdwatchers discussed the close encounters with pelagic birds and the practice of provisioning the birds. Results reveal the ethical dissonance of not agreeing with feeding wildlife while simultaneously enjoying viewing pelagic birds at close range. The results suggest that tourists are concerned about the potential negative effects of feeding pelagic birds, but accept these for the benefit of their own wildlife experience.

Distribution of the genus Zonaria (Dictyotales: Phaeophyceae) in New Zealand, and description of Zonaria cryptica sp. nov from Stewart Island

ABSTRACTThe brown algal genus Zonaria (Dictyotales: Dictyotaceae) is widely distributed in temperate waters. Two species, Zonaria turneriana J.Agardh and Zonaria aureomarginata J.A. Phillips & W.A. Nelson have previously been recorded from mainland New Zealand, and a third species, Zonaria diesingiana, has been recorded from the Kermadec Islands. As part of an ongoing study of the order Dictyotales in New Zealand, we have identified an undescribed species of Zonaria present on Stewart Island in southern New Zealand. The new species, described here as Zonaria cryptica, is very similar in external morphology to Z. turneriana, also found on Stewart Island, but differs both genetically and anatomically from Z. turneriana and from other previously described species in the genus. We present a description of the new species based on morphological and anatomical observations, as well as on DNA sequence data from three plastid markers: psaA, psbA and rbcL. Our analysis also indicates the presence of some biogeographic structuring within Z. turneriana and Z. aureomarginata.

Seasonal variation in occurrence of the sevengill shark, Notorynchus cepedianus, in two inshore habitats of southern New Zealand

ABSTRACTDespite being a large, relatively abundant predator, the distribution and seasonal occurrence of the broadnose sevengill shark, Notorynchus cepedianus, in New Zealand is poorly understood. During 71 sampling trips conducted from July 2013 to May 2015, sharks were attracted to coastal sampling sites in southern New Zealand at Ōtākou/Otago Harbour and Te Whaka ā Te Wera/Paterson Inlet, Stewart Island, using chum. Using a logistic regression model, water temperature was identified as a key predictor of encountering sevengill sharks. In addition, location, cloud cover and sea state were also identified as influential predictors. At Ōtākou, a clear seasonal pattern of sevengill shark sightings emerged. Sharks were detected on 86% of survey trips in summer, whilst no sharks were detected in winter or spring. At Te Whaka ā Te Wera, sharks were sighted throughout all seasons, but a decline in shark encounters occurred during winter. This study represents the first systematic data on seasonal habitat use by sevengill sharks in New Zealand.

Connecting with innerlandscapes: Taonga pūoro, musical improvisation and exploring acoustic Aotearoa/New Zealand

Abstract When ngā taonga pūoro (traditional instruments of the Māori) practitioners improvise music in the natural environment, they can be seen as explorers navigating and traversing the contours of the acoustic landscapes. As these practitioners come into dialogue with the non-humans of the natural environment, they are able to transform these relational experiences into sound phenomena, which in turn (re)create places that are meaningful to the practitioner and their audiences – human and otherwise. Taking a point of departure in a discussion between anthropologist Sebastian J. Lowe and renowned taonga pūoro practitioner Alistair Fraser, this article looks at how Fraser enters into Te Ao Māori (the Māori world or dimension) and comes into dialogue with the entities of Te Ao Tūroa (the natural world). In 2013, Fraser released an album called Rakiura (Stewart Island), which he made as part of a Creative New Zealand/ Department of Conservation (DOC) Wild Creations Artist Residency. Throughout his six-week field research together with local iwi Ngai Tahu in 2011, Alistair researched, made and performed taonga pūoro from the area of southern Aotearoa/New Zealand. This article, which takes Fraser’s album as an ethnographic case study, aims to challenge the way we explore, expand and extend our appreciation of acoustic Aotearoa, thereby potentially opening up new spaces for understanding, interacting and ultimately respecting our environments.

Colonial ascidians from the Foveaux Strait region of New Zealand

ABSTRACTColonial ascidians collected from wharf piles and natural substrata from Bluff Harbour and Stewart Island in the South Island of New Zealand are described in this paper. Two species, Lissoclinum violaceum sp. nov. and Didemnum marineae sp. nov. are new to science and described for the first time. The ascidian fauna in this region is a mixed assemblage of southern species, species with a New Zealand-wide distribution, and two species with trans-Tasman affinities.www.zoobank.org/urn:lsid:zoobank.org:pub:37DC0D4B-8FB9-4F1D-A5A0-E9CAB3203447

Strategic Environmental Assessment for Invasive Species Management on Inhabited Islands

Over the past decade the challenges of managing invasive species on inhabited islands have clearly become limiting factors to scaling-up the area of invasive species eradications. Step-change is required to unleash the conservation and restoration potential of biodiversity on inhabited islands around the globe, and avoid the pitfalls previous attempts to eradicate invasive species on inhabited islands have fallen into. Strategic environmental assessment (SEA) is a systematic decision support process, aiming to ensure that environmental and other sustainability aspects are considered effectively throughout policy, plan and programme making. Within the framework of SEAs, on target islands eradication planners could implement a number of tools including stakeholder engagement, social impact assessment and economic cost-benefit analysis alongside existing environmental impact assessment. Such a suite of assessments capture the immediate impacts of an eradication operation on a range of values, alongside predicted long-term changes in these tightly coupled socio-ecological systems. In this paper we outline what SEA is, and then contrast invasive species management attempts occurring outside an SEA framework on two similar but also contrasting UNESCO World Heritage islands; Lord Howe Island, Australia and Fernando de Noronha, Brazil. We then demonstrate how an SEA approach to invasive species management would assist planning in New Zealand to eradicate introduced mammalian predators from two large offshore islands in New Zealand; Aotea (Great Barrier Island) and Rakiura (Stewart Island). We conclude with future prospects for applying SEA to invasive species management on inhabited islands.

Flow and sediment transport dynamics in a slot and cauldron blowout and over a foredune, Mason Bay, Stewart Island (Rakiura), NZ

This study is the first to simultaneously compare flow and sediment transport through a blowout and over an adjacent foredune, and the first study of flow within a highly sinuous, slot and cauldron blowout. Flow across the foredune transect is similar to that observed in other studies and is primarily modulated by across-dune vegetation density differences. Flow within the blowout is highly complex and exhibits pronounced accelerations and jet flow. It is characterised by marked helicoidal coherent vortices in the mid-regions, and topographically vertically forced flow out of the cauldron portion of the blowout. Instantaneous sediment transport within the blowout is significant compared to transport onto and/or over the adjacent foredune stoss slope and ridge, with the blowout providing a conduit for suspended sediment to reach the downwind foredune upper stoss slope and crest. Medium term (4months) aeolian sedimentation data indicates sand is accumulating in the blowout entrance while erosion is taking place throughout the majority of the slot, and deposition is occurring downwind of the cauldron on the foredune ridge. The adjacent lower stoss slope of the foredune is accreting while the upper stoss slope is slightly erosional. Longer term (16months) pot trap data shows that the majority of foredune upper stoss slope and crest accretion occurs via suspended sediment delivery from the blowout, whereas the majority of the suspended sediment arriving to the well-vegetated foredune stoss slope is deposited on the mid-stoss slope. The results of this study indicate one mechanism of how marked alongshore foredune morphological variability evolves due to the role of blowouts in topographically accelerating flow, and delivering significant aeolian sediment downwind to relatively discrete sections of the foredune.

Unique and isolated: population structure has implications for management of the endangered New Zealand sea lion

Female otariids (eared seals) frequently display strong levels of philopatry, a behaviour that has the potential to influence population structure, particularly at the mitochondrial level. Conversely, male otariids often move between breeding colonies, likely facilitating nuclear gene flow between colonies. Such gender-specific movements have the potential to influence species population structure. Here we investigate the genetic population structure of the endangered New Zealand (NZ) sea lion, using nuclear (microsatellite) and mitochondrial molecular markers, with the intention to better inform conservation through identification of management units for the species. The strong levels of female philopatry in this species have potential to lead to population structure at the mitochondrial loci. In contrast, weak or no population structure is expected across nuclear loci. NZ sea lions were sampled from the main breeding areas across the species’ current distribution (three Auckland Islands sites, two Campbell Island sites, one Stewart Island site and one Otago Peninsula site). Individuals were screened for microsatellite (n = 271; 16 loci) and mitochondrial (n = 56; 1027 bp D-loop and 1189 bp cytb). Despite a small (c. 9880 individuals) population size, moderate levels of microsatellite variation are observed in the NZ sea lions, in contrast to low levels of mitochondrial genetic variation. Results from mitochondrial DNA analyses revealed no population structure, suggesting that the strong level of female philopatry in NZ sea lions alone is not sufficient to maintain genetic population structure. Due to the frequent male movements between breeding colonies, no population structure was detected across the nuclear loci either. The absence of genetic structure suggests that, from a genetic perspective, NZ sea lions can be considered to be a single population. Despite this, the differing impacts of threats (e.g. fisheries by-catch) to each individual breeding colony must also be taken into consideration when defining management units for this endangered species.

Reconstructing atmospheric circulation over southern New Zealand: Establishment of modern westerly airflow 5500 years ago and implications for Southern Hemisphere Holocene climate change

Late-twentieth century changes in the intensity and migration of Southern Hemisphere westerly winds have been implicated in spatially complex variability in atmospheric and ocean circulation, and ice-sheet dynamics, across the mid- to high-latitudes. A major uncertainty, however, is whether present day hemispheric-wide symmetrical airflow is representative of past behaviour. Here we report a multi-proxy study from Stewart Island and southern Fiordland, New Zealand (46–47°S) reconstructing Holocene changes at the northern limit of westerly airflow. Increased minerogenic input and a pronounced shift in cool-loving vegetation around 5500 years ago is consistent with the establishment of westerly airflow at this latitude in the southwest Pacific. In marked contrast, stronger winds are reported further south over the subantarctic Auckland (50°S) and Campbell (52°S) Islands from 8000 years ago. Intriguingly, reconstructions from the east Pacific suggest a weakening of core westerly airflow after 8500 years ago, but an expansion along the northern limits sometime after 5500 years ago. Our results suggest similar atmospheric circulation changes have been experienced in the Pacific since 5500 years ago, but indicate an expanded network of sites is needed to comprehensively test the driver(s) and impact(s) of Holocene mid-latitude westerly winds across the Southern Hemisphere.

Novel morphological and molecular data for Corynosoma hannae Zdzitowiecki, 1984 (Acanthocephala: Polymorphidae) from teleosts, fish-eating birds and pinnipeds from New Zealand

The polymorphid acanthocephalan, Corynosoma hannae Zdzitowiecki, 1984 is characterised on the basis of newly collected material from a New Zealand sea lion, Phocarctos hookeri (Gray), and long-nosed fur seal, Arctophoca forsteri (Lesson) (definitive hosts), and from Stewart Island shags, Leucocarbo chalconotus (Gray), spotted shags, Phalacrocorax punctatus (Sparrman) and yellow-eyed penguins, Megadyptes antipodes (Hombron & Jacquinot) (non-definitive hosts) from New Zealand. Specimens are described in detail and scanning electron micrographs for C. hannae are provided. Additionally, cystacanths of C. hannae are reported and described for the first time from the body cavity and mesenteries of New Zealand brill, Colistium guntheri (Hutton) and from New Zealand sole, Peltorhamphus novaezeelandiae Günther from Kaka Point, Otago in New Zealand. Partial sequence data for the mitochondrial cytochrome c oxidase 1 gene (cox1) for adults, immature specimens and cystacanths of C. hannae were obtained. Phylogenetic analyses of the newly-generated sequences and for available cox1 sequences of Corynosoma spp. revealed a close relationship between C. hannae and C. australe Johnston, 1937, both species infecting pinnipeds in the Southern Hemisphere. However, a morphological comparison of the species suggests that C. hannae mostly closely resembles C. evae Zdzitowiecki, 1984 and C. semerme (Forssell, 1904), the latter of which occurs in pinnipeds in the Northern Hemisphere.

Polymetallic mineralised veins in ferroan/A-type Cretaceous leucogranite, Stewart Island, New Zealand

ABSTRACTThe 140 ± 1 Ma hypersolvus, ferroan, weakly peralkaline to weakly peraluminous North Red Head leucogranite in northwest Stewart Island is cut by quartz-pyrite-rich veins that contain a wide variety of Mo, Ag, Te, Bi, Au, Co, Cu, Pb, Zn, REE, Nb, Y, Th, U, Zr, Ti, Be and F-bearing minerals. Patchy hematite-pyrite alteration locally overprints leucogranite in the vicinity of the mineralised veins. Individual veins are up to 5 m thick and 200+ m long. U–Pb dating and trace-element geochemistry indicate a direct link between leucogranite crystallisation and exsolution of the vein-forming hydrothermal fluid. Mineralised veins developed along transpressional faults within the leucogranite soon after emplacement. Incipiently mineralised quartz ± pyrite veins at Waituna Bay and the northern end of West Ruggedy Beach several kilometres from North Red Head are probably part of the same hydrothermal system as the veins at North Red Head. Metal and alteration assemblages at North Red Head most closely resemble those in rare hydrothermal systems associated with oxidised fluorine-rich A-type granites.

Polymetallic mineralisation associated with Carboniferous I-type granitoids in central Stewart Island, New Zealand

ABSTRACTCarboniferous granitoids in central Stewart Island host two metalliferous hydrothermal systems that formed during emplacement of the c. 306 ± 2 Ma old Euchre Pluton and 303 ± 2 Ma Hill 267 leucogranitoid, respectively. The Ogles Creek–Silvertown Hydrothermal System (OST) on the eastern side of South West Arm, Paterson Inlet is centred on the scheelite-bearing, ilmenite-syenogranite core of the Euchre Pluton. Here pyritic-potassic alteration and related veins contain Mo, Bi, Ag, Co, Cu, W, Pb, Zn, U–Th and rare Earth element (REE) sulphide, telluride, oxide and phosphate minerals. Peripheral quartz-rich veins contain various Ag, Au, Pb and Zn-bearing sulphide, telluride and oxide minerals. The Hill 267 Hydrothermal System (HHS) is centred on the ridge between the Scott Burn and Forked Creek where strongly altered leucogranitoid riddled with miarolitic cavities contains pyrite, W- and Nb-bearing rutile, molybdenite, tourmaline and 2–10 times background Bi, Ag, Te, Cu and Se. More prospective parts of both systems have probably been removed by erosion, but less deeply eroded correlative hydrothermal systems may be present elsewhere in New Zealand near the outboard margin of the Takaka Terrane.

Seroprevalence of Toxoplasma gondii in mainland and sub-Antarctic New Zealand sea lion (Phocarctos hookeri) populations

AIMS: To investigate the seroprevalence of antibodies to Toxoplasma gondii in New Zealand sea lions (Phocarctos hookeri), as a potential contributor to reproductive failure.METHODS: Archived sera were sourced from New Zealand sea lions from two recolonising mainland populations in the Otago Peninsula (n=15) and Stewart Island (n=12), as well as a declining population at Enderby Island (n=28) in the New Zealand sub-Antarctic. Sera were tested for antibodies to T. gondii using a commercially available ELISA (with samples considered positive if the sample to positive ratio was >30%), and latex agglutination test (LAT; with titres ≥1:32 considered positive). Western blot analysis was used to validate the results of a subset of 14 samples.RESULTS: Five samples from sea lions in mainland locations were confirmed positive for antibodies to T. gondii. Two adult females exhibited high LAT antibody titres (min 1:2048, max 1:4096) on both occasions when sampled 1 and 2 years apart, respectively. No animals from Enderby Island were seropositive.CONCLUSIONS: Toxoplasma gondii infection is unlikely to be a major contributor to poor reproductive success in New Zealand sea lions. However, continued surveillance is pertinent to assess subclinical and clinical impacts of the parasite on these threatened populations. The commercial tests evaluated here, with further species-specific threshold refinement could provide a fast, inexpensive and reliable indicator of T. gondii exposure in New Zealand sea lions.

Spatial distribution of late Holocene bird bones in the Mason Bay dune system, Stewart Island, New Zealand

ABSTRACTMany of New Zealand’s coastal sand dune systems contain naturally accumulated deposits of late Holocene bones, providing an important archive of our pre-settlement faunas. However, the accumulation and taphonomic processes that operate in natural dune deposits are poorly understood. Here, I contribute to our understanding of these processes through analysing spatial patterns of bone distribution in an extensive late Holocene dune system at Mason Bay, Stewart Island. The bone assemblage was collected between December 2002 and February 2003, and included 2880 identified bones from at least 28 bird species. These included extinct species (South Island piopio, Turnagra capensis), regionally rare species (e.g. weka, Gallirallus australis and New Zealand falcon, Falco novaeseelandiae) and locally rare species (e.g. South Island kākā, Nestor meridionalis meridionalis). Significant effects of distance to beach, and distance to the edge of woody vegetation, were found for bones of certain bird groups. The results indicate three main sources of bird bones for the Mason Bay dune system assemblage: 1. nesting colonies within the dunes; 2. storm-wrecked seabirds; and 3. birds inhabiting woody vegetation bordering the dunes. Understanding source biases for dune bone deposits will allow more informed interpretations about the composition of the local prehistoric faunal communities.

Topographic Steering of Oblique Incident Winds Across a Foredune-Parabolic Topography, Mason Bay, Stewart Island, New Zealand

ABSTRACT Wakes, S.J.; Hilton, M.J., and Konlechner, T., 2016. Topographic steering of oblique incident winds across a foredune-parabolic topography, Mason Bay, Stewart Island, New Zealand. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 343–347. Coconut Creek (Florida), ISSN 0749-0208. Climate change modelling predicts increased westerly winds across southern New Zealand, with incident winds becoming more oblique on many beaches. Of interest is the effect these increasingly oblique winds will have on beach-foredune sand flux and dune morphodynamics. We need to model wind flows over these dunes in order to understand these potential changes. Mason Bay, Stewart Island, New Zealand experiences a range of incident winds, from southwest to northwest and, therefore, provides opportunities to both model and verify topographic steering. The dune systems c...

Genetic and morphological evidence for two species ofLeucocarboshag (Aves, Pelecaniformes, Phalacrocoracidae) from southern South Island of New Zealand

Leucocarbo shags are a species-rich seabird clade exhibiting a southern circumpolar distribution. New Zealand's endemic Stewart Island shag, Leucocarbo chalconotus (G. R. Gray, 1845), comprises two regional groups (Otago and Foveaux Strait) that show consistent differences in relative frequencies between pied (black and white) and bronze (wholly dark) plumages, the extent and colour of facial carunculation, body size (based on postcranial morphometrics), and breeding season. Moreover, previous genetic research on modern and historical specimens utilizing mitochondrial DNA control-region sequences has also shown that the Otago and Foveaux lineages may not be sister taxa; instead, in several analyses the Otago lineage is sister to the endemic Chatham Island shag, Leucocarbo onslowi (Forbes, 1893). We present new ancient DNA analyses of the type specimens for the Otago and Foveaux Strait lineages of L. chalconotus, including a phylogenetic reanalysis of the available ancient, historical, and modern control-region sequence data for these lineages (including L. onslowi), and additional statistical analyses incorporating new morphometric characters. These analyses indicate that under the diagnosable species concept the two lineages of Stewart Island shag represent two separate species, which we now recognize as the Otago shag, L. chalconotus (G. R. Gray, 1845), and the Foveaux shag, Leucocarbo stewarti (Ogilvie-Grant, 1898).

Where did the rats of Big South Cape Island come from?

The ship rat invasion of Big South Cape Island/Taukihepa in the 1960s was an ecological catastrophe that marked a turning point for the management of rodents on offshore islands of New Zealand. Despite the importance of this event in the conservation history of New Zealand, and subsequent major advances in rodent eradication and biosecurity, the source and pathway of the rat invasion of Big South Cape Island has never been identified. Using modern molecular methods on contemporary and historical tissue samples, we identify the mitochondrial DNA (mtDNA) haplotype of ship rats (Rattus rattus) on Big South Cape Island and compare it to that of ship rats in the neighbouring regions of Stewart Island/Rakiura and southern New Zealand, all hypothesised as possible source sites for the invasion. We identify two haplotype clusters, each comprising three closely related haplotypes; one cluster unique to Stewart Island, and the other found in southern New Zealand and elsewhere. By a process of elimination we rule that the ship rat invasion of Big South Cape Island was neither by swimming nor boat transport from Stewart Island, and is unlikely to have come from the south coast ports of New Zealand. However, because the ship rat haplotype found on Big South Cape Island is cosmopolitan to New Zealand's South Island and elsewhere, we can only confirm that the invasion likely originated from some distance, but are not able to identify the invasion source more precisely. An unexpected consequence of our study is the discovery of five new mtDNA haplotypes for R. rattus that have not been previously reported.

Overthrowing a regime shift: displacement of sea urchins by abalone in a kelp forest ecosystem

Interactions among sea urchin and abalone populations provide an important mechanism for maintaining segregation of habitat use at small spatial scales within kelp forest ecosystems. Here we provide evidence from a long‐term study of the sea urchin, Evechinus chloroticus, and the abalone, Haliotis iris, populations in a pristine rocky harbor of Stewart Island, in southern New Zealand. Between 1998 and 2014 we observe declines in density of abalone within fished regions of the Inlet and a coincident increase in density of sea urchins. In these regions, sea urchins progressively invaded the shallow (0–3 m) depth stratum formally occupied by abalone and dense, multi‐layered stands of macroalgae. Formation of the Ulva Island Marine Reserve in 2004 released abalone populations from fishing mortality, resulting in population increases within the shallow water depth stratum. Here we observed declines in sea urchin density as the growing abalone population displaced sea urchins from the shallow water habitats. The reestablishment of a depth‐stratified distribution of abalone and sea urchins within the kelp forest provides a likely mechanism for maintenance of habitat complexity and evidence for the important role of high‐density abalone populations within kelp forest ecosystems.

Movement patterns of adult scallops (Pecten novaezealandiae) within a customary fisheries reserve: Implications for fine scale spatial management

The endemic scallop (Pecten novaezealandiae) is patchily distributed around New Zealand’s coastline and supports customary, recreational and commercial harvest. Little information exists on post-settlement movement patterns of this species, which if significant, could impact their distribution, thus influencing the effectiveness of spatial refuges to fishing such as rāhui (fisheries closure). The movements of P. novaezealandiae were examined within adult scallop habitat in a customary fisheries reserve, Te Whaka ā Te Wera (Paterson Inlet) Mātaitai, Rakiura (Stewart Island), New Zealand, by tracking the dispersal of tagged scallops from a central release point over two months. The average distance moved, calculated from recovered scallops, was 1.82m per month, and these movement rates did not differ between the five sites or the two size classes examined. No significant directional movement was observed. The distribution of adult scallops is unlikely to be significantly affected by the scale of random movement observed. Once P. novaezealandiae are settled in appropriate habitat they are likely to only move in response to potential predators. Any spatial refuge created through management intervention, is likely to have positive effects through enhanced larval recruitment due to protection of breeding aggregations, not through movement of adults. The proposed reopening of the scallop fishery to hand collection with a prohibition on underwater breathing apparatus would maintain a deep water refuge for adult scallops, with potential benefits for adjacent fished shallow habitats through larval export.

Methyl mercury concentrations in edible fish and shellfish from Dunedin, and other regions around the South Island, New Zealand

Methyl mercury (MeHg) concentrations were determined in edible fish and shellfish available in local markets in Dunedin, New Zealand. While most of the fish species were sourced in Dunedin, some specimens of fish were also collected from waters off Picton, around Stewart Island and also off-shore of the South Island in the Puysegur and Subantarctic regions. The concentrations of MeHg were analysed in 25 different fish species and shellfish (103 muscle tissue samples). Total mercury (HgT) levels were also analysed in a few (n=12) selected fish samples. Most of the Hg was in the form of MeHg (≥96%). Higher MeHg concentrations were found in fish at higher trophic levels, particularly in predatory fish species such as ling, school shark, spiny dogfish and albacore tuna. Concentrations of MeHg in all samples ranged from 0.002 to 2.515μgMeHg/g.