To assess whether demographic declines of Arctic species at the southern limit of their range will be gradual or punctuated, we compared large-scale environmental patterns including sea ice dynamics ...to ringed seal (
) reproduction, body condition, recruitment, and stress in Hudson Bay from 2003 to 2013. Aerial surveys suggested a gradual decline in seal density from 1995 to 2013, with the lowest density occurring in 2013. Body condition decreased and stress (cortisol) increased over time in relation to longer open water periods. The 2010 open water period in Hudson Bay coincided with extremes in large-scale atmospheric patterns (North Atlantic Oscillation, Arctic Oscillation, El Nino-Southern Oscillation) resulting in the earliest spring breakup and the latest ice formation on record. The warming event was coincident with high stress level, low ovulation rate, low pregnancy rate, few pups in the Inuit harvest, and observations of sick seals. Results provide evidence of changes in the condition of Arctic marine mammals in relation to climate mediated sea ice dynamics. We conclude that although negative demographic responses of Hudson Bay seals are occurring gradually with diminishing sea ice, a recent episodic environmental event played a significant role in a punctuated population decline.
Contaminant dynamics within Arctic marine food webs may be altered through the climate-driven northward invasions of temperate/boreal species. Here, we compare tissue concentrations of total mercury ...(THg) and legacy and emerging persistent organic pollutants (POPs) in native versus invading forage species sampled from 2012 to 2014 near Arviat, Clyde River, and Resolute Bay, NU, representing, low, mid- and high eastern Canadian Arctic regions, respectively. Concentrations of THg, legacy Σ-polychlorinated biphenyls (ΣPCB) and Σ-organochlorine (ΣOC) pesticides were detected in all forage species, whereas emerging halogenated flame retardants were detected in only a few individuals. Concentrations of major contaminant groups among regions did not vary for Arctic cod (Boreogadus saida), while for sculpin (Cottoidea) there was no clear latitudinal trend. Thus, considering interspecific variation, native sculpin and northern shrimp (Pandalus borealis) had the highest overall concentrations of THg (0.17 ± 0.02 and 0.21 ± 0.01 μg g−1 wet weight, respectively), ΣPCB (322 ± 35 and 245 ± 25 ng g−1 lipid weight (lw), respectively), and ΣOC (413 ± 38 and 734 ± 64 ng g−1 lw, respectively). Comparing the keystone native species, Arctic cod, to its ‘replacement’ species, capelin (Mallotus villosus) and sandlance (Ammodytes spp.), THg concentrations were higher in Arctic cod compared to capelin (p < 0.001), which was partly explained by differences in fish length. Conversely, capelin and sandlance had higher concentrations of most POPs than Arctic cod (p < 0.02). Neither feeding habitat (based on δ13C), trophic position (based on δ15N), nor fish length significantly explained these differences in POPs between Arctic cod, capelin and sandlance. Higher POPs concentrations, as well as variation in congener/compound patterns, in capelin and sandlance relative to Arctic cod seem, therefore, more likely related to a more “temperate”-type contaminant signature in the invaders. Nevertheless, the relatively small (up to two-fold) magnitude of these differences suggested limited effects of these ecological changes on contaminant uptake by Arctic piscivores.
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•THg and POP levels evaluated in Arctic non-native versus native marine forage fish.•Highest levels of THg and POPs found in Arctic natives, sculpin and Northern shrimp.•Higher levels of most POPs found in capelin and sandlance relative to Arctic cod.•Biological/Ecological factors did not explain differences among non-natives and cod.•Small magnitude of differences in THg and POPs between natives and non-natives.
Invading capelin and sandlance showed lower mercury concentrations, but up to two times higher legacy organic contaminants concentrations compared to native Arctic cod.
Killer whales (Orcinus orca) historically restricted to certain Arctic regions due to extensive sea ice have recently been documented farther north and for longer durations in the Canadian Arctic. ...These apex predators accumulate high levels of persistent organic pollutants (POPs). The objective of this study was to evaluate the concentrations and profiles of POPs in killer whales of the Canadian Arctic, thus determining potential risks for Inuit communities if consumed. Biopsies were collected from 33 killer whales across areas of the Canadian Arctic between 2009 and 2021. Significant variability in POP concentrations was observed among whales. The cumulative POP concentrations ranged from 12 to >2270 mg/kg lw, representing ∼200-fold increase from the least to the most contaminated individual. The rank order of concentrations of the top five contaminant classes was ∑DDT, ∑PCB, ∑CHL, ∑Toxaphene, and Dieldrin. Several emerging Arctic contaminants were detected, including chlorpyrifos, endosulfan, pentachloroanisole, and polychlorinated naphthalenes, although at relatively lower concentrations than legacy POPs. Considering the elevated blubber POP levels in killer whales, recommended daily consumption thresholds, established based on human tolerable daily intake (TDI) values, were notably restricted for ∑PCB (<0.14 g), ∑DDT (<6.9 g), ∑CHL (<13 g), dieldrin (<8 g) and heptachlor epoxide (<5 g). Killer whales in the Canadian Arctic exhibited higher POP concentrations than other commonly hunted species such as polar bears, ringed seals, and Arctic char. We acknowledge that a more holistic risk assessment of diet is required to assess the cumulative impacts of contaminant mixtures as well as nutritional quality of tissues commonly consumed by northern communities.
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•Climate change is increasing Inuit interactions with killer whales in the Canadian Arctic.•Some Nunavut communities within the Qikiqtaaluk region have expressed interest in hunting killer whales.•200-fold difference in sum POPs from least to most contaminated killer whale blubber.•Killer whale contaminant levels far higher than traditional country foods.•Safe human consumption of killer whale blubber is limited to <0.1–10 g per day.
As ocean temperatures rise, sub-Arctic capelin (
Mallotus villosus
) and sand lance (
Ammodytes
spp.) have become increasingly abundant in regions of the eastern Canadian Arctic. These fish have a ...similar trophic role to the keystone polar cod (
Boreogadus saida
), potentially competing for food resources when co-occurring. To evaluate this, we calculated feeding niche breadth and overlap based on fatty acids and δ
15
N- and δ
13
C-derived trophic position and carbon source, among sub-Arctic fish and 10 Arctic fish and invertebrates within low, mid, and high latitudes of the Canadian Arctic. Diverse feeding strategies including benthic
Myoxocephalus
sp., anadromous and pelagic fish, led to limited feeding niche overlap among species (13% average, range 0–96%). Feeding niche overlap between capelin and sand lance from the low Arctic was generally high (36–93%); while fatty acid niches of these fish overlapped 0–21% with polar cod in the mid and high Arctic, and their isotopic niches overlapped up to 96%. Capelin and sand lance showed 3–8 times broader feeding niches than polar cod. Regarding regional variation, polar cod had similar niche breadth between regions and highly overlapping fatty acid niches. Niche variation for
Myoxocephalus
sp. and
Gammarus
spp. between low and high Arctic was likely associated with more diverse sources of primary production in the shallower, more brackish low Arctic. Although regional variation in food availability play an important role defining feeding niches, broader niches and isotopic niche overlap with polar cod indicated a potential ecological advantage for capelin and sand lance over polar cod under climate change.
Quantifying trophic relationships within and between species in terms of trophic position, ontogeny and trophic diversity provides information on community-level structure and function. Little ...attention has been focused on examining the trophic structure and temporal changes of communities in freshwater-marine coupled systems in the subarctic and associated impacts of anthropogenic activity on trophic interactions. Therefore, the objective of this study was to quantify the trophic position of mobile consumers (15 species in total) within the lower Churchill River area (Churchill, Manitoba, Canada), examine trophic position variation in relation to ontogeny, and measure the trophic diversity of a fish assemblage before (1993–1995) and after (2019–2020) the installation of the Churchill River weir in the late 1990s. We used stable isotopes (δ
13
C and δ
15
N) to quantify individual and group-level variation in trophic position of thirteen fish species and two seal species and also assessed six community-level metrics of a three fish species assemblage between time periods. Overall, species that mainly foraged on freshwater resources occupied lower trophic positions than species that mainly consumed marine resources. Trophic position increased with fish age only in cisco, fourhorn sculpin, Greenland cod and northern pike. A temporal shift from a trophically diverse to a more trophically redundant fish assemblage occurred between 1993–1995 and 2019–2020. As a result, these predator species now play similar trophic roles. Information on the long-term change in trophic structure of this sub-Arctic estuarine system may help with understanding how anthropogenic activity and climate change have influenced the trophic diversity of a fish assemblage inhabiting this system.
Global climate change during the Late Pleistocene periodically encroached and then released habitat during the glacial cycles, causing range expansions and contractions in some species. These ...dynamics have played a major role in geographic radiations, diversification and speciation. We investigate these dynamics in the most widely distributed of marine mammals, the killer whale (Orcinus orca), using a global data set of over 450 samples. This marine top predator inhabits coastal and pelagic ecosystems ranging from the ice edge to the tropics, often exhibiting ecological, behavioural and morphological variation suggestive of local adaptation accompanied by reproductive isolation. Results suggest a rapid global radiation occurred over the last 350 000 years. Based on habitat models, we estimated there was only a 15% global contraction of core suitable habitat during the last glacial maximum, and the resources appeared to sustain a constant global effective female population size throughout the Late Pleistocene. Reconstruction of the ancestral phylogeography highlighted the high mobility of this species, identifying 22 strongly supported long‐range dispersal events including interoceanic and interhemispheric movement. Despite this propensity for geographic dispersal, the increased sampling of this study uncovered very few potential examples of ancestral dispersal among ecotypes. Concordance of nuclear and mitochondrial data further confirms genetic cohesiveness, with little or no current gene flow among sympatric ecotypes. Taken as a whole, our data suggest that the glacial cycles influenced local populations in different ways, with no clear global pattern, but with secondary contact among lineages following long‐range dispersal as a potential mechanism driving ecological diversification.
Reconstruction of the demographic and evolutionary history of populations assuming a consensus tree‐like relationship can mask more complex scenarios, which are prevalent in nature. An emerging ...genomic toolset, which has been most comprehensively harnessed in the reconstruction of human evolutionary history, enables molecular ecologists to elucidate complex population histories. Killer whales have limited extrinsic barriers to dispersal and have radiated globally, and are therefore a good candidate model for the application of such tools. Here, we analyse a global data set of killer whale genomes in a rare attempt to elucidate global population structure in a nonhuman species. We identify a pattern of genetic homogenisation at lower latitudes and the greatest differentiation at high latitudes, even between currently sympatric lineages. The processes underlying the major axis of structure include high drift at the edge of species' range, likely associated with founder effects and allelic surfing during postglacial range expansion. Divergence between Antarctic and non‐Antarctic lineages is further driven by ancestry segments with up to four‐fold older coalescence time than the genome‐wide average; relicts of a previous vicariance during an earlier glacial cycle. Our study further underpins that episodic gene flow is ubiquitous in natural populations, and can occur across great distances and after substantial periods of isolation between populations. Thus, understanding the evolutionary history of a species requires comprehensive geographic sampling and genome‐wide data to sample the variation in ancestry within individuals.
see also the Perspective by Jacobs and Therkildsen
Lipophilic persistent organic pollutants (POPs) tend to biomagnify in food chains, resulting in higher concentrations in species such as killer whales (Orcinus orca) feeding on marine mammals ...compared to those consuming fish. Advancements in dietary studies include the use of quantitative fatty acid signature analysis (QFASA) and differentiation of feeding habits within and between populations of North Atlantic (NA) killer whales. This comprehensive study assessed the concentrations of legacy and emerging POPs in 162 killer whales from across the NA. We report significantly higher mean levels of polychlorinated biphenyls (PCBs), organochlorine pesticides, and flame retardants in Western NA killer whales compared to those of Eastern NA conspecifics. Mean ∑PCBs ranged from ∼100 mg/kg lipid weight (lw) in the Western NA (Canadian Arctic, Eastern Canada) to ∼50 mg/kg lw in the mid-NA (Greenland, Iceland) to ∼10 mg/kg lw in the Eastern NA (Norway, Faroe Islands). The observed variations in contaminant levels were strongly correlated with diet composition across locations (inferred from QFASA), emphasizing that diet and not environmental variation in contaminant concentrations among locations is crucial in assessing contaminant-associated health risks in killer whales. These findings highlight the urgency for implementing enhanced measures to safely dispose of POP-contaminated waste, prevent further environmental contamination, and mitigate the release of newer and potentially harmful contaminants.
Chemical composition of tissues can act as a biological tag to discriminate among groups of animals that inhabit different areas. In Canada, subsistence hunting of the Baffin Bay narwhal (Monodon ...monoceros Linnaeus, 1758) population is managed as stocks represented by summer aggregations. However, narwhals are highly mobile and are hunted during the migration while stocks mix. Thus, information that can help managers decipher the stock origin of hunted individuals to prevent overexploitation of animals adapted to particular summering grounds is needed. Stable isotope and trace element analyses were conducted on narwhal skin tissues from five stocks in the eastern Canadian Arctic from 1990 to 2015. Discriminant analysis showed a significant difference between Admiralty Inlet and Eclipse Sound stocks in the summer residency period and both differed from Jones Sound and Somerset Island. During the migration season, there was more overlap and less distinction among stocks, but 75% of animals were classified correctly to their defined stocks in both periods. Together stable isotope and trace element analyses are useful for delineating stocks and could be used to complement other stock discrimination approaches.
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