Males miss and females forgo: Auditory masking from vessel noise impairs foraging efficiency and success in killer whales.

Understanding how the environment mediates an organism's ability to meet basic survival requirements is a fundamental goal of ecology. Vessel noise is a global threat to marine ecosystems and is increasing in intensity and spatiotemporal extent due to growth in shipping coupled with physical changes to ocean soundscapes from ocean warming and acidification. Odontocetes rely on biosonar to forage, yet determining the consequences of vessel noise on foraging has been limited by the challenges of observing underwater foraging outcomes and measuring noise levels received by individuals. To address these challenges, we leveraged a unique acoustic and movement dataset from 25 animal-borne biologging tags temporarily attached to individuals from two populations of fish-eating killer whales (Orcinus orca) in highly transited coastal waters to (1) test for the effects of vessel noise on foraging behaviors-searching (slow-click echolocation), pursuit (buzzes), and capture and (2) investigate the mechanism of interference. For every 1 dB increase in maximum noise level, there was a 4% increase in the odds of searching for prey by both sexes, a 58% decrease in the odds of pursuit by females and a 12.5% decrease in the odds of prey capture by both sexes. Moreover, all but one deep (≥75 m) foraging attempt with noise ≥110 dB re 1 µPa (15-45 kHz band; n = 6 dives by n = 4 whales) resulted in failed prey capture. These responses are consistent with an auditory masking mechanism. Our findings demonstrate the effects of vessel noise across multiple phases of odontocete foraging, underscoring the importance of managing anthropogenic inputs into soundscapes to achieve conservation objectives for acoustically sensitive species. While the timescales for recovering depleted prey species may span decades, these findings suggest that complementary actions to reduce ocean noise in the short term offer a critical pathway for recovering odontocete foraging opportunities.

Effects of pre-treatment, historical age, and sample characteristics on the stable isotope analyses of killer whale (Orcinus orca) bone.

RATIONALE: Stable isotope analysis of bone provides insight into animal foraging and allows for ecological reconstructions over time, however pre-treatment is required to isolate collagen. Pre-treatments typically consist of demineralization to remove inorganic components and/or lipid extraction to remove fats, but these protocols can differentially affect stable carbon (δ13C) and nitrogen (δ15N) isotope values depending on the chemicals, tissues, and/or species involved. Species-specific methodologies create a standard for comparability across studies and enhance understanding of collagen isolation from modern cetacean bone. METHODS: Elemental analyzers coupled to isotope ratio mass spectrometers were used to measure the δ13C and δ15N values of powdered killer whale (Orcinus orca) bone that was intact (control) or subjected to one of three experimental conditions: demineralized, lipid-extracted, and both demineralized and lipid-extracted. Additionally, C:N ratios were evaluated as a proxy for collagen purity. Lastly, correlations were examined between control C:N ratios vs. historical age and control C:N ratios vs. sample characteristics. RESULTS: No significant differences in the δ15N values were observed for any of the experimental protocols. However, the δ13C values were significantly increased by all three experimental protocols: demineralization, lipid extraction, and both treatments combined. The most influential protocol was both demineralization and lipid extraction. Measures of the C:N ratios were also significantly lowered by demineralization and both treatments combined, indicating the material was closer to pure collagen after the treatments. Collagen purity as indicated via C:N ratio was not correlated with historical age nor sample characteristics. CONCLUSIONS: If only the δ15N values from killer whale bone are of interest for analysis, no pre-treatment seems necessary. If the δ13C values are of interest, samples should be both demineralized and lipid-extracted. As historical age and specimen characteristics are not correlated with sample contamination, all samples can be treated equally.

Dietary plasticity and broad North Atlantic origins inferred from bulk and amino acid-specific δ15N and δ13C favour killer whale range expansions into Arctic waters.

Killer whales (Orcinus orca) occur seasonally in the eastern Canadian Arctic (ECA), where their range expansion associated with declining sea ice have raised questions about the impacts of increasing killer whale predation pressure on Arctic-endemic prey. We assessed diet and distribution of ECA killer whales using bulk and compound-specific stable isotope analysis (CSIA) of amino acids (AA) of 54 skin biopsies collected from 2009 to 2020 around Baffin Island, Canada. Bulk ECA killer whale skin δ15N and δ13C values did not overlap with potential Arctic prey after adjustment for trophic discrimination, and instead reflected foraging history in the North Atlantic prior to their arrival in the ECA. Adjusted killer whale stable isotope (SI) values primarily overlapped with several species of North Atlantic baleen whales or tuna. Amino acid (AA)-specific δ15N values indicated the ECA killer whales fed primarily on marine mammals, having similar glutamic acid δ15N-phenylalanine δ15N (δ15NGlx-Phe) and threonine δ15N (δ15NThr) as mammal-eating killer whales from the eastern North Pacific (ENP) that served as a comparative framework. However, one ECA whale grouped with the fish-eating ENP ecotype based δ15NThr. Distinctive essential AA δ13C of ECA killer whale groups, along with bulk SI similarity to killer whales from different regions of the North Atlantic, indicates different populations converge in Arctic waters from a broad source area. Generalist diet and long-distance dispersal capacity favour range expansions, and integration of these insights will be critical for assessing ecological impacts of increasing killer whale predation pressure on Arctic-endemic species.

Killer whale predation on an Antarctic minke whale in the northern Antarctic Peninsula.

We describe the seldom observed event of a group of type A killer whale (Orcinus orca) predating on an Antarctic minke whale (Balaenoptera bonaerensis) in austral summer 2019. A pod of 11-13 individuals was observed - and documented by photographs and video - as they killed and fed on the minke whale in the Bransfield Strait, northern Antarctic Peninsula. The pod was being observed for about one hour, when some killer whale's individuals were noticed to be performing hunting behaviour. This lasted about 10 minutes, at the end of which the minke whale was killed. Three different species of seabirds were observed feeding on the minke carcass. A video of the encounter is provided.

Nontarget and suspect screening reveals the presence of multiple plastic-related compounds in polar bear, killer whale, narwhal and long-finned pilot whale blubber from East Greenland.

The monitoring of legacy contaminants in sentinel northern marine mammals has revealed some of the highest concentrations globally. However, investigations into the presence of chemicals of emerging Arctic concern (CEACs) and other lesser-known chemicals are rarely conducted, if at all. Here, we used a nontarget/suspect approach to screen for thousands of different chemicals, including many CEACs and plastic-related compounds (PRCs) in blubber/adipose from killer whales (Orcinus orca), narwhals (Monodon monoceros), long-finned pilot whales (Globicephala melas), and polar bears (Ursus maritimus) in East Greenland. 138 compounds were tentatively identified mostly as PRCs, and four were confirmed using authentic standards: di(2-ethylhexyl) phthalate (DEHP), diethyl phthalate (DEP), di(2-propylheptyl) phthalate (DPHP), and one antioxidant (Irganox 1010). Three other PRCs, a nonylphenol isomer, 2,6-di-tert-butylphenol, and dioctyl sebacate, exhibited fragmentation patterns matching those in library databases. While phthalates were only above detection limits in some polar bear and narwhal, Irganox 1010, nonylphenol, and 2,6-di-tert-butylphenol were detected in >50% of all samples. This study represents the first application of a nontarget/suspect screening approach in Arctic cetaceans, leading to the identification of multiple PRCs in their blubber. Further nontarget analyses are warranted to comprehensively characterize the extent of CEAC and PRC contamination within Arctic marine food webs.

Climate change introduces threatened killer whale populations and conservation challenges to the Arctic.

The Arctic is the fastest-warming region on the planet, and the lengthening ice-free season is opening Arctic waters to sub-Arctic species such as the killer whale (Orcinus orca). As apex predators, killer whales can cause significant ecosystem-scale changes. Setting conservation priorities for killer whales and their Arctic prey species requires knowledge of their evolutionary history and demographic trajectory. Using whole-genome resequencing of 24 killer whales sampled in the northwest Atlantic, we first explored the population structure and demographic history of Arctic killer whales. To better understand the broader geographic relationship of these Arctic killer whales to other populations, we compared them to a globally sampled dataset. Finally, we assessed threats to Arctic killer whales due to anthropogenic harvest by reviewing the peer-reviewed and gray literature. We found that there are two highly genetically distinct, non-interbreeding populations of killer whales using the eastern Canadian Arctic. These populations appear to be as genetically different from each other as are ecotypes described elsewhere in the killer whale range; however, our data cannot speak to ecological differences between these populations. One population is newly identified as globally genetically distinct, and the second is genetically similar to individuals sampled from Greenland. The effective sizes of both populations recently declined, and both appear vulnerable to inbreeding and reduced adaptive potential. Our survey of human-caused mortalities suggests that harvest poses an ongoing threat to both populations. The dynamic Arctic environment complicates conservation and management efforts, with killer whales adding top-down pressure on Arctic food webs crucial to northern communities' social and economic well-being. While killer whales represent a conservation priority, they also complicate decisions surrounding wildlife conservation and resource management in the Arctic amid the effects of climate change.

Killer whale respiration rates.

Measuring breathing rates is a means by which oxygen intake and metabolic rates can be estimated to determine food requirements and energy expenditure of killer whales (Orcinus orca) and other cetaceans. This relatively simple measure also allows the energetic consequences of environmental stressors to cetaceans to be understood but requires knowing respiration rates while they are engaged in different behaviours such as resting, travelling and foraging. We calculated respiration rates for different behavioural states of southern and northern resident killer whales using video from UAV drones and concurrent biologging data from animal-borne tags. Behavioural states of dive tracks were predicted using hierarchical hidden Markov models (HHMM) parameterized with time-depth data and with labeled tracks of drone-identified behavioural states (from drone footage that overlapped with the time-depth data). Dive tracks were sequences of dives and surface intervals lasting ≥ 10 minutes cumulative duration. We calculated respiration rates and estimated oxygen consumption rates for the predicted behavioural states of the tracks. We found that juvenile killer whales breathed at a higher rate when travelling (1.6 breaths min-1) compared to resting (1.2) and foraging (1.5)-and that adult males breathed at a higher rate when travelling (1.8) compared to both foraging (1.7) and resting (1.3). The juveniles in our study were estimated to consume 2.5-18.3 L O2 min-1 compared with 14.3-59.8 L O2 min-1 for adult males across all behaviours based on estimates of mass-specific tidal volume and oxygen extraction. Our findings confirm that killer whales take single breaths between dives and indicate that energy expenditure derived from respirations requires using sex, age, and behavioural-specific respiration rates. These findings can be applied to bioenergetics models on a behavioural-specific basis, and contribute towards obtaining better predictions of dive behaviours, energy expenditure and the food requirements of apex predators.

Killer whale fecal samples: How to get the most out of a single extraction.

Fecal samples are a non-invasive and relatively accessible matrix for investigating physiological processes in resident killer whale (Orcinus orca) populations. The high lipid content of the diet (primarily salmonids) leads to lower density fecal material and slower dispersion, facilitating sample collection. As fecal discharge is relatively infrequent and the volume of sample is variable, maximizing analytical options is an important consideration. Here we present an extraction methodology to measure hormones and lipid content from the same fecal aliquot. Lipid extractions are commonly conducted using chloroform and methanol from Folch or Bligh and Dyer (B&D), while alcohol is the primary solvent for hormone extraction. We evaluated the possibility of using the methanol layer from lipid extractions to assess fecal steroid hormone levels. Folch and B&D methanol residues were assayed form metabolites of progesterone (PMs) and corticosterone (GCs), and results were compared to aliquots extracted in 70 % ethanol. Hormone concentrations measured in the methanol layer from Folch and B&D extractions were 55 % to 79 % lower than concentrations in 70 % ethanol. We developed mathematical corrections, using linear regression models fitted to Folch or B&D methanol vs 70 % ethanol hormone concentrations (p < 0.01). Fecal concentrations of PMs and GCs from methanol extractions were biologically validated and are significantly higher in confirmed pregnant females compared to non-pregnant individuals (p < 0.05). This study demonstrates that lipid extraction protocols may be used for the analysis of multiple biomarkers, maximizing the use of small-volume samples.

Social and genetic connectivity despite ecological variation in a killer whale network.

Philopatric kin-based societies encourage a narrow breadth of conservative behaviours owing to individuals primarily learning from close kin, promoting behavioural homogeneity. However, weaker social ties beyond kin, and across a behaviourally diverse social landscape, could be sufficient to induce variation and a greater ecological niche breadth. We investigated a network of 457 photo-identified killer whales from Norway (548 encounters in 2008-2021) with diet data available (46 mixed-diet individuals feeding on both fish and mammals, and 411 exclusive fish-eaters) to quantify patterns of association within and between diet groups, and to identify underlying correlates. We genotyped a subset of 106 whales to assess patterns of genetic differentiation. Our results suggested kinship as main driver of social bonds within and among cohesive social units, while diet was most likely a consequence reflective of cultural diffusion, rather than a driver. Flexible associations within and between ecologically diverse social units led to a highly connected network, reducing social and genetic differentiation between diet groups. Our study points to a role of social connectivity, in combination with individual behavioural variation, in influencing population ecology in killer whales.

Understanding the relationship between the Bering Sea Cold Pool and vocal presence of odontocetes in the context of climate changea).

The Cold Pool is a subsurface layer with water temperatures below 2 °C that is formed in the eastern Bering Sea. This oceanographic feature of relatively cooler bottom temperature impacts zooplankton and forage fish dynamics, driving different energetic pathways dependent upon Bering Sea climatic regime. Odontocetes echolocate to find prey, so tracking foraging vocalizations acoustically provides information to understand the implications of climate change on Cold Pool variability influencing regional food web processes. Vocal foraging dynamics of ice-associated and seasonally migrant marine mammal species suggest that sperm whales spend more time searching for prey in warm years when the Cold Pool is reduced but are more successful at capturing prey during cold years when the Cold Pool is stronger. Beluga whale foraging vocal activity was relatively consistent across climate regimes but peaked during the warm regime. Killer whale foraging vocal activity peaked in both warm and cold regimes with indicators of different ecotypes exploiting changing prey conditions across climate regimes. Foraging activity of odontocete apex predators may serve as a sentinel indicator of future ecosystem change related to prey availability that is linked to a diminishing Cold Pool as water temperatures rise and seasonal sea ice decreases due to climate change.

Foraging behaviour and ecology of transient killer whales within a deep submarine canyon system.

Transient killer whales have been documented hunting marine mammals across a variety of habitats. However, relatively little has been reported about their predatory behaviours near deep submarine canyons and oceanic environments. We used a long-term database of sightings and encounters with these predators in and around the Monterey Submarine Canyon, California to describe foraging behaviour, diet, seasonal occurrence, and habitat use patterns. Transient killer whales belonging to the outer coast subpopulation were observed within the study area 261 times from 2006-2021. Occurrences, behaviours, and group sizes all varied seasonally, with more encounters occurring in the spring as grey whales migrated northward from their breeding and calving lagoons in Mexico (March-May). Groups of killer whales foraged exclusively in open water, with individuals within the groups following the contours of the submarine canyon as they searched for prey. Focal follows revealed that killer whales spent 51% of their time searching for prey (26% of their time along the shelf-break and upper slope of the canyon, and 25% in open water). The remainder of their time was spent pursuing prey (10%), feeding (23%), travelling (9%), socializing (6%), and resting (1%). Prey species during 87 observed predation events included California sea lions, grey whale calves, northern elephant seals, minke whales, common dolphins, Pacific white-sided dolphins, Dall's porpoise, harbour porpoise, harbour seals, and sea birds. The calculated kill rates (based on 270 hours of observing 50 predation events) were 0.26 California sea lions per killer whale over 24 hours, 0.11 grey whale calves, and 0.15 for all remaining prey species combined. These behavioural observations provide insights into predator-prey interactions among apex predators over submarine canyons and deep pelagic environments.

The combined effects of predation, fishing, and ocean productivity on salmon species targeted by marine mammals in the northeast Pacific.

Along the northeast Pacific coast, the salmon-eating southern resident killer whale population (SRKW, Orcinus orca) have been at very low levels since the 1970s. Previous research have suggested that reduction in food availability, especially of Chinook salmon (Oncorhynchus tshawytscha), could be the main limiting factor for the SRKW population. Using the ecosystem modelling platform Ecopath with Ecosim (EwE), this study evaluated if the decline of the Pacific salmon populations between 1979 and 2020 may have been impacted by a combination of factors, including marine mammal predation, fishing activities, and climatic patterns. We found that the total mortality of most Chinook salmon populations has been relatively stable for all mature returning fish despite strong reduction in fishing mortality since the 1990s. This mortality pattern was mainly driven by pinnipeds, with increases in predation between 1979 and 2020 mortality ranging by factors of 1.8 to 8.5 across the different Chinook salmon population groups. The predation mortality on fall-run Chinook salmon smolts originating from the Salish Sea increased 4.6 times from 1979 to 2020, whereas the predation mortality on coho salmon (Oncorhynchus kisutch) smolts increased by a factor of 7.3. The model also revealed that the north Pacific gyre oscillation (NPGO) was the most important large-scale climatic index affecting the stock productivity of Chinook salmon populations from California to northern British Columbia. Overall, the model provided evidence that multiple factors may have affected Chinook salmon populations between 1979 and 2020, and suggested that predation mortality by marine mammals could be an important driver of salmon population declines during that time.

Polychlorinated biphenyl and polybrominated diphenyl ether profiles vary with feeding ecology and marine rearing distribution among 10 Chinook salmon (Oncorhynchus tshawytscha) stocks in the North Pacific Ocean.

Chinook salmon (Oncorhynchus tshawytscha) along the west coast of North America have experienced significant declines in abundance and body size over recent decades due to several anthropogenic stressors. Understanding the reasons underlying the relatively high levels of persistent organic pollutants (POPs) in Chinook stocks is an important need, as it informs recovery planning for this foundation species, as well for the Chinook-dependent Resident killer whales (Orcinus orca, RKW) of British Columbia (Canada) and Washington State (USA). We evaluated the influence of stock-related differences in feeding ecology, using stable isotopes, and marine rearing ground on the concentrations and patterns of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Chinook salmon. A principal components analysis (PCA) revealed a clear divergence of PCB and PBDE congener patterns between Chinook with a nearshore rearing distribution ('shelf resident') versus a more offshore distribution. Shelf resident Chinook had 12-fold higher PCB concentrations and 46-fold higher PBDE concentrations relative to offshore stocks. Shelf resident Chinook had PCB and PBDE profiles that were heavier and dominated by more bioaccumulative congeners, respectively. The higher δ13C and δ15N in shelf resident Chinook compared to the offshore rearing stocks, and their different marine distributions explain the large divergence in contaminant levels and profiles, with shelf resident stocks being heavily influenced by land-based sources of industrial contamination. Results provide compelling new insight into the drivers of contaminant accumulation in Chinook salmon, raise important questions about the consequences for their health, and explain a major pathway to the heavily POP-contaminated Resident killer whales that consume them.

Assessment of persistent organic pollutants in killer whales (Orcinus orca) of the Canadian Arctic: Implications for subsistence consumption and conservation strategies.

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.

Phthalate contamination in marine mammals off the Norwegian coast.

Phthalates are used in plastics, found throughout the marine environment and have the potential to cause adverse health effects. In the present study, we quantified blubber concentrations of 11 phthalates in 16 samples from stranded and/or free-living marine mammals from the Norwegian coast: the killer whale (Orcinus orca), sperm whale (Physeter macrocephalus), long-finned pilot whale (Globicephala melas), white-beaked dolphin (Lagenorhynchus albirostris), harbour porpoise (Phocoena phocoena), and harbour seal (Phoca vitulina). Five compounds were detected across all samples: benzyl butyl phthalate (BBP; in 50 % of samples), bis(2-ethylhexyl) phthalate (DEHP; 33 %), diisononyl phthalate (DiNP; 33 %), diisobutyl phthalate (DiBP; 19 %), and dioctyl phthalate (DOP; 13 %). Overall, the most contaminated individual was the white-beaked dolphin, whilst the lowest concentrations were measured in the killer whale, sperm whale and long-finned pilot whale. We found no phthalates in the neonate killer whale. The present study is important for future monitoring and management of these toxic compounds.

Call combination patterns in Icelandic killer whales (Orcinus orca).

Acoustic sequences have been described in a range of species and in varying complexity. Cetaceans are known to produce complex song displays but these are generally limited to mysticetes; little is known about call combinations in odontocetes. Here we investigate call combinations produced by killer whales (Orcinus orca), a highly social and vocal species. Using acoustic recordings from 22 multisensor tags, we use a first order Markov model to show that transitions between call types or subtypes were significantly different from random, with repetitions and specific call combinations occurring more often than expected by chance. The mixed call combinations were composed of two or three calls and were part of three call combination clusters. Call combinations were recorded over several years, from different individuals, and several social clusters. The most common call combination cluster consisted of six call (sub-)types. Although different combinations were generated, there were clear rules regarding which were the first and last call types produced, and combinations were highly stereotyped. Two of the three call combination clusters were produced outside of feeding contexts, but their function remains unclear and further research is required to determine possible functions and whether these combinations could be behaviour- or group-specific.

Temporal integration of tone signals by a killer whale (Orcinus orca).

A psychophysical procedure was used to measure pure-tone detection thresholds for a killer whale (Orcinus orca) as a function of both signal frequency and signal duration. Frequencies ranged between 1 and 100 kHz and signal durations ranged from 50 µs to 2 s, depending on the frequency. Detection thresholds decreased with an increase in signal duration up to a critical duration, which represents the auditory integration time. Integration times ranged from 4 ms at 100 kHz and increased up to 241 ms at 1 kHz. The killer whale data are similar to other odontocete species that have participated in similar experiments. The results have implications for noise impact predictions for signals with durations less than the auditory integration time.

Polycyclic aromatic hydrocarbon (PAH) source identification and a maternal transfer case study in threatened killer whales (Orcinus orca) of British Columbia, Canada.

The northeastern Pacific (NEP) Ocean spans the coast of British Columbia (Canada) and is impacted by anthropogenic activities including oil pipeline developments, maritime fossil fuel tanker traffic, industrial chemical effluents, agricultural and urban emissions in tandem with stormwater and wastewater discharges, and forest wildfires. Such events may expose surrounding marine environments to toxic polycyclic aromatic hydrocarbons (PAHs) and impact critical habitats of threatened killer whales (Orcinus orca). We analyzed skeletal muscle and liver samples from stranded Bigg's killer whales and endangered Southern Resident killer whales (SRKWs) for PAH contamination using LRMS. C3-phenanthrenes/anthracenes (mean: 632 ng/g lw), C4-dibenzothiophenes (mean: 334 ng/g lw), and C4-phenanthrenes/anthracenes (mean: 248 ng/g lw) presented the highest concentrations across all tissue samples. Diagnostic ratios indicated petrogenic-sourced contamination for SRKWs and pyrogenic-sourced burdens for Bigg's killer whales; differences between ecotypes may be attributed to habitat range, prey selection, and metabolism. A mother-fetus skeletal muscle pair provided evidence of PAH maternal transfer; low molecular weight compounds C3-fluorenes, dibenzothiophene, and naphthalene showed efficient and preferential exposure to the fetus. This indicates in-utero exposure of PAH-contamination to the fetus. Our results show that hydrocarbon-related anthropogenic activities are negatively impacting these top predators; preliminary data found here can be used to improve oil spill and other PAH pollution management and regulation efforts, and inform policy to conserve killer whale habitats in the NEP.

Spatiotemporal Trends Spanning Three Decades Show Toxic Levels of Chemical Contaminants in Marine Mammals.

Despite their ban and restriction under the 2001 Stockholm Convention, persistent organic pollutants (POPs) are still widespread and pervasive in the environment. Releases of these toxic and bioaccumulative chemicals are ongoing, and their contribution to population declines of marine mammals is of global concern. To safeguard their survival, it is of paramount importance to understand the effectiveness of mitigation measures. Using one of the world's largest marine mammals strandings data sets, we combine published and unpublished data to examine pollutant concentrations in 11 species that stranded along the coast of Great Britain to quantify spatiotemporal trends over three decades and identify species and regions where pollutants pose the greatest threat. We find that although levels of pollutants have decreased overall, there is significant spatial and taxonomic heterogeneity such that pollutants remain a threat to biodiversity in several species and regions. Of individuals sampled within the most recent five years (2014-2018), 48% of individuals exhibited a concentration known to exceed toxic thresholds. Notably, pollutant concentrations are highest in long-lived, apex odontocetes (e.g., killer whales (Orcinus orca), bottlenose dolphins (Tursiops truncatus), and white-beaked dolphins (Lagenorhynchus albirostris)) and were significantly higher in animals that stranded on more industrialized coastlines. At the present concentrations, POPs are likely to be significantly impacting marine mammal health. We conclude that more effective international elimination and mitigation strategies are urgently needed to address this critical issue for the global ocean health.

Determination of water balance maintenance in Orcinus orca and Tursiops truncatus using oxygen isotopes.

The secondary adaptation of Cetacea to a fully marine lifestyle raises the question of their ability to maintain their water balance in a hyperosmotic environment. Cetacea have access to four potential sources of water: surrounding salt oceanic water, dietary free water, metabolic water and inhaled water vapour to a lesser degree. Here, we measured the 18O/16O oxygen isotope ratio of blood plasma from 13 specimens belonging to two species of Cetacea raised under human care (four killer whales Orcinus orca, nine common bottlenose dolphins Tursiops truncatus) to investigate and quantify the contribution of preformed water (dietary free water, surrounding salt oceanic water) and metabolic water to Cetacea body water using a box-modelling approach. The oxygen isotope composition of Cetacea blood plasma indicates that dietary free water and metabolic water contribute to more than 90% of the total water input in weight for cetaceans, with the remaining 10% consisting of inhaled water vapour and surrounding water accidentally ingested or absorbed through the skin. Moreover, the contribution of metabolic water appears to be more important in organisms with a more lipid-rich diet. Beyond these physiological and conservation biology implications, this study opens up questions that need to be addressed, such as the applicability of the oxygen isotope composition of cetacean body fluids and skeletal elements as an environmental proxy of the oxygen isotope composition of present and past marine waters.