The expansion of killer whales (Orcinus orca) in Arctic regions driven largely by the ongoing loss of sea ice in response to climate change has significant evolutionary, ecological, and conservation implications (Gilg et al., 2012; Garroway et al., 2024). Historically, seasonal sea ice served as a natural barrier limiting access of killer whales to many Arctic areas, but with the dramatic reduction in summer sea ice cover over recent decades, killer whales have been able to extend their range into previously inaccessible regions (Higdon and Ferguson, 2009; Kovacs et al., 2011). This range expansion in the eastern Canadian Arctic (ECA) may be reshaping the structure of marine ecosystems, as killer whales are apex predators capable of exerting top-down control on prey populations that have previously relied on sea ice to minimize predation risk (Breed et al., 2017; Lennert and Richard, 2017). Their presence poses a potential threat to endemic Arctic marine mammals, including narwhals (Monodon monoceros), belugas (Delphinapterus leucas), and bowhead whales (Balaena mysticetus), which have evolved in predator-sparse environments (Ferguson et al., 2010a, 2012). These shifts in predator-prey dynamics could have cascading ecological effects, potentially altering species distribution, behavior, and survival rates (Baum and Worm, 2009), with long-term implications for Arctic biodiversity and ecosystem function. Furthermore, the increasing presence of killer whales introduces new conservation challenges, as many of the Arctic species they prey upon are already vulnerable to population decline due to the effects of climate change and human activities (Laidre and Heide-Jørgensen, 2005; Moore and Huntington, 2008; Laidre et al., 2015; Orgeret et al., 2022; Kuletz et al., 2024). Understanding the patterns of killer whale sightings in the ECA over the past two decades is crucial for assessing the broader ecological impacts of their range expansion and informing future conservation strategies.

Arctic marine ecosystems are often defined by the presence of sea ice, and ice-associated organisms (Melnikov, 1997). There are three species of endemic Arctic cetaceans: beluga, narwhal, and bowhead whale, as well as many species of marine mammal that migrate into Arctic regions during the ice free/low ice season for feeding (Darnis et al., 2012; McMeans et al., 2013; Kuletz et al., 2024). Killer whales are one such seasonal migrant with a long history of observation in the Arctic, typically observed migrating into the ECA in late spring and departing in the fall as sea ice begins to form (Lefort et al., 2020a).

Sighting data for killer whales in the ECA were collected over time from a diverse network of observers, including Inuit community members, tourists, and researchers. Inuit Traditional Ecological Knowledge (TEK) has been particularly valuable in providing consistent, long-term observations of killer whale presence and behavior (Ferguson et al., 2012; Westdal et al., 2013; Higdon et al., 2014). As human populations and activities in the ECA have increased over the years, sighting effort has expanded, contributing to a more comprehensive dataset. This growing human presence, alongside technological advancements such as larger and faster boats, drones, and aerial surveys, has enhanced the ability to document killer whale occurrence across a broader geographic range (Young et al., 2022).

The sightings dataset was analyzed in conjunction with sea ice metrics, including sea ice coverage, ablation (melting), and formation, to assess how killer whale presence aligns with seasonal changes in ice conditions. As sea ice recedes, larger ice-free areas become accessible to killer whales, enabling them to roam in search of prey. These predators target Arctic endemic species such as narwhals, belugas, bowhead whales, and seals, particularly in regions where these marine mammals congregate for breeding, nursing, and resting during ice-free periods (Laidre and Regehr, 2017). The seasonal availability of concentrated prey in these areas is essential for killer whale energetics (Ferguson et al., 2010a), but also holds critical ecological and cultural importance for Inuit communities, who rely on Arctic marine mammals for both subsistence and cultural continuity via knowledge transfer. Therefore, understanding the timing and geographic patterns of killer whale sightings will provide insight into their ecological role in this rapidly changing environment.

The primary aim of this study is to investigate the spatial and temporal patterns of killer whale sightings in the ECA from 2002 to 2023 and assess how these patterns relate to sea ice dynamics. Clustering analyses, based on the mean distance to the five closest neighboring observations, were used to assess trends in whether sightings occurred in localized hotspots or were more diffusely spread across the region. Additionally, arrival and departure dates were analyzed in relation to sea ice coverage to determine the timing of killer whale presence as it correlates with seasonal ice retreat and formation. By examining general spatial patterns and relationships with environmental variables, we seek to understand the extent and characteristics of killer whale habitat use in the ECA, especially in areas where Arctic endemic marine mammals congregate (Higdon et al., 2012, 2014; Hamilton et al., 2022). These findings are critical for assessing the ecological implications of killer whale range expansion in the Arctic, providing insight into predator-prey interactions, increased pressure on prey species, and informing conservation efforts (Matthews et al., 2020). The relevance of this work extends to both ecological research and the cultural and subsistence needs of Inuit communities that rely on Arctic marine mammals for food security (Huntington et al., 2017).

From 1850-2023 there were 674 documented killer whale observations in the Canadian Arctic. During that period there was an increase in observations ( Figure 2 ). From 2002-2023, killer whales were observed a total of 355 times in the Canadian Arctic, after removing observations outside the study area and before May 29, there were 348 in the ECA. Arrival and departure period were separated by median value, so both periods contained 174 observations. There was no trend in the number of observations across years during the study period ( Figure 2 ), with an average of 16 (range: 3-28) observations per year. Point ice values were missing for 66 of the 348 observations because the resolution of the sea ice data resulted in some marine regions along the coast being treated as land. Due to this, point ice was removed from the models to retain sample size.

In our spatial model, clustering of observations was significantly affected by latitude and longitude. Higher clustering in southern and western locations in the study area was likely driven by the high density of observations in western Hudson Bay and Foxe Basin. The effect of year on clustering suggests that over time killer whales were being observed further away from higher use areas, or spreading further into other regions in the ECA. This pattern of spatial spreading (increased clustering distance) could be linked to patterns of decreased sea ice coverage in the Arctic over time (Comiso et al., 2008; Kwok, 2018), as well as shifting effort or means of reporting, as our sighting dataset shows a slight increase in tourism related sightings and an increased number of reports collected via social media. Overall, killer whales in the ECA during summer exhibited flexible movement patterns and habitat use, likely influenced by prey availability observed across multiple seasonal visits and varying sea ice conditions. When both temporal models, arrival and departure, are considered together, there is a pattern of an extended period of killer whale observation in the ECA. Over time, arrival observations (June 5 - August 16) occurred earlier and departure observations (August 17 - December 11) occurred later. The ECA Archipelago has shown a slightly greater change in the date of freeze up in the fall versus break up in the spring (Galley et al., 2012; Walsh et al., 2022). Killer whale presence reflects this sea ice trend, as observations extended further into fall versus earlier in the spring over the study period. Previous research has quantified a decline in sea ice cover in the Canadian Arctic that has likely influenced killer whale presence (Higdon and Ferguson, 2009; Higdon et al., 2014; Stern and Laidre, 2016). Generally, the rate of earlier ECA killer whale entry and later departure over the past two decades matches the rate of sea ice decline of 1.2 days/year (Yang et al., 2023).

These findings align with earlier research on killer whale distribution and behavior in polar regions. The arrival model had a significant year x mean ice interaction term with a trend that suggests that for whales observed at a similar time (i.e., ordinal day 220), the mean regional ice cover has declined over time. When the trend of earlier arrival is combined with the year x mean ice effect it can be interpreted that there is lower sea ice concentration during arrival in later years, which contributes to killer whale sightings earlier in the year. The latitude effect suggests a trend where killer whales are observed further north later in the arrival period, which aligns with expected movement of killer whales further into the Arctic as the arrival period progresses and ice retreats (Moore and Huntington, 2008; Higdon et al., 2014; Kimber et al., 2025).

The departure model year x mean ice interaction term suggests that in later years killer whales were present later during the departure period, even when sea ice concentration was higher. The extended presence of killer whales in the Canadian Arctic aligned with the extended ice free season previously quantified (Howell et al., 2009; Rodrigues, 2009), but extended presence as sea ice concentration begins to increase at the end of the open water season could suggest unknown factors affecting extended killer whale presence. Killer whales could potentially be altering their behaviour, engaging in more risky or bold habitat selection as ice freezes (Matthews et al., 2019) or engaging in habitat associated learning. Both latitude and longitude had a significant effect in the departure model. The latitude effect suggests that killer whales are observed further south later in the year, which aligns with expected movement as sea ice freezes up and killer whales depart from the Arctic. The effect of longitude suggests that whales were observed further east later in the departure period, which is likely related to whales exiting the region east through Davis Strait during freeze up (Matthews et al., 2011; Lefort et al., 2020a). Our results emphasize the role of diminishing sea ice as a primary driver of killer whale distribution and prolonged seasonal presence. However, there are other potential drivers, including prey availability, climate variability, and anthropogenic influences.

Overall, killer whales have been arriving in the ECA 0.6 days/year earlier and departing 1.3 days/year later, leading to a near doubling of their average presence from 26 days in 2002 (6 August to 1 September) to 48 days in 2023 (27 July to 13 September), although this trend varies based on sea ice concentration. Killer whales in the Bering Strait present a stronger trend of temporally increased presence aligning with decreased ice coverage although at a smaller spatial scale than our study, with presence increasing by 32 days over only 8 years (Kimber et al., 2025). The extended period of presence provides killer whales with increased opportunities to locate and prey on marine mammals, potentially having ecological impacts on species that seasonally give birth and nurse their calves during the ice-free period (Laidre and Regehr, 2017). Bowhead, beluga, and narwhal, for instance, migrate to specific summering areas to nurse neonates: bowhead whales within icy habitats (Ferguson et al., 2010b), belugas in shallow estuaries (Smith et al., 2017), and narwhals in remote fjords (Laidre et al., 2004). The prolonged open-water season and increased killer whale presence heighten predation risks, particularly for young and inexperienced calves, potentially negatively affecting population dynamics of these vulnerable Arctic species.

There are associated shortcomings with this data set, as observations are biased by both the density and presence of human observers resulting in uneven spatial and temporal coverage. Observations are not random, and thus, results associated with habitat selection cannot be prescriptive of all killer whales in the Canadian Arctic. Sighting data that is not linked to individual or group identification limits our ability to accurately test group arrival and departure times and time spent in the ECA by groups. As a result, our analysis only reflects a general overview of all killer whale groups visiting the region in summer (Lefort et al., 2020a). This restricted the ability to include point ice in the models as it greatly reduced the sample size, which reduced the ability to identify specific individual trends with sea ice and killer whale presence. The mean ice values are potentially more applicable to killer whale presence trends, however, we are investigating arrival and departure trends, which are likely to be impacted by the killer whales’ ability to move throughout the region. The clustering metric and spatiotemporal analyses mitigate some of these data limitations while suggesting areas for improvement in monitoring.

Killer whales fulfill an apex predator trophic role in Arctic ecosystems, with multiple documented predation events on narwhal, beluga whales, bowhead whales, Atlantic walrus (Odobenus rosmarus rosmarus), and multiple species of seal (Steltner et al., 1984; Campbell, 1988; Reeves and Mitchell, 1988; Finley, 1990; Melnikov and Zagrebin, 2005; Laidre et al., 2006; Higdon, 2007; Ferguson et al., 2012; Higdon et al., 2012, 2014; Westdal et al., 2016; Breed et al., 2017). The work presented here suggests that killer whales in the Arctic are both spatially and temporally expanding their presence, moving into regions not previously observed, entering earlier, leaving later, and staying longer. This overall increase in presence has likely put more pressure on Arctic species that were previously less threatened by killer whale predation. Continued declines in sea ice cover will affect prey species by temporally increasing killer whale predation, influencing prey species behaviour, and reducing the availability of sea ice refuge (Breed et al., 2017; Matthews et al., 2020). It is unclear how prey species will respond, but they may shift their summer range further into the Canadian Archipelago or northward into the Last Ice Area (Moore et al., 2019). However, the actual response and demographic success of such changes are likely species-dependent. For example, beluga whales exhibit strong fidelity to their summer areas and show limited adaptability to changes in seasonal habitat use (O’Corry-Crowe et al., 2020; Skovrind et al., 2021). The relationships between killer whales and other species in Arctic ecosystems are expected to be dynamic, as productivity and availability of prey species is predicted to shift as climate change reduces sea ice. For example, the distribution of zooplankton species in the Arctic has changed in response to warming water (Blachowiak-Samolyk et al., 2008; Balazy et al., 2018; Abe et al., 2020), which is predicted to impact bowhead whale abundance and distribution (Laidre et al., 2008; Fortune et al., 2023). Continued documentation of Arctic killer whale sightings will be important for tracking the presence of killer whales in this ecosystem and predicting the effects of increased presence alongside other ecosystem-wide shifts.

Killer whales exhibit remarkable behavioral plasticity, enabling them to exploit newly accessible habitats, including in the Arctic as sea ice recedes (Brakes and Dall, 2016; Bester et al., 2017). This flexibility allows them to adjust their movement patterns and habitat use in response to shifting prey availability and environmental conditions (Tavares et al., 2017). The observed trend of earlier arrivals and later departures reflects an adaptive strategy that maximizes energy intake during extended open-water seasons (Kuletz et al., 2024). These extended periods in the Arctic may also align with reproductive strategies, ensuring access to abundant prey resources, via Arctic associated prey, necessary to support gestation, lactation, and calf growth (Weiss et al., 2023). Such behavioral adaptations underscore killer whales’ ability to thrive in dynamic ecosystems, further influencing predator-prey interactions and Arctic marine food web dynamics.

The increasing presence of killer whales in the ECA underscores the need for monitoring and managing their predation on culturally and economically significant prey species (Stewart, 2008, 2018; Higdon, 2010). Incorporating killer whale distribution shifts into Arctic conservation and policy frameworks is essential for mitigating their economic and cultural impacts and ensuring the sustainability of Arctic endemic species (Garroway et al., 2024). Future research should prioritize understanding prey selection and energy requirements to quantify the potential regulatory effects of killer whale predation on Arctic ecosystems (Lefort et al., 2020b; Breed, 2021). Additionally, continued research on their social structure, acoustic behavior, and genetic and cultural diversity, and similar research on prey species, will provide critical insights into population dynamics and adaptation strategies (Esteban et al., 2016; Jourdain et al., 2019; Sportelli et al., 2022). Modeling future distribution patterns under various climate scenarios will further inform proactive management strategies to address the ecological consequences of continued sea ice loss (van Weelden et al., 2021; Chambault et al., 2022).

Future research could include testing whether increasing killer whale presence is driving measurable changes in the behavior, distribution, and population dynamics of endemic Arctic prey species. For example, satellite telemetry and drone-based behavioural observations could be used to assess changes in habitat use or predator avoidance by seals, as has been explored for narwhals (Breed et al., 2017) and bowhead whales (Matthews et al., 2020). Researchers could examine whether increased killer whale presence correlates with reduced fidelity to calving or moulting sites in ice-associated species, or whether predator-induced stress is altering prey diving behaviour or acoustic signaling—detectable through passive acoustic monitoring (PAM) and biologging technologies. Comparative diet studies of Arctic killer whales and those in other rapidly warming regions (e.g., Southern Ocean, Bering Sea) could help identify convergent ecological responses to climate change.

Another promising research direction is to investigate whether migratory connectivity is shifting, for example, whether killer whales are beginning to overwinter farther north. Interannual variability in sea ice phenology may drive year-to-year variation in killer whale migration timing and extent, and continued sea ice loss could be facilitating increased inter-basin connectivity between historically distinct populations (e.g., Baffin Bay and the Beaufort Sea; Heide-Jørgensen et al., 2012). These hypotheses can be tested by combining killer whale telemetry with high-resolution sea ice datasets and applying dynamic habitat models (e.g., species distribution models, step selection functions) that incorporate both ice metrics and prey availability. Finally, future studies could test the hypothesis that killer whale migration timing is more tightly linked to sea ice concentration and freeze-thaw dynamics than to temperature or prey movements alone. This could involve using high-resolution satellite ice data alongside predictive models incorporating the Sea-Ice Model Intercomparison Project (CMIP6) sea ice projections to estimate how arrival and departure windows may shift under continued Arctic warming.

These findings highlight how climate-driven shifts may be reshaping Arctic ecosystems, where diminishing sea ice facilitates extended seasonal use of the ECA region by killer whales, a key marine predator. By adding to knowledge of killer whale demographics, and movement patterns, this study contributes to a broader understanding of predator-prey dynamics in the context of rapid environmental change (Guiden et al., 2019; Arumugam et al., 2020). As Arctic ecosystems face increasing pressure from climate change, this research provides needed insights into the ecological consequences of shifting predator distributions and underscores the importance of integrating these dynamics into conservation and management strategies.