The management and conservation of migratory marine top predators benefit from understanding their movements and how these relate to oceanographic features (Block et al., 2011; Hays et al., 2019). These features, influenced by both natural variability and anthropogenic environmental changes, complicate the understanding of species movements. The cumulative impact of environmental change is particularly pronounced in the Subpolar North Atlantic (SPNA), driven by both convective and advective processes (Hátún et al., 2017). This region, with the subpolar gyre (SPG) dominating the physical dynamics, maintains a productive ecosystem that sustains several marine predators, including Atlantic white-sided dolphins (Leucopleurus acutus) (Cipriano, 2018), hereafter referred to as white-sided dolphins. Over recent decades, environmental variability has altered SPNA ecosystems (Beaugrand, 2009; Hátún et al., 2009). This has involved declines in pre-bloom silicate concentrations (Hátún et al., 2017) and declines in prey such as copepods (Hátún et al., 2009) and krill (Edwards et al., 2021) throughout the SPG, potentially driving baleen whales (Víkingsson et al., 2015), and boreal fish species like mackerel and blue whiting from their spawning grounds west of the British Isles, toward the nutrient-richer waters of the Irminger Sea (Pacariz et al., 2016; Post et al., 2020). These ecosystem shifts indicate that the Irminger Sea may function as a multi-species feeding hotspot in the SPNA.

The white-sided dolphin inhabits cold-temperate to sub-polar waters (5°-16°C) along the continental shelf and slope, from the Gulf of St. Lawrence and the Labrador Sea in the west to the North Sea and the Norwegian Sea in the east (Cipriano, 2018). They primarily prey on mesopelagic and pelagic fish species, such as blue whiting (Micromesistius poutassou), Trisopterus sp., mackerel (Scomber scombrus), and myctophids (lanternfish) in northeast Atlantic waters (Couperus, 1997; Hernandez-Milian et al., 2016). Genetic studies suggest strong connectivity across the North Atlantic (Fernández et al., 2016; Gose et al., 2023). There is evidence of panmixia (random mating across the population), low individual relatedness (minimal genetic similarity between individuals), and a fission-fusion social structure (dynamic group formation and separation), indicating a lack of kin-associated bonds (Pugliares-Bonner et al., 2021; Gose et al., 2023).

White-sided dolphins are considered sensitive to distributional shifts driven by climate change (MacLeod, 2009; Skern-Mauritzen et al., 2022) and are subject to bycatch, and to hunts in Greenland and the Faroe Islands (Cipriano, 2018; NAMMCO, 2023). Yet, information on their offshore movements and habitat use remains limited. Satellite telemetry can help fill these gaps and improve our understanding of the species’ biology (Nowacek et al., 2016; Hays et al., 2019), which is critical for effective conservation and management (Braulik, 2019; NAMMCO, 2023). By providing information on distribution, residence time, and diving behavior, tracking top predators also helps identify biologically important areas, thus supporting ecosystem-based management (Hays et al., 2019; Skern-Mauritzen et al., 2022). Such data are especially important in the context of environmental change in the SPNA (Ramírez et al., 2017; Heide-Jørgensen et al., 2022). Here, we present movement data from healthy, free-ranging white-sided dolphins tagged in the Faroe Islands, revealing individual trans-Atlantic journeys and identifying key areas within their range. Our study provides new insights into the large-scale movements of this understudied marine predator and highlights the ecological significance of the Irminger Sea as a potential feeding hotspot.

Our study shows, for the first time, the capacity of Atlantic white-sided dolphins to undertake cross-basin migrations at consistent travel speeds over multiple days. The tracks of 20 tagged dolphins confirm that the species is usually encountered near the continental shelf and slope (Cipriano, 2018). Dolphin locations were significantly closer to the 500 m shelf edge than expected by chance. The five dolphins that went west were also associated with regions of deep mixed layer depths (MLD). Two areas of specific interest emerged: the Faroe-Shetland Channel (FSC) and the Irminger Sea.

The dolphins tagged during the same event dispersed shortly after tagging, likely reflecting their fluid social structure (Gose et al., 2023), rather than an effect of tagging. Eleven dolphins moved east after leaving the Faroe Shelf, with nine remaining in the FSC throughout most of their transmission periods. This aligns with models predicting year-round presence of the species in the area, with peak abundance in summer (Waggitt et al., 2019). The dolphins’ extended use of the FSC further underscores the ecological importance of the region, which hosts a diversity of cetaceans and seabirds (Waggitt et al., 2019; Virgili et al., 2024), along with commercially important prey such as blue whiting and mackerel (ICES, 2023, in-house data) and has been identified as an area of international importance (Skov et al., 2002). South of the FSC, near the Wyville-Thomson Ridge, dolphin #22 dove to depths of 200–300 m, possibly targeting blue whiting, myctophids, and pearl side (Maurolicus muelleri) (Couperus, 1997; Hernandez-Milian et al., 2016). The region is characterized by intense mixing driven by the equatorward flow of deep-water (Sherwin et al., 2008), and fisheries surveys confirm the high abundance of mesopelagic fish and other prey species (ICES, 2023, in-house data). Five dolphins travelled westward, all but one appearing to follow the productive southern slope of the Iceland-Faroe Ridge (de Marez et al., 2024). Two tags stopped transmitting, while the three others showed independent trans-Atlantic journeys—separated in time—to the Irminger Sea, a region frequented by top consumers like baleen whales, harbor porpoises (Phocoena phocoena), and migratory seabirds (Víkingsson et al., 2015; Nielsen et al., 2018; Davies et al., 2021). The average travel speed and short duration of these movements suggest a targeted migration rather than exploratory travel. The dolphins followed the productive corridor above the Iceland Basin (Hátún et al., 2017, Hátún et al., 2021), which is commonly used by migratory species such as tuna, mackerel, and seabirds (Bogdanova et al., 2011; MacKenzie et al., 2014; Pacariz et al., 2016). Their westward movements stayed within this corridor, where MLD is deeper than farther south (Figure 4), indicating its significance as migration corridor. Upon reaching the Irminger Sea in October, two dolphins remained southwest, near the Irminger Gyre (Figure 4), until transmissions ceased.

The move persistence analysis, though constrained by data gaps and interpolation, provides additional support for our interpretation of dolphin movements. High persistence during the trans-Atlantic crossings is consistent with directed travel at consistent speed. In contrast, areas of lower persistence—reflecting slower, more tortuous movements consistent with area-restricted search—were concentrated along the shelf edges, in the FSC, and at the Wyville-Thomson Ridge (Figure 3). Additional areas of lower persistence occurred along the east Greenland slope and in the Irminger Sea—particularly the Irminger Gyre. Taken together with the dolphins’ extended residency and the presence of boreal prey such as mackerel (Pacariz et al., 2016) and blue whiting (Post et al., 2020), as well as other marine mammals in the region (Víkingsson et al., 2015; Nielsen et al., 2018), these findings suggest that the Irminger Sea may serve as an important autumn feeding ground for white-sided dolphins.

While little is known about dolphin feeding habits in these waters, tagged harbor porpoises from West Greenland moved offshore into the Labrador Sea and the Irminger Sea in winter to target mesopelagic fish, likely the myctophid B. glaciale (Nielsen et al., 2019). Given that white-sided dolphins appear to target B. glaciale along the Reykjanes Ridge (Doksæter et al., 2008) and feed on myctophids in the northeastern Atlantic (Couperus, 1997; Hernandez-Milian et al., 2016), they likely exploit B. glaciale in the Irminger Sea. The pelagic fish species (i.e. mackerel and blue whiting) migrate eastward during autumn and winter to their main spawning grounds—opposite to the direction of the tagged dolphins—strengthens the idea that B. glaciale is a primary prey west of the Reykjanes Ridge (Doksæter et al., 2008).

The maximum (616 m) and mean (171 ± 186 m) dive depths recorded in our study exceed previous reports of the dive capacity of white-sided dolphins (Sampson et al., 2021; maximum: 191 m). The wide range in dive depths, along with significant differences in depth and duration across time periods, may reflect flexible foraging strategies—likely influenced by spatial and temporal variations in MLD and the Deep Scattering Layer across the North Atlantic, as well as individual differences. Significantly deeper nighttime dives, together with feeding events recorded at night by the STP, support the hypothesis that these dolphins exploit the diel vertical migration of mesopelagic prey, a known strategy among odontocetes (Baird et al., 2001; Nielsen et al., 2019).

In the Irminger Sea, dive depths recorded for dolphin #22 (Figure 2: nr 7–9) coincided with the upper boundary of the Deep Scattering Layer (400–500 m; Magnússon, 1996) and occurred at night or in the morning. This further supports the idea that white-sided dolphins forage on myctophids in this region, taking advantage of their diel vertical migration similarly to harbor porpoises (Nielsen et al., 2019).

The Irminger Sea emerges from our study as a previously unrecognized key area for white-sided dolphins and may function as a multi-species feeding hotspot, likely due to its unique oceanographic features, including the Irminger Gyre with deep MLDs, and associated high productivity (de Jong and de Steur, 2016; Hátún et al., 2016). The mixing hole, created in the central Irminger Sea during winters with intense ocean heat loss (Sterl and de Jong, 2022), resembles the processes observed in the northwestern Mediterranean Sea. In the latter, strong convection enhances nutrient upwelling, primary production, and fish recruitment (Mir-Arguimbau et al., 2022), attracting top predators such as striped dolphins (Stenella coeruleoalba) and fin whales (Balaenoptera physalus) (Virgili et al., 2024). Likewise, the Irminger Sea’s deep mixing processes appear to sustain a productive ecosystem that supports various marine species, similar to known marine hotspots in the Pacific (Block et al., 2011).

Recognizing and protecting such areas is crucial for understanding ecosystem resilience and ensuring the conservation of species that depend on them (Víkingsson et al., 2015; Nielsen et al., 2018; Davies et al., 2021). Despite its ecological importance, the Irminger Sea lacks formal conservation measures. It is neither designated as an Ecologically or Biologically Significant Marine Area (EBSA) (Johnson and Barrio Froján, 2021), a Marine Protected Area (MPA), nor identified as an Important Marine Mammal Area (IMMA) (IUCN, 2025). Much of the SPNA lies beyond national jurisdiction, complicating management efforts. While much oceanographic research has focused on the SPG, the Irminger Sea has received comparatively little attention from an ecological perspective. This raises concerns given ongoing environmental changes impacting the North Atlantic (Ramírez et al., 2017; IPCC, 2019), where Atlantification (i.e. increased influence of Atlantic waters) has already caused an ecosystem and regime shift along Greenland’s east coast (Heide-Jørgensen et al., 2022). Future climate projections suggest declining animal biomass over the next century due to global warming, primarily because of stronger ocean stratification and reduced nutrient upwelling (IPCC, 2019). As the northeastern Atlantic is expected to be especially affected—likely due to its sensitivity to convection processes—the Irminger Sea may emerge as the last nutritional stronghold in the region and a critical refuge for pelagic species, given projections of continued weakening of the SPG and environmental shifts (Hátún et al., 2009; IPCC, 2019). Given that marine mammals, including white-sided dolphins, are substantial consumers and a significant part of the food web in the Nordic Seas (Skern-Mauritzen et al., 2022), their presence in the Irminger Sea underscores the area’s ecological significance and the importance of its conservation. This highlights the value of tracking top predators such as the dolphins to inform ecosystem-based management by identifying biologically important areas and improving our understanding of species–environment relationships (Hays et al., 2019; Skern-Mauritzen et al., 2022).

Our study presents new insights into the large-scale movements and habitat use of Atlantic white-sided dolphins, revealing their ability to undertake cross-basin migrations at consistent travel speeds. Tracking data indicate that the Irminger Sea, particularly the Irminger Gyre, is an area of repeated use and a potential feeding hotspot, while also highlighting the significance of the Faroe-Shetland Channel as key habitat.

The species’ fission-fusion social structure, together with evidence of trans-Atlantic connectivity, supports the management of these dolphins as a single stock in the central and eastern North Atlantic. Dive records further suggest flexible foraging strategies, likely targeting mesopelagic prey associated with diel vertical migration.

Our findings can be used as guidance for conservation strategies to protect this highly mobile species. Given the absence of formal conservation measures in key habitats, further research and year-round monitoring are needed to assess potential threats and inform management strategies, especially in the context of environmental change.