Why abundance alone cannot assess sustainability in long-finned pilot whales (Globicephala melas): population structure, genetic uncertainty, and management implications

Abstract

Long-finned pilot whales (Globicephala melas) are widely distributed across the North Atlantic and are often assessed for management as a single, abundant population. However, the species exhibits strong social organisation, stable matrilineal structure, and reproduction that occurs within social units, characteristics that shape demographic connectivity. These features raise questions about whether abundance alone provides a sufficient basis for assessing the sustainability of recurrent removals from a socially structured marine mammal population. Recent genetic and ecological studies indicate broad-scale differentiation and suggest regional structuring within the North Atlantic, yet sampling remains uneven and datasets linked directly to harvested individuals are limited. Consequently, it is not currently possible to determine how removals in the Faroe Islands are distributed across potential demographically independent populations (DIPs), matrilines or family lineages. This Mini Review synthesises current evidence on population structure, identifies key uncertainties, and evaluates post-mortem genetic sampling as a practical approach to reducing uncertainty and improving sustainability assessments for North Atlantic long-finned pilot whales.

1 Introduction

Large-scale surveys such as the North Atlantic Sightings Surveys (NASS) estimate more than 100,000 long-finned pilot whales in the eastern index area (the eastern part of the standardised NASS survey region used for comparing abundance estimates over time) and approximately 253,000 across surveyed regions (Pike et al., 2019). These estimates are typically interpreted at broad spatial scales and have contributed to management approaches that treat the species as a single, abundant population. However, in highly social cetaceans, spatial overlap does not necessarily imply demographic connectivity (Palsbøll et al., 2007; Hoelzel et al., 2007a).

Long-finned pilot whales live in stable, socially cohesive groups, with evidence of matrilineal organisation and long-term associations among individuals (de Stephanis et al., 2008; Oremus et al., 2013). Although male-mediated dispersal may contribute to gene flow among groups, recruitment and social continuity are strongly shaped by these cohesive social units, meaning that genetic connectivity does not necessarily equate to demographic independence (Palsbøll et al., 2007; Alves et al., 2013; Oremus et al., 2013).

In this review, sustainability is used in the conservation sense of assessing whether repeated removals from a wild biological resource are compatible with the long-term maintenance of biodiversity. This framing is consistent with the Convention on Biological Diversity concept of sustainable use, which links biodiversity use to avoidance of long-term decline, and with IUCN sustainable-use principles, which emphasise that use of wild living resources should remain consistent with the conservation of biological diversity (CBD, 1992; IUCN, 2000).

For North Atlantic long-finned pilot whales, sustainability assessment therefore requires more than determining whether the species remains abundant at a broad regional scale. Abundance estimates describe numbers, but they do not identify whether recurrent, human-directed removals are affecting particular demographically independent populations (DIPS), matrilines or socially cohesive groups. In a species characterised by stable matrilineal social organisation, sustainability must therefore also consider whether removals are compatible with the persistence of genetic diversity, lineage continuity, social structure and potential group-specific behavioural knowledge where such variation exists (de Stephanis et al., 2008; Oremus et al., 2013; Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; Rendell and Whitehead, 2001; Whitehead et al., 2004; NOAA, 2016).

This issue is particularly relevant in the Faroe Islands, where drive hunts remove entire pods rather than dispersed individuals. In such systems, population-level impact depends not only on total abundance, but on how removals are distributed across DIPs—units whose dynamics are primarily determined by internal recruitment rather than immigration (Waples and Gaggiotti, 2006; NOAA, 2016). In wildlife and marine mammal management, human-caused removal limits are therefore most robust when assessed at the scale of demographically meaningful population units, rather than across a broad, potentially mixed population aggregate (Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; NOAA, 2016). This is particularly relevant where removals occur at group level, because the loss of entire social units may have consequences for recruitment, genetic diversity and demographic resilience that are not captured by species-level abundance alone (Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; Frankham et al., 2010; NOAA, 2016).

Accordingly, the central conservation question is not whether long-finned pilot whales remain abundant at a broad regional scale, but whether recurrent removals can be assigned to, and evaluated against, the population units that determine recruitment, lineage persistence and long-term resilience. Without this resolution, it is difficult to assess whether continued removals are compatible with the long-term maintenance of biodiversity, as required by conservation-based interpretations of sustainable use (CBD, 1992; IUCN, 2000).

Although evidence suggests regional structuring, its resolution remains insufficient to determine how removals are distributed across population units (Monteiro et al., 2015; NAMMCO Scientific Committee, 2019). It is therefore unclear how many DIPs exist, how strongly they are connected, or how removals in Faroese waters are distributed among them. This uncertainty limits the ability to evaluate whether repeated removals are compatible with long-term population persistence, genetic diversity and demographic resilience at the relevant population scale.

This review synthesises evidence on population structure and genetic connectivity and evaluates post-mortem genetic sampling as an approach to reducing uncertainty about how removals are distributed across DIPs.

2 Background: population structure, social organisation, and recent advances

2.1 Distribution, movement, and social organisation

Long-finned pilot whales are wide-ranging and highly mobile; however, movement and spatial distribution alone do not define population structure. In several cetaceans, including killer whales (Orcinus orca) and humpback whales (Megaptera novaeangliae), individuals may occupy the same areas while remaining demographically and genetically distinct, particularly where social structure, site fidelity or migratory connectivity influence population boundaries (Palsbøll et al., 1997; Palumbi, 2003; Hoelzel et al., 2007a; Palsbøll et al., 2007). Within the North Atlantic, long-finned pilot whales show seasonal movements linked to prey availability, and individuals observed in Faroese waters are unlikely to represent a local resident population (Monteiro et al., 2015; Pike et al., 2019). Therefore, the presence of long-finned pilot whales in Faroese waters cannot, by itself, identify the demographically relevant population units from which individuals are drawn (Hoelzel et al., 2007a; Palsbøll et al., 2007).

Pilot whales live in stable matrilineal family groups, with evidence that females remain associated with natal social units while males may disperse among groups (Oremus et al., 2013; Palsbøll et al., 2007). Temporary aggregations may occur but do not necessarily correspond to demographically independent populations (de Stephanis et al., 2008). Taken together, distribution, movement and social organisation indicate that abundance and spatial occurrence alone cannot identify the population units relevant for evaluating the effects of removals (Waples and Gaggiotti, 2006; Palsbøll et al., 2007; NOAA, 2016).

2.2 Why demographically independent population structure matters for sustainability assessments

In population biology and wildlife management, stock structure refers to the organisation of populations into units that differ in their degree of demographic connectivity (Waples and Gaggiotti, 2006; Palsbøll et al., 2007). In management terms, such units correspond to demographically independent populations (DIPs), whose dynamics are primarily governed by internal recruitment rather than sustained immigration (Waples and Gaggiotti, 2006; NOAA, 2016). Because human-caused mortality limits are most biologically meaningful when applied to the population units whose dynamics they affect, DIPs represent the appropriate scale at which removals should be evaluated in conservation-based sustainability assessments, including assessments of whether repeated removals are compatible with population persistence, genetic diversity and demographic resilience (Wade, 1998; Palsbøll et al., 2007; NOAA, 2016).

In long-finned pilot whales, this structure is shaped by strong social organisation and sex-biased dispersal. Females show strong association with matrilineal social groups, while male-mediated dispersal may contribute to gene flow among groups (Oremus et al., 2013; Alves et al., 2013). As a result, connectivity among social units may be uneven, and these structured populations influence how removals translate into population-level consequences (Waples and Gaggiotti, 2006; NOAA, 2016).

Recognition of this principle has shaped marine mammal management more broadly. Under the U.S. Marine Mammal Protection Act, human-caused mortality is evaluated in relation to stock structure and demographic independence rather than species-level abundance alone (Wade, 1998; NOAA, 2016). A key motivation is that abundance can mask vulnerability when removals are concentrated within particular DIPs (Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007).

For North Atlantic long-finned pilot whales, this structure remains poorly resolved. It is not known how many DIPs exist, how strongly they are connected, or how long-finned pilot whales taken in the Faroe Islands are distributed among them. Consequently, sustainability assessments of recurrent removals based solely on abundance remain incomplete (Waples and Gaggiotti, 2006; NOAA, 2016).

2.3 Genetic evidence: what has been resolved and what remains uncertain

Genetic evidence provides an important means of identifying population structure and quantifying connectivity in wide-ranging marine mammals (Palumbi, 2003; Palsbøll et al., 2007). Studies of pilot whales have demonstrated clear differentiation between long-finned and short-finned species, and between Northern and Southern Hemisphere populations of G. melas, confirming that wide-ranging movement does not imply demographic homogeneity (Oremus et al., 2009; Palumbi, 2003; Palsbøll et al., 2007). Evidence of localised hybridisation in contact zones further highlights that species boundaries may be dynamic under changing environmental conditions (Miralles et al., 2016).

Within the North Atlantic, genetic studies suggest subtle but consistent regional differentiation associated with ecology and social organisation (Monteiro et al., 2015). However, sampling remains uneven, and datasets directly linked to harvested individuals are limited. Consequently, the distribution of removals among DIPs and family lineages remains unresolved.

This uncertainty constrains sustainability assessment by limiting the population scale at which removals can be evaluated. Without better resolution of structure and connectivity, assessments cannot determine how removals affect genetic diversity, lineage persistence, or long-term resilience, even where overall abundance appears stable (Waples and Gaggiotti, 2006; NOAA, 2016).

This gap is reflected in recent recommendations from the NAMMCO Scientific Committee Working Group on Pilot Whales (2025), which identified the need for coordinated genetic monitoring, including samples from harvested individuals, to resolve population structure and assess the genetic consequences of removals.

Consequently, current datasets cannot determine which DIPs contribute to removals, the strength of connectivity among them, or whether mortality is broadly distributed or concentrated within particular lineages. Reducing these uncertainties will require consistent genetic sampling across regions, including routine inclusion of harvested individuals within a unified analytical framework. Figure 1.

Figure 1

3 Discussion: implications, gaps, and future directions

3.1 Why post-mortem genetic sampling matters

Post-mortem genetic sampling provides a practical means of reducing key uncertainties surrounding population structure and connectivity in long-finned pilot whales. Tissue collected from whales already removed through hunting allows genetic analyses without additional disturbance to live animals, while directly targeting the individuals affected by removals (Oremus et al., 2009; Monteiro et al., 2015). In contexts where removals already occur, such sampling offers a proportionate and logistically feasible approach to generating biologically relevant data.

Crucially, post-mortem genetic sampling enables removals to be examined at the same biological scale at which they occur. Drive hunts remove entire pods rather than isolated individuals, and sampling multiple whales from a single event allows assessment of relatedness, family composition and lineage structure within removals. For a species characterised by stable matrilineal social organisation, this group-level perspective is essential for determining whether removals are broadly distributed across multiple DIPs or concentrated within particular lineages. Such patterns cannot be resolved from abundance surveys alone, because abundance estimates do not identify the population units or social lineages from which removals are drawn (Palsbøll et al., 1997; Waples and Gaggiotti, 2006; Frankham et al., 2010; NOAA, 2016).

Evidence from other cetacean systems shows that genetic material derived from strandings, by-catch and historical removals can reveal population structure that is not apparent from visual or distributional data alone (Baker and Palumbi, 1994; Palsbøll et al., 1997; Fontaine et al., 2014). In these cases, genetic data have contributed to identifying biologically meaningful population units and reassessing vulnerability where broad distribution or apparent abundance obscured underlying structure. When integrated with abundance and demographic information, post-mortem genetic data therefore provide critical context for interpreting removals and their long-term consequences. Rather than replacing existing monitoring approaches, genetic sampling complements them by clarifying the population units to which abundance estimates should be applied and by illuminating how removals interact with structure and connectivity over time (Waples and Gaggiotti, 2006; International Whaling Commission, 2019; NOAA, 2016).

However, post-mortem genetic monitoring should not be interpreted as resolving all uncertainties relevant to sustainability assessment. Sampling harvested animals can identify relatedness, lineage representation and genetic clustering within removals, and can indicate whether removals repeatedly involve the same or closely related lineages. On its own, however, sampling removed animals cannot determine the proportion of each DIP taken, because that requires comparable information from the wider wild population, including the size, distribution and demographic status of the contributing DIPs. Important uncertainties may therefore remain regarding the number and spatial distribution of DIPs, rates of movement and exchange among units, reproductive output, survival, age structure, and whether harvested groups are representative of the wider population using North Atlantic waters. Genetic monitoring therefore provides an essential but partial line of evidence. Its value lies in reducing uncertainty about the population origin and relatedness of removed animals, rather than replacing abundance estimation, demographic monitoring or wider ecological studies (Palsbøll et al., 2007; Schwartz et al., 2007; Luikart et al., 2010; NOAA, 2016).

For this reason, post-mortem genetic sampling should be treated as one component of an integrated monitoring framework, rather than as a stand-alone solution. Genetic sampling of live animals, long-term photo-identification and repeated field observations can provide information on site fidelity, re-sightings, movement patterns, association histories, survival and demographic trends, while social network analysis can help quantify the stability of social units and the degree of connectedness among identified individuals or groups (Whitehead, 2008, 2009; Farine and Whitehead, 2015). In socially structured cetaceans, combining genetic data with photo-identification, behavioural observations and association data can improve inference about population boundaries and DIPs, particularly where genetic differentiation is subtle or where male-mediated gene flow may obscure matrilineal social structure (Hoelzel et al., 2007a; Palsbøll et al., 2007; Oremus et al., 2013; NOAA, 2016). Evidence from pilot whales and killer whales demonstrates the value of integrating genetic, social and demographic data when identifying biologically meaningful management units (Parsons et al., 2000; de Stephanis et al., 2008; Alves et al., 2013; Foote et al., 2016).

A further consideration is that removals of entire socially cohesive groups may also risk eliminating socially learned behaviours or local traditions if these are unevenly distributed among groups. Direct evidence for culturally transmitted behaviour in long-finned pilot whales remains limited compared with killer whales, but studies of cetaceans demonstrate that socially learned traditions can be structured by matrilines, social units or ecotypes, and may therefore vary among groups rather than being uniformly distributed across a population (Rendell and Whitehead, 2001; Whitehead et al., 2004; Ford, 1991; Yurk et al., 2002; Foote et al., 2016). Where such group-specific traditions exist, unequal or repeated removal of particular social units could therefore remove behavioural variation or local knowledge that is not represented across all groups. This possibility reinforces the need to consider removals at the scale of socially and demographically meaningful units, rather than only at the level of total abundance (Palsbøll et al., 2007; NOAA, 2016).

In the case of long-finned pilot whales, post-mortem genetic sampling therefore offers a direct means of linking removals in the Faroe Islands to underlying population structure, while also forming part of a broader monitoring framework (Baker and Palumbi, 1994; Palsbøll et al., 1997; Monteiro et al., 2015). By combining genetic data from harvested animals with abundance estimates, demographic information, live-animal genetic sampling, photo-identification and social association data where available, future assessments would be better able to evaluate whether removals are diffuse across a connected population or concentrated within particular DIPs, matrilines or lineages. Such an integrated approach is consistent with wider marine mammal management principles, which emphasise that stock boundaries, demographic independence and population-specific vulnerability should be considered when assessing human-caused mortality, rather than relying on species-level abundance alone (Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; NOAA, 2016). By aligning removals with the biological scale at which genetic diversity, lineage persistence, potential social continuity and demographic resilience are determined, this approach would strengthen conservation-based sustainability assessment for recurrent removals.

3.2 Comparative insight from killer whale genetics

Killer whales provide an instructive comparative case because they share key social and life-history traits with long-finned pilot whales, including stable matrilineal groups, long-term social cohesion and strong reliance on social learning (Ford, 1991; Parsons et al., 2000; Hoelzel et al., 2007b; Foote et al., 2016). They also illustrate the management risk of interpreting apparent abundance and spatial overlap without resolving underlying population structure. Although killer whales are widely distributed, genetic, behavioural and ecological studies have shown that individuals using overlapping or adjacent areas may belong to distinct socially structured populations or ecotypes with limited demographic connectivity (Hoelzel et al., 1998, 2007; Morin et al., 2010; Morin et al., 2015; Foote et al., 2016).

These populations differ in size, ecological specialisation and vulnerability, with southern resident killer whales providing a well-documented example of a small and at-risk population within an otherwise widely distributed species (Krahn et al., 2002; Ford et al., 2010; Lacy et al., 2017; Morin et al., 2015). This case illustrates how abundance at the species level can mask underlying structure and uneven vulnerability.

In the absence of genetic resolution and, where feasible, long-term, comprehensive photo-identification and individual-based monitoring, it may not be possible to determine which populations are being affected by removals or whether impacts are concentrated within particular lineages or socially cohesive groups. Long-term photo-identification can provide complementary information on individual identity, site fidelity, re-sightings, association patterns and social-unit stability, although such approaches may be logistically challenging and incomplete in wide-ranging populations (Whitehead, 2008, 2009; Farine and Whitehead, 2015; Alves et al., 2013). The killer whale example therefore reinforces the central argument of this review: resolving population structure through complementary genetic, demographic and long-term individual-based monitoring is necessary before abundance estimates can be interpreted confidently in relation to sustainability as defined here, particularly where removals may affect socially structured population units rather than a single homogeneous population (Parsons et al., 2000; Hoelzel et al., 2007a; Palsbøll et al., 2007; Alves et al., 2013; NOAA, 2016). Figure 2.

Figure 2

3.3 Current gaps and future directions

Despite advances in understanding the social organisation and broad-scale population structure of long-finned pilot whales, key uncertainties continue to constrain sustainability assessment in the North Atlantic. Genetic sampling remains spatially uneven and rarely includes individuals directly affected by removals (Monteiro et al., 2015; NAMMCO Scientific Committee, 2019). As a result, it is not currently possible to determine how removals in the Faroe Islands are distributed or how strongly these populations are connected.

This limitation is particularly significant in a species where mortality removes entire social groups rather than isolated individuals. Without genetic data linked to harvested whales, it remains unclear whether removals are distributed broadly across the population or concentrated within specific lineages. Consequently, abundance-only approaches may be insufficient in the absence of resolved population structure, as they cannot capture how removals interact with social organisation and connectivity (Waples and Gaggiotti, 2006; NOAA, 2016).

Consistent with recent recommendations from NAMMCO (2025), a dedicated genetic monitoring programme based on archival and newly collected samples from harvested groups and strandings provides a practical and proportionate way forward, building on existing sampling opportunities from ongoing removals and strandings. This approach enables removals to be linked directly to population structure, allowing assessment of whether impacts are diffuse across a connected system or concentrated within particular social units.

Importantly, a complete reference database is not required. Even partial and incrementally collected datasets have been shown to reveal patterns of relatedness and lineage representation, with resolution improving over time as sampling accumulates (Schwartz et al., 2007; Luikart et al., 2010). Genetic monitoring therefore provides a cumulative framework for reducing uncertainty and refining inference about how removals are distributed across population units.

A key conservation implication is that abundance-only assessments may overlook losses occurring below the level of total population size, including losses of population structure, lineage diversity, social organisation or culturally mediated variation (Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; Whitehead et al., 2004; Brakes et al., 2019; NOAA, 2016). Broad regional abundance could remain apparently high while particular DIPs, matrilines or socially cohesive groups are disproportionately depleted or lost through recurrent group-level removals, because abundance estimates do not identify the population units or social lineages from which removals are drawn (Waples and Gaggiotti, 2006; Palsbøll et al., 2007; NOAA, 2016). In such cases, the loss would not simply be numerical. It could include reduced genetic diversity, loss of lineage continuity and disruption of social structure, all of which are relevant to conservation resilience in structured populations (Frankham et al., 2010; Palsbøll et al., 2007; Oremus et al., 2013). It could also include the potential loss of group-specific behavioural knowledge or traditions where these exist (Rendell and Whitehead, 2001; Whitehead et al., 2004; Brakes et al., 2019). This possibility is biologically plausible in long-finned pilot whales because the species shows stable social organisation, matrilineal structure and long-term associations among individuals, features that can create pathways for social learning and intergenerational continuity (de Stephanis et al., 2008; Oremus et al., 2013; Augusto et al., 2017). Direct evidence for culturally transmitted behaviour in long-finned pilot whales remains limited, and this possibility should therefore be treated cautiously. However, evidence from other socially structured cetaceans demonstrates that socially learned behaviours can be structured by matrilines, social units, vocal clans or ecotypes, and that such cultural variation can have conservation relevance (Rendell and Whitehead, 2001; Whitehead et al., 2004; Yurk et al., 2002; Riesch et al., 2012; Foote et al., 2016; Brakes et al., 2019; Whitehead et al., 2023). Therefore, if recurrent removals disproportionately affect particular social units, abundance estimates alone may fail to detect the loss of lineage continuity, social structure, intergenerational knowledge or behavioural variation that may not be represented elsewhere in the population.Taken together, current evidence indicates that, despite their wide distribution and apparent abundance, the population structure of long-finned pilot whales remains insufficiently resolved to support definitive conservation-based sustainability assessments of recurrent removals based on abundance alone. As defined above, such assessments require evidence that continued removals are compatible with long-term population persistence, genetic diversity, lineage continuity, social continuity and demographic resilience at the biologically relevant management scale (CBD, 1992; IUCN, 2000; Wade, 1998; Waples and Gaggiotti, 2006; Palsbøll et al., 2007; NOAA, 2016).

References

• 1

  AlvesF.QuérouilS.DinisA.NicolauC.RibeiroC.FreitasL.et al. (2013). Population structure of short-finned pilot whales in the oceanic archipelago of Madeira based on photo-identification and genetic analyses: implications for conservation. Aquat. Conserv.: Mar. Freshw. Ecosyst.23, 758–776. doi: 10.1002/aqc.2332

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 2

  AugustoJ. F.FrasierT. R.WhiteheadH. (2017). Social structure of long-finned pilot whales (Globicephala melas) off northern Cape Breton Island, Nova Scotia. Behaviour154, 509–540. doi: 10.1163/1568539X-00003432

  • CrossRef
  • Google Scholar

• 3

  BakerC. S.PalumbiS. R. (1994). Which whales are hunted? A molecular genetic approach to monitoring whaling. Science265, 1538–1539. doi: 10.1126/science.265.5178.1538

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 4

  BrakesP.DallS. R. X.AplinL. M.BearhopS.CarrollE. L.CiucciP.et al. (2019). Animal cultures matter for conservation. Science363, 1032–1034. doi: 10.1126/science.aaw3557

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 5

  CBD (1992). Convention on Biological Diversity (Rio de Janeiro: United Nations). Available online at: https://www.cbd.int/convention/text/ (Accessed June 03, 2026).

  • Google Scholar
  • View reference in article

• 6

  de StephanisR.VerborghP.PérezS.EstebanR.Minvielle-SebastiaL.GuinetC. (2008). Long-term social structure of long-finned pilot whales (Globicephala melas) in the Strait of Gibraltar. Acta Ethol.11, 81–94. doi: 10.1007/s10211-008-0045-2

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 7

  FarineD. R.WhiteheadH. (2015). Constructing, conducting and interpreting animal social network analysis. J. Anim. Ecol.84, 1144–1163. doi: 10.1111/1365-2656.12418

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 8

  FontaineM. C.RolandK.CalvesI.AusterlitzF.PalstraF. P.TolleyK. A.et al. (2014). Postglacial climate changes and rise of three ecotypes of harbour porpoises, Phocoena phocoena, in western Palearctic waters. Mol. Ecol.23, 3306–3321. doi: 10.1111/mec.12817

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 9

  FooteA. D.VijayN.Ávila-ArcosM. C.BairdR. W.DurbanJ. W.FumagalliM.et al. (2016). Genome-culture coevolution promotes rapid divergence of killer whale ecotypes. Nat. Commun.7, 11693. doi: 10.1038/ncomms11693

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 10

  FordJ. K. B. (1991). Vocal traditions among resident killer whales (Orcinus orca) in coastal waters of British Columbia. Can. J. Zool.69, 1454–1483. doi: 10.1139/z91-206

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 11

  FordJ. K. B.EllisG. M.OlesiukP. F.BalcombK. C.Barrett-LennardL. G. (2010). Linking killer whale survival and prey abundance: food limitation in a top predator. Biol. Lett.6, 139–142. doi: 10.1098/rsbl.2009.0468

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 12

  FrankhamR.BallouJ. D.BriscoeD. A. (2010). Introduction to Conservation Genetics. 2nd Edn (Cambridge: Cambridge University Press).

  • Google Scholar
  • View reference in article

• 13

  HoelzelA. R.DahlheimM.SternS. J. (1998). Low genetic variation among killer whales (Orcinus orca) in the eastern North Pacific and genetic differentiation between foraging specialists. J. Heredity89, 121–128. doi: 10.1093/jhered/89.2.121

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 14

  HoelzelA. R.HeyJ.DahlheimM. E.NicholsonC.BurkanovV.BlackN. (2007a). Population structure and the limits of inferring biological units from spatial overlap in cetaceans. J. Evol. Biol.20, 1677–1687. doi: 10.1111/j.1420-9101.2007.01390.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 15

  HoelzelA. R.HeyJ.DahlheimM. E.NicholsonC.BurkanovV.BlackN. (2007b). Evolution of population structure in a highly social top predator, the killer whale. Mol. Biol. Evol.24, 1407–1415. doi: 10.1093/molbev/msm063

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 16

  International Whaling Commission (2019). Report of the Scientific Committee, SC/68A (Cambridge: International Whaling Commission). Available online at: https://archive.iwc.int/pages/download.php?direct=1&ext=pdf&ref=6940 (Accessed November 10, 2025).

  • Google Scholar
  • View reference in article

• 17

  IUCN (2000). IUCN Policy Statement on Sustainable Use of Wild Living Resources (Gland: International Union for Conservation of Nature). Available online at: https://portals.iucn.org/library/efiles/documents/Rep-2000-054.pdf (Accessed November 10, 2025).

  • Google Scholar
  • View reference in article

• 18

  KrahnM. M.WadeP. R.KalinowskiS. T.DahlheimM. E.TaylorB. L.HansonM. B.et al. (2002). Status Review of Southern Resident Killer Whales (Orcinus orca) under the Endangered Species Act NOAA Technical Memorandum NMFS-NWFSC-54 (Seattle, WA: NOAA Fisheries).

  • Google Scholar
  • View reference in article

• 19

  LacyR. C.WilliamsR.AsheE.BalcombK. C. I.BrentL. J. N.ClarkC. W.et al. (2017). Evaluating anthropogenic threats to endangered killer whales to inform effective recovery plans. Sci. Rep.7, 14119. doi: 10.1038/s41598-017-14471-0

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 20

  LuikartG.RymanN.TallmonD. A.SchwartzM. K.AllendorfF. W. (2010). Estimation of census and effective population sizes: the increasing usefulness of DNA-based approaches. Conserv. Genet.11, 355–373. doi: 10.1007/s10592-010-0050-7

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 21

  MirallesL.CastelloteM.de StephanisR.Mignucci-GiannoniA. A.AgnarssonI.OremusM.et al. (2016). Phylogeography of pilot whales (Globicephala spp.) in the North Atlantic. Mol. Ecol.25, 900–918. doi: 10.1111/mec.13499

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 22

  MonteiroS. S.Méndez-FernandezP.PiertneyS.MoffatC. F.FerreiraM.VingadaJ. V.et al. (2015). Long-finned pilot whale population diversity and structure in Atlantic waters assessed through biogeochemical and genetic markers. Mar. Ecol. Prog. Ser.536, 243–257. doi: 10.3354/meps11455

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 23

  MorinP. A.ArcherF. I.FooteA. D.VilstrupJ.AllenE. E.WadeP.et al. (2010). Complete mitochondrial genome phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species. Genome Res.20, 908–916. doi: 10.1101/gr.102954.109

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 24

  MorinP. A.ParsonsK. M.ArcherF. I.Ávila-ArcosM. C.Barrett-LennardL. G.Dalla RosaL.et al. (2015). Geographic and temporal dynamics of a global radiation and diversification in the killer whale. Mol. Ecol.24, 3964–3979. doi: 10.1111/mec.13284

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 25

  NAMMCO (2025). Report of the NAMMCO WG on Pilot Whales (NAMMCO/SC/PWWG/2025-01) (Tromsø, Norway: NAMMCO-North Atlantic Marine Mammal Commission), 1–140. Available online at: https://nammco.no/wpcontent/uploads/2025/12/report_pwwg_2025-01.pdf (Accessed January 10, 2026).

  • Google Scholar
  • View reference in article

• 26

  NAMMCO Scientific Committee (2019). Report of the 26th Meeting of the NAMMCO Scientific Committee, 29 October–1 November 2019, Tórshavn, Faroe Islands. (Tromsø: North Atlantic Marine Mammal Commission). Available online at: https://nammco.no/wp-content/uploads/2019/11/final-report_sc26-2019.pdf

  • Google Scholar
  • View reference in article

• 27

  NOAA (2016). Guidelines for Assessing Marine Mammal Stocks (Gamms Iii) (Silver Spring, MD: NOAA Fisheries, Office of Protected Resources).

  • Google Scholar
  • View reference in article

• 28

  OremusM.BakerC. S.HeathD. D. (2013). Genetic evidence of multiple matrilines and spatial disruption of kinship bonds in mass strandings of long-finned pilot whales (Globicephala melas). J. Heredity104, 301–311. doi: 10.1093/jhered/est007

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 29

  OremusM.GalesR.DaleboutM. L.FunahashiN.EndoT.KageT.et al. (2009). Worldwide mitochondrial DNA diversity and phylogeography of pilot whales (Globicephala spp.). Biol. J. Linn. Soc98, 729–744. doi: 10.1111/j.1095-8312.2009.01325.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 30

  PalsbøllP. J.AllenJ.BérubéM.ClaphamP. J.FeddersenT. P.HammondP. S.et al. (1997). Genetic tagging of humpback whales. Nature388, 767–769. doi: 10.1038/42005

  • CrossRef
  • Google Scholar
  • View reference in article

• 31

  PalsbøllP. J.BérubéM.AllendorfF. W. (2007). Identification of management units using population genetic data. Trends Ecol. Evol.22, 11–16. doi: 10.1016/j.tree.2006.09.003

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 32

  PalumbiS. R. (2003). Population genetics, demographic connectivity, and the design of marine reserves. Ecol. Appl.13, S146–S158. doi: 10.1890/1051-0761(2003)013[0146:PGDCAT]2.0.CO;2

  • CrossRef
  • Google Scholar
  • View reference in article

• 33

  ParsonsK. M.BalcombK. C.FordJ. K. B.DurbanJ. W.ClaridgeD. E. (2000). The social structure of southern resident killer whales (Orcinus orca) and implications for conservation. Mol. Ecol.9, 463–473. doi: 10.1046/j.1365-294x.2000.00861.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 34

  PikeD. G.GunnlaugssonT.DesportesG.MikkelsenB.VíkingssonG. A.BlochD. (2019). Estimates of the relative abundance of long-finned pilot whales (Globicephala melas) in the Northeast Atlantic from 1987 to 2015 indicate no long-term trends. NAMMCO Sci. Publ.11. doi: 10.7557/3.4643

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 35

  RendellL.WhiteheadH. (2001). Culture in whales and dolphins. Behav. Brain Sci.24, 309–324. doi: 10.1017/S0140525X0100396X

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 36

  RieschR.Barrett-LennardL. G.EllisG. M.FordJ. K. B.DeeckeV. B. (2012). Cultural traditions and the evolution of reproductive isolation: ecological speciation in killer whales? Biol. J. Linn. Soc106, 1–17. doi: 10.1111/j.1095-8312.2012.01872.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 37

  SchwartzM. K.LuikartG.WaplesR. S. (2007). Genetic monitoring as a promising tool for conservation and management. Trends Ecol. Evol.22, 25–33. doi: 10.1016/j.tree.2006.08.009

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 38

  WadeP. R. (1998). Calculating limits to the allowable human-caused mortality of cetaceans and pinnipeds. Mar. Mamm. Sci.14, 1–37. doi: 10.1111/j.1748-7692.1998.tb00688.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 39

  WaplesR. S.GaggiottiO. (2006). What is a population? An empirical evaluation of some genetic methods for identifying the number of populations. Mol. Ecol.15, 1419–1439. doi: 10.1111/j.1365-294X.2006.02890.x

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 40

  WhiteheadH. (2008). Analyzing Animal Societies: Quantitative Methods for Vertebrate Social Analysis (Chicago: University of Chicago Press).

  • Google Scholar
  • View reference in article

• 41

  WhiteheadH. (2009). SOCPROG programs: analysing animal social structures. Behav. Ecol. Sociobiol.63, 765–778. doi: 10.1007/s00265-008-0697-y

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 42

  WhiteheadH.FordJ. K. B.HornA. G. (2023). Using culturally transmitted behavior to help delineate conservation units for species at risk. Biol. Conserv.285, 110239. doi: 10.1016/j.biocon.2023.110239

  • Pubmed Abstract
  • CrossRef
  • Google Scholar

• 43

  WhiteheadH.RendellL.OsborneR. W.WürsigB. (2004). Culture and conservation of non-humans with reference to whales and dolphins: review and new directions. Biol. Conserv.120, 427–437. doi: 10.1016/j.biocon.2004.03.017

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article

• 44

  YurkH.Barrett-LennardL.FordJ. K. B.MatkinC. O. (2002). Cultural transmission within maternal lineages: vocal clans in resident killer whales in southern Alaska. Anim. Behav.63, 1103–1119. doi: 10.1006/anbe.2002.3012

  • Pubmed Abstract
  • CrossRef
  • Google Scholar
  • View reference in article