# Multispecies tracking reveals a major seabird hotspot in the North Atlantic

Tammy Davies, Ana P.B. Carneiro, Marguerite Tarzia, Ewan Wakefield, Janos Hennicke, Morten Frederiksen, Erpur Snær Hansen, Bruna Campos, Carolina Hazin, Ben Lascelles, et al.

► To cite this version:

Tammy Davies, Ana P.B. Carneiro, Marguerite Tarzia, Ewan Wakefield, Janos Hennicke, et al. Multispecies tracking reveals a major seabird hotspot in the North Atlantic. Conservation Letters, 2021, 14, pp.e12824. 10.1111/conl.12824. hal-03331141

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# Multispecies tracking reveals a major seabird hotspot in the North Atlantic

Tammy E. Davies<fnref n="1" />,†

<figure><img src="image_2.png" /></figure>

Ana P.B. Carneiro<fnref n="1" />,†

<figure><img src="image_3.png" /></figure>

Marguerite Tarzia<fnref n="1" />

Ewan Wakefield<fnref n="3" />

Janos C. Hennicke<fnref n="4" />

Morten Frederiksen⁵

Erpur Snær Hansen⁶

Bruna Campos<fnref n="2" />,⁷

Carolina Hazin<fnref n="1" />

Ben Lascelles<fnref n="1" />

Tycho Anker-Nilssen⁸

Hólmfríður Arnardóttir⁹

Robert T. Barrett¹⁰

Manuel Biscoito¹¹

Loïc Bollache¹²,¹³

Thierry Boulinier¹⁴

Paulo Catry¹⁵

Filipe R. Ceia¹⁶

Olivier Chastel¹⁷

Signe Christensen-Dalsgaard⁸

Marta Cruz-Flores¹⁸

<figure><img src="image_4.png" /></figure>

Jóhannis Danielsen¹⁹

Francis Daunt²⁰

Euan Dunn²¹

Carsten Egevang²²

Ana Isabel Fagundes²³

Annette L. Fayet²⁴

Jérôme Fort²⁵

Robert W. Furness<fnref n="3" />

Olivier Gilg¹²,¹³

Jacob González-Solís¹⁸

José Pedro Granadeiro²⁶

David Grémillet¹⁷,⁴²

Tim Guilford²⁴

Sveinn Are Hanssen⁸

Michael P. Harris²⁰

April Hedd²⁷

Nicholas Per Huffeldt⁵,²²

<figure><img src="image_5.png" /></figure>

Mark Jessopp²⁸

Yann Kolbeinsson²⁹

Johannes Krietsch³⁰,³¹

Johannes Lang³²,¹³

Jannie Fries Linnebjerg⁵

Svein-Håkon Lorentsen⁸

Jeremy Madeiros³³

Ellen Magnusdottir³⁴

Mark L. Mallory³⁵

Laura McFarlane Tranquilla³⁶

Flemming R. Merkel⁵,²²

Teresa Militão¹⁸

Børge Moe⁸

William A. Montevecchi³⁷

Virginia Morera-Pujol¹⁸

Anders Mosbech⁵

Verónica Neves³⁸

Mark A. Newell²⁰

Bergur Olsen¹⁹

Vitor H. Paiva¹⁶

Hans-Ulrich Peter³⁰

Aevar Petersen³⁹

Richard A. Phillips⁴⁰

Iván Ramírez<fnref n="1" />

Jaime A. Ramos¹⁶

Raül Ramos¹⁸

Robert A. Ronconi⁴¹

Peter G. Ryan⁴²

Niels Martin Schmidt⁵

Ingvar A. Sigurðsson⁴³

Benoît Sittler⁴⁴,¹³

Harald Steen⁴⁵

Iain J. Stenhouse⁴⁶

Hallvard Strøm⁴⁵

Geir H. R. Systad⁸

Paul Thompson⁴⁷

Thorkell L. Thórarinsson²⁹,⁴³

Rob S.A. van Bemmelen⁴⁸

Sarah Wanless²⁰

Francis Zino⁴⁹

Maria P. Dias<fnref n="1" />,¹⁵

<figure><img src="image_6.png" /></figure>

<footnote n="1">¹ BirdLife International, Cambridge, U.K.</footnote>

<footnote n="2">² EuroNatur Foundation, Radolfzell, Germany</footnote>

<footnote n="3">³ Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow, Glasgow, U.K.</footnote>

<footnote n="4">⁴ German Federal Agency for Nature Conservation, Putbus, Germany</footnote>
⁵ Department of Bioscience, Aarhus University, Roskilde, Denmark

⁶ South Iceland Nature Research Centre, Vestmannaeyjar, Iceland

⁷ Stichting BirdLife Europe, Brussels, Belgium

⁸ Norwegian Institute for Nature Research, Trondheim, Norway

⁹ Fuglavernd / BirdLife in Iceland, Reykjavík, Iceland

¹⁰ Tromsø University Museum, Tromsø, Norway

¹¹ Funchal Natural History Museum, Funchal, Portugal

¹² UMR 6249 Chrono-environnement, Université de Bourgogne Franche-Comté, Besançon, France

¹³ Groupe de Recherche en Ecologie Arctique, Francheville, France

¹⁴ Centre d'Ecologie Fonctionnelle et Evolutive, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, Montpellier, France

¹⁵ MARE - Marine and Environmental Sciences Centre, ISPA - Instituto Universitário, Lisbon, Portugal

¹⁶ University of Coimbra, MARE-Marine and Environmental Sciences Centre, Dep. Life Sciences, Coimbra, Portugal

¹⁷ Centre d'Etudes Biologiques de Chizé (CEBC), UMR 7372 CNRS-La Rochelle Université, Villiers-en-bois, France

¹⁸ Institut de Recerca de la Biodiversitat (IRBio) and Dept. de Biologia Evolutiva, Ecologia i Ciències Ambientals, Universitat de Barcelona, Barcelona, Spain

¹⁹ Faroe Marine Research Institute, Tórshavn, Faroe Islands

²⁰ UK Centre for Ecology & Hydrology, Penicuik, U.K.

²¹ RSPB, Sandy, U.K.

²² Greenland Institute of Natural Resources, Nuuk, Greenland

²³ Portuguese Society for the Study of Birds (SPEA), Lisboa, Portugal

²⁴ University of Oxford, Oxford, U.K.

²⁵ Littoral, Environnement et Sociétés (LIENSs), UMR 7266 CNRS-La Rochelle Université, La Rochelle, France

²⁶ CESAM-Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal

²⁷ Wildlife Research Division, Environment and Climate Change, Mount Pearl, NL, Canada

²⁸ School of Biological, Earth & Environmental Sciences, Environmental Research Institute, University College Cork, Ireland

²⁹ Northeast Iceland Nature Research Centre, Húsavík, Iceland

³⁰ Friedrich Schiller University, Institute of Ecology and Evolution, Jena, Germany

³¹ Max Planck Institute for Ornithology, Department of Behavioural Ecology and Evolutionary Genetics, Seewiesen, Germany

³² Justus-Liebig-University Giessen, Clinic for Birds, Reptiles, Amphibians and Fish, Working Group for Wildlife Research, Giessen, Germany

³³ Department of Environment and Natural Resources, Government of Bermuda, Paget, Bermuda

³⁴ Háskóli Íslands, University of Iceland, Reykjavik, Iceland

³⁵ Biology, Acadia University, Wolfville, NS, Canada

³⁶ Birds Canada, Sackville, NB, Canada

³⁷ Psychology Department, Memorial University of Newfoundland, St. John's, NL, Canada

³⁸ MARE - Marine and Environmental Sciences Centre, IMAR & Okeanos, Horta, Portugal

³⁹ Independent researcher, Reykjavik, Iceland

⁴⁰ British Antarctic Survey, Cambridge, U.K.

⁴¹ Canadian Wildlife Service, Environment and Climate Change Canada, Dartmouth, NS, Canada

⁴² FitzPatrick Institute of African Ornithology, Rondebosch, South Africa

⁴³ Icelandic Institute of Natural History, Garðabær, Iceland

⁴⁴ University of Freiburg, Freiburg, Germany

⁴⁵ Norwegian Polar Institute, Tromsø, Norway

⁴⁶ Biodiversity Research Institute, Portland, Maine, USA

⁴⁷ Lighthouse Field Station, School of Biological Sciences, University of Aberdeen, Cromarty, U.K.

⁴⁸ Bureau Waardenburg, Culemborg, The Netherlands

⁴⁹ Freira Conservation Project, Funchal, Portugal
**Correspondence**

Tammy E. Davies, BirdLife International,
David Attenborough Building, Pembroke
Street, Cambridge CB2 9QZ, UK.
Email: tammy.davies@birdlife.org,
tedavies23@gmail.com

† Joint authorship.

**Abstract**

The conservation of migratory marine species, including pelagic seabirds, is challenging because their movements span vast distances frequently beyond national jurisdictions. Here, we aim to identify important aggregations of seabirds in the North Atlantic to inform ongoing regional conservation efforts. Using tracking, phenology, and population data, we mapped the abundance and diversity of 21 seabird species. This revealed a major hotspot associated with a discrete area of the subpolar frontal zone, used annually by 2.9–5 million seabirds from ≥56 colonies in the Atlantic: the first time this magnitude of seabird concentrations has been documented in the high seas. The hotspot is temporally stable and amenable to site-based conservation and is under consideration as a marine protected area by the OSPAR Commission. Protection could help mitigate current and future threats facing species in the area. Overall, our approach provides an exemplar data-driven pathway for future conservation efforts on the high seas.

**KEYWORDS**

area beyond national jurisdiction, Atlantic, biologging, conservation, high seas, marine protected area, regional seas convention

# 1 | INTRODUCTION

Many seabird species are wide-ranging, traveling thousands of kilometers across jurisdictional and international waters, only returning to land to breed (Harrison et al., 2018). Such migratory species are increasingly exposed to the expanding cumulative human impacts in the oceans (Halpern et al., 2019). Consequently, seabirds are one of the most threatened groups of vertebrates, with almost half of all species (47%) experiencing population declines (Dias et al., 2019).

As higher predators, seabirds play key roles in marine ecosystems making their conservation critical (Grémillet et al., 2018). However, their high mobility makes this challenging, particularly because seabirds rely on multiple, often geographically distant ecosystems, all of which need some form of protection for successful conservation (Dunn et al., 2019). For highly pelagic species, this is further complicated by the lack of an effective governance mechanism for areas beyond national jurisdictions (De Santo et al., 2019), and often incomplete knowledge of their distribution throughout all life-history stages (Carneiro et al., 2020).

Identifying important areas at-sea has been facilitated through advances in biologging technology (Lascelles et al., 2016). Individual-based tracking, using animal-attached devices, is becoming an indispensable tool for guiding conservation efforts through the identification of areas of high species diversity and abundance (hereafter,

“hotspots”) that are critical for species survival (e.g., molting or foraging areas) (Hays et al., 2019). Recent animal tracking studies have demonstrated that many pelagic seabird species consistently occur at predictable times and places at the macroscale (Frederiksen et al., 2016), often in association with particular habitats or migratory corridors (Dias et al., 2013). This presents an opportunity for area-based conservation for migratory species, particularly because many oceanic hotspots (i.e., areas beyond continental shelves) are often associated with persistent features, such as major frontal and upwelling systems (Block et al., 2011).

The North Atlantic is a priority area for seabird conservation because over the last decade many species in this region have experienced pronounced population declines, including Atlantic Puffin (*Fratercula arctica*), Black-legged Kittiwake (*Rissa tridactyla*), Common Guillemot (*Uria aalge*), and Northern Fulmar (*Fulmarus glacialis*) (Dias et al., 2019). While colonies in the Northeast Atlantic are generally afforded good protection, their foraging areas remain poorly known and protected (Ramirez et al., 2017). Moreover, many seabird species in the North Atlantic, such as shearwaters and auks, are impacted by marine-based threats (e.g., bycatch, pollution, and overfishing; Dias et al., 2019), indicating an urgent need to identify and protect important marine areas to address the recent declines of threatened seabird species.

The Oslo-Paris-Convention on the protection of the North-East Atlantic (OSPAR) is one of two regional seas
<figure><img src="image_7.png" /><figcaption>FIGURE 1 Location of identified hotspot in the middle of North Atlantic (green) and summary information of species groups at the site. Arrows indicate the LMEs the birds are traveling from to the site, labeled with LME name and number of species. Dashed arrows are from LMEs in the South Atlantic (not visible on the map). LMEs are shown by a solid gray line, with a dashed gray line for adapted LMEs (Azores, Bermuda, Cabo Verde, Madeira; the latter analyzed with the Canary Current LME). Colonies are shown in circles (black = data used in analysis, white = data considered but not included in final analysis). Figure prepared by Terra Communications</figcaption></figure>

conventions (the other being the Commission for the Conservation of Antarctic Marine Living Resources) that have initiated actions within their remit in Areas Beyond National Jurisdiction (ABNJ), providing a unique opportunity for conservation action in ABNJ. OSPAR have established a number of marine protected areas (MPAs) in ABNJ and are working toward improving the ecological coherence of this network—including addressing an identified gap for seabirds, alongside achieving 10% protection of the OSPAR Maritime Area (Aichi Target 11) (Johnson et al., 2014; OSPAR, 2019). At-sea surveys (Bennison & Jessopp, 2015; Boertmann, 2011) and single species tracking studies (e.g., Dias et al., 2012; Egevang et al., 2010; Fayet et al., 2017) indicate that important seabird concentrations may occur around the Mid-Atlantic Ridge (MAR), and suggesting a community-level assessment of available tracking data is needed, and could help guide current policy and practice.

Here, we combine tracking, phenology, and population data on 21 Atlantic seabird species to quantify their distribution, density, and diversity in the ABNJ of OSPAR Region V. We reveal an important hotspot of unexpected extent and temporal stability. We suggest how our findings could guide conservation management, and provide

an exemplar for the use of multispecies tracking to identify sites suitable for protection in ABNJ.

## 2 | METHODS

### 2.1 | Study area

Our study area is defined as ABNJ within OSPAR Region V (www.ospar.org/convention/the-north-east-atlantic). This encompasses the deeper waters of the North Atlantic, between 35 and 62°N and from 10 to 42°W west of Iberia/France and west of the 200 m depth contour off the British Isles (Figure 1).

### 2.2 | Tracking data

We downloaded all available seabird tracking data that overlapped OSPAR Region V from the BirdLife Seabird Tracking Database (www.seabirdtracking.org) in 2016. These data comprised 2188 tracks of 23 species, from 105 colonies within 16 countries and 25 large marine ecosystems (LME), located in both the North and South Atlantic
(Figure S1). We excluded all tracks from colonies that had less than 2% overlap with the study area, unless other colonies in the same LME had higher overlap. The final analyses included 1524 tracked birds of 21 species, from 56 colonies, across 17 LMEs and 16 countries/jurisdictions (Table 1). Phenology and population data for each species and colony were obtained from the literature and verified by experts (Table S1, Figure S2). Following advice from the scientific community, and in line with other studies (e.g., Frederiksen et al., 2016; Frederiksen et al., 2012), colonies of the same species located in the same LME were combined and considered to represent unique populations. Our data were representative of the species distributions in the Atlantic (Table S2).

**2.3 | Identification of marine Important Bird and Biodiversity Areas**

We analyzed tracking data in combination with objective site selection criteria following the method developed to delineate marine Important Bird and Biodiversity Areas (IBAs) (Lascelles et al., 2016) and Key Biodiversity Areas (“track2kba” R package; Beal et al., 2020). This is a well-established, standardized approach to identify important hotspots for foraging seabirds based on kernel density analysis of tracking data, in combination with abundance estimates of the colonies of origin. The hotspots identified through this method are key sites for the persistence of species by regularly holding important numbers of a globally threatened species, or supporting > 1% of the global or biogeographic population (Lascelles et al., 2016). This method has been applied in all oceans, with many resultant sites informing conservation action (e.g., Hays et al., 2019; Waliczky et al., 2018). We checked tracked birds of nonthreatened species against the IBA criteria: 1% threshold (i.e., LME represents ≥ 1% of the global [for species breeding outside Europe] or biogeographic population [EU number of individuals for European species]). Population sizes refer to the number of mature individuals.

We conducted all analyses in R, as detailed in the Supporting Methods. In brief, we first grouped tracking data by species, LME, and breeding stage (i.e., breeding, non-breeding, migration, e.g., Black-legged Kittiwake, Iceland Shelf and Sea LME, nonbreeding; Figure S3). We followed the Lascelles et al. (2016) methodology for each group. We estimated the “core use area” of each bird in each group, defined by the 50% utilization distribution contour. We then calculated the proportion of core use areas occurring in each cell in a 0.2 × 0.2 degree grid (Lascelles et al., 2016). We then estimated the number of birds in each cell by multiplying the proportion of the tracked population in each

grid cell by the size of the LME population (Table S1) to generate one *density map/group*.

**2.4 | Species richness and abundance hotspot identification**

To identify areas that are important for multiple species at the same time of year, we aggregated the density maps in calendar seasons (Supporting Methods), defined as: Q1: January–March, Q2: April–June, Q3: July–September, and Q4: October–December. We weighted each *density map/group* by the average number of half months in each season spent in each breeding stage, based on the species’ phenology (Carneiro et al., 2020) to generate one *density map/species-LME-season*.

We combined all *density maps/species-LME-season* to produce: (1) *density maps/species-season*; (2) *density maps for all species combined/season*; and (3) *overall density map* (all species and seasons) (Figure S3). We also estimated species richness by binary coding presence/absence raster density maps and summing across species for each season. Finally, we combined the richness and density maps and used the 15% highest values to delimit the most important hotspot within the study area. We then excluded areas within extended shelf claims to facilitate the uptake of conservation measures (Ramirez et al., 2017), so the final area is located solely within ABNJ.

**2.5 | Interannual consistency of area use**

To assess the consistency in area use, we conducted additional analysis within groups with relatively large sample sizes (> 20 birds) in multiple years (Supporting Methods, Figure S4). We conducted an analysis of similarity (ANOSIM, a measure of relative within-group dissimilarity based on a bootstrap randomization; Oksanen et al., 2013) to test for differences in the distribution within and between-years using two metrics of distribution overlap (Bhattacharyya’s affinity and HR indexes; Fieberg & Kochanny, 2005).

**3 | RESULTS**

Our analysis revealed an extensive (~595,000 km²) hotspot of seabird diversity and abundance near the western boundary of OSPAR Region V (Figure 1), extending from ~41 to 53°N and 32 to 42°W. The area is bounded in the north by the Charlie–Gibbs Fracture Zone, to the west by the Flemish Cap and the Grand Banks of Newfoundland,
<table><caption>TABLE 1 Summary of the final seabird tracking data used in the analyses</caption><thead><tr><th>Species</th><th>IUCN status</th><th>No. colonies</th><th>No. birds</th><th>Tracking years (N)</th><th>Locations of colonies birds tracked from Large marine ecosystem</th><th>Country/jurisdiction</th></tr></thead><tbody><tr><td>Cory's Shearwater, Calonectris borealis</td><td>LC</td><td>6</td><td>349</td><td>2002–2015 (14)</td><td>Azores</td><td>Spain, Portugal</td></tr><tr><td>Manx Shearwater, Puffinus puffinus</td><td>LC</td><td>6</td><td>181</td><td>1999–2014 (11)</td><td>Canary Current</td><td>United Kingdom, Iceland</td></tr><tr><td>Audubon's Shearwater, Puffinus lherminieri</td><td>LC</td><td>2</td><td>23</td><td>2010–2014 (5)</td><td>Canary Current</td><td>Portugal</td></tr><tr><td>Great Shearwater, Ardenna gravis</td><td>LC</td><td>2</td><td>72</td><td>2006–2012 (6)</td><td>Tristan Gough*</td><td>Saint Helena, Ascension and Tristan da Cunha</td></tr><tr><td>Sooty Shearwater, Ardenna grisea</td><td>NT</td><td>1</td><td>18</td><td>2007–2009 (3)</td><td>Patagonian Shelf</td><td>Falkland Islands (Malvinas)</td></tr><tr><td>Northern Fulmar, Fulmarus glacialis</td><td>LC</td><td>1</td><td>72</td><td>2006–2013 (8)</td><td>North Sea</td><td>United Kingdom</td></tr><tr><td>Desertas Petrel, Pterodroma deserta</td><td>VU</td><td>1</td><td>39</td><td>2008–2013 (6)</td><td>Canary Current*</td><td>Portugal</td></tr><tr><td>Zino's Petrel, Pterodroma madeira</td><td>EN</td><td>1</td><td>12</td><td>2007–2010 (4)</td><td>Canary Current*</td><td>Portugal</td></tr><tr><td>Bermuda Petrel, Pterodroma cahow</td><td>EN</td><td>1</td><td>11</td><td>2009–2010 (2)</td><td>Bermuda*</td><td>Bermuda</td></tr><tr><td>Bulwer's Petrel, Bulweria bulwerii</td><td>LC</td><td>2</td><td>48</td><td>2009–2013 (5)</td><td>Canary Current</td><td>Portugal, Spain</td></tr><tr><td>Black-legged Kittiwake, Rissa tridactyla</td><td>VU</td><td>16</td><td>275</td><td>2007–2011 (5)</td><td>Barents Sea</td><td>Russian Federation, United Kingdom, Faroe Islands, Iceland, Denmark, Norway</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>North Sea</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>Celtic-Biscay Shelf</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>Faroe Plateau</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>Iceland Shelf and Sea</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>Norwegian Sea</td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td>West Spitsbergen</td><td></td></tr><tr><td>Sabine's Gull, Xema sabini</td><td>LC</td><td>1</td><td>8</td><td>2007–2008 (2)</td><td>Greenland Sea</td><td>Greenland</td></tr><tr><td>Arctic Tern, Sterna paradisaea</td><td>LC</td><td>1</td><td>9</td><td>2007–2008 (2)</td><td>Greenland Sea</td><td>Greenland</td></tr><tr><td>Great Skua, Catharacta skua</td><td>LC</td><td>1</td><td>11</td><td>2008–2009 (2)</td><td>Iceland Shelf and Sea</td><td>Iceland</td></tr><tr><td>South Polar Skua, Catharacta maccormicki</td><td>LC</td><td>1</td><td>32</td><td>2007–2010 (4)</td><td>South Shetland Islands</td><td>Antarctica</td></tr><tr><td>Long-tailed Jaeger, Stercorarius longicaudus</td><td>LC</td><td>6</td><td>42</td><td>2006–2015 (8)</td><td>Greenland Sea</td><td>Greenland, Norway, Sweden</td></tr><tr><td>Norwegian Sea + Barents Sea</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

(Continues)
<table><caption>TABLE 1 (Continued)</caption><thead><tr><th>Species</th><th>IUCN status</th><th>No. colonies</th><th>No. birds</th><th>Tracking years (N)</th><th>Locations of colonies birds tracked from Large marine ecosystem</th><th>Country/jurisdiction</th></tr></thead><tbody><tr><td>Atlantic Puffin, Fratercula arctica</td><td>VU</td><td>8</td><td>146</td><td>2007–2015 (9)</td><td>Celtic-Biscay Shelf</td><td>Ireland, Iceland, United Kingdom</td></tr><tr><td>Common Murre, Uria aalge</td><td>LC</td><td>3</td><td>20</td><td>2013–2014 (2)</td><td>Iceland Shelf and Sea</td><td>Iceland</td></tr><tr><td>Thick-billed Murre, Uria lomvia</td><td>LC</td><td>9</td><td>151</td><td>2007–2014 (7)</td><td>Arctic Canada</td><td>Canada, Greenland, Iceland</td></tr><tr><td>Razorbill, Alca torda</td><td>NT</td><td>3</td><td>20</td><td>2013–2015 (3)</td><td>Iceland Shelf and Sea</td><td>Iceland</td></tr><tr><td>Little Auk, Alle alle</td><td>LC</td><td>1</td><td>18</td><td>2010–2011 (2)</td><td>Greenland Sea</td><td>Greenland</td></tr></tbody></table>

Note: Tracking years show the overall year range, with the max number of years held per LME in brackets. * Species endemic to an LME. For further details on population (Table S1) and phenology (Figure S3).

to the east by the MAR and to the south by the Azores (Figure 1).

All 21 species used the identified hotspot, including five globally threatened species (endangered Bermuda Petrel [Pterodroma cahow], Zino's Petrel [Pterodroma madeira], and vulnerable Desertas Petrel [Pterodroma desertta], Black-legged Kittiwake and Atlantic Puffin; Table 1). We estimated that 2.9–5 million birds use the area throughout the year (Table 2) traveling from 56 colonies within 16 countries (Figure 1).

The highest abundance (ca. 4.4–5 million individuals) occurred during the boreal winter (October–March; Q4–Q1, Table 2). The highest number of species (n = 21) occurred in spring–summer (April–September), when ca. 2.9–3.3 million birds were present (Q2–Q3, Table 2). Consistency in area use was demonstrated for all nine species with multiyear data, with the ANOSIM index [R value] always lower than 0.12 (Supporting Methods, Figure S4).

The most abundant (2.3 million) species using the area was the Little Auk (Alle alle) during nonbreeding (January–March), followed by wintering Great Shearwater (Ardenna gravis; 1.8 million, July–September; Table 2), a migrant species breeding in Tristan da Cunha archipelago, South Atlantic. We found three species with more than 50% of their global population using the area as a winter or staging ground: South Polar Skua (Catharacta maccormicki; 64.8–68.4%, April–September), Long-tailed Jaeger (Stercorarius longicaudus; 63.3%, July–September), and Sooty Shearwater (Ardenna grisea; 61%, April–June; Figure 2). Almost 50% of the endangered Bermuda Petrel (45.8%) use the area during July–September.

Most seabirds used the area during their nonbreeding stage. This included three species of southern hemisphere breeders that winter in the area (Great Shearwater, Sooty Shearwater, and South Polar Skua), as well as Long-tailed Jaeger and Arctic Tern (Sterna paradisaea) that use the area as a staging ground for 1–4 weeks during their outward and return migrations. Seven species used the area throughout the year: Zino's Petrel, Great Skua (Catharacta skua; peak July–December), and the following species showing a peak in numbers October–March: Cory's Shearwater (Calonectris borealis), Northern Fulmar, Black-legged Kittiwake, Atlantic Puffin, and Thick-billed Murre (Uria lomvia). Four species also used the area while breeding (Manx Shearwater [Puffinus puffinus], Cory's Shearwater, Desertas Petrel, and Bulwer's Petrel [Bulweria bulwerii]).

4 | DISCUSSION

Our analysis revealed a major hotspot for foraging seabirds in the North Atlantic, used by 21 species totaling up to an
<table><caption>TABLE 2 Estimated maximum number of adults from tracked populations using the site per year quarter</caption><thead><tr><th>Species name</th><th>Biogeographic population (max mature birds)</th><th>Q1 Jan-Mar (max ind)</th><th>Q2 Apr-Jun (max ind)</th><th>Q3 Jul-Sept (max ind)</th><th>Q4 Oct-Dec (max ind)</th></tr></thead><tbody><tr><td>Cory's Shearwater</td><td>503,430</td><td>69,685</td><td>20,358</td><td>40,085</td><td>59,442</td></tr><tr><td>Manx Shearwater</td><td>982,510</td><td></td><td>71,827</td><td>167</td><td></td></tr><tr><td>Audubon's Shearwater</td><td>4084</td><td></td><td>62</td><td>743</td><td>278</td></tr><tr><td>Great Shearwater</td><td>8,000,000</td><td></td><td>1,564,472</td><td>1,819,681</td><td></td></tr><tr><td>Sooty Shearwater</td><td>600,000</td><td></td><td>368,627</td><td>338,562</td><td></td></tr><tr><td>Northern Fulmar</td><td>756,210</td><td>154,024</td><td>70,506</td><td>86,893</td><td>154,024</td></tr><tr><td>Desertas Petrel</td><td>340</td><td></td><td>12</td><td>53</td><td>13</td></tr><tr><td>Zino's Petrel</td><td>160</td><td>15</td><td>21</td><td>21</td><td>15</td></tr><tr><td>Bermuda Petrel</td><td>142</td><td></td><td></td><td>65</td><td>22</td></tr><tr><td>Bulwer's Petrel</td><td>100,000</td><td></td><td></td><td>1418</td><td></td></tr><tr><td>Black-legged Kittiwake</td><td>3,822,882</td><td>1,347,050</td><td>63,650</td><td>664,577</td><td>1,366,342</td></tr><tr><td>Sabine's Gull</td><td>3000</td><td></td><td>375</td><td></td><td></td></tr><tr><td>Arctic Tern</td><td>165,000</td><td></td><td></td><td>65,529</td><td></td></tr><tr><td>Great Skua</td><td>10,800</td><td>1964</td><td>1309</td><td>2618</td><td>2945</td></tr><tr><td>South Polar Skua</td><td>1542</td><td></td><td>999</td><td>1054</td><td></td></tr><tr><td>Long-tailed Jaeger</td><td>72,856</td><td></td><td>34,765</td><td>46,131</td><td></td></tr><tr><td>Atlantic Puffin</td><td>5,121,612</td><td>936,713</td><td>506,057</td><td>257,030</td><td>1,079,091</td></tr><tr><td>Common Murre</td><td>1,392,408</td><td></td><td>71,406</td><td>35,703</td><td></td></tr><tr><td>Thick-billed Murre</td><td>2,589,888</td><td>161,184</td><td>50,625</td><td>13,619</td><td>144,309</td></tr><tr><td>Razorbill</td><td>626,944</td><td></td><td>26,123</td><td></td><td></td></tr><tr><td>Little Auk</td><td>7,000,000</td><td>2,333,333</td><td>129,630</td><td></td><td>1,555,556</td></tr><tr><td>Total number of birds</td><td></td><td>5,003,968</td><td>2,980,824</td><td>3,373,949</td><td>4,362,037</td></tr><tr><td>Total number of species</td><td></td><td>8</td><td>18</td><td>18</td><td>11</td></tr></tbody></table>
<figure><img src="image_8.png" /><figcaption>**FIGURE 2** Percentage of biogeographic population of each species estimated to be using the hotspot for each year quarter. Colors indicate if the species breeds in the northern or southern hemisphere</figcaption></figure>

estimated 5 million adults. At-sea surveys previously indicated that relative abundance peaked in this area, but this is the first time that a seabird aggregation of this absolute abundance has been robustly quantified anywhere in the high seas. The hotspot qualifies as an IBA and can be considered the most important oceanic foraging grounds for the community of seabirds in the OSPAR maritime high seas area and one of the most important concentrations of migratory seabirds in the Atlantic. Seabirds using this hotspot originated from a minimum of 56 colonies in 16 different countries. Many of these species traveled great distances to use the area, with some using it year-round, suggesting that food availability in the area is consistently

high. Boreal breeders, such as Arctic Terns, Long-tailed Jaegers, Sabine's Gulls, Manx Shearwaters, and Cory's Shearwaters, use the area as a staging area to fuel trans-equatorial migrations (Egevang et al., 2010; Guilford et al., 2009; Sittler et al., 2011), or to fuel the last migration leg to the breeding areas (Egevang et al., 2010; van Bemmelen et al., 2017) sometimes making detours of > 5000 km to do so (Dias et al., 2013). Southern Hemisphere breeders, such as South Polar Skuas, Sooty Shearwaters, and Great Shearwaters, migrate up to 13,000 km to spend some of the annual winter in the area (Hedd et al., 2012; Kopp et al., 2011).

Our analysis included tracking data from major colonies of each species in the Atlantic, including those that
represent more than 90% of the global or Atlantic popula-
tion for many species (e.g., Cory's Shearwater, Sooty Shear-
water, Great Shearwater; all gadfly petrels, genus *Ptero-
droma*). We only used tracks of adults, because relatively
few juvenile and immature birds have so far been tracked,
which can have an influence on the overall distribution of
seabirds (Carneiro et al., 2020). Indeed, a recent study also
found the area to be used by immature Cory's Shearwaters
(Campioni et al., 2020). Thus, our estimates should be con-
sidered a minimum. Population estimates for each colony
are subject to natural variation and recording error, and the
number of birds using the area should ideally be updated
regularly.

4.1 | Biodiversity hotspot

Recent studies have found additional seabird species use
the area, including Leach's Storm-Petrel (Oceanodroma
leucorhoa) (Pollet et al., 2019), Wilson's Storm-Petrel
(Oceanites oceanicus), Great Black-backed Gull (Larus
marinus), Arctic Jaeger (Stercorarius parasiticus), Poma-
rine Jaeger (S. pomarinus), and Northern Gannet (Morus
bassanus) (Boertmann, 2011; Wakefield, 2018). Tracking
studies also demonstrate that the area is used by many
nonavian, wide-ranging species, including Blue Shark (Pri-
onace glauca), Shortfin Mako Shark (Isurus oxyrinchus)
(Queiroz et al., 2016), Basking Shark (Cetorhinus maximus)
(Gore et al., 2008), Atlantic Bluefin Tuna (Thunnus thyn-
nus) (Walli et al., 2009), Sei Whale (Balaenoptera borealis)
(Prieto et al. 2014), and Leatherback Turtle (Dermochelys
coriacea) (Fossette et al., 2014). At-sea surveys in the area
have also found many cetacean species, including Blue
Whale (Balaenoptera musculus), various beaked whales,
Common and Spotted dolphins (Wakefield, 2018). Further
work is needed to understand how these species use and
interact in the area, and the role of oceanographic drivers
in the region.

4.2 | Potential drivers of abundance and diversity

The hotspot is located in an area of complex oceanogra-
phy, dominated by the North-Atlantic Current (NAC) and
the associated Subpolar Frontal system (Belkin & Levitus
1996). These oceanographic drivers are both more intense
and spatially stable due to bathymetric steering by the
continental slope/Grand Banks to the West and Charlie-
Gibbs Fracture Zone in the East (Rossby, 1996). The asso-
ciated mesoscale turbulence creates high rates of primary
production (Longhurst, 2010), and it is likely the com-
bination of high primary production and spatiotemporal

predictability that allows the area to support large num-
bers of higher predators. Studies indicate that prey, such
as zooplankton (e.g., calanoid copepods) and mesopelagic
fish (e.g., myctophids; Fort et al., 2010; Hudson et al.,
2014), are abundant in the area, with the availability to
seabirds further enhanced through both mesoscale tur-
bulence (McGillicuddy, 2016) and the diel vertical migra-
tion of mesopelagic prey (Dias et al., 2012). See Supporting
Information—Oceanography.

**4.3 Conservation implications**

Most seabirds used the multispecies hotspot during their nonbreeding stage—a period of their lifecycle that is currently poorly protected (Ramirez et al., 2017). Conditions during nonbreeding can directly affect subsequent breeding productivity via carryover effects (Fayet et al., 2017). This stage includes the mid-winter period, when adverse weather, food, and light conditions may account for the highest mortality of some Atlantic seabirds (Mesquita et al., 2015). Many of the studied seabird species use the hotspot while molting (Hedd et al., 2012; Wakefield, 2018). Molt is a critical time for seabirds because it is energetically demanding and can compromise flight efficiency, potentially increasing the susceptibility to natural and anthropogenic threats (Grissot et al., 2019).

We contend that the identified hotspot deserves year-
round protection as an MPA, given the regular use by a
large number of birds and spatiotemporal stability of the
area (likely caused by stable physical drivers). Seventeen
of the 21 species using the area are impacted by marine-
based threats, including bycatch (65%), overfishing (29%),
energy production and mining (18%), climate change (71%),
pollution (including light pollution; 59%), and are under-
going population declines (Dias et al., 2019). Except for
climate change, these threats can be reduced via area-
based management (Game et al., 2009) and given that
many breeding colonies are already protected, there is an
urgent need for marine spatial protections. Although there
is a debate about the utility of MPAs to protect migratory
species (Game et al., 2009), there are an increasing number
of studies showing their importance, particularly during
spatially limited and vulnerable life-history stages (Péron
et al., 2013; White et al., 2017; Young et al., 2015), and there
have been demonstrated successes for seabirds when man-
agement measures have preserved their prey base (Croxall,
2008; Pichegru et al., 2010). MPAs can help reduce the like-
lihood of mortality, and even though the MPA may only
represent a small portion of a seabirds' migratory range,
they can serve a vital role in species conservation (Hooker
et al., 2011; Péron et al., 2013). Given that many migra-
tory species have limited protection at sea, even small
reductions in mortality rates can have decisive demographic benefits, especially for rare and endangered species (Caswell et al., 1999; Péron et al., 2013).

The identified hotspot is currently being discussed by the OSPAR Commission as the North Atlantic Current and Evlanov Seamount (NACES) MPA. Protection of this proposed MPA would address an identified gap in the OSPAR MPA network for seabirds (Johnson et al., 2014), and improve the coverage of nonbreeding areas more broadly (Game et al., 2009; Ramirez et al., 2017). Present threats to seabirds in the area are not fully understood: shipping lanes are predominantly in the southern part of the area (risk of disturbance, oil, and light pollution), some, limited long-line fishing occurs (bycatch risk), and recent oil exploration west of the hotspot (oil pollution and light pollution) (Impact Assessment Agency of Canada, 2020). Understanding the threats in the area, alongside the relevant contribution of other threats—both at breeding sites and across the rest of their migratory journeys—that are driving population declines should be evaluated. Understanding the relative contributions of different threats, both terrestrial and marine, that are driving population trends could help direct conservation priorities. However, it is also important to consider protection of remote areas before they become heavily exploited (McCauley et al., 2013) and to mitigate against future threats, particularly because impacts are increasing across the high seas (Halpern et al., 2019; O’Leary et al., 2020). MPAs are not a panacea for conserving marine biodiversity, and their capacity to reduce threats differs depending on their management and level of enforcement (Zupan et al., 2018). However, MPAs can contribute to biodiversity conservation where effectively managed, and the proposed NACES MPA should include measures to mitigate current and prevent future threats to seabirds. A research and monitoring plan should be adopted alongside the managed MPA, to understand more about the features supporting seabirds and other taxa, to monitor the effectiveness of the MPA, and to inform additional management measures if required. There are also increasing opportunities for monitoring remote areas using satellite and biologging technologies that could be explored (Harcourt et al., 2019; Sutherland et al., 2016). The current ABNJ MPAs under OSPAR are managed through a “Collective Arrangement” (NEAFC & OSPAR, 2015), and a collaborative approach to management would also be needed for this proposed MPA.

Overall, our analysis has demonstrated that multispecies tracking data can identify important sites in ABNJ that are suitable for protection. The ongoing work of the OSPAR Commission presents a unique opportunity for this study to inform policy and practice to benefit seabird conservation on the high seas. Once the new UN Treaty for the high seas has been adopted, replicating this approach for differ-

ent regions and taxa could provide a data-driven pathway for marine conservation in ABNJ.

## ACKNOWLEDGMENTS

This work was supported by the Global Ocean Biodiversity Initiative (GOBI) with a grant from the International Climate Initiative (IKI). The German Federal Ministry for the Environment, Nature Conservation, and Nuclear Safety (BMU) supports GOBI on the basis of a decision adopted by the German Bundestag.

The authors thank David Boyle, Vegard Brathen, Kendrew Colhoun, Jan Esefeld, Arnþór Garðarsson, H. Grant Gilchrist, Matthias Kopp, Yuri Krasnov, Mandy Shailer, Deryk Shaw, and the SEATRACK project who facilitated access to part of the data used in this study. Funding sources for the data used in this study are listed in Supporting Information—Additional Acknowledgments.

## AUTHORS’ CONTRIBUTIONS

Study conception: B.L., M.T., M.P. D., J.H., and B.C.; Methods workshop: M.T., A.P.B.C., M.P.D., B.C., C.H., J.H., H.A., J.D., E.D., M.F., J.P.G., T.G., E.S.H., B.M., V.H.P., Th.L.Th., and E.W.; Data collection/processing: T.A-N., R.T.B., M.B., L.B., T.B., P.C., F.R.C., O.C., S.C-D., M.C-F., J.D., F.D., M.P.D., C.E., A.I.F., A.L.F., J.F., M.F., R.W.F., O.G., J.G-S., J.P.G., D.G., T.G., E.S.H., S.A.H., M.P.H., A.H., N.P.H., M.J., Y.K., J.K., J.L., J.F.L., S-H.L., J.M., E.M., M.L.M., L.Mc.T., F.R.M., T.M., B.M., W.A.M., V.M-P., A.M., V.N., M.A.N., B.O., V.H.P., H-U.P., A.P., R.A.P., I.R., J.A.R., R.R., R.A.R., P.G.R., N.M.S., I.A.S., B.S., H.Ste., I.J.S., H.Str., G.H.R.S., P.T., Th.L.Th., R.S.A.Vb., S.W., and F.Z.; Data analysis; A.P.B.C. led the analysis, with support from M.P.D., T.E.D., M.T., and E.W.; Writing: T.E.D. led the writing of the manuscript with significant contributions from all coauthors. All authors reviewed and approved the final version for submission.

## ETHICS STATEMENT

The authors adhered to all relevant laws, regulations, and protocols in conducting this research.

## DATA ACCESSIBILITY STATEMENT

The data are deposited on BirdLife International’s Seabird Tracking Database http://www.seabirdtracking.org/

## CONFLICT OF INTEREST

The authors declare no conflict of interest.

## ORCID

Tammy E. Davies ID https://orcid.org/0000-0003-2535-1328

Marta Cruz-Flores ID https://orcid.org/0000-0001-9905-4727
Nicholas Per Huffeldt https://orcid.org/0000-0002-0154-2536

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## SUPPORTING INFORMATION

Additional supporting information may be found online in the Supporting Information section at the end of the article.

**How to cite this article:** Tammy E. Davies, Ana P.B. Carneiro, Marguerite Tarzia, et al. Multispecies tracking reveals a major seabird hotspot in the North Atlantic. *Conservation Letters*. 2021;14:e12824.
https://doi.org/10.1111/conl.12824