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Adult and juvenile European seabirds at risk from marine plundering off West Africa
Biological Conservation 182 (2015) 143–147
Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Short communication
Adult and juvenile European seabirds at risk from marine plundering off West Africa David Gremillet a,b,⇑, Clara Peron a,c, Pascal Provost d, Amelie Lescroel a a
CEFE-CNRS, UMR5175, 1919 route de Mende, 34293 Montpellier, France Percy FitzPatrick Institute and DST/NRF Centre of Excellence, UCT, Rondebosch 7701, South Africa c Institute for Marine and Antarctic Studies, University of Tasmania and Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050, Australia d Réserve Naturelle Nationale des Sept-Iles, Station LPO de l’Ile Grande, 22560 Pleumeur-Bodou, France b
a r t i c l e
i n f o
Article history: Received 31 July 2014 Received in revised form 28 November 2014 Accepted 1 December 2014
Keywords: Biotelemetry Connectivity Developing countries Incidental mortality IUU fisheries Migration corridor
a b s t r a c t Foreign fisheries massively harvest waters off West Africa, plundering local marine economies and threatening African food security. Here we warn that these fisheries might affect both juvenile and adult European seabirds during their autumn migration and at their wintering grounds. Using miniaturised GPS, satellite transmitters and geolocators, we tracked the migratory movements of 64 adult and juvenile Northern gannets (Morus bassanus) and Scopoli’s shearwaters (Calonectris diomedea) after their breeding season in the eastern Atlantic and the Mediterranean Sea, respectively. It was the first time ever that the movements of gannet fledglings were tracked with GPS accuracy. During winter (October to March) birds made extensive use of marine areas within the exclusive economic zones of Morocco, Western Sahara, Mauritania and Senegal. These juvenile and adult European seabirds are therefore dependent upon African marine resources and at risk from competition with fisheries, as well as intentional and incidental mortality by fishing gear. Those threats occur additionally to detrimental seabird–fishery interactions in Europe. There is an urgent need for improved marine conservation off West Africa, and our data demonstrating connectivity between specific European breeding colonies and African wintering areas are a major step towards stakeholder involvement. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Marine areas off West Africa currently experience the highest level of illegal, unreported and unregulated (IUU) fisheries in the world, which confiscate 40% of the total regional catch worth tens of millions US$ per year (Agnew et al., 2009). African coastal states often do not have the necessary legislation to protect their marine resources (Agnew et al., 2009) and the fish stocks of Morocco, Western Sahara, Mauritania and Senegal are thereby being plundered, jeopardizing West African economies and food security (Kaczynski and Fluharty, 2002; Alder and Sumaila, 2004; Agnew et al., 2009; Ramos and Grémillet, 2013; Pauly et al., 2014). Chinese fisheries have recently been accused (Pauly et al., 2014), but 238 European fishing vessels also fished legally off Western Sahara between 2007 and 2011 on the basis of an agreement between the EU and Morocco that ignores the sovereignty of Western Sahara (http://www.fishelsewhere.eu/). Such short-sighted ⇑ Corresponding author at: CEFE-CNRS, UMR5175, 1919 route de Mende, 34293 Montpellier, France. Tel.: +33 467613210. E-mail address: [email protected] (D. Gremillet). http://dx.doi.org/10.1016/j.biocon.2014.12.001 0006-3207/Ó 2014 Elsevier Ltd. All rights reserved.
‘gold-rush’ harvesting threatens regional fish stocks and food webs (Worm and Branch, 2012). Abundant marine resources off West Africa also attract marine predators (Zeeberg et al., 2006), and the area is a wintering ground for numerous seabird species and a migratory corridor for others moving further into the South Atlantic (Wynn and Knefelkamp, 2004; Camphuysen and van der Meer, 2005; González-Solís et al., 2007). West Africa is well known as a wintering area for European seabirds through direct sightings and ring recoveries (e.g. Wanless, 2002). However, it is only recently that tracking technologies have allowed following the exact movements of individual seabirds between European breeding grounds and West Africa (GonzálezSolís et al., 2007; Fort et al., 2012). Studies so far mainly focused on adult birds, which were the easiest to fit with electronic devices. However, new technologies now allow tracking juvenile birds on their very first migration (Weimerskirch et al., 2006). These advances are essential since they allow a more complete picture of population-level spatial ecology. We tracked adult and juvenile Northern gannets Morus basssanus from a colony in the English Channel and Scopoli’s shearwaters Calonectris diomedea from the Mediterranean during their
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migration from Europe to West Africa. We use this information to test the hypothesis that both juvenile and adult seabirds from specific European breeding sites move to West Africa in the autumn, where they are at threat from marine plundering.
2. Methods 2.1. Data collection Field protocols for both species and study sites were validated with respect to ethics in animal experimentation by the French Direction des Services Vétérinaires (Permit N° 34-369). Three types of electronic tags were used, which all weighed less than 4% of birds’ body masses, and complied with standards ensuring minimal device-related effects (Phillips et al., 2003). Impact studies on gannets and shearwaters during the breeding season found no measurable impact of tagging on bird performances (Grémillet et al., 2006; Authier et al., 2013). Northern gannets were equipped at their only breeding site in France (Sept-Iles Archipelago, Brittany). In June 2010, 37 adults were fitted with geolocators recording light levels (3.6 g; LAT2500, Lotek Inc, Canada) attached to leg rings. Birds were recaught in June 2011, and tags downloaded. In early August 2012, Solar GPS-PTTs (30 g, 1% of bird body mass; NorthStar Inc, USA, programmed with a duty cycle of 8 h ON/ 48 h OFF) were attached to the tails of five soon-to-fledge juvenile gannets using tape, cable ties and superglue. Similarly, Scopoli’s shearwaters, which are endemic to the Mediterranean (Sangster et al., 2012), were tracked from Riou and Frioul Islands off Marseille and Lavezzi Island in Corsica. Forty-three adults were fitted with geolocators (same as above) on Riou Island in July–August 2011. Another set of eleven adults and ten juveniles (fledglings of the year) were also tracked by solar Argos-PTT (9.5 g or 18 g, 63% bird body mass, Microwave Telemetry, USA, programmed with a duty cycle of 10 h ON/48 h OFF for 9.5 g-PTT and 12 h ON/ 24 h OFF for 18 g-PTT), which were taped to the back feathers of the birds in August or October 2011 (4 adults were equipped on Lavezzi Island, the remaining on Marseille Islands). Shearwater data have been partly published in Péron and Grémillet (2013), with no reference to the conservation context. 2.2. Data analysis Geolocators recorded light levels which were used to estimate geographic locations using an onboard algorithm, following Wilson et al. (1992). Estimated positions were then filtered to eliminate outliers using a speed criterion as in Freitas et al. (2008). Filtered positions were mapped using kernel density distributions (Wood et al., 2000; smoothing factor: 1 decimal degree), using the ‘adehabitatHR’ package developed by Calenge (2006) in R Core Team (2013). GPS-PTT data had high (<100 m) accuracy and were therefore mapped as such. PTT tracks were discontinuous due to the on/off duty cycles of the tags, and tracks were therefore reconstructed using state-space modelling allowing hourly estimates of bird positions (Jonsen et al., 2007).
3. Results Migratory movement data were collected for a total of 64 adult and juvenile Northern gannets and Scopoli’s shearwaters: Twentyfour adult Northern gannets carrying geolocators were recaught (from the 37 equipped), and estimated daily positions were gathered from 21 geolocators (3 loggers malfunctioned) across the entire inter-breeding period, from September 2010 to February 2011. Among tracked adult gannets, 62% remained in European
waters in winter, 14% entered the Mediterranean, and 24% went to off West Africa. Four out of five GPS/PTT tags deployed on juvenile gannets functioned between August and November 2012, during the migratory phase of the birds. All tracked juvenile gannets went to West Africa. It was the first time ever that the movements of gannet fledglings were tracked, and their migration paths were followed with GPS accuracy. Thirty-four adult Scopoli’s shearwaters carrying geolocators were recaught (from the 43 equipped). The 27 tags which could be downloaded provided information about entire inter-breeding movements, between October 2011 and April 2012. All birds went/travelled through West Africa during this period, and 56% of individuals remained there all winter (of the remaining birds, 22% wintered in the Northern Benguela (Angola, Namibia), 15% in the Gulf of Guinea, and 7% in the middle Atlantic). All 21 PTTs deployed on juvenile and adult Scopoli’s shearwaters functioned during the initial migratory phase (transmission lasted from one week to three months, from October to January), and 13 tagged birds were tracked from Europe to Africa during this period (6 juveniles and 7 adults). All recorded spatial data concur to designate striking coastal habits of adult and juvenile birds during the initial migration phase (September to November) along the narrow continental shelf of West Africa (depth < 200 m), and extensive winter (October to March) use of waters within the Exclusive Economic Zones (EEZ) of Morocco, Western Sahara, Mauritania and Senegal (Fig. 1). GPS and PTT data are displayed as dots along the tracks, and geolocation data as contours of kernel density distributions. Finer scale GPS movements of gannets showed highly coastal zig–zag movements typical of foraging between Agadir and Essaouira in Morocco (Fig. 2A) and Cap Blanc and Banc d’Arguin in Western Sahara and Mauritania. Scopoli’s shearwaters movements were also very coastal but located further South in Senegal, with winter foraging grounds located off Saint-Louis in Senegal, and more generally between Dakar and banc d’Arguin (Fig. 2B). 4. Discussion Results from this biotelemetry study validate our hypothesis: Juvenile and adult Northern gannets and Scopoli’s Shearwaters made extensive use of marine waters off West Africa during their autumn migration and wintering phase (Fig. 1). These findings have important conservation implications and point to the need for further investigations of fisheries impacts on the marine megafauna in this part of the world. Specifically, these impacts might take the form of competition for fish resources and/or of increased seabird incidental mortality. 4.1. Seabirds connect European and African marine ecosystems West-African marine resources attract marine predators, including a suite of migratory seabirds (Wynn and Knefelkamp, 2004; Camphuysen and van der Meer, 2005). Previous at-sea observations which highlighted seabird abundance and richness off West Africa were nonetheless conducted on birds of unknown geographic origin. For example, a gannet seen in winter off Mauritania could have come from a breeding colony in Finmark, Brittany, or even Newfoundland (Fort et al., 2012; Fifield et al., 2014). In great contrast, we tracked of birds from specific European breeding colonies to show that West Africa is a key wintering area for two seabird species fully protected by European directives within their breeding habitats in the Eastern Atlantic and the Mediterranean Sea, respectively. Biotelemetry also allowed us to define the exact periods during which those areas are important for wintering European seabirds. Further, recent studies also stressed the
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Fig. 1. Autumn migratory movements and wintering sites of (A) juvenile (n = 4) and adult (n = 21) Northern gannets from a breeding colony in Brittany (black star: Rouzic Island) and (B) juvenile (n = 6) and adult (n = 7 for Argos-PTT data, n = 27 for GLS data) Scopoli’s shearwaters from two Mediterranean colonies (white star: Marseille Islands, grey star: Lavezzi Island) along the Atlantic coast of West Africa. Note the coastal distribution of birds off West Africa, which strongly overlaps with the Exclusive Economic Zones (EEZ) of West-African countries (light blue areas).
importance of West Africa as a wintering area for adult Northern gannets across their meta-population (Fort et al., 2012). Equally, Scopoli’s shearwaters from at least 7 different populations in the Mediterranean Sea winter off West Africa (González-Solís et al., 2007; Péron and Grémillet, 2013). Moreover, tracking of Cory’s shearwaters (Calonectris borealis, closely related to Scopoli’s shearwaters) from Madeira, Salvages and the Canary Islands demonstrated the importance of West African waters as feeding grounds for this species during the breeding season (Ramos et al., 2013). All of these studies focused on adult birds, and our results fill an important gap in knowledge by detailing the movements of juveniles. Both gannets and shearwaters are affected by environmental conditions at their European breeding sites and in their African migratory areas, and conditions prevailing in these two regions should be confronted. While migratory seabirds now experience recently degraded marine habitats off West Africa, they have long been exposed to the consequences of ‘historical overfishing’ in European waters (Barrett et al., 2004). Specifically, gannets from Brittany forage in the Western English Channel during the breeding season, where they compete with fisheries for fully-exploited pelagic fish (Grémillet et al., 2006). Similarly, Scopoli’s shearwaters from French Mediterranean islands mainly forage in the Gulf of Lion where their food resource is declining rapidly (GFCM, 2011). Both populations are therefore probably exposed to chronicle nutritional stress during the breeding season. Direct mortality from fishery bycatch might occur for gannets feeding in the English Channel, and is well-documented for Scopoli’s shearwaters in the Mediterranean (Laneri et al., 2010; Báez et al., 2014). Environmental constraints affecting seabird survival probabilities should therefore be considered across the year cycle, and uncontrolled harvest
off West Africa is an additional threat to already considerably stressed seabird populations. 4.2. Juvenile and adult seabirds at threat from overfishing and incidental mortality off West Africa Small pelagic fish, especially sardinella (Sardinella sp.), are the main food resource for seabirds such as gannets and shearwaters wintering off West Africa, and are presumably their primary motivation for going there. The FAO (2012) warns that ‘the intensive operations of foreign-based vessels have undoubtedly had some impact on sardinella stocks’. Fisheries is therefore likely to compete with seabirds for diminishing sardinella stocks off West Africa. This situation mirrors seabird–fishery issues identified in the Benguela upwelling off South Africa, where purse-seine fisheries have resulted in severe food shortages for the closely related Cape gannets (Morus capensis; Okes et al., 2009). Secondly, trawlers, which are officially present in FAO statistics, or participating in IUU fisheries (Agnew et al., 2009; Pauly et al., 2014), are taking pelagic fish such as sardinella and mackerel, but also a range of bottom-dwelling fish. Processing of the latter produces fishery waste, which when thrown overboard serves as supplementary seabird food for gannets, to a lesser extent for shearwaters. Such wastes typically have lower calorific value than natural prey, and it is questionable whether they may serve as a valuable substitute in the longer term (Grémillet et al., 2008). At the international level, there is a world-wide trend towards banning the at-sea disposal of fishery waste (Condie et al., 2014). Fisheries kill seabirds by collision with towing lines or drowning on the baited hooks of longlines. Improved fishing techniques monitored by observers present onboard fishing vessels has
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Fig. 2. Detail of migratory movements and wintering sites of (A) juvenile and adult Northern gannets, (B) juvenile and adult Scopoli’s shearwaters off West Africa.
reduced this incidental mortality in well-managed fisheries (Cox et al., 2007), especially in the Southern Ocean (Waugh et al., 2008). Specifically, these adjustments aim at avoiding areas and time periods at/during which seabirds are particularly vulnerable, and at reducing their access to baited fishing lines and/or actively deterring them from fishing vessels. However, these measures are not implemented by uncontrolled fisheries such as those operating off West Africa (Anderson et al., 2011). The impact of juvenile mortality on overall population size is less severe than that of reproductive adults, yet in both species, ‘naive’ younger birds have been reported as more vulnerable to bycatch (Belda and Sanchez, 2001; Watkins et al., 2008). 4.3. A conservation hotspot off West Africa It is currently extremely difficult to assess the impact of IUU fisheries off West Africa. Numerous governmental and nongovernmental organisations are working on the issue, but data are particularly scarce. Our study is important in this context, since it demonstrates connectivity between specific European seabird breeding populations and their African migratory area threatened by IUU fisheries, thereby allowing improved stakeholder involvement. European seabirds are threatened by fisheries off Africa, so there is a need for the EU to finally address this issue. Further, our study is the first to follow the migratory movement and migratory chronology of both adults and juveniles, the latter being particularly vulnerable to food shortage and bycatch. This is not a direct proof that gannets and shearwaters are being starved or killed by fisheries, yet such fisheries impacts are real: at least 8 containers of frozen seabirds (including gannets) caught off West Africa were confiscated by Mauritanian authorities in early 2013.
These seabirds – the exact number has not been revealed but potentially tens of thousands, were boxed and labelled as fish and were being shipped to Asia for human consumption (Kees Camphuysen, pers. com.). It is urgent to clarify the legal status of international fisheries operating off West Africa, and to control their harvesting practices of targeted and non-targeted marine organisms that range from bony fish, sharks, rays and cephalopods, to seabirds, marine mammals and turtles, in order to minimize their regional and global ecological impact (Zeeberg et al., 2006; Palumbi et al., 2009). With respect to seabirds, marine important bird areas (http://maps.birdlife.org/marineIBAs/default.html), as well as irreplaceable areas (Le Saout et al. 2013; Grémillet et al., 2014) could provide a scientific basis to the definition of forthcoming marine protected areas ensuring improved conservation of these species and of marine ecosystems to which they participate. Acknowledgements This study was funded by the French Agency for Marine Protected Areas (AAMP) within the ‘‘Programme PACOMM, Natura2000 en mer’’, and by the European Union within the INTERREG program FAME (Future of the Atlantic Marine Environment). We are grateful to all fieldworkers and personnel of the Conservatoire d’Espaces Naturels de Provence-Alpes-Côte-D’Azur, the Réserve Naturelle Nationale de l’archipel de Riou, the Parc Maritime des îles du Frioul, the Réserve Naturelle des Bouches de Bonifacio and the Réserve Naturelle Nationale des Sept-Iles for their dedicated help, and to Mike P. Harris for checking our English. We thank Ursula Ellenberg and two anonymous referees for their very useful suggestions.
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Contents lists available at ScienceDirect
Biological Conservation journal homepage: www.elsevier.com/locate/biocon
Short communication
Adult and juvenile European seabirds at risk from marine plundering off West Africa David Gremillet a,b,⇑, Clara Peron a,c, Pascal Provost d, Amelie Lescroel a a
CEFE-CNRS, UMR5175, 1919 route de Mende, 34293 Montpellier, France Percy FitzPatrick Institute and DST/NRF Centre of Excellence, UCT, Rondebosch 7701, South Africa c Institute for Marine and Antarctic Studies, University of Tasmania and Australian Antarctic Division, 203 Channel Highway, Kingston, Tasmania 7050, Australia d Réserve Naturelle Nationale des Sept-Iles, Station LPO de l’Ile Grande, 22560 Pleumeur-Bodou, France b
a r t i c l e
i n f o
Article history: Received 31 July 2014 Received in revised form 28 November 2014 Accepted 1 December 2014
Keywords: Biotelemetry Connectivity Developing countries Incidental mortality IUU fisheries Migration corridor
a b s t r a c t Foreign fisheries massively harvest waters off West Africa, plundering local marine economies and threatening African food security. Here we warn that these fisheries might affect both juvenile and adult European seabirds during their autumn migration and at their wintering grounds. Using miniaturised GPS, satellite transmitters and geolocators, we tracked the migratory movements of 64 adult and juvenile Northern gannets (Morus bassanus) and Scopoli’s shearwaters (Calonectris diomedea) after their breeding season in the eastern Atlantic and the Mediterranean Sea, respectively. It was the first time ever that the movements of gannet fledglings were tracked with GPS accuracy. During winter (October to March) birds made extensive use of marine areas within the exclusive economic zones of Morocco, Western Sahara, Mauritania and Senegal. These juvenile and adult European seabirds are therefore dependent upon African marine resources and at risk from competition with fisheries, as well as intentional and incidental mortality by fishing gear. Those threats occur additionally to detrimental seabird–fishery interactions in Europe. There is an urgent need for improved marine conservation off West Africa, and our data demonstrating connectivity between specific European breeding colonies and African wintering areas are a major step towards stakeholder involvement. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Marine areas off West Africa currently experience the highest level of illegal, unreported and unregulated (IUU) fisheries in the world, which confiscate 40% of the total regional catch worth tens of millions US$ per year (Agnew et al., 2009). African coastal states often do not have the necessary legislation to protect their marine resources (Agnew et al., 2009) and the fish stocks of Morocco, Western Sahara, Mauritania and Senegal are thereby being plundered, jeopardizing West African economies and food security (Kaczynski and Fluharty, 2002; Alder and Sumaila, 2004; Agnew et al., 2009; Ramos and Grémillet, 2013; Pauly et al., 2014). Chinese fisheries have recently been accused (Pauly et al., 2014), but 238 European fishing vessels also fished legally off Western Sahara between 2007 and 2011 on the basis of an agreement between the EU and Morocco that ignores the sovereignty of Western Sahara (http://www.fishelsewhere.eu/). Such short-sighted ⇑ Corresponding author at: CEFE-CNRS, UMR5175, 1919 route de Mende, 34293 Montpellier, France. Tel.: +33 467613210. E-mail address: [email protected] (D. Gremillet). http://dx.doi.org/10.1016/j.biocon.2014.12.001 0006-3207/Ó 2014 Elsevier Ltd. All rights reserved.
‘gold-rush’ harvesting threatens regional fish stocks and food webs (Worm and Branch, 2012). Abundant marine resources off West Africa also attract marine predators (Zeeberg et al., 2006), and the area is a wintering ground for numerous seabird species and a migratory corridor for others moving further into the South Atlantic (Wynn and Knefelkamp, 2004; Camphuysen and van der Meer, 2005; González-Solís et al., 2007). West Africa is well known as a wintering area for European seabirds through direct sightings and ring recoveries (e.g. Wanless, 2002). However, it is only recently that tracking technologies have allowed following the exact movements of individual seabirds between European breeding grounds and West Africa (GonzálezSolís et al., 2007; Fort et al., 2012). Studies so far mainly focused on adult birds, which were the easiest to fit with electronic devices. However, new technologies now allow tracking juvenile birds on their very first migration (Weimerskirch et al., 2006). These advances are essential since they allow a more complete picture of population-level spatial ecology. We tracked adult and juvenile Northern gannets Morus basssanus from a colony in the English Channel and Scopoli’s shearwaters Calonectris diomedea from the Mediterranean during their
144
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migration from Europe to West Africa. We use this information to test the hypothesis that both juvenile and adult seabirds from specific European breeding sites move to West Africa in the autumn, where they are at threat from marine plundering.
2. Methods 2.1. Data collection Field protocols for both species and study sites were validated with respect to ethics in animal experimentation by the French Direction des Services Vétérinaires (Permit N° 34-369). Three types of electronic tags were used, which all weighed less than 4% of birds’ body masses, and complied with standards ensuring minimal device-related effects (Phillips et al., 2003). Impact studies on gannets and shearwaters during the breeding season found no measurable impact of tagging on bird performances (Grémillet et al., 2006; Authier et al., 2013). Northern gannets were equipped at their only breeding site in France (Sept-Iles Archipelago, Brittany). In June 2010, 37 adults were fitted with geolocators recording light levels (3.6 g; LAT2500, Lotek Inc, Canada) attached to leg rings. Birds were recaught in June 2011, and tags downloaded. In early August 2012, Solar GPS-PTTs (30 g, 1% of bird body mass; NorthStar Inc, USA, programmed with a duty cycle of 8 h ON/ 48 h OFF) were attached to the tails of five soon-to-fledge juvenile gannets using tape, cable ties and superglue. Similarly, Scopoli’s shearwaters, which are endemic to the Mediterranean (Sangster et al., 2012), were tracked from Riou and Frioul Islands off Marseille and Lavezzi Island in Corsica. Forty-three adults were fitted with geolocators (same as above) on Riou Island in July–August 2011. Another set of eleven adults and ten juveniles (fledglings of the year) were also tracked by solar Argos-PTT (9.5 g or 18 g, 63% bird body mass, Microwave Telemetry, USA, programmed with a duty cycle of 10 h ON/48 h OFF for 9.5 g-PTT and 12 h ON/ 24 h OFF for 18 g-PTT), which were taped to the back feathers of the birds in August or October 2011 (4 adults were equipped on Lavezzi Island, the remaining on Marseille Islands). Shearwater data have been partly published in Péron and Grémillet (2013), with no reference to the conservation context. 2.2. Data analysis Geolocators recorded light levels which were used to estimate geographic locations using an onboard algorithm, following Wilson et al. (1992). Estimated positions were then filtered to eliminate outliers using a speed criterion as in Freitas et al. (2008). Filtered positions were mapped using kernel density distributions (Wood et al., 2000; smoothing factor: 1 decimal degree), using the ‘adehabitatHR’ package developed by Calenge (2006) in R Core Team (2013). GPS-PTT data had high (<100 m) accuracy and were therefore mapped as such. PTT tracks were discontinuous due to the on/off duty cycles of the tags, and tracks were therefore reconstructed using state-space modelling allowing hourly estimates of bird positions (Jonsen et al., 2007).
3. Results Migratory movement data were collected for a total of 64 adult and juvenile Northern gannets and Scopoli’s shearwaters: Twentyfour adult Northern gannets carrying geolocators were recaught (from the 37 equipped), and estimated daily positions were gathered from 21 geolocators (3 loggers malfunctioned) across the entire inter-breeding period, from September 2010 to February 2011. Among tracked adult gannets, 62% remained in European
waters in winter, 14% entered the Mediterranean, and 24% went to off West Africa. Four out of five GPS/PTT tags deployed on juvenile gannets functioned between August and November 2012, during the migratory phase of the birds. All tracked juvenile gannets went to West Africa. It was the first time ever that the movements of gannet fledglings were tracked, and their migration paths were followed with GPS accuracy. Thirty-four adult Scopoli’s shearwaters carrying geolocators were recaught (from the 43 equipped). The 27 tags which could be downloaded provided information about entire inter-breeding movements, between October 2011 and April 2012. All birds went/travelled through West Africa during this period, and 56% of individuals remained there all winter (of the remaining birds, 22% wintered in the Northern Benguela (Angola, Namibia), 15% in the Gulf of Guinea, and 7% in the middle Atlantic). All 21 PTTs deployed on juvenile and adult Scopoli’s shearwaters functioned during the initial migratory phase (transmission lasted from one week to three months, from October to January), and 13 tagged birds were tracked from Europe to Africa during this period (6 juveniles and 7 adults). All recorded spatial data concur to designate striking coastal habits of adult and juvenile birds during the initial migration phase (September to November) along the narrow continental shelf of West Africa (depth < 200 m), and extensive winter (October to March) use of waters within the Exclusive Economic Zones (EEZ) of Morocco, Western Sahara, Mauritania and Senegal (Fig. 1). GPS and PTT data are displayed as dots along the tracks, and geolocation data as contours of kernel density distributions. Finer scale GPS movements of gannets showed highly coastal zig–zag movements typical of foraging between Agadir and Essaouira in Morocco (Fig. 2A) and Cap Blanc and Banc d’Arguin in Western Sahara and Mauritania. Scopoli’s shearwaters movements were also very coastal but located further South in Senegal, with winter foraging grounds located off Saint-Louis in Senegal, and more generally between Dakar and banc d’Arguin (Fig. 2B). 4. Discussion Results from this biotelemetry study validate our hypothesis: Juvenile and adult Northern gannets and Scopoli’s Shearwaters made extensive use of marine waters off West Africa during their autumn migration and wintering phase (Fig. 1). These findings have important conservation implications and point to the need for further investigations of fisheries impacts on the marine megafauna in this part of the world. Specifically, these impacts might take the form of competition for fish resources and/or of increased seabird incidental mortality. 4.1. Seabirds connect European and African marine ecosystems West-African marine resources attract marine predators, including a suite of migratory seabirds (Wynn and Knefelkamp, 2004; Camphuysen and van der Meer, 2005). Previous at-sea observations which highlighted seabird abundance and richness off West Africa were nonetheless conducted on birds of unknown geographic origin. For example, a gannet seen in winter off Mauritania could have come from a breeding colony in Finmark, Brittany, or even Newfoundland (Fort et al., 2012; Fifield et al., 2014). In great contrast, we tracked of birds from specific European breeding colonies to show that West Africa is a key wintering area for two seabird species fully protected by European directives within their breeding habitats in the Eastern Atlantic and the Mediterranean Sea, respectively. Biotelemetry also allowed us to define the exact periods during which those areas are important for wintering European seabirds. Further, recent studies also stressed the
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Fig. 1. Autumn migratory movements and wintering sites of (A) juvenile (n = 4) and adult (n = 21) Northern gannets from a breeding colony in Brittany (black star: Rouzic Island) and (B) juvenile (n = 6) and adult (n = 7 for Argos-PTT data, n = 27 for GLS data) Scopoli’s shearwaters from two Mediterranean colonies (white star: Marseille Islands, grey star: Lavezzi Island) along the Atlantic coast of West Africa. Note the coastal distribution of birds off West Africa, which strongly overlaps with the Exclusive Economic Zones (EEZ) of West-African countries (light blue areas).
importance of West Africa as a wintering area for adult Northern gannets across their meta-population (Fort et al., 2012). Equally, Scopoli’s shearwaters from at least 7 different populations in the Mediterranean Sea winter off West Africa (González-Solís et al., 2007; Péron and Grémillet, 2013). Moreover, tracking of Cory’s shearwaters (Calonectris borealis, closely related to Scopoli’s shearwaters) from Madeira, Salvages and the Canary Islands demonstrated the importance of West African waters as feeding grounds for this species during the breeding season (Ramos et al., 2013). All of these studies focused on adult birds, and our results fill an important gap in knowledge by detailing the movements of juveniles. Both gannets and shearwaters are affected by environmental conditions at their European breeding sites and in their African migratory areas, and conditions prevailing in these two regions should be confronted. While migratory seabirds now experience recently degraded marine habitats off West Africa, they have long been exposed to the consequences of ‘historical overfishing’ in European waters (Barrett et al., 2004). Specifically, gannets from Brittany forage in the Western English Channel during the breeding season, where they compete with fisheries for fully-exploited pelagic fish (Grémillet et al., 2006). Similarly, Scopoli’s shearwaters from French Mediterranean islands mainly forage in the Gulf of Lion where their food resource is declining rapidly (GFCM, 2011). Both populations are therefore probably exposed to chronicle nutritional stress during the breeding season. Direct mortality from fishery bycatch might occur for gannets feeding in the English Channel, and is well-documented for Scopoli’s shearwaters in the Mediterranean (Laneri et al., 2010; Báez et al., 2014). Environmental constraints affecting seabird survival probabilities should therefore be considered across the year cycle, and uncontrolled harvest
off West Africa is an additional threat to already considerably stressed seabird populations. 4.2. Juvenile and adult seabirds at threat from overfishing and incidental mortality off West Africa Small pelagic fish, especially sardinella (Sardinella sp.), are the main food resource for seabirds such as gannets and shearwaters wintering off West Africa, and are presumably their primary motivation for going there. The FAO (2012) warns that ‘the intensive operations of foreign-based vessels have undoubtedly had some impact on sardinella stocks’. Fisheries is therefore likely to compete with seabirds for diminishing sardinella stocks off West Africa. This situation mirrors seabird–fishery issues identified in the Benguela upwelling off South Africa, where purse-seine fisheries have resulted in severe food shortages for the closely related Cape gannets (Morus capensis; Okes et al., 2009). Secondly, trawlers, which are officially present in FAO statistics, or participating in IUU fisheries (Agnew et al., 2009; Pauly et al., 2014), are taking pelagic fish such as sardinella and mackerel, but also a range of bottom-dwelling fish. Processing of the latter produces fishery waste, which when thrown overboard serves as supplementary seabird food for gannets, to a lesser extent for shearwaters. Such wastes typically have lower calorific value than natural prey, and it is questionable whether they may serve as a valuable substitute in the longer term (Grémillet et al., 2008). At the international level, there is a world-wide trend towards banning the at-sea disposal of fishery waste (Condie et al., 2014). Fisheries kill seabirds by collision with towing lines or drowning on the baited hooks of longlines. Improved fishing techniques monitored by observers present onboard fishing vessels has
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Fig. 2. Detail of migratory movements and wintering sites of (A) juvenile and adult Northern gannets, (B) juvenile and adult Scopoli’s shearwaters off West Africa.
reduced this incidental mortality in well-managed fisheries (Cox et al., 2007), especially in the Southern Ocean (Waugh et al., 2008). Specifically, these adjustments aim at avoiding areas and time periods at/during which seabirds are particularly vulnerable, and at reducing their access to baited fishing lines and/or actively deterring them from fishing vessels. However, these measures are not implemented by uncontrolled fisheries such as those operating off West Africa (Anderson et al., 2011). The impact of juvenile mortality on overall population size is less severe than that of reproductive adults, yet in both species, ‘naive’ younger birds have been reported as more vulnerable to bycatch (Belda and Sanchez, 2001; Watkins et al., 2008). 4.3. A conservation hotspot off West Africa It is currently extremely difficult to assess the impact of IUU fisheries off West Africa. Numerous governmental and nongovernmental organisations are working on the issue, but data are particularly scarce. Our study is important in this context, since it demonstrates connectivity between specific European seabird breeding populations and their African migratory area threatened by IUU fisheries, thereby allowing improved stakeholder involvement. European seabirds are threatened by fisheries off Africa, so there is a need for the EU to finally address this issue. Further, our study is the first to follow the migratory movement and migratory chronology of both adults and juveniles, the latter being particularly vulnerable to food shortage and bycatch. This is not a direct proof that gannets and shearwaters are being starved or killed by fisheries, yet such fisheries impacts are real: at least 8 containers of frozen seabirds (including gannets) caught off West Africa were confiscated by Mauritanian authorities in early 2013.
These seabirds – the exact number has not been revealed but potentially tens of thousands, were boxed and labelled as fish and were being shipped to Asia for human consumption (Kees Camphuysen, pers. com.). It is urgent to clarify the legal status of international fisheries operating off West Africa, and to control their harvesting practices of targeted and non-targeted marine organisms that range from bony fish, sharks, rays and cephalopods, to seabirds, marine mammals and turtles, in order to minimize their regional and global ecological impact (Zeeberg et al., 2006; Palumbi et al., 2009). With respect to seabirds, marine important bird areas (http://maps.birdlife.org/marineIBAs/default.html), as well as irreplaceable areas (Le Saout et al. 2013; Grémillet et al., 2014) could provide a scientific basis to the definition of forthcoming marine protected areas ensuring improved conservation of these species and of marine ecosystems to which they participate. Acknowledgements This study was funded by the French Agency for Marine Protected Areas (AAMP) within the ‘‘Programme PACOMM, Natura2000 en mer’’, and by the European Union within the INTERREG program FAME (Future of the Atlantic Marine Environment). We are grateful to all fieldworkers and personnel of the Conservatoire d’Espaces Naturels de Provence-Alpes-Côte-D’Azur, the Réserve Naturelle Nationale de l’archipel de Riou, the Parc Maritime des îles du Frioul, the Réserve Naturelle des Bouches de Bonifacio and the Réserve Naturelle Nationale des Sept-Iles for their dedicated help, and to Mike P. Harris for checking our English. We thank Ursula Ellenberg and two anonymous referees for their very useful suggestions.
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