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Keywords:

  • discards;
  • Falkland Islands;
  • GPS;
  • stable isotopes;
  • Thalassarche melanophris;
  • Vessel Monitoring System (VMS)

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Fisheries can have profound impacts on the structure and functioning of marine ecosystems and affect seabird populations. For seabirds, impacts can include direct mortality in fishing gear, but fisheries also represent an abundant source of food that may otherwise be inaccessible. Previous studies with seabirds have revealed the occurrence of individual foraging specializations, and therefore in scavenging species some individuals may have a higher propensity to feed on fisheries discharges than the rest of the population. Here we used recently developed techniques (spatio-temporal match of positions) to detect interactions between black-browed albatrosses Thalassarche melanophris and fishing vessels, and also stable isotope analysis of tissues with different turnovers, to investigate long-term individual specialization in fishery waste products. We combined global positioning system tracking data from 89 birds with vessel monitoring system data from the entire fleet operating around the Falklands Islands, in 2009 and 2011. Interactions with vessels (freezer/factory bottom trawlers) occurred in 15 out of 89 independent albatross trips. Among individuals tracked in both years, those that associated with fisheries in 2009 were not more likely to do so again in 2011. Carbon and nitrogen isotopic signatures in whole blood and feathers of albatrosses that interacted with trawlers were similar to those of individuals that did not. Also, we found no correlation between feather and blood isotopic ratios of carbon or nitrogen, indicating no long-term consistency in the isotopic niche of study birds. These results suggest no specialization of individual albatrosses with regard to fisheries. Studies of other albatrosses have also failed to show long-term trophic consistency, which may indicate that scavenging albatrosses, a group particularly threatened by fisheries activity, do not specialize in discards. Therefore, any management actions leading to a reduction of discards will be beneficial, decreasing the numbers of birds behind vessels and consequently the likelihood of incidental mortality.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Fisheries have major impacts on the structure and functioning of marine ecosystems (Lewison et al., 2004; Halpern et al., 2008; Smith et al., 2011). Seabirds are affected in multiple ways, as fisheries make large amounts of biomass available to birds through discards and offal refuse, but may also compete for fish resources, reshape food webs and cause incidental mortality of birds in fishing gear (Xavier et al., 2004; Sullivan, Reid & Bugoni, 2006, Karpouzi, Watson & Pauly, 2007, Rolland, Barbraud & Weimerskirch, 2008; Louzao et al., 2011). Fisheries are so prevalent in most world oceans that through the mechanisms mentioned earlier, they are believed to importantly impact and modify the dynamics of seabird populations and communities (Furness, 2003; Votier et al., 2004; Bugoni et al., 2008; Heithaus et al., 2008).

It is now established that individual predators often specialize in particular types of prey, which also implies that they differ in their time-space habitat use (Bolnick et al., 2003; Svanbäck & Persson, 2004). Seabirds are presumably no exception, with some examples already documented (Bearhop et al., 2006; Cherel et al., 2006, 2007; Woo et al., 2008). Knowing that seabirds that are facultative scavengers often fill a substantial part of their population energetic requirements by foraging associated with fishing vessels (Furness, Ensor & Hudson, 1992), and may even modify their search strategies as a function of the deployment of fishing fleets (Bartumeus et al., 2010), it is conceivable that specializations might have arisen whereby some individuals have a greater propensity to feed on fisheries discards and offal products. For example, individuals with a greater ability to compete (both intra- and interspecifically) in dense feeding aggregations as typically occur behind industrial trawlers (Furness et al., 1992) may be more inclined to search for vessels, while others may consistently prefer to forage in distinct contexts, irrespective of the marine region in which they are, or of other localized conditions.

A study of gannets Morus bassanus in the north-east Atlantic, for example, suggested that some birds consistently ingested more whitefish (presumed to originate from discards) than others (Votier et al., 2010). The temporal scale of this study, however, was short (weeks within a single nesting season), and more comprehensive analyses of this issue are lacking. In fact, short-term studies of foraging consistency (e.g. Ceia et al., 2012) may potentially lead to the conclusion that seabirds are specializing in fisheries products if (1) individuals show some consistency in foraging destinations (independent of the deployment of human fisheries) and (2) the availability of fisheries discards differs among areas, presenting particular individuals with more foraging opportunities in some marine sectors. Such findings do not mean, however, that individuals are actively seeking foraging opportunities with fishing vessels as a consistent strategy. Instead, a true specialization in fisheries products should be demonstrated across a range of spatial and temporal scales, if a ‘fisheries association syndrome’ was to be attributed to some seabirds.

Most albatross species currently hold an unfavorable conservation status, and fisheries-related mortality is considered to be the most important threatening factor (e.g. Croxall et al., 2012). This possibly applies to the black-browed albatross Thalassarche melanophris. The species is currently classified as ‘endangered’ and their main populations live and forage over the Patagonian Shelf (Huin, 2002).

Black-browed albatrosses attend fishing trawlers and long-liners in large numbers and experience considerable mortality around fishing vessels over the Patagonian Shelf (Sullivan et al., 2006; Favero et al., 2010; Jiménez et al., 2010). However, overall their reliance on fisheries as a major source of food may be relatively limited (Thompson, 1992; Thompson & Riddy, 1995; Granadeiro et al., 2011). The question therefore arises: are some individual black-browed albatrosses particularly relying on food supplied by the fishing industry, and therefore potentially more susceptible to incidental mortality, but also to changes in management of discards and offal that may reduce food supplies?

If individual albatrosses specialize in fisheries products, we would expect their isotopic niches to differ from those of birds feeding predominantly on ‘natural’ prey. For example, trawlers operating on the Patagonian Shelf mainly target Argentine hake Merluccius hubbsi, kingclip Genypterus blacodes, Patagonian rock cod Patagonotothen ramsayi and hoki Macruronus magellanicus, among other demersal predatory finfish (Copello & Quintana, 2009; González-Zevallos & Yorio, 2011; Granadeiro et al., 2011). Overall, the discards of these fisheries mostly involve undersized and nontarget demersal prey mostly rejected unprocessed and offal from processed target species. There is also a significant seasonal fishery targeting the Argentinian shortfin Illex argentinus and Patagonian squid Doryteuthis gahi, mostly involving jiggers and freezer-trawlers (Agnew, 2002; Barton, 2002), with comparatively much lower volume of discards.

The ‘natural’ diet of black-browed albatrosses on the Patagonian Shelf is dominated by taxa that feed at a lower trophic level than those discarded by fisheries (e.g. Weiss et al., 2009), including epipelagic species such as Fuegian spratt Sprattus fuegensis, lobster krill Munida spp., young age-classes of Ommastrephid squid (mostly Illex argentinus), and gelatinous prey such as jellyfish and salps (Thompson, 1992, Granadeiro, Brickle & Catry, unpubl. data). In this study, we use state-of-the-art tools developed to detect albatross–fisheries interactions based on global positioning system (GPS) tracking of birds and vessels (Granadeiro et al., 2011), as well as isotope analyses of different albatross tissues to infer the relative importance of individual associations of albatrosses with fisheries. We were particularly interested in finding evidence for consistency in associations with fisheries at different temporal and spatial scales.

We reasoned that if some individual albatrosses persistently associate with human fisheries: (1) the isotopic signatures of their tissues would differ from the general population (in particular specialists should have higher nitrogen isotopic ratios); (2) there would be a correlation between the isotopic signatures of different tissues (with differing turnovers rates or times of synthesis), reflecting diet at different time-windows/seasons; and (3) individuals albatrosses would show consistency in their propensity to attend fishing vessels during foraging trips tracked in different years.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Albatross GPS tracking and sampling

This study took place on Steeple Jason (51°01′S, 61°13′W), West Falklands Islands, in the austral breeding seasons of 2009/2010 and 2011/2012 (hereafter 2009 and 2011). Steeple Jason holds the largest colony of black-browed albatrosses in the world, with numbers approaching 200 000 breeding pairs (Baylis, 2012).

Adult breeding birds were tracked during early chick-rearing in December to January each year using GPS loggers (Earth & Ocean Technologies, Kiel, Germany), weighing between 25 and 30 g, attached to the back or the tail feathers with Tesa tape. Birds were also fitted with a British Antarctic Survey Mk7 or Mk19 logger (Cambridge, UK; < 3.5 g) attached to a leg band, to record the timings of all changes of immersion state (wet–dry, with 3-s resolution) allowing the reconstruction of detailed landing patterns. The attachment of GPS and logger lasted for about 5 min, and upon release all birds immediately returned to their nest and resumed brooding of the chick. These devices represent less than 1% of the weight of an albatross, and have no effects on foraging behavior or success (Phillips, Xavier & Croxall, 2003; Granadeiro et al., 2011).

GPS loggers recorded the position of study birds every 4–14 min. The entire fishing fleet operating inside Falkland Island waters is currently surveyed through a vessel monitoring system (VMS). We obtained the exact position of each vessel every 1 h for the entire study period. In 2011/2012, at the moment of the GPS deployment, a capillary tube of blood was obtained from each individual (from a small foot web blood vessel), and four mantle feathers were cut. Blood was frozen and latter dried at 45°C. Feathers were stored in individual plastic bags.

Laboratory analyses

Dried whole blood samples were ground into powder. The four feathers were thoroughly washed, finely cut and mixed into a uniform mixture. Subsamples of 1.0 ± 0.1 mg of homogenous whole blood or feathers were weighed into 8 × 5-mm tin capsules and combusted at 1000°C in a Euro EA Elemental Analyser (EuroVector, Milan, Italy). Resultant CO2 and N2 gases were analyzed using a continuous-flow isotope ratio mass spectrometer IsoPrime (MicroMass, Isoprime, Cheadle, UK), with unknowns separated by laboratory standards. Stable isotope abundances were expressed in δ-notation as the deviation from standards in parts per thousand (‰) according to the following equation:

  • display math

where X is 13C or 15N, and R is the corresponding ratio of 13C/12C or 15N/14N, expressed in per mil notation. Rstandard values were based on Vienna Peedee Belemnite for δ13C, and atmospheric nitrogen (N2) for δ15N. Replicate measurements of laboratory standards showed measurement errors of ± 0.1‰ and ± 0.2‰ for stable nitrogen and carbon isotope measurements, respectively. Quality control samples were run before and after each sequence.

Data analyses

We produced kernel density maps of annual fishing effort using hourly position of vessels steaming at low speed (< 6 knots), which are likely to reflect fishing activity (Mills et al., 2007; Witt & Godley, 2007). We then calculated the overlap between fishing effort in both seasons as the volume of intersection between their utilization distributions (UD; Fiedberg & Kochanny, 2005):

  • display math

Positions of fishing vessels and albatrosses were linearly interpolated to 3 s to match the temporal resolution of activity records, and all datasets were combined according to exact time. Animations depicting the activity (flying or landed on the sea surface) and relative positions of albatrosses and fishing vessels allowed the identification of interactions between birds and fisheries activities with a very high degree of confidence (Granadeiro et al., 2011). In brief, a bird was considered to have interacted with a vessel whenever it landed within 3.5 km of the ship (usually after flying from a distance), or when the estimated distance between bird and ship was < 0.5 km (see Granadeiro et al., 2011 for details and sample animation). Such distances were established based on estimates of locational error in-between successive GPS positions of birds (determined at 4- to 14-min intervals) and vessels (determined at 1-h interval). Simulation work showed that the mean error [± standard deviation (sd)] of the distances for ship and albatross positions at 1-h and 14-min intervals, respectively, was 1.15 ± 1.44 km (see supporting information in Granadeiro et al., 2011). We classified each foraging trip of study birds as involving, or not involving, a direct interaction with the Falklands fishing fleet (freezer/factory bottom trawlers). Most foraging trips did not exit waters under the Falkland Islands jurisdiction, where we had complete coverage of the position of all fishing vessels. Furthermore, those fishing vessels were the closest to the nesting colony, and as such, we would predict that they would be the first to be targeted by any potential fishing vessel specialist birds.

We estimated the approximate contribution of prey from different trophic levels to the diet of the back-browed albatross using a basic isotopic mixing model in package ‘siar’ (Stable Isotope Analysis in R, Parnell et al., 2010; R Development Core Team, 2012). This package uses a Markov Chain Monte Carlo algorithm to estimate the relative importance of prey with different isotopic signals, in order to best match the isotopic signature of the consumer. Thus, the isotopic signature of the consumer is modeled as a weighted combination of the isotopic signals of food sources, taking into account tissue- and species-specific discrimination factors. The Bayesian approach used in ‘siar’ allows for the inclusion of different sources of uncertainty, including the variability in isotopic ratios of prey and in discrimination factors (Parnell et al., 2010).

We used information on carbon and nitrogen isotopic ratios of likely relevant prey species from studies carried out in the Falkland Islands and nearby Patagonian Shelf (Copello & Quintana, 2009; Weiss et al., 2009; González-Zevallos & Yorio, 2011; Granadeiro et al., 2011, Granadeiro, Brickle & Catry, unpubl. data). For the purpose of the present study, we averaged values from different preys, grouped in four main types: crustacea, demersal fish, small pelagic fish and squid (list of prey species considered available in Supporting Information Appendix S1). We used 1 and 3‰ as discrimination factors for δ13C and δ15N, respectively, following Caut, Angulo & Courchamp (2009), with no differentiation among prey. We also set the sd for δ13C and δ15N at 0.5‰, which is at the upper end of the range of values suggested by Caut et al. (2009).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

A total of 25 individual albatrosses were tracked in 2009 and 64 in 2011, with 17 individuals being tracked in both seasons. Overall, 103 trips were obtained (33 in 2009 and 70 in 2011), 78.6% of which did not extend beyond the marine areas under Falkland's jurisdiction. There were no differences among years in the distances traveled by albatrosses in trips within Falkland waters [2009: 309.0 ± 137.3 km (sd); 2011: 283.4 ± 138.2 km (sd), F1,79 = 0.54, P = 0.465], although they lasted longer in 2009 [2009: 41.9 ± 18.7 h (sd); 2011: 26.7 ± 14.3 h (sd), F1,79 = 14.8, P < 0.001].

The fishing effort in the marine area under the Falkland Islands jurisdiction was mostly concentrated to the west and northeast of the islands in both years and the inter-annual overlap of the vessel distributions was estimated at 47.2% (Fig. 1). The fleet using the area during the study period (December and January) consisted of freezer/factory bottom trawlers (12 in 2009 and eight in 2011).

figure

Figure 1. Distribution (75% kernel density contours) of the fishing effort in December and early January 2009/2010 and 2011/2012 based on hourly vessel monitoring system (VMS) records of fishing vessels steaming at less than 6 knots. Limits of the marine areas under the Falkland Islands jurisdiction are indicated in light gray and location of Steeple Jason is indicated by an asterisk (*).

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All interactions between fishing vessels and albatrosses could be unequivocally identified in both years using animations and graphics portraying their joint real-time positions, together with the location of albatross landings derived from activity loggers (Fig. 2). Overall, albatrosses interacted with vessels in 15 out of 89 (16.8%) independent trips (obtained by taking only the first trip of each individual, n = 25 in 2009 and n = 64 in 2011), with no significant differences among years in the frequency of occurrence of interactions (Fisher's exact test, P = 0.11). Among the 17 birds (34 trips) that were tracked on both seasons, we identified 10 interactions, thus providing a probability of occurrence of 0.294. Two birds followed ships in both years, six interacted on one of the years and nine were never involved in interactions. Such distribution is very close to the expected outcome assuming that each bird is equally likely to engage in an interaction (χ22 = 0.38, P = 0.83).

figure

Figure 2. Example of part of an interaction between an albatross and a fishing vessel, obtained by combining global positioning system tracking with vessel monitoring system data. Black arrows represent the position of the albatross at 5 minutes intervals and dashed grey lines link temporally matched positions of bird and vessel. Landings at sea are indicated by a grey symbol.

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There were no significant differences in the isotopic signatures (feathers and blood in 2011) of birds that interacted with fisheries in any one year as compared to those that did not (Fig. 3; multivariate analysis of variance: Wilk's lambda = 0.94, F4,55 = 0.84, P = 0.50). Furthermore, there was no correlation between feather and blood isotopic ratios of nitrogen (r58 = 0.06, P = 0.64) or carbon (r58 = 0.07, P = 0.57).

figure

Figure 3. Carbon and nitrogen stable isotope signature in whole blood (circles) and feather (triangles) of individual black-browed albatrosses that interacted (filled symbols) and did not interact (open symbols) with fishing vessels during the study period. Ellipses include 95% of the data.

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The results of the mixing model suggested a preponderance of pelagic prey, representing about 80% of assimilated food, with demersal prey accounting for c. 20% of the diet (Fig. 4).

figure

Figure 4. Contribution of each prey type (expressed as mean proportion of assimilated food ± 95% confidence interval) according to the stable isotope mixing model developed for blood of black-browed albatrosses tracked during the study period. For details of prey types, see Supporting Information Appendix S1.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

In this study, we investigated individual seabird consistency in the utilization of discards across multiple temporal scales. By combining stable isotope analysis of different tissues with tracking of birds and fishing vessels, our study provides new insights on the relationships between seabirds and fisheries.

We made three predictions regarding the foraging movements of individual albatrosses and the isotopic signatures of their different tissues that should be verified if birds consistently attended fishing vessels. As further discussed later, none of those predictions were verified by the data collected during the study, which took place at the largest black-browed albatross colony in the Patagonian Shelf (and in the world). Overall, our data suggest no significant specialization of individual black-browed albatrosses regarding fisheries operations.

All fisheries deployed inside Falkland Island waters are monitored through VMS. Nevertheless, some of the tracked study birds also foraged in areas outside Falkland's jurisdiction, where interactions with fisheries would have passed undetected. However, these were probably a minority, and even if we misclassified some trips as presenting no interactions when those actually occurred, our predictions would still apply should a strong pattern of specialization be apparent in this population.

In a previous study, we documented a lack of consistency in the association with fisheries of individual albatrosses from the Falklands tracked on two consecutive trips (Granadeiro et al., 2011). Tracking in two different nesting seasons confirm this finding at a broader temporal scale: albatrosses that were found to associate with the Falklands fishing fleet in 2009 (Granadeiro et al., 2011) were not more likely to do so again in 2011 (this study). The analyses of the 2009 data also showed that albatross foraging trips in which the fishing fleet was visited were no different in duration, distance covered, straightness index or number of landings on the sea from trips where no interactions with vessels were recorded (Granadeiro et al., 2011). This suggests that attending fishing vessels does not represent a distinct foraging strategy, in terms of the characteristics of the travel path or activity while at sea.

We compared the carbon and nitrogen isotope ratios in whole blood and feathers of individual albatrosses that interacted with trawlers during the present study with the levels of individuals that did not during the tracked foraging trips. Blood samples were taken before birds were tracked, to ensure that measured isotope ratios were not simply reflecting diet during the observed foraging trips. We could find no differences between the two groups, suggesting that individuals that interacted with fishing vessels had a similar short-to-medium [blood, which shows a turnover half-life of c. 30 days, for birds the size of a black-browed albatross (Hobson & Wassenaar, 2008)] and long-term (feathers) isotopic niche to the ones that did not interact. Given that offal and fisheries discards, which in this region consist of demersal species, will have an isotopic composition considerably different from black-browed albatross ‘natural’ prey, we would have expected some isotopic niche differentiation between the two groups, should a specialization exist. Furthermore, the results from our basic isotopic mixing model suggest a low consumption of demersal prey, which also supports the idea of an overall low reliance of this population on fisheries discharges. We should stress, however, that the available information on potential black-browed albatross prey and their isotopic composition in the Patagonian Shelf is not comprehensive, and this particular result should be seen as very preliminary.

We should note that several studies documenting an apparent specialization in seabirds have looked at isotope signatures reflecting diet (but also habitat) outside the breeding season (Furness et al., 2006; Jaeger et al., 2010). Consistency in isotope signatures outside the breeding season may reflect repeatable preferences in diet, but also philopatry to wintering sites or regions, the effects of which may be hard to disentangle in studies based on isotopic niches alone. It could be argued that tracking only one or two trips per individual is insufficient to pinpoint which birds are more often associating with fishing vessels, and that stochastic factors are also important in determining whether an individual meets a fishing vessel in any particular trip. However, the locations of fishing operations are somewhat predictable (Fig. 1, Granadeiro et al., 2011), which would argue against this. Furthermore, our third prediction concerns patterns that are independent of information obtained from tracking over a relatively narrow time-window: if a ‘fisheries association syndrome’ characterized the behavior of some of our study birds, they should consistently differ from other individuals in their isotopic niche measured across seasons. Again, this prediction was not verified.

The blood samples collected from the study birds should integrate dietary signals pertaining to the incubation (lasting from October to mid-December) and the early chick-rearing period. Also, the mantle feathers collected are molted between breeding seasons, not during incubation (pers. observation). As such, they integrate dietary information from a distinct period and likely also from different geographical areas (wintering regions). In fact, despite the relatively sedentary behavior of the albatrosses of the study population, they still differ in their spatial use of the Patagonian Shelf across seasons (Grémillet et al., 2000, Granadeiro, Brickle & Catry, unpubl. data). The lack of a correlation in δ13C and δ15N measured in those two tissues suggests no consistent trends in albatross feeding specializations that are maintained along different times of the annual cycle, as found in wandering albatrosses Diomedea exulans (Ceia et al., 2012).

Fisheries discards provide seabirds with large amounts of otherwise inaccessible food. On the other hand, the quality of such food may not be as high as that of more natural prey (Grémillet et al., 2008), which might work against the development of feeding specializations linked to fisheries. Furthermore, associating with fishing vessels entails safety risks (Sullivan et al., 2006; González-Zevallos, Yorio & Caille, 2007; Bugoni et al., 2008), which again may prevent the establishment of a ‘fisheries association syndrome’.

Management implications

The existence of extensive fisheries bycatch is an issue of conservation relevance, and is believed to be causing the decline of many populations of long-lived seabirds (Croxall et al., 2012). The discharge of such unintentional captures is widely recognized as an unsustainable aspect of industrial fisheries needing attention and further regulation (Croxall, 2008; Heithaus et al., 2008; Favero et al., 2010). Management options include bycatch retention, strategic dumping and onboard processing of fish waste [e.g. using onboard meal plants for mincing or mealing rejections (Watkins, Petersen & Ryan, 2008; Abraham et al., 2009; Pierre et al., 2012) ]. However, such options may also significantly curtail feeding opportunities for seabirds (Votier et al., 2004, 2008). The importance of these feeding opportunities, relative to alternative natural prey, varies with region and species of concern (e.g. Karpouzi et al., 2007). Studies of black-browed albatrosses have suggested that despite the large numbers of individuals attending fishing vessels, the contribution of discards and offal to the overall energy budget is likely to be small (Thompson, 1992; Thompson & Riddy, 1995). The present study goes a step further, by indicating that this species does not specialize in fisheries discards. As a consequence, no fraction of the population is potentially more vulnerable to management options involving the reduction of discards. A lack of long-term trophic consistency was recently demonstrated in the wandering albatross (Ceia et al., 2012), which may indicate that large scavenging Procellariiformes (including mainly genus Diomedea, Thalassarche and Macronectes), a group particularly threatened by fisheries activity, do not specialize in discards. This hypothesis clearly requires further support, to assess if this applies to most seabirds in other geographical regions, but our findings suggest that reducing the discharge of fisheries products is likely to be generally beneficial to seabirds, making vessels less attractive and reducing the scope for potential fatal incidents.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

The Wildlife Conservation Society granted permission for work on Steeple Jason. Fundação para a Ciência e Tecnologia (FCT-Portugal) financed the work through projects PTDC/MAR/099366/2008 and PEst-OE/MAR/UI0331/2011. Permits and further financial support was received from the Falkland Islands Government. We thank the Fisheries Department, Falkland Islands Government for supporting this work. Maria Strange, Rob and Lorraine McGill, Michael Clarke, Nick Rendell, Anton and Leigh Wolfaardt provided important support in the field and in Stanley. This work owes to the long-term commitment and support of Ian Strange.

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  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information
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acv12050-sup-0001-si.docx18K

Appendix S1. Carbon and nitrogen isotopic ratios of potential prey in the diet of black-browed albatrosses, used in the isotopic mixing model.

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