Seabirds reveal mercury distribution across the North Atlantic.

Mercury (Hg) is a heterogeneously distributed toxicant affecting wildlife and human health. Yet, the spatial distribution of Hg remains poorly documented, especially in food webs, even though this knowledge is essential to assess large-scale risk of toxicity for the biota and human populations. Here, we used seabirds to assess, at an unprecedented population and geographic magnitude and high resolution, the spatial distribution of Hg in North Atlantic marine food webs. To this end, we combined tracking data of 837 seabirds from seven different species and 27 breeding colonies located across the North Atlantic and Atlantic Arctic together with Hg analyses in feathers representing individual seabird contamination based on their winter distribution. Our results highlight an east-west gradient in Hg concentrations with hot spots around southern Greenland and the east coast of Canada and a cold spot in the Barents and Kara Seas. We hypothesize that those gradients are influenced by eastern (Norwegian Atlantic Current and West Spitsbergen Current) and western (East Greenland Current) oceanic currents and melting of the Greenland Ice Sheet. By tracking spatial Hg contamination in marine ecosystems and through the identification of areas at risk of Hg toxicity, this study provides essential knowledge for international decisions about where the regulation of pollutants should be prioritized.

The challenges of opportunistic sampling when comparing prevalence of plastics in diving seabirds: A multi-species example from Norway.

There is a need for baseline information about how much plastics are ingested by wildlife and potential negative consequences thereof. We analysed the frequency of occurrence (FO) of plastics >1 mm in the stomachs of five pursuit-diving seabird species collected opportunistically. Atlantic puffins (Fratercula arctica) found emaciated on beaches in SW Norway had the highest FO of plastics (58.8 %), followed by emaciated common guillemots (Uria aalge; 9.1 %) also found beached in either SW or SE Norway. No plastics were detected in razorbills (Alca torda), great cormorants (Phalacrocorax carbo), and European shags (Gulosus aristotelis) taken as bycatch in northern Norway. This is the first study to report on plastic ingestion of these five species in northern Europe, and it highlights both the usefulness and limitations of opportunistic sampling. Small sample sizes, as well as an unbalanced sample design, complicated the interpretation of the results.

Spatial distribution of selenium-mercury in Arctic seabirds.

Mercury (Hg) is a metallic trace element toxic for humans and wildlife that can originate from natural and anthropic sources. Hg spatial gradients have been found in seabirds from the Arctic and other oceans, suggesting contrasting toxicity risks across regions. Selenium (Se) plays a protective role against Hg toxicity, but its spatial distribution has been much less investigated than that of Hg. From 2015 to 2017, we measured spatial co-exposure of Hg and Se in blood samples of two seabird species, the Brünnich's guillemot (Uria lomvia) and the black-legged kittiwake (Rissa tridactyla) from 17 colonies in the Arctic and subarctic regions, and we calculated their molar ratios (Se:Hg), as a measure of Hg sequestration by Se and, therefore, of Hg exposure risk. We also evaluated concentration differences between species and ocean basins (Pacific-Arctic and Atlantic-Arctic), and examined the influence of trophic ecology on Hg and Se concentrations using nitrogen and carbon stable isotopes. In the Atlantic-Arctic ocean, we found a negative west-to-east gradient of Hg and Se for guillemots, and a positive west-to-east gradient of Se for kittiwakes, suggesting that these species are better protected from Hg toxicity in the European Arctic. Differences in Se gradients between species suggest that they do not follow environmental Se spatial variations. This, together with the absence of a general pattern for isotopes influence on trace element concentrations, could be due to foraging ecology differences between species. In both oceans, the two species showed similar Hg concentrations, but guillemots showed lower Se concentrations and Se:Hg than kittiwakes, suggesting a higher Hg toxicity risk in guillemots. Within species, neither Hg, nor Se or Se:Hg differed between both oceans. Our study highlights the importance of considering Se together with Hg, along with different species and regions, when evaluating Hg toxic effects on marine predators in international monitoring programs.

Variation and correlation in the timing of breeding of North Atlantic seabirds across multiple scales.

Timing of breeding, an important driver of fitness in many populations, is widely studied in the context of global change, yet despite considerable efforts to identify environmental drivers of seabird nesting phenology, for most populations we lack evidence of strong drivers. Here we adopt an alternative approach, examining the degree to which different populations positively covary in their annual phenology to infer whether phenological responses to environmental drivers are likely to be (a) shared across species at a range of spatial scales, (b) shared across populations of a species or (c) idiosyncratic to populations. We combined 51 long-term datasets on breeding phenology spanning 50 years from nine seabird species across 29 North Atlantic sites and examined the extent to which different populations share early versus late breeding seasons depending on a hierarchy of spatial scales comprising breeding site, small-scale region, large-scale region and the whole North Atlantic. In about a third of cases, we found laying dates of populations of different species sharing the same breeding site or small-scale breeding region were positively correlated, which is consistent with the hypothesis that they share phenological responses to the same environmental conditions. In comparison, we found no evidence for positive phenological covariation among populations across species aggregated at larger spatial scales. In general, we found little evidence for positive phenological covariation between populations of a single species, and in many instances the inter-year variation specific to a population was substantial, consistent with each population responding idiosyncratically to local environmental conditions. Black-legged kittiwake Rissa tridactyla was the exception, with populations exhibiting positive covariation in laying dates that decayed with the distance between breeding sites, suggesting that populations may be responding to a similar driver. Our approach sheds light on the potential factors that may drive phenology in our study species, thus furthering our understanding of the scales at which different seabirds interact with interannual variation in their environment. We also identify additional systems and phenological questions to which our inferential approach could be applied.

Seabird beachcast events associated with bycatch in the Norwegian purse seine fishery.

Beachcast events, where a large number of seabird carcasses drift ashore, occur with irregular intervals. These events are due to specific situations where mass mortality of seabirds have occurred. Disentangling the cause of these events can provide valuable information on stressors impacting seabird populations. Following several mass mortality events involving gulls in northern Norway, an investigation of the probable cause of death was initiated. In total 75 dead gulls were collected at two occasions and necropsies were carried out. The findings from the necropsy of the gulls were consistent with drowning as the primary cause of death. Bycatch in coastal purse seine fishery was considered a potential cause of the mortality and monitoring of seabird bycatch in this fishery was thus initiated. The monitoring of fishing operations revealed that 10% of 91 fishing events observed led to bycatch, with a total of 32 bycaught seabirds. These bycatch events resulted in a total estimated bycatch rate of 0.356 (95% CI = 0.133-0.949) birds per haul. These findings are consistent with the hypothesis that the registered mortality events were caused by bycatch in the purse seine fishery. The highly episodic and unpredictable nature of these events makes it demanding to achieve solid estimates of the occurrence and extent of bycatch without a very high monitoring effort. Our study shows that systematic investigation following beachcast events can shed light on the occurrence of such extreme events.

North Atlantic winter cyclones starve seabirds.

Each winter, the North Atlantic Ocean is the stage for numerous cyclones, the most severe ones leading to seabird mass-mortality events called "winter wrecks."1-3 During these, thousands of emaciated seabird carcasses are washed ashore along European and North American coasts. Winter cyclones can therefore shape seabird population dynamics4,5 by affecting survival rates as well as the body condition of surviving individuals and thus their future reproduction. However, most often the geographic origins of impacted seabirds and the causes of their deaths remain unclear.6 We performed the first ocean-basin scale assessment of cyclone exposure in a seabird community by coupling winter tracking data for ∼1,500 individuals of five key North Atlantic seabird species (Alle alle, Fratercula arctica, Uria aalge, Uria lomvia, and Rissa tridactyla) and cyclone locations. We then explored the energetic consequences of different cyclonic conditions using a mechanistic bioenergetics model7 and tested the hypothesis that cyclones dramatically increase seabird energy requirements. We demonstrated that cyclones of high intensity impacted birds from all studied species and breeding colonies during winter but especially those aggregating in the Labrador Sea, the Davis Strait, the surroundings of Iceland, and the Barents Sea. Our broad-scale analyses suggested that cyclonic conditions do not increase seabird energy requirements, implying that they die because of the unavailability of their prey and/or their inability to feed during cyclones. Our study provides essential information on seabird cyclone exposure in a context of marked cyclone regime changes due to global warming.8.

Ingested plastics in northern fulmars (Fulmarus glacialis): A pathway for polybrominated diphenyl ether (PBDE) exposure?

Although it has been suggested that plastic may act as a vector for pollutants into the tissue of seabirds, the bioaccumulation of harmful contaminants, such as polybrominated diphenyl ethers (PBDEs), released from ingested plastics is poorly understood. Plastic ingestion by the procellariiform species northern fulmar (Fulmarus glacialis) is well documented. In this study, we measured PBDEs levels in liver tissue of northern fulmars without and with (0.13-0.43 g per individual) stomach plastics. PBDE concentrations in the plastic sampled from the same birds were also quantified. Birds were either found dead on beaches in southern Norway or incidentally caught in longline fisheries in northern Norway. PBDEs were detected in all birds but high concentrations were only found in liver samples from beached birds, peaking at 2900 ng/g lipid weight. We found that body condition was a significant factor explaining the elevated concentration levels in livers of beached birds. BDE209 was found in ingested plastic particles and liver tissue of birds with ingested plastics but was absent in the livers of birds without ingested plastics. This strongly suggests a plastic-derived transfer and accumulation of BDE209 to the tissue of fulmars, levels of which might prove useful as a general indicator of plastic ingestion in seabirds.

Meeting Paris agreement objectives will temper seabird winter distribution shifts in the North Atlantic Ocean.

We explored the implications of reaching the Paris Agreement Objective of limiting global warming to <2°C for the future winter distribution of the North Atlantic seabird community. We predicted and quantified current and future winter habitats of five North Atlantic Ocean seabird species (Alle alle, Fratercula arctica, Uria aalge, Uria lomvia and Rissa tridactyla) using tracking data for ~1500 individuals through resource selection functions based on mechanistic modeling of seabird energy requirements, and a dynamic bioclimate envelope model of seabird prey. Future winter distributions were predicted to shift with climate change, especially when global warming exceed 2°C under a "no mitigation" scenario, modifying seabird wintering hotspots in the North Atlantic Ocean. Our findings suggest that meeting Paris agreement objectives will limit changes in seabird selected habitat location and size in the North Atlantic Ocean during the 21st century. We thereby provide key information for the design of adaptive marine-protected areas in a changing ocean.

Diverging phenological responses of Arctic seabirds to an earlier spring.

The timing of annual events such as reproduction is a critical component of how free-living organisms respond to ongoing climate change. This may be especially true in the Arctic, which is disproportionally impacted by climate warming. Here, we show that Arctic seabirds responded to climate change by moving the start of their reproduction earlier, coincident with an advancing onset of spring and that their response is phylogenetically and spatially structured. The phylogenetic signal is likely driven by seabird foraging behavior. Surface-feeding species advanced their reproduction in the last 35 years while diving species showed remarkably stable breeding timing. The earlier reproduction for Arctic surface-feeding birds was significant in the Pacific only, where spring advancement was most pronounced. In both the Atlantic and Pacific, seabirds with a long breeding season showed a greater response to the advancement of spring than seabirds with a short breeding season. Our results emphasize that spatial variation, phylogeny, and life history are important considerations in seabird phenological response to climate change and highlight the key role played by the species' foraging behavior.

Spatial and temporal variations in seabird bycatch: Incidental bycatch in the Norwegian coastal gillnet-fishery.

The general decline of seabird populations worldwide raises large concerns. Although multiple factors are interacting to cause the observed trends, increased mortality from incidental bycatch in fisheries has proven to be important for many species. However, the bulk of published knowledge is derived from longline fisheries, whereas bycatch in gillnet fisheries is less studied and even overlooked in some areas. We present seabird bycatch data from a 10-year time-series of fishery data from the large fleet of small-vessels fishing with gillnets along the Norwegian coast-a large area and fishery with no prior estimates of seabird bycatch. In general, we document high rates of incidental bycatch (averaging 0.0023 seabirds/net, or approximately 0.08 seabirds/fishing trip). This results in an estimated annual bycatch between 1580 and 11500 (95% CI) birds in this fishery. There was a surprisingly high percentage (43%) of surface-feeding seabirds in the bycatch, with northern fulmar being the most common species. Among the diving seabirds caught, common guillemot was most numerous. Our findings suggest that coastal gillnet fisheries represent a more general threat to a wider range of seabird populations, as opposed to longline fisheries where surface-feeding seabird species seem to dominate the bycatch. The bycatch estimates for the Norwegian gillnet-fishery varied in time, between areas, and with fishing depth and distance from the coast, but we found no clear trends in relation to the type of gillnets used. The results enabled us to identify important spatio-temporal trends in the seabird bycatch, which can allow for the development and implementation of more specific mitigation measures. While specific time closures might be an efficient option to reduce bycatch for diving seabirds, measures such as gear modification and reduction in release of wastewater during fishing operation are probably a more effective mitigation approach for reducing bycatch of surface-feeding seabirds.

Taking a trip to the shelf: Behavioral decisions are mediated by the proximity to foraging habitats in the black-legged kittiwake.

For marine top predators like seabirds, the oceans represent a multitude of habitats regarding oceanographic conditions and food availability. Worldwide, these marine habitats are being altered by changes in climate and increased anthropogenic impact. This is causing a growing concern on how seabird populations might adapt to these changes. Understanding how seabird populations respond to fluctuating environmental conditions and to what extent behavioral flexibility can buffer variations in food availability can help predict how seabirds may cope with changes in the marine environment. Such knowledge is important to implement proper long-term conservation measures intended to protect marine predators. We explored behavioral flexibility in choice of foraging habitat of chick-rearing black-legged kittiwakes Rissa tridactyla during multiple years. By comparing foraging behavior of individuals from two colonies with large differences in oceanographic conditions and distances to predictable feeding areas at the Norwegian shelf break, we investigated how foraging decisions are related to intrinsic and extrinsic factors. We found that proximity to the shelf break determined which factors drove the decision to forage there. At the colony near the shelf break, time of departure from the colony and wind speed were most important in driving the choice of habitat. At the colony farther from the shelf break, the decision to forage there was driven by adult body condition. Birds furthermore adjusted foraging behavior metrics according to time of the day, weather conditions, body condition, and the age of the chicks. The study shows that kittiwakes have high degree of flexibility in their behavioral response to a variable marine environment, which might help them buffer changes in prey distribution around the colonies. The flexibility is, however, dependent on the availability of foraging habitats near the colony.

Circumpolar dynamics of a marine top-predator track ocean warming rates.

Global warming is a nonlinear process, and temperature may increase in a stepwise manner. Periods of abrupt warming can trigger persistent changes in the state of ecosystems, also called regime shifts. The responses of organisms to abrupt warming and associated regime shifts can be unlike responses to periods of slow or moderate change. Understanding of nonlinearity in the biological responses to climate warming is needed to assess the consequences of ongoing climate change. Here, we demonstrate that the population dynamics of a long-lived, wide-ranging marine predator are associated with changes in the rate of ocean warming. Data from 556 colonies of black-legged kittiwakes Rissa tridactyla distributed throughout its breeding range revealed that an abrupt warming of sea-surface temperature in the 1990s coincided with steep kittiwake population decline. Periods of moderate warming in sea temperatures did not seem to affect kittiwake dynamics. The rapid warming observed in the 1990s may have driven large-scale, circumpolar marine ecosystem shifts that strongly affected kittiwakes through bottom-up effects. Our study sheds light on the nonlinear response of a circumpolar seabird to large-scale changes in oceanographic conditions and indicates that marine top predators may be more sensitive to the rate of ocean warming rather than to warming itself.

Negligible Impact of Ingested Microplastics on Tissue Concentrations of Persistent Organic Pollutants in Northern Fulmars off Coastal Norway.

The northern fulmar (Fulmarus glacialis) is defined as an indicator species of plastic pollution by the Oslo-Paris Convention for the North-East Atlantic, but few data exist for fulmars from Norway. Moreover, the relationship between uptake of plastic and pollutants in seabirds is poorly understood. We analyzed samples of fulmars from Norwegian waters and compared the POP concentrations in their liver and muscle tissue with the corresponding concentrations in the loads of ingested plastic in their stomachs, grouped as "no", "medium" (0.01-0.21 g; 1-14 pieces of plastic), or "high" (0.11-0.59 g; 15-106 pieces of plastic). POP concentrations in the plastic did not differ significantly between the high and medium plastic ingestion group for sumPCBs, sumDDTs, and sumPBDEs. By combining correlations among POP concentrations, differences in tissue concentrations of POPs between plastic ingestion subgroups, fugacity calculations, and bioaccumulation modeling, we showed that plastic is more likely to act as a passive sampler than as a vector of POPs, thus reflecting the POP profiles of simultaneously ingested prey.