Proof of concept evidence that stable isotopes of carbon, nitrogen and sulphur may identify individual kittiwakes breeding in different colonies.

RATIONALE: Carbon, nitrogen and sulphur stable isotopes in feathers grown by seabirds while breeding reflect the local isoscape and diet in the vicinity of the colony, so may make it possible to discriminate individual birds from different colonies. METHODS: Black-legged kittiwake Rissa tridactyla inner primary feathers from two colonies about 350 km apart in the North Sea were used to test whether δ13C, δ15N and δ34S differed between individuals from the two colonies. Feather tips cut from breeding birds caught at nests were compared with tips of moulted feathers (grown 1 year earlier) found on the ground. RESULTS: Isotopic compositions showed no overlap between the two colonies in δ13C, δ15N or δ34S in tips of newly-grown feathers sampled from breeding adult kittiwakes. There was some overlap in δ13C, δ15N and δ34S from moulted feathers, but discriminant analysis allowed >90% of individuals to be assigned to their colony. In five of six comparisons, mean isotopic compositions were the same in new and moulted feathers but not for δ34S at one of the two colonies. CONCLUSIONS: This study has demonstrated for the first time that stable isotopes in inner primary feathers of kittiwakes can allow accurate identification of the breeding colony of individual birds from two different colonies within the North Sea. Further research is required to determine if this method can be applied with greater spatial resolution and to a larger number of colonies.

Untangling local and remote influences in two major petrel habitats in the oligotrophic Southern Ocean.

Ocean circulation connects geographically distinct ecosystems across a wide range of spatial and temporal scales via exchanges of physical and biogeochemical properties. Remote oceanographic processes can be especially important for ecosystems in the Southern Ocean, where the Antarctic Circumpolar Current transports properties across ocean basins through both advection and mixing. Recent tracking studies have indicated the existence of two large-scale, open ocean habitats in the Southern Ocean used by grey petrels (Procellaria cinerea) from two populations (i.e., Kerguelen and Antipodes islands) during their nonbreeding season for extended periods during austral summer (i.e., October to February). In this work, we use a novel combination of large-scale oceanographic observations, surface drifter data, satellite-derived primary productivity, numerical adjoint sensitivity experiments, and output from a biogeochemical state estimate to examine local and remote influences on these grey petrel habitats. Our aim is to understand the oceanographic features that control these isolated foraging areas and to evaluate their ecological value as oligotrophic open ocean habitats. We estimate the minimum local primary productivity required to support these populations to be much <1% of the estimated local primary productivity. The region in the southeast Indian Ocean used by the birds from Kerguelen is connected by circulation to the productive Kerguelen shelf. In contrast, the region in the south-central Pacific Ocean used by seabirds from the Antipodes is relatively isolated suggesting it is more influenced by local factors or the cumulative effects of many seasonal cycles. This work exemplifies the potential use of predator distributions and oceanographic data to highlight areas of the open ocean that may be more dynamic and productive than previously thought. Our results highlight the need to consider advective connections between ecosystems in the Southern Ocean and to re-evaluate the ecological relevance of oligotrophic Southern Ocean regions from a conservation perspective.

Seabird diversity hotspot linked to ocean productivity in the Canary Current Large Marine Ecosystem.

Upwelling regions are highly productive habitats targeted by wide-ranging marine predators and industrial fisheries. In this study, we track the migratory movements of eight seabird species from across the Atlantic; quantify overlap with the Canary Current Large Marine Ecosystem (CCLME) and determine the habitat characteristics that drive this association. Our results indicate the CCLME is a biodiversity hotspot for migratory seabirds; all tracked species and more than 70% of individuals used this upwelling region. Relative species richness peaked in areas where sea surface temperature averaged between 15 and 20°C, and correlated positively with chlorophyll a, revealing the optimum conditions driving bottom-up trophic effects for seabirds. Marine vertebrates are not confined by international boundaries, making conservation challenging. However, by linking diversity to ocean productivity, our research reveals the significance of the CCLME for seabird populations from across the Atlantic, making it a priority for conservation action.

Legacy Pollutants are Declining in Great Skuas (Stercorarius skua) but Remain Higher in Faroe Islands than in Scotland.

To monitor environmental pollutants in Faroese biota, samples from a top predator were analysed and put into a spatial and temporal context. Analysis of 20 Great Skua eggs sampled in 2012 from the Faroe Islands showed >70 % lower concentrations of legacy persistent organic pollutants (POPs) than in samples analysed in 1977. The 2012 Faroese eggs showed higher concentrations than for eggs in Shetland from about the same period (2008). Eggshells were analysed for sub-lethal effects but there were no detectable effects of legacy POP levels on eggshell colour or thickness. A temporal decline in legacy POPs would indicate a reduction in the general pollutant levels present in the environment as has been shown in other areas of the North Atlantic, but there are significant geographic differences in POPs levels likely due to differences in diet resulting in significantly different exposures on a relatively limited spatial scale.

HPAIV outbreak triggers short-term colony connectivity in a seabird metapopulation.

Disease outbreaks can drastically disturb the environment of surviving animals, but the behavioural, ecological, and epidemiological consequences of disease-driven disturbance are poorly understood. Here, we show that an outbreak of High Pathogenicity Avian Influenza Virus (HPAIV) coincided with unprecedented short-term behavioural changes in Northern gannets (Morus bassanus). Breeding gannets show characteristically strong fidelity to their nest sites and foraging areas (2015-2019; n = 120), but during the 2022 HPAIV outbreak, GPS-tagged gannets instigated long-distance movements beyond well-documented previous ranges and the first ever recorded visits of GPS-tagged adults to other gannet breeding colonies. Our findings suggest that the HPAIV outbreak triggered changes in space use patterns of exposed individuals that amplified the epidemiological connectivity among colonies and may generate super-spreader events that accelerate disease transmission across the metapopulation. Such self-propagating transmission from and towards high density animal aggregations may explain the unexpectedly rapid pan-European spread of HPAIV in the gannet.

Dietary versus maternal sources of organochlorines in top predator seabird chicks: an experimental approach.

We examined the relative importance of dietary sources and maternal transfer on organochlorine concentrations (∑OCs) in Great skua chicks (Stercorarius skua) in Shetland by food supplementing parents with known wintering area. We predicted that experimental chicks (whose parents were supplemented) should have (i) higher growth rates and, (ii) lower ∑OCs due to growth dilution effect and/or due to being fed with less contaminated food compared to control chicks. We also predicted a significant influence of maternal wintering area on chicks' ∑OCs. Plasma ∑OCs of adults, assessed prior to the manipulation, significantly differed between wintering areas of birds. Chicks were weighed every 5 days and plasma ∑OCs were assessed at 20 days old. Based on nitrogen and carbon stable isotope analysis, the supplementary food contributed on average 20% of the dietary protein of the chicks. Although experimental chicks experienced better developmental conditions, supplementary food did not alleviate their organochlorine burden. Nevertheless, chicks whose mothers wintered in Europe showed ∑OCs 50% higher than chicks whose mothers wintered in Africa. Moreover, based on the positive relationship between ∑OCs of chicks and females, the contaminant load of Great skua chicks in Shetland appears to be more influenced by maternal transfer than by trophic transfer.

Organohalogen contaminants and Blood plasma clinical-chemical parameters in three colonies of North Atlantic Great skua (Stercorarius skua).

The present study compares blood plasma clinical-chemical parameters (BCCPs) in birds from three geographically distinct North Atlantic Great skua (Stercorarius skua) colonies. Birds from these sites bioaccumulate different POP (persistent organic pollutant) concentrations and that enabled us to compare Great skua BCCPs in different exposure scenarios. Persistent organic pollutants (organochlorines: PCB, DDT, chlordanes, HCB, HCH, mirex and brominated flame retardants: PBDEs) and nineteen BCCPs were analysed in 114 adult Great skuas sampled during summer 2009 in North Atlantic colonies at Bjørnøya (n=42), Iceland (n=57) and Shetland (n=15). Specimens from Bjørnøya had the highest blood plasma concentrations of all contaminant groups followed by Iceland and Shetland birds, respectively (ANOVA: p<0.05). Most of the 19 BCCP parameters followed the pattern of colony differences found for contaminants, with Bjørnøya having the highest concentrations. However seven BCCPs, the three liver enzymes ALKP, ALAT and GGT as well as bile acids, cholesterol, sodium and potassium, did not differ between colonies (ANOVA: p>0.05). Therefore correlation analyses of these seven BCCPs vs. POPs were done on the combined colony data while the analyses of the remaining 12 BCCPs were carried out for each colony separately. The analyses of combined colony data showed that the blood plasma concentration of liver enzymes ALAT and GGT increased with increasing concentrations of ΣPBDE and ΣHCH, HCB and ΣCHL, respectively (all Pearson's p<0.05). In Great skuas from Shetland, the important osmotic transport protein albumin increased with increasing concentrations of ΣPCB and ΣDDT, while total blood plasma protein increased with ΣPCB, ΣDDT, ΣHCH and HCB concentrations (all Pearson's p<0.05). In both Bjørnøya and Iceland skuas, blood plasma pancreatic enzyme amylase decreased with increasing ΣHCH concentrations while the erythrocyte waste product total bilirubin in blood plasma increased with increasing ΣHCH and ΣPBDE concentrations in Iceland Great skuas (all Pearson's p<0.05). In Bjørnøya birds, blood plasma urea from protein metabolism (reflects kidney function) increased with increasing ΣPBDE concentrations (Pearson's p<0.05). Furthermore, a redundancy analysis showed that 10.6% of the variations in BCCPs could be explained by the variations in POP concentrations. Based on these results we suggest that liver and renal functions could be negatively affected by different POP compounds. It is, however, uncertain if the colony BCCP differences and their relationship to POP concentrations reflect health effects that could have an overall impact on the populations via reduced survival and reproduction parameters.

Assessing vulnerability of marine bird populations to offshore wind farms.

Offshore wind farms may affect bird populations through collision mortality and displacement. Given the pressures to develop offshore wind farms, there is an urgent need to assess population-level impacts on protected marine birds. Here we refine an approach to assess aspects of their ecology that influence population vulnerability to wind farm impacts, also taking into account the conservation importance of each species. Flight height appears to be a key factor influencing collision mortality risk but improved data on flight heights of marine birds are needed. Collision index calculations identify populations of gulls, white-tailed eagles, northern gannets and skuas as of particularly high concern in Scottish waters. Displacement index calculations identify populations of divers and common scoters as most vulnerable to population-level impacts of displacement, but these are likely to be less evident than impacts of collision mortality. The collision and displacement indices developed here for Scottish marine bird populations could be applied to populations elsewhere, and this approach will help in identifying likely impacts of future offshore wind farms on marine birds and prioritising monitoring programmes, at least until data on macro-avoidance rates become available.

Environmental Samples Test Negative for Avian Influenza Virus H5N1 Four Months after Mass Mortality at A Seabird Colony.

High pathogenicity avian influenza (HPAI) profoundly impacted several seabird populations during the summers of 2021 and 2022. Infection spread rapidly across colonies, causing unprecedented mortality. At Foula, Shetland, 1500 breeding adult great skuas Stercorarius skua, totalling about two tonnes of decomposing virus-laden material, died at the colony in May-July 2022. Carcasses were left where they died as Government policy was not to remove dead birds. The factors influencing risk of further spread of infection are uncertain, but evidence suggests that HPAI can persist in water for many months in cool conditions and may be a major transmission factor for birds living in wetlands. We investigated risk of further spread of infection from water samples collected from under 45 decomposing carcasses and in three freshwater lochs/streams by sampling water in October 2022, by which time the great skua carcasses had rotted to bones, skin, and feathers. No viral genetic material was detected four months after the mortality, suggesting a low risk of seabird infection from the local environment when the seabirds would return the next breeding season. These findings, although based on a relatively small number of water samples, suggest that the high rainfall typical at Shetland probably washed away the virus from the decomposing carcasses. However, limitations to our study need to be taken on board in the design of environmental monitoring at seabird colonies during and immediately after future outbreaks of HPAI.

Individual variation in biomarkers of health: influence of persistent organic pollutants in Great skuas (Stercorarius skua) breeding at different geographical locations.

Persistent organic pollutants (POPs) have been shown to cause adverse effects on a number of biomarkers of health in birds. POPs may impair immune function and alter the stress response, defined as a suite of behavioral and physiological responses to environmental perturbations. Recent studies have also proposed that POPs can induce oxidative stress. Nevertheless, there is a lack of studies simultaneously assessing the potential damaging effects of POPs on the latter biomarkers. In this study, we examined the contribution of legacy (organochlorines; (OCs)) and emerging (flame retardants; PBDEs) POPs to individual variations in stress levels (feather corticosterone), humoral immunity (plasma immunoglobulin Y levels) and oxidative stress occurring in three breeding colonies of a top predator seabird, the Great skua (Stercorarius skua), distributed from temperate regions to the high Arctic: Shetland (60°N), Iceland (63°N) and Bjørnøya (74°N). Our results demonstrated that plasma concentrations of OCs in Great skuas from Bjørnøya are among the highest in North Atlantic seabirds, with up to 7900 µg/kg (ww) ∑OCs. Yet, a latitudinal gradient in POP levels was observed with all compounds being significantly higher in Bjørnøya than in Iceland and Shetland (on average 4-7 fold higher for OCs and 2.5-4.5 for PBDEs, respectively). Contrary to our predictions, skuas breeding at the least contaminated site (i.e., Shetland) experienced the poorest physiological condition; i.e., the highest levels of stress hormones (25% higher) and oxidative stress (50% higher) and the lowest immunoglobulin levels (15% lower) compared to the two other colonies. Finally, our results failed to point out consistent within-colony relationships between biomarkers of health and POPs. Overall, it is suggested that other ecological factors such as food availability could constrain physiological indicators more than anthropogenic contaminants.

Mercury levels and health parameters in the threatened Olrog's Gull (Larus atlanticus) from Argentina.

Mercury (Hg) exposure was investigated through feathers of Olrog's Gull and related to health parameters in adults (hematocrit, total plasma proteins, morphometric measures, sex) and chicks (hematocrit, total plasma proteins, immunoglobulins G and M) from a colony located in estuary of Bahía Blanca, Argentina. Mercury concentrations were 5.50 ± 2.59 µg g⁻¹ (n = 44) in live adults, 1.85 ± 0.45 µg g⁻¹ (n = 45) in live chicks and 1.81 ± 0.41 µg g⁻¹ (n = 41) in dead chicks. Large differences were observed between live adults and live or dead chicks and small differences between live and dead chicks. In the adults, the sex of the birds was the variable that best explained Hg concentrations. Male birds had higher concentrations than females; this suggests that the clutch provides a sink for mercury during egg laying. Hg concentrations in both adults and live chicks were associated with higher hematocrits. This could be associated with upregulated erythropoiesis to compensate for increased rate of destruction of prematurely senescent, Hg-contaminated erythrocytes. Based on our results, on the levels of Hg pollution in the past in the study area, and on the dietary specialization of Olrog's Gull, we must be vigilant about potential negative effects of Hg pollution on this population and recommend continued monitoring on this threatened species.

Effects of Sitka spruce masting on phenology and demography of siskins Spinus spinus.

Masting behaviour of Sitka spruce Picea sitchensis may influence Eurasian siskin Spinus spinus breeding ecology as breeding siskins specialize on spruce seeds. We caught siskins and other small passerines over 16 years using mist nets adjacent to large plantations of mature Sitka spruce. We sexed, aged, measured and weighed the birds and collected feather samples from fledglings to measure nitrogen and carbon stable isotope ratios. Siskins departed in late summer, and returned, and bred earlier in years of higher cone abundance. Nitrogen and carbon isotopes indicated that siskins fed their chicks on Sitka spruce seeds in most years, and more so in years of high cone production. More siskins were caught following heavy rainfall, when the cones had closed, encouraging the birds to seek alternative food sources. Fledglings were not heavier or larger in years with higher cone crops but were more numerous. However, the age ratio of siskins caught the following year was unaffected by cone crop. Given their reliance on Sitka spruce seeds, climate change may have a major impact on siskin numbers by altering the availability of Sitka spruce seeds, either through changes in masting patterns or cone opening, or due to climate-related changes in forestry practices. Siskins represent a valuable study system to conservation ecology, where a native species is ecologically reliant on introduced taxa.

Risks to different populations and age classes of gannets from impacts of offshore wind farms in the southern North Sea.

The southern North Sea holds the world's highest concentration of offshore wind farms (OWFs). Northern gannets (Morus bassanus), a species considered at high risk from OWF impacts, show a strong seasonal peak there in November, but it is unclear which populations and age classes are most at risk of collision with wind turbines. We tagged adult and juvenile gannets at the world's largest colony (Bass Rock) and reviewed two sources of survey data for different age classes to study their movements through southern North Sea waters. Tracked birds showed peak numbers in the southern North Sea in mid-October, with much smaller numbers there during November. Adults were distributed throughout the area, including waters close to OWFs, whereas juveniles were confined to the coast. Survey data indicated high proportions of immature gannets in southern North Sea waters, suggesting higher collision risk than for adults. Gannets present in November may be predominantly from colonies further north than Bass Rock.

Moving polewards in winter: a recent change in the migratory strategy of a pelagic seabird?

BACKGROUND: During the non-breeding period, many birds migrate to milder areas, found closer to the equator than their breeding sites. Opposite movements are very rare. In the Southern Ocean, the abundance of 13C declines markedly with more southern latitude, providing a characteristic 13C isoscape. This can be used as a tracer for the movement of seabirds between breeding and inter-breeding areas, by comparing stable isotope ratios of feathers grown at different times of the year. RESULTS: We studied seasonal movements of Thin-billed prions (Aves, Procellariiformes), breeding at the Subantarctic Falkland/Malvinas Islands, compared with those of Wilson's storm-petrels breeding in the Antarctic South Shetland Islands. The two species showed opposite migratory movements. While Wilson's storm-petrels moved to warmer waters north of the Drake Passage in winter, Thin-billed prions showed a reversed movement towards more polar waters. Carbon stable isotope ratios in recent and historical feathers indicated that poleward winter movements of Thin-billed prions were less common historically (45% in 1913-1915), and have only recently become dominant (92% in 2003-2005), apparently in response to warming sea temperatures. CONCLUSIONS: This study shows that pelagic seabirds can rapidly change migration strategies within populations, including migration towards more poleward waters in winter.

Black and white--does melanin change the bulk carbon and nitrogen isotope values of feathers?

Bird feathers are employed in a wide range of carbon and nitrogen isotope studies relating to diet and migration. Feathers are chemically inert with respect to carbon and nitrogen, after synthesis. It has always been assumed that feathers show isotope values characteristic of keratin, a fibrous structural protein from which they are formed. Little attention has been paid to other components of feathers such as melanin or carotenoids. Melanin is synthesized from tyrosine, which is depleted in both (13)C and (15)N. We compared isotope values of coeval black and white feathers in four different species. Black feather parts were in all cases significantly depleted in (13)C relative to white feather parts but in most species no clear trend was discernable for (15)N. We suggest that additional evaluation may be required to characterize the carbon and nitrogen isotope contribution of feather pigments like carotenoids. Care should be taken in future stable isotope studies when comparing differently coloured feathers.

Changes in fisheries discard rates and seabird communities.

It is clear that discards from commercial fisheries are a key food resource for many seabird species around the world. But predicting the response of seabird communities to changes in discard rates is problematic and requires historical data to elucidate the confounding effects of other, more 'natural' ecological processes. In the North Sea, declining stocks, changes in technical measures, changes in population structure and the establishment of a recovery programme for cod (Gadus morhua) will alter the amount of fish discarded. This region also supports internationally important populations of seabirds, some of which feed extensively, but facultatively, on discards, in particular on undersized haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus). Here we use long-term data sets from the northern North Sea to show that there is a direct link between discard availability and discard use by a generalist predator and scavenger--the great skua (Stercorarius skua). Reduced rates of discarding, particularly when coupled with reduced availability of small shoaling pelagic fish such as sandeel (Ammodytes marinus), result in an increase in predation by great skuas on other birds. This switching of prey by a facultative scavenger presents a potentially serious threat to some seabird communities.

Differences in the stable isotope signatures of seabird egg membrane and albumen--implications for non-invasive studies.

In many bird species, egg membranes can be obtained non-invasively after the chicks have hatched, and stable isotope analysis of egg membranes can be used to study the diet and foraging distribution of these birds during egg formation. It has been suggested that the enrichment factors of albumen and egg membranes differ for 13C, but are similar for 15N. In this study, we compared carbon and nitrogen stable isotopes of the membranes and albumen of individual eggs of three wild seabird species, the Southern Rockhopper penguin Eudyptes chrysocome, the Imperial shag Phalacrocorax atriceps albiventer, and the Thin-billed prion Pachyptila belcheri. We also included chicken eggs for comparison. Egg membranes were generally enriched in 13C, compared with albumen. The difference varied between species, with 2.1 per thousand in Rockhopper penguins, 1.6 per thousand in Imperial shags, but only 0.5 per thousand in Thin-billed prions and 0.4 per thousand in chicken eggs. Egg membranes were slightly enriched in 15N in Imperial shags (0.9 per thousand) and chickens (0.5 per thousand), compared with albumen, while there was no difference for Thin-billed prions and Rockhopper penguins. The isotopic values of carbon and nitrogen were correlated between albumen and egg membranes of individual eggs, suggesting that egg membranes can be used reliably to investigate trophic differences between individuals, seasons or colonies. Species-specific mathematical corrections could be used to compare results across studies that use different egg components.

Behavioural plasticity in the early breeding season of pelagic seabirds - a case study of thin-billed prions from two oceans.

BACKGROUND: In long-lived seabirds that migrate large distances independently of each other, the early part of the breeding season is crucially important for a successful reproductive attempt. During this phase, pair bonds are re-established and partners coordinate their breeding duties. We studied the early breeding season in Thin-billed prions Pachyptila belcheri breeding in the Atlantic Ocean (Falkland/Malvinas Islands) and Indian Ocean (Kerguelen). Despite overlap in the wintering areas, these two populations exhibit differences in their timing and direction of migration. We hypothesised that these differences would influence behaviour during the early breeding season. RESULTS: In line with our hypothesis, we found very strong differences in colony attendance patterns. Thin-billed prions of the Falkland population spent the late winter period over shelf waters close to the colony, first arrived back at the colony in September, and attended the nests interruptedly for one month, before departing on a pre-laying exodus. In contrast, Kerguelen birds remained in the non-breeding areas until mid-October and spent much less time attending the burrow before their pre-laying exodus. Despite this asynchronous arrival to the two colonies, the subsequent patterns resulted in remarkably synchronous incubation in both populations, with males taking on the first long incubation shift in late November, whereas females returned to sea soon after egg laying. During the pre-laying exodus and incubation, Thin-billed prions from the Falklands spread north over the Patagonian Shelf, while prions from Kerguelen travelled much further, reaching southern oceanic waters and moved at faster speeds (> 400 km per day). Although prions from Kerguelen moved much further, their isotopic niches were considerably narrower, suggesting a stronger dependence on Antarctic waters. CONCLUSIONS: The study thus suggests that Thin-billed prions show a high intraspecific plasticity in their use of either neritic or oceanic waters during the early breeding season. Breeding birds from the Falkland Islands can exploit an extensive shelf area, while Kerguelen birds have adapted to the need to forage in distant southern open waters. This difference in foraging ecology may thus have shaped the phenology of the early breeding phase.

The effect of long-range transport, trophic position and diet specialization on legacy contaminant occurrence in great skuas, Stercorarius skua, breeding across the Northeast Atlantic.

High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great skua (Stercorarius skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjørnøya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ15N values, and regurgitated pellets of undigested prey suggested that great skuas with higher δ15N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great skuas from colonies with lower δ15N and lower contaminant level fed mostly on fish. The enrichment of δ13C increased with decreasing δ15N and lower contaminant levels. Therefore, individual behavior of great skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.

Field validation, in Scotland and Iceland, of the artificial mussel for monitoring trace metals in temperate seas.

The artificial mussel (AM), a novel chemical sampling device, has been developed for monitoring dissolved trace metals in marine environments. The AM consists of Chelex-100 suspended in artificial seawater within Perspex tubing and enclosed with semi-permeable polyacrylamide gel at both ends. To validate the field performance of the AM in temperate waters, we deployed AMs alongside transplanted blue mussels Mytilus edulis in coastal environments in Scotland (Holy Loch, Loch Fyne, Loch Striven and Millport) and Iceland (Reykjavikurhöfn, Gufunes, South of thornerney, Hofsvik, Hvalfjörethur and Sandgerethi) for monitoring trace metals. While uptake patterns of Cd between the AM and M. edulis were highly comparable, discrepancies were found in the accumulation profiles of the other metals (Cu, Cr, Pb and Zn), in particular Zn. Nonetheless, the AMs gave a better resolution to accurately reveal the spatial difference in dissolved metal contamination when compared with M. edulis. AMs complement the use of mussels since AMs indicate dissolved metals in seawater, whereas uptake by mussels indicates a mixture of dissolved and particulate metals. Our results also indicated that historical metal exposure of the transplanted M. edulis could significantly confound their metal concentrations especially when the deployment period was short (i.e. <34d). This study suggested that the AM can overcome problems associated with variable biological attributes and pre-exposure history in the mussel, and provides a standardized and representative time-integrated estimate of dissolved metal concentrations in different marine environments.