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Plastic ingestion has been documented in a plethora of taxa. However, there is a significant gap in the detection of nano- and ultrafine particles due to size limitations of commonly used techniques. Using two Australian seabird species as case studies, the flesh-footed shearwater (FFSH)

Many species of seabird ingest or are provisioned with pumice stones, buoyant volcanic rocks that are thought to aide in digestion, occasionally during times of poor prey availability. Unlike other indigestible matter, like plastics, the effect of pumice on chick growth, its relationship with ingested plastics, and variation among years has not yet been examined. We analysed the amount of ingested pumice from 739 Flesh-footed (Ardenna carneipes) and 173 Wedge-tailed Shearwaters (A. pacifica) from Lord Howe Island, Australia sampled using stomach lavage between 2011 and 2022. The total mass of ingested pumice was positively related to the mass of ingested plastics in Flesh-footed, but not Wedge-tailed Shearwaters, but not when using mean stone mass. Pumice mass did not vary over time, except for one higher year for each species (2016 for Flesh-footed Shearwaters and 2014 for Wedge-tailed Shearwaters), and there was no effect of pumice mass on chick body size at fledgling. Our results are consistent with the coexistence over geological time of seabirds and floating pumice, and future work should focus on aspects of retention in the digestive system and potential interactions with and efficacy in the presence of novel materials, like plastics.

Extreme weather events are increasing in frequency, causing disruption to global ecosystems. Large-scale events, such as marine heatwaves, can impact the abundance of prey species, which consequently influences the behaviour of top-level predators such as seabirds. The short-tailed shearwater Ardenna tenuirostris is a trans-hemispheric migrant with typically a highly synchronous breeding phenology. Here, we document short-tailed shearwater colony occupancy for the period 2011-2020, with a focussed assessment of their breeding success in the 2019/20 season, which followed a marine heatwave that occurred predominantly in the non-breeding areas in the North Pacific Ocean. The return of the birds to their breeding colonies in southeast Australia was delayed by approximately 2 wk in October 2019, and the subsequent breeding season ended with only 34% breeding success, with nest abandonment beginning in the incubation phase. A North Pacific marine heatwave in 2019, associated with a mass mortality event of over 9000 birds (‘wreck’ of beach-washed birds), led to reduced adult body condition and carry-over effects causing egg and chick failures during the subsequent breeding season. Localised weather events (i.e. flooding of burrows due to heavy rainfall) also influenced breeding outcomes of the 2019/20 season. The relationship between wreck events and seabird breeding ecology is an understudied area, partly due to the difficulties around quantifying the scale of wrecks. Our study is one of few that documents poor seabird breeding success following the extreme marine conditions which have persisted in the North Pacific Ocean since 2013.

Graphic abstract In the age of the Anthropocene, the ocean has typically been viewed as a sink for pollution. Pollution is varied, ranging from human-made plastics and pharmaceutical compounds, to human-altered abiotic factors, such as sediment and nutrient runoff. As global population, wealth and resource consumption continue to grow, so too does the amount of potential pollution produced. This presents us with a grand challenge which requires interdisciplinary knowledge to solve. There is sufficient data on the human health, social, economic, and environmental risks of marine pollution, resulting in increased awareness and motivation to address this global challenge, however a significant lag exists when implementing strategies to address this issue. This review draws upon the expertise of 17 experts from the fields of social sciences, marine science, visual arts, and Traditional and First Nations Knowledge Holders to present two futures; the Business-As-Usual, based on current trends and observations of growing marine pollution, and a More Sustainable Future, which imagines what our ocean could look like if we implemented current knowledge and technologies. We identify priority actions that governments, industry and consumers can implement at pollution sources, vectors and sinks, over the next decade to reduce marine pollution and steer us towards the More Sustainable Future. Supplementary Information The online version contains supplementary material available at 10.1007/s11160-021-09674-8.

There is an absence of quantitative criteria and definitions for unusual or anomalous mortality events involving birds, often referred to as “wrecks”. These events most commonly involve seabirds, although terrestrial bird wrecks have also been documented. Typically, the peer-reviewed literature investigating wreck events lacks the details necessary to further our understanding of the circumstances and potential causes of these events. This study reviewed the peer-reviewed literature for wrecks involving Ardenna seabirds (shearwaters), and included grey literature and data collected by citizen science (community) groups. Our results showed a significant time-lag between wreck events and when the data was published in the peer-reviewed literature, which did not occur in the grey literature. Both the grey and peer-reviewed literature were often skewed towards reporting larger wreck events, with only the citizen science dataset capturing smaller wrecks. We outline a proposed framework for reporting mortality events, including the use of quantitative categories to document the numbers of birds involved and taxon-specific thresholds. In doing so, we aim to establish a framework to aid in the quantitative reporting and analyses of future seabird wrecks.

Coastlines, including estuaries, mudflats, and beaches, are particularly susceptible to plastic pollution, which can accumulate from both marine and terrestrial sources. While numerous studies have confirmed the presence of microplastics (1-5 mm) along coastlines, few have focused on very small particles (1 μm) or quantified exposure within the organisms that inhabit these areas, such as shorebirds. Here, we quantified small plastics (200 nm-70 μm) in two resident shorebird species in Tasmania, and compared this to quantities found in the surrounding sediments in order to investigate the potential exposure and transfer of particles within these ecosystems. Analysis was performed using a combination of flow cytometry for quantification of micro- and nanoplastics (200 nm-70 μm), and μm-FT-IR for validation and polymer identification of particles5.5 × 5.5 μm. Micro- and nano-plastics were detected in 100% of guano samples from surface-feeding Eastern Hooded Plovers (Thinornis cucullatus) and 90% of Australian Pied Oystercatcher (Haematopus longirostris) guano, a species that forages for coastal invertebrates at 60-90 mm depth, and 100% of beach sediments. Hooded Plover guano contained 32 × more plastics, on average, than Pied Oystercatcher guano. Interestingly, the abundance of plastic particles within sediments collected from shorebird foraging sites did not appear to have a significant effect on the number of plastics the birds had ingested, suggesting the difference between species is likely a result of other variables, such as prey selection. The results of this study highlight the importance of including techniques that provide quantitative data on the abundance and size of the smallest possible particle sizes, and demonstrate the significant proportion of small plastics that are 'missed' using standard analysis tools.

Plastic is an omnipresent pollutant in marine ecosystems and is widely documented to be ingested among seabird species. Procellariiformes are particularly vulnerable to plastic ingestion, which can cause internal damage, starvation, and occasionally mortality. In this study, 34 fledgling Fairy Prions (Pachyptila turtur) recovered during a wreck event in south-eastern Tasmania in 2022 were examined for ingested plastics and body condition (e.g., wing chord length). While many of the birds exhibited poor body condition, this was not correlated with the count or mass of ingested plastics. We hypothesise the marine heatwave event, and resulting lack of prey, contributed to bird body condition and subsequent mortality. We provide some of the first data on the size of individual plastic particles ingested by seabirds and make recommendations for future studies to report this important metric in a consistent manner that ensures data are comparable.

Flesh-footed shearwater (Ardenna carneipes) is recognized as vulnerable seabird species in Western Australia and New South Wales, Australia, and its genetic variability and a well-resolved phylogeny is imperative for the species’ conservation. Here, we report the first sequenced mitogenome of the Australian A. carneipes. The mitogenome of A. carneipes was 16,370 bp in total length and encompassed 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, and one non-coding region (D-loop). All of the genes were encoded on the H-strand with the exception of ND6 and eight tRNAs, which is a conserved pattern of the mitogenome for other vertebrates. The mitogenome of A. carneipes was dominated by higher AT (56.5%) than GC (43.5%) content. In the resulting phylogenetic tree using complete mitogenome sequences, flesh-footed shearwater and gray petrel (Procellaria cinerea) grouped together despite the high genetic distance (11.0%) between them, belonging to family Procellariidae. However, the phylogenetic tree was consistent with a previous study using partial nucleotide sequences of the cytochrome b gene. These results highlight that further mitogenome sequences will be required from the closely related species under the genus Ardenna to delineate well-resolved phylogenetic classification at the genus and or species level. The present study provides a reference mitochondrial genome of flesh-footed shearwater for further molecular studies.

We investigated the concentrations of 45 per- and polyfluoroalkyl substances (PFASs) in fledgling flesh-footed shearwater (Ardenna carneipes; n = 33) and wedge-tailed shearwater (A. pacifica; n = 9) livers via liquid chromatography-tandem mass spectrometry and their relationship to body morphometrics and ingested plastic mass recorded in 2019 on Lord Howe Island (NSW, Australia). Sixteen PFASs were detected, of which perfluorooctanesulfonate (PFOS) was the dominant compound, detected in 100% of birds (1.34-13.4 ng/g wet wt). Long-chain perfluorocarboxylic acids, including perfluorodecanoic acid (PFDA

Highlights: • First study to compare microplastic effects over a wide biogeographical range • Comparison between natural inorganic microparticles and plastic microparticles • Significant effects on byssus production, respiration and clearance rates, but small effect sizes • No ecologically relevant difference between impact of plastic and natural inorganic microparticles on Mytilidae Abstract: Microplastics are ubiquitous in the marine environment and studies on their effects on benthic filter feeders at least partly revealed a negative influence. However, it is still unclear whether the effects of microplastics differ from those of natural suspended microparticles, which constitute a common stressor in many coastal environments. We present a series of experiments that compared the effects of six-week exposures of marine mussels to two types of natural particles (red clay and diatom shells) to two types of plastic particles (Polymethyl Methacrylate and Polyvinyl Chloride). Mussels of the family Mytilidae from temperate regions (Japan, Chile, Tasmania) through subtropical (Israel) to tropical environments (Cabo Verde) were exposed to concentrations of 1.5 mg/L, 15 mg/L and 150 mg/L of the respective microparticles. At the end of this period, we found significant effects of suspended particles on respiration rate, byssus production and condition index of the animals. There was no significant effect on clearance rate and survival. Surprisingly, we observed only small differences between the effects of the different types of particles, which suggests that the mussels were generally equally robust towards exposure to variable concentrations of suspended solids regardless of whether they were natural or plastic. We conclude, that microplastics and suspended solids elicit similar effects on the tested response variables, and that both types of microparticles mainly cause acute responses rather than more persistent carry-over effects.

Here, we report the complete mitochondrial genome sequence of a seabird, wedge-tailed shearwater ( Ardenna pacifica ). The circular genome has a size of 16,434 bp and contains 13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes. The study provides a reference mitochondrial genome of wedge-tailed shearwater for further molecular studies.

Plastic pollution in the world's oceans is ubiquitous and increasing. The environment is inundated with microplastics ( 1 mm), and the health effects of these less conspicuous pollutants is poorly known. In addition, there is now evidence that macroplastics can release microplastics in the form of shedding or digestive fragmentation, meaning there is potential for macroplastic exposure to induce direct and indirect pathology through microplastics. Therefore, there is an urgent need for data from wild populations on the relationship between macro- and microplastic exposure and the potential compounding pathological effects of these forms of plastics. We investigated the presence and impact of microplastics in multiple tissues from Flesh-footed Shearwaters Ardenna carneipes, a species that ingests considerable quantities of plastics, and used histopathological techniques to measure physiological responses and inflammation from the plastics. All organs examined (kidney, spleen, proventriculus) had embedded microplastic particles and this correlated with macroplastic exposure. Considerable tissue damage was recorded, including a significant reduction in tubular glands and rugae in the proventriculus, and evidence of inflammation, fibrosis, and loss of organ structures in the kidney and spleen. This indicates macroplastics can induce damage directly at the site of exposure, while microplastics can be mobilised throughout the body causing widespread pathology. Collectively, these results indicate the scope and severity of the health impacts of plastic pollution may be grossly underestimated.

PUBLISHED IN REVIEWS IN FISH BIOLOGY AND FISHERIES: https://doi.org/10.1007/s11160-021-09674-8Kathryn A. Willis1,2,5†, Catarina S. Goncalves1,3, Kelsey Richardson1,2,5, Qamar A. Schuyler2, Halfdan Pedersen8, Kelli Anderson4, Jonathan Stark7, Joanna Vince1,5, Britta D. Hardesty2, Chris Wilcox2, Barbara Nowak4, Jennifer L. Lavers3, Jayson M. Semmens3, Dean Greeno1,6, Catriona MacLeod3, Per Ole Frederiksen (Nunnoq)9,10, Peter S. Puskic1,3*†1 Centre for Marine Sociology, University of Tasmania, Hobart, Tasmania, Australia2 CSIRO Ocean & Atmosphere, Hobart, Tasmania, Australia3 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia4 Institute for Marine and Antarctic Studies, Fisheries and Aquaculture, University of Tasmania, Newnham, Tasmania, Australia5 School of Social Sciences, College of Arts, Law and Education, University of Tasmania, Hobart, Tasmania, Australia6 School of Creative Arts and Media, College of Arts, Law and Education, University of Tasmania, Hobart, Tasmania, Australia7 Australian Antarctic Division, Hobart, Tasmania, Australia8 Pikkoritta Consultancy, Greenland9 The PSUNA Project, Qaasuitsup Municipality, Attu, Greenland10 Snowchange Cooperative, Selkie, Finland*Corresponding Author: Peter S. Puskic (peter.puskic@utas.edu.au), Centre for Marine Sociology & Institute for Marine and Antarctic Studies; University of Tasmania, Hobart, Tasmania, Australia.† P.S. Puskic and K.A. Willis share equal lead authorship on this paper.

Marine debris is distributed worldwide and constitutes an increasing threat to our environment. The exponential increase in the level of plastic debris raises numerous concerns and has led to an intensification in plastic monitoring and research. However, global spatial and temporal patterns and knowledge gaps in debris distribution, both on land and at sea, are relatively poorly understood, mainly due to a lack of comprehensive data sets. Here, we critically review the quality of the available information about beach plastic debris worldwide to highlight where the most urgent actions are required and to promote the standardization of reporting metrics and sampling methods among researchers. From a total of 174 studies evaluated, 27.0% reported marine debris densities in metrics that were not comparable. Some studies failed to report basic parameters, such as the date of the sampling (9.8%) or the size of the collected debris (19.5%). Our findings show that current research regarding beach debris requires significant improvement and standardization and would benefit from the adoption of a common reporting framework to promote consensus within the scientific community.

Plastic debris is a major global threat to marine ecosystems and species. However, our knowledge of this issue may be incomplete due to a lack of a standardized method for quantifying ingested ultrafine particles (1 μm - 1 mm) in wildlife. This study provides the first quantification of ultrafine plastic in seabirds using chemical and biological digestion treatments to extract plastic items from seabird gizzards. The alkaline agent, potassium hydroxide, outperformed the enzyme corolase, based on cost and efficiency (e.g., digestion time). Ultrafine plastics were observed in 7.0% of Flesh-footed Shearwater (Ardenna carneipes) gizzards collected from Lord Howe Island, Australia and accounted for 3.6% of all plastic items recovered (13 out of 359 items). Existing methods for extracting ingested plastic from seabirds do not account for ultrafine particles, therefore our results indicate current seabird plastic loads, and the associated physical and biological impacts, are underestimated.

Marine debris is pervasive worldwide, and affects biota negatively. We compared the characteristics of debris incorporated within brown booby (Sula leucogaster) nests throughout their pantropical distribution by assessing the type, colour and mass of debris items within nests and in beach transects at 18 sites, to determine if nests are indicators of the amount of debris in local marine environments. Debris was present in 14.4% of nests surveyed, with the proportion of nests with debris varying among sites (range: 0-100%). There was minimal overlap between the type or colour of debris found in nests and on adjacent beaches at individual sites. This suggests that brown boobies do not select debris uniformly across their distribution. We propose that the nests of brown boobies can be used as a sentinel of marine debris pollution of their local environment.

Unlike records of plastic ingestion and entanglement in seabirds which date back to the 1960s, the literature regarding debris in bird nests is comparatively limited. It is important to identify standardised methods early so that data are collected in a consistent manner, ensuring that future studies can be comparable. Here, we outline a method that can be applied to photographs for estimating the proportion of visible debris at the surface of a nest. This method uses ImageJ software to superimpose a grid onto a photograph of a nest/s. The number of cells with and without debris are then counted. Our proposed method is repeatable, straightforward, and accessible. We optimised the method to estimate the level of visible debris in Northern Gannet (Morus bassanus) nests, however, with some modification (i.e., adjustment of grid cell size), it could be applied to other seabird species, and terrestrial birds, that incorporate debris within nests.

Marine animals that traverse coastal and offshore environments are potentially exposed to multiple sources of pollution. Baseline data of pollutant concentrations of these fauna are needed in remote areas as human populations grow and economic development increases because changes may affect local wildlife in unforeseen ways. Persistent organic pollutant (POPs) concentrations were quantified in an understudied seabird, the great-winged petrel (Pterodroma macroptera), that breeds in southern Western Australia. Organochlorine pesticides, polychlorinated biphenyls (PCBs), and novel brominated flame retardants (NBFRs) were measured in adults. Total POPs concentrations ranged 5.6–46.4 ng g−1 ww. The most frequently detected POPs were the dichlorodiethyltrichloroethane (DDT) metabolite 4,4'DDE, the PCB CB-28, and the BFR polybrominated diphenyl ether BDE-99. These results contribute to the limited POPs data in marine fauna in this remote region, and the Southern Hemisphere, adding to the growing body of evidence that remote regions are affected by global trends of POPs distributions.

Plastics are an environmental threat; however, their fate once in the pelagic environment is poorly known. We compare results from assessments of floating plastics in the South Pacific Ocean with accumulated beach plastics from Henderson Island. We also compare accumulated plastic mass on Henderson during 2015 and 2019 and investigate the presence of nanoplastics. There were differences between the size classes of beach and pelagic plastics, and an increase in microplastics (0.33–5 mm) on the beach between 2015 and 2019. Micro- and nanoplastics were found at all sites (mean ± SE: 1960 ± 356 pieces/kg dw). Across the whole beach this translates to >4 billion plastic particles in the upper 5 cm. This is concerning, particularly given Henderson is uninhabited and distant from urban centres (~2350 km from Pape'ete, French Polynesia). The vast number of small particles on Henderson may make nearshore filter feeders susceptible to ingestion and subsequent detrimental impacts.

The world's oceans are under increasing pressure from anthropogenic activities, including significant and rapidly increasing inputs of plastic pollution. Seabirds have long been considered sentinels of ocean health, providing data on physical and chemical pollutants in their marine habitats. However, long-term data that can elucidate important patterns and changes in seabird exposure to marine pollutants are relatively limited but are urgently needed to identify and support effective policy measures to reduce plastic waste. Using up to 12 years of data, we examined the benefits and challenges of different approaches to monitoring plastic in seabirds, and the relationship between plastic and body size parameters. We found the mass and number of ingested plastics per bird varied by sample type, with lavage and road-kill birds containing less plastic (9.17–9.33 pieces/bird) than beach-washed or otherwise dead birds (27.62–32.22 pieces/bird). Beached birds therefore provide data for only a particular subset of the population, mostly individuals in poorer body condition, including those severely impacted by plastics. In addition, the mass and number of plastics in beached birds were more variable, therefore the sample sizes required to detect a change in plastic over time were significantly larger than for lavaged birds. The use of lavaged birds is rare in studies of plastic ingestion due to ethical and methodological implications, and we recommend future work on ingested plastics should focus on sampling this group to ensure data are more representative of a population's overall exposure to plastics.

Seabirds are apex predators in the marine environment and well-known ecosystem engineers, capable of changing their terrestrial habitats by introducing marine-derived nutrients via deposition of guano and other allochthonous inputs. However, with the health of the world’s oceans under threat due to anthropogenic pressures such as organic, inorganic, and physical pollutants, seabirds are depositing these same pollutants wherever they come to land. Using data from 2018 to 2020, we quantify how the Flesh-footed Shearwater (Ardenna carneipes) has inadvertently introduced physical pollutants to their colonies on Lord Howe Island, a UNESCO World Heritage site in the Tasman Sea and their largest breeding colony, through a mix of regurgitated pellet (bolus) deposition and carcasses containing plastic debris. The density of plastics within the shearwater colonies ranged between 1.32 and 3.66 pieces/m2 (mean ± SE: 2.18 ± 0.32), and a total of 688,480 (95% CI: 582,409–800,877) pieces are deposited on the island each year. Our research demonstrates that seabirds are a transfer mechanism for marine-derived plastics, reintroducing items back into the terrestrial environment, thus making seabird colonies a sink for plastic debris. This phenomenon is likely occurring in seabird colonies across the globe and will increase in severity as global plastic production and marine plastic pollution accelerates without adequate mitigation strategies.

Global plastics production is increasing exponentially and contributing to significant pollution of the marine environment. Of particular concern is ingestion and entanglement risks for marine wildlife, including when items such as rope are incorporated into nest structures. These events are commonly documented using photographic and visual surveys, and each presents a number of challenges and benefits for species conservation and monitoring. Here we compare an invasive (i.e., removing debris from nests) and non-invasive (i.e., photographs) sampling method for quantifying nest debris using the silver gull (Chroicocephalus novahollandiae) as a case study. Overall, 17 debris items were detected in 9% of gull nests. While the use of photographs to monitor nest debris is increasingly popular, the invasive method detected one additional debris item not identified using photography. We therefore recommend caution for nest debris and other monitoring programs where identifying small or cryptic items may require a high level of skill.

Elevated concentrations of PFASs in the liver may pose a toxicological risk to bird species and humans that consume them. This study aimed to determine concentrations of 43 per- and polyfluoroalkyl substances (PFASs) in livers (n = 80) of Australian Shelducks (Tadorna tadornoides), Pacific Black Ducks (Anas superciliosa), and Teals (Anas sp.), as well as water and sediment from a remote Australian environment. Maximum concentrations of PFBA (1.9 ng L

Highlights: • Mussel BCI was 14% lower after exposure to PVC particles in comparison to red clay. • Byssus production, respiration and survival did not differ between particle types. • Mussels suffered little from the five-week particle exposure up to 150 mg l−1. Abstract: Effects of microplastics on marine taxa have become a focal point in marine experimental biology. Almost all studies so far, however, assessed the influence of microplastics on animals only in relation to a zero-particle group. Documented microplastic impacts may thus be overestimated, since many marine species also experience natural suspended solids as a stressor. Here, we compared the effects of polyvinyl chloride (PVC) and red clay (mean for both particles: ~12–14 μm) on the Mediterranean mussel Mytilus galloprovincialis across three particle concentrations (1.5, 15, 150 mg l−1). Exposure to PVC for 35 days lowered mussel body condition index by 14% in relation to clay, but no difference in byssus production, respiration and survival rates emerged between the two particle types. This suggests that the effects of synthetic particles on filter feeders may emulate those of natural suspended solids, and highlights the importance of including natural particles in microplastic exposure studies.

Latex balloons are a poorly-studied aspect of anthropogenic pollution that affects wildlife survival, aesthetic value of waterways, and may adsorb and leach chemicals. Pure latex needs to be vulcanised with sulphur and requires many additional compounds to manufacture high quality balloons. Yet, balloons are often marketed as "biodegradable", which is confusing to consumers. Due to the persistence of latex balloons in the environment and the lethal, documented threat to wildlife, degradation behaviours of latex balloons were quantified in freshwater, saltwater and industrial compost. Using the metrics mass change, ultimate tensile strength (UTS) and superficial composition via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), latex balloon degradation was documented for 16 weeks. Overall, latex balloons retained their original shape and size. Composted balloons lost 1-2% mass, but some balloons in freshwater gained mass, likely due to osmotic processes. Balloons' UTS decreased from 30.7 ± 10.8-9.5 ± 4.1 Newtons in water, but remained constant (34.3 ± 13.4 N) in compost. ATR-FTIR spectra illustrated compositional and temporal differences between treatments. Taken together, latex balloons did not meaningfully degrade in freshwater, saltwater, or compost indicating that when released into the environment, they will continue to contribute to anthropogenic litter and pose a threat to wildlife that ingest them.

© 2020 The Authors Plastic pollution in the oceans is a priority environmental issue. The recent increase in research on the topic, coupled with growing public awareness, has catalyzed policymakers around the world to identify and implement solutions that minimize the harm caused by plastic pollution. To aid and coordinate these efforts, we surveyed experts with scientific experience identified through their peer-reviewed publications. We asked experts about the most pressing research questions relating to how biota interact with plastic pollution that in turn can inform policy decisions and research agendas to best contribute to understanding and reducing the harm of plastic pollution to biota. We used a modified Horizon Scan method that first used a subgroup of experts to generate 46 research questions on aquatic biota and plastics, and then conducted an online survey of researchers globally to prioritize questions in terms of their importance to inform policy development. One hundred and fifteen experts from 29 countries ranked research questions in six themes. The questions were ranked by urgency, indicating which research should be addressed immediately, which can be addressed later, and which are of limited relevance to inform action on plastics as an environmental pollutant. We found that questions relating to the following four themes were the most commonly top-ranked research priorities: (i) sources, circulation and distribution of plastics, (ii) type of harm from plastics, (iii) detection of ingested plastics and the associated problems, and (iv) related economies and policy to ingested plastics. While there are many research questions on the topic of impacts of plastic pollution on biota that could be funded and investigated, our results focus collective priorities in terms of research that experts believe will inform effective policy and on-the-ground conservation.

Evidence is accumulating about the impacts of plastics on marine life. The prevalence of plastics in seabird nests has been used as an indicator of levels of this pollutant in the ocean. However, the lack of a framework for defining sample sizes and errors associated with estimating the prevalence of plastic in nests prevents researchers from optimising time and reducing impacts of fieldwork. We present a method to determine the confidence intervals for the prevalence of debris in seabird nests and provide, for the first time, information on the prevalence of these items in nests of the Hartlaub's gull Larus hartlaubii, the African penguin Spheniscus demersus, the great white pelican Pelecanus onocrotalus, and the white-breasted cormorant Phalacrocorax lucidus in South Africa. The method, based on observations and resampling simulations and tested here for nests of 12 seabird species from 15 locations worldwide, allows for straightforward hypothesis testing. Appropriate sample sizes can be defined by combining this method with a Bayesian approach. We show that precise estimates of prevalence of debris in nests can be obtained by sampling around 250 nests. Smaller sample sizes can be useful for obtaining rough estimates. For the Hartlaub's gull, the African penguin, the great white pelican, and the white-breasted cormorant, debris were present in 0.75%, 3.00%, 6.41%, and 25.62% of the respective nests. Our approach will help researchers to determine errors associated with the prevalence of debris recorded in seabird nests and to optimise time and costs spent collecting data. It can also be applied to estimate confidence intervals and define sample sizes for assessing prevalence of plastic ingestion by any organism.

Annual rates of plastic production have been increasing rapidly since the 1950s. Inadequate or improper disposal of plastic products has contributed to a significant increase in plastic debris in the world's oceans and a corresponding increase in the number of species negatively affected by this debris. Here we investigate trends in the type, amount, and colour of ingested plastic over time, and determine whether ingested plastic contributes to reduced health of Wedge-tailed Shearwaters (Ardenna pacifica) on Lord Howe Island, Australia. The results show no clear influence of ingested plastic on body condition, while trends in the prevalence, number, and mass of plastic items ingested per bird during 2005 and 2013-2018 were more variable. There was some evidence adult birds are selecting plastic by colour. Future monitoring of this pan-tropical seabird would provide a unique opportunity to gather data from multiple sites, concurrently.

SummaryInvasive rodents detrimentally affect native bird species on many islands worldwide, and rodent eradication is a useful tool to safeguard endemic and threatened species. However, especially on tropical islands, rodent eradications can fail for various reasons, and it is unclear whether the temporary reduction of a rodent population during an unsuccessful eradication operation has beneficial effects on native birds. Here we examine the response of four endemic land bird species on subtropical Henderson Island in the Pitcairn Island Group, South Pacific Ocean, following an unsuccessful rodent eradication in 2011. We conducted point counts at 25 sampling locations in 14 survey periods between 2011 and 2015, and modelled the abundance trends of all species using binomial mixture models accounting for observer and environmental variation in detection probability. Henderson Reed Warbler Acrocephalus taiti more than doubled in abundance (2015 population estimate: 7,194-28,776), and Henderson Fruit Dove Ptilinopus insularis increased slightly between 2011 and 2015 (2015 population estimate: 4,476–10,072), while we detected no change in abundance of the Henderson Lorikeet Vini stepheni (2015 population estimate: 554–3014). Henderson Crake Zapornia atra increased to pre-eradication levels following anticipated mortality during the operation (2015 population estimate: 4,960–20,783). A temporary reduction of rat predation pressure and rat competition for fruit may have benefitted the reed warbler and the fruit dove, respectively. However, a long drought may have naturally suppressed bird populations prior to the rat eradication operation in 2011, potentially confounding the effects of temporary rat reduction and natural recovery. We therefore cannot unequivocally ascribe the population recovery to the temporary reduction of the rat population. We encourage robust monitoring of island biodiversity both before and after any management operation to better understand responses of endemic species to failed or successful operations.

Data on the prevalence of anthropogenic debris in seabird nests can be collected alongside other research or through community science initiatives to increase the temporal and spatial scale of data collection. To assess the usefulness of this approach, we collated data on nest incorporation of debris for 14 seabird species from 84 colonies across five countries in northwest Europe. Of 10,274 nests monitored 12% contained debris, however, there was large variation in the proportion of nests containing debris among species and colonies. For several species, the prevalence of debris in nests was significantly related to the mean Human Footprint Index (HFI), a proxy for human impact on the environment, within 100 km of the colony. Collecting opportunistic data on nest incorporation of debris by seabirds provides a cost-effective method of detecting changes in the prevalence of debris in the marine environment across a large geographic scale.