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Indicators of seabird reproductive performance demonstrate the impact of commercial fisheries on seabird populations in the North Sea

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... 'Annual colony failure rate', that is, the percentage of colonies failing per year, per species (from Cook et al. 2014a). Cook et al. (2014a) quantify failure as when the mean annual productivity of a breeding colony is 0.1 or less chicks per pair, clutch or nest. ...
... 'Annual colony failure rate', that is, the percentage of colonies failing per year, per species (from Cook et al. 2014a). Cook et al. (2014a) quantify failure as when the mean annual productivity of a breeding colony is 0.1 or less chicks per pair, clutch or nest. The assessment value used for determining failure can be adjusted according to knowledge of the colony in question. ...
... The assessments for each species are constructed from a time series of annual estimates of breeding success at a sample of colonies. Missing annual observations were predicted using a Generalised Linear Model (GLM) framework with a binomial error structure (after Cook et al. 2014 and2014a). Breeding success for each colony in each year was calculated, and where this value was 0.1 or less chicks per pair, clutch or nest, the colony was assessed as having failed in that year. Breeding success or failure was modelled in relation to year and site, because not all sites were covered in all years. ...
Technical Report
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The inconsistency in the determination of the Good Environmental Status for species assessment under the first cycle of the EU’s Marine Strategy Framework Directive emerged in a harmonisation exercise. This exercise was launched with the species’ identification of MSFD Descriptor’s 1 concern and the collection of the operational or developing indicators and methods for the status assessment and classification of marine species. The latter was materialised with this report, by collecting information from several sources including the Regional Sea Conventions and the relevant marine and environment EU policies. The methodological standards and the threshold setting processes can be harmonised at three levels, to achieve consistent GES determination for the species assessed under the MSFD: i) MSFD criteria; ii) species groups, and iii) spatial scale. The next step will be to further evaluate the operability and suitability of these indicators and methods, associate them with data availability and propose the best possible option for the status classification of species at those three levels.
... Correlative analyses between sandeel fishing mortality in the Dogger Bank region (~100km from the UK coast) and kittiwake productivity at Flamborough and Filey Coast SPA revealed a similar negative relationship, but with a two year lag effect, suggesting a more complex link . Furthermore, kittiwake breeding success was negatively linked to fishery effort indices -denoted as a product of vessel size and the number of days spent in the area in Frederiksen et al. (2008) -and by the interaction between the sandeel population size and the proportion of the population harvested (Cook et al. 2014). ...
... rising Sea Surface Temperature (SST). In the North Sea, previous studies have provided support for a negative relationship between kittiwake breeding success and SST in February and March of the previous year (Cook et al. 2014;Frederiksen et al. 2004), and for a negative relationship between kittiwake adult survival and SST of the current year (Frederiksen et al. 2004). Further work reported negative correlations between winter SST and kittiwake productivity across multiple colonies in the UK (Frederiksen et al. 2007), and indicated that kittiwake breeding success in Britain and Ireland synchronised in relation to spatial aggregations of sandeels (Frederiksen et al. 2005b). ...
... The bottom-up effect of lagged spring SST on kittiwake productivity has been shown to vary in strength among colonies and regions. For example, several studies have found only weak support for an indirect link between SST and kittiwake productivity both in eastern Scotland (Eerkes-Medrano et al. 2017) and across Britain and Ireland (Carroll et al. 2015;Cook et al. 2014;Lauria et al. 2013Lauria et al. , 2012. Furthermore, at Fowlsheugh SPA, kittiwake breeding success was related to 0-group sandeel abundance only when two of the twelve years of data were removed from the analysis, indicating other factors were also important (Eerkes-Medrano et al. 2017). ...
Technical Report
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Offshore windfarms are seen as a key part of efforts to combat climate change. However, there are a number of significant concerns about the potential of these windfarms to have a negative impact on wildlife and biodiversity, particularly in relation to birds. This is of particular concern as the scale of offshore windfarm development expands so that the risk of reaching unacceptable levels of cumulative impacts also increases. This work has been undertaken on behalf of the Offshore Wind Strategic Monitoring and Research Forum (OWSMRF). The report presents a summary of existing evidence, and potential research opportunities, to better understand the population dynamics of black-legged kittiwakes and how their populations might respond to potential additional mortality from offshore windfarm development and conservation management measures. The intention is that this report provides a signpost towards research that can facilitate meaningful and precise cumulative impact assessments, and thus contribute to reducing uncertainty in decision making around offshore windfarm consenting in the next few years. Full report can be found here: https://hub.jncc.gov.uk/assets/c563bfa5-8177-4dc0-bcb3-4aeafef24b59
... An example is the black-legged kittiwake reference point (Table 3) in which breeding success is assessed relative to that expected under current environmental conditions (Cook, Dadam, Mitchell, Ross-Smith, & Robinson, 2014). Such reference points generally require a model to determine the expected state. ...
... Conservation objectives are generally framed in terms of population size (Croxall et al., 2012;Schipper et al., 2008), which is unlikely to be a particularly sensitive or timely indicator of stress. Some variables, such as reproductive success or offspring growth, provide an early indication of stress that could eventually translate into population changes (Cook et al., 2014). Thus, reference points based on these so-called "leading" or "threshold" indicators are likely to be more useful for timely adjustment of fishing activities than reference points based on population size alone (Cook et al., 2014;Hall & Mainprize, 2004). ...
... Some variables, such as reproductive success or offspring growth, provide an early indication of stress that could eventually translate into population changes (Cook et al., 2014). Thus, reference points based on these so-called "leading" or "threshold" indicators are likely to be more useful for timely adjustment of fishing activities than reference points based on population size alone (Cook et al., 2014;Hall & Mainprize, 2004). ...
Article
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Ecosystem‐based management of fisheries aims to allow sustainable use of fished stocks while keeping impacts upon ecosystems within safe ecological limits. Both the FAO Code of Conduct for Responsible Fisheries and the Aichi Biodiversity Targets promote these aims. We evaluate implementation of ecosystem‐based management in six case‐study fisheries in which potential indirect impacts upon bird or mammal predators of fished stocks are well publicized and well studied. In particular, we consider the components needed to enable management strategies to respond to information from predator monitoring. Although such information is available in all case‐studies, only one has a reference point defining safe ecological limits for predators and none has a method to adjust fishing activities in response to estimates of the state of the predator population. Reference points for predators have been developed outside the fisheries management context, but adoption by fisheries managers is hindered a lack of clarity about management objectives and uncertainty about how fishing affects predator dynamics. This also hinders the development of adjustment methods because these generally require information on the state of ecosystem variables relative to reference points. Nonetheless, most of the case‐studies include precautionary measures to limit impacts on predators. These measures are not used tactically and therefore risk excessive restrictions on sustainable use. Adoption of predator reference points to inform tactical adjustment of precautionary measures would be an appropriate next step towards ecosystem‐based management.
... The number of chicks that did not fledge was calculated by subtracting the number of fledglings from the total number of laid eggs. This response variable accounts for varying numbers of nests surveyed (Carroll et al., 2015(Carroll et al., , 2017Cook, Dadam, Mitchell, Ross-Smith, & Robinson, 2014) and can be transformed back to the number of fledged chicks per pair. ...
... explore the reasons for the regional differences in productivity trends. However, a later study by Cook et al. (2014) found a strong negative relationship between sandeel (Ammodytes spp.) fishing pressure and little tern breeding failure in the North Sea; most little tern North Sea colonies are in the southern region, particularly south-east England. The most intensive North Sea sandeel fishing area is the Dogger Bank, and this may affect the availability of larvae to foraging little terns breeding in the east of England (Cook et al., 2014). ...
... However, a later study by Cook et al. (2014) found a strong negative relationship between sandeel (Ammodytes spp.) fishing pressure and little tern breeding failure in the North Sea; most little tern North Sea colonies are in the southern region, particularly south-east England. The most intensive North Sea sandeel fishing area is the Dogger Bank, and this may affect the availability of larvae to foraging little terns breeding in the east of England (Cook et al., 2014). However, little terns also feed on other species including Clupeidae (Perrow, Gilroy, Skeate, & Tomlinson, 2011) and crustaceans (Davies, 1981). ...
Article
Little terns in the UK have undergone a population decline of 37 % over the last three decades despite protection efforts at their breeding sites during this time. In 2014, a five-year Little Tern Recovery Project was launched in the UK through the European Union LIFE + funding stream, deploying a more coordinated, comprehensive and strategic programme of conservation measures at 29 breeding sites across England and Wales. We compared little tern productivity (fledging probability per egg) during the project with that experienced in the five years prior to the project and included data from both project sites and reference sites. We found a positive relationship between productivity and colony size as well as differences in productivity between ‘northern’ and ‘southern’ regions of the UK, with colonies in the northern region doing better. There was a positive effect on productivity associated with the project’s enhanced measures, but this interacted negatively with colony size, such that increased productivity was only seen for colonies with ≤91 pairs (which comprised 90 % of our dataset). Although average modelled breeding success across all project sites during the project was low (0.37 chicks/pair), we found it was on average more than double (164 % increase) than it would have otherwise been in the absence of the enhanced management measures. For colonies with ≤91 pairs, the predicted increase was 208 %. However, for colonies >91 pairs, there was a predicted 20 % reduction in breeding success in the presence of enhanced management. This counter-intuitive result may be due to threats at larger sites already being managed as far as practicable prior to the project, and poor breeding success during the project being mainly due to stochastic, less manageable threats such as severe weather. In addition, fewer data were available to inform the model for larger colonies. Overall, we estimate that an additional 1,785 chicks fledged as a result of the project. Those that survive their first few years are expected to recruit back into the UK and Irish population, benefitting from the legacy of protection, habitat restoration and creation measures established as part of the project. However, a simple population model indicates that even if the elevated breeding success levels achieved by the project were maintained, the projected population decline between 2020–2050 would only be slowed by 30 %, so more needs to be done to achieve population stabilisation. However, the project’s beneficial impact has bought valuable time that can be used to further develop and deploy innovative solutions.
... Although the maximum foraging distance for kittiwakes is considered to be 120 km (Thaxter et al., 2012), GPS tracking has shown that kittiwakes from eastern England forage throughout this area (Figure 1b). Sandeels constitute up to 60% of kittiwake diet in this region (Furness & Tasker, 2000), and the fishery could exceed sustainable levels for kittiwakes (Cook, Dadam, Mitchell, Ross-Smith, & Robinson, 2014), so kittiwake populations may still be affected by the fishery. One such colony is at Flamborough Head and Bempton Cliffs Special Protection Area (SPA) in east Yorkshire (Figure 1a). ...
... To examine relationships with breeding success, generalized linear mixed models (GLMMs) were fitted, with binomial error and logit link function. The response variable was the number of fledged chicks (taken directly from the data) and failed chicks (estimated based on the assumption of two eggs per nest) each year, thus accounting for varying numbers of nests surveyed, and representing breeding success as 'fledging probability per egg' (Carroll et al., 2015;Cook et al., 2014). Owing to the limited dataset (28 observations), models were first fitted with single predictors to avoid overfitting. ...
... On the Isle of May, kittiwake productivity declined when an industrial sandeel fishery was active locally (Frederiksen et al., 2004). More widely, North Sea seabird productivity is sensitive to the proportion of sandeels taken by fisheries (Cook et al., 2014). The negative correlation found in the present study provides first evidence of a link between the Dogger Bank fishery and seabirds in the southern North ...
Article
• In the North Sea, sandeels provide a vital food source for breeding seabirds, but are also the target of an industrial fishery. GPS tracking suggests that the most productive fishing grounds overlap with foraging areas of black‐legged kittiwakes from eastern England, raising the prospect that the fishery could affect the birds. Rising sea temperatures also threaten sandeels, so kittiwake food supplies could be affected by local and larger‐scale processes. • Drivers of kittiwake breeding success at Flamborough Head and Bempton Cliffs Special Protection Area, the UK's largest colony, and one of the closest to the sandeel fishing grounds, were examined. Relationships between sandeel stocks, sea surface temperature and kittiwake breeding success were analysed with generalized linear mixed models and generalized linear models, with model performance assessed using the Akaike Information Criterion and R². • Higher kittiwake breeding success was associated with higher sandeel spawning stock biomass (SSB; biomass of sexually mature fish) the preceding winter (R² = 21.5%) and lower sandeel fishing mortality two years previously (R² = 22.3%). After temporal trends were removed, only the fishing mortality effect remained. Models with multiple predictors supported the importance of fishing mortality. Higher sandeel SSB was associated with lower temperatures (R² = 15.2–38.6%) and lower sandeel fishing mortality (R² = 24.2–26.1%). • Hence, lower temperatures and fishing mortality were positively associated with sandeel biomass, and higher sandeel biomass and lower fishing mortality were positively associated with kittiwake productivity. In light of worsening environmental conditions and declining sandeel and kittiwake populations, careful consideration should be given to the requirements of sandeel‐dependent predators when making fishery management decisions.
... Top predators, such as seabirds are often suggested as reliable indicators of climate driven ecosystem change because they are relatively easy to monitor and many are sensitive to changes in food supply, which itself responds to climate change (Durant et al., 2009;Hoegh-Guldberg and Bruno, 2010;Montevecchi, 1993). In particular seabird breeding success is often suggested as an indicator because this demographic parameter is easily and regularly monitored (Cook et al., 2014). Species at the base of the food web may also serve as ecological indicators when plankton characteristics such as biomass, abundance, and size are correlated with fish recruitment, biogeochemical cycles and regime shifts (Beaugrand, 2005). ...
... breeding success expressed as chicks per nest). GLMMs and generalized linear models have been used in other recent studies of seabird breeding success, colony abundance, and breeding failures (Carroll et al., 2015;Cook et al., 2014). Explanatory variables are described in Table 1. ...
... The use of such correlations is tempting because in some cases and at certain spatial and temporal scales environmental parameters, such as SST, significantly correlate with biological parameters. For example, phytoplankton abundance increases with warming SST in cooler areas of the North Atlantic (Richardson and Schoeman, 2004); North Sea sandeel recruitment decreases with warming temperatures (Arnott and Ruxton, 2002) and North Sea and eastern Scotland kittiwake breeding success correlates negatively with lagged winter SST (Cook et al., 2014;Frederiksen et al., 2007a). However, at smaller scales, the complexities of relationships become apparent. ...
Article
This study examined the inter-relationships between kittiwake breeding success and sandeel abundance, Calanus copepods, chlorophyll and temperature. The validity of past proxies of sandeel prey (Calanus and temperature) suggested in the literature was also examined. Winter temperature was not found to be a reliable indicator of the abundance of sandeel or lower trophic levels, although the present study did support past evidence for a dependence of kittiwake breeding success on local sandeel abundance as, with the exception of two years, there was a linear relationship with log age-0 sandeel abundance. The abundance of sandeel was positively linked to the dates of predicted peak egg abundance in C. finmarchicus and C. helgolandicus. This supported earlier evidence that the match with prey timing is important to sandeel recruitment. Neither Calanus species was associated with temperature in the February to March period nor in the April–May period, which may explain the lack of a temperature effect that propagates through the trophic levels. Consequently, although kittiwake breeding success appears to show some sensitivity and specificity to changes in their prey, this responsiveness was not found to extend to the lowest trophic level (Calanus abundance) or to temperature. As such kittiwake breeding success was not a reliable indicator of climate-driven changes in the local food web.
... Reduced breeding success and survival of Kittiwake breeding in the North Sea has been specifically linked to reduced sandeel availability . However, this relationship has not been established elsewhere, likely due to a combination of insufficient data on diet and demographic rates, notably in the Irish and Celtic seas (Cook et al., 2014;Frederiksen et al., 2007), and regional or colony specific variation in prey ecology and availability (Harris and Wanless, 1990;Olin et al., 2020). Climate change can also impact populations directly though adverse weather conditions, affecting chick Newell et al., 2015) and adult survival (Frederiksen et al., 2004c;Wanless et al., 2009). ...
... Both climate change and fishing activity can operate over large spatial scales and therefore impact multiple colonies within a region (Cook et al., 2014;Frederiksen et al., 2007). Greater regional representation of Kittiwake breeding success monitoring has enabled differences in productivity to be detected and linked to local sandeel prey availability (Frederiksen et al., 2005;Olin et al., 2020). ...
Article
Species face a multitude of stressors due to human activities, especially in marine environments. Seabirds are among the most threatened group of birds globally. A key challenge in their conservation is quantifying the impact of multiple interacting stressors on populations effectively, especially for species that undertake large-scale movements. We use the relatively well-studied Black-legged Kittiwake Rissa tridactyla as a case study to highlight knowledge gaps in demographic rates and how key stressors act on populations across different parts of their biogeographic range. From this starting point we provide a strategic approach to identify and prioritise data collection and research efforts from species and regions where data are currently lacking. Obtaining accurate and precise empirical data on demographic rates and movement will increase the pre-dictive accuracy, and realism, of population models, and confidence in how populations will respond to multiple stressors over the life and annual cycle, facilitating better management decisions.
... Several studies have shown correlations between abundance of forage fish stocks in the North Sea and seabird diet composition (Anderson et al. 2014, Church et al. 2018, Wanless et al. 2018. Many more show correlations with breeding success (Furness and Tasker 2000, Frederiksen et al. 2005, Danhardt and Becker 2011, Cook et al. 2014, Carroll et al. 2017, Vedder et al. 2019, JNCC 2020, Olin et al. 2020. Few show correlations with adult survival (Oro andFurness 2002, Davis et al. 2005), or breeding numbers (Jennings et al. 2012, Perkins et al. 2018, Miller et al. 2019, JNCC 2020. ...
... Diet plasticity may also explain why a seabird species may be a good bioindicator for a certain area, and not for others. In the North Sea, Black-legged Kittiwake rely almost exclusively on sandeels, and their breeding success is a good indicator of the sandeel stock ); however in the Celtic Sea other prey may be available, making this species less reliable as a quantitative indicator of sandeel abundance for this area (Cook et al. 2014). ...
... On a local to fine spatial scales, there has been a lot of work to relate SST with breeding success of kittiwakes (Frederiksen et al., 2005(Frederiksen et al., , 2007Scott et al., 2006;Cook et al., 2014a), with most recent studies suggesting that temperature affects the abundance and timing of sandeels and their prey, which in turn has complex implications for kittiwakes, which are surfacefeeders specializing on sandeels (Eerkes-Medrano et al., 2017;Wanless et al., 2018;Régnier et al., 2019). The relationships between SST and breeding success have been documented for other seabirds as well, including northern fulmar, Arctic tern, Atlantic puffin, and European shag (Durant et al., 2006;Borstad et al., 2011;Burthe et al., 2014;Cook et al., 2014a;Howells et al., 2017). ...
... On a local to fine spatial scales, there has been a lot of work to relate SST with breeding success of kittiwakes (Frederiksen et al., 2005(Frederiksen et al., , 2007Scott et al., 2006;Cook et al., 2014a), with most recent studies suggesting that temperature affects the abundance and timing of sandeels and their prey, which in turn has complex implications for kittiwakes, which are surfacefeeders specializing on sandeels (Eerkes-Medrano et al., 2017;Wanless et al., 2018;Régnier et al., 2019). The relationships between SST and breeding success have been documented for other seabirds as well, including northern fulmar, Arctic tern, Atlantic puffin, and European shag (Durant et al., 2006;Borstad et al., 2011;Burthe et al., 2014;Cook et al., 2014a;Howells et al., 2017). However, this mechanism of "trophic mismatch, " where warming SSTs may affect seabirds though temporal mismatch between prey availability and energy demands during breeding is still unclear and poses challenges, due to the interacting effects from other factors (e.g., weather events, ORE developments) (Mitchell et al., 2020). ...
Article
Full-text available
There is about to be an abrupt step-change in the use of our coastal seas, specifically by the addition of large-scale offshore renewable energy developments to combat climate change. Many trade-offs will need to be weighed up for the future sustainable management of marine ecosystems between renewables and other uses (e.g., fisheries, marine protected areas). Therefore, we need a much greater understanding of how different marine habitats and ecosystems are likely to change with both natural and anthropogenic transformations. This work will present a review of predictive Bayesian approaches from ecosystem level, through to fine scale mechanistic understanding of foraging success by individual species, to identify consistent physical (e.g., bottom temperature) and biological (e.g., chlorophyll-a) indicators of habitat and ecosystem change over the last 30 years within the North Sea. These combined approaches illuminate the feasibility of integrating knowledge across scales to be able to address the spatio-temporal variability of biophysical indicators to ultimately strengthen predictions of population changes at ecosystem scales across broadly different habitat types. Such knowledge will provide an effective baseline for more strategic and integrated approaches to both monitoring studies and assessing anthropogenic impacts to be used within marine spatial planning considerations.
... Two studies have attempted to calculate a productivity figure that would ensure a stable Kittiwake population (assuming survival remains the same). Frederiksen et al. (2004) suggested that the population on the Isle of May would need to achieve a productivity of 1.17 young/AON per year to stabilise the population, while Cook & Robinson (2010) concluded that productivity of 1.5 young/AON per year would be required to stabilise national breeding numbers, and that the mean productivity of 0.68 young/AON per year observed across 54 UK colonies between 1986 and 2008 would lead to a 25% reduction in population over 25 years. Cook & Robinson threshold. ...
... The mechanisms underlying change are likely to be complex and the various factors involved may be additive in their effect. For example, while industrial sandeel fisheries in the North Sea during 1990-98 consistently had a significant negative effect on Kittiwake productivity through reduced sandeel availability (Frederiksen et al. 2004;Cook et al. 2014), it is possible that this was exacerbating more significant, climate-driven changes in the marine food web, associated with changing sea temperatures and the timing and strength of ocean stratification (Beaugrand et al. 2003;Scott et al. 2006;van Deurs et al. 2009;Scott et al. 2010). ...
Article
Full-text available
Kittiwake Rissa tridactyla numbers declined across Britain & Ireland by 63% between 1986 and 2014. While the main focus of recent research has been on the causes of decline in large, northern colonies, losses towards the southern edge of the species' range have been no less worrying. Since the 1985-88 Seabird Colony Register, 58% of colonies in Kent, Sussex, Dorset, Devon, Cornwall and the Isles of Scilly have been abandoned. Numbers at remaining colonies have declined by 66% since the 1998-2002 Seabird 2000 survey. Breeding success across the region has been exceptionally poor, far below that required to maintain population size. Colonies elsewhere at the southern edge of the species' European range have also been abandoned or are declining, and modest increases around the southern North Sea and the Irish Sea fail to balance the losses. There is an urgent need for better annual productivity and population monitoring, and for a new national census.
... Here, we examine drivers of productivity for multiple seabird colonies, considering SST and stratification. We consider the black-legged kittiwake Rissa tridactyla (hereafter 'kittiwake'), as it is a sensitive indicator of environmental conditions , Cook et al. 2014. We focus on the UK and Ireland, which support around 14% of the biogeographic kittiwake population and for which population data are routinely collected (JNCC 2014). ...
... Therefore, numbers of fledged and failed chicks were modelled as a binomial response, with fledged chicks taken from the data, and failed chicks estimated as [(2 × nests) − fledged], based on the mean and modal UK kittiwake clutch size of 2 (range 1 to 3; Coulson & Porter 1985, Coulson 2011, thus preventing negative predictions and allowing prior weights to account for varying nest numbers. Hence, breeding success was modelled as chicks fledged per egg (Cook et al. 2014). To ensure results were robust to these assumptions, fledged chicks were also modelled as a Poisson response with an offset of log(nests); results were very similar to the binomial analysis (Supplement 3). ...
Conference Paper
The black-legged kittiwake (Rissa tridactyla) is one of the UK's most abundant seabirds but the population has declined by 60% since the 1980s. Declines have been linked to rising sea surface temperatures (SSTs) that are believed to affect recruitment and growth of the lesser sandeel (Ammodytes marinus), a key kittiwake prey species, in turn causing reduced breeding success. However, these relationships have often been derived from a small number of intensively-studied colonies from a geographically limited area, and analyses have primarily considered SST within arbitrarily-defined areas surrounding breeding colonies. Consequently, important national-scale drivers may not have been detected and oceanographic indices may not accurately reflect the conditions experienced. We have attempted to address these issues by using tracking data to estimate colony-specific foraging areas for eleven colonies. Estimates of SST, stratification strength, and stratification onset date from these areas were linked to colony productivity. Higher productivity was associated with lower SSTs and weaker early-year stratification. Climate change projections indicated that rising SSTs could drive substantial kittiwake productivity declines by the late 21st Century. Finally, food web components linking physical conditions to kittiwake productivity were explored using Continuous Plankton Recorder data. Higher productivity was associated with higher sandeel abundance, which in turn was associated with higher calanoid copepod abundance. Higher Calanus finmarchicus abundance was associated with later stratification and weaker early-year stratification, whilst higher Calanus helgolandicus abundance was associated with stronger stratification throughout the year. Hence, our analyses show how changing oceanographic conditions can influence kittiwake food webs, in turn influencing breeding success; further examination of such links should improve understanding of the threats posed by climate change.
... Here, we examine drivers of productivity for multiple seabird colonies, considering SST and stratification. We consider the black-legged kittiwake Rissa tridactyla (hereafter 'kittiwake'), as it is a sensitive indicator of environmental conditions , Cook et al. 2014. We focus on the UK and Ireland, which support around 14% of the biogeographic kittiwake population and for which population data are routinely collected (JNCC 2014). ...
... Therefore, numbers of fledged and failed chicks were modelled as a binomial response, with fledged chicks taken from the data, and failed chicks estimated as [(2 × nests) − fledged], based on the mean and modal UK kittiwake clutch size of 2 (range 1 to 3; Coulson & Porter 1985, Coulson 2011, thus preventing negative predictions and allowing prior weights to account for varying nest numbers. Hence, breeding success was modelled as chicks fledged per egg (Cook et al. 2014). To ensure results were robust to these assumptions, fledged chicks were also modelled as a Poisson response with an offset of log(nests); results were very similar to the binomial analysis (Supplement 3). ...
Article
Full-text available
As apex predators in marine ecosystems, seabirds may primarily experience climate change impacts indirectly, via changes to their food webs. Observed seabird population declines have been linked to climate-driven oceanographic and food web changes. However, relationships have often been derived from relatively few colonies and consider only sea surface temperature (SST), so important drivers, and spatial variation in drivers, could remain undetected. Further, explicit climate change projections have rarely been made, so longer-term risks remain unclear. Here, we use tracking data to estimate foraging areas for 11 black-legged kittiwake Rissa tridactyla colonies in the UK and Ireland, thus reducing reliance on single colonies and allowing calculation of colony-specific oceanographic conditions. We use mixed models to consider how SST, the potential energy anomaly (indicating density stratification strength) and the timing of seasonal stratification influence kittiwake productivity. Across all colonies, higher breeding success was associated with weaker stratification before breeding and lower SSTs during the breeding season. Eight colonies with sufficient data were modelled individually: higher productivity was associated with later stratification at 3 colonies, weaker stratification at 2, and lower SSTs at one, whilst 2 colonies showed no significant relationships. Hence, key drivers of productivity varied among colonies. Climate change projections, made using fitted models, indicated that breeding success could decline by 21 to 43% between 1961-90 and 2070-99. Climate change therefore poses a longer-term threat to kittiwakes, but as this will be mediated via availability of key prey species, other marine apex predators could also face similar threats.
... virtually no chicks being produced at a colony) across breeding sites and years, and produced an index of the frequency of breeding failure in a specific area. This indicator was shown to be more responsive to, for example, fisheries impacts than abundance-based indicators are (Cook et al. 2014). However, a challenge with this approach is interpretation: is the observed frequency of breeding failure actually a problem for the population? ...
Article
Vertebrate populations are often monitored as part of broader assessments of ecosystem status, where they are expected to provide information on the ability of the ecosystem to support higher‐level predators. However, because many vertebrates are long‐lived and often only subsets of their populations can be monitored, abundance may not be sufficiently responsive to ecosystem status to provide early warnings of impending changes. Marine birds are often used as indicators of ecosystem status but, due to their long lifespan and delayed recruitment to the breeding population, changes in abundance are generally slow and often difficult to interpret. Their breeding productivity is, however, also widely monitored and much more responsive to ecosystem status, but the relevance of variation in productivity may be difficult to assess. We propose a model‐based indicator that integrates monitoring of abundance and breeding productivity through demographic matrix models. The metric of the proposed indicator is the expected population growth rate, given the observed level of breeding productivity. This expected growth rate is then compared with a threshold derived from the criteria employed for red‐listing of threatened species by the International Union for the Conservation of Nature. We demonstrate the suggested approach using data from Black‐legged Kittiwakes Rissa tridactyla in the Greater North Sea region, Northwest Europe. The proposed indicator shows that the current level of breeding productivity is expected to lead to a population decline of 3–4% per year, which is equivalent to a red‐list status as Endangered for the species in this region. Our indicator approach is used in OSPAR's Quality Status Report 2023 and is expected to be used by European Union member states for reporting under the Marine Strategy Framework Directive in 2024. Our approach represents a major step forward in assessing the status of marine bird populations; the ideal next step would be to develop a coherent Integrated Population Modelling (IPM) framework that would allow inclusion of all data on population abundance and demography collected across the large and diverse marine ecosystems involved.
... With increasing interest for conservation of biodiversity, and increasing demands for food to feed expanding human populations, challenges arise to fish these waters, while keeping sufficient resources and space, for wildlife (e.g., Cury et al. (2011)). Many studies deal with direct competition for resources between humans and wildlife, such as the competition for forage fish and the demonstrated effects on reproduction and survival (e.g., Cook et al. (2014)). In addition to advocating prey biomass reservations for seabirds (Cury et al., 2011) there has been an increased focus on the spatial aspect of prey availability, for example in relation to seabird breeding sites to increase the efficiency of protective measures (e.g., Hentati-Sundberg et al. (2021)). ...
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Shallow coastal zones are intensely used by humans but simultaneously are biodiversity hotspots, with a crucial role in the life cycle of many marine species. The competition for food or space between humans and protected wildlife intensifies under pressure of an increased need for marine resources for human consumption. For successful management it is important to establish the key components driving such conflicts of interest. Here we focus on the protected common scoter (Melanitta nigra), a sea duck wintering in coastal habitats that are rich in food, but also among the most disturbed marine systems worldwide. Due to the scoters' shyness disturbance impacts the birds' ability to forage and poses a conflict for balancing bird conservation and economics, including a fishery on its main bivalve prey Spisula subtruncata. In this study, we use an energy budget model to quantify the consequences of depth, currents and disturbance on scoter energetics and carrying capacity. Energetics were described using physical parameters and field data on food availability and disturbance. Results reveal non-linear relationships and a threshold value for when a scoter can no longer maintain its energy balance. This is caused by limited foraging time, rather than food availability. From a conservation perspective, this implies that a precautionary principle should be used, because there will be no warning when an area becomes unsuitable. In addition, the model was applied to study the effects of disturbance from different kinds of shipping in a coastal area of the North Sea, north of The Netherlands. Cargo shipping has the largest impact on the carrying capacity, where there is spatial overlap of prey and an intensively used shipping lane. In other prey distribution situations shrimp vessels may cause most disturbance. Spisula-Ensis fisheries did not limit the potential carrying capacity due to the limited catches and number of fishing trips. Scoter protection should be aimed at flexible spatial management and on only those vessel types above a Spisula bed with a large number of trips, and above all should work from a precautionary principle given the critical thresholds for scoter presence.
... The impact of commercial fishing for sandeels on North Sea seabirds highly dependent on this prey species is also acknowledged (Frederiksen 2006, Cook et al. 2014 although there is no evidence so far that this has negatively impacted roseate terns. In the Irish Sea also, concerns have been expressed over commercial exploitation of forage fish, notably sprat, in relation to the long-term viability of colonies of roseate tern and other seabirds (Cummins et al. 2016). ...
... Fisheries around the world have been implicated in changes in seabird behaviour, energetics, demography and population dynamics (Frederiksen et al., 2008, Pichegru et al., 2012, Cury et al., 2011, Sherley et al., 2018. In the North Sea, rates of breeding failure in nine seabird species, including the four studied here, have been linked to their sensitivity to fishing pressure (Cook et al., 2014). However, quantifying the effect of fisheries management on seabird demography is inherently difficult, requiring large scale, quasi-experimental field data, ideally from both prey and seabird populations experiencing broadly similar environmental conditions (Frederiksen et al., 2008;Sydeman et al., 2017;Sherley et al., 2018). ...
... Furthermore, fisheries of low or intermediate trophic level such as forage fish have been shown to have strong impacts on upper trophic level species (Frederiksen et al., 2006;Wanless et al., 2007;Fauchald et al., 2011b;Smith et al., 2011;Lauerburg et al., 2018). As one of the indicators of fishing impact in the region, the abundance of fish sensitive to fisheries can also give an indication on possible other impacts of fisheries such as by-catch of untargeted species, damage to the seafloor, of disruption of the ecosystem food chain and size structure (Gislason, 1994;Bergman and van Santbrink, 2000;Rumohr and Kujawski, 2000;Cook et al., 2014;Church et al., 2019). The understanding of the consequences of a decline in biomass of species sensitive to fisheries for the rest of the ecosystem is assessed as good. ...
... If marine protected areas are able to encompass areas of spatiotemporal variation in key prey resources at an appropriate scale to marine predators their effectiveness is likely to be enhanced (Oppel et al., 2018). Many seabird species are recognised as indicators of ecosystem status (Cook et al., 2014;Sydeman et al., 2017;Tam et al., 2017) and used as barometers for assessing the health of marine ecosystems under statutory obligations in many countries (e.g. the EU Marine Strategy Framework Directive). Eliciting understanding of the relationships between environmental variation and key demographic processes in this community is, therefore, of prime importance to efforts to safeguard our oceans from the myriad of threats they currently face. ...
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Understanding how ecological processes combine to shape population dynamics is crucial in a rapidly changing world. Evidence has been emerging for how fundamental drivers of density dependence in mobile species are related to two differing types of environmental variation—temporal variation in climate, and spatiotemporal variation in food resources. However, to date, tests of these hypotheses have been largely restricted to mid‐trophic species in terrestrial environments and thus their general applicability remains unknown. We tested if these same processes can be identified in marine upper trophic level species. We assembled a multi‐decadal data set on population abundance of 10 species of colonial seabirds comprising a large component of the UK breeding seabird biomass, and covering diverse phylogenies, life histories and foraging behaviours. We tested for evidence of density dependence in population growth rates using discrete time state‐space population models fit to long time‐series of observations of abundance at seabird breeding colonies. We then assessed if the strength of density dependence in population growth rates was exacerbated by temporal variation in climate (sea temperature and swell height), and attenuated by spatiotemporal variation in prey resources (productivity and tidal fronts). The majority of species showed patterns consistent with temporal variation in climate acting to strengthen density dependent feedbacks to population growth. However, fewer species showed evidence for a weakening of density dependence with increasing spatiotemporal variation in prey resources. Our findings extend this emerging theory for how different sources of environmental variation may shape the dynamics and regulation of animal populations, demonstrating its role in upper trophic marine species. We show that environmental variation leaves a signal in long‐term population dynamics of seabirds with potentially important consequences for their demography and trophic interactions.
... With increasing interest for conservation of biodiversity, and increasing demands for food to feed expanding human populations, challenges arise to fish these waters, while keeping sufficient resources and space, for wildlife (e.g., Cury et al. (2011)). Many studies deal with direct competition for resources between humans and wildlife, such as the competition for forage fish and the demonstrated effects on reproduction and survival (e.g., Cook et al. (2014)). In addition to advocating prey biomass reservations for seabirds (Cury et al., 2011) there has been an increased focus on the spatial aspect of prey availability, for example in relation to seabird breeding sites to increase the efficiency of protective measures (e.g., Hentati-Sundberg et al. (2021)). ...
... declining reproductive success and colony size. 13,42 However, our study also demonstrates that the interaction between colony size and foraging range should not be ignored in any model that aims to extrapolate habitat use across colonies of different sizes. 13 Generalizable models, informed by ecological theory, are an important contribution to informing conservation for such species on a large spatial scale. ...
Article
Density-dependent prey depletion around breeding colonies has long been considered an important factor controlling the population dynamics of colonial animals.1, 2, 3, 4 Ashmole proposed that as seabird colony size increases, intraspecific competition leads to declines in reproductive success, as breeding adults must spend more time and energy to find prey farther from the colony.¹ Seabird colony size often varies over several orders of magnitude within the same species and can include millions of individuals per colony.⁵,⁶ As such, colony size likely plays an important role in determining the individual behavior of its members and how the colony interacts with the surrounding environment.⁶ Using tracking data from murres (Uria spp.), the world’s most densely breeding seabirds, we show that the distribution of foraging-trip distances scales to colony size⁰.33 during the chick-rearing stage, consistent with Ashmole’s halo theory.¹,² This pattern occurred across colonies varying in size over three orders of magnitude and distributed throughout the North Atlantic region. The strong relationship between colony size and foraging range means that the foraging areas of some colonial species can be estimated from colony sizes, which is more practical to measure over a large geographic scale. Two-thirds of the North Atlantic murre population breed at the 16 largest colonies; by extrapolating the predicted foraging ranges to sites without tracking data, we show that only two of these large colonies have significant coverage as marine protected areas. Our results are an important example of how theoretical models, in this case, Ashmole’s version of central-place-foraging theory, can be applied to inform conservation and management in colonial breeding species.
... Change in bird indicators (Marine birds: Non-breeding abundance (B1-A), Marine birds: breeding abundance (B1-B), Marine bird breeding success/failure (B3)) is driven by both climate change and fishing, with climate change having an indirect effect on birds through food supply (e.g. forage fish, which are responding to warming), while fishing directly removes fish as a food source for birds from the ecosystem (Cook et al., 2014;Frederiksen et al., 2004). The indicators for Recovery in the population abundance of sensitive fish species (FC1, Greenstreet et al., 2012), Proportion of large fish -Large Fish Index (FC2, Greenstreet et al., 2010), and Mean Maximum Length of fish (FC3, Greenstreet and Rogers, 2006) were constructed to be responsive to the effects of fishing. ...
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The Northeast Atlantic, a highly productive maritime area, has been exposed to a wide range of direct human pressures, such as fishing, shipping, coastal development, pollution, and non-indigenous species (NIS) introductions, in addition to anthropogenically-driven global climate change. Nonetheless, this regional sea supports a high diversity of species and habitats, whose functioning provides a variety of ecosystem services, essential for human welfare. In 2017, OSPAR, the Northeast Atlantic Regional Seas Commission, delivered an assessment of marine biodiversity for the Northeast Atlantic. This assessment examined biodiversity indicators separately to identify changes in Northeast Atlantic biodiversity, but stopped short of determining the status of biodiversity for many species and habitats. Here, we expand on this work and for the first time, a semi-quantitative approach is applied to evaluate holistically the state of Northeast Atlantic marine biodiversity across marine food webs, from plankton to top predators, via fish, pelagic and benthic habitats, including xeno-biodiversity (i.e. NIS). Our analysis reveals widespread degradation in marine ecosystems and biodiversity, particularly for marine birds and coastal bottlenose dolphins, as well as for benthic habitats and fish in some regions. The poor biodiversity status of these ecosystem components is likely the result of cumulative effects of human activities, such as habitat destruction or disturbance, overexploitation, eutrophication, the introduction of NIS, and climate change. Bright spots are also revealed, such as recent signs of recovery in some fish and marine bird communities and recovery in harbour and grey seal populations and the condition of coastal benthic communities in some regions. The status of many indicators across all ecosystem components, but particularly for the novel pelagic habitats, food webs and NIS indicators, however, remains uncertain due to gaps in data, unclear pressure-state relationships, and the non-linear influence of some pressures on biodiversity indicators. Improving monitoring and data access and increasing understanding of pressure-state relationships, including those that are non-linear, is therefore a priority for enabling future assessments, as is consistent and stable resourcing for expert involvement.
... Previously environmentally mediated variability in prey availability has been shown to influence the non-breeding distributions of seabirds and which have led to carry-over effects into the proceeding breeding season [21][22][23][24][25][26] . Therefore, if fisheries influence the availability of the seabirds' prey outside the breeding season it will likely influence non-breeding seabirds' foraging behaviour, in a similar way as fisheries influence the foraging behaviour and breeding success of breeding seabirds [27][28][29] . ...
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The population of the Endangered African penguin Spheniscus demersus has decreased by > 65% in the last 20 years. A major driver of this decrease has been the reduced availability of their principal prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. To date, conservation efforts to improve prey availability have focused on spatial management strategies to reduce resource competition with purse-seine fisheries during the breeding season. However, penguins also undergo an annual catastrophic moult when they are unable to feed for several weeks. Before moulting they must accumulate sufficient energy stores to survive this critical life-history stage. Using GPS tracking data collected between 2012 and 2019, we identify important foraging areas for pre- and post-moult African penguins at three of their major colonies in South Africa: Dassen Island and Stony Point (Western Cape) and Bird Island (Eastern Cape). The foraging ranges of pre- and post-moult adult African penguins (c. 600 km from colony) was far greater than that previously observed for breeding penguins (c. 50 km from colony) and varied considerably between sites, years and pre- and post-moult stages. Despite their more extensive range during the non-breeding season, waters within 20 and 50 km of their breeding colonies were used intensively and represent important foraging areas to pre- and post-moult penguins. Furthermore, penguins in the Western Cape travelled significantly further than those in the Eastern Cape which is likely a reflection of the poor prey availability along the west coast of South Africa. Our findings identify important marine areas for pre- and post-moult African penguins and support for the expansion of fisheries-related spatio-temporal management strategies to help conserve African penguins outside the breeding season.
... The apparent competition for forage fish between industrial fisheries and marine top predators is one such conflict that has been difficult to resolve due to a lack of knowledge of the prey requirements for top predators and how they vary over time and space (Cury et al., 2011;Furness & Tasker, 2000;Grémillet et al., 2018;Hill et al., 2020;Sydeman et al., 2017). Despite the well-known fact that forage fish fisheries can affect reproduction and survival of marine top predators (Bertrand et al., 2012;Cook et al., 2014), management measures to protect their prey are relatively rare (but see for example North Sea: Frederiksen et al., 2008;Namibia: Ludynia et al., 2012;South Africa: Sherley et al., 2015). Furthermore, it is unknown whether targets commonly used to ensure sustainable exploitation of fish stocks, that is, maintaining biomasses (B) corresponding to Maximum Sustainable Yield (MSY) or a precautionary approach (PA;Jennings et al., 2001;List of Abbreviations), are compatible with top predator conservation (Cury et al., 2011). ...
Article
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Conflicts of interest between resource extraction and conservation are widespread, and negotiating such conflicts, or trade‐offs, is a key issue for ecosystem managers. One such trade‐off is resource competition between fisheries and marine top predators. Managing this trade‐off has so far been difficult due to a lack of knowledge regarding the amount and distribution of prey required by top predators. Here, we develop a framework that can be used to address this gap: a bio‐energetic model linking top predator breeding biology and foraging ecology with forage fish ecology and fisheries management. We apply the framework to a Baltic Sea colony of common guillemots Uria aalge and razorbills Alca torda, two seabird species sensitive to local prey depletion, and show that densities of forage fish (sprat Sprattus sprattus and herring Clupea harengus) corresponding to the current fisheries management target BMSY are sufficient for successful breeding. A previously proposed fisheries management target for conserving seabirds, 1/3 of historical maximum prey biomass (B1/3), was also sufficient. However, the results highlight the importance of maintaining sufficient prey densities in the vicinity of the colony, suggesting that fine‐scale spatial fisheries management is necessary to maintain high seabird breeding success. Despite foraging on the same prey, razorbills could breed successfully at lower prey densities than guillemots but needed higher densities for self‐maintenance, emphasizing the importance of considering species‐specific traits when determining sustainable forage fish densities for top predators. Synthesis and applications. Our bio‐energetic modelling framework provides spatially explicit top predator conservation targets that can be readily integrated with current fisheries management. The framework can be combined with existing management approaches such as dynamic ocean management, marine spatial planning and management strategy evaluation to inform ecosystem‐based management of marine resources.
... The Common Guillemot Uria aalge (hereafter Guillemot) is one of the most abundant and well-studied seabirds in the North Atlantic and North Pacific (Gaston & Jones 1998, Ainley et al. 2002. Breeding success is monitored at colonies throughout much of the range, and the results used as indicators of local marine conditions and integrated into multicolony analyses to provide information at regional scales (Boekelheide et al. 1990, Cook et al. 2014, JNCC 2015b, Dragoo et al. 2018, Anker-Nilssen et al. 2018, Perkins et al. 2018). Estimating the breeding success of Guillemots is very time consuming. ...
Article
Capsule: A data-thinning approach was used to assess the effects of reducing the frequency of nest-checks on estimates of breeding success of Common Guillemots Uria aalge. Inter-year and inter-colony differences in fledging age and their implications for setting a minimum age after which a chick could be assumed to have fledged were evaluated. Aims: To assess the consequences of reducing sampling frequency on the estimation of breeding success, and on the robustness of the assumption that breeding has been successful if a chick survives to 15 days old. Methods: Breeding success, ages at fledging and loss of chicks were estimated from daily checks at two Scottish colonies over a six-year period. Data-thinning was used to assess the consequences of reducing checks from daily to every two or three days. Breeding success was recalculated assuming that all chicks surviving to 15 days fledged. Results: Reducing the frequency of checks from daily to every second or third day resulted in a small but statistically significant increase in the estimate of success. Between 20% and 25% of chick losses occurred when chicks were ≥15 days old. Assuming that these chicks had fledged resulted in significant increases in breeding success. Conclusion: Assumptions about whether or not a chick fledged had a greater impact on the estimate of breeding success than reducing the frequency of nest-checks from daily to every second or third day. There was no threshold age after which a chick could be assumed to have fledged. These findings are relevant to other monitoring schemes where there is pressure to reduce input. Sampling methods used in monitoring schemes need to be clearly stated and changes in protocols documented so that sampling effects can be incorporated into future analyses.
... It is important to note that the relationship between SST and breeding success is apparent in other seabirds, including northern fulmar, Atlantic puffin and Arctic tern (Burthe et al., 2014;Cook et al., 2014a). Reed et al. (2015) demonstrated that average frequency of skipped breeding in common guillemots was greater in years where SST was higher. ...
Chapter
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EXECUTIVE SUMMARY • The seabird declines that commenced at the end of the last century have continued during the last two decades. • Further research into the causes of these declines is required if we are to fully understand the complex mechanisms operating, which are known to vary geographically. Climate change is considered to be one of the main causes of the declines. The principal mechanism is the effect of climate warming on food supply. • There is growing evidence that short-term weather conditions have an important effect, including extreme weather events. Climate models predict further warming and increased severity and frequency of extreme weather events in UK waters. • Seabirds face an uncertain future and may decline further in the coming decades, as the interacting effects of new and existing influences will pose additional challenges.
... This indicates a coupling between the 0-group strength and the kittiwake breeding success. Kittiwakes are widely used as indicators of marine ecosystem status (Hamer et al., 1993;Frederiksen et al., 2007a;Wanless et al., 2007;Cook et al., 2014;Hátún et al., 2017b). Similar fluctuations are furthermore identified in a broad selection of higher trophic level records from the Faroe shelf Steingrund and Gaard, 2005;ICES, 2018). ...
Article
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Comprehensive late June surveys have for decades been carried out on the Faroe shelf in order to estimate the abundance of juvenile fish – the 0-group. The abundance of cod juveniles has previously been used in recruitment studies, while the ecological implication of the 0-groups has hitherto received less attention. Here we examined the pelagic 0-group stage in four of the main fish species on the Faroe shelf: cod, haddock, Norway pout and sandeel, representing more than 90% of all juvenile fish on the shelf. A positive relationship between length and abundance at the 0-group stage is observed for all juveniles, and the inter-annual variability was highly similar among the four fish species. Based on this knowledge, we produced a new ecological indicator for the central Faroe shelf ecosystem – the 0-group length index. The 0-group length index is characterized by marked peaks in 1984, 1987, 1994, 2000, 2009, and 2017, which appear to be related to the shelf primary production from spring to mid-summer, and possibly to the marine climate surrounding the Faroe shelf. There is a better temporal overlap between the fish larvae and their prey (i.e., small- to medium sized zooplankton) in years with an early and intensive bloom, while late and/or weak blooms lead to unfavorable feeding conditions. We furthermore show that a large abundance of 0-group fish has the potential to graze down and thus regulate the biomass of large-sized zooplankton during late June. In addition to this top-down influence the 0-group fish clearly impact commercial fish stocks and seabird colonies, and our 0-group length index is therefore a key ecological indicator for the state of the entire central Faroe shelf ecosystem.
... This in turn has had negative consequences for upper trophic level consumers such as seabirds and marine mammals, which were previously reliant on the large biomass and high lipid content characteristics of these fish (Wanless et al., 2005;Frederiksen et al., 2006;MacLeod et al., 2007). As a consequence, seabird species previously reliant on sandeels declined to their lowest levels since systematic recording began (Cook et al., 2014;JNCC, 2013). Nevertheless, seabird species differences in their ability to find alternative foods mean effects have been uneven across taxa, leading to changes in seabird community structure (Mitchell et al., 2004). ...
Article
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Understanding anthropogenic impacts are crucial to maintain marine ecosystem health. The North Sea has changed in recent decades, largely due to commercial fishing and climate change. Seabirds can act as useful indicators of these changes. By analyzing n ¼ 20 013 pellets and n ¼ 24 993 otoliths regurgitated by great skuas Stercorarius skua in northern Scotland over five decades from the 1970s to the 2010s (in 36 years 1973-2017), we reveal how the diet of this top predator has changed alongside the changing North Sea ecosystem. Sandeels Ammodytes spp. were the most common dietary item during the 1970s, but became virtually absent from the 1980s onward. Discarded white-fish dominated skua diets from the 1980s to the present day, despite long-term declines in North Sea discard production. However, the discarded fish eaten by great skuas has become smaller and the species composition changed. Skua pellets only rarely contained avian prey in the 1970s but this increased during the 1980s, and fluctuated between 10% and 20% from the 1990s to 2010s. There have also been changes in the avian prey in the diet-black-legged kittiwakes Rissa tridactyla generally being replaced by auks Alcid spp. and northern fulmars Fulmarus glacialis. The Shetland marine ecosystem has experienced steep declines in sandeel stocks and in seabirds that feed on them. Great skuas have been able to prey switch to respond to this change, supported by abundant discards, enabling them to maintain a favourable population status while other seabird species have declined.
... Models were fitted in the 'lme4' R package (Bates et al., 2015). The response variable was the number of fledged chicks (measured directly as described above) and failed chicks (estimated from an assumed mean clutch size of 2.6 for both species based on (Cramp and Simmons, 1983) and the number of breeding pairs), thus accounting for varying numbers of nests surveyed, and representing productivity as 'fledging probability per egg' (Cook et al., 2014;Carroll et al., 2015;Carroll et al., 2017). Each measure of fox predation risk (scat density, nightly sighting rate and fox presence/absence) was fitted in separate models as fixed factors. ...
Technical Report
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The dramatic breeding population declines in Britain and Ireland of Herring Larus argentatus and Lesser Black-backed Gulls L. fuscus over recent decades have been linked to several causes including changes in food availability, botulism, predation and culling. This study compared productivity of both gull species across eight study colonies in northern England and Wales in relation to the risk of predation from the Red Fox Vulpes vulpes, measured by baited camera traps and scat transects. In addition, the effects of predator-exclusion fences on nest survival and productivity were investigated at one of the study colonies. There was a significant negative relationship between fox sighting rate and productivity, and a significant difference in productivity (but not nest survival) between fenced and unfenced areas. However, fox sighting rate explained relatively little variation in productivity, and some colonies with no evidence of fox predation risk still had relatively low breeding success. For most of the study colonies, breeding success was below the level required for population stability. The role of fox control measures is discussed within the context of other potential conservation measures available to help combat population declines.
... Wadden Sea data is used for the implementation of the EU-Bird Directive and its Natura 2000 network. More recently, the bird data (both data on abundance and breeding success) has also been incorporated in the biodiversity indicators of the Marine Strategy Framework Directive (Cook et al., 2014;OSPAR Commission, 2016), in order to assess the environmental status of marine areas. Due to the ongoing declines observed in many species, a special breeding bird action plan was issued in 2016 and adopted by the Wadden Sea Board (JMBB, 2016). ...
Chapter
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The Wadden Sea hosts large numbers of coastal breeding birds and for several species supports an important share of the flyway population. They use a network of breeding and feeding sites, both at sea (partly offshore), on the intertidal mud flats, salt marshes, dunes and wetlands behind the seawall. Data from the breeding bird monitoring, carried out in the framework of TMAP, shows that 17 out of 29 bird species have declined since the monitoring started 1991, i.e. they do not meet the targets of the Wadden Sea Plan. This trend is observed among all species-groups, including those species for which the Wadden Sea is an important breeding area, like Redshank, Oystercatcher, Common Tern and Avocet (actually in several of these species, the rate of decline has accelerated recently). Several waders are currently even on the brink of extinction, e.g. the southern race schinzii of Dunlin and Ruff. Also both raptor species that are typical for the Wadden Sea, Hen Harrier and Short-eared Owl, have decreased to very low population levels. In contrast, 9 bird species have shown increases, mainly some colonial breeding birds like Spoonbill, Lesser Black-backed Gull and Common Gull. In some species (e.g. Barnacle Goose) the increase in the Wadden Sea is part of a general range expansion. Stable trends were recorded in Little Tern, Sandwich Tern and Gull-billed Tern (but these species experienced declines before the trilateral monitoring started in 1991). Overall, there are more declining species in the Netherlands and Lower Saxony/ Hamburg, than in Schleswig-Holstein and Denmark. Data on breeding success, collected within TMAP since 2009 for a selection of species, show that in many coastal breeding birds, reproductive output is rather poor. Notably Oystercatcher, Avocet and Artic Tern have a very low annual breeding success, which is insufficient to maintain the population even at a stable level. This is not a only a recent phenomenon, as several studies have pointed out that decreasing trends in breeding success already started in the late 1990s or early 2000s. This is confirmed by assessments of breeding success in the Dutch Wadden Sea, carried out since 2005. Predation risk and flooding were among the most frequent causes observed during monitoring of breeding success, albeit causes for poor reproductive performance are not always known in detail, and also interfere with other factors. Additional causes are starvation (lack of food resources) and unfavourable weather, locally also trampling by livestock-grazing and increased agricultural pressure in coastal grasslands. Predation is especially an issue along the mainland coast and at islands which are connected to the mainland coast by barrier dams (including connections to the Hallig islands in Schleswig-Holstein). Flooding has been observed both on islands and the mainland coast as a factor of importance for all breeding species that breed on sites exposed to tidal influence. It is caused by an increase in catastrophic flooding events in the past decades, as a result of sea level rise and climate change. Lack of food resources is suspected at least for colonial breeding birds (gulls and terns), but difficult to assess without specific research. Contaminants in bird eggs are currently assumed not to have an impact on breeding success of coastal breeding birds.
... (Fig. 4) For example, indicators of seabird population size and breeding success are formally assessed at the OSPAR level within the MSFD [52,53] and are useful indicators of the food web repercussions of direct pressures targeted at the lower levels of the food web, such as fishing pressure on forage fish prey [54,55]. For effective ecosystem-based management, management of forage fish exploitation must account for the need to sustain top predators and as forage fish biomass and productivity is highly variable, the setting of acceptable fishing levels must remain adaptive [56,57]. With a reduction in the recruitment success of key forage fish species such as sandeel predicted under climate change [58], reducing fishing pressure on forage fish through precautionary management measures may be needed to maintain Good Environmental Status of seabirds under future climate conditions [59]. ...
Article
The Marine Strategy Framework Directive (MSFD) uses an indicator-based approach for ecosystem assessment; indicators of the state of ecosystem components ('state indicators') are used to determine whether, or not, these ecosystem components are at ‘Good Environmental Status’ relative to prevailing oceanographic conditions. Here, it is illustrated that metrics of change in plankton communities frequently provide indications of changing prevailing oceanographic conditions. Plankton indicators can therefore provide useful diagnostic information when interpreting results and determining assessment outcomes for analyses of state indicators across the food web. They can also perform a strategic role in assessing these state indicators by influencing target setting and management measures. In addition to their primary role of assessing the state of pelagic habitats against direct anthropogenic pressures, plankton community indicators can therefore also fulfil an important 'surveillance' role for other state indicators used to formally assess biodiversity status under the MSFD.
... Becker and Chapdelaine (2003) pointed out that relative abundance in diet may not track availability closely when availability is high. Cook et al. (2014) cautioned that plasticity in seabird diet might obscure relationships between diet and food supply. We view these legitimate points as deserving further research with these and other datasets. ...
Article
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Ecosystem-based fishery management requires understanding of relationships between exploited fish and their predators, such as seabirds. We used exploratory regression analyses to model relationships between Atlantic herring (Clupea harengus) in the diet of seabird chicks at nine nesting colonies in the Gulf of Maine, and four types of fishery- and survey-derived herring data. We found several strong relationships, which suggests spatial structuring in herring stocks and likely patterns of herring movements before they recruit into the fishery. Some types of herring data seldom used in stock assessments – notably acoustic surveys, fixed-gear landings, and weight-at-age – correlated as strongly with seabird data as more commonly used series, such as mobile-gear landings and modeled spawning stock biomass. Seabird chick diets collected at specific locations thus offer a promising means to assess the size, distribution, and abundance of juvenile herring across a broad area prior to recruitment, which is a major source of uncertainty in fisheries. Common terns showed the most potential as a bioindicator, correlating well and showing consistent spatial patterns with 11 of 13 fishery data series.
... Relatively few studies have examined the proximate causal factors that influence individual seabird reproductive success, or attempted to apply contemporary parameter estimation methods to seabird reproductive success (Wanless et al. 2007;Einoder 2009;Cook et al. 2014). When variation in seabird reproductive success is suggested to indicate changes in the marine environment without identifying the proximate causes of such variation, inference is limited to association, and the proximate causes themselves (such as parental care or diet) could prove more effective as indicators (Mallory et al. 2010 year, 2) variation in reproductive success between years, and 3) compared nest success to individual egg and chick success between years. ...
Thesis
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Variation in reproductive success is widely measured in seabird biology in an effort to indicate changes in the marine environment, or understand basic questions about ecology or conservation of seabirds. When variation in seabird reproductive success is suggested to indicate changes in the marine environment without identifying the proximate causes of such variation, inference is limited to association, and the proximate causes themselves could prove more effective as indicators. My study informs this problem by examining and quantifying proximate causes of variation in reproductive success, at the level of nests and individual chicks. I used video of Brandt's Cormorant (Phalacrocorax penicillatus) nests on Castle Rock National Wildlife Refuge (NWR) to monitor parental care behaviors and test their influence on reproductive success in 2015. I also estimated annual variation in survival of both nests and individual eggs and chicks from 2011-2015 on Castle Rock NWR. Lastly, I compared nest survival to individual egg and chick survival to evaluate and improve upon how seabird reproductive success is traditionally measured. iii Parental care behaviors had no statistical influence on survival in 2015, but nest and individual egg and chick survival varied dramatically from 2011-2015 (nest survival range: 0.083-0.942; individual survival range: 0.037-0.719). Derived estimates of nest survival from egg and chick survival demonstrated validity of measuring individual survival. My results demonstrated that inclusion of proximate causal factors that influence reproductive success and contemporary parameter estimation methods help inform seabird biology and current monitoring techniques.
... Top predator populations, such as seabirds, reflect the variation of lower trophic levels they depend on [19]. Therefore, demographic parameters such as breeding success are valuable as an ecological indicator of environmental changes and anthropogenic pressures [20]. In the context of the regulatory framework, Blacklegged kittiwake (Rissa tridactyla) productivity, for example, is used as a state indicator as well as a target to monitor progress towards achieving Good Environmental Status under the EU Marine Strategy Framework Directive (2008/56/EC). ...
Article
The marine environment provides a range of ecosystem services and benefits for society. A previous study in Marine Policy (Potts et al., 2014) [1] advocated a matrix approach to demonstrate the relative degree of ecosystem service provision from habitats and species within UK Marine Protected Areas (MPAs), but excluded seabird species in its assessment. Despite the number of existing UK MPAs designated specifically for individual seabird species and/or seabird assemblages, and the fact that seabird species have long been used as policy-relevant indicators for the monitoring and management of the marine environment, as yet little research has focussed on the direct role of seabird species in the provision of ecosystem services and how these are captured for marine spatial planning purposes in the context of MPAs. Building on the matrix approach, this paper develops and populates a matrix to illustrate the relationship between key UK breeding seabird species and their relative contribution to the delivery of intermediate ecosystem services and goods/benefits. The original matrix approach has been strengthened to include the development and testing of a set of rules for combining multiple matrices. Confidence scores relating to the underlying evidence base are built into the matrix to provide an illustration of the current understanding and to identify current gaps in evidence. Following a sense check by external seabird experts the matrix is applied in the context of four existing UK MPA case study sites. Further developments and applications of the seabird matrix are discussed within the context of wider marine management.
... Such a holistic approach, however , is difficult in studies of wild systems because it requires long-term datasets on population size, multiple demographic parameters and multiple potential ecological factors, which are often not feasible to collect. Diagnosis of reasons for long-term decreases in population size is particularly valuable for ecological indicator species and small or declining populations that may receive conservation attention and management20212223. Seabirds and marine mammals are the top predators in marine systems and are consequently useful indicators of the state of inshore and offshore communities; seabirds also provide a tractable opportunity to study marine dynamics because they can be studied on land when they come ashore to breed [20, 24, 25]. ...
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Determining which demographic and ecological parameters contribute to variation in population growth rate is crucial to understanding the dynamics of declining populations. This study aimed to evaluate the magnitude and mechanisms of an apparent major decline in an Atlantic Puffin Fratercula arctica population. This was achieved using a 27-year dataset to estimate changes in population size and in two key demographic rates: adult survival and breeding success. Estimated demographic variation was then related to two ecological factors hypothesised to be key drivers of demographic change, namely the abundance of the main predator at the study site, the Great Skua Stercorarius skua, and Atlantic Puffin chick food supply, over the same 27-year period. Using a population model, we assessed whether estimated variation in adult survival and reproductive success was sufficient to explain the population change observed. Estimates of Atlantic Puffin population size decreased considerably during the study period, approximately halving, whereas Great Skua population estimates increased, approximately trebling. Estimated adult Atlantic Puffin survival remained high across all years and did not vary with Great Skua abundance; however, Atlantic Puffin breeding success and quantities of fish prey brought ashore by adults both decreased substantially through the period. A population model combining best possible demographic parameter estimates predicted rapid population growth, at odds with the long-term decrease observed. To simulate the observed decrease, population models had to incorporate low immature survival, high immature emigration, or increasingly high adult non-breeding rates. We concluded that reduced recruitment of immatures into the breeding population was the most likely cause of population decrease. This study showed that increase in the size of a predator population does not always impact on the survival of adult prey and that reduced recruitment can be a crucial determinant of seabird population size but can easily go undetected.
... Despite potentially overlapping foraging ranges, dietary differences between Kittiwakes from estuarine and marine colonies (Bull et al. 2004) in southeast Scotland stress the importance of local foraging resources. However, recent analyses suggest that commercial sandeel fisheries may have a more widespread impact (Cook et al. 2014). Given that birds nesting on the Tyne Bridge have to fly 17 km along the River Tyne to reach coastal or inshore waters, the location of this colony may be dependent, at least in part, on the presence of good foraging areas associated with the Tyne estuary. ...
Article
Capsule Black-legged Kittiwakes Rissa tridactyla from an inland and a maritime colony in the North Sea had similar patterns of foraging behaviour, using coastal as well as distant offshore areas for foraging. Aims To compare the foraging behaviour of Black-legged Kittiwakes Rissa tridactyla nesting at two contrasting colonies in the North Sea, a colony on one of the outermost Farne Islands and a unique inland colony on the Tyne Bridge, Newcastle upon Tyne, and to test the hypothesis that foraging by birds from the inland colony would be in more-coastal waters compared to the island colony. Methods Global positioning system loggers were used to compare foraging strategies of birds from the two sites. Foraging locations were inferred from analysis of movement patterns from fine-scale positional data. Results The characteristics of foraging trips were similar for birds from both sites, with trips lasting up to 17.6 hours and covering distances of 6.2–370.6 km. Behaviour during the trips was partitioned into direct flight, not-foraging behaviour and foraging behaviour. Contrary to expectation and despite the 72 km distance between colonies, there was some overlap in foraging locations of the tagged birds from each colony. Furthermore, the foraging locations included coastal waters and areas over 100 km from land. Conclusion These data suggest that factors other than proximity to foraging areas may be more important for inland-nesting Kittiwakes.
... For migratory seabirds, conditions in the marine environment are most limiting (Schreiber 2001;Cook et al. 2014), especially through the long-and short-term fluctuations of fish stocks (Montevecchi 1993;Gröger et al. 2010;Dänhardt and Becker 2011a). Hunting of fish can be impeded by adverse weather, such as storms, wind and rain (Finney et al. 1999;Daunt et al. 2006), while food availability is influenced by local weather conditions (Misund et al. 1997(Misund et al. , 1998. ...
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We estimated annual apparent survival rates, as well as local recruitment rates in different age groups and for different breeding status in the common tern Sterna hirundo using mark-recapture analysis on a long-term individual-based dataset from a breeding colony in Germany. Strong inter-annual variability in survival rates became apparent, especially in prospectors. Local recruitment also varied strongly between years and age groups. To explain these fluctuations, we linked survival and recruitment estimates to several environmental covariates expected to be limiting during the wintering period and migration, including the global climate indices of North Atlantic Oscillation and Southern Oscillation, fish abundance indices, and marine primary productivity in the West African wintering area. Contrary to expectations, global indices did not seem to be linked strongly to vital rates. Results showed that primary productivity had the strongest effect on annual survival, especially in young and inexperienced individuals. Primary productivity in the wintering area was also strongly associated with the probability of recruitment in the following breeding season, indicating that conditions during winter can have carry-over effects on the life cycle of individuals.
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The Atlantic Puffin (Fratercula arctica; hereafter ‘puffin’) breeds at the southern limit of its range in the Gulf of Maine, where waters are warming faster than most of the world’s oceans. Puffin productivity and survival have decreased in the Gulf of Maine with warming, but population-level declines have not been detected. Understanding the connectivity between Gulf of Maine breeding colonies and colonies to the north has become a priority to determine the demographic importance of immigration, but mark-recapture and tracking studies have yet to resolve this question. In this study, we used double digest restriction-site associated DNA sequencing (ddRADseq) to quantify neutral genetic differentiation among five breeding colonies in Atlantic Canada, identify outlier single nucleotide polymorphisms (SNPs), and determine if puffins can be reliably assigned to their breeding colony. We identified a new genetic cluster of puffins, represented by Machias Seal Island, and recommend that this colony be considered separately from Newfoundland and Québec for management. We found three outlier SNPs, with the rare alleles predominantly present in Machias Seal Island puffins, and recommend further research to determine the extent that selection may be contributing to the differentiation of Machias Seal Island. Puffins could be reliably assigned to the Machias Seal Island or the northern-colony genetic cluster, including with a subset of the 200 highest-FST\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$F_{ST}$$\end{document} SNPs. Finally, we did not identify evidence of inbreeding at any colony, suggesting that effective population sizes are large enough to buffer against these negative effects.
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Offshore wind farms (OWFs) are a key part of efforts to mitigate the impacts of climate change. However, they have the potential to negatively impact seabird species through collisions with turbine blades, displacement from preferred foraging habitat and the perception of wind farms as a barrier to migrating or foraging birds. Whilst the data available to model these impacts are increasing, many data gaps remain, particularly in relation to the impacts of barrier effects. We analyse the movements of Sandwich terns in relation to an offshore wind farm cluster using data collected as part of a multi-year GPS tracking study. Over the course of the study, two additional wind farms were built within the home range of the breeding colony. The construction of these wind farms coincided with a change in the foraging and commuting areas used by breeding terns. Whilst birds entered OWFs when foraging, they appeared to avoid them when commuting, driving an apparent ‘funnelling’ effect to important feeding locations. We discuss if this could be driven by changes to the prey base, subsequent displacement and potentially altered routes reflecting new favourable airflow patterns following OWF construction. Our results suggest that behavioural responses of birds to OWFs may be the result of a complex series of ecological and environmental interactions, as opposed to simplistic assumptions around the perception of the OWF as a barrier to movement.
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Knowledge of fisheries impacts, past and present, is essential for understanding the ecology and conservation of seabirds, but in a rapidly changing world, knowledge and research directions require updating. In this Introduction and in the articles in this Themed Set "Impacts of fishing on seabirds" , we update our understanding of how fishing impacts seabird communities and identify areas for future research. Despite awareness of the problems and mitigation ef for ts for > 20 years, fisheries still negatively impact seabirds via the effects of bycatch, competition, and discards. Bycatch continues to kill hundreds of thousands of seabirds annually, with negative population-level consequences. Fisheries for forage fish (e.g. anchovy, sandeel, and krill) negatively impact seabirds by competing for the same stocks. Historically, discards supplemented seabird diets, benefitting some species but also increasing bycatch rates and altering seabird community composition. However, declining discard production has led to potentially deleterious diet switches, but reduced bycatch rates. To improve research into these problems, we make the following recommendations: (1) improve data collection on seabird-vessel interaction and bycatch rates, on fishing ef for t and vessel movements (especially small-scale fleets), and on mitigation compliance, (2) counter the current bias towards temperate and high-latitude ecosystems, larger-bodied species and particular life stages or times of year (e.g. adults during breeding), and (3) advance our currently poor understanding of combined effects of fisheries and other threats (e.g. climate change, offshore renewables). In addition, research is required on under-studied aspects of fishing impacts: consequences for depleted sub-surface predators, impacts of illegal, unreported and unregulated fishing, artisanal and emerging fisheries, such as those targeting mesopelagic fish, have received insufficient research attention. Some of these shortfalls can be overcome with new tools (e.g. electronic monitoring, remote sensing, artificial intelligence, and big data) but quantifying and addressing fishing impacts on seabirds requires greater research investment at appropriate spatio-temporal scales, and more inclusive dialogue from grassroots to national and international levels to improve governance as fishing industries continue to evolve. Background and motivation for a themed article set
Article
Terns are a highly migratory group of seabirds that are found worldwide. In Ireland, there are five species of commonly breeding tern: Little Tern Sternula albifrons, Roseate Tern Sterna dougallii, Arctic Tern S. paradisaea, Common Tern S. hirundo and Sandwich Tern S. sandvicensis. Prior work has demonstrated that whilst many Irish tern species, including Common and Roseate Terns, are increasing in abundance, the productivity of these species can be low. Multiple factors may influence the ability of adult terns to successfully raise chicks, including food availability, provisioning rates, colony density, dependence effects, and/or disease. Here, we investigated factors contributing to the mortality of young terns from Rockabill Island in the Republic of Ireland, which supports the largest breeding population of Roseate Terns in Europe. To better understand the factors contributing to the deaths of young birds, we analysed the macroscopic and microscopic characteristics of necropsies of 60 young Common, Arctic and Roseate Terns. Of the carcasses that we examined, 41 showed congested blood circulation in the lungs and head simultaneously, and of the remaining 19 birds, only five presented a clear cause of death. Here, we outline descriptions of these carcasses in addition to recommendations of further investigations that might help to confirm the causal factors leading to young tern mortality.
Chapter
Fisheries in all of the earth’s oceans entail direct and indirect effects on marine food webs and on seabirds in particular. Fisheries that target forage species are associated with precipitous declines of seabird populations in the eastern boundary currents of the Pacific and Atlantic Oceans. Uncertainties and variation in physical and biological conditions and in prey and predator distributions however make the attribution of fishing effects to seabird responses extremely difficult. Cascading effects associated with the removal of large piscivorous fishes and other apex predators have had both positive and negative indirect trophic influences on seabirds by either increasing or decreasing the availability of small fishes and other prey in temperate and tropical ocean systems, respectively. Fishery discards and wastes have provided otherwise inaccessible demersal food sources that have benefitted surface-feeding seabirds. Their low nutritive value (“junk food hypothesis”) and subsequent reduction and termination is however having negative effects on inflated populations of scavenger species. Bycatch in fishing gear kills hundreds of thousands of birds annually, though limited collection of systematic data underestimates total mortality. Pelagic long-lines, that target tuna, swordfishes, and sharks in tropical and temperate regions, hook and drown surface feeders (albatrosses, tube-nosed seabirds) many of which are threatened with extinction. Demersal long-lines set for groundfish in temperate, subpolar and polar waters kill large numbers of fulmars and shearwaters. Gillnets in temperate and subpolar regions entangle and drown numerous diving species (auks, penguins, seaducks). Disturbances created by light-based fishing activity for squid and forage and pelagic fishes attract nocturnal seabirds, escalating risks of collisions and gear entanglement. Marine and freshwater aquaculture sites displace and attract seabirds that are often shot, and at times, they provision predatory birds such as eagles. The feed requirements of the expanding aquaculture industry, which produces more fish than capture fisheries, will likely increase the value and intensity of forage fisheries. Increasing consumer demands for wild seafood will ratchet fishing pressure in warming oceans subject to more frequent heat waves and other extreme weather events. These circumstances will create further challenges for the behavior and ecology of marine birds and their populations and diversity. The incorporation of seabird and other predator requirements and information from seabird indicators in ecosystem management would improve biological conservation and fishing sustainability.
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Over four decades there were pronounced within‐season changes in the proportion of a key prey species (Lesser Sandeel Ammodytes marinus) in Common Guillemot Uria aalge chick diet. As Sandeels became scarcer their occurrence was largely confined to the early part of the chick period. Consequently, the mean annual proportion of Sandeels was poorly estimated if sampling occurred within a short time window, particularly if this was early or late in the season. Within‐season variation is rarely considered in diet monitoring, but our results highlight the need for further analyses across other species and sites to develop a deeper understanding of how best to optimise sampling protocols.
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Fisheries for forage fish may affect the survival and reproduction of piscivorous predators, especially seabirds. However, seabirds have evolved life history strategies to cope with natural fluctuations in prey and it is difficult to separate effects of fishing on seabirds from impacts of natural variability. To date, potential impacts of forage fisheries on seabirds have mainly been explored using ecosystem models that simplify seabird–forage‐fish dynamics. We sought to explore how different forage fish harvest policies affect seabirds, accounting for structured population dynamics, life history specifics, and variation in forage fish dependencies across life stages; and how impacts vary across seabird and forage fish life histories. To explore these impacts, we developed an age‐stage structured seabird model that incorporates seabird diet specialization, foraging behavior, and reproductive strategy, as well as different functional responses between prey availability and adult survival, juvenile survival, reproductive success, and breeder propensity. We parameterized this model for two contrasting seabird life histories: (1) a low fecundity, limited foraging range, diet specialist (“restricted”); and (2) a high fecundity, wide ranging, diet generalist (“flexible”). Each was paired with two different forage fish prey archetypes that were fished under various control rules. The restricted seabird population was expectedly less robust to constant fishing pressure than the flexible seabird, and this sensitivity was mainly due to functional response parameterization, rather than other life history parameters. Particularly, the restricted seabird was highly sensitive to the relationship between prey availability and adult survival but was not sensitive to the relationship between prey and reproductive success. An adaptive biomass‐limit harvest rule for forage fish resulted in substantially higher seabird abundance compared to constant fishing across all scenarios, with minimal trade‐offs to the fishery (depending on fishery management objectives). However, mechanisms governing the impact of the forage fish fishery on the seabird varied by forage fish type. Therefore, tailoring forage fish management strategies to forage fish life history can lead to mutually acceptable outcomes for fisheries and seabirds. If data or time are limited, an adaptive control rule is likely a safe bet for meeting seabird conservation objectives with limited impacts to fisheries.
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Recently detected invertebrate population declines are likely to have far-reaching impacts for ecosystem function. However, very little large-scale monitoring of invertebrates, especially soil invertebrates, has taken place. To address this gap, we established a school-based citizen science project to collect data on soil invertebrate abundance and bird counts across the UK. We examined the association between earthworms (which comprised 93% of the total soil invertebrate biomass in the surface soil) and 15 bird species on school playing fields over three years. We also tested whether simple bird counts of species that rely on earthworms could be used to indicate the earthworm abundance in soil. We found a clear link between earthworm abundance and counts of robins (Erithacus rubecula), blackbirds (Turdus merula) and other thrushes (Turdus pilaris, Turdus viscivorus, Turdus philomelos and Turdus iliacus), all of which rely on earthworms as an important component of their diet. None of these relationships varied with season. There were no correlations found between earthworm abundance and bird counts for species that do not rely on earthworms. We found that the total thrush count (including blackbirds) could be used as a simple indicator of earthworm abundance, explaining up to 20% of the variation in earthworm counts. In spite of the uncertainties associated with the data, these results raise the possibility that existing, robust, long-term bird monitoring data could, with further research, be used to infer changes in soil invertebrates, such as earthworms, and therefore aspects of soil health. We conclude by identifying a series of criteria that would need to be fulfilled in order for such inference to be robust.
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The State of Nature report 2019 presents an overview of how wildlife is faring in the UK and its Overseas Territories and Crown Dependencies. Additionally, it assesses the pressures that are acting on nature, and the responses being made, collectively, to counter these pressures.
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Aktuelle Verbreitung, Bestände und Trends von Seevögeln auf See im Offshore-Bereich des nieder-sächsischen Küstenmeers und des Nationalparks Niedersächsisches Wattenmeer. Vogelkdl. Ber. Niedersachs. 46: 1-69. In den letzten Jahrzehnten gibt es zunehmende Erkenntnisse über die Verbreitung und Bestände von Seevögeln auf dem Meer. Für die deutsche Nordsee gibt es seit 1990 und für die deutsche Ostsee seit 2000 standardisierte Erfassungen auf See. Diese waren eine wesent-liche Basis für umfangreiche Schutzgebietsausweisungen in der Ausschließlichen Wirtschafts-zone und in den Hoheitsgebieten der Küstenbundesländer. Vor dem Hintergrund einer immer intensiveren Nutzung der Meere und nationaler wie europäischer Umweltrichtlinien besteht zunehmendes Interesse und die Pflicht den Erhaltungszustand von geschützten Seevogelarten zu erfassen. Eine erste Studie für das niedersächsische Küstenmeer wertete Daten von 1991 bis 2003 aus. Aktuelle Auswertungen zu Verbreitung, Beständen und Bestandstrends von Seevögeln für die jüngere Vergangenheit fehlten. Diese Lücken sollten im Rahmen des Projektes "Seevogel auf See-Daten-Auswertung im Offshore-Bereich des Nationalparks und der Ho-heitsgewässer Niedersachsens (SASANI)" geschlossen werden. Dazu wurde das Forschungs-und Technologiezentrum (FTZ) der Universität Kiel von der Nationalparkverwaltung Nieder-sächsisches Wattenmeer (NLPV) beauftragt, den umfangreichen Datenbestand, den das FTZ im Rahmen des Marinen Biodiversitätsmonitorings des Bundesamtes für Naturschutz (BfN) sowie gezielter Forschungsvorhaben gesammelt hat, auszuwerten. Ziel war es die aktuelle Datenlage für das niedersächsische Küstenmeer umfassend zu beurteilen, aktuelle saisonale Verbreitungskarten der häufigsten Seevogelarten zu erstellen, saisonale Bestände zu berechnen und soweit möglich Bestandstrends zu ermitteln. Außerdem sollten die für die NLPV durchge-führten Eiderentenflüge im Nationalpark für die küstennahe und-fernere Verbreitung der Art miteinbezogen werden. Die gewonnenen Erkenntnisse sollten dazu dienen, ggf. vorhandene Lücken zu identifizieren und Verbesserungsvorschläge zur Erfassung von Seevögeln im Küs-tenmeer zu erarbeiten. Dazu wurden Daten von standardisierten Schiffsurveys (2000 bis 2015) und Flugsurveys (2002 bis 2015) aus der Seabirds at Sea-Datenbank des FTZ ausgewertet. Es zeigte sich, dass sich die Datenlage von überwiegend schiffsbasierten Erfassungen zu Beginn zu überwiegend flugzeuggestützten Erfassungen ab 2003 verändert hat. Für das Frühjahr ist die Datengrundlage am besten, gefolgt von Winter, Sommer und Herbst. Anhand der Daten lassen sich grundlegende Charakteristika der Seevogelvorkommen im niedersäch-sischen Küstenmeer gut beschreiben. Für Auswertungen wie Trendanalysen, die eine umfas-sende Datenbasis mit hoher zeitlicher Auflösung erfordern, ist die Datenlage jedoch nicht ausreichend. Für die 20 häufigsten Seevogelarten Eiderente Somateria mollissima, Trauerente Melanitta nigra, Samtente Melanitta fusca, Sterntaucher Gavia stellata, Prachttaucher Gavia arctica, Eissturmvogel Fulmarus glacialis, Basstölpel Sula bassana, Kormoran Phalacrocorax carbo, Lachmöwe Larus ridibundus, Sturmmöwe Larus canus, Silbermöwe Larus argentatus, Heringsmöwe Larus fuscus, Mantelmöwe Larus marinus, Zwergmöwe Hydrocoeleus minutus, Dreizehenmöwe Rissa tridactyla, Brandseeschwalbe Sterna sandvicensis, Flussseeschwalbe Sterna hirundo, Küstenseeschwalbe Sterna paradisaea, Trottellumme Uria aalge und Tordalk Alca torda wurden artspezifische saisonale Verbreitungskarten erstellt und mittlere Bestandszahlen für alle vier Jahreszeiten berechnet. Für 9 der 20 Arten konnten mit Hilfe der Software TRIM Bestandstrends für das Frühjahr basierend auf Flugsurveys berechnet werden. Dabei zeigte sich, dass das niedersächsische Küstenmeer und die seewärtigen Teile des Nationalparks ganzjährig bedeutende Seevogelvorkommen beherbergen. Die Bestände von 5 Seevogelarten sind international bedeutsam. Dies sind Eiderente, Trauerente, Heringsmöwe, Zwergmöwe und Brandseeschwalbe. Zusätzlich sind die Bestände von 11 weiteren Seevogelarten national bedeutsam. Dies umfasst Sterntaucher, Prachttaucher, Basstölpel, Sturmmöwe, Silbermöwe, Mantelmöwe, Dreizehenmöwe, Flussseeschwalbe, Küstenseeschwalbe, Trottellumme und Tordalk. Damit ergibt sich eine nationale bzw. internationale Verantwortung Niedersachsens, die Vorkommen der Seevögel regelmäßig zu erfassen, um die Berichtspflichten auf Landesebene, sowie auf nationaler und internationaler Ebene (EU Vogelschutzrichtlinie, EU Meeresstrategie-Rahmenrichtlinie, OSPAR Meeresschutzkonvention www.ospar.org) zu erfüllen. Im Vergleich zu 1991 bis 2003 ließen sich bei einigen Arten wie Eider- und Trauerente Änderungen in ihrer Verbreitung beobachten. Diese Arten nutzten stärker als früher auch küstenfernere Bereiche. Die Dreizehenmöwe war deutlich seltener als früher, ihr Bestandstrend ist stark negativ. Sie folgte damit dem überregionalen Trend und dem starken Rückgang der Brutpopulation. Der Mantelmöwenbestand war ebenfalls deutlich geringer als im Zeitraum von 1993 bis 2003, ihr Bestandstrend für die gesamte deutsche Nordsee ist ebenfalls stark negativ. Da die relevanten Brutpopulationen stabil sind, ist anzunehmen, dass sich die Vorkommen massiv verlagert haben. Der Zwergmöwenbestand im Frühjahr war im Vergleich zu früher deutlich höher, die Verbreitung auf küstenfernere Bereiche erweitert. Hierbei ist es wahrscheinlich, dass dieses Ergebnis durch den steigenden Anteil von Flugsurveys gegenüber Schiffsurveys bedingt ist. Flugsurveys finden grundsätzlich vorwiegend in Schwachwindphasen statt und erfassen großräumig das Zuggeschehen der Zwergmöwen, das unter diesen Wetterbedingungen vermutlich als Breitbandzug quer durch die Deutsche Bucht erfolgt. Die Datenbasis ließ für 11 der 20 häufigen Arten keine Trendberechnung zu, darunter Charakterarten wie Eiderente, Trauerente, Heringsmöwe und Zwergmöwe mit international bedeutsamen Beständen. Bei den meisten der übrigen 9 Arten wiesen die Trendkurven zudem große Standardfehler auf und spiegeln damit die unsichere Datenbasis wider. Da die untersuchten Seevögel sehr mobil sind und das niedersächsische Küstenmeer nur einen kleinen Teil ihres Verbreitungsgebiets ausmacht, haben Trends auf dieser Ebene generell nur begrenzte Aussagekraft. Im Rahmen des Marinen Biodiversitätsmonitorings des BfN/FTZ sind je ein Flugsurvey im Frühjahr und Winter, sowie alle 3 Jahre im Herbst zur Nachbrutzeit geplant, die auch das niedersächsische Küstenmeer abdecken. Diese Surveys und die Lage der Transekte zielen auf eine großräumige Erfassung der gesamten deutschen Nordsee ab. Sie reichen nicht aus, um die jahreszeitlichen Hauptvorkommen der Seevögel vor Niedersachsen vollständig zu erfassen. Daher empfehlen wir dringend gesonderte Seevogel auf See-Erfassungen per Flugzeug und Schiff, die den regionalen Besonderheiten hinsichtlich des räumlich-zeitlichen Auftretens der Seevögel Rechnung tragen. Da insbesondere der küsten- und inselnahe Bereich in den letzten Jahren wenig beprobt wurde, dieser für viele Seevogelarten aber einen Verbreitungsschwerpunkt bildet, schlagen wir ein küstenparalleles Transektdesign vor, das das gesamte niedersächsische Küstenmeer abdeckt. Zudem empfehlen wir, im Rahmen der bereits im Nationalpark stattfindenden Eiderentenflüge der NLPV standardmäßig alle Seevogelarten mit zu erfassen, um die Datenbasis gerade in den Watt- und Flussmündungsbereichen deutlich zu erhöhen.
Article
Understanding drivers of population change is critical for effective species conservation. In the northeast Atlantic Ocean, recent changes amongst seabird communities are linked to human and climate change impacts on food webs. Many species have declined severely, with food shortages, and increased predation reducing productivity. Arctic skua Stercorarius parasiticus , a kleptoparasite of other seabirds, is one such species. The aim of the study was to determine relative effects of bottom‐up and top‐down pressures on Arctic skuas across multiple colonies in a rapidly declining national population. Long‐term monitoring data were used to quantify changes in population size and productivity of Arctic skuas, their hosts (black‐legged kittiwake Rissa tridactyla , common guillemot Uria aalge , Atlantic puffin Fratercula arctica , Arctic tern Sterna paradisaea ) and an apex predator (great skua Stercorarius skua ) over 24 years (1992–2015) in Scotland. We used digital mapping and statistical models to determine relative effects of bottom‐up (host productivity) and top‐down (great skua density) pressures on Arctic skuas across 33 colonies, and assess variation between three colony types classified by host abundance. Arctic skuas declined by 81% and their hosts by 42%–92%, whereas at most colonies great skuas increased. Annual productivity declined in Arctic skuas and their hosts, and reduced Arctic skua breeding success was a driver of the species’ population decline. Arctic skua productivity was positively associated with annual breeding success of hosts and negatively with great skua density. Intercolony variation suggested Arctic skua trends and productivity were most sensitive to top‐down pressures at smaller colonies of host species where great skuas had increased most, whereas bottom‐up pressures dominated at large colonies of host species. Scotland's Arctic skua population is declining rapidly, with bottom‐up and top‐down pressures simultaneously reducing breeding success to unsustainably low levels. Marine food web alterations, strongly influenced by fisheries management and climate change, are driving the decline, and this study demonstrates severe vulnerability of seabirds to rapid change in human‐modified ecosystems. Potential but untested conservation solutions for Arctic skuas include marine protected areas, supplementary feeding within colonies and management of great skuas.
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Technical Report
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The aim of this literature review is to inform the understanding of the current state of knowledge of selected seabird species (northern gannet Morus bassanus hereafter ‘gannet’, black-legged kittiwake Rissa tridactyla hereafter ‘kittiwake’, lesser black-backed gull Larus fuscus, great black-backed gull L. marinus, common guillemot (=common murre) Uria aalge, razorbill Alca torda, and red-throated diver Gavia stellata), and to identify key knowledge gaps in terms of assessing impacts of offshore wind farms for these seabird species and specifically for their populations in the southern North Sea.
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Many studies have shown that seabirds are sensitive to changes in food supply, and therefore have potential as monitors of fish stocks. For most seabird species breeding parameters suitable for biomonitoring have yet to be measured over a wide range of prey densities. However, it is clear that responses vary among species and care must be taken when interpreting seabird data as a proxy for fish abundance. For many years seabirds have also been used as monitors of pollution, especially oil pollution. Beached bird surveys provide important evidence of geographical and temporal patterns, and, for example, show consistent declines in oil release into the southern North Sea over the last 15 years. Analysis of oil on birds can now permit fingerprinting of sources, allowing prosecution of polluters. As predators high in marine food webs, seabirds also have potential as monitors of pollutants that accumulate at trophic levels. Recent work on mercury in seabirds has permitted an analysis of spatial patterns and of the rates of increase in mercury contamination of ecosystems over the last 150 years, since mercury concentrations in feathers of museum specimens can be used to assess contamination in the birds when they were alive. Surprisingly, pelagic seabirds show higher increases than most coastal ones, and increases have been greatest in seabirds feeding on mesopelagic prey. This seems to relate to patterns of methylation of mercury in low-oxygen, deeper water. Accurate measurement of long-term trends in mercury contamination depend on the assumption that seabird diet composition has not changed. This can be assessed by analysis of stable isotopes of N and C from the same feathers used for mercury measurement, a technique that also permits the monitoring of trophic status over time or between regions. While high mercury contamination of seabirds in the southern North Sea is unsurprising, we cannot yet explain certain unexpected results, such as high levels in seabirds from north Iceland compared with those from south Iceland or Scotland.
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We investigated the roles of food shortage and predation in anticipated breeding failure of black-legged kittiwakes Rlssa trldactyla at Great Island, Kr~tless Bay, Newfoundland, Canada In 1992 and 1993, following widespread failure in 1991 Reduced and delayed availability of capelin Mallotus villosus, plus elimination of previously plentiful fish offal and discards following an eastern Canadian groundfish moratorium in 1992, induced food-stress on kitt~wakes and on large predatory Larus gulls. Breeding was late, a low proportion of pairs laid eggs, and egg and clutch sizes were small, indicating that feeding condlt~ons for kittiwakes were poor early in the season. Extreme food-stress resulted in low b r e e d ~ n g success of Larns gulls that turned to kittiwake eggs as an alternate food source. Forced egg predation by great black-backed gulls Larus marinus was the primary cause of low hatching success (10 to 11 %) in both years. Durations of incubation and chick-rearing shifts decreased following the inshore arrival of capelin, and chicks that hatched after capelin arrival survived longer than earlier hatched chicks. Unattended nests were uncommon, probably in response to predation. In 1992, earlier hatching, later capelin arrival, and apparent lack of alternate prey resulted in many chicks starving and poor fledging success (7%). In 1993, food appeared to be more available both before and after capelin arrival, parents were able to provision chicks, and fledging success was normal (68%) The interactive effects of food shortage and predation have important linplications for the use of kittiwakes as indicator species and for the indirect effects of fishery activities on seabird interactions. Kittiwake productivity also reflects the resource base of t h e ~ r predators and caution is required when llnking kittiwake breeding success to prey abundance. Moreover, fishery activities, such as the eastern Canadian groundfish morator~um that eliminated fish discards and offal for large scavenging gulls, can have profound second-order effects on other seabird species that are preyed on by scavengers.
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We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1° latitude-longitude grid from 1871. The companion HadMAT1 runs monthly from 1856 on a 5° latitude-longitude grid and incorporates new corrections for the effect on NMAT of increasing deck (and hence measurement) heights. HadISST1 and HadMAT1 temperatures are reconstructed using a two-stage reduced-space optimal interpolation procedure, followed by superposition of quality-improved gridded observations onto the reconstructions to restore local detail. The sea ice fields are made more homogeneous by compensating satellite microwave-based sea ice concentrations for the impact of surface melt effects on retrievals in the Arctic and for algorithm deficiencies in the Antarctic and by making the historical in situ concentrations consistent with the satellite data. SSTs near sea ice are estimated using statistical relationships between SST and sea ice concentration. HadISST1 compares well with other published analyses, capturing trends in global, hemispheric, and regional SST well, containing SST fields with more uniform variance through time and better month-to-month persistence than those in GISST. HadMAT1 is more consistent with SST and with collocated land surface air temperatures than previous NMAT data sets.
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We discuss methodological and implementation issues of spatial, temporal and combined spatio-temporal backtracking and illustrate larval backtracking for North Sea lesser sandeel Ammodytes marinus larvae, using a combined hydrodynamical and individual-based model. It was found that dispersal effects are important for larval backtracking predictions. Our results show large differences in average transport distance, as well as in shape and extent of predicted hatch areas, when backtracking advected larval cohorts in different regions of the North Sea, thus emphasizing the importance of using realistic, spatially and temporally resolved diffusivity fields in simulations of larval transport. In all cases, biologically likely hatching areas have been predicted. We discuss issues of methodological consistency and present a new scheme for including life-history stochasticity effects on growth in backtracking in a consistent way, as well as procedures for assessing the effects of larval mortality. Finally, fundamental limitations of larval backtracking are clarified, most importantly the time horizon and spatial resolution limit for backward prediction.
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The population dynamics of marine top predators such as seabirds may be self-regulating through local prey depletion, or they may reflect environmentally induced fluctuations in prey availability. Both mechanisms are not mutually exclusive. We examined spatio-temporal variation in breeding success of black-legged kittiwakes Rissa tridactyla, a seabird widely monitored in the British Isles. Kittiwakes here feed mostly on lesser sandeels Ammodytes marinus, a species that is strongly tied to specific sediment types and therefore shows a strong regional population structure. Neither kittiwake colony growth rate nor breeding success correlated negatively with colony size as expected under local prey depletion in the absence of regional variation in carrying capacity. We used multivariate analyses of breeding success data for 42 kittiwake colonies to identify clusters showing synchronised variation in success, and compared these with known sandeel aggregations identified from fish and fishery surveys. A number of geographically distinct clusters of kittiwakes were identified, and these were largely congruent with sandeel aggregations. Major sandeel aggregations with clear associated clusters of kittiwake colonies occurred off of east England and east Scotland, while western coasts of Britain were characterised by smaller aggregations and less obvious kittiwake clusters. There was considerable regional variability in sandeel recruitment, and this was reflected in mostly uncorrelated time series of kittiwake breeding success between different regions. These results indicate that regional variation in prey availability had a stronger effect on kittiwake dynamics than local prey depletion. An appreciation of the appropriate spatial scale of prey dynamics thus improves understanding of the dynamics of marine predator – prey systems.
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Sandeels Ammodytes marinus are important food for many breeding seabirds in the North Sea, and are harvested in large quantities by an industrial fishery. There is very little evidence of the fishery reducing availability of sandeels to breeding seabirds, but there is concern that fishery managers should take account of the needs of breeding seabirds. Here we present a quantitative index of the sensitivity of different seabird species' breeding success to reduced abundance of sandeels. The index is based on seabird size, cost of foraging, potential foraging range, ability to dive, amount of 'spare' time in the daily budget, and ability to switch diet. Testing the index with empirical data from Shetland during periods of reduced sandeel abundance shows a close correlation between seabird breeding performance and predictions from the index. Mapping the distributions around the North Sea of seabirds with breeding success highly sensitive to sandeel abundance shows that the majority of sensitive seabirds breed in Shetland and Orkney. industrial fishing in those regions should be closely controlled to avoid depleting the local sandeel stocks on which seabirds depend. This analysis considers only impacts on seabird breeding. There is a need for analysis of possible influences on other aspects of seabird demography.
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The lesser sandeel Ammodytes marinus is a key prey species for many marine birds in the North Sea. This fish is currently the target of the largest single species fishery in the area, and this has led to concern about the potential impact of the fishery on seabirds. There are 2 critical issues: does the breeding success of seabirds depend on sandeel availability and does the fishery reduce sandeel availability to a level at which avian reproductive output is affected? This paper investigates the first question in detail and briefly touches on the second by testing for correlations between productivity, breeding effort and diet in 3 species of seabird with contrasting foraging and dietary characteristics (common guillemot Uria aalge, black-legged kittiwake Rissa tridactyla, and European shag Phalacrocorax aristotelis) and an index of availability of 1 group and older sandeels derived from catch per unit effort statistics from the Danish sandeel fishery. Breeding success in all 3 species was significantly reduced when sandeel availability to the fishery in June was low. There was also evidence that the timing of peak sandeel availability influenced reproductive output such that success was lower when availability peaked early. We speculate that these effects are linked to annual variations in sandeel Life history events and, in particular, to the onset of burying behaviour of 1+ group fish and the arrival of 0 group sandeels on the seabirds' feeding grounds. Although the timing of these events is unlikely to be directly influenced by the sandeel fishery, since most catches are taken in June, it is possible that the fishery could exacerbate a difficult situation for seabirds by further reducing the biomass of available 1+ group fish. We suggest that this may have occurred in one of the years of the study.
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The lesser sandeel Ammodytes marinus is a key prey species for many avian predators in the North Sea, and is the target of the largest single species fishery in the area. This has led to concern about the potential impact of the fishery on seabirds. The most vulnerable predatory species are small and surface-feeding, characteristics that are exemplified by the black-legged kittiwake Rissa tridactyla. This paper reports on the first assessment of seasonal changes in prey composition and prey size for the kittiwake in the North Sea during 4 breeding seasons (1997 to 2000) in which breeding success varied dramatically. Kittiwake diet showed little inter-annual variation, with a well-defined seasonal change from planktonic crustacea in early spring, to 1+ group sandeels in April and May, to 0 group sandeels in June and July. However, there was evidence that temporal differences in sandeel life history events were well reflected in both kittiwake diet and breeding success. Thus, the most successful year (2000) was characterised by the earliest appearance of 0 group sandeels, while the least successful season had the latest appearance. There was also a link between annual variations in breeding success and sandeel size such that success was lower when 0 group sandeels were smaller and hence of lower energy value. Our study included 3 seasons (1997, 1998, 1999) during which the industrial fishery was operating within 50 km of the study colony and 1 (2000) in which the fishing grounds were closed. The higher breeding success in 2000 than in the other years suggests that the closure of the fishery might have had an immediate and positive effect on kittiwake productivity. However, as the dietary data indicated, the earlier appearance and rapid growth rates of 0 group sandeels in 2000 suggests that the enhanced breeding success was more likely to have been a response to environmental factors influencing the growth and timing of life history transitions of this prey.
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Breeding performance of seabirds reflects conditions in the marine environment, and seabirds are often considered suitable indicators because they are sensitive to variations in food sup- ply and relatively easy to observe. However, any individual parameter (e.g. breeding success of a particular species at one site) may also be affected by drivers other than food supply, and selecting a suitable univariate indicator can be difficult, particularly if independent estimates of food availability on the appropriate scale are unavailable. We propose combining several data sets to overcome this limitation: if a given temporal pattern occurs for several parameters measured at one site, or for the same parameter measured at several sites, it is likely to reflect important spatiotemporal environmen- tal variation, probably linked to food supply. Multivariate statistical techniques, such as principal component analysis (PCA), can be used to extract common signals from a number of intercorrelated time series. Examples from seabirds in the North Sea demonstrate that such common signals are correlated with physical and biological environmental variables. We propose a preliminary 'North Sea seabird index' and discuss how this index could be used in ecosystem-based management.
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Many seabirds in the North Sea feed on lesser sandeels Ammodytes marinus during the breed- ing season. Unprecedented breeding failures were recorded at many seabird colonies on the east coast of Britain in 2004. We used demographic, dietary and behavioural data from a long-term study of a colony of common guillemots Uria aalge, the most abundant seabird species in the North Sea, to set the 2004 season in context. Birds at this colony showed greatly reduced breeding success and those chicks that did survive left the colony in very poor condition. The main prey item fed to chicks in 2004 was sprat Sprattus sprattus rather than sandeels, and parents increased the amount of time spent foraging, frequently leaving chicks unat- tended in order to maintain a normal feeding rate. The calculated daily food intake of chicks derived from these values did not differ markedly from previous years and therefore the magnitude of the impact on chick growth and breeding success appeared dispro- portionately large. However, nutrient analyses of fish collected from birds in 2004 revealed them to be of sig- nificantly lower energy value than expected. Poor food quality therefore appeared to be the proximate cause of seabird breeding failure in 2004 giving support to the 'junk-food' hypothesis. Single-prey loaders such as guillemots will be particularly sensitive to reductions in the energy value of food items. The reasons for the poor fish condition in this part of the North Sea are currently unknown, but the results provide further evidence of major changes in the North Sea food web.
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In this review we detail the impact of climate change on marine productivity, on marine environmental stochasticity and cyclicity, and on the spatio-temporal match-mismatch of seabirds and their prey. We thereby show that global warming has a profound bottom-up impact upon marine top-predators, but that such effects have to be studied in conjunction with the (top-down) impact of human fisheries upon seabird food resources. Further, we propose seabird ecological features, such as memory effects and social constraints, that make them particularly sensitive to rapid environmen- tal change. We provide examples of how seabirds may nonetheless adapt when facing the conse- quences of climate change. We conclude that our understanding of the spatial ecology of seabirds facing environmental change is still rudimentary, despite its relevance for the conservation of these vulnerable organisms and for the management of marine ecosystems. We define the following research priorities. (1) Determine the factors affecting seabird distribution and movements at sea using biotelemetry, as well as colony dynamics on land. (2) Link seabird distribution patterns to those of their prey. (3) Determine further the role of historical and metapopulation processes in contribut- ing to the dynamics of the spatial distribution of seabirds. (4) Assess phenotypic plasticity and the potential for microevolution within seabird spatial responses to climate change, since both will greatly affect the quality of modelling studies. (5) Adapt existing models to define and predict the impact of climate change onto seabird spatial dynamics. (6) Synthesize all gathered information to define marine protected areas and further conservation schemes, such as capacity reduction of fish- eries. This research effort will require maintaining existing long-term monitoring programmes for seabirds, as well as developing new approaches to permit the integration of processes occurring at various scales, in order to be able to fully track the population responses of these long-lived verte- brates to environmental changes. Resale or republication not permitted without written consent of the publisher Contribution to the Theme Section 'Spatiotemporal dynamics of seabirds in the marine environment' OPEN PEN
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Upcoming reform of the European Union (EU) Common Fisheries Policy will be the biggest change in European fisheries management for a generation. A central plank of this reform is a proposed ban on discards, to aid the creation of economically and environmentally sustainable fisheries. This, together with a global trend for declining discards, may have unforeseen knock-on consequences for the large number of scavenging seabirds that consume this plentiful subsidy. Discards have shaped many aspects of seabird foraging, distribution and population dynamics. Here, we review these effects and consider the potential for both negative and positive impacts of discard reforms for seabirds, with particular focus on the EU, and propose recommendations for ongoing research and conservation. EU seabird scavengers are dominated by a relatively small number of large generalist taxa. Many of these occur at globally significant numbers within the EU, but may be able to buffer a decline in discards by switching to feed on alternative foods. A discard ban may have negative consequences by creating a food shortage for scavenging birds. Some species may offset this by feeding more on other birds, with potentially negative population-level impacts, or by moving into novel environments. Benefits of a discard ban may be a reduction in seabird bycatch in fishing gears, as well as a reduction in populations of large generalist species that currently dominate some seabird communities. Synthesis and applications. Reform of the Common Fisheries Policy and global discard declines are essential components towards creating sustainable fisheries, but may have both detrimental and beneficial effects on seabird communities. The nature of these impacts is still poorly understood, highlighting the need for detailed long-term seabird monitoring, as well as building resilience into populations through policy measures that incorporate remedial action on major seabird conservation priorities. Research should focus on understanding how seabird foraging, in terms of functional responses and searching behaviour, is influenced by both changing discards and natural fish prey availability, and how they impact upon fitness. It is also essential to link individual-level responses with population-, community- and ecosystem-level change. Understanding these links is fundamental to ongoing seabird management and conservation, and an ecosystem-based approach to fisheries management.
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Capsule We examined regurgitates from Black-legged Kittiwakes during the early chick-rearing period over two breeding seasons at two colonies in Ireland where diet has not been studied previously. Clupeids were the dominant food source at both colonies, which contrasts with other studies throughout the British Isles that suggest Kittiwakes feed mainly on sandeels during this period. Our study is limited by sample size and restricted to the early breeding season, but suggests a link between reproductive success and dietary composition which should be investigated further.
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We have calculated a time series of larval transport indices for the central and southern North Sea covering 1970-2004, using a combined three-dimensional hydrodynamic and individual-based modelling framework for studying sandeel (Ammodytes marinus) eggs, larval transport, and growth. The egg phase is modelled by a stochastic, nonlinear degree-day model describing the extended hatch period. The larval growth model is parameterized by individually backtracking the local physical environment of larval survivors from their catch location and catch time. Using a detailed map of sandeel habitats in the North Sea, the importance of hydrography for early life stages of sandeel to their recruitment success is explored. We find that the sandeel larval transport patterns in the North Sea are relatively robust toward uncertainties in biological parameters, when mortality aspects are included. We find only weak spatiotemporal correlations between elements of the transport indices in the time series, mainly positive correlation between retention terms for the same year. The transport connectivity of sandeel habitats in the North Sea and the dynamical properties of the North Sea transport system are also analyzed, and we introduce novel a scheme to quantify direct and indirect connectivity on equal footings in terms of an interbank transit time scale.
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Conservation biologists struggle to decide how many animals to save. In this article, I outline 18 approaches to setting population target levels (PTLs) for animals, with rules of thumb and analytical recommendations for each approach. Minimally viable populations, the most common target level, are necessary but not sufficient for most efforts, given the range of values that bear on conservation. Reference ecosystems, either extant or historical, are key for setting practical target levels. Setting PTLs sufficient for conserved populations to be animals in all respects (including functional, social, landscape, ethical, aesthetic, and spiritual aspects) is a critical consensus point. In many cases densities as well as overall population size will need to be specified. I suggest a four-tiered system of setting incrementally higher population target levels such that conservation provides first for demographic sustainability, then ecological integrity, then sustainable use, and finally restoration of historical numbers of wildlife, based on times when human beings had less impact on the planet than we do today.
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Climate change has had profound effects upon marine ecosystems, impacting across all trophic levels from plankton to apex predators. Determining the impacts of climate change on marine ecosystems requires understanding the direct effects on all trophic levels as well as indirect effects mediated by trophic coupling. The aim of this study was to investigate the effects of climate change on the pelagic food web in the Celtic Sea, a productive shelf region in the Northeast Atlantic. Using long-term data, we examined possible direct and indirect 'bottom-up' climate effects across four trophic levels: phytoplankton, zooplankton, mid-trophic level fish and seabirds. During the period 1986-2007, although there was no temporal trend in the North Atlantic Oscillation index (NAO), the decadal mean Sea Surface Temperature (SST) in the Celtic Sea increased by 0.66±0.02°C. Despite this, there was only a weak signal of climate change in the Celtic Sea food web. Changes in plankton community structure were found, however this was not related to SST or NAO. A negative relationship occurred between herring abundance (0- and 1-group) and spring SST (0-group: p = 0.02, slope = -0.305±0.125; 1-group: p = 0.04, slope = -0.410±0.193). Seabird demographics showed complex species-specific responses. There was evidence of direct effects of spring NAO (on black-legged kittiwake population growth rate: p = 0.03, slope = 0.0314±0.014) as well as indirect bottom-up effects of lagged spring SST (on razorbill breeding success: p = 0.01, slope = -0.144±0.05). Negative relationships between breeding success and population growth rate of razorbills and common guillemots may be explained by interactions between mid-trophic level fish. Our findings show that the impacts of climate change on the Celtic Sea ecosystem is not as marked as in nearby regions (e.g. the North Sea), emphasizing the need for more research at regional scales.
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Marine wind farms have attracted substantial public interest. The construction of wind facilities offshore may become Europe's most extensive technical development in marine habitats. Due to political pressure to complete construction soon, assessments of possible wind farm locations, for example in the German sectors of the North Sea and Baltic Sea, have to be based on existing knowledge. In this study, we developed a wind farm sensitivity index (WSI) for seabirds. We applied this index to the Exclusive Economic Zone and the national waters of Germany in the North Sea. We chose nine factors, derived from species’ attributes, to be included in the WSI: flight manoeuvrability; flight altitude; percentage of time flying; nocturnal flight activity; sensitivity towards disturbance by ship and helicopter traffic; flexibility in habitat use; biogeographical population size; adult survival rate; and European threat and conservation status. Each factor was scored on a 5‐point scale from 1 (low vulnerability of seabirds) to 5 (high vulnerability of seabirds). Five of these factors could be dealt with by real data but four could only be assessed by subjective considerations based on at‐sea experience; in the latter cases, suggestions of the first author were independently modulated by experts. Species differed greatly in their sensitivity index (SSI). Black‐throated diver Gavia arctica and red‐throated diver Gavia stellata ranked highest (= most sensitive), followed by velvet scoter Melanitta fusca , sandwich tern Sterna sandvicensis and great cormorant Phalacrocorax carbo . The lowest values were recorded for black‐legged kittiwake Rissa tridactyla , black‐headed gull Larus ridibundus and northern fulmar Fulmarus glacialis . A WSI score for areas of the North Sea and Baltic Sea was calculated from the species‐specific sensitivity index values. Coastal waters in the south‐eastern North Sea had values indicating greater vulnerability than waters further offshore throughout the whole year. Derived from the frequency distribution of the WSI, we suggest a ‘level of concern’ and a ‘level of major concern’ that are visualized spatially and could act as a basis for the selection of marine wind farm locations. Synthesis and applications. The wind farm sensitivity index might be useful in strategic environmental impact assessments (EIA). Results of small‐scale EIA from wind installations should be considered within a more global perspective, provided, for example, by large mapping projects and detailed behavioural studies. This is difficult in normal EIA, particularly in highly dynamic coastal/marine habitats, and the results of this study fill an important gap by providing information on the potential sensitivity of seabirds and the importance of locations of wind installations.
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Many of the breeding seabird populations in Britain and Ireland are of international importance; consequently, there is a statutory duty to protect these populations, as part of national biodiversity strategies and under Article 4 of the EU's Directive on the Conservation of Wild Birds (EC/79/409). As part of this process, populations have been monitored annually at a sample of colonies since the mid-1980s and (near) complete surveys have been undertaken twice. Results of this monitoring are currently reported regionally, in an effort to reflect the impact of spatially varying environmental drivers of change; however, there is concern that these regions reflect policy requirements rather than ecological relevance, particularly for mobile species. We used the monitoring data to identify a series of ecologically coherent regions in which trends in abundance and breeding success varied in a consistent fashion and examined how closely the annually sampled data matched the change quantified by the whole population surveys. The number of ecologically coherent regions identified varied from 2 for the northern gannet Morus bassanus and common guillemot Uria aalge to 7 for the great cormorant Phalacrocorax carbo. Trends imputed for ecologically coherent regions more closely matched those observed between whole population censuses and were more consistent than those identified for more policy-driven monitoring regions. By accounting for ecology in the design of monitoring regions, population variation in mobile species can be more accurately represented, leading to the design of more realistic monitoring regions.
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Seabirds are frequently used as indicators of the state of the marine environment. The kittiwake (Rissa tridactyla) is a common and widespread surface-feeding seabird often used for such a purpose. Data were collected on the food of chicks, breeding success, and chick neglect at a colony in south-east Scotland every summer in the period 1986–1996. Breeding success declined significantly over the period and breeding became later. In one year, many adults failed to breed. A similar decline in breeding success was also recorded at colonies over a 250–300 km section of coast in south-east Scotland and north-east England. Sandeels (Ammodytes marinus), especially 0-group fish (young of the year), made up the bulk of the diet in all years; herring (Clupea harengus) and sprat (Sprattus sprattus), waste from trawlers, and planktonic Crustacea was of lesser importance. Nesting success increased significantly with the proportion of 0-group sandeels in the diet of chicks and with the average energy value of 0-group sandeels, variables which were significantly and positively correlated. Clupeids and trawler waste were probably taken only when sandeels were unavailable. Brood neglect was not a good indicator of annual total breeding success. The decline in nesting success appeared to commence before the development of a large local industrial fishery for sandeels.
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Several recent studies of seabirds have found high levels of nonbreeding by experienced adults. By contrast, just 8.9% (range 4-14%) of experienced Great Skuas (Ca-tharacta skua) on Foula, Shetland Islands, deferred breeding between 1989-1996. For Par-asitic Jaegers (Stercorarius parasiticus), a corresponding value of 5.5% (range 3-8%) was found between 1993-1994. Only 3% of the territorial pairs of Parasitic Jaegers, including new recruits, failed to lay eggs. Higher incidence of nonbreeding in Great Skuas was re-corded in years when fledging production was low. Loss of mate due to death or divorce was the main direct cause of nonbreeding. Loss of territory also was important for male birds. In Great Skuas, more males missed a breeding season than females, but the same did not apply to Parasitic Jaegers. Very young and very old Great Skuas were more likely to defer breeding than mid-aged birds. Evidence is presented that the decline in breeding frequency of old birds was due to senescence as opposed to increased frequency of mate-changes resulting from a high mortality of old partners.