- Offshore Renewable Developments (ORDs) can make a significant contribution to the Scottish Government's target to generate 50% of overall energy consumption from renewable sources by 2030, but there is a requirement on Scottish Government to deliver them in a sustainable manner in accordance with the requirements of the Marine Strategy Framework Directive (EC/2008/56), the Habitats Directive (EC/92/43) and the Birds Directive (EC/79/409). Offshore renewable developments have the potential to affect seabirds that are protected by the EU Birds Directive, and transposed domestic legislation, notably from collisions with turbine blades and through displacement from important habitat.
- A key current concern is that Population Viability Analyses that are the standard method of forecasting future population change of seabirds as part of ORD assessments, do not account for any effects of environmental change on populations. However, many seabird species in the UK have shown marked declines in recent decades and there is widespread evidence that these are in part caused by changes in marine ecosystems as a result of climate change. Climate change can affect seabird populations indirectly via changes in food supply, or directly such as through mortality from extreme weather.
- In this project, we examined the potential impacts of climate change by quantifying the effects of climate on seabird distribution, abundance and demography. We developed future estimates for the spatial distribution and abundance at seabird foraging areas and for demographic rates, abundance, and the influence of varying foraging ranges at seabird breeding colonies on access to suitable climate conditions.
- To identify climate variables of relevance to seabird demographics we conducted a literature review in Web of Science (WoS) using the terms 'seabirds', 'climate', 'productivity', 'breeding success', 'survival' and 'demography'. This identified 20 published studies, which we summarised into two sets of climate variables (terrestrial and marine) relating to breeding success or adult survival. We focused on variables for the analysis that were sufficiently spatially or spatio-temporally resolved to be relevant to seabirds breeding on the east coast of the UK, and which were also available in projected future climate scenarios, with the exception of terrestrial wind which we included in the retrospective analyses because the literature review highlighted its important effects on demography. The list of variables included three terrestrial (minimum air temperature; max precipitation; mean wind speed) and four marine (sea surface temperature, sea surface salinity, North Atlantic Oscillation and Atlantic Multidecadal Oscillation). All predictions for future climate were made using forecasted variables from UKCP09 projections for the SRES Scenario A1B (medium). Spatiotemporal forecast variables represented an average over 30 years (2070-2099), and predictions represented a 'typical' year across this period. This was the only set of climate projections for all marine and terrestrial variables available at the onset of the project, and as such, the resulting predictions show potential changes to seabird distribution and demography under future climate conditions fifty years hence. Therefore, predictions probably represent a more extreme set of changes than is likely over the next 20-30 years of relevance to the lifetime of currently consented and planned offshore wind farms.
- We constructed statistical models to link at-sea survey data on the spatial distribution of birds and colony-based estimates of productivity and abundance to key climate-related variables in the form of a retrospective analysis of historical data. We then used modelled estimates for relationships between distribution, demographic rates and climate to forecast future projected change in at-sea distributions, productivity, adult survival (indirectly estimated from counts and breeding success) and population growth rates. At-sea distribution and abundance were modelled using a Generalised Estimated Equation – Generalised Linear Model (GEE-GLM) modelling approach, building upon previous models developed for the NERC/DEFRA MERP and ORJIP Sensitivity Mapping Tool projects. We analysed the effect of climate variables on productivity and adult survival via both frequentist generalised linear mixed models (GLMMs), which are very widely used in statistical ecology, and Bayesian approaches which offer a more flexible approach for formulating ecological processes within models. We used colony-specific and year-specific data on counts and productivity from the Seabird Monitoring Programme (SMP) for breeding colonies throughout the region of interest.
- Modelling of seabird at-sea distribution and climate showed that two species, Atlantic puffin and black-legged kittiwake, favoured the coldest waters and were therefore most likely to respond negatively to climate warming. In contrast, three species (common guillemot, razorbill and in particular northern gannet) showed an association with warmer waters, and were therefore least likely to be negatively affected by warming.
- At-sea distribution modelling resulted in widespread predicted declines under future climate projections among the majority of the species analysed. This was particularly the case for Atlantic puffin and black-legged kittiwake, in which declines were predicted to occur in both summer and winter. Common guillemot, herring gull and razorbill were predicted to decline during the summer months only, and great black-backed gull were predicted to decline during only winter months. In contrast, northern gannet were predicted to increase in both summer and winter, and notably razorbill were also expected to increase in winter months.
- Relative spatial distributional changes were only apparent in two species, common guillemot and razorbill, both of which were predicted to increase in the northern North Sea and decrease in the southern North Sea. Temporal shifts in distribution were predicted for Atlantic puffin and northern gannet, both of which were predicted to use the North Sea region more extensively in summer than winter, a pattern predicted to remain under the future climate scenario. Four species: common guillemot, razorbill, great black-backed gull and herring gull consistently showed higher numbers across the North Sea during winter. For common guillemot and razorbill these differences between winter and summer densities were predicted to become more marked under future climate conditions. These projections imply that common guillemot and razorbill may shift to have greater interactions with ORDs in the North Sea during the non-breeding period than currently, if future climate projections are manifest. Black-legged kittiwake were predicted to continue to use the North Sea throughout the year.
- These overall declines in abundance and spatial and temporal shifts in distribution are in line with previous work, suggesting that seabird habitat suitability, driven by changes in climate, will shift northwards in the North Sea over the next century, with associated widespread declines for many species.
- Productivity models demonstrated strong links between productivity and key climate variables in five species (Atlantic puffin, black-legged kittiwake, common guillemot, great black-backed gull, northern gannet), particularly highlighting associations with marine climate, with terrestrial climate playing a much more minor role. In four of the five species where strong climatic effects on productivity were detected, future climate projections indicated large declines in productivity relative to current productivity rates – this was the case for: Atlantic puffin, black-legged kittiwake, common guillemot and great black-backed gull. Only one species, northern gannet, was predicted to have increased productivity under future climate projections. In all five species, modelling indicated there would be very limited or no opportunity for species to increase productivity under future conditions by expanding foraging ranges around breeding colonies to access more suitable climatic conditions.
- An important finding from the analysis of productivity and climate was that pre-breeding conditions were generally more important than conditions during the breeding season. This may result from the effect of such conditions on the quality or abundance of prey during the period of peak energy demand during breeding. Alternatively, it may represent a carry-over effect whereby conditions experienced by seabirds in one season (in this case late winter) have downstream consequences on subsequent seasons.
- These predicted declines in productivity, together with predicted declines in at-sea density and shifts in range in certain species, support past work on effects of climate warming on distribution and demography that threaten the future well-being of many breeding seabirds in the UK. Only one species, the northern gannet, showed future predictions of increased abundance and productivity, likely reflecting its more catholic diet, with less dependence on prey species that are negatively affected by warming. Our results suggest there will be profound changes to the North Sea seabird community in the coming century. This work has used a multi-colony, multi-species approach to broaden the knowledge base for understanding how seabirds breeding in the UK eastern seaboard may be affected by future climate change, demonstrating expected potential declines in a wider suite of species than previously identified.
- Our analyses on indirectly estimating adult survival from counts and breeding success data has highlighted the difficulties in robustly estimating adult survival from these data. A key area for future work is, therefore, to expand empirical observations more directly linked to survival, such as mark-recapture and mark-resighting data across a wide range of colonies and environmental conditions. Similarly, there is a nationwide lack of empirical data on juvenile survival in seabirds, which greatly inhibits current attempts to predict future population responses of seabirds to pressures.
- The results of these analyses suggest that climate change will have substantial impacts on demography and abundance of seabirds in the North Sea over the 21st century, and the impacts are likely to vary, in magnitude and form, between species. A failure to account for these changes in ORD assessments may lead to misidentification of the key affected populations, as well as misjudgement of the extent to which seabirds are likely to interact with ORDs over time, and inclusion in assessments could be considered at the scoping stage of the Environmental Impact Assessment (EIA) process. Any directional shift in habitat use, from South to North, will mean that the number and source populations of individual birds interacting with specific OW footprints will alter over time. This could mean that a static assessment identifying the protected populations of concern using apportioning methods applied to current day distributions could fail to identify populations that would come to interact with those footprints as their population sizes evolve over time, and their spatial habitat use changes in coming decades.
- Similarly, the evidence supporting potential seasonal shifts in habitat use of the North Sea for two species (common guillemot and razorbill) suggests that the seasonal period of greatest importance for ORD impacts on protected populations may change as climate alters. If species begin to use the North Sea proportionately more in the overwinter period than the breeding season, ORD impact assessments in the non-breeding season will become more critical to performing robust and accurate assessments. This is particularly challenging because at present, available methods for assessing impacts of ORD in the non-breeding season, and apportioning impacts back to protected colonies, are much cruder than those available for the breeding season. Moreover, it will become increasingly important that cross-border efforts to assess impacts for seabirds originating from different countries are better developed, because the ratio of seabirds from UK and non-UK populations in the North Sea during winter is likely to alter under future climate change.
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