Feasibility of extending SeabORD to the entire breeding season: study

SeabORD is a method that can assess displacement and barrier effects from offshore renewables on seabirds, but is currently limited to four species during the chick-rearing season. This review examined ways to improve the SeabORD model including extending to the entire breeding season.

Executive Summary

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.

In this project, we have reviewed the available data and methodologies for improving the estimation of displacement and barrier effects from offshore wind farms (OWFs), and their resulting demographic consequences, using the individual based model, SeabORD (Searle et al. 2014, 2018). SeabORD is an individual-based simulation model that predicts the time/energy budgets of breeding seabirds during the chick-rearing period for four species of UK seabirds (Atlantic puffin, common guillemot, black-legged kittiwake and razorbill), and translates these into projections of population level adult annual survival and productivity. The model simulates foraging decisions of individual seabirds under the assumption that they are acting in accordance with optimal foraging theory. In the model, foraging behaviour of individual seabirds is driven by prey availability, travel costs, provisioning requirements for offspring, and behaviour of conspecifics. The model estimates productivity and adult survival, the latter resulting from estimates of adult mass at the end of the breeding season and published relationships between adult mass and subsequent survival. Baseline scenarios are compared with scenarios containing one or more ORDs.

In this project, we examined the possibility for improving SeabORD in a number of key areas:

Extending SeabORD to cover the entire breeding season:

  • During incubation, tracking, at-sea survey and monitoring data have been collected for most species, often at multiple colonies and/or years, providing good basis for extending SeabORD to this breeding phase.
  • Much less data exist for the pre-laying and post-fledging phases. Monitoring data for these are limited and tracking data are mainly obtained from geolocation immersion loggers, which are generally not of sufficient resolution to investigate distributions and foraging trip characteristics. An exception are the large gull species where higher resolution data have been collected using state-of the art GPS-accelerometer-altimeter technology. The scope for extending SeabORD to these breeding phases is therefore limited.
  • For the additional species we considered (European shag, northern gannet, herring gull, lesser black-backed gull and Manx shearwater), there is potential for extending SeabORD to the incubation and chick-rearing phases. Substantial amounts of data are available for chick-rearing in particular.

Improving the use of prey availability data within SeabORD:

  • The most promising improvement for how SeabORD currently incorporates prey data is the soon to be published Marine Scotland sandeel occupancy and density map (Langton et al. 2021). This map will be at a sufficiently fine spatial resolution to allow for seabird-sandeel interactions to be simulated within SeabORD, and should provide a more defensible estimate of prey density than that estimated indirectly from bird foraging tracks. The map is derived from a long time series of data, and should therefore represent a long-term average of sandeel occupancy and density in the modelled region, which will be useful in terms of predicting seabird-sandeel interactions based on historical and current conditions.
  • However, given the known impact of changing climate on North Sea ecosystem dynamics and sandeel distribution and dynamics, more research is needed to understand and derive spatially explicit models for how the future distribution and availability of this key prey species may change over the lifespans of ORDs currently being built.
  • Ideally, in the same way that SeabORD assumes a re-distribution of seabird foraging locations post OWF construction (via displacement and barrier effects), the model should also include a re-distribution of prey availability due to OWF construction and operation, as appropriate. This information is broadly lacking for key seabird prey species like sandeels, and therefore represents an important knowledge gap for improving SeabORD, and ORD assessments more widely.

Adapting SeabORD to work with individual offshore wind turbines:

  • To implement bird behaviour around individual turbines requires the ability to parameterise different scales of avoidance behaviour – micro, meso and macros – such that biologically appropriate displacement and barrier behaviours can be simulated within SeabORD. Empirical evidence on these alternative scales of avoidance are currently only available for a limited number of species (e.g., gannets) and locations. Further empirical work is needed to better quantify these rates for different species, and to understand how rates may vary in relation to environmental and site-specific characteristics.
  • Once these data are available, it will be reasonably straightforward to implement a version of SeabORD capable of simulating bird interactions within individual turbines.

Improving the quantification of uncertainty within SeabORD:

  • The current Monte Carlo (i.e. simulation-based) approach to quantification of uncertainty within SeabORD should be retained, but this approach should be extended to incorporate uncertainty in a much wider range of parameters and inputs than those currently considered. As uncertainty is accounted for more comprehensively within SeabORD the set of model outputs should also be updated and expanded to capture this.
  • Further improvements to the computational efficiency of SeabORD are necessary so that it is possible to increase the number of simulations used in running it, because the reliability and stability of results obtained using the Monte Carlo approach to uncertainty are directly related to the number of simulations used.
  • A sensitivity analysis should be used to identify the parameters and inputs to SeabORD that are most influential in determining variations in model outputs, and the set of key parameters whose values are best estimated via calibration against observed data relating to model outputs should be re-evaluated based upon the outcomes of this sensitivity analysis..
  • The calibration process should be adapted so as to incorporate uncertainty, including the quantification of structural uncertainty. Emulation, and associated history matching methods, currently (given the computational constraints on running SeabORD) provide the most promising methodological approach for achieving this.
  • An updated literature review, and an associated expert elicitation exercise, should be used to update the values of the remaining parameters, and to quantify levels of uncertainty and variability associated with each of them.

Developing more realistic foraging tracks within SeabORD

  • We have identified and assessed four statistical methodologies that could provide possible contributions to developing more realistic simulated foraging return trips (and density maps*) in SeabORD:
    • Hidden Markov Models (HMMs)
    • Integrated continuous-time HMMs (ictHMMs)
    • Markov chain Monte Carlo step selection (MCMC ctHMM)
    • Langevin diffusion continuous-time model (LdctM)
  • In addition to the methodological advances we have suggested above, we suggest that simulating more realistic foraging trips based on tracking data could provide insight into more nuanced behaviours around ORD developments. For example, the refinement of typical flight paths due to barrier effects, and the estimation of barrier and displacement effects empirically before, during, and after ORD construction, as well as assessing non-permanent barrier effects such as varying spatio-temporal permeability.

Development of an individual-based model for the non-breeding season

  • There are marked differences in the ecology of seabirds in winter, with breeding adults operating independently from offspring and in many species not operating out of a central place (in contrast to the breeding season). Furthermore, data quality is poorer than during the breeding season, although it is improving
  • As such, there is potential to develop an individual-based model for the non-breeding season. Such a model would simulate time/energy budgets and translate these into projections of adult survival and subsequent productivity, incorporating available data on non-breeding season distribution, activity, energetics and demography including carry-over effects on productivity.
  • The model could be structured to apportion individuals to colony SPAs in species with sufficient data (e.g., guillemot and razorbill).

Incorporating uncertainty in mass-survival relationships within SeabORD:

  • We recommend replacing all current mass survival relationship estimates within SeabORD with the corresponding estimates from Daunt et al 2018, with the exception of Razorbills, which should use a composite set of estimates derived from Atlantic puffin and common guillemot estimates from the same report.
  • We recommended that the uncertainties associated with the revised relationships should, alongside this, also be incorporated into SeabORD, via a simulated-based approach, and that the outputs of SeabORD should be revised to include additional metrics that characterise uncertainty.

In conclusion, we provide a summary of the research recommendations arising from this project for developing the individual-based model, SeabORD, with associated broad estimates for the level of resourcing required for delivery.


Email: ScotMER@gov.scot

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