Feasibility of extending SeabORD to the entire breeding season: study

Introduction

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 and have decarbonised the energy system almost completely by 2045^[1]. However, the Scottish Government has a duty to ensure that ORDs are delivered 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 (Drewitt & Langston 2006; Masden et al. 2010; Scottish Government 2011).

Individual-based simulation models (IBMs) are a useful tool for assessing the cumulative effects of behavioural decisions and energetics in animals, particularly in situations where empirical data is lacking, meaning correlative methods may not be used. However, as for all models, the outputs of IBMs are subject to uncertainties in model parameterisation and the inputs used to drive models. When based on well-grounded assumptions and reliable parameter estimates, individual-based simulation models can provide a valuable framework for estimating the demographic consequences of a variety of environmental perturbations. As such, this approach can be used to estimate demographic effects for seabirds of offshore renewable developments mediated via the costs of barrier effects and displacement from habitat, whilst incorporating some of the uncertainty surrounding these estimates, where possible.

An individual-based simulation model, SeabORD (Searle et al. 2014, Searle et al. 2018), has been developed to predict 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 to translate 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 (Oro and Furness 2002, Erikstad et al. 2009). Baseline scenarios are compared with scenarios containing one or more ORDs.

It is increasingly recognised that impacts of ORDs on seabirds are not only manifest during chick-rearing, but are likely to operate throughout the year, and notably during pre-laying, incubation and post-fledging phases of the breeding season when many adults are attending colonies and therefore restricted to act as central place foragers. New science is now needed to extend SeabORD to cover the whole of the breeding season for each of the four species currently parameterised within the model, for which the model currently only simulates over the chick-rearing period. Note that full extension to the whole of the breeding season (pre-breeding attendance, incubation, chick-rearing, post-fledging attendance) may not be possible for all species due to a lack of data. Full implementation of this extension would necessitate a large project, with several key stages: 1. Data collection and processing, 2. Theoretical model development, 3. Model coding and testing, and 4. Model validation, QA and sensitivity analysis.

In this project, we have undertaken an initial 'feasibility study' to make a broad assessment for each of the four species currently modelled within SeabORD in terms of key parameters and ecological processes, data availability, data and knowledge gaps, and development of theory for seabird behaviour and constraints in each of the breeding season phases. This feasibility study can inform the scope and design of potential follow-on projects aimed at filling in data or knowledge gaps, extending SeabORD to include new species, and to model ORD impacts over the wider breeding season. We have also explored the potential for additional species to be modelled within SeabORD across different phases of the breeding season, and provided an assessment for how the recommendations from the NatureScot marine bird impact assessment guidance workshop could be implemented within the model.