Offshore renewable developments - developing marine mammal dynamic energy budget models: report

2 Introduction

The offshore wind industry in the process of a significant expansion with a move towards clean energy and a green economic recovery. The sustainable expansion of offshore wind requires a robust understanding the impacts of construction and operation and appropriate levels of conservatism and realism in assessments. The potential risk of injury and/or disturbance to marine mammals during construction of offshore renewable energy developments (e.g., pile driving, removal of unexploded ordnance, increased vessel presence offshore) has been identified as a key consenting risk for projects in UK waters. Possible consequences of exposure to underwater noise include; disturbance that could cause marine mammals to either move away or change behaviour (which could result in reduced net energy intake) or suffer temporary and permanent hearing damage.

The scale of offshore wind farm developments means there is the potential for significant cumulative impacts on marine mammals, which would need to be considered and mitigated at a project and regional level. The interim framework for assessing the Population Consequences of Disturbance (PCoD) was released in 2014 (Harwood et al. 2014, King et al. 2015). The iPCoD model relies on relationships between disturbance experienced by an animal and how that disturbance impacts vital rates like the probability of surviving to the next year or the chance of giving birth to a viable pup or calf. The relationships used in iPCoD were obtained from expert elicitations. In these elicitations, experts are asked to estimate the number of days of disturbance an animal can tolerate before a vital rate is affected, and the number of days of disturbance required to cause the maximum effect of disturbance in order to parameterize the transfer function required. The iPCoD tool has been updated with new elicitations and other improvement in recent years (including updated elicitations) (e.g., Booth and Heinis 2018, Booth et al. 2019). This resulted in version 5 of the iPCoD code which is publicly available – this tool is currently being integrated into the Cumulative Effects Framework. Despite these model updates, the reliance on expert judgement is a source of uncertainty in assessments and risk for decision makers (as it relies on the carefully solicited judgments of experts rather than empirical datasets).

The overall objective of this project is to describe Dynamic Energy Budget (DEB) frameworks for harbour seal (Phoca vitulina), grey seal (Halichoerus grypus), bottlenose dolphin (Tursiops truncatus) and minke whale (Balaenoptera acutorostrata) to help improve marine mammal assessments for offshore renewable developments. The aim is to produce final models for these species, to go along with the harbour porpoise DEB model (Harwood et al. 2020) that can be applied to project level assessments to help address potential risk to marine mammals from offshore wind and other developments.

This study provides new tools to move towards a more empirically-based framework to reduce this uncertainty. Of course, all models require subjective decisions in the selection of parameters and so we cannot remove all expert judgment from such processes. But we can provide greater transparency of where the knowledge gaps are and the key sensitivities of models. Such models are yet to be used in formal assessments, but by developing the models, it adds to the suite of tools available when an energetic pathway is being considered (as is largely the case with disturbance effects). In the future, this will help understand the potential knock-on effects population demographic of disturbance, therefore providing a more in-depth assessment of how disturbance might affect population growth rate (over a longer time periods) and highlight life history stages that are particularly vulnerable to disturbance.

2.1 Document Structure

Section 3 provides background the energetics and disturbance and an introduction to DEB theory. In Section 4 we outline the overview, design and details of DEB models – following the ODD (Overview, Design concepts, and Details) protocol of Grimm et al. (2020). Section 5, 6, 7 and 8 describes the data used to parameterise the models for harbour seals, grey seals, bottlenose dolphins and minke whales respectively. This provides complete transparency of the main data gaps that remain as we move towards a more empirically-based framework. In each of those sections there are explorations of the simulated effects of disturbances. Section 9 explores how we can account for uncertainty in energetics models. Section 10 covers another important feature of assessments of disturbance – considering the movement ecology of species (which affects the probability of exposure – a key determinant of impacts). The report concludes in Section 11, with consideration of future developments required with respect to energetics, movement and understanding the effects of disturbance.