Harbour porpoise responses to the installation of XXL monopiles without noise abatement; implications for noise management in the Southern North Sea

Report

Title: Harbour porpoise responses to the installation of XXL monopiles without noise abatement; implications for noise management in the Southern North Sea

Author:

Benhemma-Le Gall, A.; Hastie, G.; Brown, A.; Booth, C.; Graham, I.M.; Fernandez-Betelu, O.; Iorio-Merlo, V.; Bashford, R.; Swanson, H.; Cheney, B.J.; Abad Oliva, N.; Thompson, P.M.

Publication Date:

August 1, 2024

Document Number:

PrePARED Report No. 004

Pages:

Affiliation

University of Aberdeen, Sea Mammal Research Unit (SMRU), SMRU Consulting, Ocean Winds

Sponsoring Organization:

The Crown Estate, Crown Estate Scotland, Offshore Wind Evidence and Change Programme

Technology:

Wind Energy, Fixed Offshore Wind

Stressor:

Noise

Receptor:

Marine Mammals, Cetaceans

Document Access

Attachment:

Access File

Citation

Benhemma-Le Gall, A.; Hastie, G.; Brown, A.; Booth, C.; Graham, I.M.; Fernandez-Betelu, O.; Iorio-Merlo, V.; Bashford, R.; Swanson, H.; Cheney, B.J.; Abad Oliva, N.; Thompson, P.M. (2024). Harbour porpoise responses to the installation of XXL monopiles without noise abatement; implications for noise management in the Southern North Sea (Report No. PrePARED Report No. 004 ). Report by University of Aberdeen. Report for The Crown Estate.

Abstract

This report presents the results of PrePARED research that builds upon consent monitoring undertaken during the installation of monopile foundations at Ocean Winds’ Moray West Offshore Wind Farm in 2023. No noise abatement systems were required by regulators for this project, providing an important opportunity to use these data to support management in UK waters. The management of impulsive noise in the Southern North Sea Special Area of Conservation (SNS SAC) for harbour porpoises uses time-area thresholds to limit the number of days on which activities producing impulsive noise are permitted. Licencing of these activities is underpinned by Effective Deterrent Ranges (EDR), which are used to assess the spatial scale of disturbance from different noise sources. There are no direct estimates of an EDR for monopiles which are being installed without noise abatement systems. Instead, the current EDR for installation of monopile foundations is 26 km, based on early data from pin-piling. More recent data and reviews of the source of this figure highlight that this estimate of EDR is conservative. Reducing this conservatism and associated uncertainty over disturbance from installation of large monopiles would ease management constraints that risk delaying delivery of offshore wind in and around the SNS SAC. Data on harbour porpoise detections were collected from a broad-scale array of 60 echolocation detectors (CPODs) moored up to 33.4 km from the pile-driving vessel. Analyses focused on the installation of seven XXL (9.5 m and 10.0 m diameter) monopiles where responses in the 24 h after piling could be compared with a matched period three days before piling started. We used the approach previously used to characterize porpoise responses to piling at the Beatrice Offshore Wind Farm, which informed the EDR used in the SNS SAC for pin pile installation. Despite noise levels for the installation of XXL monopiles being much higher, the response of porpoises to monopile installation at Moray West was similar to that observed in studies of pin-piling at Beatrice. The resulting proxy deterrence function indicates that an EDR based on these new data for monopiles would be 9.4 km. Comparison of these results with previous studies highlights the need for broader investigation of existing data and approaches to explore how other factors such as seasonal variation in foraging patterns, vessel traffic, use of acoustic deterrent devices and differences in experimental design shape the magnitude of observed response to different piling noise levels. In the meantime, we suggest that our estimated EDR of < 10 km provides a strong case for reducing the current 26 km EDR for monopiles.