TY - RPRT
TI - Assessing fatality risk of bats at offshore wind turbines
AU - Lagerveld, S
AU - Noort, C
AU - Meesters, L
AU - Bach, L
AU - Bach, P
AU - Geelhoed, S
AB - Recent research shows that bats regularly occur offshore, in particular during the migration season. At the same, time land-based studies show that bats frequently become victim of wind turbines, and it is plausible that fatalities occur at sea as well. Given the fast development of the offshore wind sector it is urgently needed to determine the offshore fatality rate in order to assess the impact of offshore wind turbines on bat populations.On land the methodology for assessing the fatality rate is rather straightforward. This includes regular carcass searching under the wind turbines and adjusting the number of fatalities for causes of imperfect detection. Offshore, however, carcass searching is virtually impossible and therefore a model-based or technical solution may be a more appropriate approach, which may be also applicable for assessing bird fatalities.This report aims to provide guidance on how offshore fatalities could be monitored in the future. The first option is a model-based approach which assesses the offshore fatality rate by extrapolating onshore fatality rates based on the measured post-construction acoustic bat activity. The main advantages and disadvantages of this solution are:Advantages Relatively easy to implementDisadvantagesPossibly biased results:When wind turbines with different dimensions are used for the reference dataWhen reference data is gathered at locations with different species compositions, season and environmental conditions.Not applicable for birdsA second option is a more empirical approach, in which fatalities are being monitored using measurement equipment that is able to detect the actual event, as well as the species involved. The application to monitor bat (and bird) fatalities should ideally consist of:A radar, which detects approaching flying objects and identifies the potential relevant ones (bats and birds).Thermal cameras, in order to obtain footage to assess collisions/barotrauma, as well as for the identification of bird species. Furthermore, thermal cameras may be used to record a falling corpse from the Rotor Swept Area (RSA).An ultrasonic detector (bat detector) to record bat echolocation and social calls and subsequently for the identification of individual bat species.A bird sound recorder to record flight calls and subsequently for the identification of bird species.LIDAR (no clear advantages over radar and less well developed), daylight cameras (not useful at night), near-infrared cameras (possibly change behaviour due to insect attraction because of the needed artificial lighting) and impact sensors (not able to assess barotrauma and most likely not able to assess collisions of bats and small birds as well) should not be part of the technical solution.After evaluating potentially suitable monitoring techniques as well as the available systems on the market or in development, there seem to be three potential technical applications/solutions that should be able to monitor bat and bird fatalities offshore: MUSE (Multi Sensor), B-finder and TSVA (Thermal Stereo Vision Application). However, none of them is able to perform this task straight away. They all require adjustments and development time. The main advantages and disadvantages per system are:MUSE Advantages Able to identify potential relevant objects (bats and birds) by radar • Extensive thermal camera detection range possible (zoom) • Camera footage aiding species identificationFew thermal cameras needed per wind turbineOperational system and tested offshoreApplicable for birds as wellDisadvantages Underestimation of the fatality rate, due to radar and camera shadow behind the tower, multiple individuals cannot be tracked at the same time and doubtful whether individuals (in particular bats) can be followed during prolonged periods in the Rotor Swept Area (RSA)System needs to be modified: the daylight camera needs to be replaced by at least two thermal cameras, and a bat detector and bird sound recorder need to be added and integrated into the system.B-finder AdvantagesSpecifically aimed to assess fatalitiesThe system is able to predict the location of the fallen carcass and this information can be used to assess detection functions to compensate for the number of fatalities missed.Applicable for birds as wellDisadvantages Currently not suitable for species identificationEarly stage of developmentNot operational and tested offshoreSystem needs to be modified, thermal cameras, bat detector and bird sound recorder need to be added and integrated into the systemTSVA AdvantagesSpecifically aimed to assess fatalitiesCamera footage facilitating species identificationIncludes bat detectorApplicable for birds as wellDisadvantagesVery early stage of development, not operational and tested offshoreSystem needs to be modified, bird sound recorder needs to be added and integrated into the system
DA - 2020/03//
PY - 2020
SP - 39
PB - Wageningen University and Research Centre
SN - C025/20
UR - https://research.wur.nl/en/publications/assessing-fatality-risk-of-bats-at-offshore-wind-turbines
LA - English
KW - Wind Energy
KW - Fixed Offshore Wind
KW - Collision
KW - Bats
KW - Birds
ER -