Predicting acoustic dose associated with marine mammal behavioural responses to sound as detected with fixed acoustic recorders and satellite tags

Abstract

To understand the consequences of underwater noise exposure for cetaceans, there is a need for assessments of behavioural responses over increased spatial and temporal scales. Bottommoored acoustic recorders and satellite tags provide such long-term, and large spatial coverage of behaviour compared to short-duration acoustic-recording tags. However these tools result in a decreased resolution of data from which an animal response can be inferred, and no direct recording of the sound received at the animal. This study discusses the consequence of the decreased resolution of data from satellite tags and fixed acoustic recorders on the acoustic dose estimated by propagation modelling, and presents a method for estimating the range of sound levels that animals observed with these methods have received. This problem is illustrated using experimental results obtained during controlled exposures of northern bottlenose whales (Hyperoodon ampullatus) exposed to naval sonar, carried out near Jan Mayen, Norway. It is shown that variability and uncertainties in the sound field, resulting from limited sampling of the acoustic environment, as well as decreased resolution in satellite tag locations, can lead to quantifiable uncertainties in the estimated acoustic dose associated with the behavioural response (in this case avoidance and cessation of foraging).

Northern bottlenose whales in a pristine environment respond strongly to close and distant navy sonar signals

“…Von Benda-Beckmann et al . [22] provide a detailed description of this analysis, summarized here. Propagation loss modelling was based upon sound speed measurements and the characteristic of the source (vertical beamwidth and in-beam source level (SL); table 1).…”

“…To relate the acoustic dose of the sonar to the inferred behaviour, we modelled the received level of each transmitted sonar pulse with Bellhop [21]. Von Benda-Beckmann et al [22] provide a detailed description of this analysis, summarized here. Propagation loss modelling was based upon sound speed measurements and the characteristic of the source (vertical beamwidth and in-beam source level (SL); table 1).…”

“…A similar approach was used for animals near the moored acoustic recorder location. However, as the exact location of the animals was unknown, we placed simulated animals at depths that were randomly drawn from pre-exposure satellite tag data and assumed an acoustic detection range of 1 -4 km around the mooring location [22].…”

Assessing the Role of Sampling Uncertainty When Predicting Behavioral Responses of Tagged Cetaceans Exposed to Naval Sonar

“…By contrast, implantable S-TAGs allow animals to be tracked over far wider spatial domains (several hundreds of km; e.g., Schorr et al, 2009) and much longer timeframes (several months; e.g., Falcone et al, 2017), though this often comes at the cost of lower resolution with respect to surface locations and individual behaviors (Nowacek et al, 2016). Importantly, most S-TAGs lack on-board acoustic recorders and sacrifice the ability to take in situ measurements of received sound levels, which must then be inferred indirectly from knowledge of both the acoustic transmission properties of the area of interest and the animals' position relative to the noise source at the time of exposure (von Benda-Beckmann et al, 2019). Tags transmitting via Service Argos can also suffer from substantial geo-localisation errors, which may range anywhere between 150 m and > 10 km (Nicholls et al, 2007;Irvine et al, 2020) and are likely to compromise estimates of the sound dose experienced by exposed individuals (Schick et al, 2019;von Benda-Beckmann et al, 2019).…”

“…Importantly, most S-TAGs lack on-board acoustic recorders and sacrifice the ability to take in situ measurements of received sound levels, which must then be inferred indirectly from knowledge of both the acoustic transmission properties of the area of interest and the animals' position relative to the noise source at the time of exposure (von Benda-Beckmann et al, 2019). Tags transmitting via Service Argos can also suffer from substantial geo-localisation errors, which may range anywhere between 150 m and > 10 km (Nicholls et al, 2007;Irvine et al, 2020) and are likely to compromise estimates of the sound dose experienced by exposed individuals (Schick et al, 2019;von Benda-Beckmann et al, 2019). Such differences in data quality and resolution between monitoring technologies raise important questions regarding the optimisation of their use in BRSs (Harris et al, 2018).…”