Right, Killer and Beluga whales need a lift: SMRU Consulting’s CAB Guardian is ready to help pick them up!
Populations of North Atlantic Right Whale (NARW), St. Lawrence Estuary Beluga (LEB), and Southern Resident Killer Whale (SRKW) are all in trouble, with all three species showing very clear population declines in the last decade. Canada’s Oceans Protection Plan (OPP) has outlined several new initiatives aimed at addressing the threats currently facing these species, which include entanglement, underwater noise, ship strikes, environmental contamination and reduction in prey availability.
If President Biden gets his wish, then offshore wind developments on both east and west coasts will boom in the next decade which will help the US increase its clean, renewable energy portfolio. However, the construction of these offshore wind developments will require thousands of turbines to be installed (mainly pile-driven), in addition to a clear increase in vessel traffic during the construction phase and for routine maintenance post-construction. The noise and traffic associated with the construction process remains a primary concern for whales in the vicinity.
US Federal regulators leased the first coastal offshore wind areas in 2012, at a time when designated lease areas were considered less important to Right Whales, but dramatic changes in distribution have since occurred due to climate change – perhaps changing the distributions of their prey – and some of these original lease areas (such as southeast of Cape Cod) are now relatively close to Right Whale foraging hot spots. The need for long-term monitoring and adaptive management has never been clearer. This also means we need to ensure that injury and disturbance ‘safety’ zones around wind turbine piling sites are free of protected species, an area potentially covering up to 10 km from the construction site.
Real-time passive acoustic monitoring (PAM) is one mitigation tool that has been recommended by US regulators to help protect right whales during piling operations. It’s a 24/7 monitoring tool that can listen for and detect calling whales throughout the day and night and in poor weather, unlike human observers using traditional visual methods which are largely limited to monitoring during daylight hours and subject to fatigue! Traditionally, hydrophones are deployed as single units, and a detection of a whale call can inform us of when a whale is somewhere in the vicinity of our hydrophones.
SMRU Consulting has been building and deploying real-time PAM buoys for more than a decade, utilizing the industry standard detection software PAMGuard, written by the University of St Andrews’ own Dr Doug Gillespie, and a high-end DAQ processor called Decimus. The first SMRU Consulting PAM buoys were very large, solar powered ocean buoys and these proved expensive to moor and keep quiet in bad weather. Consequently, we soon switched to smaller lightweight, battery powered “Coastal Acoustic Buoys” (CABs), with the smart brains completely contained within the buoy. These CAB Sentinels (Figure 1) can be handled by a single person from a small vessel and deployed with moorings or allowed to drift. The single hydrophone and smaller devices proved ideal for SRKW (Figure 2) and noise monitoring by San Juan County and source level measurements on behalf of the Vancouver Fraser Port Authority’s ECHO Program. But a different solution is needed for the monitoring of safety exclusion zones during longer-term construction mitigation activities, like installing wind turbine foundations.
Figure 1: CAB Sentinel being deployed off San Juan Island, Washington
Figure 2: Calls from a Southern Resident Killer Whale
In 2018, SMRU Consulting secured multi-year funding from the US Department of Energy and Maryland Department of Natural Resources to develop a cost-effective and robust system for mitigation monitoring of whales during US offshore wind construction, with a focus on Right Whales. This allowed for a redesign of the CAB to provide longer-term deployments and the ability to acoustically track and localize whales. In contrast to typical single-hydrophone PAM systems, the new CAB Guardian was designed with three hydrophones attached, allowing for not just the detection of a Right Whale call, but also enabling us to determine where the whale is calling from (and to track that over time as the animal moves). It does this by measuring the tiny differences in the time that an individual whale call arrives at on each hydrophone – which tells us which direction the signal is coming from. This means that a single CAB Guardian unit can give a bearing to calling whales.
Figure 3: CAB Guardian being deployed in Puget Sound, Washington
However, for mitigation monitoring to determine whether or not a whale is within an exclusion zone, we ideally need to know the location of the whale, not just the direction in which it is relative to our sensors. With multiple CAB Guardians, one can calculate the location of the call (by seeing where the bearings from solo CAB Guardians intersect), and in particular, whether the whale is inside any pre-defined safety exclusion zone. Whales determined to be inside of the safety exclusion zone typically result in the noisy activity (like piling) stopping until the animal has moved well away from the safety area. Whales acoustically localized to be clearly outside of the safety exclusion zone would not trigger ceases in construction activity, unless they subsequently moved inside (Figure 4). Thus, our approach of multiple CAB Guardians simultaneously deployed will avoid unnecessary construction delays.
Figure 4: Detection probability simulation showing correct mitigation actions (purple) and unrequired shutdowns (yellow) for five CAB Guardian with 3 hydrophones (top panel) and five sensors with 1 hydrophone (bottom panel). The Shiny App allows one to change ambient noise and whale call source levels as well as location and number of sensors. The aim of the simulation is to test efficiency of different hydrophone deployment scenarios under different conditions.
A challenge with any real-time PAM equipment is to increase battery life and improve communications capability. To achieve this, Principal Acoustician Dr Jason Wood and our US-based engineers, led by Paul King, worked with the University of Washington’s Applied Physics Lab to move the Decimus brains and lots more batteries into a bottom lander unit, which was then connected to a 3G or Wi-Fi communication buoy via a robust Falmat data cable.
Figure 5: Schematic of CAB Guardian with bottom lander connected to the communication buoy
Figure 6: Dr Jason Wood and Sam Tabbutt performing the last checks before a CAB Guardian deployment
We undertook a full-scale field validation of five CAB Guardians in offshore Maryland waters in November 2021. To be able to optimize monitoring an exclusion zone, we needed to better understand: 1) how far away the system could reliably detect Right Whale calls under different real-world noise conditions, 2) how accurately one could determine the direction of a vocalizing Right Whale, and finally, 3) we wanted to quantify the benefits of a localizing PAM system versus using traditional single hydrophone systems (which turned out to be extensive!).
Figure 7: Drone shot of five CAB Guardians ready for simultaneous deployment and full-scale validations off the coast of Maryland.
Figure 8: Deployment locations of 5 CAB Guardians (yellow circles) deployed off the coast of Maryland (left panel) and locations of Right Whale playbacks (black dots) during US DOE validation study
Figure 9: CAB Guardian about to submerge. The white shields on the hydrophones reduce current flow noise and the yellow cylinder attached to the top is an Edgetech acoustic release that is released once the unit is safely on the sea bottom.
The multi-CAB validation study has recently been published by bio-acoustician Dr Kaitlin Palmer in Methods in Ecology and Evolution. After playbacks of 3500 simulated Right Whale calls from known locations (Figure 8), we demonstrated detection ranges from 4–7.3 km depending on source and ambient noise levels. We learned from our trials that the mitigation would be most effective if the placement and configuration of the CAB Guardian units reflected anticipated ambient noise conditions, including noise from piling and nearby vessels. Importantly, simulations showed that incorporating bearing detections provides a substantial improvement in false alarm rates (an improvement of 6 - 12x over a single system - depending on number of units, placement, and signal to noise conditions) with a small increase in the risk of missed detections inside of the exclusion zone (1%–3%). Given false alarm rates will extend the presence of time-scarce and very high-cost piling vessels that are active in the area, we consider there is clear value in using PAM sensors with whale tracking capabilities. The trial also resulted in improvements in the right whale detector performance.
Since the final validation trial was completed, the CAB Guardian has been used in multiple marine conservation contexts. These include applications by Fisheries and Oceans Canada (DFO) to assess winter usage by killer whales in the Strait of Georgia (near Point Roberts, Washington), testing PAM whale detection concurrently with thermal imaging off the coast of Vancouver Island (part of a DFO strike risk reduction program), and by Quiet Sound to acoustically monitor the noise reduction benefits of a two-month commercial vessel slowdown in Northern Puget Sound, Washington, USA. The engineers have also incorporated the CAB brains into a tethered PAM system (to monitor St Laurence River Beluga) and into an Uncrewed Surface Vehicle (USV), built by Open Ocean Robotics. This USV is essentially a boat-drone which tows one or two hydrophones, so potentially opening the door to cost-effective mobile acoustic monitoring (Figure 10).
Figure 10: Open Ocean Robotics USV towing 2 hydrophones off the coast of San Juan Island, Washington
We are hoping that our new acoustic mitigation monitoring technologies can play a part in reducing underwater noise threats to endangered whales and help their populations thrive again, while at the same time, safely facilitating a greener future.
Questions? Comments? Get in touch: info@smruconsulting.com