Recordings from: Evaluation of a coastal acoustic buoy for cetacean detections, bearing accuracy, and exclusion zone monitoring

1. There is strong socio-political support for offshore wind development
in US territorial waters, and construction is planned off several east
coast states. Some of the planned development sites coincide with
important habitat for critically endangered North Atlantic right whales.
Both exclusion zones and passive acoustic monitoring are important tools
for managing interactions between marine mammals and human activities.
Understanding where animals are with respect to exclusion zones is
important to avoid costly construction delays while minimizing the
potential for negative impacts. Impact piling from construction of
hundreds of offshore wind turbines likely requires exclusion zones as
large as 10 km. 2. We have developed a three-hydrophone passive acoustic
monitoring system that provides bearing information along with marine
mammal detections to allow for informed management decisions in real-time.
Multiple units form a monitoring system designed to determine whether
marine mammal calls originate from inside or outside of an exclusion zone.
In October 2021 we undertook a full system validation, with a focus on
evaluating the detection range and bearing accuracy of the system with
respect to right whale upcalls. Five units were deployed in Mid-Atlantic
waters and we played more than >3,500 simulated right whale upcalls
at known locations to characterize the detection function and bearing
accuracy of each unit. The modeled results of the detection function error
were then used to compare the effectiveness of a bearing-based system to a
single sensor that can only detect a signal but not ascertain directivity.
3. Field trials indicated maximum detection ranges from 4–7.3 km depending
on source and ambient noise levels. Simulations showed that incorporating
bearing detections provides a substantial improvement in false alarm rates
(6 to 12 times depending on number of units, placement, and signal to
noise conditions) for a small increase in the risk of missed detections
inside of an exclusion zone (1–3%).  4. We show that the system
can be used for monitoring exclusion zones and clearly highlight the value
of including bearing estimation into exclusion zone monitoring plans while
noting that placement and configuration of units should reflect
anticipated ambient noise conditions.