Discrete-space continuous-time models of marine mammal exposure to Navy sonar

Assessing the patterns of wildlife attendance to specific areas is
relevant across many fundamental and applied ecological studies,
particularly when animals are at risk of being exposed to stressors within
or outside the boundaries of those areas. Marine mammals are increasingly
being exposed to human activities that may cause behavioural and
physiological changes, including military exercises using active sonars.
Assessment of the population-level consequences of anthropogenic
disturbance requires robust and efficient tools to quantify the levels of
aggregate exposure for individuals in a population over biologically
relevant time frames. We propose a discrete-space, continuous-time
approach to estimate individual transition rates across the boundaries of
an area of interest, informed by telemetry data collected with
uncertainty. The approach allows inferring the effect of stressors on
transition rates, the progressive return to baseline movement patterns,
and any difference among individuals. We apply the modelling framework to
telemetry data from Blainville's beaked whale (Mesoplodon
densirostris) tagged in the Bahamas at the Atlantic Undersea Test and
Evaluation Center (AUTEC), an area used by the US Navy for fleet readiness
training. We show that transition rates changed as a result of exposure to
sonar exercises in the area, reflecting an avoidance response. Our
approach will support the assessment of the aggregate exposure of
individuals to sonar and the resulting population-level consequences. The
approach has potential applications across many applied and fundamental
problems where telemetry data are used to characterise animal occurrence
within specific areas.