Estimating the effect of mid-frequency active sonar on the population health of Blainville's beaked whales (Mesoplodon densirostris) in the Tongue of the Ocean
Passive acoustic methods were used to study the effect of mid-frequency active sonar (MFAS)
on a population of Blainville’s beaked whales (Mesoplodon densirostris, Md) at the U.S. Navy
Atlantic Undersea Test and Evaluation Centre (AUTEC), Bahamas. AUTEC contains an array
of bottom-mounted hydrophones that can detect Md echolocation clicks. Methods to estimate
abundance, the risk of behavioural disruption, and the population level effect of repeated MFAS
exposure are presented. A passive acoustic abundance estimation method, a parametric equation
that predicts the probability of foraging dive disruption as a function of MFAS received level and
an Md bioenergetics model were developed. The effect of changes in energy flow on the
demographic characteristics of an Md population were explored. Passive acoustic data from
AUTEC were used to estimate the behavioural disturbance resulting from sonar operations;
combined with the bioenergetic model, this suggested that the effect of sonar operations could
cause an increase in a female’s age at maturity, a longer inter-calf-interval, calf survival rate and
probability of giving birth that could in turn result in a declining population. Model results were
also compared to those from an expert elicitation study. A power analysis for predicting
abundance via passive acoustic and visual monitoring were used to inform recommendations for
a long-term monitoring plan that includes passive acoustic monitoring of Md abundance
combined with a photo-identification study at both AUTEC and a reference site (Abaco) to
improve demographic rate estimates
