Estimating spatio-temporal reproductive dynamics of fish populations with passive acoustic monitoring: A state-space model approach

Passive acoustic monitoring (PAM) has been used to estimate the presence
and spatial distribution of target organisms using biological sounds
received by microphones. Due to its cost-effectiveness and
non-invasiveness, PAM is becoming a promising approach for studying the
spatiotemporal dynamics of large groups in response to environmental
changes. However, conventional PAM can face significant constraints in
dealing with the collective vocalisations of organisms. Here, we extend
the traditional sound propagation equation for targeting a collectively
vocalising group and propose a state-space model that estimates the
acoustic group’s location and size with a limited number of microphones.
These developments overcome traditional limitations, such as financial,
operational, and methodological costs and problems associated with the use
of numerous microphones. Simulation studies confirmed that the model
produced systematically unbiased estimates of acoustic group size and
location across varying group parameters. Furthermore, the estimations of
the acoustic group locations were robust to a violation of the model
assumption that the spatial extent of the acoustic group is temporally
constant. As an empirical demonstration, applying the proposed approach to
white croaker (Pennahia argentata) tracked the daily movement of the
acoustic group centre in relation to tidal conditions. Moreover, the
approach not only revealed temporal variations in acoustic group size with
a 10-minute resolution but also revealed temporal shifts in the peak
timing of choruses. These findings demonstrate the potential for novel
biological insights. The proposed approach enables long-term and
comprehensive assessment of biological status and supports effective
resource management through spatiotemporally fine-scale predictions of
future distribution and abundance. Moreover, this approach can be applied
to collectively vocalising groups across a wide range of taxonomic groups,
including birds, insects and amphibians, even when using a limited number
of microphones.