From calls to communities: acoustic monitoring of contact calls indicates spatial structure in endangered belugas

Abstract

Animal populations often exhibit complex patterns of spatial or social structure, with various levels of organization below the population level. Acoustic monitoring can reveal such structure, particularly when animals produce calls that contain individual or group-level signatures. In this study, we monitored the complex contact calls of belugas, Delphinapterus leucas, in the St Lawrence Estuary, Canada, across six sites during five field seasons. Using a mark–recapture-based movement network, we examined the movement of belugas by tracking the occurrence of distinctive contact calls across sites. Our movement network revealed a high degree of population structure and the presence of two distinct communities: one within the Saguenay Fjord, recorded at two locations (i.e. the ‘Saguenay community’), and another along the southern shore of the estuary, recorded at four locations (i.e. the ‘South Shore community’). These results align with findings of a previous photo-identification-based study that suggested the presence of clusters of individuals inhabiting the Saguenay Fjord and southern shore of the estuary. Our study provides the first acoustic evidence of fine-scale population structure in the endangered St Lawrence Estuary beluga population. These findings, together with the population's exposure to significant anthropogenic disturbances across its range, reinforce the need to expand the Saguenay–St Lawrence Marine Park to protect the core habitats and home ranges of both communities. More broadly, our results demonstrate that passive acoustic monitoring can reveal population spatial structure and inform behaviour-driven conservation action.