Passive acoustic monitoring is useful for augmenting visual surveys to assess temporal and spatial changes in the density and behaviour of some animals. This is particularly where animals are difficult to survey via traditional techniques, where their behaviour makes them unavailable to traditional visual surveying. Animals maybe present but not observed – this is a false positive.
Acoustic surveying can provide additional behavioural information where there are age-related differences in vocalizing behaviour.
The leopard seal is ideal for acoustic surveying. Very few animals are encountered in traditional visual surveys despite a large survey effort.
Uncommon or cryptic? Challenges in estimating leopard seal abundance by conventional but state-of-the-art methods
Antarctic leopard seals vocalize underwater during the breeding season, at the time of surveys and there are age-related differences in vocalizations.
Age-related differences in the acoustic characteristics of male leopard seals, Hydrurga leptonyx
They produce loud vocalizations (up to 177 dB re 1 μPa at 1 m)
Source levels of the underwater calls of a male leopard seal (L)
in a repetitive, stylized sequence making their vocalizations ideal for acoustic surveying.
Individual variation in the acoustic behavior of the adult male leopard seal, Hydrurga leptonyx
Determining the spatial distribution of an Antarctic top predator using passive acoustics.
Illustration by Danielle Clackson