Pacific white-sided dolphin hourly binned echolocation clicks

This study investigates the biogeographic patterns of Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the Eastern North Pacific based on long-term passive acoustic records (2005-2021). We aim to elucidate the ecological and behavioral significance of distinct echolocation click types and their implications for population delineation, geographic distribution, environmental adaptation, and management. Over 50 cumulative years of Passive Acoustic Monitoring (PAM) data from 14 locations were analyzed using a deep neural network to classify two distinct Pacific white-sided dolphin echolocation click types. The study assessed spatial, diel, seasonal, and interannual patterns of the two click types, correlating them with major environmental drivers such as the El Niño Southern Oscillation and the North Pacific Gyre Oscillation, and modeling long-term spatial-seasonal patterns. Distinct spatial, seasonal, and diel patterns were observed for each click type. Significant biogeographical shifts in presence were observed following the 2014-2016 marine heatwave event. Distinct spatial distributions of the two click types support the hypothesis that Pacific white-sided dolphins produce population-specific echolocation clicks. Seasonal and diel patterns suggest spatio-temporal niche partitioning between the populations in Southern California. Lastly, interannual changes, notably initiated during the 2014-2016 marine heatwave, indicate climate-driven range expansions and contractions related to the gradual tropicalization of the Southern California Bight.

Methods
Raw acoustic data was passed through a click detector which returned all acoustic signals within an expected frequency range and duration of odontocete echolocation clicks. An unsupervised clustering algorithm was run on the detections to group them into 5-minute bin-level averages. Cluster bins were then labeled as one of six categories by a trained neural network. Clusters labeled as either one of two Pacific white-sided dolphin click types were extracted and manually verified. Verified pacific white-sided dolphin detections were then binned into 'click-positive minutes per hour', where a click positive minute was a minute that contained any number of clicks. The timeseries of click-positive minutes per hour, for each click type, at multiple long-term recording locations, is included here.