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.