A seven-year time series of fin whale (Balaenopteraphysalus) acoustic detections in the Equatorial Pacific Ocean was examined in combination with regional environmental parameters to better understand fin whale seasonal distribution and behavioral ecology in a traditionally undersampled ocean region. Ecological modeling of environmental variables related to fin whale vocal presence indicated that median sound pressure spectral density level in the 5 to 115 Hz band, chlorophyll concentration, and sea surface temperature (SST) were the strongest predictors of fin whale presence. Fin whale vocal presence increased with increasing median sound level and decreased with increasing SST. Variation in seasonal fin whale call density and estimated animal density varied annually with one of the largest estimates occurring in the only year of the study when both the El Niño–Southern Oscillation and Pacific Decadal Oscillation were in a positive phase. This work illustrates the feasibility and value of applying knowledge of call detection bearings and received levels from long-term, sparse array recordings to estimate animal density of marine mammals in the context of regional environmental conditions.