This record represents sei whale sound production detected from raw passive acoustic data. The Low Frequency Detection and Classification System (LFDCS) call library contains the 82 – 34 Hz sei whale downsweeps, which was the call type we focused on in this study. All sei whale downsweep detections with a Mahalanobis distance of 3.0 or less were manually screened for the daily presence of a doublet or triplet, doublets and triplets were defined as 2 or 3 repeated downsweeps, respectively, with roughly 3.5 seconds elapsed between the start of successive calls. Sei whales were considered present if a true detection (at least one downsweep detected within a doublet or triplet) was found for that day. Only the occurrence of the downsweeps as doublet or triplets were selected to ensure confidence in species identification. These data were recorded at SanctSound site SB01_05 between August 2, 2019 and October 5, 2019.