Spatial and Temporal Changes in Bigg’s “Transient” Killer Whale ( Orcinus orca rectipinnis ) Distribution Within the Central Salish Sea from 2001-2025

Abstract

Within the central Salish Sea, Bigg’s “transient” killer whales ( Orcinus orca rectipinnis ) have become an increasingly common occurrence, but little published research is available on their spatial and temporal shifts. This paper aims to categorize the changes in the distribution of Bigg’s killer whales throughout the central Salish Sea region by compiling and analyzing public sighting records from 2001 to 2025. Metadata was taken from sighting records publicly available on Orca Network, a 501(c)(3) nonprofit organization, and unique sightings were sorted by major region. 3,875 unique encounters were documented over 2,849 unique days, with a mean sighting frequency of 155 sightings per year. Sightings increased from 38 in 2001 to 385 in 2024. Temporal variation on a monthly scale was observed, with the greatest number of sightings occurring in late spring (April-September) and late summer (August-September), with a decline in July sightings that coincides with peak harbor seal ( Phoca vitulina ) pupping seasons in the Puget Sound Region. A spatial change has been documented since 2001 as well, with an increasing area of habitat use within the central Salish Sea. A potential cause for this could be an increase in both prey availability and Bigg’s population size. A larger-scale or range-wide spatial and temporal analysis would be beneficial in contextualizing the changes and trends observed in this paper to determine what factors may be playing the biggest role in determining changes.