The Killers of California and Oregon

abstract
Photo-identification studies of transient killer whales (Orcinus orcas) off western North America have primarily been conducted in the coastal inland waterways of Washington State, British Columbia, and southeastern Alaska. Less is known about transient killer whales along the outer coast and offshore waters of Oregon and central and northern California. We examined 13 years of photo-identification data to identify individuals and obtain a minimum census for this region, and to summarize information that could be useful for evaluating a hypothesis that whales using this area belong to a distinct assemblage. Data contributions came from opportunistic marine mammal surveys, whale watch ecotours, and dedicated line transect surveys. Transient killer whale photographs were obtained from 146 encounters between 2006 – 2018. These included 136 encounters in Monterey Bay, California, 5 encounters off central and northern California, and 5 encounters off Oregon. The number of unique individuals seen during this time totaled 155, of which 150 were considered to be alive (as of 2018). These included 34 adult males, 51 adult females, 24 sub-adults, and 41 juveniles. Through repeated observations of association patterns, a total of 30 matrilineal groups were identified. New whales were identified each year, including previously unidentified adults and new calves. Identification images of the dorsal fins, saddle patches and postocular patches were obtained. Details on sex, maternal ancestry, sighting history, and distribution are provided where known. These cataloged transient killer whales were predominantly encountered off the outer coast near the continental shelf break or in deep pelagic waters overlying the Monterey Submarine Canyon. The vast majority (>83 %) of whales identified in the study area could not be matched to transient killer whales in photo ID catalogs for coastal waters of the Pacific Northwest. These factors are consistent with there being a distinct “outer coast” assemblage within the west coast population of transient killer whales, but more research is needed to investigate this further.