Case definition: Killer whale predation as the cause of death in gray whales and other Pacific large whale species

Killer whale predation has long been recognized as a source of mortality to large whale species in the Pacific Ocean. Mysticete and large odontocete species for which killer whale predation events have been documented include: gray, humpback, bowhead, minke, southern right, fin, blue, sei, and sperm whales. This case definition provides the first systematic method to assign a level of certainty of killer whale predation as a cause of death depending upon findings. The case definition can be used as part of hands-on examination of a carcass or when only sufficient imagery (i.e., photos, video) is available. The case definition can assist in determining the extent of killer whale predation, as well as spatial and temporal changes in predation. The assessment of predation can also be utilized to differentiate mortality events and in the evaluation of long-term ecological processes (e.g., changing environmental conditions and changing distribution of species).