Blackfish as a conservation unit: a review of five Globicephalinae species with a focus on the Pacific

Cetaceans living in the open ocean face many challenges associated with the unpredictability of pelagic environments. The inaccessibility and vastness of these ocean environments has also contributed to critical knowledge gaps in population abundance estimates, genetic structure and foraging ecology of many pelagic cetacean species. This review focuses on one such group of large delphinids, the ‘blackfish’. Within this group, we highlight five species with similar morphologies and overlapping global distributions: false killer whales (Pseudorca crassidens), pilot whales (Globicephala spp.), melon-headed whales (Peponocephala electra) and pygmy killer whales (Feresa attenuata), focusing on populations within the Pacific Ocean basin. These species are highly mobile, socially complex, long-lived and slow to reproduce, and often occur in small or disjunct island-associated populations. They are also frequently misidentified and considerably understudied, complicating efforts to assess their conservation status and manage populations effectively. Using a combination of keyword-based searches and synthesis of peer-reviewed and grey literature, we compiled information across seven key thematic areas: taxonomy and subspecies, population abundance estimates and trends, global distribution, social organisation and association patterns, genetic population structure, foraging ecology and habitat use, and conservation concerns, management efforts and future directions. Synthesising available information across species enables meaningful comparisons and consideration of shared conservation challenges. Here, we show that most existing knowledge of blackfish species in the Pacific comes from a few well-studied populations, while all other regions and species remain largely data deficient. This highlights the need for continued future research and implementation of cross-jurisdictional management strategies in this region.