On 14 February 2023, during the 2022/2023 Japanese Abundance and Stock-structure Surveys in the Antarctic (JASS-A) cruises, two individual whales were sighted in the Southwestern Pacific. These whales were identified as pygmy right whales (Caperea marginata) by their prominently arched jawline, relatively narrow rostrum, dorsal fin located two-thirds of the way from the tip of the snout, and small body size. This species is one of the most mysterious whales, with few sightings at sea. Several measurements were taken from aerial videography using a small uncrewed aerial vehicle (UAV) for 9 min and 49 s. One individual swam slowly for 128.9 m in 53 s, with a swimming speed of 4.7 knots. A comparison of the external measurements of the whale in this study with those of whales reported to have a similar body length indicated no significant differences between photogrammetric and manual measurements. These sightings represent the second and third recorded occurrences of this species in the Southwestern Pacific, in highly pelagic waters near the northern boundary of the Subtropical Convergence Zone. This region is known for its high primary productivity, where whale prey species are concentrated.

Bowhead whales (Balaena mysticetus) were previously thought to carry only one species of cyamid (whale louse), Cyamus ceti, which co-occurs on eastern and western gray whale (Eschrichtius robustus) stocks. We analyzed partial mtDNA COI gene sequences from archived cyamid samples to determine species present and the phylogenetic placement of bowhead whale cyamids. We explicitly tested Callahan’s hypothesis (2008) that C. ceti on gray and bowhead whales represent distinct evolutionary lineages and may necessitate separate species level status. Findings from this study indicate that C. ceti on bowhead whales differs from C. ceti on gray whales, implying that bowhead and gray whale cyamids likely represent different evolutionary lineages. The C. ceti bowhead clade is shared between Bering-Chukchi-Beaufort Seas and Okhotsk Sea bowhead whales, suggesting that these cyamids likely shared a common ancestor relatively recently in their evolutionary history. We also document the limited presence of C. scammoni on bowheads, perhaps indicating horizontal transmission from interactions with gray whales.

This paper presents and overview of the biological and ecological features of the J-stock common minke whale (Balaenoptera acutorostrata scammoni) in waters around Japan based on analyses of genetically identified individuals. Reviewed information included spatial/temporal distribution, morphology, morphometrics, reproductive characteristics, feeding ecology, environmental pollutants, and ecological markers. Except for feeding ecology and environmental pollutants, these features (e.g., spatial/temporal distribution, morphology such as flipper and fluke color pattern and ecological markers such as cookie cutter shark scars) confirm the biological and ecological uniqueness of the J-stock within the North Pacific common minke whale. Our analysis also confirms the existence of distinct genetically, biologically and ecologically independent stocks with characteristics so far not identified in any other baleen whales in the Western North Pacific, and corroborates the view that the minke whale J-stock should be managed independently.