Results of the Japanese Abundance and Stock structure Survey in the Antarctic (JASS-A) during the 2024/2025 austral summer season

The results of the sixth research cruise of the Japanese Abundance and Stock structure Surveys in the Antarctic (JASS-A) are reported. Two dedicated sighting vessels (SVs) were engaged in the survey based on the line transect method for 41 days, from 1 January to 10 February 2025 in Area IV-East (100°E–130°E).  For the survey, the research area was divided into northern and southern strata, and two survey modes were used, Normal Passing mode (NSP) and Independent Observer mode (IO) for abundance estimation, including g(0) correction. This survey design was based on IWC/IDCR-SOWER survey procedures. The total searching distance in the research area was 2,491.5n.miles (4,614.3km), including 1,230.8n.miles covered in NSP mode and 1,260.8n.miles in IO mode. The survey coverage was 84% in the northern stratum, 85% in the southern stratum. Antarctic blue (19 schools/25 individuals), fin (28/72), Antarctic minke (148/332), humpback (850/1,514), southern right (3/3) and at least three toothed whale species, sperm (3/3), southern bottlenose (12/22) and killer whales (9/234), were sighted in the research area. Estimated Angle and Distance Experiments were completed to correct the observer's distance and angle measurements. Routine photo-ID and biopsy sampling on large whales were also conducted during the whole survey (including transit). A total of 79 photo-IDs (24 Antarctic blue, 36 humpback, 3 southern right and 15 killer whales) were obtained. A total of 128 biopsy samples were collected from 12 Antarctic blue, 18 fin, 35 Antarctic minke, 52 humpback, 3 southern right, 5 killer, one long-finned pilot whale, and one spectacled porpoise during the whole survey. Satellite tags were deployed on 10 fin, 25 Antarctic minke, and 2 humpback whales during the whole survey. Oceanographic observations were conducted at 164 casts using the eXpendable Conductivity, Temperature and Depth (XCTD). One marine debris was observed in the research area.  Data and samples collected in this survey will be analysed in conjunction with data and samples obtained during past research programs in the Antarctic (JARPA, JARPAII, NEWREP-A), in the context of the primary and secondary objectives of the JASS-A. The results of the JASS-A program may also be reported to CCAMLR in the future and could contribute to Antarctic krill management.