Summary of the dedicated sighting survey for large whale species under the Japanese Abundance and Stock structure Surveys in the Antarctic (JASS-A) during the 2023/24 austral summer season

This document outlines the research cruise of dedicated sighting surveys under the non-lethal Japanese Abundance and Stock structure Surveys in the Antarctic (JASS-A program) during the 2023/24 austral summer season. The main research objectives of JASS-A are i) the study of the abundance and abundance trends of large whale species, and ii) the study of the distribution, movement and stock structure of large whale species. Two dedicated sighting vessels (SVs) were engaged in the survey based on the line transect method for 36 days, from 7 January to 11 February 2024 in a part of Area IV-West (70–100°E). For the survey, the research area was divided into northern, southern strata and Prydz Bay. In addition, surveys were conducted in coastal ice-free waters in the Davis Sea. The total searching distance in the research area was 3,278.3 n.miles, including 1,595.0 n.miles covered in NSP mode and 1,683.3 n.miles in IO mode. Four baleen whale species, Antarctic blue (15 schools/18 individuals), fin (200/467), Antarctic minke (111/178), humpback (874/1,706) and at least two toothed whale species, sperm (42/43), and killer (19/263) whales, were sighted in the research area. Distance and angle estimation experiments for corrections of reported values by observers, were conducted. Experiments (photo-ID, biopsy sampling, and satellite tagging on large whales) as well as oceanographic and debris observations, were also conducted. The obtained sighting data will be used to estimate abundance and abundance trend of large whales as well as other studies. These estimates are required for the estimation of krill consumption by whales in the Indian and Pacific sectors of the Antarctic, which are in the interest of WG-EMM