Why do male sperm whales make groups?

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K06350
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 45040:Ecology and environment-related
• Research Institution: Nagasaki University
• Principal Investigator: Amano Masao 長崎大学, 水産・環境科学総合研究科(水産), 教授 (50270905)
• Co-Investigator(Kenkyū-buntansha): 西田 伸 宮崎大学, 教育学部, 教授 (40423561)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 社会生態 / マッコウクジラ / 社会構造 / 血縁度 / ハクジラ類

Outline of Final Research Achievements

Male sperm whales develop social relationships that do not directly aim at breeding. This is very rare among mammals. Possible reasons for this include the possibility of cooperation among related individuals for future reproductive success and following older animals to gain learning opportunities from them. We studied these possibilities by examining social relationships, distance between individuals, body size, and kinship among individually identified young male sperm whales migrating to the Goto Submarine Canyon off Nagasaki Prefecture, Japan. Neither kinship nor body length difference influenced social relationships or distance between whales, so both possibilities were not supported. However, it was found that there were large individuals with an exceptionally high betweenness centrality and eigenvector centrality. These individuals may play a key role in transferring information in situations such as choosing foraging areas.

Free Research Field

海棲哺乳類学

Academic Significance and Societal Importance of the Research Achievements

マッコウクジラについては、最近の研究でコミュニケーション音に集団の帰属を表す文化的な要素があることや、音楽のようにテンポや要素を変えて情報を伝えていることなど、高度な社会性を示すことがわかってきている。このような知見は全て母系の群れを形成するメスでの事例であり、メスの群れから離れて暮らすオスの社会については非常に知見が少ない。オスにも社会性があるにも関わらず、それがメスのように血縁や高齢個体の知識利用と直接的に結びついていないことを明らかにした本研究は、マッコウクジラという種の社会の理解のみならず、哺乳類の社会や文化の進化を理解する上でも非常に重要なものである。