Dear MARMAM Readers, My co-authors and I are pleased to announce the publication of our article: Citation: Kobayashi H, Whitehead H, Amano M (2020) Long-term associations among male sperm whales (*Physeter macrocephalus*). PLoS ONE 15(12): e0244204. https://doi.org/10.1371/journal.pone.0244204 Abstract Little is known about the social structure of male sperm whales (*Physeter macrocephalus*) after they leave their natal units. While previous studies found no evidence for preferred associations among males, the observation of mass-strandings consisting exclusively of males, suggest that they have strong social bonds. To investigate the social associations among male sperm whales, we used half-weight index of association, permutation tests and standardized lagged association rate models on a large photo-identification database collected between 2006 and 2017 in Nemuro Strait, Japan. Our results suggest that while male sperm whales are not as social as females, they do form long-term associations, have preferred companionship, and forage in social proximity to each other. The best-fitting model to the standardized lagged association rate showed that associations among males last for at least 2.7 years and as most males leave the area after 2 years, associations may last for longer. Twenty dyads were observed associating over more than 2 years, for a maximum 5 years. One dyad was observed associating on 19 different days and clustered on 7 different days. Male associations may function to enhance foraging or to fend off predators. Such relationships seem to be adapted to a pelagic habitat with uncertain resource availability and predation pressure. The open-access article can be downloaded from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0244204 Kind regards, Hayao Kobayashi ********************************************************** Hayao Kobayashi PhD. candidate Graduate School of Fisheries and Environmental Sciences, Nagasaki University 1-14, Bunkyo-machi, Nagasaki 852-8521, JAPAN Marine Mammal Research Lab. TEL：080-5270-9906 Mail：physeter0809@gmail.com **********************************************************