Sexual Behavior and Anatomy in Porpoises

Abstract Among the taxonomic family of porpoises (Phocoenidae), mating behavior in nature has been described in detail only for the harbor porpoise ( Phocoena phocoena ). We review this species’ unusual mating habits based on a study in San Francisco Bay, California, USA, and present new data from across its range in the North Pacific, North Atlantic, Black Sea, and managed care. Results confirm the male’s unique laterality oriented solely to the female’s left side as contact occurred both in nature and managed care. The male’s high-energy sexual approach to the female led to splashy aerial behavior at the surface in nature. Drone footage provided observations of subsurface mating behavior, including evidence of male–male sexual interactions and a male calf interacting sexually with its mother. Harbor porpoise reproductive anatomy is also presented, with new comparative information on the vaquita ( Phocoena sinus ). The harbor porpoise’s lateralized behavior and anatomy (i.e., long asymmetric penis, large testes size, convoluted asymmetric female reproductive tract) may have coevolved. We note gaps in knowledge, suitable platforms for future investigations (drones, bridges, boats, and coastal cliffs), and what is known about mating behavior in other porpoise species, including hybridization. We conclude with conservation implications for porpoises and encourage researchers to recognize and report mating behavior as baseline data valuable for establishing marine conservation areas.