The mating system of B. arnuxii is not known. Scarring on the bodies of males and females may indicate social aggression, possibly around mating, but these behaviors have not been observed.
Little is known about the mating and reproductive habits of Berardius arnuxii. Investigation of the sister species, B. bairdii, is informative, but information on the reproduction of this species is also sparse and debated. Berardius bairdii becomes sexually mature at about 8 to 10 years of age at lengths of 10 m for females and 9.5 m for males. Some researchers claim that females mature first while others state that males mature first and live longer than females. Males are more numerous and older based on research conducted on B. bairdii around Japan, but this could be due to a difference in geographical ranges between the sexes or sampling bias (Kasuya 1986). The gestation period is between 10 and 17 months with a three year interval between birthing events. Calving occurs mostly in the spring, but some births take place from late winter through summer and fall. The mating peak occurs from fall to early winter. Due to their smaller overall size and the few records of mature or pregnant stranded individuals, B. arnuxii seems to mature at younger ages and smaller sizes than B. bairdii.
Breeding interval: Breeding interval in B. arnuxii is unknown.
Breeding season: Breeding seasonality in B. arnuxii is unknown.
Range gestation period: 10 to 17 months.
Key Reproductive Features: iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous
Like all mammals, females B. arnuxii invest heavily in their young through gestation and lactation. Otherwise, little is known about parental investment in Arnoux’s beaked whales.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)