Reproductive parameters of the Amazon river dolphin or boto, Inia geoffrensis (Cetacea: Iniidae); an evolutionary outlier bucks no trends

Abstract

Reproductive parameters of the Amazon river dolphin, or boto Inia geoffrensis, were estimated from a population of individually recognizable animals in the Brazilian Amazon throughout 24 years. Gestation lasts 12.3-13 months, and calves are nursed for 1.5-5.8 years. The mean inter-birth interval is 4.6 years, and there is no evidence of reproductive senescence. Females first give birth at a mean age of 9.7 years and become sexually mature at body lengths of 180-200 cm. Body length at birth averages 84 cm. The annual pregnancy rate was ~0.4, but the annual birth rate was 0.22; therefore, almost half of pregnancies do not result in a calf seen by our research team. Entanglement of neonates in monofilament gillnets might account, at least in part, for these losses. Births can occur year round, but peak at low water, when botos and their newborn calves are concentrated on river margins. Despite profound physical and behavioural adaptations over millions of years to a life in shallow, fresh waters and complex habitats, the boto has remarkably similar reproductive characteristics to those of its marine counterparts, dolphins of the family Delphinidae. The fundamental reproductive characteristics of small odontocetes have apparently been robust to change over a very considerable evolutionary timespan. © 2018 The Linnean Society of London, Biological Journal of the Linnean Society.