Bowhead Whale Reproductive Strategies

Abstract Bowhead whales ( Balaena mysticetus ) have adopted growth and reproductive strategies to survive in a challenging environment where no other mysticete whales reside. They grow slowly, become sexually mature at around 25 years (later than other mammals), and do not give birth until they have sufficient energy reserves for the best possible chance of survival of the calf to weaning and long-term survival of the mother. To compensate for late maturity and long inter-birth intervals, some seem to have the capability to live to 200+ years of age, making them the longest-lived mammal known to date. Bowhead whale males have large testes per body size, and it is hypothesized that the basic polygynandrous system of females and males mating with multiple partners per estrous cycle allows for males to not compete violently against each other. Instead, they use sperm competition by volume of sperm for enhanced capability to father as many offspring as possible. Also, as in right whales ( Eubalaena spp.), the length of the penis is proportionally longer than those of balaenopterids. Details of sperm volume, potential variabilities of sperm viabilities, and actual paternities are unknown, but some patterns can be inferred from the closely related right whales with similar morphologies.