Mirounga angustirostrisMirounga angustirostris male & female
Reproductive variance in Northern Elephant Seals (Mirounga angustirostris)

The photos show Northern Elephant Seal (Mirounga angustirostris) females and pups [above, left] from the colony (rookery) at Año Nuevo Island, off the California coast. Males are several times larger than the females [above, right], with marked secondary sex characteristics including an inflatable proboscis. Reproduction is dominated by an "alpha male" who controls access to a "harem" of reproductive females by agonistic combat with other males [below, left]. The chart [below, right] shows that this single male may be responsible for >90% of the pup production in any year; most males have few or no pups. Female reproductive success is more evenly distributed. This strong variance in male reproductive success, combined with a population history in which the species was "bottlenecked" to < 20 individuals from over-hunting in the 19th century, has kept genetic variation in Mirounga very low.Conservation efforts have restored numbers.

        male-male combatReoproductive

Text material © 2020 by Steven M. Carr