Sea otters mating. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior. Sea otters have a polygynous mating system. Many males actively defend territories and will mate with females that inhabit their territory or seek out females in estrus if no territory is established. Males and females typically bond for the duration of estrus, or about 3 days. Elkhorn Slough National Estuarine Research Reserve, Moss Landing, California, USA