Initially, the sea mink was believed to be one of the many subspecies of the extant American mink (Mustela vison); it was only after its extinction that the sea mink was recognised as a species in its own right. This was due mostly to its impressive size and the structure of its teeth, which were better adapted to a different food source, implying it had diverged to inhabit a distinct ecological niche (4). The sea mink is recognised as one of the most aquatic of all the mustelids, excluding only the otters (4). Similar to the others mustelids, the sea mink would have been a voracious predator, although its diet was probably more specialised than other species in the Mustela genus, consisting mostly of fish, seabirds and their eggs, and molluscs. Despite minks being thought to have poor underwater eyesight, it is believed that much of this animal’s time would have been spent in the ocean, hunting its preferred prey (4).
Little is known about the social behaviour of the sea mink, but other species in the Mustela genus are characterised by a solitary, nocturnal existence. All minks are territorial but males are particularly aggressive towards other males. Each male defends a linear territory usually extending a few kilometres along a river bank or shoreline, and several female territories may overlap with a male’s but one male’s territory will never extend into another male’s. Scent marks signal an individual’s presence and trespassing usually results in violent conflicts (7). Both sexes are promiscuous and mate with several partners during the months of April and May, with males tending to roam from their territory to seek more partners. The blind, hairless and helpless young tend to be born after a gestation period of about 34 days, although it may last up to 70 days as delayed implantation often occurs. The litter of five to ten young stays with the mother until 13 to 14 weeks of age; however, the step to independence and finding a territory is usually fraught with dangers and high mortality (7).