Nineteenth-century sealers hunted northern elephant seals for their blubber oil until the species was thought extinct. A small remnant survived on Isla de Guadalupe off Baja California; the surviving number is usually given as somewhere between about twenty and a hundred animals. Mexican and later American protection followed, and the seals recolonised beaches northward along the California coast.
The recovery is genuine and large: the species now numbers in the low hundreds of thousands. But genetic surveys find strikingly little variation, particularly in the mitochondrial control region and at immune-related loci, compared with the southern elephant seal, which was never squeezed so hard.
What this means for the species' future is contested. Low diversity is often argued to raise vulnerability to disease or environmental change, yet the population has grown steadily for a century without an obvious fitness cost. The precise size of the surviving remnant is also uncertain, since the counts come from sealers' and naturalists' reports rather than systematic surveys.