The Asian sea otter is the largest subspecies, followed by the northern sea otter, leaving the southern sea otter as the smallest.
The Asian sea otter is the largest subspecies and has a slightly wider skull and shorter nasal bones than both other subspecies.
Northern sea otters are slightly larger than Californian otters. Adult male northern sea otters weigh 27 to 39 kilograms, while females weigh 16 to 27 kilograms. Adult male southern sea otters average 29 kilograms in mass, while females average 20 kilograms. Northern sea otters possess longer mandibles (lower jaws) while southern sea otters have longer rostrums and smaller teeth.
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• Sources | (Allegra & Gunderson 2012; Campbell & Santana, 2017; Cronin, Bodkin, Ballachey, Estes, & Patton, 1996; Doroff & Burdin, 2015; Estes, 1980; Lockwood, 2006; Nowak, 1999; Paine, 1993; The Wikimedia Foundation, 2020b; Wilson, Bogan, Brownwell, Burdin, & Maminov, 1991)