American Mink Mainly nocturnal
Otters hunt by sight in clear water, but in poor visibility, they use their whiskers to detect prey. Fish are usually caught by the mouth.
Eurasian Otter Nocturnal & diurnal (on coasts)
Mink vision is better on ground than in water. Their diet changes in response to otter presence and they tend to hunt more on the ground than in water.
Otters swim lower than minks, with their bodies mostly submerged. They create a U-shaped wave on the surface of the water.
Minks swim higher than otters, showing almost the whole length of their backs. The wave created by their nose is narrow and V-shaped.