The most successful mammal aquatic carnivores next to seals are otters. They have webbed feet and tuft whiskers. They spend of their time in the water. They even sleep on the surface of the water. They forage for food in the water. They feed on invertebrates. Sea otters use tools like a flat rock to break open mollusks. They grow to about 85 to 140 inches from head to the end of their body. The otters use their tails to propel them through the water.