She watched as the mother left her child to float alone in the water

Ms Eszterhas used a long telephoto lens to photograph the mother and pup without disturbing their activities.

The California-based photographer said: 'I have been photographing sea otters for over 20 years, so I know sea otter behavior well.

'Most sea otter mothers are quite shy with their babies, but this mother was very habituated to people and she was very relaxed as she lovingly raised her pup in a busy harbor.

'Sometimes, she swam right up to the dock and left her pup floating on the water's surface right in front of me while she foraged for food.