Why do marine otters stay close to shore?

The term "marine otter" refers to a specific species (Lontra felina) that inhabits the rocky Pacific coast of South America, rather than a general category for all otters in the ocean.12

Unlike the sea otter (Enhydra lutris), which is fully aquatic and can be found far offshore, the marine otter stays within approximately 100 meters (330 feet) of the shore. This species is essentially a freshwater otter that has adapted to occupy marine environments. It remains close to the coastline because it relies on land-based features for its survival; it makes its dens in sea caves, along windswept beaches, or within gaps in rock outcrops. These land-based shelters are essential for the marine otter's daytime rest, breeding, giving birth, and raising its young.12