Animals in colder regions and fish of cold water have thick subcutaneous fat layer because fat acts as a good insulator and trap the body heat under the skin. This helps them survive in colder temperatures.
Habitat in cold region has lack of nutrition, so the fat layer also store nutrients that help the animal when required.
The animals in cold regions have layer of fat below their skin so that they should not feel cold...
The first coat is often a layer of fat hidden under the skin called “blubber.” In addition to being a good thermal insulator—it does not allow heat to pass through it easily—fat has the added benefit of serving as a welcome food reserve.